Control method and device for reactive power and imbalance of low-voltage distribution network three-phase system

Abstract

The present application belongs to the technical field of low-voltage distribution network, and particularly relates to a kind of low-voltage distribution network three-phase system reactive power and unbalance treatment control method and device.The control method includes, obtaining three-phase active current value and three-phase reactive current value;Based on the given working mode and three-phase active current value or three-phase reactive current value, active compensation current instruction or reactive compensation current instruction is obtained to realize active current compensation or reactive current compensation;The given working mode includes constant reactive mode, reactive compensation mode, unbalanced current compensation mode, unbalanced and reactive compensation mode and reactive and unbalanced compensation mode.The present application can realize accurate compensation and fast compensation of current by designing constant reactive mode, reactive compensation mode, unbalanced current compensation mode, unbalanced and reactive compensation mode and reactive and unbalanced compensation mode.

Description

Technical Field

[0001] This invention belongs to the field of low-voltage distribution network technology, specifically relating to a method and device for controlling reactive power and imbalance in a three-phase system of a low-voltage distribution network. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Because low-voltage power distribution systems almost exclusively use single-phase loads on the user side, and electricity consumption varies with time, the distribution transformer system is highly susceptible to reactive power failure and three-phase current imbalance. This can result in negative-sequence and zero-sequence currents, and the system current imbalance can severely exceed acceptable limits. Furthermore, due to the long power supply radius of low-voltage distribution systems, three-phase current imbalance can easily lead to low voltage and voltage imbalance at the power supply end, affecting user experience. Additionally, three-phase current imbalance in the distribution transformer can cause some phases to be overloaded while others are underloaded, leading to severe overheating, reduced transformer lifespan, and even transformer burnout.

[0004] Currently, the main method for addressing three-phase imbalance in compensation devices is to use phase-switching switches. These switches adjust the phase containing the load to achieve three-phase current balance. However, phase-switching switches cannot continuously, smoothly, or quickly adjust the three-phase unbalanced current.

[0005] Currently, most three-phase unbalanced treatment devices using power electronic control extract current commands in a three-phase coordinate system. Therefore, it is difficult to implement current compensation flexibly and accurately according to actual needs and the capacity of the compensation system during control. At the same time, when the grid voltage is unbalanced, the working stability of such compensation devices decreases, and in severe cases, the device may fail to operate under protection. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a method and device for controlling reactive power and imbalance in a three-phase low-voltage distribution network. By designing constant reactive power mode, reactive power compensation mode, unbalanced current compensation mode, unbalanced and reactive power compensation mode, and current compensation schemes under reactive power and unbalanced compensation modes, this invention can achieve accurate and rapid current compensation.

[0007] According to some embodiments, the present invention adopts the following technical solution:

[0008] In the first aspect, the present invention provides a method for managing and controlling reactive power and imbalance in a three-phase system of a low-voltage distribution network.

[0009] Methods for managing and controlling reactive power and imbalance in three-phase low-voltage distribution networks include:

[0010] Obtain the three-phase active current and three-phase reactive current values;

[0011] Based on the given operating mode and the three-phase active current value or three-phase reactive current value, an active current compensation command or a reactive current compensation command is obtained to achieve active current compensation or reactive current compensation.

[0012] The given operating modes include constant reactive power mode, reactive power compensation mode, unbalanced current compensation mode, unbalanced and reactive power compensation mode, and reactive power and unbalanced compensation mode.

[0013] Secondly, the present invention provides a device for managing reactive power and imbalance in a three-phase system of a low-voltage power distribution network.

[0014] A device for managing reactive power and imbalance in a three-phase system of a low-voltage distribution network includes a three-phase current imbalance management controller, which performs the steps in the method for managing reactive power and imbalance in a three-phase system of a low-voltage distribution network as described in the first aspect, and further includes an inverter power unit, an LCL filter unit, a circuit breaker, and a load-side current transformer.

