A power regulation method suitable for distributed photovoltaic inverters

Abstract

The present application relates to the technical field of distributed power generation, and discloses a power regulation method suitable for a distributed photovoltaic inverter, which comprises the following steps: S1, combing low-voltage transformer area topology relationship; S2, determining node priority; S3, collecting grid-connected point voltage and active power of each inverter, and determining reference values of node active power, rated power and voltage; S4, judging each node voltage event; S5, executing different processes according to different events; S6, determining actual target active power or actual target active power percentage of each inverter, and issuing to each inverter for power regulation; and S7, jumping to S3. The present application is based on transformer area topology hierarchical information, selects appropriate photovoltaic inverters to perform power regulation in a certain proportion, reduces unnecessary photovoltaic power regulation, and ensures fairness and full utilization of photovoltaic inverters.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed power generation, and in particular to a power regulation method applicable to a distributed photovoltaic inverter. Background Art

[0002] With the growing global demand for renewable energy, distributed photovoltaic power generation, as a key renewable energy utilization method, has seen rapid growth in installed capacity worldwide. Distributed photovoltaic power generation systems typically use inverters to convert direct current (DC) power into alternating current (AC) power for grid integration. However, with the increasing number of distributed photovoltaic inverters connected to low-voltage grids, voltage control issues at these grid connection points have become increasingly prominent.

[0003] Existing solutions primarily rely on changing inverter control strategies, such as adopting constant reactive power control or constant voltage control, to regulate grid connection point voltage. Furthermore, some studies have proposed communication-based coordinated control strategies, which achieve coordinated control of grid connection point voltage by exchanging information with higher-level dispatching organizations or adjacent inverters.

[0004] However, the existing solution regulates all photovoltaic inverters when the voltage at the photovoltaic grid-connected point is high, causing some photovoltaic inverters with weak correlation to participate in the regulation process, affecting the power generation efficiency. Summary of the Invention

[0005] In response to the shortcomings and defects of the existing technology, the present invention provides a power regulation method suitable for distributed photovoltaic inverters. Based on the substation topology hierarchy, the priority relationship of photovoltaic inverters is given. When the voltage at a certain photovoltaic grid-connected point is high, the photovoltaic inverter with high priority is adjusted, and the power generation power of other photovoltaic inverters is retained to the greatest extent under the premise of controlling the node voltage.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A power regulation method applicable to a distributed photovoltaic inverter comprises the following steps:

[0008] S1: Sort out the topological relationship of the low-voltage substation area, determine the distribution line type, photovoltaic grid connection point location, and the phase and rated power of the distributed photovoltaic inverter at the photovoltaic grid connection point;

[0009] S2, sort out the photovoltaic grid-connected points and determine the node priority;

[0010] In step S3, the intelligent fusion terminal in the substation collects the grid connection point voltage and active power of each distributed photovoltaic inverter. Then, based on the location of the photovoltaic grid connection point, the phase and rated power of the distributed photovoltaic inverter, the active power reference value, rated power reference value, and voltage reference value of the photovoltaic grid connection point are determined through pre-matching.

[0011] S4, judging the voltage events of each photovoltaic grid-connected point based on the collected grid-connected point voltage;

[0012] S5, when the voltage event is a node high voltage event, obtain the highest voltage and the photovoltaic grid-connected point with the highest voltage, select high-priority, medium-high-priority, and medium-priority photovoltaic grid-connected points from them, and obtain impedance; calculate the active current to be reduced for each selected photovoltaic grid-connected point according to a certain ratio based on the voltage and impedance to be reduced at the photovoltaic grid-connected point; calculate the active power to be reduced based on the voltage reference value and the active current to be reduced for each selected photovoltaic grid-connected point; based on the active power reference value of each selected photovoltaic grid-connected point, reduce the active power of the photovoltaic inverters of the medium- and low-priority photovoltaic grid-connected points according to a certain ratio; calculate the target active power of each selected photovoltaic grid-connected point based on the active power to be reduced;

[0013] When the voltage event is other events, jump to S3;

[0014] When the voltage event is an over-regulation event, the rated power reference value of each selected photovoltaic grid-connected point is used as its target active power;

[0015] S6, combining the target active power of each photovoltaic grid-connected point, determines the actual target active power or the actual target active power percentage of each distributed photovoltaic inverter through formal matching, and sends it to each distributed photovoltaic inverter through the power line carrier for power control;

[0016] S7, jump to S3.

