阅读说明：本技术 有能力追踪并优化电力使用的调变器 (Modulator with capability of tracking and optimizing power usage ) 是由 徐文泰 于 2018-12-07 设计创作，主要内容包括：一种控制组件,可控制顺序性地去撷取电能,应用于三相DC/AC调变器。这种三相DC/AC调变器中有三个单相DC/AC调变器,而每个单相调变器各有一组PWM(电力)撷取器。PWM的负载工作因子是依据其相对应的当下(时)AC电力周期的位准来进行调整。这种顺序性控制器能够保证三个PWM电力撷取器彼此间不会产生重迭的工作周期,使每个单相DC/AC调变器都能按顺序地,而不会同时地执行电能撷取。这样设计的三相调变器就能改善从DC电源撷取DC电力的效率。(A control module for controlling sequential extraction of electrical energy for use in a three-phase DC/AC modulator. The three-phase DC/AC modulator has three single-phase DC/AC modulators, and each single-phase modulator has a set of PWM (pulse width modulation) extractor. The load duty factor of the PWM is adjusted according to the level of its corresponding current (time) AC power cycle. The sequential controller can ensure that the three PWM power extractors do not generate the overlapped work period, so that each single-phase DC/AC modulator can sequentially and not simultaneously execute the power extraction. The three-phase modulator thus designed improves the efficiency of extracting DC power from the DC power source.)

1. A sequential power extraction control module for a three-phase DC/AC modulator configured from three single-phase DC/AC modulators, the control module being configured to control the sequence of each single-phase modulator during DC power extraction and the duration of the power extraction:

a first set of PWM power extractors is disposed in a first single-phase modulator of the three-phase DC/AC modulator, and is capable of extracting DC power from a DC power source, converting the DC power into a first set of AC power to be transmitted to a first pair of cables of a three-phase AC power grid, wherein the frequency of the AC power and the first phase of the AC power are consistent with a grid specification of the AC power transmitted on the first pair of cables of the three-phase AC power grid;

a second single-phase modulator of the three-phase DC/AC modulator is provided with a second set of PWM power extractors, the second set of extractors being arranged to extract DC power from the DC power source and convert it to a second set of AC power for transmission to a second pair of cables of the three-phase AC power network, the AC power having the same frequency as the first set of AC power but having a second set of AC power matching the grid code of the AC power transmitted over the second pair of cables of the three-phase AC power network;

and a third single-phase modulator of the three-phase DC/AC modulator is provided with a third set of PWM power extractors, the third set of extractors being configured to extract DC power from the DC power source and convert the DC power to a third set of AC power having the same frequency as the first set of AC power but having a third frequency that meets grid specifications for AC power delivered by a third pair of cables present in the three-phase AC power grid;

the sequential power extraction control assembly includes:

configuring a sequential controller such that a first PWM power extractor has a first duty cycle during a period of performing DC power extraction, a second PWM power extractor has a second duty cycle during a period of performing DC power extraction, and a third PWM power extractor has a third duty cycle during a period of performing DC power extraction; sequentially controlling the first, second and third duty cycles to be non-overlapping during operation, and sequentially enabling the first, second and third PWM extractors to perform power extraction;

the sequential controller may also direct and adjust the load duty factor of the first, second and third PWM power extractors based on the power corresponding to the level of a particular set of AC power cycles (one of the first set or the second set or the third set of AC power) at the current time.

2. The sequential power extraction control module of claim 1, wherein the load duty factor of the 3 PWM power extractors is adjusted during the ac power cycle such that the time function of the first load duty factor is 2/3cos²(ω t) making the time function of the second load duty factor 2/3cos²(ω t +120 °) and make the time function of the third load duty factor 2/3cos²(ωt-120°)。

3. The sequential power harvesting control assembly of claim 1, comprising:

a timer;

a time schedule; has a plurality of rows, and the parameters of each row respectively correspond to the level information on a group of AC power cycles. And the parameter may represent sufficient information to determine first, second and third load operation factors for the AC power on the grid; and

a starter; the starter is configured to use sufficient information in the schedule to sequentially start the first, second and third PWM power extractors to extract their respective powers.

4. The sequential power extraction control module of claim 3, wherein the sufficient information is a start time and an end time of a first PWM power extraction operation.

5. The sequential power extraction control unit of claim 3, wherein the schedule comprisesA plurality of rows, and at least two values in each row; the first value being equal to D (2/3) cos²(ω t), the second number being equal to D (2/3) cos²(ω t + 120), where D is the PWM duty cycle length and t is a time within the AC power cycle.

6. The sequential power extraction control device of claim 1, wherein the sequential controller is configured to adjust all of the corresponding load duty factors according to a signal from the director.

7. The sequential power extraction control unit of claim 1, wherein a time interval between completion of the one PWM power extraction and start of a next PWM power extraction is not greater than one-third of the PWM duty cycle.

8. The sequential power extraction control unit of claim 1, wherein a time interval between an end of one PWM power extraction and a start of a next PWM power extraction is not more than one fifth of the PWM duty cycle.

9. The sequential power extraction control unit of claim 1, wherein a time interval between an end of the one PWM power extraction and a start of a next PWM power extraction is not greater than one twentieth of the PWM duty cycle.

10. The sequential power extraction control unit of claim 1, wherein a time interval from an end of the one PWM power extraction to a start of a next PWM power extraction is not greater than one percent of the PWM duty cycle.

11. A sequential power extraction control element; the three-phase DC/AC modulator is applied to a three-phase DC/AC modulator, and the three-phase DC/AC modulator comprises a first single-phase DC/AC modulator, a second single-phase DC/AC modulator and a third single-phase DC/AC modulator. The first single-phase DC/AC modulator further includes a first PWM power extractor for extracting power from the DC power source and converting the power to a first set of AC power having a first phase that meets grid specifications. The second single-phase DC/AC modulator includes a second set of PWM power extractors that extract power from the DC power source and convert the power into a second set of AC power having a second phase that meets grid specifications. A third PWM power extractor of the third single-phase DC/AC modulator extracts power from the DC power source and converts the power to a third AC power having a third phase that meets grid codes.

The sequential power extraction control unit includes:

a sequential controller; when the first PWM power extractor extracts power, the first PWM power extractor is guided to have a first load work factor.

When the second PWM power extractor extracts power, the second PWM power extractor is guided to have a second load duty factor. And

when the third PWM power extractor extracts power, the third PWM power extractor is guided to have a third load duty factor.

The sequential controller can ensure that the first, second and third load operation factors do not overlap during power extraction, and the power extraction is performed sequentially according to the first, second and third load operation factors.

And the configuration of the sequential controller; the duty cycles of the first, second and third PWM power extractors may be directed and adjusted according to the power corresponding to the level of a current set of AC power cycles (one of the first set, the second set, or the third set of AC power). And the configuration of the sequential controller; bringing the time function of the first load duty factor to 2/3cos during the AC power cycle²(ω t) making the time function of the second load duty factor 2/3cos²(ω t +120 °) bringing the time function of the third load duty factor to 2/3cos²(ωt-120°)。

12. A three-phase DC/AC modulator system comprising;

a three-phase DC/AC modulator includes a first, a second and a third single-phase DC/AC modulator. The first single-phase DC/AC modulator includes a first PWM power extractor for directing the first PWM power extractor to have a first load duty factor when performing power extraction. The second single-phase DC/AC modulator includes a second PWM power extractor for directing the second PWM power extractor to have a second load duty factor when performing power extraction. And a third PWM power extractor included in the third single-phase DC/AC modulator directs the third PWM power extractor to have a third load duty factor when performing power extraction.

The sequential controller can ensure that the first, second and third load operation factors do not overlap during the power extraction, and the power extraction is performed sequentially according to the first, second and third load operation factors.

