Photovoltaic power plant control system and method

Abstract

The application provides a photovoltaic power station control system and method, the system comprising: a power station control layer and a voltage outer loop controller; the voltage outer loop controller is connected with the power station control layer, and is further used for being connected with a grid-connected point of a grid-structured photovoltaic power station and a plurality of photovoltaic inverters, each photovoltaic inverter is connected with the grid-connected point; the power station control layer is used for sending an adjustment instruction of the grid-structured photovoltaic power station to the voltage outer loop controller; the voltage outer loop controller is used for receiving the adjustment instruction of the grid-structured photovoltaic power station sent by the power station control layer and receiving grid-connected point working data sent by the grid-connected point; according to the adjustment instruction and the grid-connected point working data, a current instruction corresponding to each photovoltaic inverter is determined, and the current instruction is sent to the corresponding photovoltaic inverter, so that each photovoltaic inverter adjusts its own current according to the corresponding current instruction. The application can improve the stability of photovoltaic power station control, and further can ensure the stable operation of the grid-structured photovoltaic power station.

Description

Technical Field

[0001] The present application relates to the field of new energy technology, and in particular to a photovoltaic power station control system and method. Background Art

[0002] New energy sources have replaced synchronous power sources in large quantities, the system's rotational inertia has decreased, and the frequency and voltage regulation capabilities have decreased. The role of new energy sources has gradually changed from an auxiliary power source to a main power source, and from "passive following" to "active support" for grid security, becoming the main carrier for maintaining grid frequency and voltage. Grid-type photovoltaic inverters are increasingly appearing in photovoltaic power stations.

[0003] At present, the control method of photovoltaic power stations mainly uses the photovoltaic inverters of the photovoltaic power station itself for control. Each photovoltaic inverter uses a dual closed-loop control method of voltage outer loop and current inner loop to control the photovoltaic power station. Figure 1 Given an existing distributed photovoltaic power station architecture, the above control method is difficult to apply to a grid-type photovoltaic power station with a large number of grid-type photovoltaic inverters running in parallel and relying on a distributed photovoltaic power station architecture. The reasons are as follows:

[0004] According to the voltage outer loop control method of the photovoltaic inverter, the voltage speed, terminal voltage amplitude and electrical angle of each photovoltaic inverter will be determined by the input torque. The input torque of different photovoltaic inverters may be different. Therefore, the voltage speeds of multiple photovoltaic inverters will have slight differences, the terminal voltage amplitudes will have slight differences, and the electrical angles will also have slight differences. When multiple photovoltaic inverters are operated in parallel and the voltage outer loop control is performed separately, the introduction of different voltage speeds, terminal voltage amplitudes and electrical angles will generate active circulating current or oscillation. Since the terminal voltages of each photovoltaic inverter are different, reactive station circulating current will be caused in multiple photovoltaic inverters. Summary of the Invention

[0005] In response to at least one problem in the prior art, the present application proposes a photovoltaic power station control system and method, which can improve the stability of photovoltaic power station control and thereby ensure the stable operation of a grid-type photovoltaic power station.

[0006] In order to solve the above technical problems, this application provides the following technical solutions:

[0007] In a first aspect, the present application provides a photovoltaic power station control system comprising: a power station control layer and a voltage outer loop controller;

[0008] The voltage outer loop controller is connected to the power station control layer and is also used to connect to the grid connection point and multiple photovoltaic inverters of the grid-type photovoltaic power station, and each photovoltaic inverter is connected to the grid connection point; wherein,

[0009] The power station control layer is used to send an adjustment instruction of the grid-type photovoltaic power station to the voltage outer loop controller;

[0010] The voltage outer loop controller is used to receive the adjustment instructions of the grid-connected photovoltaic power station sent by the power station control layer and the grid connection point working data sent by the grid connection point; determine the current instruction corresponding to each photovoltaic inverter based on the adjustment instructions and the grid connection point working data, and send the current instruction to the corresponding photovoltaic inverter, so that each photovoltaic inverter adjusts its own current according to the corresponding current instruction.

[0011] Furthermore, the voltage outer loop controller includes: a first current determining unit and a second current determining unit;

[0012] The first current determining unit is configured to determine a total current control instruction of the grid-connected photovoltaic power station according to the adjustment instruction and the grid-connected point working data;

[0013] The second current determining unit is configured to determine the current instructions corresponding to each photovoltaic inverter according to the current control general instruction and a preset current distribution rule; and send the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter.

[0014] Furthermore, the photovoltaic power station control system further includes: a plurality of data acquisition devices;

[0015] Each data acquisition device is connected to the voltage outer loop controller, each photovoltaic inverter is connected to its unique corresponding data acquisition device, and each data acquisition device is connected to at least one photovoltaic inverter;

[0016] The voltage outer loop controller sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter through the data acquisition device.

[0017] Furthermore, the photovoltaic power station control system further includes: a backup voltage outer loop controller; the backup voltage outer loop controller is connected to each photovoltaic inverter and the voltage outer loop controller respectively; wherein,

[0018] The backup voltage outer loop controller is used to receive the adjustment instruction and obtain the grid-connected point working data when the voltage outer loop controller fails; determine the current instruction corresponding to each photovoltaic inverter based on the adjustment instruction and the grid-connected point working data, and send it to the corresponding photovoltaic inverter.

[0019] Furthermore, the voltage outer loop controller is further configured to monitor whether there is a maximum power point photovoltaic inverter among the photovoltaic inverters whose output active current is less than the direct-axis current command in the current command and whose current difference between the output active current and the direct-axis current command is greater than a first current difference threshold value; if so, controlling the current difference to be distributed to the inverters that have not reached the maximum power point until all photovoltaic inverters reach the maximum power point inverter or the current difference between the actual value of the output active current of the grid-connected point and the preset grid-connected point output active current standard value is less than or equal to the second current difference threshold value;

[0020] The inverters that have not reached the maximum power point are all photovoltaic inverters except the photovoltaic inverter at the maximum power point.

[0021] Furthermore, the multiple photovoltaic inverters are divided into multiple groups, each group includes at least two photovoltaic inverters, the photovoltaic inverters in the same group are connected via a busbar, and the photovoltaic inverters in different groups correspond to different busbars. Each photovoltaic inverter is used to connect to the grid connection point via the busbar.

[0022] Furthermore, the voltage outer loop controller includes:

[0023] a determination unit configured to monitor whether there is an abnormal bus whose voltage exceeds a preset normal bus voltage range among the buses, and if so, determine a reactive current change value of the abnormal bus based on a preset bus reactive voltage coefficient, the normal bus voltage range, and the bus voltage of the abnormal bus;

[0024] The regulating unit is used to regulate the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value.

