Photovoltaic grid-connected reactive power compensation wall-mounted box and reactive power distribution method thereof

Abstract

The invention provides a photovoltaic grid-connected reactive power compensation wall-mounted box and a reactive power distribution method thereof, the wall-mounted box comprises a wall-mounted box main body, the wall-mounted box main body is internally provided with an SVG reactive power compensation device and an intelligent capacitor which are in communication connection through an RS485 module, the lower part of the wall-mounted box main body is provided with a plurality of wire outlet holes, and the wire outlet holes are communicated with the wall-mounted box main body. The SVG reactive power compensation device is provided with a power grid side signal acquisition module and a load side signal acquisition module, and the acquisition ends of the power grid side signal acquisition module and the load side signal acquisition module are led out from the wire outlet holes through signal wires. The SVG reactive power compensation device and the intelligent capacitor are both provided with output units, the output ends of the output units are led out from the wire outlet holes through power lines, a parallel control current tracking control strategy is adopted, a system reactive power distribution control method is provided, and therefore reactive current of a user power distribution room is compensated accurately and effectively.

Description

Technical Field

[0001] The present invention relates to the technical field of reactive power distribution, and in particular to a wall-mounted box for photovoltaic grid-connected reactive power compensation and its reactive power distribution method. Background Art

[0002] When constructing a 10kV dedicated transformer user distribution room, reactive power compensation is generally configured according to 30-40% of the transformer capacity, and the power factor can meet the requirements. The reactive power compensation device is mostly an intelligent capacitor. When a user connects to a distributed photovoltaic system, since the active power consumed is the electric energy generated by the photovoltaic, the active power drawn from the grid decreases, while the reactive power remains unchanged, resulting in a decrease in the power factor and failing to meet the requirements. Due to the instability of photovoltaic output, the intelligent capacitor can only perform hierarchical regulation and cannot solve the flicker and imbalance generated by the photovoltaic. Disadvantages of existing reactive power compensation control schemes: Using intelligent capacitors: Intelligent capacitors are currently relatively common intelligent reactive power compensation devices, which have low costs and have great advantages in large-capacity reactive power compensation. However, they can only perform hierarchical compensation and cannot control flicker and imbalance. Using SVG reactive power compensation devices: SVG already represents a new generation of reactive power compensation systems, which have fast regulation speed, wide operating range, and can control harmonics in the compensation current. However, large-capacity SVG has a complex structure, high control difficulty, and high costs. Summary of the Invention

[0003] The present invention solves the problem that the intelligent capacitor can only perform hierarchical regulation, and proposes a wall-mounted box for photovoltaic grid-connected reactive power compensation and its reactive power distribution method. By adopting a current tracking control strategy of parallel control, a reactive power distribution control method for the system is given, so as to effectively and accurately compensate the reactive current of the user distribution room.

[0004] To achieve the above object, the following technical solutions are proposed: A wall-mounted box for photovoltaic grid-connected reactive power compensation includes a wall-mounted box main body. An SVG reactive power compensation device and an intelligent capacitor that are communicatively connected through an RS485 module are arranged in the wall-mounted box main body. A plurality of wire outlet holes are provided below the wall-mounted box main body. The SVG reactive power compensation device is provided with a grid-side signal acquisition module and a load-side signal acquisition module. The acquisition ends of the grid-side signal acquisition module and the load-side signal acquisition module are led out from the wire outlet holes through signal lines. Both the SVG reactive power compensation device and the intelligent capacitor are provided with output units, and the output ends of the output units are led out from the wire outlet holes through power lines.

[0005] The present invention mainly consists of a parallel combination of an SVG reactive power compensation device and intelligent capacitors. The hybrid reactive power compensation system takes the controller of the SVG reactive power compensation device as the reactive power coordination control center. First, the grid-side signal acquisition module uses voltage and current sensors to detect the grid voltage and current in real time, and the load-side signal acquisition module uses current sensors to detect the load-side current signal in real time. The reactive current is calculated through the reactive current detection method, and then the average reactive current is further calculated to obtain the total reactive power to be compensated. Then, according to the reactive power distribution principle, the number of intelligent capacitors to be switched is calculated, and the switching of the intelligent capacitors is controlled through the RS485 communication method. At the same time, the reactive current that the SVG reactive power compensation device needs to compensate is calculated, and accurate reactive power compensation is achieved by controlling the SVG reactive power compensation device, thereby realizing the reactive power compensation of the entire system. Based on the user's original reactive power compensation system, the present invention adds an SVG reactive power compensation device. On the basis of fully reducing the transformation cost of the user's reactive power system, a current tracking control strategy of parallel type control is adopted, and a reactive power distribution control method for the system is given, so as to effectively and accurately compensate the reactive current in the user's distribution substation.

[0006] Preferably, the wall-mounted box body includes a box, a partition is provided in the box, the intelligent capacitor is arranged on the partition, and the SVG reactive power compensation device is fixed on the inner side wall of the box below the partition.

[0007] The wall-mounted box body of the present invention includes a box and a partition provided in the box for partitioning. The intelligent capacitor is fixedly arranged on the partition, and the SVG reactive power compensation device is fixedly arranged on the inner side wall of the box and is located below the partition.

[0008] Preferably, the acquisition end of the grid-side signal acquisition module includes a voltage signal acquisition end and a current signal acquisition end, and the acquisition end of the load-side signal acquisition module includes a load-side current signal acquisition end.

