Photovoltaic power generation system load distribution and bus voltage regulation method based on hierarchical control

Abstract

The invention relates to a photovoltaic power generation system load distribution and bus voltage regulation method based on hierarchical control, and the method comprises the steps: building a model for each distributed photovoltaic power generation unit in a photovoltaic power generation system, and achieving the one-time droop control of the photovoltaic power generation system; and correcting the bus voltage deviation based on the output current of the adjacent photovoltaic power generation unit. According to the method, distributed secondary control is introduced, load distribution errors existing in traditional droop control are effectively corrected, voltage fluctuation in system operation is effectively dealt with, and therefore stable control over bus voltage is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of load distribution and bus voltage stable operation in a photovoltaic power generation system, and more specifically to a method for load distribution and bus voltage regulation in a photovoltaic power generation system based on hierarchical control. Background Art

[0002] With the increasing popularity of distributed generation, photovoltaic power generation has been proposed as an effective solution for regional power supply. Droop control is widely used to achieve current distribution between photovoltaic power generation units due to its simplicity and decentralized characteristics. However, traditional droop control methods cannot coordinate current distribution and voltage regulation well at the same time, and cannot achieve zero-difference control.

[0003] In the research on load distribution and bus voltage control of photovoltaic power generation system, centralized hierarchical control is mostly used, but the centralized algorithm lacks flexibility and has large errors in load distribution; therefore, distributed algorithms based on communication networks are gradually being applied, but most distributed control algorithms of communication networks require high-bandwidth communication, which not only increases the burden on the communication network, but also causes frequent data loss and communication delays, affecting the overall stable operation of the photovoltaic power generation system, and the uncertainty of these network systems will reduce the control performance and even cause system failures. In addition, this method has not yet performed closed-loop large signal stability analysis on these distributed controllers, and cannot ensure that the two control objectives can be achieved at the same time.

[0004] Therefore, how to solve the above-mentioned deficiencies and ensure the safe and stable operation of photovoltaic power generation systems is a technical problem that urgently needs to be solved. Summary of the invention

[0005] In view of this, in order to at least partially solve the above technical problems, the present invention provides a method for load distribution and bus voltage regulation of a photovoltaic power generation system based on hierarchical control, mainly by introducing a distributed secondary event trigger controller to correct the load distribution and DC bus voltage deviation existing in droop control, thereby improving current balanced distribution and bus voltage stability control.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for load distribution and bus voltage regulation of a photovoltaic power generation system based on hierarchical control, comprising:

[0008] Construct a model for each distributed photovoltaic power generation unit in the photovoltaic power generation system to achieve primary droop control of the photovoltaic power generation system;

[0009] The bus voltage deviation is corrected based on the output current of the adjacent photovoltaic power generation unit; the steps include:

[0010] Determine the current distribution error according to the output current of the adjacent photovoltaic power generation units;

[0011] The average output voltage of the distributed photovoltaic power generation unit is obtained according to the current distribution error, and the voltage control error is determined in combination with the current bus reference voltage;

[0012] The bus reference voltage is updated when the photovoltaic power generation system is stable based on the current distribution error and the voltage control error.

[0013] Preferably, the distributed photovoltaic power generation unit model is:

[0014]

[0015] In the formula, I DPPGi Represents the output current of the i-th photovoltaic power generation unit, I Loadi represents the load current of the ith photovoltaic power generation unit, G ij represents the conductance of the tie line between the busbar of the i-th photovoltaic power generation unit and the busbar of the j-th photovoltaic power generation unit, U DPPGi represents the bus voltage of the ith photovoltaic power generation unit, U DPPGj represents the bus voltage of the jth photovoltaic power generation unit, Represents the set of other distributed photovoltaic power generation units connected to the i-th photovoltaic power generation unit.