[0017] Preferably, when sorting out the photovoltaic grid-connected points, name the nodes in the format of abc;

[0018] Where a is the main branch number on the transformer side, b is the sequence number of the secondary branches on the transformer side under the main branch a from near to far from the transformer, and c is the sequence number of the tertiary branches on the transformer side under the secondary branch b from near to far from its upper branch;

[0019] When there is no secondary branch on the transformer side, b and c are 0; when there is no tertiary branch on the transformer side, c is 0.

[0020] Preferably, when determining the node priority, the high-priority photovoltaic grid-connected points are (a, b, c) to (a, b, N1), the medium-high priority photovoltaic grid-connected points are (a, b, 1) to (a, b, c-1), the medium-priority photovoltaic grid-connected points are (a, b, 0), (a, b+1, :) to (a, N3, :), the medium-low priority photovoltaic grid-connected points are (a, 1, :) to (a, b-1, :), and other photovoltaic grid-connected points are low priority;

[0021] Among them, N1 and N3 are the number of third-level branches under the secondary branch ab and the number of secondary branches under the main branch a respectively, and (a, j, :) is all the third-level branches under the j-th secondary branch under the main branch a.

[0022] Preferably, the pre-matching process is to use the sum of the active powers of the photovoltaic inverters of the same phase at the same photovoltaic grid-connected point as the active power reference value of the node, the sum of the rated powers of the photovoltaic inverters of the same phase at the same photovoltaic grid-connected point as the rated power reference value of the node, and the voltage of any distributed photovoltaic inverter at the same photovoltaic grid-connected point as the voltage reference value of the node; the formal matching process is to convert the target active power of the same photovoltaic grid-connected point into the actual target active power or the actual target active power percentage of each distributed photovoltaic inverter according to the rated power ratio.

[0023] Preferably, the specific process of determining the voltage events of each photovoltaic grid-connected point is as follows:

[0024] Determine whether the voltage of any distributed photovoltaic inverter exceeds the overvoltage threshold:

[0025] If yes, it is defined as a node high voltage event; otherwise, it is determined whether the maximum voltage of the distributed photovoltaic inverter is lower than the recovery threshold after power regulation. If yes, it is defined as an over-regulation event;

[0026] Otherwise defined as other events.

[0027] Preferably, the active current I to be reduced at each selected photovoltaic grid-connected point is:

[0028]

[0029] Among them, z1 is the impedance of the high priority photovoltaic grid connection point, z3 is the impedance of the medium priority photovoltaic grid connection point, and z 2i is the impedance of the i-th medium-high priority PV grid-connected point, n1, n2, and n3 are the numbers of high-priority, medium-high priority, and medium-priority PV grid-connected points, respectively, and ΔU is the voltage to be reduced.

[0030] Preferably, the current reduction ratio of photovoltaic grid-connected points of high priority, medium-high priority and medium priority is 5:2:1.

[0031] The beneficial technical effects of the present invention are as follows: based on the topological level information of the substation area, suitable photovoltaic inverters are selected to perform power regulation in a certain proportion, thereby reducing unnecessary photovoltaic power regulation, ensuring fairness and full utilization of photovoltaic inverters. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the overall flow chart of the present invention.

[0033] Figure 2Schematic diagram of the low-voltage area topology according to an embodiment of the present invention.

[0034] Figure 3 This is a voltage change trend diagram of different control schemes when there is a high voltage node in the low-voltage area in an embodiment of the present invention.