[0015] The imbalance control device is connected to the low-voltage side of the transformer through a circuit breaker; the circuit breaker, LCL filter unit and inverter power unit are connected in series in sequence, and the LCL filter unit and inverter power unit are respectively connected to the three-phase current imbalance control controller; the primary side of the load-side current transformer is connected to the load and connected to the low-voltage side, and the secondary side is connected to the three-phase current imbalance control controller.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This invention designs schemes for constant reactive power mode, reactive power compensation mode, unbalanced current compensation mode, unbalanced and reactive power compensation mode, and current compensation under reactive power and unbalanced compensation modes, which can achieve accurate and rapid current compensation.

[0018] This invention automatically samples and detects the three-phase current on the low-voltage bus, and quickly detects the reactive power and unbalanced current of the system by using a single-phase control method. Based on the device settings, it continuously, smoothly, and quickly adjusts the power grid, effectively solving the common problems of reactive power and three-phase current imbalance on the low-voltage side of the distribution network. It is highly reliable, intelligent, easy to use, and meets the needs of practical applications. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 This is a logic diagram of constant reactive mode current command generation shown in Embodiment 1 of the present invention;

[0021] Figure 2 This is a logic diagram of the reactive power compensation mode current command generation shown in Embodiment 1 of the present invention;

[0022] Figure 3 This is a logic diagram of unbalanced current compensation mode current command generation shown in Embodiment 1 of the present invention;

[0023] Figure 4 This is a logic diagram for generating current commands in unbalanced and reactive power compensation modes as shown in Embodiment 1 of the present invention.

[0024] Figure 5 This is a logic diagram of the current command generation in reactive and unbalanced compensation mode shown in Embodiment 1 of the present invention;

[0025] Figure 6 This is a topology diagram of the imbalance control device shown in Embodiment 2 of the present invention;

[0026] Figure 7 This is a topology diagram of the control unit of the imbalance control device shown in Embodiment 2 of the present invention;

[0027] Figure 8 This is a block diagram of a single-phase phase-locked loop structure shown in Embodiment 2 of the present invention;

[0028] Figure 9 This is a block diagram of a second-order generalized integrator structure shown in Embodiment 2 of the present invention;

[0029] Figure 10 This is a block diagram of the single-phase reactive current and active current extraction structure shown in Embodiment 2 of the present invention;

[0030] Figure 11 This is a control block diagram of the imbalance control device shown in Embodiment 2 of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the term "comprising" is used in this specification, it indicates the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] In this invention, terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0035] Example 1

[0036] This embodiment provides a method for managing and controlling reactive power and imbalance in a three-phase system of a low-voltage distribution network.

[0037] Methods for managing and controlling reactive power and imbalance in three-phase low-voltage distribution networks include:

[0038] Obtain the three-phase active current and three-phase reactive current values;

[0039] Based on the given operating mode and the three-phase active current value or three-phase reactive current value, an active current compensation command or a reactive current compensation command is obtained to achieve active current compensation or reactive current compensation.

[0040] The given operating modes include constant reactive power mode, reactive power compensation mode (Q), unbalanced current compensation mode (B), unbalanced and reactive power compensation mode (B+Q), and reactive power and unbalanced compensation mode (Q+B).

[0041] As one or more implementation methods, such as Figure 1 As shown, in constant reactive power mode, the given set three-phase reactive current value i xq_set Sending reactive current to the power grid, at this time the output active power compensation current command i x_d_ref The value is zero. Determine if the reactive current value of any phase (a, b, c) is greater than the rated reactive current value. If so, the reactive current compensation command i is executed. x_q_ref The value is the rated reactive current to achieve reactive current compensation; otherwise, the reactive current compensation command i is output. x_q_ref For a given set three-phase reactive current value i xq_set This is to achieve reactive current compensation. (Where x represents phases a, b, and c)

[0042] As one or more implementation methods, such as Figure 2 As shown, in reactive power compensation mode, based on the acquired three-phase reactive current value i x_q Determine the reactive current value i of any phase abc. x_q Is it greater than the rated reactive current value? If so, output the active power compensation current command i. x_d_ref Zero, reactive power compensation current command i x_q_refThe value is a negative of the rated reactive current to achieve reactive current compensation; otherwise, the output active power compensation current command i is used. x_d_ref Zero, reactive power compensation current command i x_q_ref The original three-phase reactive current value i x_q The negative number is used to achieve reactive current compensation.

