Distributed photovoltaic voltage out-of-limit treatment method for active and reactive power proportion optimization

Abstract

The invention provides a distributed photovoltaic voltage out-of-limit treatment method for active and reactive power proportion optimization. The method comprises the following steps: when detecting that the voltage of a grid-connected point is out of limit, giving up a working mode of maximum power tracking when the voltage is out of limit, and executing the following steps: calculating reactive and active power proportionality coefficients which should be injected into the grid-connected point by a photovoltaic power generation system after the voltage of the grid-connected point is out of limit; the reactive power and active power proportionality coefficient enables the active power injected into the power distribution network bus by the photovoltaic power generation system to be maximum under the condition that the grid-connected point voltage is not out of limit; calculating an active power instruction and a reactive power instruction by using reactive and active power proportionality coefficients; based on the active power instruction and the reactive power instruction, obtaining a current reference value on a dq axis in a dq coordinate system subjected to constant-amplitude coordinate transformation; and adjusting the active power and reactive power of the photovoltaic injection grid-connected point based on the current reference value on the dq coordinate axis so as to adjust the voltage of the grid-connected point. Under the condition that the voltage of the grid-connected point does not exceed the limit, the active power flowing to the grid-connected point can be ensured to be maximum.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic grid-connected over-limit control, and in particular to a distributed photovoltaic voltage over-limit control method with optimized active and reactive power ratios. Background Art

[0002] As the penetration rate of photovoltaics in the distribution network increases, the flow of traditional distribution networks will change, and even reverse flow will occur, resulting in voltage rise at the end of the distribution network. In rural distribution networks with less load, the voltage rise phenomenon is more serious due to the low total load and high photovoltaic penetration rate. The end voltage rise will affect the stability of the power grid. When the voltage rises too high, it may even damage household appliances and cause photovoltaic grid-connected inverters to stop operating. This is also one of the main reasons that hinder the increase in the proportion of renewable energy in the power grid.

[0003] In recent years, research on the voltage over-limit problem at the grid-connected point of distributed photovoltaic power generation systems has shown that when the voltage exceeds the limit, providing the system with dynamic reactive power support can effectively improve the degree of voltage over-limit at the grid-connected point and improve the safety and stability of the grid-connected distributed photovoltaic power generation system. At present, research on the voltage over-limit problem at the photovoltaic grid-connected point mainly focuses on two aspects: reactive voltage regulating equipment and the remaining capacity of photovoltaic grid-connected inverters. For reactive voltage regulating equipment, the prior art divides the time scale and dynamic response performance of various reactive voltage regulating equipment, and considers the reactive power replacement between reactive voltage regulating equipment to ensure the system's better dynamic voltage support capability. Although this method can have a strong dynamic support capability in the process of meeting the reactive power demand of the system, the use of fast reactive compensation devices (such as static reactive compensators, static reactive generators) increases the cost of the system, and the voltage regulation capability of slow voltage regulating equipment (such as on-load voltage regulating transformers, capacitor banks) cannot meet the system's fast reactive power requirements. For the remaining capacity of photovoltaic grid-connected inverters, the prior art uses the remaining capacity of grid-connected inverters to provide a certain amount of reactive power for the system to adjust the voltage. Photovoltaic grid-connected inverters have the ability to quickly compensate for reactive power, and the use of their remaining capacity can reduce the investment cost of reactive power compensation equipment in the system, but there is a problem of insufficient reactive capacity. To address this problem, further improvements have been made to use the entire remaining capacity of photovoltaic grid-connected inverters for reactive power compensation while reducing the active output of photovoltaics to suppress the voltage limit at the grid connection point. However, this will greatly increase line losses, resulting in very little active power received by the distribution network, while also receiving more reactive power. Summary of the invention

[0004] In order to solve the above technical problems or at least partially solve the above technical problems, the present invention provides a distributed photovoltaic voltage over-limit management method, device and storage medium with optimized active and reactive ratio.

