A method, device and medium for low-voltage area three-phase imbalance and low-voltage collaborative governance based on multiple converters

Abstract

The present application relates to the technical field of low-voltage power distribution network power quality treatment, and discloses a low-voltage transformer area three-phase imbalance and low-voltage collaborative treatment method, equipment and medium based on multiple converters, which comprises the following steps: constructing a collaborative treatment architecture through two flexible interconnected low-voltage transformer area head-end voltage source converters and tail-end series compensation converters, and establishing a power interaction channel through the common DC bus of the three converters. Among them, VSC1 adopts a positive, negative and zero sequence power composite control strategy to maintain the stability of the DC bus voltage and eliminate three-phase imbalance power; VSC2 realizes dynamic mutual aid of three-phase power between transformer areas; and VSC3 dynamically improves the tail-end voltage in combination with 3D-SVPWM modulation. The present application eliminates three-phase imbalance current while improving voltage quality through collaborative control of multiple converters, and has fast response, high compensation accuracy, strong power supply reliability, and effectively solves the three-phase load imbalance and low-voltage composite power quality problem of low-voltage distribution transformer areas.

Description

Technical Field

[0001] This invention relates to the field of power quality management technology for low-voltage distribution networks, and in particular to a method, equipment, and medium for the coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters. Background Technology

[0002] In low-voltage distribution networks, due to the wide distribution of power users and the significant spatial and temporal differences in load characteristics, the connection of a large number of single-phase loads, nonlinear loads, and impulsive loads inevitably leads to the system operating in a state of three-phase imbalance for extended periods. Such loads not only cause fundamental current / voltage imbalance but also generate complex power quality problems such as harmonic pollution, voltage drops, and fluctuations. Specifically, current imbalance increases active power losses in the grid, voltage imbalance causes reverse-sequence torque in rotating machines, and significantly increases the risk of transformer overload, capacitor bank resonance, and maloperation of protection systems. Of particular concern is the widespread voltage drop problem at the end of low-voltage distribution areas with long-distance power supply. Traditional mechanical voltage regulators, due to their slow response speed and low adjustment accuracy, are unable to adapt to dynamic load changes. While existing static var compensators (SVCs) can partially improve the power factor, they are limited by fixed capacitor bank configurations and open-loop control methods, making it impossible to achieve phase-by-phase dynamic compensation. For example, parallel capacitor voltage regulation schemes, although they can adjust voltage through capacitor switching, suffer from aggravated voltage fluctuations due to their stepped compensation characteristics and lack of ability to suppress neutral line overload current.

[0003] The three-phase imbalance problem on the low-voltage distribution side is becoming increasingly serious, and the voltage drop at the end of the distribution area has become a prominent problem that urgently needs to be solved in the operation of the low-voltage distribution network. If the low-voltage distribution network is in a state of three-phase imbalance for a long time, it will have a significant negative impact on the economic operation and safe and stable operation of the low-voltage distribution network. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a method for the coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters. It can achieve power mutual assistance between distribution areas by controlling the converters, thereby solving the three-phase imbalance problem in each distribution area and the low voltage problem at the end of the distribution area.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters, comprising: measuring the real-time phase current and voltage of the three phases at the beginning of the low-voltage distribution network, calculating the real-time load of the three phases, and determining whether the real-time load of the three phases is balanced; when the load is unbalanced, separating the positive and negative zero-sequence of the three-phase unbalanced current at the beginning of the three phases, calculating the negative zero-sequence power command, balancing the load through reverse compensation, and calculating the active and reactive power output commands of each phase line after balancing; measuring the real-time phase current and voltage at the end of the low-voltage distribution network of the long transmission line to determine whether the phase voltage reaches the rated voltage level; when the rated voltage level is not reached, calculating the power of each of the three phases at the end, and subtracting it from the power of each phase when the load voltage is the rated voltage to obtain the active and reactive power commands to be compensated; based on the active and reactive power control commands, selecting the corresponding control to realize the self-management of three-phase imbalance and low voltage in the distribution area and the coordinated power management between distribution areas.

[0007] As a preferred embodiment of the method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters described in this invention, the low-voltage distribution network includes a converter parallel system, DC interconnection, and a converter series system. The parallel converter system consists of two three-phase four-bridge converters connected back-to-back via a common DC bus. In the parallel converter system, the two low-voltage distribution stations are flexibly interconnected via a common DC bus. The converter series system includes a converter connected in series with the end of the low-voltage distribution network via a coupling transformer, and the DC side of the converter is connected to a common DC bus.

[0008] The flexible interconnection includes embedding parallel converter devices into two low-voltage distribution networks. The parallel converter devices are respectively connected to the starting ends of the two low-voltage distribution substations through LC filters. The series converter devices are connected to the end ends of the low-voltage distribution networks through LC filters and coupling transformers.