[0043] As one or more implementation methods, such as Figure 3 As shown, in the unbalanced current compensation mode, based on the acquired three-phase active unbalanced current value i x_d_ub and the three-phase reactive unbalanced current value i x_q_ub Sending reverse three-phase active power imbalance current value i to the power grid x_d_ub and the three-phase reactive unbalanced current value i x_q_ub To balance the current in each phase of the power grid; when the system capacity is limited, priority is given to compensating for the three-phase active power imbalance current, the specific process of which includes:

[0044] Extracting the three-phase active unbalanced current value i x_d_ub The maximum value in the range is used to determine the maximum value of the active power imbalance current i. max_d_ub Is it greater than the set first threshold? If so, based on the first threshold and the maximum value of the active power imbalance current i... max_d_ub Calculate the first coefficient; where the first coefficient and the three-phase active power imbalance current value i x_q_ub The negative of the product is the active power compensation current command i. x_d_ref Reactive power compensation current command i x_q_ref The value is set to zero to achieve active current compensation.

[0045] Otherwise, based on the three-phase active power imbalance current value i x_d_ub and the three-phase reactive unbalanced current value i x_q_ub Calculate the three-phase current compensation command i x_ref Determine the three-phase current compensation command i x_ref Is it greater than the set second threshold? If so, based on the second threshold and the active power imbalance current value i of phase a... a_d_ub and the reactive unbalanced current value i of phase a a_q_ub Calculate the second coefficient; where the active power compensation current command i x_d_ref The original three-phase active unbalanced current value i x_d_ub The second coefficient is related to the three-phase reactive power imbalance current value i. x_q_ub The negative of the product is the reactive power compensation current command i. x_q_ref According to the active power compensation current command i x_d_ref And reactive power compensation current command to achieve current compensation i x_q_ref ;

[0046] Otherwise, the active power compensation current command i x_d_refThe original three-phase active unbalanced current value i x_d_ub The reactive power compensation current command is the original three-phase reactive power imbalance current value i. x_q_ub This is to achieve current compensation.

[0047] As one or more implementation methods, the three-phase active power imbalance current value i x_d_ub The three-phase reactive unbalanced current value i is obtained from the difference between the three-phase active current value and the average value of the three-phase active current. x_q_ub It is obtained from the difference between the three-phase reactive current value and the average value of the three-phase reactive current.

[0048]

[0049]

[0050] As one or more implementation methods, such as Figure 4 As shown, in unbalanced and reactive power compensation modes, based on the acquired three-phase active unbalanced current value i x_d_ub and three-phase reactive current value i x_q Sending reverse three-phase active power imbalance current value i to the power grid x_d_ub and three-phase reactive current value i x_q To balance the current in each phase of the power grid and improve the system power factor, when the system capacity is limited, priority is given to compensating for the three-phase active power imbalance current. The specific process includes:

[0051] Extracting the three-phase active unbalanced current value i x_d_ub The maximum value in the range is used to determine the maximum value of the active power imbalance current i. max_d_ub Is it greater than the set third threshold? If so, based on the third threshold and the maximum value of the active power imbalance current i... max_d_ub Calculate the third coefficient; based on the third coefficient and the three-phase active power imbalance current value i x_d_ub The first three-phase active reference current value i is obtained. x_d_tem1 Based on the third threshold and the first three-phase active reference current value i x_d_tem1 The second and third phase active power reference current values ​​i are obtained. x_d_tem2 ;

[0052] Determine the active reference current value i for the second and third phases x_d_tem2 Is it greater than the three-phase reactive current value i? x_q If so, the active power compensation current command i x_d_ref The third coefficient and the three-phase active unbalanced current value i x_d_ub The negative of the product, reactive power compensation current command i x_q_ref The three-phase reactive current value i x_q The negative number is used to achieve current compensation; if the active reference current value of the second and third phases is i x_d_tem2Is it less than the three-phase reactive current value i? x_q Active power compensation current command i x_d_ref The third coefficient and the three-phase active unbalanced current value i x_d_ub The negative of the product, reactive power compensation current command i x_q_ref Based on the third threshold, the third coefficient, and the three-phase active power imbalance current value i x_d_ub The decision was made to achieve current compensation;

