Power-grid-friendly distributed photovoltaic grid-connected control system and method

Abstract

The invention discloses a power-grid-friendly distributed photovoltaic grid-connected control system and method, and relates to the technical field of grid-connected control, and the system comprises a distributed solar photovoltaic unit, a phase selection soft switch, and an intelligent grid-connected control system considering the three-phase unbalance degree of a power distribution network. The distributed solar photovoltaic unit is used for generating photovoltaic electric energy, boosting the generated direct current through a direct current conversion circuit and converting the direct current into alternating current; the phase selection soft switch is used for realizing flexible interconnection among three phases in a three-phase four-wire system low-voltage power distribution network; the intelligent grid-connected control system considering the three-phase unbalance degree of the power distribution network is used for realizing grid-connected control. According to the power-grid-friendly distributed photovoltaic grid-connected control system provided by the invention, photovoltaic can be selectively connected into the phase sequence of the power grid according to different moments and different load conditions, and the photovoltaic output condition is controlled according to the load quantity connected into the phase sequence, so that a power-grid-friendly photovoltaic grid-connected control strategy is realized, and clean energy is better utilized and absorbed.

Description

Technical Field

[0001] This invention relates to the field of grid-connected control technology, specifically to a grid-friendly distributed photovoltaic grid-connected control system and method. Background Technology

[0002] Because low-voltage distribution networks have numerous and dispersed power users, there are a large number of single-phase loads with unbalanced spatial and temporal distribution, making three-phase imbalance unavoidable. With the increase in load types and electricity consumption, as well as the growing proportion of single-phase, nonlinear, and impulsive loads, especially with the large number of electric vehicle charging stations now connected to low-voltage distribution networks, the three-phase imbalance in low-voltage distribution networks is quite severe in actual operation. Furthermore, electric vehicle charging loads, depending on their charging power, include both three-phase and single-phase components, resulting in an asymmetrical load. In addition, factors such as user behavior, charging methods, and the scale of development inevitably lead to a high degree of randomness in electric vehicle charging loads, further contributing to three-phase load imbalance in the power grid.

[0003] Current and voltage imbalances caused by loads such as electric vehicle charging stations are often accompanied by other forms of interference, including harmonics, voltage drops, and voltage fluctuations. Current imbalances increase active power losses in the power grid, thus reducing efficiency; furthermore, voltage imbalances negatively impact rotating electrical machines, causing severe material damage and shortening their lifespan. Transformers, capacitor banks, and some protection systems are also affected by unbalanced power supply currents and voltages.

[0004] Faced with the highly random and spatiotemporal demands of photovoltaic power grid connection, the fixed phase sequence of traditional single-phase photovoltaic grid-connected inverters can exacerbate three-phase imbalance. However, by using intelligent soft switching (SOP) and reasonable control strategies, the phase sequence of photovoltaic power grid connection can be controlled, which will not exacerbate three-phase imbalance. This indirectly enhances the distribution network's capacity to support highly random single-phase users and achieves a grid-friendly photovoltaic grid-connected control strategy. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the technical problem solved by this invention is: for distributed photovoltaic power generation (roof PV, high-rise building wall PV, etc.) built on the exterior surface of buildings, the main characteristics of this type of distributed photovoltaic power source are: small installed capacity, significant environmental influence, low grid connection requirements, and the use of mostly single-phase photovoltaic grid-connected inverters. Given these characteristics, if the traditional single-phase photovoltaic grid-connected inverter structure is used, with a fixed phase sequence when connected to the low-voltage distribution network, the traditional photovoltaic grid-connected structure will exacerbate the three-phase imbalance of the low-voltage distribution network, given the large number of single-phase loads in the distribution network and the strong temporal and spatial randomness of distributed photovoltaics.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a grid-friendly distributed photovoltaic grid-connected control method, comprising:

[0008] Distributed solar photovoltaic units, phase-selective soft switches, and intelligent grid-connected control systems that take into account the three-phase imbalance of the distribution network;

[0009] The distributed solar photovoltaic unit is used to generate photovoltaic power and convert the generated DC power into AC power through a DC-DC converter circuit.

[0010] The phase-selective soft switch includes a three-port converter device for realizing flexible interconnection between three phases in a three-phase four-wire low-voltage distribution network; the three-port converter device includes three single-phase H-bridge sub-converters, each sub-converter being connected to phases A, B, and C and the neutral line respectively through an L filter and a switch group.

