阅读说明：本技术 变换装置 (Conversion device ) 是由 刘腾 应建平 乔理峰 王欣 肖宏伟 于 2020-05-26 设计创作，主要内容包括：本发明实施例提供一种变换装置,连接于交流电网和负载之间,所述变换装置包括：电感,与所述交流电网电连接；第一级变换器,其第一端与所述电感电连接且第二端电连接至母线,用以根据所述交流电网输出母线电压,所述第一级变换器包括N电平的交流-直流变换器,所述N电平的交流-直流变换器包括多个开关桥臂,其中所述交流-直流变换器的每一开关桥臂的上桥臂和下桥臂均包含多个串联的半导体器件,且每一半导体器件的额定耐压值Vsemi大于等于(Vbus*δ)/((N-1)*Nseries*λ)；以及第二级变换器,其第一端与所述母线电连接且第二端与所述负载电连接,用以将所述母线电压转换为输出电压以给负载提供能量。本发明的技术方案可以降低变换装置的体积和成本。(An embodiment of the present invention provides a conversion device, connected between an ac power grid and a load, including: an inductor electrically connected to the AC power grid; a first-stage converter, a first end of which is electrically connected to the inductor and a second end of which is electrically connected to a bus, for outputting a bus voltage according to the ac power grid, wherein the first-stage converter includes an N-level ac-dc converter, the N-level ac-dc converter includes a plurality of switching legs, an upper leg and a lower leg of each switching leg of the ac-dc converter each include a plurality of semiconductor devices connected in series, and a rated withstand voltage value Vsemi of each semiconductor device is greater than or equal to (Vbus δ)/((N-1) × Nseries λ); and a second stage converter having a first end electrically connected to the bus and a second end electrically connected to the load for converting the bus voltage to an output voltage for energizing the load. The technical scheme of the invention can reduce the volume and the cost of the conversion device.)

1. A converter assembly for connection between an ac power grid and a load, the converter assembly comprising:

an inductor electrically connected to the AC power grid;

a first stage converter having a first end electrically connected to the inductor and a second end electrically connected to a bus for outputting a bus voltage according to the AC power grid, the first stage converter comprises an N-level AC-DC converter including a plurality of switching legs, wherein the upper and lower bridge arms of each switching leg of the ac-dc converter comprise a plurality of semiconductor devices connected in series, and the rated withstand voltage value Vsemi of each semiconductor device is equal to or greater than (Vbus δ)/((N-1) × Nseries λ), wherein Vbus represents the bus voltage, δ represents bus ripple, N represents the number of levels of the first stage converter, λ represents a voltage derating coefficient of the semiconductor device, and lambda is less than or equal to 1, Nseries represents the number of the semiconductor devices connected in series, and Nseries is more than or equal to 2; and

a second stage converter having a first end electrically connected to the bus and a second end electrically connected to the load for converting the bus voltage to an output voltage for energizing the load.

2. The converter assembly of claim 1, wherein said load comprises a dc load, and wherein said second stage converter comprises a dc-dc converter, said dc-dc converter being electrically connected to said dc load.

3. The converter assembly of claim 1, wherein said load comprises an ac load, and said second stage converter comprises a dc-ac converter electrically connected to said ac load.

4. The converter arrangement of claim 1, wherein said first stage converter comprises at least two parallel ac-dc converters.

5. The converter arrangement according to claim 4, wherein the second stage converter comprises at least two DC-DC converters or DC-AC converters, which are connected in series or in parallel.

6. The converter according to claim 4, further comprising a controller for detecting the power of the load and controlling the operation of the at least two parallel AC-DC converters according to the power of the load.

7. The converter according to claim 6, wherein all of said ac-dc converters are operated when the load is fully loaded.

8. The converter according to claim 6, wherein the controller controls some of the at least two parallel ac-dc converters to operate and the other ac-dc converter to not operate when the load is light or half-loaded.

9. The inverter of claim 1, further comprising a controller and a dc circuit breaker, wherein the dc circuit breaker is disposed between the first stage inverter and the second stage inverter, and wherein the dc circuit breaker is electrically connected to the controller and controls the dc circuit breaker according to a control signal sent by the controller.