[0035] Figure 4 This is a power change trend diagram of different control schemes when there is a high voltage node in the low-voltage area in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Example:

[0038] like Figures 1 to 4 As shown, a power regulation method applicable to a distributed photovoltaic inverter includes the following steps:

[0039] S1: Sort out the topological relationship of the low-voltage substation area, determine the distribution line type, photovoltaic grid connection point location, and the phase and rated power of the distributed photovoltaic inverter at the photovoltaic grid connection point;

[0040] The low voltage distribution area line is 70 square aluminum wire. The distance between the photovoltaic inverter grid connection point and each section of the line is as follows: Figure 2 shown.

[0041] S2, sort out the photovoltaic grid-connected points and determine the node priority;

[0042] For node (a, b, c), the high-priority photovoltaic grid-connected points are (a, b, c) to (a, b, N1), the medium-high priority photovoltaic grid-connected points are (a, b, 1) to (a, b, c-1), the medium-priority photovoltaic grid-connected points are (a, b, 0), (a, b+1, :) to (a, N3, :), the medium-low priority photovoltaic grid-connected points are (a, 1, :) to (a, b-1, :), and other photovoltaic grid-connected points are low priority; among them, N1 and N3 are the number of third-level branches under the secondary branch ab and the number of secondary branches under the main branch a, respectively, and (a, j, :) are all third-level branches under the jth secondary branch under the main branch a.

[0043] like Figure 2 As shown, taking node 1-6-2 as an example, the high priority nodes are 1-6-2 to 1-6-7, the medium-high priority node is 1-6-1, the medium priority nodes are 1-6 to 1-10, and the medium-low priority nodes are 1-1 to 1-5.

[0044] Calculate the line impedance from each grid connection point to the transformer location. For example, if the line is a 70 square aluminum wire and the line impedance of node 1-6-1 is calculated as follows:

[0045]

[0046] In step S3, the intelligent fusion terminal in the substation collects the grid connection point voltage and active power of each distributed photovoltaic inverter. Then, based on the location of the photovoltaic grid connection point, the phase and rated power of the distributed photovoltaic inverter, the active power reference value, rated power reference value, and voltage reference value of the photovoltaic grid connection point are determined through pre-matching.

[0047] The pre-matching process is to use the sum of the active power of the photovoltaic inverters of the same phase at the same photovoltaic grid-connected point as the active power reference value of the node, the sum of the rated power of the photovoltaic inverters of the same phase at the same photovoltaic grid-connected point as the rated power reference value of the node, and the voltage of any distributed photovoltaic inverter at the same photovoltaic grid-connected point as the voltage reference value of the node.

[0048] S4, judging the voltage events of each photovoltaic grid-connected point based on the collected grid-connected point voltage;

[0049] The specific process for determining voltage events at each photovoltaic grid-connected point is as follows: determine whether the voltage of any distributed photovoltaic inverter exceeds the overvoltage threshold, which is 235.4V (+7% of the normal voltage). If so, it is defined as a node high voltage event; otherwise, determine whether the maximum voltage of the distributed photovoltaic inverter after power regulation is lower than the recovery threshold, which is 225V. If so, it is defined as an over-regulation event; otherwise, it is defined as other events.

[0050] S5, when the voltage event is a node high voltage event, obtain the highest voltage and the photovoltaic grid-connected point with the highest voltage, select high-priority, medium-high-priority, and medium-priority photovoltaic grid-connected points from them, and obtain impedance; calculate the active current to be reduced for each selected photovoltaic grid-connected point according to a certain ratio based on the voltage to be reduced (current voltage minus voltage limit) and impedance of the grid-connected point; calculate the active power to be reduced based on the voltage reference value and active current to be reduced of each selected photovoltaic grid-connected point; based on the active power reference value of each selected photovoltaic grid-connected point, reduce the active power of the photovoltaic inverters of the medium- and low-priority photovoltaic grid-connected points according to a certain ratio; calculate the target active power of each selected photovoltaic grid-connected point based on the active power to be reduced;