[0011] The intelligent grid-connected control system that considers the three-phase imbalance of the distribution network is used to monitor the real-time load of each phase of the distribution network and to dynamically control the phase selection soft switch based on the three-phase imbalance of the load, thereby realizing grid-connected control.

[0012] As a preferred embodiment of the grid-friendly distributed photovoltaic grid-connected control system described in this invention, the distributed solar photovoltaic unit grid connection is composed of a two-stage DC / DC-DC / AC configuration, wherein the DC / AC inverter stage is composed of a phase-selection soft switch.

[0013] As a preferred embodiment of the grid-friendly distributed photovoltaic grid-connected control system described in this invention, the intelligent grid-connected control system considering the three-phase imbalance of the distribution network includes a photovoltaic output constraint equation, expressed as:

[0014]

[0015] Among them, P s * To control the active power delivered by the three-port converter to the distribution network, P s P represents the total power generation of solar photovoltaic power on building surfaces. a,b,c * This refers to the active power command value of each port converter, which is the active power transmitted to the distribution network through each port converter.

[0016] As a preferred embodiment of the grid-friendly distributed photovoltaic grid-connected control system described in this invention, the three-phase imbalance is expressed as:

[0017]

[0018] Where δ represents the three-phase imbalance expressed by the power of each phase; Pav This refers to the average power transmitted from the secondary side of the distribution transformer after the photovoltaic system is connected to the grid.

[0019] As a preferred embodiment of the grid-friendly distributed photovoltaic grid-connected control system described in this invention, the average power output is expressed as:

[0020]

[0021] As a preferred embodiment of the grid-friendly distributed photovoltaic grid-connected control system described in this invention, the intelligent grid-connected control system (300) considering the three-phase imbalance of the distribution network includes an objective equation based on minimizing the three-phase imbalance, which adjusts the power command values ​​of each port converter to connect the photovoltaic power source to the grid, expressed as:

[0022]

[0023] As a preferred embodiment of the grid-friendly distributed photovoltaic grid-connected control system described in this invention, the intelligent grid-connected control system adopts V... dc -Q control and PQ control strategies.

[0024] Another objective of this invention is to provide a grid-friendly distributed photovoltaic grid-connected control method. This method replaces the traditional single-phase DC / AC grid-connected device with a phase-selective soft switch composed of a three-port converter. It allows photovoltaic power to selectively connect to the phase sequence according to different times and load conditions, and controls its output according to the load of the connected phase sequence to achieve a grid-friendly photovoltaic grid-connected control strategy. This indirectly enhances the distribution network's capacity to support highly random single-phase users, while also better and more rationally utilizing and consuming clean energy.

[0025] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a grid-friendly distributed photovoltaic grid-connected control method, comprising: collecting three-phase voltage and current and calculating three-phase real-time load in distribution automation; judging the three-phase load imbalance based on the three-phase real-time load; considering the three-phase imbalance of the distribution network, obtaining the active power command value; and controlling the three-port converter according to the active power command value to achieve grid-friendly photovoltaic grid connection.

[0026] A computer device includes a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the grid-friendly distributed photovoltaic grid-connected control method described above.

[0027] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the grid-friendly distributed photovoltaic grid-connected control method described above.

[0028] The beneficial effects of this invention: The grid-friendly distributed photovoltaic grid-connected control method provided by this invention embeds a three-port converter system and a photovoltaic system between the three phases of a three-phase four-wire low-voltage distribution network. The three-port single-phase converter achieves flexible interconnection between the three phases through a common DC bus, while a distributed photovoltaic power source is connected to the DC side of the converter system. For distributed photovoltaic power generation based on building exterior surfaces (rooftop photovoltaics, high-rise building wall photovoltaics, etc.), the main characteristics of this type of building exterior surface distributed photovoltaic power source are: small installed capacity, significant environmental influence, low grid connection requirements, and the use of mostly single-phase photovoltaic grid-connected inverters. Given these characteristics, if the traditional single-phase photovoltaic grid-connected inverter structure is used, with a fixed phase sequence when connected to the low-voltage distribution network, the traditional photovoltaic grid-connected structure will exacerbate the three-phase imbalance of the low-voltage distribution network, given the large number of single-phase loads in the distribution network and the strong temporal and spatial randomness of distributed photovoltaics. This invention targets distributed photovoltaic (PV) power generation on the surfaces of large buildings. First, the total output of distributed PV power generation in the building complex is obtained through PV aggregation. Then, the output is boosted by a DC / DC converter and connected to the DC side of a three-port converter system. Based on an "intelligent phase selection control system that considers the three-phase imbalance of the distribution network," the PV can selectively connect to the grid phase sequence according to different times and load conditions. Furthermore, the PV output can be controlled according to the load of the connected phase sequence, realizing a grid-friendly PV grid-connected control strategy, while better utilizing and absorbing clean energy. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is an overall structural diagram of a grid-friendly distributed photovoltaic grid-connected control system provided in one embodiment of the present invention.