10. The converter according to claim 1, wherein the ac-dc converter comprises any one of the following ac-dc converters:

a two-level rectifier, a three-level wiener rectifier and a three-level mid-point clamped converter.

11. The converter according to claim 1, further comprising a filter network, wherein said filter network has a first terminal, a second terminal, and a third terminal, a first rc circuit is disposed between said first terminal and said third terminal of said filter network, a second rc circuit is disposed between said second terminal and said third terminal of said filter network, said first terminal of said filter network is electrically connected to said ac power grid, said second terminal of said filter network is electrically connected to said bus terminal or said second terminal of said second stage converter, and said third terminal of said filter network is grounded through a first capacitor.

12. The conversion device according to claim 11, wherein a second capacitor and a third capacitor are connected in series between the buses, and the second end of the filter network is electrically connected between the second capacitor and the third capacitor.

13. The conversion device according to claim 11, wherein a fourth capacitor is connected between the bus bars.

14. The converter assembly of claim 1 wherein said inductor comprises a common mode and differential mode integrated inductor, said inductor being disposed between said ac power grid and said first stage converter.

15. The transformation device according to claim 1,

the inductor comprises a differential mode inductor and a common mode inductor, the differential mode inductor is connected between the alternating current power grid and the first-stage converter, and the common mode inductor is arranged between the alternating current power grid and the second end of the second-stage converter.

16. The transformation device according to claim 11,

the inductor comprises a differential mode inductor and a common mode inductor, the differential mode inductor is connected between the alternating current power grid and the first-stage converter, and the common mode inductor is arranged between the first end and the second end of the filter network.

17. The transformation device according to claim 11,

the first resistance-capacitance circuit comprises the first resistor and the fifth capacitor which are connected in series, and the second resistance-capacitance circuit comprises the second resistor and the sixth capacitor which are connected in series.

Technical Field

The invention relates to the technical field of power electronics, in particular to a conversion device.

Background

In recent years, power transmission systems represented by direct current have been receiving more attention in the industry than conventional alternating current power distribution systems. With the development of new energy technology and the increase of direct current load, the advantages of direct current power transmission combined with new energy power generation are more and more prominent. The direct current transmission saves the link of mutual conversion from Direct Current (DC) to Alternating Current (AC), and reduces the system cost. At a user end, with the development of the internet technology, the scale of a data center reaches several megawatts or even dozens of megawatts. The electric automobile industry is developed vigorously, the quantity of electric automobiles in China is increased rapidly, the electric automobiles have wide growth prospect, and the requirement of the development of the electric automobiles on high-power charging piles is gradually expanded.

Conventional conversion devices have a number of problems in high power applications. As shown in fig. 1, in the topology of the converter for providing the charging power 103 for the electric vehicle 104, the primary side of the medium voltage transformer 101 is connected to a Medium Voltage (MV) grid, the secondary side multi-winding provides a Low Voltage (LV) ac output, the medium voltage transformer 101 can implement medium voltage isolation, and the subsequent power electronic converter 102 can adopt a non-isolation scheme. The scheme has the advantages of high full-load efficiency (98%), mature technology and high reliability, but the adopted transformer is large in size, and has the defects of low efficiency, high harmonic content (THD) and the like under the condition of light-load output. For example, at a system power of 2.4MW, the efficiency is only 92.5% if the system is lightly loaded at 100kW output. In practical application, the full load condition is less, and most of conditions are the conditions of working under light load and half load.

As shown in fig. 2, in the converter that supplies power to the load 201 by using the medium-voltage conventional scheme, the cascaded structure of the modules 202 is adopted, which has the advantages of mature and reliable technology, but because the dc bus capacitor of the module 202 is located in each single-phase bridge arm, and the phase current of each phase flows through the capacitor of each phase alone, which may cause the power to fluctuate by two times, a large number of capacitors need to be configured to reduce the ripple voltage of the capacitors, which may result in the reduction of the power density of the power module and the increase of the volume of the system.

