Optimal output control of alternating current in a multi-power stacked inverter
阅读说明：本技术 多功率堆叠逆变器内的交流电最优产出控制 (Optimal output control of alternating current in a multi-power stacked inverter ) 是由 V.马图赖 D.R.戈拉普迪 B.阿尔普塔纳坦 于 2019-06-13 设计创作，主要内容包括：提供了一种用于在逆变器内执行AC最优产出控制的方法,所述逆变器包括：配置成供应DC功率的多个DC功率源,用于将直流电功率转换为要被供应给负载的交流电功率的多个转换器,连接到在DC功率源处的DC互连母线并且配置成提供短路保护的多个短路保护装置,配置成感测在短路保护装置处的循环电流的多个电流传感器,以及控制器。控制器控制转换器并监视经由电流传感器沿DC互连母线感测的循环电流,并且当在DC功率源中的一个DC功率源处发生功率降低时,执行闭环控制电流操作以将沿DC互连母线的循环电流可控制地增加到大于短路保护装置的损坏下限。(A method is provided for performing AC optimal production control within an inverter, the inverter comprising: the system includes a plurality of DC power sources configured to supply DC power, a plurality of converters for converting the DC power to ac electrical power to be supplied to a load, a plurality of short-circuit protection devices connected to a DC interconnect bus at the DC power sources and configured to provide short-circuit protection, a plurality of current sensors configured to sense circulating current at the short-circuit protection devices, and a controller. The controller controls the converter and monitors the circulating current sensed along the DC interconnect bus via the current sensor, and when a power reduction occurs at one of the DC power sources, performs a closed-loop control current operation to controllably increase the circulating current along the DC interconnect bus to greater than a damage lower limit of the short-circuit protection device.)
1. An inverter, comprising:
a plurality of DC power sources configured to supply DC power,
a plurality of converters for converting direct current electrical power to alternating current electrical power to be supplied to a load or a utility grid,
a plurality of short-circuit protection devices connected to the DC interconnect bus at the plurality of DC power sources and configured to provide short-circuit protection,
a plurality of current sensors configured to sense a circulating current at the short circuit protection device, an
A controller configured to:
(i) controlling the plurality of converters and monitoring the circulating current sensed along the DC interconnect bus via the current sensor, an
(ii) When a power reduction occurs at one of the plurality of DC power sources, performing a closed loop control current operation to controllably increase the circulating current along the DC interconnect bus to approximately equal a fuse damage lower limit of the plurality of short circuit protection devices.
2. The inverter of claim 1, wherein the calculation of the fuse damage limit is performed using the following equation:
(fuse damage limitation)
Wherein I ib_max Is the maximum circulating current, I ib12 、I ib23 And I ib34 Is a current sensed at a respective short-circuit protection device of the DC interconnect bus, wherein the maximum circulating current I ib_max Greater than one means that the inverter has reached the lower damage limit or continuous current rating of the short-circuit protection device.
3. The inverter of claim 1, wherein the residual AC current based on the inter-bridge circulating current is performed using the following equation:
wherein, I r Is based on point I ib12 、I ib23 And I ib34 Residual line current, I, calculated from the magnitude of the measured maximum circulating current limit Is an AC current limit, where I load Is a measured AC current delivered to the grid.
4. The inverter of claim 3, wherein the closed loop current control operation is performed using the following equation:
wherein I res_t Is the remaining line current limit at instance t calculated dynamically using a closed loop control technique as given in the equation, G is the gain control loop and dT is the sampling resolution of the controller.
5. The inverter of claim 1, wherein the plurality of DC power sources comprises a plurality of photovoltaic arrays.
6. The inverter of claim 1, further comprising:
a plurality of direct current circuit breakers, each of the direct current circuit breakers connected between a respective DC power source and an input of a converter of the plurality of converters, and
a plurality of alternating current circuit breakers, each of the alternating current circuit breakers connected at each converter and at an output of a converter of the plurality of converters.
7. The inverter of claim 6, further comprising a line filter having a protection circuit and a respective AC circuit breaker connected at each of the plurality of converters and configured to remove noise from the AC power at the output of the converter.