And the configuration of the sequential controller; the duty cycles of the first, second and third PWM power extractors can be directed and adjusted according to the power corresponding to the level of the next set of AC power cycles (either the first set or the second set, or one of the third set of AC power cycles).

The sequential controller comprises:

a timer;

a time schedule; has a plurality of rows, and the parameters of each row respectively correspond to the level information on a group of AC power cycles. And the parameter may represent sufficient information to determine first, second and third load operation factors for the AC power on the grid; and

a starter; the starter is configured to use sufficient information in the schedule to sequentially start the first, second and third PWM power extractors to extract their respective powers.

13. The sequential power extraction control module of claim 12, wherein the sufficient information is a start time and an end time of a first PWM power extraction operation.

14. According to the rightThe three-phase DC/AC modulator system of claim 12, wherein said schedule comprises a plurality of columns, and wherein each column has at least two values; the first value being equal to D (2/3) cos²(ω t), the second number being equal to D (2/3) cos²(ω t + 120), where D is the PWM duty cycle length and t is a time within the AC power cycle.

Background

A single-phase "direct current to alternating current" (DC/AC) modulator may convert electrical power (energy) from a "direct current" (DC) source to "alternating current" (AC) power that meets grid codes. Under grid codes, the AC power ripple carried on the grid must be a positive (/ cosine) waveform, with a specific fixed peak voltage and a specific fixed frequency.

A conventional 3-phase DC/AC inverter can supply AC power to 3 pairs of power lines, each pair of power lines requiring 120 ° phase difference between the transmitted power (referred to as "a-phase, B-phase, and C-phase"). The core architecture of the three-phase DC/AC inverter is composed of three single-phase DC/AC inverters. Each single-phase inverter performs the extraction and conversion of the DC power, and then transmits the AC power with the same RMS power to the corresponding power line. One of the single phase DC/AC inverters supplies AC power having a phase a on-line to the first pair of power lines. A second single phase DC/AC inverter supplies AC power having phase B on-line to a second pair of power lines. A third single-phase DC/AC inverter supplies AC power having a C-phase on-line to a third pair of power. In other words, the three single-phase DC/AC inverters each extract about the same amount of DC power; then converting the captured DC power into AC power, wherein the phases of the supplied three AC powers must be 120 degrees; the 3 inverters would then feed 3 sets of ac power into a grid configured with 3 or 4 power lines. Thus, each pair of power lines carries a single phase ac power of the same frequency and has approximately the same rms power as the ac power of the other two pairs of power lines; and must be 120 deg. out of phase with each other. The term "as used in the technical field of the present application: the words "inverter", "converter" and "modulator" (and in terms of "inverting", "converting" and "modulating") are interchangeable and are therefore used interchangeably herein.

The scope of this patent is not limited to addressing only the shortcomings of the foregoing practical cases or the environments in which they are used. Rather, the background description of the patent is provided as an illustration of one technical area in which an embodiment of the invention may be practiced.

Disclosure of Invention

The embodiments set forth herein relate to a sequential controller; the three-phase inverter is applied to a 3-phase DC/AC modulator, so that three single-phase inverters can extract power according to time sequence. A three-phase inverter; a first single-phase DC/AC modulator includes a first set of PWM power extractors that extract DC power from a DC power source and convert the DC power to a first set of AC power having a first phase that also meets grid specifications. The second single-phase DC/AC modulator includes a second set of PWM power extractors that extract DC power from the DC power source and convert the DC power to a second set of AC power having a second phase that also meets grid codes. And a third PWM power extractor of the third single-phase DC/AC modulator extracts DC power from the DC power source and converts the DC power into a third AC power having a third phase that meets the grid code. The duty cycle of the PWM power extractor in the three sets of single-phase inverters is adjusted according to the level of the corresponding current AC power cycle.

When the sequential controller is used for guiding the first PWM power extractor to execute power extraction, a first PWM duty cycle is generated. And then guiding the second group of PWM power extractors to generate a second group of PWM duty cycles when the second group of PWM power extractors execute power extraction. Then, the third PWM power extractor is guided to generate a third set of PWM duty cycle when executing power extraction. Unlike conventional 3-phase DC/AC inverters, the sequential controller ensures that the PWM duty cycles of the first, second and third groups do not overlap, allowing the first, second and third groups of PWM power extractors to extract power sequentially, rather than simultaneously; this improves the efficiency of extracting DC power from the DC power source.

This summary is provided to introduce a selection of concepts in a simplified form. These concepts will be described in further detail below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the claimed subject matter.

Drawings

In order that the manner in which the above recited and other advantages and features of the invention are obtained will be understood, a more particular description of various embodiments will be rendered by reference to the appended drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which an embodiment is described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1A shows modules of a solar power generation sequence to illustrate and explain the terms of art mentioned herein, such as power extraction, regulation, modulation of DC/AC, and delivery of AC power.

FIG. 1B symbolically shows that the DC/AC modulator delivers a sine-cosine time-varying AC voltage oscillation representative of the AC message to a particular power line of the grid;

fig. 2A shows a single-phase power extraction/regulation (or regulation) component described in a typical circuit of a Boost DC/DC modulator;

FIG. 2B shows a single-phase power extraction/conversion block described in a typical circuit of a Buck DC/DC converter;

FIG. 2C illustrates an interactive bridge configuration of switching elements to control the polarity of the power output by the DC/DCBuck modulator; an output AC voltage oscillation as shown in fig. 1B may be generated;

FIG. 2D is a schematic representation of sine and cosine AC power ripple delivered by a DC/AC modulator to the switches of the interactive bridge configuration;

FIG. 2E symbolically shows the output DC power regulated by the Booster modulator during one PWM duty cycle; is depicted as 3 regions: region-I represents the captured energy, and regions-II and-III represent the remaining energy regions;

FIG. 3A shows a circuit of a power extractor using a conventional 3-phase DC/AC modulator;

FIG. 3B symbolically shows input DC power ripple during one PWM duty cycle;

FIG. 3C symbolically shows the 3 power extractors of FIG. 3, with power extracted simultaneously during one PWM duty cycle;

FIG. 4 symbolically shows that one DC power source provides DC power P_mxWithout the MEUPT component, at a rated power P declared by the DC power supply manufacturer_mxTo two identical 3-phase DC/AC modulators;

FIG. 5A shows 3 circuits for A-phase, B-phase, and C-phase power extraction using MEUPT modulators;

FIG. 5B symbolically shows the timing sequence of power extraction for phase A, phase B and phase C as adjusted by the sequential controller of FIG. 5A;

FIG. 6A shows an experimental power plant architecture diagram of an example embodiment in which two sets of AC power generation units are provided, each set of power generation units being configured with a power meter and a kilowatt hour meter for measuring the AC power and electrical energy output by each power generation unit; and

figure 6B shows a modified architecture diagram of the power plant of figure 6A, supplemented with components including decoupling and energy storage means, and used to demonstrate improved efficiency of power output to the grid.

Detailed Description

Fundamentally, a 3-phase DC/AC modulator consists of 3 single-phase DC/AC modulators. Each single-phase DC/AC modulator is used for performing the functions of power extraction, regulation and conversion of DC power into AC power; then providing approximately equal alternating current root mean square power to the 3 pairs of AC power lines; the 3 sets of AC power must be 120 out of phase with each other. Therefore, in order to understand the operation mechanism of the three-phase DC/AC modulator, it is necessary to have a clear understanding of the single-phase DC/AC modulator; in particular, to the "power (energy) extraction" function referred to herein. Additionally, the meanings of power lines and cables described herein are generally interchangeable herein and in the relevant art.