[0009] The acquisition end of the grid-side signal acquisition module of the present invention includes a current signal acquisition end and a voltage signal acquisition end. The acquisition end of the load-side signal acquisition module is provided with a load-side current signal acquisition end. The current signal acquisition end obtains the current signals of the grid side and the load side through current sensors, and the voltage signal acquisition end obtains the grid-side voltage signal through voltage sensors.

[0010] Preferably, the current tracking control strategy of the SVG reactive power compensation device adopts a weighted parallel-type repetitive control, a weighting coefficient β is added to the PI control branch, and a weighting coefficient α is added to the repetitive control branch.

[0011] The present invention adopts a weighted parallel-type repetitive control: select a better weight ratio to balance the roles of PI and repetitive control. The weighted parallel-type repetitive control adds weighting coefficients α and β to the PI and repetitive branches to balance the roles of PI and repetitive control. The purpose of the weighted parallel-type repetitive control is to strengthen the role of PI control during dynamic conditions while weakening the role of repetitive control during steady state. On the premise of ensuring stability, signal distortion caused by repetitive control is eliminated. When setting the weights, it is necessary to satisfy α + β = 1. As the weight ratio β / α increases, the role of repetitive control is gradually weakened and the role of PI control is strengthened.

[0012] Preferably, the intelligent capacitor includes several groups of intelligent capacitors with the same output voltage. The output end of each group of intelligent capacitors is connected with a switching switch, and the switching switch is electrically connected with an intelligent capacitor control module. The intelligent capacitor control module exchanges data with the SVG reactive power compensation device through the RS485 module.

[0013] The intelligent capacitor of the present invention includes several groups of intelligent capacitors. Each group of intelligent capacitors consists of at least one intelligent capacitor monomer. The output voltages of each group of intelligent capacitors are the same, and the output end of each group of intelligent capacitors is connected with a switching switch for controlling output on and off. All the switching switches are electrically connected to the intelligent capacitor control module, and data exchange between the intelligent capacitor control module and the SVG reactive power compensation device is carried out through the RS485 module.

[0014] Preferably, the intelligent capacitor control module is electrically connected with a power management system. The power management system judges whether there is a fault in the line according to the received signal on the grid side. If so, the working intelligent capacitor is cut off. If not, it judges whether the power of the working intelligent capacitor is sufficient. If so, it continues to work. If not, the intelligent capacitor is switched.

[0015] The purpose of setting the power management system in the present invention is to detect the voltage and current signals of the power grid. When there is a fault on the grid side, the working capacitor is cut off to protect the main circuit.

[0016] A reactive power distribution method for a photovoltaic grid-connected reactive power compensation wall-mounted box, adopting the above-mentioned photovoltaic grid-connected reactive power compensation wall-mounted box, includes the following steps: S1, the SVG reactive power compensation device collects the signals on the grid side and the load side to obtain the reactive current I that needs to be compensated on the grid side Q ; S2, preset several reactive current ranges and the corresponding intelligent capacitor input functions for each reactive current range, and then according to the reactive current I that needs to be compensated on the grid side Q select the corresponding intelligent capacitor input function to obtain the number of intelligent capacitors to be input and the reactive current I that the SVG reactive power compensation device needs to compensate SVG 。

[0017] The total reactive power I of the system of the present invention Q is mainly compensated by intelligent capacitors. However, intelligent capacitors can only perform step compensation. Further, the SVG reactive power compensation device is used to complete the reactive power compensation between steps, and then accurate compensation of reactive power is achieved. In addition, within the compensation capacity range of the SVG reactive power compensation device, the SVG reactive power compensation device is used for compensation to minimize the switching times of intelligent capacitors.

[0018] Preferably, the acquisition process of the reactive current I Q is as follows: periodically acquire a number of DC components ig of the reactive current, and calculate the average value of all DC components ig of the reactive current in the current period as the reactive current I to be compensated on the grid side Q .

[0019] Preferably, the range of the reactive current is as follows: When kI C -I SVG <I Q ≤kI C +I SVG , all intelligent capacitors are put into operation, and the SVG reactive power compensation device outputs at full capacity; When kI C -I SVG <I Q ≤kI C , some intelligent capacitors are put into operation, and the SVG reactive power compensation device compensates for the remaining reactive current -I SVG <I Q ≤0; When kI C <I Q ≤kI C +I SVG , some intelligent capacitors are put into operation, and the SVG reactive power compensation device compensates for the remaining reactive current 0<I Q ≤I SVG ; When kI C -I SVG <I Q ≤kI C +I SVG , all reactive current is compensated by the SVG reactive power compensation device; Wherein: k is the number of groups of intelligent capacitors put into operation, I C is the reactive current compensated by a single group of intelligent capacitors, and I SVG is the reactive current output by the SVG reactive power compensation device for compensation.

[0020] Preferably, the range of the said I SVG is -3I SVGmax / 4<I Q ≤3ISVGmax / 4, where I SVGmax is the maximum reactive current compensated and output by the SVG reactive power compensation device, which plays a role in saving the dynamic output capacity of the SVG and preventing the SVG from being in a full-load output state all the time.