[0025] Furthermore, the adjustment unit includes:

[0026] a first current regulating subunit, configured to determine whether the reactive current change value is greater than zero, and if so, to adjust the total output reactive current of the photovoltaic inverter corresponding to the abnormal busbar to increase the absolute value of the reactive current change value, and to adjust the total output reactive current of the photovoltaic inverter corresponding to each normal busbar to decrease the absolute value of the reactive current change value, wherein the normal busbar is each busbar among all the busbars except the abnormal busbar;

[0027] The second current regulating subunit is used to determine whether the reactive current change value is less than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is adjusted to reduce the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is adjusted to increase the absolute value of the reactive current change value.

[0028] In a second aspect, the present application provides a photovoltaic power station control method, which is applied to the photovoltaic power station control system, and the method includes:

[0029] The power station control layer sends an adjustment instruction of the grid-type photovoltaic power station to the voltage outer loop controller;

[0030] The voltage outer loop controller receives the adjustment instruction of the grid-connected photovoltaic power station sent by the power station control layer and receives the grid connection point working data sent by the grid connection point;

[0031] The voltage outer loop controller determines the current instruction corresponding to each photovoltaic inverter according to the adjustment instruction and the grid connection point working data, and sends the current instruction to the corresponding photovoltaic inverter;

[0032] Each photovoltaic inverter adjusts its own current according to the corresponding current command.

[0033] Furthermore, the voltage outer loop controller determines a current instruction corresponding to each photovoltaic inverter according to the adjustment instruction and the grid connection point working data, and sends the current instruction to the corresponding photovoltaic inverter, including:

[0034] The voltage outer loop controller determines the total current control instruction of the grid-connected photovoltaic power station according to the adjustment instruction and the grid-connected point working data;

[0035] The voltage outer loop controller determines the current instructions corresponding to each photovoltaic inverter according to the current control general instruction and the preset current distribution rule; and sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter.

[0036] Furthermore, the voltage outer loop controller sending the current instruction to the photovoltaic inverter includes:

[0037] The voltage outer loop controller sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter through the data acquisition device.

[0038] Furthermore, the photovoltaic power station control method further includes:

[0039] When the voltage outer loop controller fails, the backup voltage outer loop controller receives the adjustment instruction and obtains the grid connection point working data; according to the adjustment instruction and the grid connection point working data, the backup voltage outer loop controller determines the current instruction corresponding to each photovoltaic inverter and sends it to the corresponding photovoltaic inverter, so that each photovoltaic inverter receives the current instruction sent by the voltage outer loop controller and adjusts its own current according to the current instruction.

[0040] Furthermore, after each photovoltaic inverter adjusts its own current according to the corresponding current instruction, the method further includes:

[0041] The voltage outer loop controller monitors whether there is a maximum power point photovoltaic inverter among each photovoltaic inverter, whose output active current is less than the direct-axis current command in the current command and the current difference between the output active current and the direct-axis current command is greater than a first current difference threshold. If so, the voltage outer loop controller controls the distribution of the current difference to the inverter that has not reached the maximum power point until all photovoltaic inverters reach the maximum power point inverter or the current difference between the actual value of the output active current of the grid-connected point and the preset grid-connected point output active current standard value is less than or equal to the second current difference threshold;

[0042] The inverters that have not reached the maximum power point are all photovoltaic inverters except the photovoltaic inverter at the maximum power point.

[0043] Furthermore, after each photovoltaic inverter adjusts its own current according to the corresponding current instruction, the method further includes:

[0044] The voltage outer loop controller monitors whether there is an abnormal bus whose voltage exceeds a preset normal range of bus voltage among the buses. If so, the reactive current change value of the abnormal bus is determined based on a preset bus reactive voltage coefficient, the normal range of bus voltage and the bus voltage of the abnormal bus;

[0045] The voltage outer loop controller adjusts the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value.

[0046] Furthermore, the voltage outer loop controller adjusts the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value, including:

[0047] The voltage outer loop controller determines whether the reactive current change value is greater than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is increased by the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is decreased by the absolute value of the reactive current change value. The normal bus is each bus among all the buses except the abnormal bus;

[0048] The voltage outer loop controller determines whether the reactive current change value is less than zero. If so, it adjusts the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus to reduce the absolute value of the reactive current change value, and adjusts the total output reactive current of the photovoltaic inverter corresponding to each normal bus to increase the absolute value of the reactive current change value.

[0049] It can be seen from the above technical solution that the present application provides a photovoltaic power station control system and method. Among them, the system includes: a power station control layer and a voltage outer loop controller; the voltage outer loop controller is connected to the power station control layer, and is also used to connect to the grid connection point and multiple photovoltaic inverters of the grid-type photovoltaic power station, and each photovoltaic inverter is connected to the grid connection point; wherein, the power station control layer is used to send the adjustment instructions of the grid-type photovoltaic power station to the voltage outer loop controller; the voltage outer loop controller is used to receive the adjustment instructions of the grid-type photovoltaic power station sent by the power station control layer and receive the grid connection point working data sent by the grid connection point; according to the adjustment instructions and the grid connection point working data, the current instruction corresponding to each photovoltaic inverter is determined, and the current instruction is sent to the corresponding photovoltaic inverter, so that each photovoltaic inverter adjusts its own current according to the corresponding current instruction, which can improve the stability of the photovoltaic power station control and thus ensure the stable operation of the grid-type photovoltaic power station; in the prior art, the photovoltaic inverters operate in parallel to generate active circulating current or oscillation. The reason for this is usually that when multiple photovoltaic inverters execute the voltage inner loop control, the introduced voltage speed, generator voltage amplitude, and electrical angle are different. This solution replaces the original voltage control closed loop of the photovoltaic inverter with current instructions, eliminating the need to introduce voltage speed, generator voltage amplitude, and electrical angle during the photovoltaic inverter voltage outer loop control. This can destroy the active / reactive circulating current and oscillation conditions formed by the photovoltaic inverter's multiple voltage control, prevent the photovoltaic inverter from generating active circulating current or oscillation, and avoid causing reactive circulating current within the photovoltaic inverter. This can improve the stability of the photovoltaic power station control and ensure the stable operation of the grid-connected photovoltaic power station. The output reactive current of the photovoltaic inverter can be adjusted by the bus voltage, which can prevent the bus voltage from exceeding the normal bus voltage range and achieve protection for the grid-connected photovoltaic power station. In addition, current regulation can be used to ensure that all photovoltaic inverters reach the maximum power point inverter, reducing power loss and improving the safety and stability of the grid-connected photovoltaic power station operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0051] Figure 1 This is a schematic diagram of a photovoltaic power station topology in the prior art;