Based on the problems, the concept of the medium-voltage direct-current micro-grid is provided, the direct-current power grid is combined with new energy and an energy storage technology, the requirements of rapid development of a data center and a high-power automobile charging station are met, local power generation and nearby power utilization can be realized, and the loss of cables is reduced. In addition, the direct current can not generate reactive loss, the problems of reactive power balance and stability are solved, and the system efficiency and the operation reliability of the power grid can be improved.

The basic topology architecture of the medium-voltage direct-current microgrid comprises an AC/DC converter connected with an alternating-current power grid, and the AC/DC converter controls an output direct-current bus. AC/DC converters generally use high voltage semiconductor devices that operate at lower frequencies and require filters with lower cut-off frequencies, resulting in increased size and cost of the filters and, in turn, of the conversion devices between the AC grid and the load.

In summary, how to reduce the size and cost of the conversion device is a technical problem to be solved.

It is to be noted that the information disclosed in the above background section is only for enhancement of understanding of the background of the present disclosure, and thus may include information that does not constitute prior art known to those of ordinary skill in the art.

Disclosure of Invention

It is an object of the present disclosure to provide a transducer arrangement, which in turn reduces the size and cost of the transducer arrangement at least to some extent.

According to an embodiment of the present invention, there is provided a converter device connected between an ac power grid and a load, the converter device including: an inductor electrically connected to the AC power grid; a first stage converter having a first end electrically connected to the inductor and a second end electrically connected to a bus for outputting a bus voltage according to the AC power grid, the first stage converter comprises an N-level AC-DC converter including a plurality of switching legs, wherein the upper and lower bridge arms of each switching leg of the ac-dc converter comprise a plurality of semiconductor devices connected in series, and the rated withstand voltage value Vsemi of each semiconductor device is equal to or greater than (Vbus δ)/((N-1) × Nseries λ), wherein Vbus represents the bus voltage, δ represents bus ripple, N represents the number of levels of the first stage converter, λ represents a voltage derating coefficient of the semiconductor device, and lambda is less than or equal to 1, Nseries represents the number of the semiconductor devices connected in series, and Nseries is more than or equal to 2; and

a second stage converter having a first end electrically connected to the bus and a second end electrically connected to the load for converting the bus voltage to an output voltage for energizing the load.

In some embodiments, the load comprises a dc load and the second stage converter comprises a dc-dc converter electrically connected to the dc load.

In some embodiments, the load comprises an ac load, and the second stage converter comprises a dc-ac converter electrically connected to the ac load.

In some embodiments, the first stage converter comprises at least two parallel ac-dc converters.

In some embodiments, the second stage converter comprises at least two dc-dc converters or dc-ac converters connected in series or in parallel.

In some embodiments, the converter further comprises a controller, and the controller detects the power of the load and controls the working state of the at least two parallel ac-dc converters according to the power of the load.

In some embodiments, all of the ac-dc converters are operated when the load is fully loaded.

In some embodiments, when the load is light load or half load, the controller controls some of the at least two parallel ac-dc converters to operate, and the other ac-dc converters do not operate.

In some embodiments, the inverter further includes a controller and a dc breaker disposed between the first-stage inverter and the second-stage inverter, wherein the dc breaker is electrically connected to the controller and controls the dc breaker to operate according to a control signal sent by the controller.

In some embodiments, the ac-dc converter comprises any one of the following ac-dc converters: a two-level rectifier, a three-level wiener rectifier and a three-level mid-point clamped converter.

In some embodiments, the inverter further comprises a filter network, wherein the filter network has a first terminal, a second terminal and a third terminal, a first rc circuit is disposed between the first terminal and the third terminal of the filter network, a second rc circuit is disposed between the second terminal and the third terminal of the filter network, the first terminal of the filter network is electrically connected to the ac power grid, the second terminal of the filter network is electrically connected to the bus terminal or the second terminal of the second-stage inverter, and the third terminal of the filter network is grounded through a first capacitor.

In some embodiments, a second capacitor and a third capacitor are connected in series between the bus bars, and the second end of the filter network is electrically connected between the second capacitor and the third capacitor.

In some embodiments, a fourth capacitor is connected between the bus bars.