[0021] The beneficial effects of the present invention are as follows: The present invention adds an SVG reactive power compensation device on the basis of the user's original reactive power compensation system. On the basis of fully reducing the transformation cost of the user's reactive power system, a current tracking control strategy of parallel control is adopted, and a reactive power distribution control method for the system is given, so as to effectively and accurately compensate the reactive current in the user's distribution room. Brief Description of the Drawings

[0022] Figure 1 is a schematic diagram of the overall structure of the present invention.

[0023] Figure 2 is a schematic diagram of the working principle of the present invention.

[0024] Figure 3 is a schematic diagram of the weighted parallel repetitive control structure of the present invention.

[0025] Figure 4 is a schematic diagram of the operating characteristics of the hybrid reactive power compensation of the present invention.

[0026] Wherein: 1, box body; 2, box door; 3, partition; 4, intelligent capacitor; 5, SVG reactive power compensation device; 6, RS485 module; 7, wire outlet hole. Detailed Embodiments

[0027] Embodiment 1: This embodiment proposes a wall-mounted box for photovoltaic grid-connected reactive power compensation. Referring to Figure 1 , it includes a wall-mounted box main body, an intelligent capacitor 4, an SVG reactive power compensation device 5 and an RS485 module 6. The intelligent capacitor 4, the SVG reactive power compensation device 5 and the RS485 module 6 are all arranged in the wall-mounted box main body. The SVG reactive power compensation device 5 communicates with the intelligent capacitor 4 through the RS485 module. A plurality of wire outlet holes 7 are provided below the wall-mounted box main body. The SVG reactive power compensation device 5 is provided with a load-side signal acquisition module and a grid-side signal acquisition module. The acquisition ends of the load-side signal acquisition module and the grid-side signal acquisition module are led out from the wire outlet hole 7 through signal lines. Both the intelligent capacitor 4 and the SVG reactive power compensation device 5 are provided with output units. The output ends of the output units of the intelligent capacitor 4 and the SVG reactive power compensation device 5 are led out from the wire outlet hole 7 through power lines.

[0028] The present invention is mainly composed of a parallel connection of an SVG reactive power compensation device 5 and an intelligent capacitor 4. Referring to Figure 2, the hybrid reactive power compensation system uses the controller of the SVG reactive power compensation device 5 as the reactive power coordination control center. First, the grid-side signal acquisition module uses voltage and current sensors to detect the grid voltage and current in real time, and the load-side signal acquisition module uses current sensors to detect the load-side current signal in real time. The reactive current is calculated through the reactive current detection method, and then the average reactive current is further calculated, and the total reactive power to be compensated is obtained. Then, according to the reactive power distribution principle, the number of intelligent capacitors to be switched is calculated, and the switching of the intelligent capacitors is controlled through the RS485 communication method. At the same time, the reactive current that the SVG reactive power compensation device 5 needs to compensate is calculated, and the accurate reactive power compensation is achieved by controlling the SVG reactive power compensation device 5, thereby realizing the reactive power compensation of the entire system. Based on the user's original reactive power compensation system, the present invention adds an SVG reactive power compensation device. On the basis of fully reducing the transformation cost of the user's reactive power system, a current tracking control strategy of parallel control is adopted, and a reactive power distribution control method for the system is given, so as to effectively and accurately compensate the reactive current in the user's distribution substation.

[0029] The acquisition end of the grid-side signal acquisition module of the present invention includes a current signal acquisition end and a voltage signal acquisition end. The acquisition end of the load-side signal acquisition module is provided with a load-side current signal acquisition end. The current signal acquisition end obtains the current signals of the grid side and the load side through current sensors, and the voltage signal acquisition end obtains the grid voltage signal through voltage sensors.

[0030] The current tracking control strategy of SVG often adopts PI control. The structure of PI control is simple and easy to implement, but the PI control has poor tracking ability for periodic signals and disturbance suppression ability. Repetitive control can effectively solve the compensation problems of periodic signal tracking and disturbance suppression. Refer to Figure 3 , Q(z) will affect the stability of repetitive control. Q(z) is generally set to a constant less than and close to 1, or can also be set to a function with low-pass filtering properties. When Q(z) = 0.95, the system is in a stable state. The present invention adopts weighted parallel repetitive control: select a better weight ratio to balance the effects of PI and repetitive control. The weighted parallel repetitive control adds weighting coefficients α and β to the PI and repetitive branches to balance the effects of PI and repetitive control. The purpose of the weighted parallel repetitive control is to strengthen the role of PI control during dynamic times and weaken the role of repetitive control during steady state. On the premise of ensuring stability, eliminate the signal distortion caused by repetitive control. When setting the weights, it is necessary to satisfy α + β = 1. As the weight ratio β / α increases, the role of repetitive control is gradually weakened and the role of PI control is strengthened.

[0031] The intelligent capacitor 4 of the present invention includes several groups of intelligent capacitors. Each group of intelligent capacitors is composed of at least one intelligent capacitor monomer. The output voltages of each group of intelligent capacitors are the same, and a switching switch for controlling the output on-off is connected to the output end of each group of intelligent capacitors. All the switching switches are electrically connected to the intelligent capacitor control module. Data exchange is carried out between the intelligent capacitor control module and the SVG reactive power compensation device 5 through the RS485 module.