U.S. publication patents US2016/0036232 and US2017/0149250a1 disclose a discovery; that is, the conventional single-phase modulator can only extract, adjust, convert, and output less than half of the DC power input to the single-phase modulator from a Direct Current (DC) power source. From the teachings of these issued patents: in order to efficiently extract the generated DC power supply for conversion into the power used on the grid, the designed power extraction component characteristics need to be matched with the power generation unit in order to efficiently extract the generated DC power.

In addition, these issued patents also teach; other components associated with the power extractor must also be well matched to condition and/or deliver the extracted power to make the use of electrical energy more efficient. Proposed by the reference bulletin; the maximum use electric energy tracker is used as an optimizer of the solar power station. This optimizer, referred to herein as a "MEUPT optimizer," can be used to replace the optimizers used in existing commercial Photovoltaic (PV) plants. This commercially available optimizer is commonly referred to as a "Maximum Power Point Tracking (MPPT) unit. However, the name more closely related to this commercially available optimizer shall be called "maximum power production voltage point tracking (mppvt)" device.

According to the referenced publication, the MEUPT optimizer is designed to capture "surplus energy" or "surplus power," which is defined as "power produced (or electricity) that is not captured and/or imported to the grid for use. The definition of surplus power (or surplus electrical energy) as used herein is also the same as that of the patent publication referred to. Since the phase difference between the surplus power and the power grid is about 90 °, the surplus power cannot be directly sold to the same power grid. However, in the referenced patent, the MEUPT optimizer is also designed to temporarily store all of the captured excess power into the energy storage; the stored electrical energy is then conditioned by the optimizer and transmitted to the grid for use. Thus, when the photovoltaic power plant is combined with the MEUPT optimizer, the income of power generation sales can be increased.

In the relevant art, there are many techniques that may be applied to perform what is referred to herein as DC power extraction, power regulation, power conditioning, and power delivery. While in the principles set forth in this patent technology, these technologies are not necessarily related to the kind of DC power source being produced. In the present case, however, only the string of solar panels is used as a DC power source. And the actual conditions of the solar power plant are illustrated and described in terms of the terminology referred to herein, such as power capture, regulation and delivery. In other words, the principles and techniques described herein are not limited to use in the field of solar power generation, and may be used in a wide variety of power industries. Also, although "electrical energy," "electrical power," and "power" have physically different meanings, they are often used interchangeably in the professional field of electrical power unless otherwise specified. In addition, although the physical "AC power ripple" and "AC voltage oscillation" also have different physical meanings, they are used interchangeably herein unless otherwise specified.

The sequence 10 in FIG. 1A is used to illustrate the arrangement of the components of the photovoltaic power plant. The sequence 10 starts with a photoelectric conversion part (photovoltaic solar panel string) 101 that is capable of converting light energy (e.g., solar energy) as initial energy into DC power, but the voltage of this power is often not fixed due to various factors. These factors include the shade of the cloud from sun, the angle of incidence of the sun, unequal efficiency of different photovoltaic cells, and many other factors. This produced DC power of an unfixed voltage is regulated and regulated to a DC power (source) of a fixed voltage by the DC/DC Boost converter 201 connected subsequently. The constant voltage DC power is then converted to sinusoidal time varying pulsating DC power by the DC/AC modulation module 223 connected to 201. The sinusoidal time-varying pulsating dc power is then converted to AC power with positive (/ cosine) time-varying voltage oscillations shown in fig. 1B by a polarity-switching controller 224 added behind the module 223.

For example; the DC/AC modulation module 223 may be a Buck module operated by a pulse (wave) width (PWM) modulation module; the Buck module can also be regarded as a DC/AC inversion module; the DC power with fixed voltage is adjusted into sine wave time-varying pulsating DC power. One example of a Bridge configuration module 224 is shown in FIG. 2C, and the component name of this configuration is referred to herein and in the relevant art as an Integrated Bridge Gate Transistor (IBGT). As shown in FIG. 2C, the bridge configuration 224 includes 4 sets of switches (S1, S2, S3, and S4) for controlling the synchronization and polarity of the output AC power ripple of the DC/AC modulator. The LOAD shown represents the transformer 225 connected to the bridge structure 224 and all the electrical LOADs connected thereto. The combination of modules 201 and 223 may also be referred to herein as a "PWM power extractor".

The AC voltage oscillations output by the bridge structure 224 are specifications that must be met by the grid. The AC power ripple is regulated by the transformer 225 and then delivers AC power to the connected grid 300 (electrical load). Fig. 2A shows an exemplary circuit of a boost DC/DC converter 201, where the module 201 regulates a varying DC supply voltage to a constant DC supply voltage. The circuit of fig. 2B is a Buck module circuit operated by PWM in the single-phase DC/AC modulator 223, which converts the constant voltage DC power generated by the module 201 into time varying sine/cosine DC power pulses. The interactive bridge structure (Switchbridge structure)224 shown in fig. 2C is used to regulate the time-varying DC power ripple output by the single-phase DC/AC modulator 223 to a polarity that matches the grid requirements and is synchronized with the AC power delivered by the grid. The single-phase DC/AC modulator 223 (or a module combining both the boost DC/DC converter 201 and the single-phase DC/AC modulator 223, referred to as "PWM power extractor") is applied to a conventional single-phase modulation module (3 single-phase modulators constituting the conventional three-phase DC/AC modulator) as a module for performing power extraction/conversion.

A first stage: discussing conventional DC/AC power conversion

Generally, in practical situations, the voltage at the maximum power point (mppv) of the pv string is not fixed, and the DC voltage is usually smaller than the peak voltage specified by the AC power grid. Therefore, the photovoltaic string requires a voltage-boost power extractor to perform power extraction and adjustment; the power extractor can adjust the non-fixed low voltage DC power supply into a fixed high voltage DC power supply.

Fig. 2A shows a Boost circuit of the DC/DC Boost module 201, which is composed of the following components: an inductor L; a controllable switch Q regulated by a feedback controlled load factor regulator (FCDFA; not shown); there is also a diode D. In this circuit; the switch Q, which may operate at high frequencies (typically about 18kHz in commercial products), uses an adjustable load duty factor (ADF) to perform on/off switching. The FCDFA is used to regulate the load duty factor such that the DC/DC Boost module 201 produces a substantially constant DC output voltage (V)₀). In other words, the DC/DC Boost module 201 regulates the DC power supply of the unfixed voltage to the fixed voltage v₀DC power supply (generally, V)₀＝V_pkIn which V is_pkIs the peak voltage of the AC grid) so that the DC power source can match the subsequent components connected in the circuit (i.e., the DC/AC modulation module 223 in the case of fig. 1A). The DC/AC modulation module 223 converts the DC power with a specific peak voltage into sine/cosine time varying power ripple that meets the power grid specification.

During the period that the switch Q remains on, the designed inductor L draws power from the power input unit (in the case of fig. 1A, this power input unit is referred to as PV solar panel string 101). Specifically, the inductor L is charged by inputting power during a pass period set by the PWM switching for feedback-controlling the load duty factor. When charging takes place, the voltage V across the switch Q_SWWill increase towards the input voltage V_inUp to the voltage V across the switch_SWA suitable equilibrium value is reached. During the off period of the switch Q, current flows from the inductor through the diode D, charging the designed capacitor C, producing a regulated voltage equal to the output voltage requirement (in the grid-connected case, V ═ V-₀＝V_pk). By using feedback control to adjust the duty factor of the load, the loadThe output voltage can be adjusted from V by adjusting the on/off period of the switch Q under the properly designed fixed PWM frequency_inStep up to a specified peak voltage V of the AC grid₀＝V_pk. Therefore, the voltage-Boost circuit can generate the proper peak voltage output to the subsequently connected DC/AC modulation module. Such circuits are referred to herein in the art as "Boost DC/DC converters" or "Boost converters".