In some embodiments, the inductor comprises a common mode and differential mode integrated inductor disposed between the ac power grid and the first stage converter.

In some embodiments, the inductance includes a differential mode inductance and a common mode inductance, the differential mode inductance being connected between the ac grid and the first stage converter, the common mode inductance being disposed between the ac grid and the second terminal of the second stage converter.

In some embodiments, the inductance includes a differential mode inductance and a common mode inductance, the differential mode inductance being connected between the ac power grid and the first stage converter, the common mode inductance being disposed between the first and second ends of the filter network.

In some embodiments, the first resistance-capacitance circuit includes the first resistor and the fifth capacitor connected in series, and the second resistance-capacitance circuit includes the second resistor and the sixth capacitor connected in series.

The conversion device comprises a first-stage converter and a second-stage converter, wherein a plurality of semiconductor devices which are connected in series are arranged on an upper bridge arm and a lower bridge arm of each switching bridge arm of the first-stage converter, so that the switching frequency of each semiconductor device is increased, the first-stage converter works at a higher switching frequency, the cut-off frequency of a filter is increased, the size of the filter is reduced, and the cost of the filter is reduced.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure. It is to be understood that the drawings in the following description are merely exemplary of the disclosure, and that other drawings may be derived from those drawings by one of ordinary skill in the art without the exercise of inventive faculty.

Fig. 1 is a schematic view showing a structure of a converter apparatus using a medium voltage transformer in the related art;

fig. 2 is a schematic diagram showing a structure of a conversion apparatus using a cascade H-bridge structure in the related art;

FIG. 3 is a schematic diagram illustrating the structure of a changer according to an embodiment of the present invention;

FIG. 4 schematically illustrates a schematic diagram of an AC/DC topology in an embodiment of the present invention;

FIG. 5 schematically illustrates a schematic diagram of another AC/DC topology in an embodiment of the present invention;

FIG. 6 schematically illustrates a schematic diagram of yet another AC/DC topology in an embodiment of the present invention;

FIG. 7 schematically illustrates a schematic diagram of a DC/DC topology in an embodiment of the present invention;

FIG. 8 schematically illustrates a schematic diagram of another DC/DC topology in an embodiment of the present invention;

FIG. 9 schematically illustrates a schematic diagram of yet another DC/DC topology in an embodiment of the present invention;

FIG. 10 schematically illustrates a schematic diagram of yet another DC/DC topology in an embodiment of the present invention;

FIG. 11 schematically illustrates a schematic diagram of yet another DC/DC topology in an embodiment of the present invention;

FIG. 12 is a schematic view showing the structure of another conversion apparatus according to the embodiment of the present invention;

FIG. 13 is a schematic diagram showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 14 is a schematic diagram showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 15 is a schematic view showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 16 is a schematic diagram showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 17 is a schematic view showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 18 is a schematic view showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 19 is a schematic diagram showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 20 is a schematic view showing the structure of still another conversion apparatus according to the embodiment of the present invention;

FIG. 21 is a schematic diagram showing the structure of still another conversion apparatus according to the embodiment of the present invention;

fig. 22 is a schematic structural diagram of another conversion apparatus according to an embodiment of the present invention.

Detailed Description

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, devices, steps, and so forth. In other instances, well-known methods, devices, implementations or operations have not been shown or described in detail to avoid obscuring aspects of the invention.

The block diagrams shown in the figures are functional entities only and do not necessarily correspond to physically separate entities. I.e. these functional entities may be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different networks and/or processor means and/or microcontroller means.

The flow charts shown in the drawings are merely illustrative and do not necessarily include all of the contents and operations/steps, nor do they necessarily have to be performed in the order described. For example, some operations/steps may be decomposed, and some operations/steps may be combined or partially combined, so that the actual execution sequence may be changed according to the actual situation.

In the related art, an AC/DC (alternating Current/Direct Current) converter in a medium-voltage Direct-Current microgrid converts electric energy of an alternating Current power grid into Direct Current bus output. According to the current industry habit, the medium-voltage alternating current voltage is more than or equal to 1kVAC, and the medium-voltage direct current voltage is more than or equal to 1.5 kVDC.