[0009] As a preferred embodiment of the method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters described in this invention, the method for determining whether the three-phase real-time load is balanced includes calculating the three-phase real-time load by measuring the real-time phase current and real-time phase voltage of each phase at the beginning of the low-voltage distribution network. Three-phase real-time load balancing ensures that the power of the three phases A, B, and C at the beginning of the transformer substation is equal by injecting or absorbing power from the substation through the converter. in, These are the active power of phases A, B, and C, respectively. These are the reactive power values ​​for phases A, B, and C, respectively.

[0010] As a preferred embodiment of the three-phase imbalance and low voltage co-management method for low-voltage distribution areas based on multiple converters described in this invention, the flexible interconnection further includes: designating the converter connected to the beginning of distribution area I as VSC1, the series converter connected to the end of distribution area I as VSC3, and the converter connected to the beginning of distribution area II as VSC2.

[0011] As a preferred embodiment of the multi-converter-based method for co-managing three-phase imbalance and low voltage in low-voltage distribution areas according to the present invention, the converter connected to the beginning of distribution area I, VSC1, includes: real-time measurement and calculation of the three-phase imbalance power at the beginning of the distribution area; separation of the three-phase imbalance current into positive, negative, and zero-sequence currents to obtain the negative-sequence and zero-sequence currents at the beginning of the distribution area; and control of the DC bus voltage U via a PI controller. dc The positive sequence current component is obtained, and the positive sequence, negative sequence, and zero sequence current components are transformed by coordinate transformation to obtain the reference values ​​of the three-phase current. The control signal for VSCI is obtained through MPC current inner loop control and PWM modulation, enabling the converter to stabilize the DC bus voltage and compensate for the unbalanced power in the transformer area I.

[0012] As a preferred embodiment of the method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters described in this invention, the converter connected to the beginning of distribution area II, VSC2, includes: real-time measurement and calculation of the unbalanced power at the beginning of the distribution area; multiplying the sum of the active and reactive loads of the three-phase unbalanced power at the beginning of the distribution area by the active and reactive power balance coefficients respectively to obtain the compensation power reference value for each phase; obtaining the dq component of the current reference value by passing the reference value and the actual value through a PI controller; and obtaining the reference value of the three-phase current through coordinate transformation. The modulation signal is generated by the MPC current inner loop and PWM modulation to achieve three-phase power balance at the head end of transformer area II.

[0013] As a preferred embodiment of the three-phase imbalance and low voltage co-management method for low-voltage distribution areas based on multiple converters described in this invention, the compensation power reference value includes the active and reactive power of each phase calculated according to the single-phase generalized instantaneous power theory. The calculated three-phase real-time load , Summing yields the total active power of the three-phase load. Total reactive load Then sum the active power of the three-phase load. Multiplying the active power balance factor m / 3 by the active power output of each phase line after balance is obtained. Sum of the three-phase loads Multiplying the reactive power output by the reactive power balance factor n / 3 yields the balanced reactive power output of each phase of the line. The balance coefficients m and n are related to the power limit of the converter.

[0014] As a preferred embodiment of the multi-converter-based method for the coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas according to the present invention, wherein: the series converter connected to the end of distribution area I is VSC3, which includes measuring the voltage at the end of distribution area I and calculating the power at the end of distribution area I, and comparing it with their respective rated voltages U ref Power compensation reference values ​​are generated through power calculation; A phase-separated power control strategy is adopted, and the reference voltages of the three phases A, B, and C are obtained through the outer power loop, voltage loop, and inner current loop. The modulation signal of converter VSC3 is generated by 3D-SVPWM modulation, and the dynamic voltage boost of the I terminal of the transformer area is realized by VSC3.

[0015] The present invention provides a computer device, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of a method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters.

[0016] The present invention provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of a method for the coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters are implemented.

[0017] The beneficial effects of this invention are as follows: This invention addresses the three-phase imbalance and low voltage problems in three-phase four-wire low-voltage distribution networks using multiple converters, offering flexibility, speed, and controllability. This is primarily manifested in the flexible interconnection between and within distribution areas via a common DC bus. When addressing three-phase imbalance and low voltage, VSC1 initiates the process, stabilizing the capacitor voltage to provide a stable and reliable DC voltage to the other converters while simultaneously compensating for the negative-sequence and zero-sequence currents in the distribution area, thus mitigating the three-phase imbalance. VSC2 can address the three-phase imbalance power in its distribution area by adjusting its compensation power reference value. Within constraints, changing the values ​​of m and n adjusts the magnitude of power mutual assistance. Simultaneously, a converter is connected in series at the end of the distribution area to dynamically compensate for the voltage at the end. Compared to traditional voltage regulation via capacitor switching, this method offers faster response and allows for real-time adjustment of the compensation power based on changes in the end load. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The control flowchart of a method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters is provided in one embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of a converter VSC1 control scheme for a method of coordinated management of three-phase imbalance and low voltage in low-voltage areas based on multiple converters, provided as an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of a converter VSC2 control scheme for a method of coordinated management of three-phase imbalance and low voltage in low-voltage substations based on multiple converters, provided as an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of a converter VSC3 control scheme for a method of coordinated management of three-phase imbalance and low voltage in low-voltage substations based on multiple converters, provided as an embodiment of the present invention.