[0031] Figure 2 The wiring diagram of a grid-friendly distributed photovoltaic grid-connected control system is provided as an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of a control strategy for a grid-friendly distributed photovoltaic grid-connected control system provided in one embodiment of the present invention.

[0033] Figure 4 This is an overall structural diagram of a grid-friendly distributed photovoltaic grid-connected control method provided in one embodiment of the present invention. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0036] Example 1

[0037] Reference Figure 1 As an embodiment of the present invention, a grid-friendly distributed photovoltaic grid-connected control method is provided, comprising:

[0038] Distributed solar photovoltaic unit 100, optional soft switch 200, and intelligent grid-connected control system 300 that takes into account the three-phase imbalance of the distribution network.

[0039] The distributed solar photovoltaic unit 100 is connected to the grid in a two-stage DC / DC-DC / AC configuration, wherein the DC / AC inverter stage is composed of an optional soft switch 200.

[0040] The optional soft switch 200 is a three-port converter device, which is composed of three single-phase H-bridge converters connected back to back.

[0041] The three-port converter device and the three-phase four-wire low-voltage distribution network are described. The three ports of the three-port converter device are connected to phases A, B, and C and the neutral line respectively through an L filter and a switch group. The port converter connected to phase A is named the A-port converter, the port converter connected to phase B is named the B-port converter, and the port converter connected to phase C is named the C-port converter; the structure is as follows. Figure 1 As shown.

[0042] The distributed solar photovoltaic unit 100 is connected to the grid in a two-stage DC / DC-DC / AC configuration, wherein the DC / AC inverter stage is composed of an optional soft switch 200.

[0043] The optional soft switch 200 is a three-port converter device, which is composed of three single-phase H-bridge converters connected back to back.

[0044] The three-port converter device and the three-phase four-wire low-voltage distribution network are described above. The three ports of the three-port converter device are connected to the three phases A, B, and C and the neutral line respectively through L filters and switch groups. The port converter connected to phase A is named A-port converter, the port converter connected to phase B is named B-port converter, and the port converter connected to phase C is named C-port converter.

[0045] To better control the selective grid connection of distributed solar photovoltaic units 100, specifically by controlling the optional soft switch 200 composed of a three-port converter, selective phase sequence integration of solar photovoltaic units is achieved. The grid-friendly distributed photovoltaic grid-connected control model can be expressed by the following objective function equation:

[0046] P s * =P a * +P b * +P c * ,P s * ≤(P s ) max (1)

[0047]

[0048] Equation (1) is the constraint equation for solar photovoltaic power output, where P s * To control the active power delivered by the three-port converter to the distribution network, P s P represents the total power generation of solar photovoltaic power on building surfaces. a,b,c * This refers to the active power command value of each port converter, which is the active power transmitted to the distribution network through each port converter.

[0049] Equation (2) is the three-phase unbalance equation of the distribution network after the solar photovoltaic power generation is connected to the grid, where δ is the three-phase unbalance expressed by the power of each phase; P av P represents the average power transmitted from the secondary side of the distribution transformer after the photovoltaic system is connected to the grid. av The expression is given by equation (3); the other symbols have the same meaning as in equation (1).

[0050] From equations (1), (2), and (3), we have that the goal of "intelligent grid-connected control considering the three-phase imbalance of the distribution network" is to simultaneously consider the three-phase load of the distribution network and the photovoltaic power generation output, and to maximize the absorption of clean solar photovoltaic energy while ensuring the minimum three-phase imbalance. That is, to ensure the minimum δ while letting P s * The minimum value is given by equation (4).