The AC/DC converter employs a low operating frequency of the high voltage semiconductor device, and thus a low cut-off frequency of the filter, which results in an increase in the size and cost of the filter and the converter.

The present exemplary embodiment provides a conversion apparatus to reduce the size and cost of the conversion apparatus.

As shown in fig. 3, an embodiment of the present invention provides a converter device connected between an AC (Alternating Current) grid and a load 301, including: the inductor Lf is electrically connected with the alternating current power grid; a first-stage converter 302 having a first end electrically connected to the inductor Lf and a second end electrically connected to a DC BUS (Direct Current BUS), i.e., a BUS, for outputting a BUS voltage according to an ac power grid; and a second stage inverter 303 having a first end electrically connected to the bus and a second end electrically connected to the load 301 for converting the bus voltage to an output voltage for energizing the load 301.

The first-stage converter 302 may be an N-level ac-dc converter, where the N-level ac-dc converter includes multiple switch bridge arms, where an upper bridge arm and a lower bridge arm of each switch bridge arm of the ac-dc converter both include multiple semiconductor devices connected in series, and a rated withstand voltage value Vsemi of each semiconductor device is greater than or equal to (Vbus δ)/((N-1) × Nseries λ), where Vbus represents a bus voltage, δ represents a bus fluctuation, N represents a level number of the first-stage converter, λ represents a voltage derating coefficient of the semiconductor devices, and λ is less than or equal to 1, Nseries represents a number of semiconductor devices connected in series, and Nseries is greater than or equal to 2.

When a plurality of semiconductor devices are connected in series, a semiconductor device having a high switching frequency can be connected in series. For example, instead of the IGBT having a breakdown voltage of 4500V, 3 IGBT (Insulated gate bipolar Transistor) switches having a breakdown voltage of 1700V may be used in series. Because the switching frequency of the IGBT with the withstand voltage value of 1700V can reach the highest switching frequency of 3kHz, the maximum switching frequency is far greater than that of the IGBT with the withstand voltage value of 4500V. Therefore, the converter can work at a higher switching frequency, thereby improving the cut-off frequency of the filter, reducing the size of the filter and reducing the cost of the filter.

In the embodiment of the present invention, the first-stage converter may be a two-level or three-level AC/DC converter, and is not limited thereto. As shown in fig. 4, 5 and 6, the topology of the AC/DC converter includes, but is not limited to: a two-level rectifier, a three-level wiener rectifier and a three-level mid-point clamped converter.

In the three-phase two-level rectifier shown in fig. 4, the upper arm and the lower arm of each phase each include two semiconductor devices, i.e., power transistors S401, connected in series. The power transistor shown in fig. 4 is an IGBT, but is not limited to this in practical applications.

In the prior art, each phase of bridge arm of a three-phase three-level vienna rectifier includes a bidirectional switch formed by a power tube and four diodes, and an upper diode and a lower diode which play a role of freewheeling. In the three-phase three-level VIENNA (VIENNA) rectifier shown in fig. 5, the power transistor of each phase leg of the prior art three-phase three-level VIENNA rectifier is replaced by two series connected power transistors S402, and each diode of each leg of the prior art three-phase three-level VIENNA rectifier is replaced by two series connected diodes D401.

In the prior art, a bridge arm of each phase of a three-phase three-level midpoint clamping type converter comprises four power tubes and two diodes. As shown in fig. 6, in a three-phase three-level midpoint Clamped (NPC) converter, a power tube of each phase bridge arm of the three-phase three-level midpoint Clamped converter in the prior art is replaced by two power tubes S403 connected in series, and each diode of each phase bridge arm of the three-phase three-level midpoint Clamped converter in the prior art is replaced by two diodes D402 connected in series.

In an exemplary embodiment of the present invention, the load may be a dc load, and correspondingly, the second stage converter may be a dc-dc converter electrically connected to the dc load. In addition, the load may be an ac load, and correspondingly, the second-stage converter may be a dc-ac converter electrically connected to the ac load.