[0005] In a first aspect, the present invention provides a distributed photovoltaic voltage over-limit management method with optimized active and reactive ratio, comprising:

[0006] After the photovoltaic system injects active power into the grid connection point under maximum power tracking, the grid connection point voltage is detected. If the grid connection point voltage is detected to be out of limit, the maximum power tracking working mode is abandoned and the following operations are executed:

[0007] Based on the distribution network bus voltage, the active power at the end of the line, the reactive power at the end of the line, the grid point voltage over-limit value and the line parameters, the reactive and active power ratio coefficient k that the photovoltaic power generation system should inject into the grid point after the grid point voltage exceeds the limit is calculated. The reactive and active power ratio coefficient k makes the active power P injected by the photovoltaic power generation system into the distribution network bus without exceeding the grid point voltage limit. g maximum:

[0008]

[0009] Where R is the line resistance, X is the line reactance, P L is the active power at the end of the line, Q L is the reactive power at the end of the line, U lim The grid voltage exceeds the limit, U S is the bus voltage of the distribution network;

[0010] The active power command P is calculated by using the reactive power and active power ratio coefficient k. PV_ref , reactive power command Q PV_ref ;

[0011] In the dq coordinate system after the equal amplitude coordinate transformation, based on the active power command P PV_ref , reactive power command Q PV_ref Get the current reference value on the dq coordinate axis;

[0012] The active and reactive power injected into the grid-connected point by photovoltaic power is adjusted based on the current reference value on the dq coordinate axis to regulate the voltage of the grid-connected point.

[0013] Furthermore, when the grid connection point voltage is detected, a mean filter is used to stabilize the detected grid connection point voltage.

[0014] Furthermore, based on the equivalent circuit model of the distributed photovoltaic power generation system connected to the distribution network, the connection between the grid connection point voltage and the distribution network bus voltage is established:

[0015]

[0016] Among them, P PV Q is the active power that the distributed photovoltaic power generation system should inject into the grid connection point. PVis the reactive power that the distributed photovoltaic power generation system should inject into the grid connection point, R is the line resistance, X is the line reactance, and U PCC is the grid connection point voltage.

[0017] Furthermore, the calculation process of the reactive and active power ratio coefficient k that the photovoltaic power generation system should inject into the grid connection point is as follows:

[0018] The active power P flowing to the distribution network bus is calculated based on the grid connection point voltage, line end active power, line end reactive power, grid connection point voltage over-limit value, line parameters, distributed photovoltaic power generation system to be injected into the grid connection point active power and distributed photovoltaic power generation system to be injected into the grid connection point reactive power. g for:

[0019]

[0020] Assume that the reactive power and active power ratio coefficient k = Q PV / P PV (k<0), then the active power P flowing to the distribution network bus g for:

[0021]

[0022] when When the distribution network bus can obtain the maximum active power under the premise that the voltage does not exceed the limit, substitute it into Get P g Regarding the relationship between the proportionality coefficient k, and then taking the derivative of k, we get Re-order Solving for k is:

[0023]

[0024] By monotonicity, P g exist Get the maximum value at.

[0025] Furthermore, considering the constraint that the grid connection point voltage does not exceed the limit, the photovoltaic power generation system should inject active power P PV Need to meet:

[0026]

[0027] right Medium PV Take the derivative and set 0 = dP g / dP PV We can get:

[0028]

[0029] According to the monotonicity correlation theory, P g Get the maximum value,

[0030] Consider the grid connection point voltage limit constraint, and also consider Much smaller than Therefore, when When the voltage does not exceed the limit, the grid connection point obtains the most active power.

[0031] Furthermore, the reactive power and active power ratio coefficient k is used to calculate the active power command P PV_ref , reactive power command Q PV_ref The formula is as follows:

[0032]

[0033] Furthermore, based on the active power command P PV_ref , reactive power command Q PV_ref In the dq coordinate system after the equal amplitude coordinate transformation, the current reference value on the dq coordinate axis is obtained:

[0034]

[0035] Among them, i d_ref is the current reference value of the d-axis, i q_ref is the current reference value of the q axis, u d is the d-axis voltage component of the dq coordinate system.