[0051]

[0052] For the objective equation given in equation (4), it is not difficult to see that by changing the power command value P of the three-port converter... a,b,c * This allows for the selective integration of solar photovoltaic power into the grid, promoting the consumption of clean energy and alleviating the current three-phase imbalance. To ensure stable operation of the three-port converter and achieve stable power control, a constant DC-side voltage is a necessary condition. Therefore, the "intelligent grid-connected control considering the three-phase imbalance of the distribution network" adopts V... dc -Q control and PQ control.

[0053] For example: a) Port A converter. The Port A converter uses active power-reactive power control (PQ control) as the outer loop control and current loop control as the inner loop control. The controller uses a traditional PI controller.

[0054] b. B-port converter: The B-port converter uses active power-reactive power control (PQ control) as the outer loop control and current loop control as the inner loop control. The controller is a traditional PI controller.

[0055] c. C-port converter: The C-port converter adopts DC bus voltage-reactive power control, i.e., V... dc -Q control serves as the outer loop control, while the inner loop uses current loop control. The controller employs a traditional PI controller. The control block diagram is shown below. Figure 3 As shown.

[0056] Figure 3 This is a wiring diagram of a grid-friendly distributed photovoltaic (PV) grid-connected control method according to the present invention. The invention targets distributed PV power generation on the surfaces of large buildings. First, the total output of distributed PV power generation across the building complex is obtained through PV aggregation. Then, the output is boosted by a DC / DC converter and connected to the DC side of a three-port converter system. Based on an "intelligent phase selection control system considering the three-phase imbalance of the distribution network," the PV can selectively connect to the grid phase sequence according to different times and load conditions. Furthermore, the PV output can be controlled based on the load of the connected phase sequence, achieving a grid-friendly PV grid-connected control strategy. The traditional single-phase grid-connected inverter is replaced with an optional soft switch 200. The optional soft switch 200 consists of three single-phase H-bridge converters connected back-to-back along a common DC bus. The distributed PV is connected to the DC side of the optional soft switch 200 via a fully controlled DC / DC boost circuit. This structure, which enables intelligent grid connection of PV power based on three-phase imbalance, is as follows: Figure 1As shown, the distributed photovoltaic system, DC / DC boost circuit, and optional soft switch 200 are connected via the DC bus. The phase sequence of the distributed photovoltaic system selectively connected to the grid can be controlled simply by adjusting the active power command values ​​of the three single-phase H-bridge converters according to the three-phase load imbalance, thus achieving grid-friendly photovoltaic grid connection. Based on grid information such as voltage and current at the PCC point collected by the distribution transformer terminal, the three-phase load imbalance and the real-time load P of each phase are calculated. The optimal solution for the active power command value of the three-port converter can be obtained from the grid-friendly distributed photovoltaic grid connection control model equation given by equation (4). The load in the figure is a single-phase load connected between phases A, B, and C and the neutral line. P in the figure... a P b P c P represents the real-time active power of each of the three phases A, B, and C. a *、P b *、P c * These represent the active power command values ​​for adjusting the converter control system, P s * To control the active power delivered by the three-port converter to the distribution network, P s This represents the total power generation of the building's surface solar photovoltaic system. The relationships and constraints between the various power command values ​​are as follows:

[0057] P a * +P b * +P c * =P s *

[0058] P s * ≤P s

[0059] Figure 3 The schematic diagram of the intelligent grid-connected control strategy of the present invention, which considers the three-phase imbalance of the distribution network, shows that V is typically used depending on the different functional requirements of the converters at each port. dc -Q control and PQ control, with specific control schemes as follows:

[0060] The A-port converter employs active-reactive power control (PQ control) as the outer loop and current loop control as the inner loop. The controller uses a traditional PI controller. The active power command value of the outer loop is obtained through the active power modulation stage of load balancing. A positive active power command value indicates that energy flows from the grid side to the converter, while a negative value indicates that energy flows from the converter to the grid side. Thus, by adjusting the sign and magnitude of the active power command value, the power flow to the balanced three-phase load can be controlled through the three-port converter system. The reactive power command value is determined by the reactive power situation on the grid side. When reactive power compensation from the grid side is required by the converter, the reactive power command value is set to negative; conversely, when reactive power absorption from the grid side is required by the converter, the reactive power command value is set to positive. Thus, by adjusting the sign and magnitude of the reactive power command value, the reactive power situation on the grid side can be regulated through the three-port converter. To simplify the controller design, a coordinate transformation is introduced to convert the AC quantities in the stationary coordinate system into DC quantities in the dq coordinate system. Coordinate transformation requires two orthogonal AC components, which a single-phase system clearly does not meet. Since coordinate transformation is merely a mathematical transformation and has no practical significance, an AC quantity with a 90° phase difference from that in a single-phase system can be artificially constructed to achieve the dq coordinate transformation. In fact, simply delaying the actual AC quantity in a single-phase system by 90° can virtually create an orthogonal component. Detailed procedures can be found in relevant materials. Due to the coupling relationship between the d and q axes, a feedforward decoupling control strategy is used to achieve active and reactive power decoupling control. d-axis control: Active power command value P kref (k = a, b) and real-time load value P k The difference between (k = a, b) is used by the PI controller to form the command value i for the inner current loop. kref (k = a, b), its instruction value i kref (k = a, b) and then compared with the real-time current value i dk The difference between (k = a, b) is processed by a PI controller and its feedforward decoupling stage to generate a PWM modulation signal. SPWM modulation technology is then used to generate a control signal to control the converter and thus the direction of active power flow. q-axis control: Reactive power command value Q. kref (k = a, b) and real-time reactive power value Q k The difference between (k = a, b) is used by the PI controller to form the command value i for the inner current loop. kref (k = a, b), its instruction value i kref (k = a, b) and then compared with the real-time current value i qk The difference between (k=a, b) is processed by a PI regulator and its feedforward decoupling circuit to generate a PWM modulation signal. SPWM modulation technology is used to generate a control signal to control the converter to control the reactive power exchange between the converter and the grid side.

[0061] The converter connected to phase C employs a dual-loop closed-loop control system for DC voltage / reactive power and current, primarily for stabilizing the DC side voltage of the three-port converter. The outer loop controls DC voltage / reactive power, while the inner loop controls current. A traditional PI controller is used. The outer loop's DC voltage command value is set to a constant 10kV to maintain the DC side voltage of the three-port converter at 10kV. For the active power control channel, the voltage control loop is considered the outer loop, i.e., d-axis control: DC voltage command value V dcref With feedback DC voltage value V dc The difference is compared and then processed by a PI controller to generate the current command value i for the inner current loop. drefc Its instruction value i drefc Then compared with the real-time current value i dc The difference is processed by a PI regulator and its feedforward decoupling stage to generate a PWM modulation signal. SPWM modulation technology is then used to generate a control signal to control the converter and stabilize the DC-side voltage. For the reactive power control channel, i.e., q-axis control: the reactive power command value Q... kref (k=c) and real-time reactive power value Q k The difference between (k=c) is used by the PI regulator to form the command value i for the inner current loop. qrefc Its instruction value i qrefc Then compare with the real-time current value i qc The difference is processed by a PI regulator and its feedforward decoupling circuit to generate a PWM modulation signal. SPWM modulation technology is used to generate a control signal to control the converter and control the reactive power exchange between the converter and the grid side.

[0062] Example 2

[0063] Reference Figure 4 As an embodiment of the present invention, a grid-friendly distributed photovoltaic grid-connected control method is provided, comprising:

[0064] S1: Distribution automation collects three-phase voltage and current and calculates the real-time three-phase load P. a P b P c .

[0065] S2: The three-phase load imbalance is determined based on the data from S1.

[0066] S3: Considering the three-phase imbalance of the distribution network, and combining the output of building-distributed photovoltaic power, the active power command values ​​P for adjusting the three-port converter control system are obtained from equation (4). a *、P b *、P c *

[0067]

[0068] S4: The active power command value P of the three-port converter control system derived from S3. a *、P b *、P c *Control the three-port converter to enable grid-friendly photovoltaic grid connection.