When the second-stage converter may be a DC-DC converter, i.e., a DC/DC (Direct Current/Direct Current) converter, the DC-DC converter may have various topological structures, a single module on the primary side of the DC-DC converter may adopt a two-level or multi-level topology, a semiconductor device of the DC-DC converter may adopt a single semiconductor device, or a structure in which a plurality of semiconductor devices are connected in series, in parallel, or in series-parallel, the secondary side and the primary side of the DC-DC converter may adopt an output mode of isolated output or non-isolated output, and the secondary side of the DC-DC converter may be connected in parallel, or in series-parallel according to the requirement of a load.

Specifically, the dc-dc converter of the embodiment of the present invention may be: a full-Bridge LLC DC/DC converter connected in series at the primary side as shown in fig. 7, a DC/DC converter including a half-Bridge LLC circuit connected in series at the primary side as shown in fig. 8, a DC/DC converter including a three-level half-Bridge LLC circuit connected in series at the primary side as shown in fig. 9, a DC/DC bidirectional converter including a DAB (Dual-Active-Bridge) circuit connected in series at the primary side as shown in fig. 10, and a non-isolated DC/DC bidirectional converter as shown in fig. 11.

As shown in fig. 12, the converter may further include a filter network, wherein the filter network has a first terminal, a second terminal, and a third terminal, a first rc circuit 701 is disposed between the first terminal and the third terminal of the filter network, a second rc circuit 702 is disposed between the second terminal and the third terminal of the filter network, the first terminal of the filter network is electrically connected to the ac power grid, and the third terminal of the filter network is grounded through a first capacitor C71.

The first rc circuit 701 includes a first resistor R71 and a fifth capacitor C75 connected in series, and the second rc circuit 702 includes a second resistor R72 and a sixth capacitor C76 connected in series. As shown in fig. 12, the first end of the filter network is a three-phase access end, and each phase of the filter network includes a first rc circuit 701. One end of the three-phase first resistance-capacitance circuit 701 corresponds to three-phase input of an alternating current power grid respectively, and the other end of the three-phase first resistance-capacitance circuit 701 is connected with a third end of the filter network. The second end of the filter network is a single-phase access end, wherein one end of the second rc circuit 702 is connected to the second end of the filter network, and the other end of the second rc circuit 702 is connected to the third end of the filter network.

As shown in fig. 12, the second end of the filter network is electrically connected to the bus terminal. Specifically, a second capacitor C72 and a third capacitor C73 are connected in series between the bus bars, and a second end of the filter network is electrically connected between the second capacitor C72 and the third capacitor C73.

As shown in fig. 13, the difference from fig. 12 is that: the third terminal of the filter network may be further grounded through a first capacitor C71 and a seventh capacitor C77, respectively.

As shown in fig. 14, the difference from fig. 12 is that: a fourth capacitor C74 is connected between the busbars. The second end of the filter network is electrically connected to the second end of the second stage converter. Specifically, an eighth capacitor C78 is further connected between the second ends of the second converters. One end of the second resistance-capacitance circuit is electrically connected with one of the second ends of the second converter. In one embodiment, one end of the second rc circuit is electrically connected to the ground terminal of the second end of the second converter.

In the embodiment of the present invention, as shown in fig. 12, 13, and 14, the inductor may be a common-mode and differential-mode integrated inductor Lf. As shown in fig. 15, 16, 17, 18, and 19, the inductors may include independent common mode inductors Lcm and differential mode inductors Ldiff.

When the converter works, a system common-mode voltage is generated due to the adoption of a Pulse Width Modulation (PWM) Modulation technology, the common-mode voltage is superposed with a differential-mode voltage, so that the voltages to earth at positions such as an AC input end and a bus midpoint are increased, a common-mode current is generated in a loop due to the existence of the common-mode loop, and if the common-mode loop is not processed, the problems of insulation, interference, heat dissipation and the like are generated.

In the embodiment of the invention, the common-mode inductor is adopted in the filter network to form the common-mode filter network.