[0053] If the maximum value of the active power imbalance current is i max_d_ub If it is less than the set third threshold, then based on the active power imbalance current value i of phase a. a_d_ub and the reactive unbalanced current value i of phase a a_q_ub Calculate the three-phase current compensation command i x_ref ; Determine the three-phase current compensation command i x_ref Is it greater than the set third threshold? If so, then issue the active power compensation current command i. x_d_ref The original three-phase active unbalanced current value i x_d_ub The negative number, reactive power compensation current command i x_q_ref The three-phase reactive unbalanced current value i x_q_ub The negative number is used to achieve current compensation; otherwise, the active power compensation current command i is used. x_d_ref The original three-phase active unbalanced current value i x_d_ub The negative number, reactive power compensation current command i x_q_ref Based on the third threshold and the active power imbalance current value i of phase a a_d_ub The decision was made to achieve current compensation.

[0054] As one or more implementation methods, such as Figure 5 As shown, in reactive and unbalanced compensation modes, based on the acquired three-phase active unbalanced current value i x_d_ub and three-phase reactive current value i x_q Sending reverse three-phase active power imbalance current value i to the power grid x_d_ub and three-phase reactive current value i x_q To improve the system power factor and balance the current in each phase of the grid, when the system capacity is limited, priority is given to compensating for three-phase reactive current. The specific process includes:

[0055] Extracting the three-phase reactive current value i x_q The maximum value in the range is used to determine the maximum value of the three-phase reactive current i. max_q If the reactive current value is greater than the set fourth threshold, check if the reactive current value of each phase is greater than the fourth threshold. If so, issue an active power compensation current command i for that phase. x_d_ref The reactive power compensation current command i is 0. x_q_ref It is a negative number of the fourth threshold to achieve current compensation;

[0056] If the reactive current values ​​of other phases are all greater than the fourth threshold, the active power compensation current command i is not satisfied. x_d_ref The reactive power compensation current command i is 0. x_q_ref It is a negative number of the three-phase reactive current value to achieve current compensation;

[0057] If the maximum value of the three-phase reactive current is i max_q If it is less than the set fourth threshold, then based on the fourth threshold and the three-phase reactive current value i x_q Calculate the third phase active reference current value i x_d_tem1 ;

[0058] Determine any phase i x_d_tem1 Greater than |i x_d_ub | Whether it is true or false, if at least one phase is true, then according to the third phase active power reference current value i x_d_tem1 and the three-phase active unbalanced current value i x_d_ub Calculate the three-phase coefficient K x_2 Extracting the three-phase coefficient K x_2 The minimum value in; then the active power compensation current command i x_d_ref The minimum value of the three-phase coefficient K min_2 With the three-phase active unbalanced current value i x_d_ub The negative of the product, reactive power compensation current command i x_q_ref The three-phase reactive current value i x_q The negative number is used to achieve current compensation;

[0059] If none of the three phases are met, then the active power compensation current command i x_d_ref The three-phase active unbalanced current value i x_d_ub The negative number, reactive power compensation current command i x_q_ref The three-phase reactive current value i x_q The negative number is used to achieve current compensation.

[0060] Example 2

[0061] This embodiment provides a device for managing reactive power and imbalance in a three-phase low-voltage power distribution network system.

[0062] like Figure 6 As shown, the reactive power and imbalance control device for a three-phase system of a low-voltage distribution network includes a three-phase current imbalance control controller, which executes the steps in the reactive power and imbalance control method for a three-phase system of a low-voltage distribution network described in Embodiment 1. It also includes an inverter power unit, an LCL filter unit, a circuit breaker, and a load-side current transformer.