[0032] This embodiment also proposes a reactive power distribution method for a photovoltaic grid-connected reactive power compensation wall-mounted box. Using the above-mentioned photovoltaic grid-connected reactive power compensation wall-mounted box, it includes the following steps: S1. The SVG reactive power compensation device 5 collects the current and voltage signals on the grid side and the current signal on the load side, and calculates the reactive current I to be compensated on the grid side. Q The system detects the DC component ig of the reactive current, and calculates the average value of ig once in each cycle as the reactive current required by the grid in the current cycle, denoted as IQ.

[0033] S2. Compare the reactive current I to be compensated on the grid side Q with the preset reactive current range, and select the intelligent capacitor input function corresponding to the reactive current range to obtain the number of intelligent capacitors to be input and the reactive current I to be compensated by the SVG reactive power compensation device 5. SVG .

[0034] In the hybrid reactive power compensation system, a group of SVG reactive power compensation devices and multiple groups of intelligent capacitors are used to jointly complete reactive power compensation. The compensation principle of the hybrid reactive power compensation system is as Figure 4 shown. As can be seen from Figure 4 , the total reactive power I of the system Q is mainly compensated by the intelligent capacitors. However, the intelligent capacitors can only complete step-by-step compensation. Further, the SVG reactive power compensation device is used to complete the reactive power compensation between levels, and then accurate compensation of the reactive power is achieved. In addition, within the compensation capacity range of the SVG reactive power compensation device, the SVG reactive power compensation device is used for compensation to minimize the number of switching operations of the intelligent capacitors.

[0035] The reactive current range is as follows: 1. When kI C -I SVG <I Q ≤kI C +I SVG , at this time k > N. At this moment, the total reactive power to be compensated is greater than the compensation capacity of the hybrid system, so all the intelligent capacitors are input, n = N, and the SVG reactive power compensation device 5 outputs at full capacity: I SVG = I SVGmax ; 2. When kIC -I SVG <I Q ≤ kI C When this occurs, where 0 < k < N, the reactive power to be compensated is greater than the compensation capacity of the SVG. Therefore, part of the intelligent capacitors are put into operation, and the number of capacitors put in is n = k. The SVG reactive power compensation device 5 compensates the remaining reactive current -I SVG <I Q ≤ 0, at this moment the intelligent capacitors are in an over-compensation state, and the SVG emits inductive reactive power for compensation; 3. When kI C <I Q ≤ kI C +I SVG When this occurs, where 0 < k < N, part of the intelligent capacitors are put into operation, and the number of capacitors put in is n = k. The SVG reactive power compensation device 5 compensates the remaining reactive current 0 < I Q ≤ I SVG , at this moment the intelligent capacitors are in an under-compensation state, and the SVG emits capacitive reactive power for compensation; 4. When kI C -I SVG <I Q ≤ kI C +I SVG When this occurs, where k < 0, the reactive power to be compensated is small, and there is no need to switch the intelligent capacitors. So n = 0, and all reactive power is compensated by the SVG; Among them: k is the number of groups of intelligent capacitors put into operation, and k is defined as an integer. I C is the reactive current compensated by a single group of intelligent capacitors, and I SVG is the reactive current output and compensated by the SVG reactive power compensation device 5. The total number of intelligent capacitors is denoted as N, and the number to be put into operation at the current moment is n. The reactive power distribution rule of the hybrid system is shown in Table 1. From Table 1, the switching control principle of the intelligent capacitors can be obtained.

[0036] Table 1 Reactive Power Distribution Table System average reactive current range k range Number of intelligent capacitors put into operation n <![CDATA[kI C -I SVG <I Q ≤kI C +I SVG > k > N N <![CDATA[kI C -I SVG <I Q ≤kI C > 0 < k < N k <![CDATA[kI C <I Q ≤kI C +I SVG > 0 < k < N k <![CDATA[kI C -I SVG <I Q ≤kI C +I SVG > k<0 0 Example 2: In this example, on the basis of Example 1, the wall-mounted box body and the intelligent capacitor control module are improved, and a wall-mounted box for photovoltaic grid-connected reactive power compensation is proposed. Refer to Figure 1, including a wall-mounted box body, an intelligent capacitor 4, an SVG reactive power compensation device 5, and an RS485 module 6. The intelligent capacitor 4, the SVG reactive power compensation device 5, and the RS485 module 6 are all arranged inside the wall-mounted box body. The SVG reactive power compensation device 5 communicates with the intelligent capacitor 4 through the RS485 module. A plurality of wire outlet holes 7 are provided below the wall-mounted box body. The SVG reactive power compensation device 5 is provided with a load-side signal acquisition module and a grid-side signal acquisition module. The acquisition ends of the load-side signal acquisition module and the grid-side signal acquisition module are led out from the wire outlet holes 7 through signal lines. Both the intelligent capacitor 4 and the SVG reactive power compensation device 5 are provided with output units. The output ends of the output units of the intelligent capacitor 4 and the SVG reactive power compensation device 5 are led out from the wire outlet holes 7 through power lines.