[0052] Figure 2 This is a schematic diagram of a control loop of a networked (voltage source) photovoltaic inverter in the prior art;

[0053] Figure 3 This is a schematic diagram of a topological junction structure of a photovoltaic power generation unit in the prior art;

[0054] Figure 4 This is a schematic diagram of a grid-following (current source) photovoltaic inverter control loop in the prior art;

[0055] Figure 5 is a schematic diagram of the relationship between the photovoltaic power station control system and the photovoltaic power station in the embodiment of the present application;

[0056] Figure 6 This is a voltage outer loop control block diagram of a voltage outer loop controller in an example of the present application;

[0057] Figure 7 This is a block diagram of the current inner loop control of a photovoltaic inverter in an example of the present application;

[0058] Figure 8 is a logic diagram of a photovoltaic power station control system in an embodiment of the present application;

[0059] Figure 9 This is a logic diagram of the photovoltaic power station control system in the application example of this application;

[0060] Figure 10 This is a schematic diagram of a first flow chart of a photovoltaic power station control method in an embodiment of the present application;

[0061] Figure 11 is a second flow chart of the photovoltaic power station control method in an embodiment of the present application;

[0062] Figure 12 3 is a schematic diagram of a third flow chart of a photovoltaic power station control method in an embodiment of the present application;

[0063] Figure 13 This is a fourth flow chart of the photovoltaic power station control method in an embodiment of the present application. DETAILED DESCRIPTION

[0064] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0065] In traditional AC power systems, which are primarily powered by synchronous power sources like hydropower and thermal power, renewable energy sources serve as auxiliary power sources, primarily replacing clean energy. Establishing and maintaining grid frequency and voltage primarily relies on synchronous power sources. Renewable energy sources, such as photovoltaic and wind power, will gradually become the primary energy source.

[0066] Currently, grid-connected photovoltaic inverters typically employ power supply control strategies, including virtual synchronous generator (VSG) control, voltage-frequency (VF) mode, and droop control. VSG control strategies still rely on dual closed-loop control to achieve stable voltage output. The outer voltage loop actively supports frequency and voltage by simulating the device's equations of motion and electromagnetic transient equations, while the inner current loop accelerates system response and prevents transient overcurrent damage to power electronic devices. Existing photovoltaic power station-level control is designed based on traditional photovoltaic inverters. Figure 2 A dual closed-loop control method of the voltage outer loop and current inner loop of the photovoltaic inverter based on the VSG control strategy is proposed. Figure 2 In, P e is the actual value of the electromagnetic power of the photovoltaic inverter, P ref is the electromagnetic power command value of the photovoltaic inverter, K f is the primary frequency modulation coefficient of the photovoltaic inverter, J is the inertia coefficient of the photovoltaic inverter, ω0 is the rated speed of the photovoltaic inverter, ω is the voltage speed of the photovoltaic inverter, s is the differential operator of the photovoltaic inverter, θ is the electrical angle of the photovoltaic inverter, V ref is the terminal voltage command value of the photovoltaic inverter, V is the actual terminal voltage value of the photovoltaic inverter, and D q is the reactive power droop coefficient of the photovoltaic inverter, Q is the actual output reactive power value of the photovoltaic inverter, Q ref is the output reactive power command value of the photovoltaic inverter, e is the terminal voltage amplitude of the photovoltaic inverter, U d * is the direct-axis voltage command value of the photovoltaic inverter, U d is the actual value of the direct-axis voltage of the photovoltaic inverter, U q * is the quadrature-axis voltage command value of the photovoltaic inverter, U q is the actual value of the quadrature axis voltage of the photovoltaic inverter, Cf is the filter capacitor of the photovoltaic inverter, Lf is the filter inductor of the photovoltaic inverter, I d * is the direct-axis current command value of the photovoltaic inverter, I d is the actual value of the direct-axis current of the photovoltaic inverter, I q * is the quadrature-axis current command value of the photovoltaic inverter, I q is the actual value of the quadrature axis current of the photovoltaic inverter, e a , eb and e c is the amplitude of the three-phase abc terminal voltage of the photovoltaic inverter. The dual closed-loop control method is also applied to the PI controller, DP / ABC converter, PWM pulse width modulator and control switch circuit.

[0067] The grid-type units provided by this solution can be applied to the following scenarios:

[0068] (1) New energy base delivery scenario without conventional power supply support

[0069] Large-scale new energy bases do not have the conditions to build supporting conventional power sources such as thermal power generation. Large-scale new energy bases will face the challenge of operating without the support of synchronous machines, and the power system safety and stability issues brought about by their grid connection will also become more prominent and severe.

[0070] (2) New energy base and conventional power supply bundled delivery scenario

[0071] Due to the inverse distribution of energy resources and load centers, the development and utilization of new energy sources is characterized by large-scale development and long-distance transmission. Large-scale new energy power generation bases often bundle with local thermal power plants and transmit AC and DC power to other locations. However, this AC and DC transmission method for new energy and thermal power has always faced prominent issues such as insufficient supporting thermal power capacity, insufficient synchronous support reserve capacity, and system stability. In particular, issues such as transient stability, small-disturbance stability, and subsynchronous oscillations have increased significantly in recent years.

[0072] (3) New energy access to weak power grid scenarios

[0073] As the proportion of renewable energy installed capacity continues to increase, the integration of renewable energy into weak local grids has triggered new stability issues. In the future, most renewable energy sites will be located in remote areas and connected to the grid via long-distance transmission lines. Traditional current source control methods have many limitations in terms of system voltage and frequency regulation. They have limited synchronization support capabilities for grids stretching hundreds of kilometers, and cannot meet the requirements for stable operation in weak grids.

[0074] (4) New energy isolated grid operation scenario

[0075] At the distribution network level, the traditional form, structure, and function of the network will undergo transformation. Ensuring supply, stability, and safety will become major challenges for future distribution networks, and "new energy + energy storage" will become the mainstream development model. As installed capacity of new energy sources continues to increase, the failure rate of distribution networks will also increase under current technological conditions. In the event of a grid failure, the "new energy + energy storage + load" approach, forming an isolated, source-grid-load-storage system, can improve power supply reliability for users.