As shown in fig. 12, 13, and 14, the inductor Lf is a differential-mode integrated reactor, and may filter a differential-mode signal and a common-mode signal at the same time. One end of the common mode filter network shown in fig. 12 is connected to the midpoint of the bus, i.e., the connection point of the second capacitor C72 and the third capacitor C73, and the other end is connected to the ac power grid and grounded through the safety capacitor C71. Thus, the voltage at the midpoint of the bus is forced to a potential close to ground. The power grid side is also connected with the ground through a resistor-capacitor, and the voltage of the power grid side to the ground is reduced.

The design of the common mode filter network can effectively reduce the bus midpoint voltage and the power grid side voltage to ground, and limit the amplitude of the common mode current.

Specific indexes for reducing the point-to-ground voltage in the power grid side and the direct current bus are as follows: under a rated working condition, the voltage to ground of the AC input is less than or equal to 1.5 x phase voltage peak value, and the common mode voltage jump is less than or equal to 1500V/uS.

In the embodiment of the invention, when the inductor comprises a differential mode inductor and a common mode inductor, the differential mode inductor Ldiff is connected between the alternating current power grid and the first-stage converter, and the common mode inductor Lcm is arranged between the differential mode inductor and the second-stage converter.

Specifically, as shown in fig. 15 and 16, the converter device includes three-phase differential mode inductors Ldiff and three-phase common mode inductors Lcm, and the differential mode inductors Ldiff and the common mode inductors Lcm are connected in series in each phase and electrically connected between the ac power grid and the first-stage converter. Here, the common mode inductor and the differential mode inductor are independently designed and are arranged at an access end of the alternating current power grid after being connected in series.

As shown in fig. 17, 18 and 19, the common mode inductor Lcm and the differential mode inductor Ldiff may be designed independently, and the three-phase differential mode inductor Ldiff is electrically connected between the ac grid and the first-stage converter. The two-phase common mode inductors Lcm are respectively disposed between two phases of the dc bus, i.e., between the ac power grid and the second end of the second-stage converter, and further may be disposed between the first end and the second end of the filter network.

In fig. 17, the common mode inductor Lcm is disposed between the second terminal of the first-stage converter and the series branch formed by the second capacitor C72 and the third capacitor C73. In fig. 18 and 19, the common mode inductor Lcm is disposed between the fourth capacitor C74 and the series branch formed by the second capacitor C72 and the third capacitor C73. At this time, the fourth capacitor C74 can absorb leakage inductance energy of the leakage inductance of the common mode inductor, so as to solve the leakage inductance influence of the common mode reactor.

In an embodiment of the present invention, the converter further includes a controller (not shown in the figure), and the controller detects the power of the load and controls the operating states of the at least two parallel ac-dc converters according to the power of the load. As shown in fig. 20, the converter further includes a dc breaker 801 disposed between the first-stage converter and the second-stage converter, wherein the dc breaker 801 is electrically connected to the controller, and controls the dc breaker 801 to operate according to a control signal sent by the controller.

In a medium-voltage direct-current micro-grid system, new energy bodies are more conveniently accessed, the line cost is low, the loss is small, the problems of reactive power balance and stability do not exist, and the operation reliability of a power grid is higher. Based on the advantages of the dc microgrid, as shown in fig. 20, in the dc microgrid system according to the embodiment of the present invention, new energy resources such as a dc load 802, a battery 803, and a photovoltaic panel 804 may be connected to implement power generation and utilization functions of the dc microgrid, and energy flows bidirectionally.

The direct current power grid has the defects of small inertia, high rising speed of short-circuit current, high peak current and the like when short circuit occurs. Aiming at the short-circuit fault of the direct-current microgrid, a direct-current breaker 801 is connected in series at the access end of the energy body, and reliable disconnection is realized under the condition of the short-circuit fault.

In the framework of the medium-voltage direct-current microgrid provided by the embodiment of the invention, new energy bodies such as batteries and photovoltaic panels are connected and disconnected with a medium-voltage direct-current bus through a direct-current circuit breaker 801, the direct-current circuit breaker 801 can automatically detect the operation condition, when a fault occurs, a fault point is disconnected, information is transmitted to a controller, and the controller carries out overall management according to the uploaded signals. The overall management can be as follows: the controller sets the priority of the fault, if the short circuit is the first priority, the overcurrent is the second priority, when the fault is in the first priority, the DC breaker automatically cuts off the fault when finding the fault; and when the fault is at the second priority or the later priority, the controller sends a cutting signal to control the on-off of the direct current breaker according to the information of the direct current breaker.