[0016] Preferably, when a droop control is performed based on the model, the load balancing distribution control target is:

[0017]

[0018] In the formula, I DPPGi_max represents the maximum current capacity of the i-th photovoltaic power generation unit, I DPPGj_max It represents the maximum current capacity of the jth photovoltaic power generation unit, and Ne is the number of nodes in the photovoltaic power generation system network.

[0019] Preferably, when a droop control is performed based on the model, the bus voltage control target is:

[0020]

[0021] In the formula, is the average output voltage of each distributed photovoltaic power generation unit, U n is the nominal voltage of the photovoltaic power generation unit, n is the number of photovoltaic power generation units, U i is the output voltage of the i-th photovoltaic power generation unit.

[0022] Preferably, the current sharing error is defined as:

[0023]

[0024] In the formula, e DPPGIi (t) represents the current distribution error at time t, h ij represents the communication relationship between the i-th photovoltaic power generation unit and the j-th photovoltaic power generation unit, I DPPGi (t) is the output current of the ith photovoltaic power generation unit at time t, I DPPGj (t) is the output current of the jth photovoltaic power generation unit at time t, I DPPGi_max represents the maximum current capacity of the i-th photovoltaic power generation unit, I DPPGj_max Represents the maximum current capacity of the jth photovoltaic power generation unit.

[0025] Preferably, the average output voltage of the distributed photovoltaic power generation unit is collected according to the following formula:

[0026]

[0027] In the formula, is the average output voltage of each distributed photovoltaic power generation unit at time t, U i (t) represents the output voltage of the ith photovoltaic power generation unit at time t; K I >0 and K U >0 is the control gain coefficient, e DPPGIi represents the current distribution error; e DPPGIi Represents the current sharing error.

[0028] The voltage control error expression is:

[0029]

[0030] Where U n is the nominal voltage of the photovoltaic power generation unit.

[0031] Preferably, the bus reference voltage when the photovoltaic power generation system is stable is updated based on the current distribution error and the voltage control error according to the following formula:

[0032]

[0033] Where U n (t) represents the updated nominal voltage of the photovoltaic power generation unit at time t, K r Indicates the voltage droop coefficient, L δDPPGi Indicates the current deviation, K I >0 and K U >0 is the control gain coefficient, e DPPGIi represents the current distribution error, e DPPGUi Represents the voltage control error.

[0034] Preferably, a time trigger condition is introduced, and when the condition is triggered, the connected photovoltaic power generation units exchange current distribution information to increase the communication bandwidth;

[0035] Preferably, when When the event triggers:

[0036]

[0037] In the formula, Indicates the DC bus voltage reference value, U i is the output voltage of the ith photovoltaic power generation unit, e tr Indicates the event triggering condition, K I >0 and K U >0 is the control gain coefficient, λ B_min is the minimum eigenvalue of matrix B, B is the Lapse matrix L Ne and L Nc The incidence matrix, L Ne is the node admittance matrix in the photovoltaic power generation system network theory, L Nc is the Laplace matrix of the communication network, ζ1>0, And 0<δ<1 is a set constant, DPPG i and DPPG j The observed current sharing error between DPPG i and DPPG j The observed voltage distribution error between .

[0038] The photovoltaic power generation system load distribution and bus voltage regulation method based on hierarchical control disclosed in the present invention has the following advantages:

[0039] 1. By introducing distributed secondary control, the load distribution error existing in traditional droop control is effectively corrected, and more accurate current balanced distribution is achieved;

[0040] 2. The bus reference voltage is updated by combining the current distribution error and the voltage control error to ensure the stable control of the bus voltage. By adjusting the bus reference voltage in real time, the voltage fluctuation in the system operation is effectively dealt with, and the robustness of the voltage control is improved.

[0041] 3. Using event trigger conditions for information exchange reduces the number of unnecessary communications, thereby reducing the burden on the communication network and improving the communication bandwidth.