[0063] The imbalance control device is connected to the low-voltage side of the transformer through a circuit breaker; the circuit breaker, LCL filter unit and inverter power unit are connected in series in sequence, and the LCL filter unit and inverter power unit are respectively connected to the three-phase current imbalance control controller; the primary side of the load-side current transformer is connected to the load and connected to the low-voltage side, and the secondary side is connected to the three-phase current imbalance control controller.

[0064] As one or more implementation methods, such as Figures 7-8 As shown, the three-phase current imbalance control controller includes: a processor, a sampling module, and an IGBT drive module; the processor is connected to the sampling module and the FPGA module respectively, and the FPGA module is connected to the protection circuit and the IGBT drive module respectively.

[0065] The sampling module acquires the set voltage and current signals and sends them to the processor. The processor samples the voltage and current signals and generates a PWM modulation wave to control the inverter power unit. The PWM modulation wave is then sent to the IGBT drive module.

[0066] The FPGA module performs logical judgments on the drive signals sent by the processor, blocks PWM when the device fails, and implements the logic of first blocking the outer transistor and then locking the inner transistor in a three-level manner.

[0067] The IGBT driver module amplifies the PWM signal to drive the inverter power unit IGBT, and at the same time handles the IGBT short circuit and generates a corresponding signal to be sent to the processor.

[0068] As one or more implementation methods, such as Figures 8-10 As shown, the three-phase current imbalance control controller performs phase-locked loop on the input AC bus voltage to generate the grid voltage phase θ and angular velocity ω. The load-side current is decomposed into fundamental positive-sequence component, fundamental negative-sequence component, and fundamental zero-sequence component by a generalized second-order integrator and a positive-negative-sequence decomposition algorithm. The fundamental positive-sequence component is decomposed and transformed to obtain the fundamental positive-sequence reactive component. A current command is generated based on the sum of the fundamental positive-sequence reactive component, the fundamental negative-sequence component, and the fundamental zero-sequence component. The current command generates a PWM wave through a closed-loop control algorithm, and the PWM wave drives the IGBT.

[0069] like Figure 11 As shown, the imbalance mitigation device employs a dual-loop control strategy. The outer loop is a voltage loop for stabilizing the DC bus, and the inner loop is a current loop, using a direct current control (PR) strategy. The outer loop includes a bus capacitor voltage stabilization loop and a positive and negative bus capacitor voltage equalization loop. To improve grid-connected current quality, grid voltage feedforward control is added.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling reactive power and imbalance in a three-phase low-voltage distribution network system, characterized in that, include: Obtain the three-phase active current and three-phase reactive current values; Based on the given operating mode and the three-phase active current value or three-phase reactive current value, an active current compensation command or a reactive current compensation command is obtained to achieve active current compensation or reactive current compensation. The given operating modes include constant reactive power mode, reactive power compensation mode, unbalanced current compensation mode, unbalanced and reactive power compensation mode, and reactive power and unbalanced compensation mode. In unbalanced and reactive power compensation mode, based on the acquired three-phase active unbalanced current and three-phase reactive current values, reverse three-phase active unbalanced current and three-phase reactive current values ​​are sent to the grid to balance the currents in each phase of the grid and improve the system power factor. When the system capacity is limited, three-phase active unbalanced current is compensated first. The specific process includes: Extract the maximum value among the three-phase active unbalanced current values, determine whether the maximum value of the active unbalanced current is greater than the set third threshold, if so, calculate the third coefficient based on the third threshold and the maximum value of the active unbalanced current; obtain the first three-phase active reference current value based on the third coefficient and the three-phase active unbalanced current values. Based on the third threshold and the first three-phase active reference current value, the second three-phase active reference current value is obtained; Determine whether the second and third phase active reference current values ​​are greater than the three-phase reactive current values. If so, the active compensation current command is the negative of the product of the third coefficient and the three-phase active unbalanced current value, and the reactive compensation current command is the negative of the three-phase reactive current value, in order to achieve current compensation. If the second and third phase active reference current values ​​are less than the three-phase reactive current values, the active compensation current command is the negative of the product of the third coefficient and the three-phase active unbalanced current value, and the reactive compensation current command is determined based on the third threshold, the third coefficient, and the three-phase active unbalanced current value, in order to achieve current compensation. If the maximum value of the active unbalanced current is less than the set third threshold, then the three-phase current compensation command is calculated based on the active unbalanced current value and the reactive unbalanced current value of phase a. It is then determined whether the three-phase current compensation command is greater than the set third threshold. If so, the active compensation current command is the negative of the original three-phase active unbalanced current value, and the reactive compensation current command is the negative of the three-phase reactive unbalanced current value, to achieve current compensation. Otherwise, the active compensation current command is the negative of the original three-phase active unbalanced current value, and the reactive compensation current command is determined based on the third threshold and the active unbalanced current value of phase a, to achieve current compensation. In reactive and unbalanced compensation modes, based on the acquired three-phase active unbalanced current value i x_d_ub and three-phase reactive current value i x_q Sending reverse three-phase active power imbalance current value i to the power grid x_d_ub and three-phase reactive current value i x_q To improve the system power factor and balance the current in each phase of the power grid, when the system capacity is limited, priority is given to compensating the three-phase reactive current.