As previously mentioned, boost converters are designed to be able to regulate an unfixed-voltage DC power source (e.g., PV string) to a substantially constant-voltage DC power source, which may have a voltage equal to a peak voltage value specified in the AC power grid. Note that in order to prevent voltage decay of the peak voltage of the DC power supply occurring under normal operation for one AC power cycle, the capacitor C in the Boost circuit shown in fig. 2A needs to be designed with an appropriate capacitance value. That is, the capacitor C is designed to maintain an essentially constant voltage over the duration of an AC power cycle. The capacitor used to maintain this DC voltage constant is known in the art as a "direct current Link" capacitor. Since in the grid specifications the voltage variations that can be tolerated by the DC link must be very small, the capacitors required for the DC link are not designed to store a large amount of surplus electrical energy. In order to store a large amount of surplus energy, a large (and expensive) capacitor with a high capacitance is required to store the surplus energy and maintain the output AC power output stable within the allowable voltage variation range of the maximum voltage specified by the AC power grid.

The exemplary DC/AC modulation module 223 shown in FIG. 2B; which includes an inductor LL, a set of controllable switches QQ regulated by a load factor regulator (DFA), a set of diodes DD and a set of DC link capacitors CC. The switch QQ is controlled by an adjustable load duty factor (ADF) to switch on/off at high frequencies (typically about 18kHz in commercial products). The switch QQ (often referred to as a "PWM switch") is controlled by the PWM output signal. The load duty factor of the PWM switch is adjusted by DFA so that the AC power pulse generated by the modulation module 223 can meet the grid specification. The DC/AC modulation module 223 shown in fig. 2B is referred to herein by the term "Buck converter" in the art. The Buck converter 223 associated with the DFA may convert DC power source power that meets peak voltage specifications to sine/cosine time varying pulsating AC power. This time-varying pulsating ac power is sent through the interactive bridge configuration shown in fig. 2C (fig. 2C may be used as an example of the polarity/synchronization controller 224 of fig. 1A); the AC power is then transmitted to a power grid (e.g., power grid 300 in fig. 1A) via a transformer (e.g., transformer 225 in fig. 1A). As described above, the interactive bridge configuration is a controller for adjusting the polarity and synchronization of the sine/cosine time varying power ripple output.

As shown in fig. 2C, when both switches S1 and S2 are on and switches S3 and S4 are off, a positive voltage is applied across the load. Conversely, when switches S3 and S4 are on and switches S1 and S2 are off, a negative voltage is applied across the load. When these switches are controlled by a "sync director" (not shown in fig. 2C) or referred to as a "sync director", which senses the exact time of the positive/negative voltage (or zero voltage pass) transition on the grid and uses it to direct and perform the on/off switching function, the components of the bridge structure 224 in combination with the DFA can effectively control the sine/cosine time varying power pulses output by the single phase DC/AC modulator to conform to the polarity of the AC grid and to synchronize with the AC grid.

A synchronous director (synchronous regulator) can timely adjust the time-varying PWM load work factor; generating a pure (/ cosine) sinusoidal pulse wave, which is cos²(ω t + θ) of the waveform, ω being the angular frequency required for the output sine/cosine time varying power pulses, V_pkThe peak voltages of the sine/cosine time varying power pulses are required, and theta is the phase angle of the pulse, and is synchronized with the corresponding power line on the power grid. When the synchronous inductor is combined with the input DC pulse power with fixed voltage and coexists with the parasitic inductance and parasitic capacitance on the grid, the inductor LL and the capacitor CC can be reduced or even omitted in practical applications. The term "as used in the technical field of the present application: "inverter", "converter" and "modulator" (and as for "inverter", "converter" and "Modulation ") are interchangeable and are therefore used interchangeably herein.

The DFA adjusts the load work factor according to the design of the power pulsation, and the work factor is a function of time to control the switch QQ of the Buck inverter module to carry out on/off work. Therefore, with properly designed circuits and adjusted peak voltages, the Buck modulation module can generate AC power with output voltage, power form, frequency and phase required to meet design requirements, to meet the requirements of the AC grid specifications, and to meet the power ripple phase existing on the corresponding grid power line. In the case of grid-connected devices, AC synchronous directors (usually built into the DC/AC modulator) are used, which can adjust the AC power to be output to the grid in accordance with the peak voltage or grid frequency drift. This resulting AC power (not voltage) output signal is shown in fig. 2E. In other words, using the PWM power extractor, the single-phase DC/AC modulator can extract the fixed-voltage DC power from the DC power source and convert the DC power into the output AC power conforming to the power grid specification.

Of great importance is the output power P (t) of the single-phase modulator in cos over time²The pulsating form of (ω t + θ) changes. The electric energy transmitted through the power line of the grid during a certain period is therefore equal to the time integral of the electric power ripple output over time during this period. The resulting transmitted power (integral value) is only equal to half the power supplied by the initial power source, the integral of the voltage DC power over time, over the same period of time. In other words, the conventional single-phase modulator can only extract, convert and then deliver half of the energy provided by the DC power source. The remaining and unused energy is more than half of the available input energy. That is, this remaining energy that is not delivered occupies a substantial portion of the remaining energy described in the above-referenced patent.

For the purpose of conveniently and intuitively explaining the following analysis; let us assume that the DC power supply has a constant power P over a period of several AC ripple cycles_mx. FIG. 2E shows operation at a PWMThe DC power pulses captured in the period (having period D). As will be demonstrated; extracted DC Power P_xLess than or equal to DC power P of the power supply_mx. The load duty factor "D (t)/D" of the PWM duty cycle is adjusted to be equal to D (t)/D (cos)²(ω t + θ) such that the generated power is equal to P_x*cos²(ω t + θ), where θ is the phase of the power ripple corresponding to the presence on the grid power line, to substantially conform the power ripple to the grid specifications. Fig. 2E (specifically, the lower half of fig. 2E) also shows a coordinate system of power versus time (referred to as an energy coordinate system), where D represents one PWM duty cycle length; input DC power is P_mx(ii) a And the extracted DC power is P_x。

As shown in fig. 2E, the energy coordinate may be divided into 3 regions. region-I represents the captured power P_xThe extracted DC power pulses; when the pulse duration is D cos²(ω t + θ), at any time t corresponding to the PWM extraction period, the DC power pulse is converted into a single-phase ac power pulse P (t) P_x*cos²(ω t + θ). region-I is also referred to as the "power capture area" or "power capture region". Between DC power source P_mxAnd capturing the power P_xThe area in between is region III. region-II is the area behind the power capture region of PWM duty cycle D. The combination of region-II and region-III shows the remaining power area in the energy coordinate system. The energy in the remaining energy area (area) is not extracted, not converted to AC power and therefore not used on grid codes. Instead, this surplus electrical energy is ultimately converted into heat in the system.

To reiterate, the conventional DC/AC single-phase modulator employs a Boost module to adjust a DC power having an unfixed voltage into a DC power having a substantially fixed set voltage (e.g., a peak voltage of a power grid), and supplies the DC power to a PWM power extractor, where the fixed voltage DC power is extracted by the PWM power extractor and converted into a DC power pulse signal. The load duty factor is in one PWM duty cycle according to cos²(ω t + θ) with respect to the time function (phase θ is relativeThe power oscillation phase that should exist on-line with the grid power) is adjusted, and the AC power output to the grid can meet the grid specifications. When the input electric power is above a certain high level, the input electric energy in each PWM working period consists of two areas on an energy coordinate system; into an extracted energy region (e.g., region I in fig. 2E) and a residual energy region (e.g., a combination of regions II and III in fig. 2E). The captured energy is converted into AC power and provided to corresponding power lines on the power grid; the remaining energy, however, can only be converted to thermal energy unless captured and stored in a facility such as the MEUPT optimizer ….