[0036] Furthermore, adjusting the active and reactive power of the photovoltaic injection into the grid-connected point based on the current reference value on the dq coordinate axis to adjust the grid-connected point voltage includes: sending the current reference value on the dq coordinate axis and the actual value into the PI regulator as a difference, and summing the output of the PI regulator with the voltage on the dq coordinate axis; generating a dq axis reference voltage in the dq coordinate system based on the summation result and the voltage phase information in the abc coordinate system obtained by the phase-locked loop, and then obtaining a modulation signal after coordinate system transformation, performing SVPWM modulation on the modulation signal, and using the modulated output signal as the control signal of the photovoltaic grid-connected inverter to adjust the active and reactive power of the photovoltaic injection into the grid-connected point to adjust the grid-connected point voltage.

[0037] In the second aspect, the present invention provides a distributed photovoltaic voltage over-limit control device with optimized active and reactive power ratio, comprising: at least one processing unit, the processing unit, the storage unit and the photovoltaic inverter are interconnected through a bus unit, the storage unit stores a computer program, and when the computer program is executed by the processing unit, the distributed photovoltaic voltage over-limit control method with optimized active and reactive power ratio is implemented.

[0038] In a second aspect, the present invention provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the distributed photovoltaic voltage over-limit control method with optimized active and reactive power ratio.

[0039] The above technical solution provided by the embodiment of the present invention has the following advantages compared with the prior art:

[0040] This application detects that the voltage at the grid point exceeds the limit, and when the limit is exceeded, the maximum power tracking working mode is abandoned, and the following is performed: calculating the reactive power and active power ratio coefficients that the photovoltaic power generation system should inject into the grid point after the grid point voltage exceeds the limit, and the reactive power and active power ratio coefficients make the active power injected by the photovoltaic power generation system into the distribution network bus maximum when the grid point voltage does not exceed the limit; using the reactive power and active power ratio coefficients to calculate the active power command and reactive power command; based on the active power command and reactive power command, in the dq coordinate system after the equal amplitude coordinate transformation, obtain the current reference value on the dq axis; based on the current reference value on the dq coordinate axis, adjust the active and reactive power injected by the photovoltaic power generation system into the grid point to adjust the grid point voltage. The present invention has a positive effect on solving the problem of voltage exceeding the limit at the grid point of distributed photovoltaic power generation, and can ensure that the active power flowing to the grid point is maximized while the grid point voltage does not exceed the limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0043] Figure 1 This is the equivalent circuit diagram of the distributed photovoltaic power generation system before it is connected to the distribution network;

[0044] Figure 2 It is a voltage drop vector diagram before the distributed photovoltaic power generation system is connected to the distribution network;

[0045] Figure 3 This is the equivalent circuit diagram of the distributed photovoltaic power generation system after it is connected to the distribution network;

[0046] Figure 4 A flow chart of an optimization method for suppressing voltage over-limit in distributed photovoltaic based on the ratio of active and reactive power injected into the grid connection point provided by an embodiment of the present invention;

[0047] Figure 5A control block diagram for suppressing voltage exceeding a limit at a grid connection point provided by an embodiment of the present invention;

[0048] Figure 6 The simulation results of the voltage change at the grid connection point when the active power of photovoltaic is injected into the grid connection point under maximum power tracking;

[0049] Figure 7 The simulation result of the voltage change at the grid connection point under the proportional coefficient provided by the embodiment of the present invention;

[0050] Figure 8 This is the simulation result of the active power received by the distribution network bus under the proportional coefficient and other coefficients provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0053] Example 1

[0054] See also Figure 1 As shown, the technology of the present invention realizes a distributed photovoltaic voltage over-limit control method with optimized active and reactive ratios, including:

[0055] Step 1: After the photovoltaic power is injected into the grid connection point with active power under maximum power tracking, the grid connection point voltage is detected, and the grid connection point voltage is compared with the set grid connection point voltage over-limit value to detect whether the grid connection point voltage exceeds the limit.

[0056] When detecting the grid connection point voltage, a mean filter is used to stabilize the detected grid connection point voltage to eliminate the grid connection point voltage fluctuation and obtain an accurate grid connection point voltage detection result.