[0076] Figure 3A schematic diagram of the topology of a traditional photovoltaic power generation unit is also provided. Traditional photovoltaic power stations use current source type (grid-following type) photovoltaic inverters. Each inverter collects the terminal voltage and performs phase locking to obtain the amplitude and angle of the grid voltage, and achieves maximum power output through the voltage / power outer loop and current inner loop. Figure 4 As shown in the figure, in a conventional current source photovoltaic inverter control strategy, each inverter is controlled independently, and the entire photovoltaic power station is composed of several inverters connected in parallel. For example, a 100MW photovoltaic power station is composed of 200 0.5MW photovoltaic inverters connected in parallel.

[0077] The details are described in detail through the following embodiments.

[0078] Figure 5 Schematic diagram of the relationship between the photovoltaic power station control system and the photovoltaic power station in the embodiment of the present application. Figure 5 As shown, in order to improve the stability of photovoltaic power station control and thereby ensure the stable operation of the grid-type photovoltaic power station, this embodiment provides a photovoltaic power station control system. In this embodiment, the photovoltaic power station control system includes: a power station control layer and a voltage outer loop controller; the voltage outer loop controller is connected to the power station control layer, and is also used to connect to the grid connection point and multiple photovoltaic inverters of the grid-type photovoltaic power station, and each photovoltaic inverter is connected to the grid connection point; wherein, the power station control layer is used to send the adjustment instruction of the grid-type photovoltaic power station to the voltage outer loop controller; the voltage outer loop controller is used to receive the adjustment instruction of the grid-type photovoltaic power station sent by the power station control layer and receive the grid connection point working data sent by the grid connection point; according to the adjustment instruction and the grid connection point working data, determine the current instruction corresponding to each photovoltaic inverter, and send the current instruction to the corresponding photovoltaic inverter, so that each photovoltaic inverter adjusts its own current according to the corresponding current instruction.

[0079] Specifically, the adjustment instruction may include: the active power instruction P of the grid-type photovoltaic power station ref0 , reactive power command Q ref0 And the voltage command V ref0 , the grid voltage can be adjusted to V ref0 The grid point working data may include: the actual active power P of the grid point e0 , the actual grid connection point voltage V0, the actual grid connection point reactive power Q0, the endogenous voltage angular velocity ω1 of the outer loop voltage controller, and (50 + the frequency dead zone of the outer loop voltage controller) × 2 × π. The endogenous voltage angular velocity and frequency dead zone can be pre-set according to actual conditions. The grid connection point is connected to the voltage outer loop controller to detect the grid connection point voltage. The grid-connected photovoltaic power station can have a large number of grid-connected photovoltaic inverters operating in parallel. The photovoltaic inverter's own current can include active current and reactive current.

[0080] Specifically, the power station control layer can be the power station automatic voltage control (AVC), automatic generation control (AGC), and primary frequency control system. This layer is the dispatching automation requirement equipment, which is consistent with the traditional power station configuration and function, that is, it accepts the active power P issued by the dispatching agency. ref0 , reactive power instruction Q ref0 , voltage command V ref0 , after considering the loss in the station, the active power P ref0 , reactive power instruction Q ref0 It is sent to the next layer; at the same time, it communicates with the middle control layer to collect, count, store and send the four remote control information of the photovoltaic power station.

[0081] In order to further improve the accuracy of determining the current instruction, in one embodiment of the present application, the voltage outer loop controller includes: a first current determination unit and a second current determination unit; the first current determination unit is used to determine the total current control instruction of the grid-connected photovoltaic power station according to the adjustment instruction and the grid-connected point working data; the second current determination unit is used to determine the current instruction corresponding to each photovoltaic inverter according to the total current control instruction and the preset current distribution rule; the current instruction corresponding to each photovoltaic inverter is sent to the photovoltaic inverter.

[0082] Specifically, the regulation instructions, grid connection point working data, rotor motion equations and simulated electromagnetic equations can be applied to determine the total current control instructions of the grid-connected photovoltaic power station; the preset current distribution rules can be equal distribution, distribution according to margin, proportional distribution or more complex rules.

[0083] Specifically, the functions implemented by the voltage outer loop controller are equivalent to the functions implemented by an independent control layer, which is the master control unit of the so-called master-slave control structure and is responsible for the voltage outer loop control of the grid-type photovoltaic power station.

[0084] See also Figure 6 In one example, the voltage outer loop controller can construct a stable output voltage of the outer loop voltage controller (which is expressed as a stable voltage amplitude e0 and angular velocity θ0) through the rotor operation equation and the simulated electromagnetic equation, P ref0 is the electromagnetic power instruction value of the photovoltaic power station issued by the AGC, which can be equivalent to the above-mentioned active power instruction; P e0 is the grid-connected power, which can be equivalent to the actual value of the electromagnetic power of the photovoltaic power station; w1 is the endogenous voltage angular velocity of the photovoltaic power station, which can be equivalent to the voltage rotation speed; w 00is the rated speed of the photovoltaic power station, and the rated power can be (50+frequency dead zone)×2×π; V ref0 is the grid connection point voltage command, which can be equivalent to the terminal voltage command value of the photovoltaic power station; V0 is the actual grid connection point voltage, which can be equivalent to the actual terminal voltage value of the photovoltaic power station; Q ref0 is the output reactive power command value of the photovoltaic power station, Q0 is the actual reactive power of the grid connection point, and the actual reactive power of the grid connection point can be equivalent to the actual output reactive power value of the photovoltaic power station; K f0 is the primary frequency modulation coefficient of the photovoltaic power station; J0 is the inertia coefficient of the photovoltaic power station; s0 is the differential operator of the photovoltaic power station; θ0 is the electrical angle of the photovoltaic power station; D q0 is the reactive power droop coefficient of the photovoltaic power station; e0 is the terminal voltage amplitude of the photovoltaic power station; is the direct-axis voltage command value of the photovoltaic power station, which can be equivalent to the direct-axis intrinsic voltage; U d0 is the actual value of the direct-axis voltage of the photovoltaic power station; is the quadrature-axis voltage command value of the photovoltaic power station, which is equivalent to the quadrature-axis intrinsic voltage; U q0 is the actual value of the quadrature axis voltage of the photovoltaic power station, Cf0 is the filter capacitor of the photovoltaic power station, is the direct-axis current command value of the photovoltaic power station, is the quadrature axis current command value of the photovoltaic power station. The direct axis current command value and the quadrature axis current command value of the photovoltaic power station can be equivalent to the total current control command of the entire photovoltaic power station. After feedback adjustment, the total current control instruction of the entire photovoltaic power station is generated The direct-axis current can be equivalent to the active current, and the alternating current can be equivalent to the reactive current.