As mentioned above, the cited published patent teachings; when the extracted power is integrated over a period of several AC power cycles, the remaining power is at least as great as the extracted power. In other words, the conventional single-phase DC/AC modulator can only extract half of the input DC power at most. In other words, when using a conventional single-phase DC/AC modulator, at least half of the input DC power becomes surplus energy; is not picked up, is not converted, is not transmitted to a power grid, and is not used by a load; and eventually converted to thermal energy.

It is also emphasized in the patent publication that the root cause of the low power extraction efficiency of a single-phase DC/AC modulator is continued to exist in a conventional 3-phase DC/AC modulator. This is because essentially a three-phase DC/AC modulator consists of 3 single-phase DC/AC modulator architectures, each performing power extraction and conversion functions, and then providing 3 pairs of power lines of the grid with approximately time root mean square AC power, 3 output AC power pulses must be 120 ° out of phase with each other.

A second section:power harvesting for a conventional 3-phase modulator

The conventional 3-phase DC/AC modulator has three single-phase DC/AC modulators built therein. Each single-phase DC/AC modulator is provided with a PWM power extractor. The three power extractors are regulated by a synchronization director so that they operate at the same frequency (referred to as the "PWM frequency"). FIG. 3A shows; the three circuits 301,302 and 303 are equivalent to three PWM power extractors. The circuits 301,302 and 303 employ the same single phase power extractor and use the same operating principles as described above. The single-phase power extractor 301 outputs a-phase AC power and has a switch QA; the single-phase power extractor 302 outputs B-phase AC power and has a switch QB; the single-phase power extractor 303 outputs a C-phase alternating current and has a switch QC. The sync director 310 is designed to activate the paths of the 3 switches QA, QB, QC of the 3 power extractors simultaneously and extract power at the same frequency but different load duty factors.

Suppose that the DC power supply has a constant input DC power P during one AC power cycle_mx. And one PWM duty cycle is indeed a fraction of the entire AC power cycle. Fig. 3B represents the input DC power during one PWM duty cycle, as is presented symbolically in fig. 3C. In one PWM duty cycle, 3 power extractors extract DC power. The height of the extracted power is P in FIG. 3C_xIn FIG. 3B, P_xLower than the input DC power P _mx1/3 of (1). The duty factor of the PWM duty cycle of the A-phase power extractor is adjusted to be equal to cos²(ω t) (or sin)²(ω t)) so that the output AC power is equal to P_x*cos²(ω t) (or P_x*sin²(ω t)), the specification of the single-phase output AC power can be conformed. Similarly, the duty factor of the PWM duty cycle of the B-phase power extractor is adjusted to be equal to cos²(ω t +120 °) (or sin²(ω t +120 °)) so that the output power is equal to P_x*cos²(ω t +120 °) (or P_x*sin²(ω t +120 °)). In addition, the load duty factor of the C-phase power extractor in the PWM duty cycle is adjusted to be equal to cos²(ω t-120 °) (or sin²(ω t-120 °)) so that the output power is equal to P_x*cos²(ω t) -120 ° (or P)_x*sin²(ω t-120 °)). In addition, in order to comply with the three-phase grid specifications, the phase difference between the single-phase output powers of the three-phase ac power must be 120 °.

Note that a typical conventional 3-phase DC/AC modulator has overlapping time periods during power extraction (symbolically shown in fig. 3C). The three extractors extract power in overlapping time periods is referred to herein as "simultaneous power extraction"; and the director (as shown in figure 3A) that extracts power at this same time period is referred to herein as a "simultaneous regulator".

After the law of conservation of energy is combined with the electric energy characteristic of extremely short service life, the sum of the electric power captured by three single-phase electric power in the simultaneous electric power capture is forced to be not larger than the input DC power supply P_mx(or P)_mx>P_x+P_x+P_x(ii) a Or P_x<(1/3)P_mx). Power summation for conventional three-phase AC power output: p (t) ═ P_x(sin²(ωt)+sin²(ωt+120°)+sin²(ω t-120 °)); or P (t) ═ P_x(cos²(ωt)+cos²(ωt+120°)+cos²(ω t-120 °)). Due to (sin)²(ωt)+sin²(ωt+120°)+sin²(ωt-120°))＝(cos²(ωt)+cos²(ωt+120°)+cos²(ω t-120 °)) 3/2. Thus, P (t) ═ (3/2) P_x<(3/2)*(1/3)P_mx＝1/2P_mx. In other words, the sum of the output power of the conventional DC/AC modulator cannot be larger than (1/2) P because three single-phase power extractors extract power simultaneously_mxOnly half of the input DC power.

In other words, the output total AC power of the conventional 3-phase DC/AC modulator cannot be greater than half of the input DC power. Alternatively, when such conventional modulators are used in photovoltaic power plants, conventional 3-phase DC/AC modulators can only capture and convert less than half of the DC power produced by Photovoltaic (PV) solar panel strings. At least half of the dc power generated by the photovoltaic power plant becomes surplus power. Unless the surplus power is captured and stored in the equipment using the MEUPT, the surplus power is converted into heat energy.

Restated, a conventional three-phase DC/AC modulator basically operates three single-phase DC/AC modulators to perform the functions of extracting and converting power, the single-phase DC/AC modulators providing similar time-root-mean-square AC power to a 3-phase grid of 3 or 4 power lines; the output single-phase ac power must be 120 ° out of phase with each other. In other words, the conventional 3-phase DC/AC modulator is a DC/AC modulator that operates three single-phase DC/AC modulators. The DC power input to each single-phase DC/AC modulator is 1/3 of the DC power input to the 3-phase modulator, and 1/3 of the power input to the unidirectional modulator, only half of the DC power is extracted and converted into single-phase AC power, and the phase difference between the 3 output single-phase powers must be 120 °; and outputs three single phase ac power to a three phase grid of 3 or 4 power lines. Each pair of power lines carries a single phase alternating current power of the same frequency (AC power frequency) and has the same time root mean square power; but the unidirectional AC power must be 120 ° out of phase with each other. The wording "power line" and "cable" is used interchangeably herein and in the professional field.

According to the derivation results set forth in the referenced issued patents; and again confirmed in the theoretical derivation described above; each input of DC power to a single phase modulator (in a 3-phase DC/AC modulator) that is less than or equal to 1/3 of the input of DC power to the three phase modulator, only less than half of this DC power is extracted and converted to a single phase AC power output. Thus, the maximum three-phase AC power that any conventional three-phase DC/AC modulator outputs (extracts and converts) at any one time can only be half the DC power produced; that is, P (t) 3 (1/2) × (1/3) P_mx＝(1/2)P_mx。

It is emphasized here that; the theoretical derivation described above reveals the serious consequences of the "simultaneous extraction of power" design used in the conventional three-phase DC/AC modulator industry. This design has long been followed in the three-phase DC/AC modulator industry; the inverter industry is not even aware of the serious consequences of such a design. The theory herein deduces that the serious result of this kind of electric energy capturing method is disclosed for the first time. The serious consequence of such de-design results in "the sum of the 3 AC power outputs of a conventional three-phase DC/AC modulator is less than half the input DC power". The conventional (common) simultaneous capture power design approach disclosed herein has indeed been designed for use in the green power industry; particularly in the photovoltaic power industry.