[0037] The present invention is mainly composed of an SVG reactive power compensation device 5 and an intelligent capacitor 4 connected in parallel. Refer to Figure 2 , the hybrid reactive power compensation system takes the controller of the SVG reactive power compensation device 5 as the reactive power coordination control center. First, the grid-side signal acquisition module uses voltage and current sensors to detect the grid voltage and current in real time, and the load-side signal acquisition module uses current sensors to detect the load-side current signal in real time. The reactive current is calculated through the reactive current detection method, and further the average reactive current is calculated, and the total reactive power to be compensated is obtained. Then, according to the reactive power distribution principle, the number of intelligent capacitors to be switched is calculated, and the switching of the intelligent capacitors is controlled through the RS485 communication method. At the same time, the reactive current that the SVG reactive power compensation device 5 needs to compensate is calculated, and the accurate reactive power compensation is achieved by controlling the SVG reactive power compensation device 5, thereby realizing the reactive power compensation of the entire system. The present invention adds an SVG reactive power compensation device on the basis of the user's original reactive power compensation system. On the basis of fully reducing the transformation cost of the user's reactive power system, the current tracking control strategy of parallel connection type control is adopted, and a reactive power distribution control method for the system is given, so as to effectively and accurately compensate the reactive current in the user's distribution substation.

[0038] The acquisition end of the grid-side signal acquisition module of the present invention includes a current signal acquisition end and a voltage signal acquisition end. The acquisition end of the load-side signal acquisition module is provided with a load-side current signal acquisition end. The current signal acquisition end obtains the current signals of the grid side and the load side through current sensors, and the voltage signal acquisition end obtains the grid-side voltage signal through voltage sensors.

[0039] The current tracking control strategy of SVG often adopts PI control. The structure of PI control is simple and easy to implement, but the PI control has poor tracking ability for periodic signals and disturbance governance ability. Repetitive control can effectively solve the compensation problems of periodic signal tracking and disturbance governance. Refer to Figure 3, Q(z) affects the stability of repetitive control. Q(z) is generally set to a constant less than and close to 1, or can also be set to a function with low-pass filtering properties. When Q(z) = 0.95, the system is in a stable state. The present invention adopts a weighted parallel repetitive control: select a better weight ratio to balance the effects of PI and repetitive control. The weighted parallel repetitive control adds weighting coefficients α and β to the PI and repetitive branches to balance the effects of PI and repetitive control. The purpose of the weighted parallel repetitive control is to strengthen the role of PI control during dynamic conditions and weaken the role of repetitive control during steady state. On the premise of ensuring stability, eliminate the signal distortion caused by repetitive control. When setting the weights, it is necessary to satisfy α + β = 1. As the weight ratio β / α increases, the role of repetitive control is gradually weakened and the role of PI control is strengthened.

[0040] The intelligent capacitor 4 of the present invention includes several groups of intelligent capacitors. Each group of intelligent capacitors consists of at least one intelligent capacitor monomer. The output voltages of each group of intelligent capacitors are the same, and a switching switch for controlling the output on-off is connected to the output end of each group of intelligent capacitors. All the switching switches are electrically connected to the intelligent capacitor control module. The intelligent capacitor control module and the SVG reactive power compensation device 5 exchange data through the RS485 module.

[0041] The intelligent capacitor control module is electrically connected to a power management system for monitoring the working states of the grid side and the intelligent capacitors. The power management system is used to judge whether faults such as overcurrent, overvoltage, and overheating occur in the line. If so, cut off the working intelligent capacitors. If not, judge whether the power of the working intelligent capacitors is sufficient. If not, switch the intelligent capacitors; if so, continue to work.

[0042] The purpose of setting the power management system in the present invention is to detect the voltage and current signals of the grid. When there is a fault on the grid side, cut off the working capacitors to protect the main circuit.

[0043] The wall-mounted box body of the present invention includes a box body 1 and a partition 3 arranged in the box body 1 for partitioning. The intelligent capacitor 4 is fixedly arranged on the partition 3. The SVG reactive power compensation device 5 is fixedly arranged on the inner side wall of the box body 1 and is located below the partition 3. A box door 2 is hinged on the outside of the box body 1.

[0044] This embodiment also proposes a reactive power distribution method for a photovoltaic grid-connected reactive power compensation wall-mounted box. Using the above-mentioned photovoltaic grid-connected reactive power compensation wall-mounted box, it includes the following steps: S1, the SVG reactive power compensation device 5 collects the current and voltage signals on the grid side and the current signal on the load side, and calculates the reactive current I that needs to be compensated on the grid side Q; The system detects the DC component ig of the reactive current, calculates the average value of ig once per cycle as the reactive current that the power grid needs to compensate in the current cycle, denoted as IQ.

[0045] S2. Compare the reactive current I to be compensated on the grid side Q with the preset reactive current range, select the intelligent capacitor input function corresponding to the reactive current range to obtain the number of intelligent capacitors to be input and the reactive current I to be compensated by the SVG reactive power compensation device 5 SVG .

[0046] In the hybrid reactive power compensation system, a group of SVG reactive power compensation devices and multiple groups of intelligent capacitors are jointly used to complete reactive power compensation. The compensation principle of the hybrid reactive power compensation system is as Figure 4 shown. It can be seen from Figure 4 that the total reactive power I of the system Q is mainly compensated by the intelligent capacitors. However, the intelligent capacitors can only complete stepped compensation. Further, the SVG reactive power compensation device is used to complete the reactive power compensation between steps, and then accurate compensation of the reactive power is achieved. In addition, within the compensation capacity range of the SVG reactive power compensation device, the SVG reactive power compensation device is used for compensation to minimize the switching times of the intelligent capacitors.