[0042] Compared with the existing technology,

[0043] Distributed control algorithms are more flexible than centralized algorithms and can better adapt to system changes and uncertainties. At the same time, by performing closed-loop large signal stability analysis on distributed controllers, it ensures that control targets are achieved simultaneously and improves system reliability. At the same time, it avoids high-bandwidth communication requirements, reduces data loss and communication delays, and provides a strong guarantee for the safe and stable operation of photovoltaic power generation systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0045] Figure 1 The present invention is a flow chart of a method for load distribution and bus voltage regulation of a photovoltaic power generation system based on hierarchical control;

[0046] Figure 2 It is a hierarchical control diagram of the photovoltaic power generation system of the present invention;

[0047] Figure 3 An event trigger controller for the photovoltaic power generation system of the present invention;

[0048] Figure 4 This is the event triggering moment principle diagram of the present invention;

[0049] Figure 5 The output power conversion curve diagram of the four distributed power sources of the present invention;

[0050] Figure 6 The DC bus voltage and output power curve of the distributed power supply of the present invention;

[0051] Figure 7 It is a curve diagram of the droop coefficient variation of the distributed power supply of the present invention;

[0052] Figure 8 This is a curve diagram of the output power variation of the distributed power supply when the load suddenly drops according to the present invention;

[0053] Fig. 9 This is a curve diagram of the output voltage change of the distributed power supply when the load suddenly drops according to the present invention;

[0054] Fig.10 The droop coefficient variation curve diagram of the present invention when the load suddenly drops;

[0055] Fig.11 This is a diagram of the triggering time of a voltage-controlled distributed event according to the present invention;

[0056] Fig.12 This is a diagram of the distributed event triggering timing of power control according to the present invention. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] This application studies the load distribution and bus voltage stable operation in photovoltaic power generation systems, as well as the communication burden between the controllers of each unit. First, a hierarchical control structure photovoltaic power generation system is designed, and a network model composed of distributed photovoltaic power generation units (Distributed Photovoltaic Power Generation) is established considering different line impedances; secondly, the control targets of load distribution and bus voltage are determined according to the operating characteristics of the photovoltaic power generation system; thirdly, a secondary distributed voltage controller is designed based on the primary droop control in the photovoltaic power generation system, and the DC bus voltage deviation existing in the droop control is corrected by the introduced controller;

[0059] In order to further reduce the communication demand, the event trigger condition is introduced, and each local controller only exchanges current distribution information with the adjacent controller connected to it when the trigger condition occurs, thereby improving the communication bandwidth problem. This provides certain research value for the stable operation of the photovoltaic power generation system.

[0060] In one embodiment, the method for load distribution and bus voltage regulation of a photovoltaic power generation system based on hierarchical control disclosed in the present invention comprises the following steps: Figure 1 ,include:

[0061] Construct a model for each distributed photovoltaic power generation unit in the photovoltaic power generation system to achieve primary droop control of the photovoltaic power generation system;

[0062] The bus voltage deviation is corrected based on the output current of the adjacent photovoltaic power generation unit; the steps include:

[0063] Determine the current distribution error according to the output current of the adjacent photovoltaic power generation units;

[0064] The average output voltage of the distributed photovoltaic power generation unit is obtained according to the current distribution error, and the voltage control error is determined in combination with the current bus reference voltage;

[0065] The bus reference voltage is updated when the photovoltaic power generation system is stable based on the current distribution error and the voltage control error.

[0066] According to the structural characteristics and control principle of the photovoltaic power generation system, the present invention adopts a distributed hierarchical control structure to divide the photovoltaic power generation system into a first-layer control and a second-layer control. Figure 2 As shown; each layer of control has its own implementation function, and the deviation of system parameters and the load and communication distribution problems between nodes can be eliminated through distributed hierarchical control. This embodiment mainly includes the following two parts:

[0067] 1. According to the structure of distributed photovoltaic power generation system, establish each distributed photovoltaic power generation unit model, and then determine the control targets of load distribution and bus voltage according to the operation characteristics of photovoltaic power generation system, so as to realize the primary droop control of photovoltaic power generation system;

[0068] In this embodiment, the distributed photovoltaic power generation unit model is:

[0069]

[0070] In the formula, I DPPGi Represents the output current of the i-th photovoltaic power generation unit, I Loadi represents the load current of the ith photovoltaic power generation unit, G ij represents the conductance of the tie line between the busbar of the i-th photovoltaic power generation unit and the busbar of the j-th photovoltaic power generation unit, U DPPGi represents the bus voltage of the ith photovoltaic power generation unit, U DPPGj represents the bus voltage of the jth photovoltaic power generation unit, Represents the set of other distributed photovoltaic power generation units connected to the i-th photovoltaic power generation unit.