In other words; the traditional photovoltaic power industry does employ simultaneous capture of electrical energyAnd (4) designing a mode. Conversely, the law of conservation of energy combined with the very short-lived power characteristics forces each single-phase DC/AC modulator designed in this way to extract the maximum power (P)_x) Is less than the maximum power (P) of the photovoltaic power generation DC power supply_mx) One third of (i.e., P)_x<(1/3)P_mx). So at any time, the sum of conventional three-phase AC power delivery is P (t) ═ (3/2) P_x(ii) a That is to say P (t)<(3/2)*(1/3)*P_mx<(1/2)P_mxOr spoken: less than half the maximum DC power for PV generation. Thus, using a conventional three-phase DC/AC modulator, at least half of the DC power generated by the PV strings becomes surplus power. This remaining electrical energy can only be converted to thermal energy unless captured and stored in a facility such as the MEUPT optimizer ….

As described above, at least half of the input DC power becomes surplus power using the conventional 3-phase DC/AC modulator. Based on the messages disclosed herein, the next problem may be: "we may not capture, convert and deliver DC surplus power to provide an alternating current (power) source using more than one conventional three-phase DC/AC modulator"? As will be understood from the following description, the answer is negative.

As shown in FIG. 4, two identical sets of 3-phase DC/AC modulators 4210 and 4220 (each set having a manufacturer's declared power rating P)_mx) Upon connection to the PV generator 4110, the absence of a connection to the PV generator 4110 may capture and store the maximum DC power P that the remaining power devices (e.g., MEUPT optimizer) can provide_mx. The law of conservation of energy only allows one of the two parallel DC/AC modulators 4210 and 4220 to extract half of the total input DC power P_mx(i.e., each modulator only fetches 1/2P_mxAs input power). In other words, the input DC power of each of the two identical 3-phase DC/AC modulators can only be 1/2P_mx。

The 3 power extractors cited above (in a conventional 3-phase DC/AC modulator) follow a simultaneous power extraction design. Each three-phase DC/AC modulator is capable of converting only half of the input DC power to produce output AC power; is equal to (1/2) ((1/2)*P_mxOr P is_mx1/4 of (1). The total AC power output from the two modulators is 2 × P (1/4)_mx(ii) a Still equal to (1/2) P_mx. The same conclusions can be drawn by the above reasoning, also with a higher power rating or with a higher number of DC/AC modulators for the case analysis concerned. It is emphasized again that "simultaneous extraction of electrical energy" is the root cause of more than half of the generated dc power being the remaining electrical energy.

The next problem may be: "can we design an experiment to clearly demonstrate that half of the electrical energy generated by a photovoltaic string becomes surplus energy when extracting power through a conventional three-phase DC/AC modulator? "an experimental design is described immediately herein. It is used to demonstrate that if a conventional three-phase DC/AC modulator is used to extract the DC power generated by a PV string, at least more than half of the generated DC power becomes residual energy.

Third stage: conclusive experimental evidence

The MEUPT optimizer is designed to capture/use the above-mentioned surplus power-surplus energy. The experimental setup and experimental execution steps described below, in combination with the MEUPT optimizer, are intended to clearly demonstrate that at least half of the photovoltaic power generation becomes surplus power when power is extracted by a conventional three-phase DC/AC modulator.

Fig. 6A illustrates a power plant of PV power plant 6000A merged by 2 AC power production units 6100A and 6200A. The AC power generation units 6100A and 6200A each use MPPT design; the captured DC power is converted to three-phase ac power for provision to the grid 6600A. AC power production unit 6100A includes (30kW) DC generator 6110A and (30kW) 3-phase DC/AC modulator 6130A. The AC power production unit 6200A then includes a (30kW) DC power generator 6220A and a (30kW) 3-phase DC/AC modulator 6230A. Generator 6110A uses 2 parallel PV bank strings 6111A and 6112A to produce DC power. Generator 6220A uses another 2 parallel PV bank strings 6221A and 6222A to produce DC power. Each of the 4 PV strings is composed of 25 solar panels connected in series; each solar panel is capable of generating 300W of DC power in the clear, cloudless sky at midday.

DC generator 6110A supplies DC power to 3-phase DC/AC modulator 6130A; the DC generator 6220A supplies DC power to the 3-phase DC/AC modulator 6230A. Then, the two modulators 6130A and 6230A convert the supplied DC power into 3-phase AC power. In this experiment, the output AC power of the power generation units 6100A and 6200A was measured by two 3-phase AC wattmeters (in kilowatts) 6351A and 6352A, respectively. The AC power (in kilowatt hours) produced by the two power generation units 6100A and 6200A is also measured by two wattmeters 6361A and 6362A, respectively, to accumulate the power. The generated three-phase AC power is then supplied to grid 6600A through transformer 6500A. Photovoltaic plant experiments were then performed and the cumulative electrical energy generated by the two AC power production units 6100A and 6200A was measured.

Since all components (including two sets of instruments for measuring power and electric energy) are identical based on the two power generation units 6100A and 6200A, the readings of the two meters each day show equal values of generated electric energy during the 7-day experimental period described above, confirming that the two sets of equipment are sufficiently identical. After the 7-day operation, one of the two AC power generation units "6200A" remains unchanged, while the other AC power generation unit "6100A" is modified to a different configuration "6100B", as illustrated in the left side of fig. 6B.

The power generation unit 6200B of fig. 6B is the same as the unmodified power generation unit 6200A of fig. 6A. Further, the components 6351B, 6361B, 6352B, 6362B, 6500B, 6600B of fig. 6B are the components 6351A, 6361A, 6352A, 6362A, 6500A, 6600A of fig. 6A. Further, although the configuration of the power production unit 6100B in fig. 6B is different from the power production unit 6100A of fig. 6A, the power components in the power production unit 6100B of fig. 6B are still the components configured in the production unit 6100A of fig. 6A. For example, PV bank strings 6111B and 6112B of fig. 6B are the same as PV bank strings 6111A and 6112A of fig. 6A, respectively. The same DC/AC modulator 6130B of fig. 6B is the same component as DC/AC modulator 6130A of fig. 6A.

Six (6) steps in the next section describe how to modify the power generation unit 6100A to 6100B architecture, such that 6100B is the same as the architecture configured on the left side of fig. 2B. Step 1 is to add a set of decoupling diodes 6311B between the parallel solar array strings 6111B and 6112B and the 3-phase DC/AC modulator 6130B following MPPT architecture. Step 2 is to add a set of energy storages 6410B configured in the architecture of 6100B. Step 3 further connects the energy storage 6410B to the DC input of the DC/AC modulator 6130B through another set of decoupling diodes 6312B and switch SW 1. Step 4 adds another three-phase DC/AC modulator 6130S (20kW) into the 6100B architecture, and the modulator 6130S operates according to the designed orientation of MEUPT controller 6420B. Step 5 is to connect DC/AC modulator 6130S to accumulator 6410B through another set of decoupling diodes 6313B and switch SW 2. Step 6 is to connect the output of modulator 6130S to wattmeter 6351B and kilowatt-hour meter 6361B through switch SW 3. Note that, as referred to herein as a "set of stop-coupled diodes," a classification in the diode art may be referred to as "blocking diodes. In addition, the switches SW1, SW2 and SW3 in FIG. 1B are configured to enable 6100B to introduce the relevant devices into the experiment (or separate them from the experiment) at appropriate times according to the execution steps of the experiment design.

The first night after the above configuration is adjusted; the SW2 and SW3 switches are switched off and SW1 is switched on. Thus, modulators 6130B and 6230B may begin operating early the next day. The meters 6351B and 6352B measuring the two power outputs of the power generation units 6100B and 6200B both give the same accumulated readings before this operation. In addition, it can be confirmed from the measurement of the rise in the terminal voltage of accumulator 6410B that accumulator 6410B starts charging early. As shown by the daily cumulative readings of kilowatt-hour meters 6361B and 6362B, the two power generation units 6100B and 6200B provide equal amounts of electrical energy to the three-phase AC power grid. This experimental procedure does prove that the added chopper diode set 6311B and energy storage 6410B do not change the power and the generated electric energy of the power generation unit 6100B.