[0047] The said reactive current range is as follows: 1. When kI C - I SVG < I Q ≤ kI C + I SVG at this time, k > N. At this moment, the total reactive power to be compensated is greater than the compensation capacity of the hybrid system, so all the intelligent capacitors are put into operation, n = N, and the SVG reactive power compensation device 5 outputs at full capacity: I SVG = I SVGmax ; 2. When kI C - I SVG < I Q ≤ kI C at this time, 0 < k < N. The reactive power capacity to be compensated is greater than the compensation capacity of the SVG. Therefore, some of the intelligent capacitors are put into operation, and the number of capacitors put in is n = k. The SVG reactive power compensation device 5 compensates the remaining reactive current -I SVG < I Q ≤ 0. At this moment, the intelligent capacitors are in an over-compensation state, and the SVG emits inductive reactive power for compensation; 3. When kI C < I Q ≤ kI C + I SVG at this time, when 0 < k < N, some of the intelligent capacitors are put into operation, and the number of capacitors put in is n = k. The SVG reactive power compensation device 5 compensates the remaining reactive current 0 < IQ ≤ I SVG At this moment, the intelligent capacitor is in an under-compensation state, and the SVG emits capacitive reactive power for compensation; 4. When kI C - I SVG < I Q ≤ kI C + I SVG At this time, k < 0, and the reactive power to be compensated is small, so there is no need to switch the intelligent capacitor, so n = 0, and all reactive power is compensated by the SVG; Where: k is the number of groups of intelligent capacitors put into operation, k is defined as an integer, I C is the reactive current compensated by a single group of intelligent capacitors, I SVG is the reactive current output by the SVG reactive power compensation device 5. The total number of intelligent capacitors is denoted as N, and the number to be put into operation at the current moment is n. The reactive power distribution rule of the hybrid system is shown in Table 1. From Table 1, the switching control principle of the intelligent capacitor can be obtained.

[0048] Table 1 Reactive Power Distribution Table Example 3: In this example, on the basis of Example 2, the range of I SVG is limited, and a wall-mounted box for photovoltaic grid-connected reactive power compensation is proposed. Refer to Figure 1 , which includes a wall-mounted box body, intelligent capacitors 4, an SVG reactive power compensation device 5, and an RS485 module 6. The intelligent capacitors 4, the SVG reactive power compensation device 5, and the RS485 module 6 are all arranged in the wall-mounted box body. The SVG reactive power compensation device 5 communicates with the intelligent capacitors 4 through the RS485 module. There are several wire outlet holes 7 at the lower part of the wall-mounted box body. The SVG reactive power compensation device 5 is provided with a load-side signal acquisition module and a grid-side signal acquisition module. The acquisition ends of the load-side signal acquisition module and the grid-side signal acquisition module are led out from the wire outlet holes 7 through signal lines. Both the intelligent capacitors 4 and the SVG reactive power compensation device 5 are provided with output units. The output ends of the output units of the intelligent capacitors 4 and the SVG reactive power compensation device 5 are led out from the wire outlet holes 7 through power lines.

[0049] The present invention is mainly composed of an SVG reactive power compensation device 5 and intelligent capacitors 4 connected in parallel. Refer to Figure 2, the hybrid reactive power compensation system takes the controller of the SVG reactive power compensation device 5 as the reactive power coordination control center. First, the grid-side signal acquisition module uses voltage and current sensors to detect the grid voltage and current in real time, and the load-side signal acquisition module uses current sensors to detect the load-side current signal in real time. The reactive current is calculated through the reactive current detection method, and then the average reactive current is calculated, and the total reactive power to be compensated is obtained. Then, according to the reactive power distribution principle, the number of intelligent capacitors to be switched is calculated, and the switching of the intelligent capacitors is controlled through the RS485 communication method. At the same time, the reactive current that the SVG reactive power compensation device 5 needs to compensate is calculated, and the accurate reactive power compensation is achieved by controlling the SVG reactive power compensation device 5, thereby realizing the reactive power compensation of the entire system. Based on the user's original reactive power compensation system, the present invention adds an SVG reactive power compensation device. On the basis of fully reducing the transformation cost of the user's reactive power system, the current tracking control strategy of parallel connection type control is adopted, and the reactive power distribution control method of the system is given, so as to effectively and accurately compensate the reactive current in the user's distribution substation.

[0050] The acquisition end of the grid-side signal acquisition module of the present invention includes a current signal acquisition end and a voltage signal acquisition end. The acquisition end of the load-side signal acquisition module is provided with a load-side current signal acquisition end. The current signal acquisition end obtains the current signals on the grid side and the load side through current sensors, and the voltage signal acquisition end obtains the grid voltage signal through voltage sensors.

[0051] The current tracking control strategy of SVG often adopts PI control. The structure of PI control is simple and easy to implement. However, the PI control has poor tracking ability for periodic signals and disturbance suppression ability. Repetitive control can effectively solve the compensation problems of periodic signal tracking and disturbance suppression. Refer to Figure 3 , Q(z) will affect the stability of repetitive control. Q(z) is generally set to a constant less than and close to 1, or can also be set to a function with low-pass filtering properties. When Q(z) = 0.95, the system is in a stable state. The present invention adopts weighted parallel repetitive control: select a better weight ratio to balance the effects of PI and repetitive control. The weighted parallel repetitive control adds weighting coefficients α and β to the PI and repetitive branches to balance the effects of PI and repetitive control. The purpose of the weighted parallel repetitive control is to strengthen the role of PI control during dynamic times and weaken the role of repetitive control during steady state. On the premise of ensuring stability, the signal distortion caused by repetitive control is eliminated. When setting the weights, it is necessary to satisfy α + β = 1. As the weight ratio β / α increases, the role of repetitive control is gradually weakened and the role of PI control is strengthened.