8. The inverter of claim 7, further comprising a main AC system circuit breaker connected with the plurality of AC circuit breakers and configured to supply the AC power directly to the load.
9. The inverter of claim 8, further comprising a plurality of power interface boards, each corresponding to a respective converter of the plurality of converters and connected together to interface between the plurality of converters and the controller for controlling operation and monitoring a status of each converter, the plurality of power interface boards each configured to supply control signals from the controller to a plurality of converters.
10. A method for performing AC optimal yield control within an inverter having a plurality of converters and corresponding short circuit protection devices, the method comprising:
the DC power is supplied via a plurality of DC power sources,
the direct-current electric power is converted into alternating-current electric power to be supplied to a load or a utility grid via a plurality of converters,
providing short circuit protection via a plurality of short circuit protection devices connected to the DC interconnect bus at the plurality of DC power sources,
sensing a circulating current at the short circuit protection device along the DC interconnect bus via a plurality of current sensors, an
When a power reduction occurs at one of the plurality of DC power sources, performing a closed loop control current operation to controllably increase the circulating current along the DC interconnect bus to greater than a damage lower limit of the plurality of short circuit protection devices.
Technical Field
The present invention relates generally to inverters. In particular, the present invention relates to AC optimal yield control of parallel stacked inverters with passive short circuit protection deployed between interconnected DC busses.
Background
Conventional multi-power stacked solar inverters are used to convert Direct Current (DC) power to Alternating Current (AC) power to be supplied for commercial and residential use. The DC power source may be a solar cell array (e.g., a plurality of solar cell arrays). The multi-stack includes a plurality of power stacks (e.g., power converters) that operate together to generate AC power to be supplied.
Multi-power stacked solar inverters typically employ passive short circuit protection devices between interconnected DC busses. The purpose of such an arrangement is to avoid the consequences of a short circuit situation in a particular power converter DC bus propagating to other power converters. But it naturally leads to uncontrolled current circulation between interconnected DC bridges via passive short-circuit protection devices during uncertain conditions where the interconnected DC power sources (e.g., PV arrays) are not proportional. This situation may damage the short-circuit protection circuit itself. Thus, these inverters limit the delivered AC power to be proportional to the minimum DC power extracted from the different DC power sources (e.g., PV arrays). However, derating the power converter to avoid this problem will successively lower the resulting AC power generated. The probability of occurrence is so high because environmental conditions (e.g., clouds) can affect one or more of the PV arrays on a daily basis.
Disclosure of Invention
In view of the aforementioned drawbacks, there is a need for a method and inverter that allows an inverter to increase the delivered Alternating Current (AC) power by increasing the current flowing through the short-circuit protection devices within the aggregated inverter in a controlled manner. This process desirably simultaneously controls current flow by using a closed loop current control operation that controllably increases but deterministically limits the circulating current at the short circuit protection device. In this way, limitations of power generation due to mismatch in power availability of different DC sources (e.g., PV arrays) supplying DC power to the inverter are balanced at the aggregate power converter stage.
According to one embodiment, an inverter is provided. The inverter includes: a plurality of DC power sources configured to supply DC power; a plurality of converters for converting the direct-current electric power into alternating-current electric power to be supplied to a load; a plurality of short-circuit protection devices connected to the DC interconnect bus at the DC power source and configured to provide short-circuit protection; a plurality of current sensors configured to sense a circulating current at the short circuit protection device; and a controller. The controller controls the converter and monitors the circulating current sensed along the DC interconnect bus via the current sensor, and when a power reduction occurs at one of the DC power sources, performs a closed-loop current control operation to controllably increase the circulating current along the DC interconnect bus to slightly less than a short-circuit protection device damage limit or equal to a continuous current rating of the short-circuit protection device, and thereby utilizes the continuous current rating of the protection circuit in a system method to increase the final power delivered on the AC side.
The foregoing has outlined broadly some of the aspects and features of various embodiments that should be construed to be merely illustrative of various potential applications of the disclosure. Other beneficial results can be obtained by applying the disclosed information in a different manner or by combining various aspects of the disclosed embodiments. Accordingly, other aspects and a more complete understanding may be obtained by reference to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings, in addition to the scope defined by the claims.