The switches SW1, SW2, and SW3 are all switched on at night after the first day of operation (second night). Modulators 6130B and 6230B also begin operating in the next morning, while modulator 6130S operates at a lower power within about 15 minutes after modulators 6130B and 6230B begin operating. Thereafter, modulator 6130S increases the DC/AC converted power approximately every 2 minutes; this process of increasing the converted power is consistent with the designed energy storage control program. The two power generation units 6100B and 6200B going down the day until the power supplied to the three-phase grid near sunset can be derived from the readings of two kilowatt-hour meters at the end of the second day. As a result, the cumulative daily increase reading for kilowatt-hour meter 6351B (for cell 6100B) reaches more than twice the cumulative daily increase reading for kilowatt-hour meter 6352B (for cell 6200B). Thus, the above experimental results show that the cumulative increased power per day provided to the grid from the configuration adjusted generator 6100B is more than twice the cumulative increased power provided by the unadjusted generator 6200B. After six consecutive days of this experiment, switches SW1, SW2 and SW3 remain on, and the regulated power generation unit 6100B continues to provide more than twice as much power per day to the grid as power generation unit 6200B.

The evening after the six day experiment, the SW2 and SW3 switches were turned off. During the continuous 5 days during which the switches SW2 and SW3 remain open, the power supplied to the grid from the power generation units 6100B and 6200B every day is returned to the same amount of power supply. Later night SW2 and SW3 are switched on again. And keeping the switches SW2 and SW3 operating with the passage for the subsequent 5 consecutive days, the daily accumulated power supply energy measured by the power generation unit 6100B per day becomes more than twice the daily accumulated power supply energy of the power generation unit 6200B again.

As previously explained; performing this experiment can be confirmed without any doubt; predictions presented in the second section of patent publications (US2016/0036232 and US2017/0149250A 1); there is indeed surplus electrical energy present in PV power plants. Particularly, after the DC power generated by the PV power station is extracted by the 3-phase DC/AC modulator, about half of the DC power is still left unretracted, and the surplus power becomes surplus power.

There are two ways in which the aforementioned undesirable consequences can be eliminated. The first approach is to incorporate the MEUPT optimizer into the power generation system following the principles described in the referenced issued patents. Another approach follows the principles described herein, and in accordance with the present invention: the power is sequentially extracted according to the adjustment of the load duty factors of the A, B and C phases. Please note that the present invention replaces the conventional simultaneous power acquisition method with the sequential power acquisition method.

And a fourth section: proposal for sequential electric energy capture

A proposal in the principles described herein; the sequential power extraction of the phases A, B and C can ensure that the power extraction time of the three phases does not overlap. When sequential power acquisition is carried out in each PWM working period, the phase A firstly acquires DC power timely; the phase B acquires DC power immediately after the phase A acquires power; c extracting DC power corresponding to the last time. By doing so, the relatively large intensity of the extracted power is P_xAnd may be equal to the input maximum DC power value P in each phase_mx. The sequential power extraction method is different from the simultaneous energy extraction method in that the maximum power extracted by the simultaneous energy extraction method can only be equal to P_mxOne third (1/3).

To make the following analysis intuitive and realistic, let us assume that the AC frequency is 50Hz and the PWM frequency is 18 KHz. This assumption may be such that the phase angle of the AC power advances exactly 1 for the duration of each PWM duty cycle⁰. Fig. 5A shows a proposed circuit for applying the new power extractor. The new power extraction circuit is similar to the conventional circuit shown in fig. 3A. Please note that the synchronous regulator 310 used in the conventional power extractor shown in fig. 3A is replaced by the sequential controller 510 in the current design, and becomes the circuit shown in fig. 5A.

It is emphasized here that; the power extraction regulated by the concurrency regulator is power extraction initiated at the same time; that is, the way to extract power simultaneously is to absolutely follow 3 single-phase DC/AC modulators to start power extraction at the same time. Conversely, the power extraction regulated by the sequential controller is performed in time sequence; that is, the power extraction process performed by the sequential power extractor follows the proposed adjustment of the load duty factors of the phases a, B and C to sequentially extract power.

Enumerating an implementation case; a 3-phase DC/AC modulator using a sequential controller to control 3-phase power extraction is shown in fig. 5B. In performing this power extraction mode, the A-phase power extraction is arranged (controlled) to start at the start of the PWM duty cycle for a duration d_A(t); the B-phase power acquisition arrangement (control) is started at the end of the A-phase power acquisition for a duration d_B(t); and the C-phase power extraction is arranged (controlled) to start at the end of the B-phase power extraction for a duration d_C(t) of (d). In this way, the 3-phase power extraction is arranged (controlled) to operate sequentially and seamlessly. As can be seen from fig. 5B, this power extraction method ensures that no overlapping power extraction periods occur. In practice, there may be a transition time interval between the end of one power acquisition and the beginning of the next power acquisition. However, the time interval can be very short in each PWM duty cycle, which can be designed to be 33%, 20%, 10% or even less than 1% of the PWM duty cycle. Therefore, the maximum intensity P of the extracted power of each phase_xCan be designed to be equal to the input maximum DC power value P_mx(ii) a If the simultaneous power extraction method is used, only the maximum DC power P relative to the input is extracted_mxA certain proportion (at most one third).

Let us set the duration of each PWM duty cycle to D. The load duty factor of the A-phase power extraction is defined as d_A(t)/D; the load work factor of the B-phase captured power is d_B(t)/D; the load work factor of the C-phase power extraction is equal to d_C(t)/d. in accordance with the principles described herein, it is proposed herein to set these three load duty factors to: d_A(t)/D＝2/3cos²(ωt),d_B(t)/D＝2/3cos²(ω t +120 °), and d_C(t)/D＝2/3cos²(ω t-120 °). Then, 3 respective corresponding time lengths of power extraction are allocated according to the calculated load duty factor. Please note the sum of the power extraction durations of the three phases; dA (t) + dB (t) + dC (t) is exactly equal toD, the duration of one PWM duty cycle.

As previously described, the period of one PWM duty cycle is equal to 1 advance in the AC power cycle⁰The time interval of the phase angle; therefore, if the phase difference among the A phase, the B phase and the C phase is 120 DEG + -1⁰(ii) a This- + also fits well within the tolerance of the existing grid phase. The sum of the power carried in the three pairs of power lines p (t); p (t) ═ P_A(t)+P_B(t)+P_C(t)＝P_mx(2/3)(cos²(ωt)+cos²(ωt+120°)+cos²(ωt-120°))＝P_mx(2/3)(3/2)＝P_mx. In other words, the total power carried by the three-phase power line at any one time may be substantially equal to the maximum DC power generated. That is, if the sequential power capturing manner is followed, there is no surplus power. Another way is that: in conjunction with the sequential power extractor, the 3-phase DC/AC modulator is able to fully extract all of the generated DC power, essentially achieving zero residual power.

To reiterate, the principles described herein propose to sequentially and seamlessly extract the relative power of each of the 3-phase power. When the 3-phase power extraction mode is changed to sequential mode, the extracted power strength can be designed to be equal to the maximum DC power P inputted_mx. It is then further proposed according to the principles described herein; adjusting the load work factors of 3 phases to 2/3cos of A phase²(ω t), 2/3cos for phase B²(ω t +120 °), and 2/3cos for phase C²(ω t-120 °). By doing so, the 3-phase power extraction process can be sequentially performed; the 3-phase power extraction can be completed in a PWM working period completely and seamlessly; and the phase difference between the output AC power of the phase A, the phase B and the phase C is within the acceptable range of 120 +/-1 DEG for the power grid.