[0085] It should be noted that the rotor motion equation and the electromagnetic equation are only one method of constructing the voltage. Other methods such as VF control and droop control can also be used, which are not enumerated here. The slave control unit of this solution can be a photovoltaic inverter.

[0086] Specifically, the functions implemented by the above-mentioned photovoltaic inverters in combination can be equivalent to the functions implemented by an execution layer. Based on the voltage outer loop control structure of the intermediate layer of the grid-type photovoltaic power station, the photovoltaic inverters have no voltage outer loop and are all configured with a current inner loop. In one example, Figure 7 As shown, the input of each inverter current loop is the current command I d0 , I q0 , I d0 , I q0 It is the total current control instruction of the intermediate control layer Calculated based on equal distribution, allocation according to margin, equal proportion or more complex methods; Figure 7Where ω is the voltage-speed of the photovoltaic inverter, Lf is the filter inductance of the photovoltaic inverter, and U d is the actual value of the direct-axis voltage of the photovoltaic inverter, U q is the actual value of the quadrature axis voltage of the photovoltaic power station, I d0 is the direct-axis current command value of the photovoltaic inverter, I q0 is the quadrature-axis current command value of the photovoltaic inverter, I d1 is the inverter direct-axis current command value after fault ride-through judgment, I q1 is the inverter quadrature-axis current command value after fault ride-through judgment, e a , e b and e c is the amplitude of the three-phase abc terminal voltage of the photovoltaic inverter.

[0087] In order to ensure that each photovoltaic inverter receives the current instruction approximately at the same time and improve the communication speed, such as Figure 8 As shown, in one embodiment of the present application, the photovoltaic power station control system further includes: multiple data acquisition devices; each data acquisition device is connected to the voltage outer loop controller, each photovoltaic inverter is connected to its uniquely corresponding data acquisition device, and each data acquisition device is connected to at least one photovoltaic inverter; the voltage outer loop controller sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter through the data acquisition device.

[0088] Specifically, each data acquisition device can be used to receive current commands for each photovoltaic inverter corresponding to the data acquisition device, sent by the voltage outer loop controller, and forward these current commands to the corresponding photovoltaic inverter. By configuring the data acquisition devices, the time from when the current signal is sent by the voltage outer loop controller to when it is received by each inverter is no more than 20 milliseconds. The data acquisition devices are not interconnected, and each data acquisition device can be connected to one or more photovoltaic inverters. The data acquisition devices can also be servers.

[0089] In order to improve the stability of the photovoltaic power station control system, in one embodiment of the present application, the photovoltaic power station control system also includes: a backup voltage outer loop controller; the backup voltage outer loop controller is respectively connected to each photovoltaic inverter and the voltage outer loop controller; wherein, the backup voltage outer loop controller is used to receive the adjustment instruction and obtain the grid connection point working data when the voltage outer loop controller fails; determine the current instruction corresponding to each photovoltaic inverter according to the adjustment instruction and the grid connection point working data, and send it to the corresponding photovoltaic inverter.

[0090] In order to reduce power loss and thereby ensure the stable operation of the grid-connected photovoltaic power station, in one embodiment of the present application, the voltage outer loop controller is also used to monitor whether there is a maximum power point photovoltaic inverter in each photovoltaic inverter whose output active current is less than the direct-axis current instruction in the current instruction and the current difference between the output active current and the direct-axis current instruction is greater than a first current difference threshold. If so, the current difference is controlled to be distributed to the inverter that has not reached the maximum power point until all photovoltaic inverters reach the maximum power point inverter or the current difference between the actual value of the output active current of the grid-connected point and the preset grid-connected point output active current standard value is less than or equal to the second current difference threshold; the inverter that has not reached the maximum power point is each photovoltaic inverter among all photovoltaic inverters except the maximum power point photovoltaic inverter.

[0091] Specifically, a photovoltaic inverter whose output active current is less than the direct-axis current instruction and whose current difference between the output active current and the direct-axis current instruction is greater than a first current difference threshold can be determined as a maximum power point photovoltaic inverter; the first current difference threshold, the second current difference and the grid-connected point output active current standard value can all be set according to actual needs, and this application does not impose any restrictions on this. For example, the first current difference threshold is 1% × current instruction I d0 The second current difference threshold is 1% × the preset grid-connected point output active current standard value. If (output active current - current command I d0 )>1%×current command I d0 , then determine the output active current and current command I d0 For a maximum power point photovoltaic inverter whose current difference is greater than the first current difference threshold, if (the actual value of the output active current of the grid-connected point - the preset standard value of the output active current of the grid-connected point) ≤ 1% × the preset standard value of the output active current of the grid-connected point, it is determined that the current difference between the actual value of the output active current of the grid-connected point and the preset standard value of the output active current of the grid-connected point is less than or equal to the second current difference threshold.

[0092] Specifically, this embodiment provides an active current optimization strategy that takes into account the inverter feedback value. Since the grid-connected photovoltaic power station should respond to grid frequency fluctuations and participate in grid frequency regulation and inertia, it generally does not operate in the Maximum Power Point Tracking (MPPT) mode. The voltage outer loop controller calculates the direct axis current command value of the photovoltaic power station. Based on the proportion of the inverter installed capacity, it is distributed to each inverter I d0 , if an inverter outputs active current Less than I d0 , and the deviation is greater than 1%, then the inverter is considered to have reached MPPT mode; if an inverter outputs active current with I d0 If the deviation between them is less than or equal to 1%, it is considered that the inverter has not reached the MPPT mode.

[0093] Specifically, the active current difference of the inverters that are already in MPPT mode is distributed to the inverters that have not reached MPPT mode in proportion to their installed capacity, until the deviation between the actual value of the output active current of the power station's grid-connected point and the preset standard value of the output active current of the grid-connected point is less than or equal to 1%, or all inverters are in MPPT mode.

[0094] In one embodiment of the present application, the multiple photovoltaic inverters are divided into multiple groups, each group includes at least two photovoltaic inverters, the photovoltaic inverters in the same group are connected via a busbar, and the photovoltaic inverters in different groups correspond to different busbars. Each photovoltaic inverter is used to connect to the grid point via the busbar.