[0071] Furthermore, according to the operating characteristics of the photovoltaic power generation system, the control targets of its load distribution and bus voltage are determined, including:

[0072] If the load size is expressed by current, the control target of load balancing distribution is set as:

[0073]

[0074] In the formula, I DPPGi_max represents the maximum current capacity of the i-th photovoltaic power generation unit, I DPPGj_max It represents the maximum current capacity of the jth photovoltaic power generation unit, and Ne is the number of nodes in the photovoltaic power generation system network.

[0075] The randomness of the load will cause the bus voltage to fluctuate continuously. To ensure the stability of the bus voltage, the control target of the bus voltage is set:

[0076]

[0077] In the formula, is the average output voltage of each distributed photovoltaic power generation unit, U n is the nominal voltage of the photovoltaic power generation unit, which generally takes a specific value, n is the number of photovoltaic power generation units, U i is the output voltage of the i-th photovoltaic power generation unit.

[0078] 2. In one embodiment, a secondary distributed voltage controller is designed based on the primary droop control in the photovoltaic power generation system, and the DC bus voltage deviation existing in the droop control is corrected by the introduced controller.

[0079] First, during the droop control process, the PV power generation unit transfers the respective load current ratios to its adjacent units. Therefore, the current distribution error between the PV power generation units can be defined as:

[0080]

[0081] In the formula, h ij represents the communication relationship between the i-th photovoltaic power generation unit and the j-th photovoltaic power generation unit. In this embodiment, the vertex of the communication network is the controller of the local distributed photovoltaic power generation unit, and the connecting edge of the communication network is the communication line. If connected, h>0 is the user-defined communication weight. If not connected, h=0. DPPGi is the output current of the ith photovoltaic power generation unit, I DPPGi_max represents the maximum current capacity of the i-th photovoltaic power generation unit, I DPPGj_max represents the maximum current capacity of the jth photovoltaic power generation unit, and t represents the time corresponding to the current current distribution error.

[0082] Secondly, the system's voltage controller controls its voltage to the set bus reference voltage, so the voltage control error is:

[0083]

[0084] In the formula, is the average output voltage of each distributed photovoltaic power generation unit at time t, U n is the nominal voltage of the photovoltaic power generation unit.

[0085] In this embodiment, when calculating the voltage control error, it is necessary to collect the voltage of each photovoltaic power generation unit and then The value is calculated. The collection calculation can be performed using the following formula:

[0086]

[0087] Where U i (t) represents the output voltage of the ith photovoltaic power generation unit at time t; K I>0 and K U >0 is the control gain coefficient, e DPPGIi represents the current sharing error. The average voltage calculation uses only the DPPG i The current voltage of the controller connected to it is calculated by load current sharing error information.

[0088] The integral here is called the convolution integral, and its result is a function of t, where τ is a fictitious variable used for integral calculation. The convolution operation satisfies the commutative law, the associative law, and the distributive law, and can be flexibly applied when processing complex signals.

[0089] Furthermore, combined with the voltage and current droop control, the bus reference voltage is updated when the photovoltaic power generation system is stable.

[0090] Regarding voltage and current droop control, in the photovoltaic power generation system DPPG i In the equation, power, voltage and current satisfy the following relationship:

[0091]

[0092] In the formula, I δDPPGi is the current deviation, P δDPPGi is the power deviation, U DPPGi is the bus voltage of the i-th photovoltaic power generation unit.