[0051] When the voltage event is other events, jump to S3;

[0052] When the voltage event is an over-regulation event, the rated power reference value of each selected photovoltaic grid-connected point is used as its target active power;

[0053] The priority current in the regulated photovoltaic inverter (grid point) is

[0054]

[0055] Among them, z1 is the impedance of the high priority photovoltaic grid-connected point, z3 is the impedance of the medium priority photovoltaic grid-connected point, and z 2i is the impedance of the i-th medium-high priority PV grid connection point, n1, n2, and n3 are the number of high-priority, medium-high-priority, and medium-priority PV grid connection points, respectively, and ΔU is the voltage to be reduced. The voltage of medium- and low-priority PV inverters can be gradually reduced at a ratio of 0.95 to 0.99.

[0056] S6, combining the target active power of each photovoltaic grid-connected point, determines the actual target active power or the actual target active power percentage of each distributed photovoltaic inverter through formal matching, and sends it to each distributed photovoltaic inverter through the power line carrier for power control;

[0057] The formal matching process is to convert the target active power of the same phase photovoltaic inverter at the same photovoltaic grid-connected point into the actual target active power or actual target active power percentage of each distributed photovoltaic inverter according to the proportion of rated power.

[0058] S7, jump to S3.

[0059] The present invention further illustrates a power regulation method for distributed photovoltaic inverters proposed in the embodiment. A simulation model is built using MATLAB software. The simulation topology of the low-voltage power distribution system is as follows: Figure 2 shown.

[0060] Figure 3 The voltage diagram of each node under different high voltage management strategies is shown, where the voltage upper limit is 235.4V, which is +7% of the normal voltage. Figure 3 It can be seen that the equal-value control strategy can play a certain role in limiting the node voltage exceeding the limit, but the voltage range after control is 224.8V~234.3V, and the voltage difference is 9.5V. The voltage range after control proposed by the solution of the present invention is 228.6V~234.6V, and the voltage difference is 6V. Compared with the equal-value control, the voltage is more stable.

[0061] Figure 4 The photovoltaic power of each node under different high voltage management strategies is shown. Figure 4 It can be seen that the equivalent control strategy limits different devices to the same level, so the total power generation power of the substation is limited to the minimum output; the solution proposed in this invention has fewer restrictions on photovoltaic output power through precise control, adheres to the principle of maximum power generation, reduces ineffective photovoltaic power control, and significantly improves the total power generation power of the entire substation, and the overall power generation efficiency of the system is higher.

[0062] The above embodiments are illustrations of specific implementation methods of the present invention, rather than limitations of the present invention. Technicians in the relevant technical fields may make various transformations and changes to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A power regulation method applicable to distributed photovoltaic inverters, characterized in that: The following steps are involved: S1: Sort out the topological relationship of the low-voltage substation area, determine the distribution line type, photovoltaic grid connection point location, and the phase and rated power of the distributed photovoltaic inverter at the photovoltaic grid connection point; S2, sort out the photovoltaic grid-connected points and determine the node priority; In step S3, the intelligent fusion terminal in the substation collects the grid connection point voltage and active power of each distributed photovoltaic inverter. Then, based on the location of the photovoltaic grid connection point, the phase and rated power of the distributed photovoltaic inverter, the active power reference value, rated power reference value, and voltage reference value of the photovoltaic grid connection point are determined through pre-matching. S4, judging the voltage events of each photovoltaic grid-connected point based on the collected grid-connected point voltage; S5, when the voltage event is a node high voltage event, obtain the highest voltage and the photovoltaic grid-connected point with the highest voltage, select high-priority, medium-high-priority, and medium-priority photovoltaic grid-connected points from them, and obtain impedance; calculate the active current to be reduced for each selected photovoltaic grid-connected point according to a certain ratio based on the voltage and impedance to be reduced at the photovoltaic grid-connected point; calculate the active power to be reduced based on the voltage reference value and the active current to be reduced for each selected photovoltaic grid-connected point; based on the active power reference value of each selected photovoltaic grid-connected point, reduce the active power of the photovoltaic inverters of the medium- and low-priority photovoltaic grid-connected points according to a certain ratio; calculate the target active power of each selected photovoltaic grid-connected point based on the active power to be reduced; When the voltage event is other events, jump to S3; When the voltage event is an over-regulation event, the rated power reference value of each selected photovoltaic grid-connected point is used as its target active power; S6, combining the target active power of each photovoltaic grid-connected point, determines the actual target active power or the actual target active power percentage of each distributed photovoltaic inverter through formal matching, and sends it to each distributed photovoltaic inverter through the power line carrier for power control; S7, jump to S3.