[0052] The intelligent capacitor 4 of the present invention includes several groups of intelligent capacitors. Each group of intelligent capacitors consists of at least one intelligent capacitor monomer. The output voltages of each group of intelligent capacitors are the same, and a switching switch for controlling the output on-off is connected to the output end of each group of intelligent capacitors. All the switching switches are electrically connected to the intelligent capacitor control module. Data exchange between the intelligent capacitor control module and the SVG reactive power compensation device 5 is carried out through the RS485 module.

[0053] The intelligent capacitor control module is electrically connected to a power management system for monitoring the working states of the grid side and the intelligent capacitors. The power management system is used to judge whether faults such as overcurrent, overvoltage, and overheating occur in the circuit. If so, the working intelligent capacitors are cut off. If not, it is judged whether the power of the working intelligent capacitors is sufficient. If not, the intelligent capacitors are switched; if so, they continue to work.

[0054] The purpose of setting the power management system in the present invention is to detect the voltage and current signals of the grid. When a fault exists on the grid side, the working capacitors are cut off to protect the main circuit.

[0055] The wall-mounted box body of the present invention includes a box body 1 and a partition 3 arranged in the box body 1 for partitioning. The intelligent capacitor 4 is fixedly arranged on the partition 3. The SVG reactive power compensation device 5 is fixedly arranged on the inner side wall of the box body 1 and is located below the partition 3. A box door 2 is hinged to the outside of the box body 1.

[0056] This embodiment also proposes a reactive power distribution method for a photovoltaic grid-connected reactive power compensation wall-mounted box. Using the above-mentioned photovoltaic grid-connected reactive power compensation wall-mounted box, it includes the following steps: S1, the SVG reactive power compensation device 5 collects the current and voltage signals on the grid side and the current signal on the load side, and calculates the reactive current I to be compensated on the grid side. Q The system detects the DC component ig of the reactive current, and calculates the average value of ig once in each cycle as the reactive current required by the grid in the current cycle, denoted as IQ.

[0057] S2, compare the reactive current I to be compensated on the grid side with the preset reactive current range, and select the intelligent capacitor input function corresponding to the reactive current range to obtain the number of intelligent capacitors to be input and the reactive current I to be compensated by the SVG reactive power compensation device 5. Q SVG

[0058] In a hybrid reactive power compensation system, a group of SVG reactive power compensation devices and multiple groups of intelligent capacitors jointly complete reactive power compensation. The compensation principle of the hybrid reactive power compensation system is as Figure 4 shown. From Figure 4 it can be seen that the total reactive power I of the system QThe compensation is mainly completed by intelligent capacitors. However, intelligent capacitors can only perform step compensation. Further, the reactive power compensation between steps is completed by the SVG reactive power compensation device, and then accurate reactive power compensation is achieved. In addition, within the compensation capacity range of the SVG reactive power compensation device, the SVG reactive power compensation device performs the compensation to minimize the switching times of the intelligent capacitors.

[0059] In the reactive power distribution principle of this embodiment, the action threshold of the SVG is -3I SVGmax / 4 < I Q ≤ 3I SVGmax / 4, which plays a role in saving the dynamic output capacity of the SVG and avoiding the SVG being in a full-load output state all the time.

[0060] The range of the reactive current is as follows: 1. When kI C -3I SVGmax / 4 < I Q ≤ kI C +3I SVGmax / 4, at this time k > N, and the total reactive power to be compensated is greater than the compensation capacity of the hybrid system. Then all intelligent capacitors are put into operation, n = N, and the SVG reactive power compensation device 5 outputs at full load: I SVG = I SVGmax ; 2. When kI C -3I SVGmax / 4 < I Q ≤ kI C , at this time 0 < k < N, and the reactive power to be compensated is greater than the compensation capacity of the SVG. Therefore, part of the intelligent capacitors are put into operation, the number of capacitors put in is n = k, and the SVG reactive power compensation device 5 compensates the remaining reactive current -I SVG < I Q ≤ 0. At this moment, the intelligent capacitors are in an over-compensation state, and the SVG emits inductive reactive power for compensation; 3. When kI C < I Q ≤ kI C +3I SVGmax / 4 , at this time 0 < k < N, part of the intelligent capacitors are put into operation, the number of capacitors put in is n = k, and the SVG reactive power compensation device 5 compensates the remaining reactive current 0 < I Q ≤ I SVG . At this moment, the intelligent capacitors are in an under-compensation state, and the SVG emits capacitive reactive power for compensation; 4. When kI C -3I SVGmax / 4 < I Q ≤ kI C +3I SVGmax / 4, at this time k < 0, and the reactive power to be compensated is small, so there is no need to switch the intelligent capacitors. Therefore, n = 0, and all reactive power is compensated by the SVG; Where: k is the number of groups of intelligent capacitors put into operation, and k is defined as an integer, I C is the reactive current compensated by a single group of intelligent capacitors, I SVG is the reactive current compensated and output by the SVG reactive power compensation device 5. The total number of intelligent capacitors is denoted as N, and the number to be put into operation at the current moment is n. The reactive power distribution rule of the hybrid system is shown in Table 2, and the switching control principle of the intelligent capacitors can be obtained from Table 2.