[0093] In order to balance the power in each DPPG system, when there is a difference between the power provided by the distributed generation and the load power, the bus voltage will fluctuate. δDPPGi The droop relationship shown below is satisfied:

[0094] U DPPGi =U n -D r (P Loadi -P DPPGi )

[0095] Where D r is the power droop coefficient, U n is the nominal voltage of the photovoltaic power generation unit.

[0096] Combining the above formulas, we can get the droop relationship between voltage and current:

[0097] U DPPGi =U n -K r I δDPPGi

[0098] In the formula, K r Indicates the voltage droop coefficient, I δDPPGi is the current deviation.

[0099] In order to achieve the control objectives of voltage and load distribution, the control errors of voltage and current must be equal to zero under steady-state operation. Therefore, the derivative of the DC bus voltage reference value can be designed through the current and voltage errors as:

[0100]

[0101] Integrating the above formula, we get:

[0102]

[0103] Therefore, in this embodiment, the updated bus reference voltage when the system is stable can be expressed as:

[0104]

[0105] Where U n (t) represents the updated nominal voltage of the photovoltaic power generation unit at time t, K r Indicates the voltage droop coefficient, I δDPPGi Indicates the current deviation, K I >0 and K U >0 is the control gain coefficient, e DPPGIi represents the current distribution error, e DPPGUi Represents the voltage control error.

[0106] To further optimize the above technical solution, in one embodiment, an event-triggered control technology is adopted, that is, the current distribution information is exchanged with the adjacent controller connected to it only when the preset conditions are met, thereby significantly reducing the burden on the communication network, reducing communication requirements, and improving communication bandwidth.

[0107] In this embodiment, according to the change of system load, an event-triggered controller is used to realize current balanced distribution and bus voltage stability control. The control process is as follows: Figure 3 The triggering conditions of this algorithm can be evaluated based on information from local and neighboring subsystems.

[0108] Specifically include: at the time t corresponding to the set trigger condition k , the controller updates the local load current distribution information and passes it to the connected controller. Before the next triggering moment, this information is kept. At the moment t corresponding to the next triggering condition, k+1 Next, repeat the above process.

[0109] In one embodiment, according to the above process, DPPG i and DPPG j The current sharing error between is:

[0110]

[0111] In the formula, Indicates that at t k Moment DPPG i Updated current observations. Indicates that at t k Moment DPPG j Updated current observations.

[0112] Similarly, the average voltage is:

[0113]

[0114] In the formula, Indicates that at t k Moment DPPG i Updated global average voltage observation.

[0115] The observed voltage error is:

[0116]

[0117] According to the above formula, the distributed event trigger controller is:

[0118]

[0119] Integrate to get:

[0120]

[0121] in, DPPG i and DPPG j The observed current sharing error between is the observed voltage error, is the DC bus voltage reference value.

[0122] when hour, Indicates the DC bus voltage reference value, U i is the output voltage of the ith photovoltaic power generation unit, e tr Indicates the event triggering conditions. The event triggering conditions are:

[0123]

[0124] In the formula, e tr Indicates the event triggering condition, K I >0 and K U >0 is the control gain coefficient, λ B_min is the minimum eigenvalue of matrix B, B is the Lapse matrix L Ne and L NcThe incidence matrix, L Ne is the node admittance matrix in the photovoltaic power generation system network theory, L Nc is the Laplace matrix of the communication network. In this embodiment, L Ne =L Nc ,λ B_min =1,ζ l >0, And 0<δ<1 is a set constant. Photovoltaic power generation network L Ne and its communication network L Nc Certain conditions must be met to achieve the control objectives.

[0125] e tr Finally, it is a curve, such as Figure 4 The event-triggered controller designed by the present invention also has good control performance when the load changes.

[0126] In order to further verify the effect of this application, the following simulation analysis was performed on droop control and event-triggered control:

[0127] Object: Four distributed photovoltaic power generation units, among which DPPG1 and DPPG2 carry the same load, and DPPG3 and DPPG4 carry the same load.