Thus, when a three-phase DC/AC modulator is added to the proposed sequential power extraction controller; the designed DC/AC modulator can extract and convert the maximum DC power P generated by the whole photovoltaic string_mxWithout surplus power; and the output alternating current power can be matched with the power gridAnd (5) standardizing.

The fifth section: design considerations for sequential controllers

For one embodiment; it is proposed that the start time of PWM can be applied to start the power extraction of phase a, with duration (2/3) D × cos (ω t); then the signal change of A phase power extraction (from the period opening to the period closing of A phase power extraction) is applied to trigger and start B phase power extraction, and the duration is (2/3) D × cos (ω t +120 °); the signal change of the B-phase power extraction (from the B-phase power extraction cycle on to the cycle off) is then applied to trigger and start the C-phase extraction power.

As another example: explicitly advancing the AC power phase value (e.g., 1) due to one PWM duty cycle⁰) Thus, a list can be constructed; the determined end time of the a-phase power acquisition is taken as the "first time value", and the determined end time of the B-phase power acquisition is taken as the "second time value". This list includes an expanded column of entries that may represent a cycle of the entire power cycle (e.g., 180 columns representing 180)⁰Each 1 of (1)⁰Phase change). Since the power supplied is proportional to the square of the voltage and the square of the oscillating voltage of sine and cosine pulses generates power pulses with twice the frequency of the oscillating voltage, 360⁰The power cycle generated by the voltage cycle of (1) becomes 180⁰。

Two continuous time axes are adopted in each row of the time schedule, and the two time axes which can be periodically set in a PWM period are designed to correspond to the starting time of A-phase power extraction (the starting of PWM) and the ending time of power extraction (the first time value in the row); corresponding to the start time of the B-phase power extraction (the first time value in the row) and the end time of the power extraction (the second time value in the row); then corresponds to the start time (second time value in the row) and its end time (end of PWM) of the C-phase power extraction. When 180 rows are completed, it means that the DC/AC modulation conversion process of one AC power cycle is completed. The same process may then be repeated for the next DC/AC modulation conversion …, and so on. But in this embodiment a (clock) clock with a time resolution better than 1/180,000 seconds (or 5 microseconds) must be used.

The 'synchronization module' or 'simultaneous control module' in the traditional three-phase DC/AC modulator is used for synchronously starting PWM by using the maximum power and the minimum power point of an AC power cycle; in this way, as the phase/frequency occasionally drifts in the grid, the output ac power ripple phase can drift with it. In addition, the principle of the synchronization module described herein can also use a synchronization component to guide the power acquisition in response to phase/frequency drift in the power grid.

Section six: conclusion

As described in the first section, conventional DC/AC single-phase modulators employ a PWM power extractor to extract input DC power. When at time t is counted by cos²(ωt)(or sin²(ω t)) the output AC power conforms to grid specifications when the load duty factor in one PWM duty cycle is adjusted. Note that there are two regions in the energy space for each PWM duty cycle; one is the extracted energy region and the other is the residual energy region. The referenced publication teaches that when integrated over several periods of AC power cycles, the amount of remaining electrical energy is at least as great as the extracted electrical energy. In other words, a single-phase DC/AC modulator can only extract and convert at most half of the input DC power. The captured electric energy is converted into AC power and is supplied to a corresponding power transmission line on a power grid; the remaining energy, however, can only be converted to thermal energy unless captured and stored in a facility such as the MEUPT optimizer ….

As described in the second section, a conventional three-phase DC/AC modulator operates three identical single-phase DC/AC modulator operations. Each single-phase DC/AC modulator may extract and convert half of the input DC power to AC power that complies with the grid specifications. Please note that, since the 3 modulators start energy extraction simultaneously, the input dc power can only be equal to one third of the maximum generated dc power. Thus, a three-phase DC/AC modulator can only extract at most half of the power provided by the DC power source and convert it to AC power that meets the grid specifications. The output AC powers of the three single-phase DC/AC modulators must be 120 ° out of phase with each other. In addition, the 3 single-phase output ac power is provided to customers using power on the grid through 3 or 4 power lines.

In other words; the conventional photovoltaic power generation industry employs a conventional DC/AC modulator, which is designed using a simultaneous power extraction mechanism; therefore, the law of conservation of energy forces three maximum power intensities P to be extracted_xIs less than the maximum power P of the DC power generated by the PV group string_mxOne third of (i.e., P)_x<(1/3)P_mx). Mathematically, it can be derived that the conventional three-phase ac power output has a maximum power sum of P (t) (3/2) P_x(ii) a I.e. less than (1/2) P_mx(or half of the dc power generated by the PV string). Thus, when using a conventional three-phase DC/AC modulator, at least half of the DC power produced by the PV strings becomes surplus power. The remaining energy, however, can only be converted to thermal energy unless captured and stored in a facility such as the MEUPT optimizer ….

The theoretical derivation described in the second section herein reveals the serious consequences that can result from the use of a "simultaneous extraction of power" design in the conventional three-phase DC/AC inverter industry. This design has long been followed in the three-phase DC/AC modulator industry; the inverter industry is not even aware of the serious consequences of such a design. It is theorized herein that the serious consequences of such an electrical energy capture are disclosed for the first time. The serious consequence of such de-design results in "the sum of the 3 AC power outputs of a conventional three-phase DC/AC modulator is less than half the input DC power". The conventional (common) design of captured electrical energy disclosed herein has indeed been designed for use in the green power industry; particularly in the photovoltaic power industry.

There are two ways in which the above-mentioned adverse consequences can be eliminated. The first approach is to incorporate the MEUPT optimizer into the energy system following the principles described in the referenced issued patent. Another approach is to follow the principles described herein; to use sequential power extraction following the proposed adjustment of the load duty factors for phases a, B and C.

The fourth section describes the proposed sequential power extraction and negationCarrying the principle of work factor adjustment. Sequentially capturing electrical energy in each PWM working period; firstly, capturing DC power in time of phase A; the phase B is to extract DC power immediately after the phase A extracts power; and finally, the DC power is extracted when the C phase is right. In this way, the intensity P of the maximum power extracted_xIn A, B, or C phase, may be equal to the maximum input DC power P produced_mx. The sequential power extraction method is completely different from the simultaneous power extraction method, and the maximum power extracted by the simultaneous power extraction method can only be equal to P_mxOne third (1/3).

The principles described herein suggest: the power acquisition start times of the A, B, and C phases are commanded and adjusted by the sequence controller. Thus, the 3-phase power extraction is converted into 3 dependent sequential power extraction; the maximum power level extracted in this way may be equal to the maximum DC power P input by the generator_mx. Furthermore, the 3 load work factors can be further adjusted to 2/3cos for phase A respectively by applying the principle described herein²(ω t), 2/3cos for phase B²(ω t +120 °) and 2/3cos in C phase²(ω t-120 °). By such adjustment, the 3-phase power extraction process can be successfully completed in a PWM duty cycle, sequentially and completely seamlessly. Thus, the phase difference of the AC power output by the phase A, the phase B and the phase C is within 120 +/-1 degrees; is within the tolerance of the grid codes. Thus, when using the 3-phase DC/AC modulator of the proposed sequential power extractor; the newly designed DC/AC modulator can extract and convert all (or substantially all) of the maximum power P produced_mxThere is no (or little) excess remaining energy. Furthermore, the generated output AC power may also easily comply with 3-phase AC grid specifications.

The patented invention may be embodied in other specific forms without departing from its spirit or essential characteristics. Accordingly, the scope of coverage of this patent is defined by the claims appended hereto, and not by the foregoing description. Any alterations and further modifications of the principles as applied herein, without departing from the scope of the patent and its equivalents, are intended to be covered by the claims.