2. A power regulation method applicable to distributed photovoltaic inverters according to claim 1, characterized in that: When sorting out photovoltaic grid-connected points, name the nodes in the abc format; Where a is the main branch number on the transformer side, b is the sequence number of the secondary branches on the transformer side under the main branch a from near to far from the transformer, and c is the sequence number of the tertiary branches on the transformer side under the secondary branch b from near to far from its upper branch; When there is no secondary branch on the transformer side, b and c are 0; when there is no tertiary branch on the transformer side, c is 0.

3. A power regulation method applicable to distributed photovoltaic inverters according to claim 2, characterized in that: When determining node priority, high-priority photovoltaic grid-connected points are (a, b, c) to (a, b, N1), medium-high priority photovoltaic grid-connected points are (a, b, 1) to (a, b, c-1), medium-priority photovoltaic grid-connected points are (a, b, 0), (a, b+1, :) to (a, N3, :), medium-low priority photovoltaic grid-connected points are (a, 1, :) to (a, b-1, :), and other photovoltaic grid-connected points are low priority; Among them, N1 and N3 are the number of third-level branches under the secondary branch ab and the number of secondary branches under the main branch a respectively, and (a, j, :) is all the third-level branches under the j-th secondary branch under the main branch a.

4. The power regulation method for distributed photovoltaic inverters according to claim 1, characterized in that: The pre-matching process is to use the sum of the active power of the same-phase PV inverters at the same PV grid-connected point as the active power reference value of the node, the sum of the rated power of the same-phase PV inverters at the same PV grid-connected point as the rated power reference value of the node, and the voltage of any distributed PV inverter at the same PV grid-connected point as the voltage reference value of the node; The formal matching process is to convert the target active power of the same photovoltaic grid-connected point into the actual target active power or actual target active power percentage of each distributed photovoltaic inverter according to the rated power ratio.

5. The power regulation method for distributed photovoltaic inverters according to claim 1, characterized in that: The specific process of determining the voltage events of each photovoltaic grid-connected point is as follows: Determine whether the voltage of any distributed photovoltaic inverter exceeds the overvoltage threshold: If yes, it is defined as a node high voltage event; otherwise, it is determined whether the maximum voltage of the distributed photovoltaic inverter is lower than the recovery threshold after power regulation. If yes, it is defined as an over-regulation event; Otherwise defined as other events.

6. The power regulation method for distributed photovoltaic inverters according to claim 1, characterized in that: The active current I to be reduced at each selected photovoltaic grid-connected point is: Among them, z1 is the impedance of the high priority photovoltaic grid connection point, z3 is the impedance of the medium priority photovoltaic grid connection point, and z 2i is the impedance of the i-th medium-high priority PV grid-connected point, n1, n2, and n3 are the numbers of high-priority, medium-high priority, and medium-priority PV grid-connected points, respectively, and ΔU is the voltage to be reduced.

7. The power regulation method for distributed photovoltaic inverters according to claim 1, characterized in that: The current reduction ratio for high-priority, medium-high-priority, and medium-priority PV grid-connected points is 5:2:1.

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