2. The method for controlling reactive power and imbalance in a three-phase low-voltage distribution network system according to claim 1, characterized in that, In constant reactive power mode, a set three-phase reactive current value is given to send reactive power to the grid, and the output active power compensation current command is zero. It is determined whether the reactive current value of any one of the given phases a, b, and c is greater than the rated reactive current value. If so, the reactive power compensation current command is the rated reactive current value to achieve reactive current compensation; otherwise, the reactive power compensation current command is the set three-phase reactive current value to achieve reactive current compensation.

3. The method for controlling reactive power and imbalance in a three-phase low-voltage distribution network system according to claim 1, characterized in that, In reactive power compensation mode, based on the acquired three-phase reactive current values, it is determined whether the reactive current value of any phase abc is greater than the rated reactive current value. If so, the output active power compensation current command is zero, and the reactive power compensation current command is a negative number of the rated reactive current value to achieve reactive current compensation; otherwise, the output active power compensation current command is zero, and the reactive power compensation current command is a negative number of the original three-phase reactive current value to achieve reactive current compensation.

4. The method for controlling reactive power and imbalance in a three-phase low-voltage distribution network system according to claim 1, characterized in that, In unbalanced current compensation mode, based on the acquired three-phase active unbalanced current values ​​and three-phase reactive unbalanced current values, reverse three-phase active unbalanced current values ​​and three-phase reactive unbalanced current values ​​are sent to the grid to balance the currents in each phase of the grid; when the system capacity is limited, three-phase active unbalanced current is compensated first, and the specific process includes: Extract the maximum value of the three-phase active unbalanced current, and determine whether the maximum value of the active unbalanced current is greater than the set first threshold. If so, calculate the first coefficient based on the first threshold and the maximum value of the active unbalanced current. The negative number of the product of the first coefficient and the three-phase active unbalanced current is the active compensation current command, and the reactive compensation current command is zero, so as to realize active current compensation. Otherwise, based on the three-phase active unbalanced current value and the three-phase reactive unbalanced current value, calculate the three-phase current compensation command and determine whether the three-phase current compensation command is greater than the set second threshold; if so, calculate the second coefficient based on the second threshold, the active unbalanced current value of phase a, and the reactive unbalanced current value of phase a; where the active compensation current command is the original three-phase active unbalanced current value; the negative number of the product of the second coefficient and the three-phase reactive unbalanced current value is the reactive compensation current command, and current compensation is achieved based on the active compensation current command and the reactive compensation current command. Otherwise, the active power compensation current command is the original three-phase active power imbalance current value, and the reactive power compensation current command is the original three-phase reactive power imbalance current value, so as to achieve current compensation.

5. The method for controlling reactive power and imbalance in a three-phase low-voltage distribution network system according to claim 4, characterized in that, The three-phase active unbalanced current value is obtained by the difference between the three-phase active current value and the average value of the three-phase active current, and the three-phase reactive unbalanced current value is obtained by the difference between the three-phase reactive current value and the average value of the three-phase reactive current.