[0095] In order to reduce power consumption and thereby ensure stable operation of a grid-type photovoltaic power station, in one embodiment of the present application, the voltage outer loop controller includes:

[0096] A determination unit is used to monitor whether there is an abnormal bus among each bus whose voltage exceeds a preset normal range of bus voltage. If so, the reactive current change value of the abnormal bus is determined based on the preset bus reactive voltage coefficient, the normal range of bus voltage and the bus voltage of the abnormal bus.

[0097] Specifically, a bus whose voltage exceeds the preset normal range of bus voltage can be determined as an abnormal bus; the preset normal range of bus voltage can be set according to actual conditions, and this application does not impose any restrictions on this. For example, the normal operating range of the 35kV bus voltage is set to 35~37.5kV. If the bus voltage is lower than the lower limit of the normal operating range of 35kV, the reactive current change value = (35-V*)×K; if the bus voltage is higher than the upper limit of the normal operating range of 37.5kV, the reactive current change value = (37.5-V*)×K, where V* is the bus voltage and K is the reactive voltage coefficient of the 35kV bus.

[0098] The regulating unit is used to regulate the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value.

[0099] In order to further reduce power consumption and ensure stable operation of the grid-type photovoltaic power station, in one embodiment of the present application, the regulating unit includes:

[0100] The first current regulating subunit is used to determine whether the reactive current change value is greater than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is increased by the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is reduced by the absolute value of the reactive current change value. The normal bus is each bus among all the buses except the abnormal bus.

[0101] Specifically, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus can represent the sum of the output reactive currents of each photovoltaic inverter in the abnormal bus; the total output reactive current of the photovoltaic inverter corresponding to each normal bus can represent the sum of the output reactive currents of each photovoltaic inverter in the photovoltaic power station except the photovoltaic inverter corresponding to the abnormal bus.

[0102] Specifically, this embodiment provides a reactive current optimization strategy that takes into account the bus voltage within the station. Since the control point of the grid-connected photovoltaic power station in this solution is the grid connection point and the SVG configuration is omitted in the station, for 110kV and 220kV grid-connected photovoltaic power stations, multiple 35kV buses in the station may be too high or too low. In one example, assuming that the photovoltaic power station has three buses, namely busbars 1#, 2#, and 3#, and the normal operating range of the 35kV bus voltage is set to 35-37.5kV (which can be set according to the actual situation of the power station), then while keeping the total photovoltaic inverter output reactive current unchanged, it is first distributed in proportion to the reactive current margin of each inverter (or in proportion to the installed capacity of the inverter, reactive current equalization, etc.). If the 1# bus voltage V* is lower than the preset bus voltage normal range, the total inverter reactive current output by each inverter under busbar 1# increases by (35-V*)×K, and the increased total inverter reactive current can be equivalent to the actual total output reactive current corresponding to the above-mentioned abnormal bus; each inverter under busbars 2# and 3# is evenly distributed in proportion to the reactive current margin (or in proportion to the installed capacity of the inverter, reactive current equalization, etc.) -(35-V*)×K.

[0103] The second current regulating subunit is used to determine whether the reactive current change value is less than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is adjusted to reduce the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is adjusted to increase the absolute value of the reactive current change value.

[0104] In the above example, if the voltage V* of bus 1# is too high, the total inverter reactive current output by each inverter under bus 1# will be reduced by (V*-37.5)×K, and each inverter under bus 2# and 3# will be evenly divided by (V*-37.5)×K in proportion to the reactive current margin (or by proportion of inverter installed capacity, reactive current equalization, etc.).

[0105] Figure 9 This is a logical diagram of the photovoltaic power station control system in the application example of this application, such as Figure 9 To further illustrate this solution, the present application provides an application example of a photovoltaic power station control system. In this application example, the photovoltaic power station control system includes: a power station control layer, an intermediate control layer, and an execution layer, which are specifically described as follows:

[0106] The power station control layer can be the power station automatic voltage control (AVC), automatic generation control (AGC), and primary frequency regulation control system. This layer is the dispatching automation requirement equipment, which is consistent with the traditional power station configuration and function. That is, it accepts the active power, reactive power, and voltage instructions issued by the dispatching agency, and converts the active power into reactive power after considering the loss in the station. ref0 , reactive power instruction Q ref0 And the voltage command V ref0 It is sent to the next layer; at the same time, it communicates with the middle control layer to collect, count, store and send the four remote control information of the photovoltaic power station.

[0107] The independent control layer is the master control unit of the so-called master-slave control structure, which is responsible for the voltage outer loop control of the grid-type photovoltaic power station. The voltage outer loop controller can build a stable output voltage (which is expressed as a stable voltage amplitude e0 and angular velocity θ0) through the rotor operation equation and the simulated electromagnetic equation. ref0 is the power command issued by AGC, P e0 is the grid-connected power, w1 is the endogenous voltage angular velocity, w 00 = (50 + frequency dead zone) × 2 × π, V ref0 is the grid connection point voltage issued by the dispatcher, V0 is the actual grid connection point voltage, Q ref0 is the reactive power command issued by the power station control layer, Q0 is the actual reactive power of the grid connection point; the endogenous voltage Generate the total current control instruction of the entire power station through feedback regulation

[0108] The execution layer is based on the voltage outer loop control structure of the intermediate layer of the grid-type photovoltaic power station. The photovoltaic inverter has no voltage outer loop and is configured with a current inner loop. The current loop input of each photovoltaic inverter is the current command I d0 , I q0 , I d0 , I q0 It is the total current control instruction of the intermediate control layer Calculated based on equal distribution, allocation according to margin, equal proportion or more complex methods.

[0109] Figure 10 This is a first flow chart of the photovoltaic power station control method according to an embodiment of the present application. Figure 10 As shown, in order to improve the stability of photovoltaic power station control and thereby ensure the stable operation of a grid-type photovoltaic power station, this embodiment provides a photovoltaic power station control method, which is applied to the photovoltaic power station control system. The method includes:

[0110] Step 100: The power station control layer sends an adjustment instruction of the grid-type photovoltaic power station to the voltage outer loop controller.

[0111] Step 101: the voltage outer loop controller receives the adjustment instruction of the grid-connected photovoltaic power station sent by the power station control layer and receives the grid connection point working data sent by the grid connection point.

[0112] Step 102: The voltage outer loop controller determines a current instruction corresponding to each photovoltaic inverter according to the adjustment instruction and the grid-connected point operation data, and sends the current instruction to the corresponding photovoltaic inverter.

[0113] Step 103: Each photovoltaic inverter adjusts its own current according to the corresponding current instruction.