[0057] If the grid connection point voltage exceeds the limit, the maximum power tracking mode is abandoned and the following operations are executed:

[0058] Step 2: Based on the distribution network bus voltage, the active power at the end of the line, the reactive power at the end of the line, the voltage over-limit value at the grid connection point and the line parameters, the reactive and active power ratio coefficient k of the photovoltaic power generation system that should be injected into the grid connection point after the voltage over-limit at the grid connection point is calculated. The reactive and active power ratio coefficient k makes the active power P injected into the grid connection point by the photovoltaic power generation system without exceeding the grid connection point voltage limit. g maximum:

[0059]

[0060] Where R is the line resistance, X is the line reactance, P L is the active power at the end of the line, Q L is the reactive power at the end of the line, U lim The grid voltage exceeds the limit, U S is the bus voltage of the distribution network.

[0061] In the specific implementation process, the above steps include: establishing the connection between the grid connection point voltage and the distribution network bus voltage based on the equivalent circuit model of the distributed photovoltaic power generation system connected to the distribution network:

[0062] The equivalent circuit diagram of the distributed photovoltaic power generation system before connecting to the distribution network is as follows: Figure 1 As shown. Due to line loss, there will be a voltage difference between the node m corresponding to the grid connection point and the node n on the distribution network bus, as shown Figure 2 As shown, vector analysis shows that there will be a voltage difference between node m and node n due to line loss:

[0063]

[0064] Here, the real and imaginary parts are expressed in terms of power and impedance as:

[0065]

[0066] From the above relationship, it can be seen that the voltage difference between nodes m and n depends on the line impedance R+jX and the local power P of the line. L +jQ L .in, is the voltage vector of node n, that is, the bus voltage vector of the distribution network, is the voltage vector of node m, i.e. the voltage vector of the grid connection point, is the current vector on the line. Since the phase angle difference between the two nodes m and n is very small in the distribution network compared to the transmission network, the real part has a much greater impact on the voltage offset than the imaginary part, so the relationship between the voltage difference between nodes m and n can be equivalent to the following:

[0067]

[0068] The equivalent circuit diagram of the distributed photovoltaic power generation system after connecting to the distribution network is as follows: Figure 3 As shown. When the photovoltaic power source is not connected to the grid, the power flow is often from the head end to the end end. Due to line losses, low voltage usually occurs at the end of the line. After the photovoltaic power source is connected, since the photovoltaic power source itself generates power, when the power generated by the photovoltaic power source exceeds the absorption capacity of the node load, the surplus power is sent back along the line to the distribution network, forming a reverse flow, thereby causing the terminal node voltage to rise. Based on the equivalent circuit model of the distributed photovoltaic power generation system connected to the distribution network, the connection between the grid connection point voltage and the distribution network bus voltage is established as follows:

[0069]

[0070] Among them, P PV Q is the active power that the distributed photovoltaic power generation system should inject into the grid connection point. PV The reactive power that should be injected into the grid connection point for the distributed photovoltaic power generation system.

[0071] The active power P flowing to the distribution network bus is calculated based on the grid connection point voltage, line end active power, line end reactive power, grid connection point voltage over-limit value, line parameters, distributed photovoltaic power generation system to be injected into the grid connection point active power and distributed photovoltaic power generation system to be injected into the grid connection point reactive power. g for:

[0072]

[0073] Assume that the reactive power and active power ratio coefficient k = Q PV / P PV (k<0), then the active power P flowing to the distribution network bus g for:

[0074]

[0075] The reactive power / active power ratio coefficient k is such that the active power P injected into the grid point by the photovoltaic power generation system does not exceed the grid voltage limit. g Maximum, considering the grid voltage limit constraint, the photovoltaic power generation system should inject active power P PV Need to meet:

[0076]

[0077] right Medium PV Take the derivative and set 0 = dP g / dPPV We can get:

[0078]

[0079] According to the monotonicity correlation theory, Get the maximum value at

[0080] Also consider Much smaller than Therefore When the distribution network bus can obtain the maximum active power under the premise that the voltage does not exceed the limit, substitute it into Get P g Regarding the relationship between the proportionality coefficient k, and then taking the derivative of k, we get Re-order Solving for k is:

[0081]

[0082] By monotonicity, P g exist Get the maximum value at.