The invention also provides the following technical scheme:
technical solution 1. an inverter, comprising:
a plurality of DC power sources configured to supply DC power,
a plurality of converters for converting direct current electrical power to alternating current electrical power to be supplied to a load or a utility grid,
a plurality of short-circuit protection devices connected to the DC interconnect bus at the plurality of DC power sources and configured to provide short-circuit protection,
a plurality of current sensors configured to sense a circulating current at the short circuit protection device, an
A controller configured to:
(i) controlling the plurality of converters and monitoring the circulating current sensed along the DC interconnect bus via the current sensor, an
(ii) When a power reduction occurs at one of the plurality of DC power sources, performing a closed loop control current operation to controllably increase the circulating current along the DC interconnect bus to approximately equal a fuse damage lower limit of the plurality of short circuit protection devices.
Technical solution 2 the inverter according to technical solution 1, wherein the calculation of the fuse damage limit is performed using the following equation:
(fuse damage limitation)
Wherein I ib_max Is the maximum circulating current, I ib12 、I ib23 And I ib34 Is a current sensed at a respective short-circuit protection device of the DC interconnect bus, wherein the maximum circulating current I ib_max Greater than one means that the inverter has reached the lower damage limit or continuous current rating of the short-circuit protection device.
Technical solution 3 the inverter according to technical solution 1, wherein the remaining AC current based on the inter-bridge circulating current is performed using the following equation:
wherein, I r Is based on point I ib12 、I ib23 And I ib34 Residual line current, I, calculated from the magnitude of the measured maximum circulating current limit Is AC electricityFlow restriction of wherein load Is a measured AC current delivered to the grid.
Technical solution 4 the inverter according to technical solution 3, wherein the closed loop current control operation is performed using the following equation:
wherein I res_t Is the remaining line current limit at instance t calculated dynamically using a closed loop control technique as given in the equation, G is the gain control loop and dT is the sampling resolution of the controller.
The inverter of claim 1, wherein the plurality of DC power sources comprises a plurality of photovoltaic arrays.
Claim 6. the inverter according to claim 1, further comprising:
a plurality of direct current circuit breakers, each of the direct current circuit breakers connected between a respective DC power source and an input of a converter of the plurality of converters, and
a plurality of alternating current circuit breakers, each of the alternating current circuit breakers connected at each converter and at an output of a converter of the plurality of converters.
Claim 7 the inverter of claim 6, further comprising a line filter having a protection circuit and a respective ac circuit breaker connected at each of the plurality of converters and configured to remove noise from the ac power at the output of the converter.
Claim 8 the inverter of claim 7, further comprising a main ac system circuit breaker connected with the plurality of ac circuit breakers and configured to supply the ac power directly to the load.
Claim 9 the inverter of claim 8, further comprising a plurality of power interface boards, each corresponding to a respective converter of the plurality of converters and connected together to interface between the plurality of converters and the controller for controlling operation and monitoring a status of each converter, the plurality of power interface boards each configured to supply control signals from the controller to the plurality of converters.
Technical solution 10. a method for performing AC optimal yield control in an inverter having a plurality of converters and corresponding short circuit protection devices, the method comprising:
the DC power is supplied via a plurality of DC power sources,
the direct-current electric power is converted into alternating-current electric power to be supplied to a load or a utility grid via a plurality of converters,
providing short circuit protection via a plurality of short circuit protection devices connected to the DC interconnect bus at the plurality of DC power sources,
sensing a circulating current at the short circuit protection device along the DC interconnect bus via a plurality of current sensors, an
When a power reduction occurs at one of the plurality of DC power sources, performing a closed loop control current operation to controllably increase the circulating current along the DC interconnect bus to greater than a damage lower limit of the plurality of short circuit protection devices.
Claim 11 the method of claim 10, wherein the calculation of the fuse damage limit is performed using the following equation:
(fuse damage limitation)
Wherein I ib_max Is the maximum circulating current, I ib12 、I ib23 And I ib34 Is a current sensed at a respective short-circuit protection device of the DC interconnect bus, wherein the maximum circulating current I ib_max Greater than one means that the inverter has reached the lower damage limit or the short-circuit protection device is exceededContinuous current rating.