6. The method for controlling reactive power and imbalance in a three-phase low-voltage distribution network system according to claim 1, characterized in that, Extracting the three-phase reactive current value i x_q The maximum value in the range is used to determine the maximum value of the three-phase reactive current. If the reactive current value is greater than the set fourth threshold, check if the reactive current value of each phase is greater than the fourth threshold. If so, issue an active power compensation current command for that phase. The reactive power compensation current command is 0. It is a negative number of the fourth threshold to achieve current compensation; If the reactive current values ​​of other phases are all greater than the fourth threshold, the active power compensation current command is not satisfied. The reactive power compensation current command is 0. It is a negative number of the three-phase reactive current value to achieve current compensation; If the maximum value of the three-phase reactive current If it is less than the set fourth threshold, then based on the fourth threshold and the three-phase reactive current value i x_q Calculate the third phase active reference current value. ; Determine any phase Greater than Whether it is valid or not, if at least one phase is valid, then based on the third phase active power reference current value. and the three-phase active unbalanced current value i x_d_ub Calculate the three-phase coefficient Extracting three-phase coefficients The minimum value in the range; then the active power compensation current command. The minimum value of the three-phase coefficient With the three-phase active unbalanced current value i x_d_ub The negative of the product indicates the reactive power compensation current command. The three-phase reactive current value i x_q The negative number is used to achieve current compensation; If none of the three phases are met, then the active power compensation current command will be issued. The three-phase active unbalanced current value i x_d_ub Negative numbers, reactive power compensation current command The three-phase reactive current value i x_q The negative number is used to achieve current compensation.

7. A device for controlling reactive power and imbalance in a three-phase low-voltage distribution network system, characterized in that, The system includes a three-phase current imbalance control controller, which performs the steps of the reactive power and imbalance control method for a three-phase system in a low-voltage distribution network as described in any one of claims 1-6, and further includes an inverter power unit, an LCL filter unit, a circuit breaker, and a load-side current transformer. The imbalance control device is connected to the low-voltage side of the transformer through a circuit breaker; the circuit breaker, LCL filter unit and inverter power unit are connected in series in sequence, and the LCL filter unit and inverter power unit are respectively connected to the three-phase current imbalance control controller; the primary side of the load-side current transformer is connected to the load and connected to the low-voltage side, and the secondary side is connected to the three-phase current imbalance control controller.

8. The reactive power and imbalance control device for a three-phase low-voltage distribution network system according to claim 7, characterized in that, The three-phase current imbalance control controller includes: a processor, a sampling module, and an IGBT drive module; the processor is connected to the sampling module and the FPGA module respectively, and the FPGA module is connected to the protection circuit and the IGBT drive module respectively. The sampling module acquires the set voltage and current signals and sends them to the processor. The processor samples the voltage and current signals and generates a PWM modulation wave to control the inverter power unit. The PWM modulation wave is then sent to the IGBT drive module. The FPGA module performs logical judgments on the drive signals sent by the processor, blocks PWM when the device fails, and implements the logic of first blocking the outer transistor and then locking the inner transistor in a three-level manner. The IGBT driver module amplifies the PWM signal to drive the inverter power unit IGBT, and at the same time handles the IGBT short circuit and generates a corresponding signal to be sent to the processor.

9. The reactive power and imbalance control device for a three-phase low-voltage distribution network system according to claim 7, characterized in that, The three-phase current imbalance control controller performs phase-locking on the input AC bus voltage to generate the grid voltage phase θ and angular velocity ω. The load-side current is decomposed into fundamental positive-sequence component, fundamental negative-sequence component and fundamental zero-sequence component by a generalized second-order integrator and positive-negative-sequence decomposition algorithm. The fundamental positive sequence component is decomposed and transformed to obtain the fundamental positive sequence reactive component. A current command is generated based on the sum of the fundamental positive sequence reactive component, the fundamental negative sequence component, and the fundamental zero sequence component. The current command generates a PWM wave through a closed-loop control algorithm, and the PWM wave drives the IGBT.

Images