[0083] Step 3: Calculate the active power command P using the reactive power and active power ratio coefficient k PV_ref , reactive power command Q PV_ref :

[0084]

[0085] Step 4: Based on the active power command P PV_ref , reactive power command Q PV_ref In the dq coordinate system after the equal amplitude coordinate transformation, the current reference value on the dq coordinate axis is obtained:

[0086]

[0087] Among them, i d_ref is the current reference value of the d-axis, i q_ref is the current reference value of the q axis, u d is the d-axis voltage component of the dq coordinate system.

[0088] Step 5, based on the current reference value on the dq coordinate axis, adjust the active and reactive power injected by the photovoltaic power plant into the grid-connected point to adjust the voltage at the grid-connected point. The current reference value on the dq coordinate axis is subtracted from the actual value and sent to the PI regulator, and the output of the PI regulator is summed with the voltage on the dq coordinate axis; based on the summation result and the voltage phase information in the abc coordinate system obtained by the phase-locked loop, a dq axis reference voltage in the dq coordinate system is generated, and then the modulation signal is obtained after the coordinate system transformation, and the modulation signal is modulated by SVPWM. The modulated output signal is used as the control signal of the photovoltaic grid-connected inverter to adjust the active and reactive power injected by the photovoltaic power plant into the grid-connected point to adjust the voltage at the grid-connected point. The corresponding control block diagram is shown as follows: Figure 5 shown.

[0089] The maximum voltage normally allowed at the grid connection point is 1.1UN, where UN is the rated voltage. Figure 6 This is the simulation result of the voltage change at the grid point when the active power of the photovoltaic is injected into the grid point under the maximum power tracking. At this time, the voltage at the grid point has exceeded the limit; Figure 7 The simulation result of the grid connection point voltage change under the proportional coefficient provided by the embodiment of the present invention, at this time, the grid connection point voltage has stabilized near the over-limit value; Figure 8 The simulation results of the active power received by the distribution network bus under the proportional coefficient and other coefficients provided in the embodiment of the present invention are as follows. After calculation, when k=-0.5156, compared with other proportional coefficients, the grid connection point receives the most active power.

[0090] Example 2

[0091] The embodiment of the present invention provides a distributed photovoltaic voltage over-limit management device with active and reactive ratio optimization, comprising: at least one processing unit, the processing unit, the storage unit and the photovoltaic inverter are interconnected through a bus unit, the storage unit stores a computer program, and when the computer program is executed by the processing unit, the distributed photovoltaic voltage over-limit management method with active and reactive ratio optimization is implemented, comprising:

[0092] After the photovoltaic system injects active power into the grid connection point under maximum power tracking, the grid connection point voltage is detected. If the grid connection point voltage is detected to be out of limit, the maximum power tracking working mode is abandoned and the following operations are executed:

[0093] Based on the distribution network bus voltage, the active power at the end of the line, the reactive power at the end of the line, the grid point voltage over-limit value and the line parameters, the reactive and active power ratio coefficient k that the photovoltaic power generation system should inject into the grid point after the grid point voltage exceeds the limit is calculated. The reactive and active power ratio coefficient k makes the active power P injected into the grid point by the photovoltaic power generation system without exceeding the grid point voltage limit. g maximum:

[0094]

[0095] Where R is the line resistance, X is the line reactance, P L is the active power at the end of the line, Q L is the reactive power at the end of the line, U lim The grid voltage exceeds the limit, U S is the bus voltage of the distribution network;

[0096] The active power command P is calculated by using the reactive power and active power ratio coefficient k. PV_ref , reactive power command Q PV_ref ;

[0097] In the dq coordinate system after the equal amplitude coordinate transformation, based on the active power instruction P PV_ref , reactive power command Q PV_ref Get the current reference value on the dq coordinate axis;

[0098] The active and reactive power injected into the grid-connected point by photovoltaic power is adjusted based on the current reference value on the dq coordinate axis to regulate the voltage of the grid-connected point.