[0061] Table 2 Reactive Power Distribution Table System average reactive current range k range Number of intelligent capacitors put into operation n <![CDATA[kI C -3I SVGmax / 4<I Q ≤kI C +3I SVGmax / 4]]> k > N N <![CDATA[kI C -3I SVGmax / 4<I Q ≤kI C > 0 < k < N k <![CDATA[kI C <I Q ≤kI C +3I SVGmax / 4 > 0 < k < N k <![CDATA[kI C -3I SVGmax / 4<I Q ≤kI C +3I SVGmax / 4]]> k<0 0

Claims

1. A photovoltaic grid-connected reactive power compensation wall-mounted box, characterized in that: The invention comprises a wall-mounted box body, wherein an SVG reactive power compensation device (5) and an intelligent capacitor (4) are arranged in the wall-mounted box body, which are connected for communication via an RS485 module (6); a plurality of outlet holes (7) are arranged below the wall-mounted box body; the SVG reactive power compensation device (5) is provided with a grid-side signal acquisition module and a load-side signal acquisition module; the acquisition ends of the grid-side signal acquisition module and the load-side signal acquisition module are led out of the outlet hole (7) via signal lines; the SVG reactive power compensation device (5) and the intelligent capacitor (4) are both provided with output units, and the output ends of the output units are led out of the outlet hole (7) via power lines.

2. A photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 1, characterized in that: The acquisition end of the grid-side signal acquisition module includes a voltage signal acquisition end and a current signal acquisition end, and the acquisition end of the load-side signal acquisition module includes a load-side current signal acquisition end.

3. A photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 2, characterized in that: The current tracking control strategy of the SVG reactive power compensation device (5) adopts weighted parallel repetitive control, a weighting coefficient β is added to the PI control branch, and a weighting coefficient α is added to the repetitive control branch.

4. The photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 1 is characterized in that: The smart capacitor (4) comprises a plurality of groups of smart capacitors with consistent output voltages, the output end of each group of smart capacitors being connected to a switch, the switch being electrically connected to a smart capacitor control module, and the smart capacitor control module exchanging data with the SVG reactive power compensation device (5) via an RS485 module.

5. The photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 4 is characterized in that: The smart capacitor control module is electrically connected to a power management system, which determines whether there is a fault in the line based on the signal received from the power grid side. If so, the working smart capacitor is cut off. If not, it determines whether the power of the working smart capacitor is sufficient. If so, it continues to work. If not, the smart capacitor is switched.

6. A photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 1 or 2 or 3 or 4 or 5, characterized in that: The wall-mounted box body comprises a box body (1), a partition (3) is provided inside the box body (1), the intelligent capacitor (4) is arranged on the partition (3), and the SVG reactive power compensation device (5) is fixed on the inner wall of the box body (1) below the partition (3).

7. A reactive power distribution method for a photovoltaic grid-connected reactive power compensation wall-mounted box, using a photovoltaic grid-connected reactive power compensation wall-mounted box as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: S1, SVG reactive power compensation device (5) collects signals from the grid side and the load side to obtain reactive current I that needs to be compensated on the grid side Q ; S2, preset several reactive current ranges and the smart capacitor input functions corresponding to each reactive current range, and then calculate the reactive current I that needs to be compensated on the grid side. Q Select the corresponding smart capacitor input function to obtain the number of smart capacitors and the reactive current I that needs to be compensated by the SVG reactive compensation device (5) SVG .

8. The reactive power distribution method of a photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 7 is characterized in that: The reactive current I Q The acquisition process is as follows: Periodically obtain several reactive current DC components ig, and calculate the average value of all reactive current DC components ig in the current cycle as the reactive current I that needs to be compensated on the grid side. Q .

9. The reactive power distribution method of a photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 7 is characterized in that: The reactive current range is as follows: When kI C -I SVG Q ≤kI C +I SVG When , all the smart capacitors are put into use, and the SVG reactive power compensation device (5) outputs at full capacity;​ When kI C -I SVG Q ≤kI C When the intelligent capacitor is partially put into operation, the SVG reactive power compensation device (5) compensates for the remaining reactive current -I SVG Q ≤0;​​ When kI C Q ≤kI C +I SVG When the intelligent capacitor is partially put into operation, the SVG reactive power compensation device (5) compensates for the remaining reactive current 0 Q ≤I SVG ;​​ When kI C -I SVG Q ≤kI C +I SVG When , all reactive currents are compensated by the SVG reactive compensation device (5);​ Where: k is the number of groups of smart capacitors, I C is the reactive current compensated by a single group of smart capacitors, I SVG The reactive current output by the SVG reactive power compensation device (5) is compensated.

10. The reactive power distribution method of a photovoltaic grid-connected reactive power compensation wall-mounted box according to claim 9, characterized in that: I SVG The range is -3I SVGmax / 4 Q ≤3I SVGmax / 4, where I SVGmax It is the maximum reactive current compensated and output by the SVG reactive power compensation device (5).​

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