[0069] This invention employs a grid-friendly distributed photovoltaic (PV) grid-connected control method to embed a three-port converter system and a PV system between the three phases of a three-phase four-wire low-voltage distribution network. The three-port single-phase converter achieves flexible interconnection between the three phases via a common DC bus, while a distributed PV power source is connected to the DC side of the converter system. For distributed PV power generation based on building exteriors (rooftop PV, high-rise building wall PV, etc.), the main characteristics of this type of building exterior distributed PV power source are: small installed capacity, significant environmental influence, low grid connection requirements, and the use of mostly single-phase PV grid-connected inverters. Given these characteristics, if a traditional single-phase PV grid-connected inverter structure is used, with a fixed phase sequence connected to the low-voltage distribution network, the traditional PV grid-connected structure will exacerbate the three-phase imbalance of the low-voltage distribution network, given the large number of single-phase loads in the distribution network and the strong temporal and spatial randomness of distributed PV. This invention targets distributed photovoltaic (PV) power generation on the surfaces of large buildings. First, the total output of distributed PV power generation in the building complex is obtained through PV aggregation. Then, the output is boosted by a DC / DC converter and connected to the DC side of a three-port converter system. Based on an "intelligent phase selection control system that considers the three-phase imbalance of the distribution network," the PV can selectively connect to the grid phase sequence according to different times and load conditions. Furthermore, the PV output can be controlled according to the load of the connected phase sequence, realizing a grid-friendly PV grid-connected control strategy, while better utilizing and absorbing clean energy.

[0070] Example 3

[0071] One embodiment of the present invention differs from the previous two embodiments in that:

[0072] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0073] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0074] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0075] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0076] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A grid-friendly distributed photovoltaic grid-connected control system, characterized in that: include: Distributed solar photovoltaic unit (100), phase selection soft switch (200) and intelligent grid-connected control system (300) taking into account the three-phase imbalance of the distribution network; The distributed solar photovoltaic unit (100) is used to generate photovoltaic electric energy and to boost the generated direct current through a direct current conversion circuit and convert it into alternating current; The phase selection soft switch (200) comprises a three-port converter device, which is used to realize flexible interconnection between three phases in a three-phase four-wire low-voltage distribution network; the three-port converter device comprises three single-phase H-bridge sub-converters, each of which is respectively connected to the three phases A, B, C and the neutral line through an L filter and a switch group; The intelligent grid-connected control system (300) considering the three-phase imbalance of the distribution network is used to monitor the real-time load conditions of each phase of the distribution network, and dynamically control the phase selection soft switch (200) based on the three-phase imbalance of the load to achieve grid-connected control.

2. The grid-friendly distributed photovoltaic grid-connected control system according to claim 1, characterized in that: The distributed solar photovoltaic unit (100) is connected to the grid in a two-stage DC / DC-DC / AC manner, wherein the DC / AC inversion link is composed of a phase-selective soft switch (200).

3. The grid-friendly distributed photovoltaic grid-connected control system according to claim 2, characterized in that: The intelligent grid-connected control system (300) considering the three-phase imbalance of the distribution network includes a photovoltaic output constraint equation, which is expressed as: Among them, P s * To control the active power delivered by the three-port converter to the distribution network, P s is the total power generated by solar photovoltaic power on the building surface, P a,b,c * is the active power command value of each port converter, that is, the active power transmitted to the distribution network through each port converter.

4. The grid-friendly distributed photovoltaic grid-connected control system according to claim 3, characterized in that: The three-phase unbalance is expressed as: Among them, δ is the three-phase imbalance expressed by the power of each phase; P av It is the average power transmitted by the secondary side of the distribution transformer after the photovoltaic power plant is connected to the grid.

5. The grid-friendly distributed photovoltaic grid-connected control system according to claim 4, characterized in that: The average power is expressed as:

6. The grid-friendly distributed photovoltaic grid-connected control system according to claim 5, characterized in that: The intelligent grid-connected control system (300) considering the three-phase imbalance of the distribution network includes a target equation based on minimizing the three-phase imbalance, and adjusting the power command value of each port converter to connect the photovoltaic power source to the grid, which is expressed as:

7. The grid-friendly distributed photovoltaic grid-connected control system according to claim 6, characterized in that: The intelligent grid-connected control system (300) adopts V dc -Q control and PQ control strategies.

8. A method using a grid-friendly distributed photovoltaic grid-connected control system as claimed in any one of claims 1 to 7, characterized in that: include: Distribution automation collects three-phase voltage and current and calculates three-phase real-time load; Determine the three-phase load imbalance according to the three-phase real-time load; Considering the three-phase imbalance of the distribution network, the active power command value is obtained; The three-port converter is controlled according to the active power command value to achieve grid-friendly photovoltaic grid connection.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the grid-friendly distributed photovoltaic grid-connected control method described in claim 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the grid-friendly distributed photovoltaic grid-connected control method described in claim 7 are implemented.

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