The topology shown in fig. 20 integrates the structures of power grid, load, power generation, energy storage, and the like. The central control system where the control is located can receive the control instruction of the monitoring system to charge and discharge the battery, and the energy storage system where the battery is located is used for quickly absorbing or releasing energy, so that the voltage fluctuation of photovoltaic grid-connected power generation is smoothed, the balance level of active power and reactive power of the system is improved, and the stability is enhanced. The energy storage Z system is utilized to improve the scheduling performance of photovoltaic power generation, the local power peak-valley time distribution condition and the electricity price can be analyzed, a charging and discharging control mode is formulated, low-suction and high-throw are realized, and the maximization of economic benefit is achieved. The energy storage system is matched with the photovoltaic power station to further improve the good matching between the photovoltaic power generation and the power grid, through smooth power output, peak clipping and valley filling are realized, the problems of large loading capacity and small generating capacity of the photovoltaic power generation are solved, the requirement of the conventional photovoltaic power station on the power transmission capacity of the power grid is greatly reduced, and the restriction of insufficient power grid construction on the power generation of the photovoltaic power station is avoided.

As shown in fig. 21 and 22, the first stage converter may include two or more ac-dc converters connected in parallel. The second stage converter may comprise two or more dc-dc converters. As shown in fig. 21, M or more dc-dc converters in the second-stage converter are provided, where M is a natural number equal to or greater than 2. As shown in fig. 22, M or more dc-dc converters in the second-stage converter are connected in series, where M is a natural number equal to or greater than 2. In addition, the second-stage converter can also comprise two or more DC-AC converters, and the two or more DC-AC converters can be connected in parallel or in series.

In the embodiment of the invention, all the AC-DC converters work under the condition that the load is full. When the load is light load or half load, the controller controls part of the at least two parallel AC-DC converters to work, and the other AC-DC converters do not work.

Specifically, as shown in fig. 21, the AC/DC converters in the converter device are connected in parallel by multiple machines, the output side of the DC/DC converter is connected in parallel by multiple machines, when the load end is fully loaded, the AC/DC converters operate by multiple machines, and when the load end is lightly loaded or half loaded, the controller may turn off a part of the AC/DC converters according to the power of the load, so that the rest of the AC/DC converters operate at the rated load or the optimal efficiency operating point, thereby achieving the purpose of maximizing efficiency.

As shown in fig. 22, the AC/DC converters in the converter device are connected in parallel by multiple units, and the output side of the DC/DC converter can be connected in series by multiple unit secondary side outputs according to the voltage requirement of the load, when the load end is fully loaded, the AC/DC multiple units operate, and when the load end is lightly loaded or half loaded, the controller can turn off a part of the AC/DC converters according to the power of the load, so that the rest of the AC/DC converters operate at the rated load or the optimal efficiency operating point, thereby achieving the purpose of maximizing efficiency.

In addition, in many practical applications, the floor where the electricity-using end is located may be inconvenient for carrying the equipment. If place whole conversion equipment at the power consumption end, not only have the problem of transport, still can occupy great floor area, increase the bearing of floor. According to the conversion device provided by the embodiment of the invention, the first-stage converter and the second-stage converter can be separately arranged, and the first-stage converter can be arranged at a far end such as a basement. The second-stage converter is close to the power utilization end and is connected with the power utilization end through a medium-voltage direct-current power grid.

The conversion device comprises a first-stage converter and a second-stage converter, wherein a plurality of semiconductor devices which are connected in series are arranged on an upper bridge arm and a lower bridge arm of each switching bridge arm of the first-stage converter, so that the switching frequency of each semiconductor device is increased, the first-stage converter works at a higher switching frequency, the cut-off frequency of a filter is increased, the size of the filter is reduced, and the cost of the filter is reduced.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.