Solution 12. the method of solution 11, wherein the residual AC current based on the inter-bridge circulating current is performed using the following equation:
wherein, I r Is based on point I ib12 、I ib23 And I ib34 Residual line current, I, calculated from the magnitude of the measured maximum circulating current limit Is an AC current limit, where I load Is a measured AC current delivered to the utility grid.
The method of claim 12, wherein the closed-loop control current operation is performed using the following equation:
wherein I res_t Is the remaining line current limit at instance t calculated dynamically using a closed loop control technique as given in the equation where G is the gain control loop and dT is the sampling resolution of the controller.
The method according to claim 10, further comprising:
supplying the alternating current power directly to the load via a main circuit breaker connected with a plurality of alternating current circuit breakers at the outputs of the plurality of converters.
The method of claim 14, further comprising:
interfacing the plurality of converters with the controller for controlling operation and monitoring a state of each converter via a plurality of power interface boards by supplying control signals from the controller to the plurality of converters.
An inverter according to claim 16, comprising:
a plurality of DC power sources configured to supply DC power,
a pair of parallel single-stage converters for converting direct current electric power into alternating current electric power to be supplied to a load or a utility grid,
a short-circuit protection device connected to the DC interconnect bus at the plurality of DC power sources and configured to provide short-circuit protection,
a current sensor configured to sense a circulating current at the short circuit protection device, an
A controller configured to:
(i) controlling the pair of converters and monitoring the circulating current sensed along the DC interconnect bus via the current sensor, an
(ii) When a power reduction occurs at one of the plurality of DC power sources, performing a closed loop control current operation to controllably increase the circulating current along the DC interconnect bus to greater than a damage lower limit of the short protection device.
Drawings
The drawings are only for the purpose of illustrating preferred embodiments and are not to be construed as limiting the disclosure. The novel aspects of this disclosure should become apparent to those skilled in the art in view of the following enabling description of the drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of embodiments of the invention.
Fig. 1 is an exemplary schematic diagram illustrating an inverter (e.g., a solar inverter) including a plurality of converters in accordance with one or more embodiments of the present invention.
Fig. 2 is a graph illustrating results of an exemplary method of AC optimal yield control in which the aggregated inverter of fig. 1 connected to different DC power sources is controlling itself to optimize the delivered AC current compared to other DC power sources that may be implemented within embodiments.
Fig. 3 is a flow chart illustrating an exemplary method of AC optimal yield control in an inverter having multiple converters as shown in fig. 1, according to an embodiment.
FIG. 4 is a block diagram illustration of an exemplary computer system upon which aspects of embodiments of the invention may be practiced.
Detailed Description
As required, detailed embodiments are disclosed herein. It must be understood that the disclosed embodiments are merely exemplary of various and alternative forms. As used herein, the word "exemplary" is used broadly to refer to an embodiment that serves as a description, specimen, model, or pattern. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components.
In other instances, well-known components, devices, materials, or methods that are known to those skilled in the art have not been described in detail in order to avoid obscuring the present disclosure. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art.
As noted above, embodiments provide systems and methods for automatic power control of a multi-stack converter within a solar inverter (e.g., a single stage 1500V DC stage parallel stack air-cooled solar inverter). The invention is not limited to being employed within a particular inverter and may be modified to suit other applications.
Fig. 1 is a schematic diagram illustrating a solar inverter 100 for supplying AC power to a load 50, the solar inverter 100 including Photovoltaic (PV) arrays (e.g., multiple solar cell arrays) 102A-102D, multiple power converters 110A-110D, and multiple DC circuit breakers 104A-104D. And a main circuit breaker 125 connected to the AC circuit breakers 120A-120D and supplying AC power to the load 50.
Each PV array 102A-102D is a DC power source formed from a string of solar cells having a plurality of solar cell modules connected together and having an output power. Solar inverter 100 is configured to convert the DC power supplied by each PV array 102A-102D to AC power via a plurality of converters 110A-110D.