[0128] At the initial moment of the simulation, under the droop control mode, the power output quickly reaches stability, such as Figure 5 As shown, P1, P2, P3, and P4 represent the power curves of four distributed photovoltaic power generation units respectively. When t=1s, the event triggers the controller to start working, and the output power recovers to stable output after a short period of fluctuation.

[0129] When only one layer of droop control is used at the initial moment of the simulation, such as Figure 6 , U1, U2, U3, and U4 represent the voltage change curves of four distributed photovoltaic power generation units, respectively. Figure 6 It can be seen that after each distributed power source carries the corresponding load, the bus voltage will deviate greatly from the rated value, which is not conducive to the stable control of the bus voltage. At t=1s, the second-layer distributed event trigger control method is added. Under the action of the distributed event trigger controller, the output voltage of the four distributed power sources begins to rise, and finally realizes the voltage deviation control, overcoming the voltage deviation defect of the droop control.

[0130] further, Figure 7is the droop coefficient change curve. KP1, KP2, KP3 and KP4 represent the droop control change curves of the four distributed photovoltaic power generation units respectively. At the initial moment of the simulation, the droop controller starts to work, and the droop output value of the voltage power difference gradually increases to 0.375 and remains stable. At t=1s, the distributed event trigger controller starts to change the droop coefficient. Under the action of the second-layer controller, the voltage deviation is corrected. Finally, when the bus voltage returns to the rated voltage, the droop coefficient remains unchanged.

[0131] The fluctuation of load is the main reason for the bus voltage fluctuation of DC microgrid. The control performance of event-triggered controller when the load changes is analyzed below. Figure 8-Figure 10 It is the change of the distributed power output power P, bus voltage U and droop coefficient KP when the load of the distributed photovoltaic power generation system suddenly drops. When t=3s, the load of the distributed power suddenly drops, and the output of each distributed power source changes under the joint action of the first-layer droop control and the second-layer event trigger controller, and the output power reaches stability after a short time. The bus voltage also stabilizes near the rated voltage after a small fluctuation, which also well illustrates that the distributed event trigger controller can also maintain power balance and bus voltage stability when the load changes.

[0132] Figure 11-Figure 12 , is the distributed event triggering time diagram of voltage and power control of four distributed power sources, DPPG1 is the black curve, DPPG2 is the red curve, DPPG3 is the blue curve, and DPPG4 is the green curve; in order to maintain the voltage at the set value, the controller triggers relatively evenly. In order to maintain the output power stability, at the initial moment of event triggering controller input (t = 1s) and the initial moment of power change (t = 3s), the triggering control is relatively intensive. As the power change gradually becomes smooth, the number of event triggering also gradually decreases. This shows that the time-triggered controller designed in this paper only transmits voltage and load ratio information between the connected distributed power controllers when the event triggering conditions are met. This greatly reduces the burden of the communication system while achieving the control target of the DC microgrid, which is beneficial to the stable operation of the microgrid.

[0133] The distributed event-triggered controller in this application can achieve balanced distribution of loads among different power sources, and can well correct bus voltage deviations during traditional droop control, and also has good control performance when the load changes.

[0134] At the same time, the event-triggered controller of the present application transmits information between distributed power sources only when the trigger condition is met, which greatly reduces the communication burden between distributed power source controllers while ensuring load distribution and bus voltage stability.

[0135] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0136] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for load distribution and bus voltage regulation of a photovoltaic power generation system based on hierarchical control, characterized in that: include: Construct a model for each distributed photovoltaic power generation unit in the photovoltaic power generation system to achieve primary droop control of the photovoltaic power generation system; The bus voltage deviation is corrected based on the output current of the adjacent photovoltaic power generation unit; the steps include: Determine the current distribution error according to the output current of the adjacent photovoltaic power generation units; The average output voltage of the distributed photovoltaic power generation unit is obtained according to the current distribution error, and the voltage control error is determined in combination with the current bus reference voltage; The bus reference voltage is updated when the photovoltaic power generation system is stable based on the current distribution error and the voltage control error.