[0114] Figure 11 This is a second flow chart of the photovoltaic power station control method in the embodiment of the present application. Figure 11 As shown, in order to improve the accuracy of determining the current instruction, in one embodiment of the present application, step 102 includes:

[0115] Step 1021: The voltage outer loop controller determines a total current control instruction of the grid-connected photovoltaic power station according to the adjustment instruction and the grid-connected point working data.

[0116] Step 1022: The voltage outer loop controller determines the current instruction corresponding to each photovoltaic inverter according to the current control general instruction and the preset current distribution rule; and sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter.

[0117] In order to ensure that each photovoltaic inverter receives the current instruction approximately simultaneously and improve the communication speed, in one embodiment of the present application, the voltage outer loop controller in step 102 sends the current instruction to the photovoltaic inverter including:

[0118] The voltage outer loop controller sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter through the data acquisition device.

[0119] In order to improve the stability of photovoltaic power station control, in one embodiment of the present application, the photovoltaic power station control method further includes:

[0120] When the voltage outer loop controller fails, the backup voltage outer loop controller receives the adjustment instruction and obtains the grid connection point working data; according to the adjustment instruction and the grid connection point working data, the current instruction corresponding to each photovoltaic inverter is determined and sent to the corresponding photovoltaic inverter, so that each photovoltaic inverter receives the current instruction sent by the voltage outer loop controller and adjusts its own current according to the current instruction; the photovoltaic power station control system also includes: a backup voltage outer loop controller.

[0121] Figure 12 This is a third flow chart of the photovoltaic power station control method in the embodiment of the present application, such as Figure 12 As shown, in order to reduce power consumption and thereby ensure stable operation of the grid-type photovoltaic power station, in one embodiment of the present application, after step 103, the following is further included:

[0122] Step 201: The voltage outer loop controller monitors whether there is a maximum power point photovoltaic inverter in each photovoltaic inverter, where the output active current is less than the direct-axis current instruction in the current instruction and the current difference between the output active current and the direct-axis current instruction is greater than a first current difference threshold. If so, execute step 202.

[0123] Step 202: The voltage outer loop controller controls the distribution of the current difference to the inverters that have not reached the maximum power point until all photovoltaic inverters have reached the maximum power point inverter or the current difference between the actual value of the output active current of the grid-connected point and the preset grid-connected point output active current standard value is less than or equal to a second current difference threshold; the inverters that have not reached the maximum power point are all photovoltaic inverters except the maximum power point photovoltaic inverter.

[0124] Figure 13 This is a fourth flow chart of the photovoltaic power station control method in the embodiment of the present application, such as Figure 13 As shown, in order to reduce power consumption and thereby ensure stable operation of the grid-type photovoltaic power station, in one embodiment of the present application, after step 103, the following is further included:

[0125] Step 301: The voltage outer loop controller monitors whether there is an abnormal bus among each bus whose voltage exceeds the preset normal range of bus voltage. If so, the reactive current change value of the abnormal bus is determined based on the preset bus reactive voltage coefficient, the normal range of bus voltage and the bus voltage of the abnormal bus.

[0126] Step 302: The voltage outer loop controller adjusts the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value.

[0127] In order to further reduce power consumption and ensure stable operation of the grid-type photovoltaic power station, in one embodiment of the present application, step 302 includes:

[0128] Step 3021: The voltage outer loop controller determines whether the reactive current change value is greater than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is adjusted to increase the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is adjusted to reduce the absolute value of the reactive current change value. The normal bus is each bus among all the buses except the abnormal bus.

[0129] Step 3022: The voltage outer loop controller determines whether the reactive current change value is less than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is adjusted to reduce the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is adjusted to increase the absolute value of the reactive current change value.

[0130] The processing flow of the embodiment of the photovoltaic power station control method provided in this specification can be specifically implemented by applying the embodiment of the above-mentioned photovoltaic power station control system. Its functions are not described in detail here, and reference can be made to the detailed description of the embodiment of the above-mentioned photovoltaic power station control system.

[0131] It can be seen from the above description that the photovoltaic power station control system and method provided by the present application can improve the stability of the photovoltaic power station control, and thus can ensure the stable operation of the grid-type photovoltaic power station; specifically, the voltage outer loop controller can be used to implement the voltage outer loop control of the grid-type photovoltaic power station, and obtain the current instructions of each photovoltaic inverter of the grid-type photovoltaic power station, which can avoid the photovoltaic inverter from generating active circulating current or oscillation, and avoid causing reactive station circulating current of the photovoltaic inverter, thereby improving the stability of the photovoltaic power station control and ensuring the stable operation of the grid-type photovoltaic power station; it can also reduce power consumption through current regulation, and improve the safety and stability of the operation of the grid-type photovoltaic power station.

[0132] Specific embodiments are used in this application to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A photovoltaic power station control system, characterized in that: include: Power station control layer and voltage outer loop controller; The voltage outer loop controller is connected to the power station control layer and is also used to connect to the grid connection point and multiple photovoltaic inverters of the grid-type photovoltaic power station, and each photovoltaic inverter is connected to the grid connection point; wherein, The power station control layer is used to send an adjustment instruction of the grid-type photovoltaic power station to the voltage outer loop controller; The voltage outer loop controller is configured to receive an adjustment instruction of the grid-connected photovoltaic power station sent by the power station control layer and receive grid connection point operating data sent by the grid connection point; determine a current instruction corresponding to each photovoltaic inverter based on the adjustment instruction and the grid connection point operating data, and send the current instruction to the corresponding photovoltaic inverter, so that each photovoltaic inverter adjusts its own current according to the corresponding current instruction; The voltage outer loop controller is further configured to monitor whether there is a maximum power point photovoltaic inverter among the photovoltaic inverters, whose output active current is less than the direct-axis current instruction in the current instruction and whose current difference between the output active current and the direct-axis current instruction is greater than a first current difference threshold; if so, control the current difference to be distributed to the inverters that have not reached the maximum power point until all photovoltaic inverters reach the maximum power point inverter or the current difference between the actual value of the output active current of the grid-connected point and the preset grid-connected point output active current standard value is less than or equal to the second current difference threshold; The inverters that have not reached the maximum power point are all photovoltaic inverters except the photovoltaic inverter at the maximum power point.

2. The photovoltaic power station control system according to claim 1, characterized in that: The voltage outer loop controller includes: a first current determination unit and a second current determination unit; The first current determining unit is configured to determine a total current control instruction of the grid-connected photovoltaic power station according to the adjustment instruction and the grid-connected point working data; The second current determining unit is configured to determine the current instructions corresponding to each photovoltaic inverter according to the current control general instruction and a preset current distribution rule; and send the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter.