The DC circuit breakers 104A-104D are connected to a DC interconnect bus 105, which DC interconnect bus 105 includes a plurality of short-circuit protection devices 106A-106C for providing short-circuit protection. A plurality of current sensors 107A-107C are provided at each short-circuit protection circuit 106A-106C to measure the current passing therethrough.
The DC and AC circuit breakers 104A-104D and 120A-120D act as isolators to independently isolate each converter 110A-110D and associated components (e.g., PV arrays 102A-102D and PIBs 130A-130B (discussed below)) from the remaining healthy converters 110A-110D when a fault occurs.
In the exemplary illustration of fig. 1, a line filter 108 is connected between each converter 110A-110D and a respective AC circuit breaker 120A-120B. Line filter 108 is a low pass filter that removes noise from the AC current on the line of the respective converter 110A-110D.
The inverters within the multiple converters 110A-110D are configured to be substantially identical, including identical components. Each converter 110A-110D includes a semiconductor device such as an insulated gate bipolar transistor. According to an embodiment, converters 110A-110D are DC to AC converters, although the invention is not so limited.
Converters 110A-110D may be any type of converter suitable for the purposes set forth herein. Although fig. 1 illustrates a single stage of four parallel stacked DC inter-bridge short-circuit protection converters, the present invention is not so limited and may include any particular number and/or type of converters 110A-110D, which converters 110A-110D include corresponding short-circuit protection devices 106A-106C (e.g., fuses).
Solar inverter 100 further includes a plurality of Power Interface Boards (PIBs) 130A-130D. Each PIB 130A-130D corresponds to a respective converter 110A-110D and is coupled to the controller 150. This arrangement is configured to control and monitor the state of each converter 110A-110D.
The PIBs 130A-130D are configured to supply control signals from the controller 150 to the respective converters 110A-110D when received.
According to an exemplary embodiment of the present invention, as shown in fig. 2 and 3, the controller 150 is an integrated power electronic input/output (I/O) controller having a dual core Central Processing Unit (CPU) and a plurality of ethernet ports to be connected to the PIBs 130A-130D. However, the present invention is not limited to integrated power electronic I/O controllers.
In fig. 1, during normal operation, the DC breakers 104A-104D are closed and the PV arrays 102A-102D supply DC power directly to the converters 110A-110D. The DC power is converted at the converters 110A-110D and the noise is removed via each line filter 108. The AC circuit breakers 120A-120D are closed along with the main AC circuit breaker 125 to allow AC power to be supplied to the load 50 (e.g., a utility grid).
If the DC power to be supplied from the PV arrays 102A-102D decreases at any one of the PV arrays 102A-102D, for example due to a reduced weather condition, the controller 150 is configured to control the current detected at the short-circuit protection devices 106A-106C. This control occurs through closed loop control techniques via the current sensors 107A-107C to limit the circulating current based on the continuous current rating of the short circuit protection devices 106A-106C. By optimizing the current, the total AC power supplied to the load 50 may be increased regardless of the reduction in DC power generated by one or more of the PV arrays 102A-102D.
Controller 150 is configured to perform closed loop current control operations according to the following exemplary expression:
(fuse damage limitation)
Wherein, I ib_max Is the maximum circulating current, I ib12 Is the current sensed at current sensor 107A, I ib23 Is the current sensed at current sensor 107B, and I ib34 Is the current sensed at current sensor 107C. Maximum circulating current I ib_max Less than the fuse damage limit of the short-circuit protection devices 106A-106CIn the preparation method, the raw materials are mixed,
wherein I r Is the residual load current of the aggregate inverter scaled up to the maximum inter-bridge circulating current measured,
wherein IresIs a closed loop AC residual current calculation technique that will be deployed in this approach to make the current limiting functionality dynamic, but the current allowing functionality is filtered to avoid fluctuations in the generated load current.
As shown in FIG. 2, an exemplary graph 200 illustrates an example of a method of AC optimal yield control. In the example of fig. 2, the DC power source 102C (PV source 3) of the inverter of fig. 1 generates less power than the other DC power sources 102A, 102B, and 102D (PV source 1, PV source 2, and PV source 4) as shown in fig. 1, and the control technique deterministically allows current to flow from 102A, 102B, and 102D (PV source 1, PV source 2, and PV source 4) to 102C (PV source 3) via the short-circuit protection devices 106B and 106C at points 204 and 304.