[0099] Of course, the computer program stored in the storage unit of a distributed photovoltaic voltage over-limit control device with optimized active and reactive power ratio provided in an embodiment of the present invention is not limited to the method operations described above, but can also execute related operations in a distributed photovoltaic voltage over-limit control method with optimized active and reactive power ratio provided in any embodiment of the present invention.

[0100] Example 3

[0101] An embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program. When the computer program is executed, the distributed photovoltaic voltage over-limit management method with active power and reactive power ratio optimization is implemented, including:

[0102] After the photovoltaic system injects active power into the grid connection point under maximum power tracking, the grid connection point voltage is detected. If the grid connection point voltage is detected to be out of limit, the maximum power tracking working mode is abandoned and the following operations are executed:

[0103] Based on the distribution network bus voltage, the active power at the end of the line, the reactive power at the end of the line, the grid point voltage over-limit value and the line parameters, the reactive and active power ratio coefficient k that the photovoltaic power generation system should inject into the grid point after the grid point voltage exceeds the limit is calculated. The reactive and active power ratio coefficient k makes the active power P injected into the grid point by the photovoltaic power generation system without exceeding the grid point voltage limit. g maximum:

[0104]

[0105] Where R is the line resistance, X is the line reactance, P Lis the active power at the end of the line, Q L is the reactive power at the end of the line, U lim The grid voltage exceeds the limit, U S is the bus voltage of the distribution network;

[0106] The active power command P is calculated by using the reactive power and active power ratio coefficient k. PV_ref , reactive power command Q PV_ref ;

[0107] In the dq coordinate system after the equal amplitude coordinate transformation, based on the active power command P PV_ref , reactive power command Q PV_ref Get the current reference value on the dq coordinate axis;

[0108] The active and reactive power injected into the grid-connected point by photovoltaic power is adjusted based on the current reference value on the dq coordinate axis to regulate the voltage of the grid-connected point.

[0109] A computer-readable storage medium provided in an embodiment of the present invention stores a computer program which is not limited to the method operations described above, but can also execute related operations in a distributed photovoltaic voltage over-limit management method with optimized active and reactive power ratio provided in any embodiment of the present invention.

[0110] In the embodiments provided by the present invention, it should be understood that the disclosed structures and methods can be implemented in other ways. For example, the structural embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, structures or units, which can be electrical, mechanical or other forms.

[0111] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0112] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0113] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A distributed photovoltaic voltage over-limit control method with active and reactive power ratio optimization, characterized in that: include: After the photovoltaic system injects active power into the grid connection point under maximum power tracking, the grid connection point voltage is detected. If the grid connection point voltage is detected to be out of limit, the maximum power tracking working mode is abandoned and the following operations are executed: Based on the distribution network bus voltage, the active power at the end of the line, the reactive power at the end of the line, the grid point voltage over-limit value and the line parameters, the reactive and active power ratio coefficient k that the photovoltaic power generation system should inject into the grid point after the grid point voltage exceeds the limit is calculated. The reactive and active power ratio coefficient k makes the active power P injected into the grid point by the photovoltaic power generation system without exceeding the grid point voltage limit. g maximum: Where R is the line resistance, X is the line reactance, P L is the active power at the end of the line, Q L is the reactive power at the end of the line, U lim The grid voltage exceeds the limit, U S is the bus voltage of the distribution network; The active power command P is calculated by using the reactive power and active power ratio coefficient k. PV_ref , reactive power command Q PV_ref ; In the dq coordinate system after the equal amplitude coordinate transformation, based on the active power instruction P PV_ref , reactive power command Q PV_ref Get the current reference value on the dq coordinate axis; The active and reactive power injected into the grid-connected point by photovoltaic power is adjusted based on the current reference value on the dq coordinate axis to regulate the voltage of the grid-connected point.

2. The distributed photovoltaic voltage over-limit control method with active power and reactive power ratio optimization according to claim 1 is characterized in that: When detecting the grid connection point voltage, a mean filter is used to stabilize the detected grid connection point voltage.