2. The method according to claim 1, characterized in that The distributed photovoltaic power generation unit model is: In the formula, I DPPGi Represents the output current of the i-th photovoltaic power generation unit, I Loadi represents the load current of the ith photovoltaic power generation unit, G ij represents the conductance of the tie line between the busbar of the i-th photovoltaic power generation unit and the busbar of the j-th photovoltaic power generation unit, U DPPGi represents the bus voltage of the ith photovoltaic power generation unit, U DPPGj represents the bus voltage of the jth photovoltaic power generation unit, Represents the set of other distributed photovoltaic power generation units connected to the i-th photovoltaic power generation unit.

3. The method according to claim 2, characterized in that When a droop control is performed based on the model, the load balancing distribution control target is: In the formula, I DPPGi_max represents the maximum current capacity of the i-th photovoltaic power generation unit, I DPPGj_max It represents the maximum current capacity of the jth photovoltaic power generation unit, and Ne is the number of nodes in the photovoltaic power generation system network.

4. The method according to claim 2, characterized in that: When a droop control is performed based on the model, the bus voltage control target is: In the formula, is the average output voltage of each distributed photovoltaic power generation unit, U n is the nominal voltage of the photovoltaic power generation unit, n is the number of photovoltaic power generation units, U i is the output voltage of the i-th photovoltaic power generation unit.

5. The method according to claim 1, characterized in that: The current sharing error is defined as: In the formula, e DPPGIi (t) represents the current distribution error at time t, h ij represents the communication relationship between the i-th photovoltaic power generation unit and the j-th photovoltaic power generation unit, I DPPGi (t) is the output current of the ith photovoltaic power generation unit at time t, I DPPGj (t) is the output current of the jth photovoltaic power generation unit at time t, I DPPGi_max represents the maximum current capacity of the i-th photovoltaic power generation unit, I DPPGj_max Represents the maximum current capacity of the jth photovoltaic power generation unit.

6. The method according to claim 1, characterized in that The average output voltage of distributed photovoltaic power generation units is collected according to the following formula: In the formula, is the average output voltage of each distributed photovoltaic power generation unit at time t, U i (t) represents the output voltage of the ith photovoltaic power generation unit at time t; K I >0 and K U >0 is the control gain coefficient, e DPPGIi Indicates the current distribution error; The voltage control error expression is: Where U n is the nominal voltage of the photovoltaic power generation unit.

7. The method according to claim 1, characterized in that Based on the current distribution error and voltage control error, the bus reference voltage is updated when the photovoltaic power generation system is stable as follows: Where U n (t) represents the updated nominal voltage of the photovoltaic power generation unit at time t, K r Indicates the voltage droop coefficient, I δDPPGi Indicates the current deviation, K I >0 and K U >0 is the control gain coefficient, e DPPGli represents the current distribution error, e DPPGUi Represents the voltage control error.

8. The method according to claim 1, characterized in that A time trigger condition is introduced. When the condition is triggered, the connected photovoltaic power generation units exchange current distribution information to improve the communication bandwidth.

9. The method according to claim 8, characterized in that when When the event triggers: In the formula, is the DC bus voltage reference value, U i is the output voltage of the ith photovoltaic power generation unit, e tr is the event trigger condition, K I >0 and K U >0 is the control gain coefficient, λ B_min is the minimum eigenvalue of matrix B, B is the Lapse matrix L Ne and L Nc The incidence matrix, L Ne is the node admittance matrix in the photovoltaic power generation system network theory, L Ne (i, i) represents the self-admittance of node i, L Nc is the Laplace matrix of the communication network, ζ1>0, And 0<δ<1 is a set constant, DPPG i and DPPG j The observed current sharing error between DPPG i and DPPG j The observed voltage distribution error between .

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