As shown, when the availability of power is relatively small at the DC power source 102C, the controller 150 increases the DC current input to 2240 amps (a) at point 202 until the current at the current sensors 107A, 107B, and 107C (as depicted in fig. 1) reaches a set point value of 180A at point 204. In the case where the controller 150 does not perform optimal yield control of the circulating current, the DC current will be limited to 2100A, shown at point 302, while the current at the bus 105 reaches the set point value of 180A at point 304.
Fig. 3 is a flow chart illustrating an exemplary method 300 of AC optimal yield control in an inverter having multiple converters as depicted in fig. 1. In fig. 3, the method 300 begins supplying DC power via a plurality of DC power sources at operation 310. At operation 320, the plurality of converters convert the DC power to AC current power to be supplied to the load. At operation 330, short circuit protection is provided via a plurality of short circuit protection devices connected to the DC interconnect bus at the plurality of DC power sources.
At operation 340, the method 300 continues by sensing, via a plurality of current sensors, a circulating current at the short-circuit protection device along the DC interconnect bus. At operation 350, when a power reduction occurs at one of the plurality of DC power sources, performing a closed loop control current operation is performed to controllably increase the circulating current along the DC interconnect bus to a damage limit nearly equal to the plurality of short circuit protection devices. The closed loop control current operation performed by the controller may be performed using the equations mentioned above.
FIG. 4 illustrates a block diagram of a computer controller 400, on which computer controller 400 aspects of the present invention may be implemented, such as step 350 of FIG. 3. The computer controller 400 includes a processor 402 having a particular structure. The specific structure is imparted to the processor 402 by instructions stored in the memory 404 included therein and/or by instructions 420 that may be retrieved by the processor 402 from a storage medium 418.
As shown, the storage medium 418 may be co-located with the controller 400, or it may be located elsewhere and communicatively coupled to the controller 400. The controller 400 may be a stand-alone programmable system, or it may be a programmable module located in a much larger system. For example, the controller 400 may be integrated, i.e., embedded within a circuit.
The controller 400 may include one or more hardware and/or software components configured to acquire, decode, execute, store, analyze, distribute, evaluate, diagnose, and/or classify information. Further, the controller 400 may include an I/O module 414, the I/O module 414 configured to interface with a plurality of remote devices such as a variable frequency drive controller module and/or a switch matrix or bypass module.
Processor 402 may include one or more processing devices or cores (not shown). In some embodiments, processor 402 may be multiple processors, each with one or more cores. The processor 402 may be configured to execute instructions retrieved from the memory 404 (i.e., from one of the memory block 412, the memory block 410, the memory block 408, or the current control module 406) or may retrieve instructions from the storage medium 418 or from a remote device connected to the controller 400 via the communication interface 416.
The present invention provides the advantage of increasing the total AC power generated in the inverter and also avoids damage to the short circuit protection components during certain environmental conditions where power may be reduced at one of the DC power sources.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or apparatus and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Parts list
FIG. 1 shows a schematic view of a
50 load
100 inverter
102A PV array
102B PV array
102C PV array
102D PV array
104A circuit breaker
104B circuit breaker
104C circuit breaker
104D circuit breaker
105 interconnecting bus bar
106A protection device
106B protection device
106C protection device
107A current sensor
107B current sensor
107C current sensor
108 filter
110A converter
110B converter
110C converter
110D converter
120A circuit breaker
120B circuit breaker
120C circuit breaker
120D circuit breaker
125 breaker
130A PIB
130B PIB
130C PIB
130D PIB
150 controller
FIG. 2
200 points
202 point
Point 204
302 point
304 point
FIG. 3
310 operation
320 operation
330 operation
340 operation
350 operation
FIG. 4
400 controller
402 processor
404 memory
406 module
408 memory Block
410 memory block
412 memory block
414I/O module
416 communication interface
418 storage device
420 instruction
- 上一篇：一种医用注射器针头装配设备
- 下一篇：基于三端口分布式光伏储能混合结构的变换器