3. The distributed photovoltaic voltage over-limit control method with active power and reactive power ratio optimization according to claim 1 is characterized in that: Based on the equivalent circuit model of the distributed photovoltaic power generation system connected to the distribution network, the connection between the grid connection point voltage and the distribution network bus voltage is established: Among them, P PV is the active power that the distributed photovoltaic power generation system should inject into the grid connection point, Q PV is the reactive power that the distributed photovoltaic power generation system should inject into the grid connection point, R is the line resistance, X is the line reactance, and U PCC is the grid connection point voltage.

4. The distributed photovoltaic voltage over-limit control method with active power and reactive power ratio optimization according to claim 1 is characterized in that: The calculation process of the reactive and active power ratio coefficient k that the photovoltaic power generation system should inject into the grid connection point is as follows: The active power P flowing to the distribution network bus is calculated based on the grid connection point voltage, line end active power, line end reactive power, grid connection point voltage over-limit value, line parameters, distributed photovoltaic power generation system to be injected into the grid connection point active power and distributed photovoltaic power generation system to be injected into the grid connection point reactive power. g for: Assume that the reactive power and active power ratio coefficient k = Q PV / P PV (k<0), then the active power P flowing to the distribution network bus g for: when When the distribution network bus can obtain the maximum active power under the premise that the voltage does not exceed the limit, substitute it into Get P g Regarding the relationship between the proportionality coefficient k, and then taking the derivative of k, we get Re-order Solving for k is: By monotonicity, P g exist Get the maximum value at.

5. The distributed photovoltaic voltage over-limit control method with active power and reactive power ratio optimization according to claim 4 is characterized in that: Considering the constraint that the grid connection point voltage does not exceed the limit, the photovoltaic power generation system should inject active power P PV Need to meet: right Medium PV Take the derivative and set 0 = dP g / dP PV We can get: According to the monotonicity correlation theory, P g Get the maximum value, Also consider Much smaller than Therefore, when When the voltage does not exceed the limit, the grid connection point obtains the most active power.

6. The distributed photovoltaic voltage over-limit control method with active power and reactive power ratio optimization according to claim 1 is characterized in that: The active power command P is calculated by using the reactive power and active power ratio coefficient k. PV_ref , reactive power command Q PV_ref The formula is as follows:

7. The distributed photovoltaic voltage over-limit control method with active power and reactive power ratio optimization according to claim 1 is characterized in that: Based on the active power command P PV_ref , reactive power command Q PV_ref In the dq coordinate system after the equal amplitude coordinate transformation, the current reference value on the dq coordinate axis is obtained: Among them, i d_ref is the current reference value of the d-axis, i q_ref is the current reference value of the q axis, u d is the d-axis voltage component of the dq coordinate system.

8. The distributed photovoltaic voltage over-limit control method with active power and reactive power ratio optimization according to claim 1 is characterized in that: Adjusting the active and reactive power of photovoltaic injection into the grid-connected point based on the current reference value on the dq coordinate axis to adjust the voltage of the grid-connected point includes: sending the current reference value on the dq coordinate axis and the actual value into the PI regulator as a difference, and summing the output of the PI regulator with the voltage on the dq coordinate axis; generating a dq axis reference voltage in the dq coordinate system based on the summation result and the voltage phase information in the abc coordinate system obtained by the phase-locked loop, and then obtaining a modulation signal after the coordinate system transformation, performing SVPWM modulation on the modulation signal, and using the modulated output signal as the control signal of the photovoltaic grid-connected inverter to adjust the active and reactive power of photovoltaic injection into the grid-connected point to adjust the voltage of the grid-connected point.

9. A distributed photovoltaic voltage over-limit control device with optimized active and reactive ratio, characterized in that: include: At least one processing unit, interconnecting the processing unit, the storage unit and the photovoltaic inverter through a bus unit, the storage unit storing a computer program, and when the computer program is executed by the processing unit, a distributed photovoltaic voltage over-limit control method with optimized active and reactive power ratio as described in any one of claims 1-8 is implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by the processor, the distributed photovoltaic voltage over-limit control method with optimized active and reactive power ratio as described in any one of claims 1-8 is implemented.

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