3. The photovoltaic power station control system according to claim 1, characterized in that: Also includes: multiple data acquisition devices; Each data acquisition device is connected to the voltage outer loop controller, each photovoltaic inverter is connected to its unique corresponding data acquisition device, and each data acquisition device is connected to at least one photovoltaic inverter; The voltage outer loop controller sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter through the data acquisition device.

4. The photovoltaic power station control system according to claim 1, characterized in that: Also includes: Backup voltage outer loop controller; The backup voltage outer loop controller is connected to each photovoltaic inverter and the voltage outer loop controller respectively; wherein, The backup voltage outer loop controller is used to receive the adjustment instruction and obtain the grid-connected point working data when the voltage outer loop controller fails; determine the current instruction corresponding to each photovoltaic inverter based on the adjustment instruction and the grid-connected point working data, and send it to the corresponding photovoltaic inverter.

5. The photovoltaic power station control system according to claim 1, characterized in that: The multiple photovoltaic inverters are divided into multiple groups, each group includes at least two photovoltaic inverters, the photovoltaic inverters in the same group are connected via a busbar, and the photovoltaic inverters in different groups correspond to different busbars. Each photovoltaic inverter is used to connect to the grid connection point via the busbar.

6. The photovoltaic power station control system according to claim 5, characterized in that: The voltage outer loop controller includes: a determination unit configured to monitor whether there is an abnormal bus whose voltage exceeds a preset normal bus voltage range among the buses, and if so, determine a reactive current change value of the abnormal bus based on a preset bus reactive voltage coefficient, the normal bus voltage range, and the bus voltage of the abnormal bus; The regulating unit is used to regulate the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value.

7. The photovoltaic power station control system according to claim 6, characterized in that: The adjustment unit includes: a first current regulating subunit, configured to determine whether the reactive current change value is greater than zero, and if so, to adjust the total output reactive current of the photovoltaic inverter corresponding to the abnormal busbar to increase the absolute value of the reactive current change value, and to adjust the total output reactive current of the photovoltaic inverter corresponding to each normal busbar to decrease the absolute value of the reactive current change value, wherein the normal busbar is each busbar among all the busbars except the abnormal busbar; The second current regulating subunit is used to determine whether the reactive current change value is less than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is adjusted to reduce the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is adjusted to increase the absolute value of the reactive current change value.

8. A photovoltaic power station control method, characterized in that: Applied to the photovoltaic power station control system according to any one of claims 1 to 7, the method comprises: The power station control layer sends an adjustment instruction of the grid-type photovoltaic power station to the voltage outer loop controller; The voltage outer loop controller receives the adjustment instruction of the grid-connected photovoltaic power station sent by the power station control layer and receives the grid connection point working data sent by the grid connection point; The voltage outer loop controller determines the current instruction corresponding to each photovoltaic inverter according to the adjustment instruction and the grid connection point working data, and sends the current instruction to the corresponding photovoltaic inverter; Each photovoltaic inverter adjusts its own current according to the corresponding current command; After each photovoltaic inverter adjusts its own current according to the corresponding current instruction, the method further includes: The voltage outer loop controller monitors whether there is a maximum power point photovoltaic inverter among each photovoltaic inverter, whose output active current is less than the direct-axis current command in the current command and the current difference between the output active current and the direct-axis current command is greater than a first current difference threshold. If so, the voltage outer loop controller controls the distribution of the current difference to the inverter that has not reached the maximum power point until all photovoltaic inverters reach the maximum power point inverter or the current difference between the actual value of the output active current of the grid-connected point and the preset grid-connected point output active current standard value is less than or equal to the second current difference threshold; The inverters that have not reached the maximum power point are all photovoltaic inverters except the photovoltaic inverter at the maximum power point.

9. The photovoltaic power station control method according to claim 8, characterized in that: The voltage outer loop controller determines a current instruction corresponding to each photovoltaic inverter according to the adjustment instruction and the grid connection point working data, and sends the current instruction to the corresponding photovoltaic inverter, including: The voltage outer loop controller determines the total current control instruction of the grid-connected photovoltaic power station according to the adjustment instruction and the grid-connected point working data; The voltage outer loop controller determines the current instructions corresponding to each photovoltaic inverter according to the current control general instruction and the preset current distribution rule; and sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter.

10. The photovoltaic power station control method according to claim 8, characterized in that: The voltage outer loop controller sends the current instruction to the photovoltaic inverter, comprising: The voltage outer loop controller sends the current instruction corresponding to each photovoltaic inverter to the photovoltaic inverter through the data acquisition device.

11. The photovoltaic power station control method according to claim 8, characterized in that: Also includes: When the voltage outer loop controller fails, the backup voltage outer loop controller receives the adjustment instruction and obtains the grid connection point working data; According to the adjustment instruction and the grid-connected point working data, the current instruction corresponding to each photovoltaic inverter is determined and sent to the corresponding photovoltaic inverter, so that each photovoltaic inverter receives the current instruction sent by the voltage outer loop controller and adjusts its own current according to the current instruction.

12. The photovoltaic power station control method according to claim 8, characterized in that: After each photovoltaic inverter adjusts its own current according to the corresponding current instruction, the method further includes: The voltage outer loop controller monitors whether there is an abnormal bus whose voltage exceeds a preset normal range of bus voltage among the buses. If so, the reactive current change value of the abnormal bus is determined based on a preset bus reactive voltage coefficient, the normal range of bus voltage and the bus voltage of the abnormal bus; The voltage outer loop controller adjusts the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value.

13. The photovoltaic power station control method according to claim 12, characterized in that: The voltage outer loop controller adjusts the total output reactive current of the photovoltaic inverter corresponding to each bus according to the reactive current change value, including: The voltage outer loop controller determines whether the reactive current change value is greater than zero. If so, the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus is increased by the absolute value of the reactive current change value, and the total output reactive current of the photovoltaic inverter corresponding to each normal bus is decreased by the absolute value of the reactive current change value. The normal bus is each bus among all the buses except the abnormal bus; The voltage outer loop controller determines whether the reactive current change value is less than zero. If so, it adjusts the total output reactive current of the photovoltaic inverter corresponding to the abnormal bus to reduce the absolute value of the reactive current change value, and adjusts the total output reactive current of the photovoltaic inverter corresponding to each normal bus to increase the absolute value of the reactive current change value.

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