[0023] Figure 5 This is a schematic diagram of the overall topology of a method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters, provided in one embodiment of the present invention.

[0024] Figure 6 The power waveform diagram of the distribution area I is provided as an embodiment of the present invention for a method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters.

[0025] Figure 7 The power waveform diagram of substation II is provided as an embodiment of the present invention for a method for coordinated management of three-phase imbalance and low voltage in low-voltage substations based on multiple converters.

[0026] Figure 8 The voltage waveform diagram at the end of transformer area I is provided as an embodiment of the present invention for a method for coordinated management of three-phase imbalance and low voltage in low-voltage transformer areas based on multiple converters. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0028] Example 1, referring to Figure 1 This is the first embodiment of the present invention, which provides a method for the coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters, including: S1: Calculate the real-time three-phase load by measuring the real-time phase current and voltage of the three phases at the beginning of the low-voltage distribution network, and determine whether the real-time three-phase load is balanced.

[0029] S2: When the load is unbalanced, the three-phase unbalanced current at the beginning of the three phases is separated into positive and negative zero sequence. The negative zero sequence power command is obtained by calculation. The load is balanced by reverse compensation, and the active and reactive power output commands of each phase line after balance are calculated.

[0030] S3: By measuring the real-time phase current and voltage at the end of the low-voltage distribution network of a long transmission line, it can be determined whether the phase voltage has reached the rated voltage level.

[0031] S4: When the rated voltage level is not reached, calculate the power of each of the three phases at the end and subtract it from the power of each phase when the load voltage is the rated voltage to obtain the active and reactive power command to be compensated.

[0032] S5: Based on the active and reactive power control commands, select the corresponding control to realize the self-control of three-phase imbalance and low voltage in the transformer area, as well as the coordinated power cooperation between transformer areas.

[0033] Example 2, refer to Figures 2-6 As an embodiment of the present invention, based on the above embodiment, a method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters is provided.

[0034] Furthermore, in this embodiment of the application, step S1 involves measuring the real-time phase current and voltage of the three phases at the beginning of the low-voltage distribution network, calculating the real-time three-phase load, and determining whether the real-time three-phase load is balanced. The specific steps include: Low-voltage distribution networks include parallel converter systems, DC interconnection, and series converter systems; The converter parallel system consists of two three-phase four-bridge converters connected back-to-back via a common DC bus. In the converter parallel system, two low-voltage distribution substations are flexibly interconnected via a common DC bus. The converter series system includes a converter connected in series with the end of the low-voltage distribution network via a coupling transformer, and the DC side of the converter is connected to a common DC bus.

[0035] Flexible interconnection includes embedding parallel converter devices into two low-voltage distribution networks. The parallel converter devices are respectively connected to the beginning of the two low-voltage distribution substations through LC filters; the series converter devices are connected to the end of the low-voltage distribution network through LC filters and coupling transformers.

[0036] The converter connected to the beginning of transformer area I is designated as VSC1, the series converter connected to the end of transformer area I is designated as VSC3, and the converter connected to the beginning of transformer area II is designated as VSC2.

[0037] Reference Figure 5 Connect parallel converter VSC1 to the beginning of transformer area I, connect parallel converter VSC2 to the beginning of transformer area II, and connect converter VSC3C in series to the end of transformer area I (arrow direction is positive reference direction). Multiple converters are flexibly interconnected through a common DC bus voltage.

[0038] Furthermore, in this embodiment of the application, when the load is unbalanced, step S2 involves separating the positive and negative zero-sequence unbalanced currents at the three-phase starting point, calculating the negative zero-sequence power command, balancing the load through reverse compensation, and calculating the active and reactive power output commands for each phase of the line after balancing. The specific steps include: The three-phase real-time load is calculated by measuring the real-time phase current and real-time phase voltage of each phase at the beginning of the low-voltage distribution network. ; Three-phase real-time load balancing ensures that the power of the three phases A, B, and C at the beginning of the transformer substation is equal by injecting or absorbing power from the substation through the converter. in, These are the active power of phases A, B, and C, respectively. These are the reactive power values ​​for phases A, B, and C, respectively.

[0039] Furthermore, in this embodiment, step S3 determines whether the phase voltage has reached the rated voltage level by measuring the real-time phase current and voltage at the end of the low-voltage distribution network of the long transmission line. The specific steps include: The three-phase unbalanced power at the beginning of the transformer substation is measured and calculated in real time. The three-phase unbalanced current is separated into positive, negative, and zero sequence to obtain the negative and zero sequence currents at the beginning of the substation. The DC bus voltage U is then controlled by a PI controller. dcUpon receiving the active power command, the positive-sequence, negative-sequence, and zero-sequence current components are transformed using coordinates to obtain reference values ​​for the three-phase current. The VSCI control signal is obtained through MPC current inner-loop control and PWM modulation, enabling the converter to stabilize the DC bus voltage and compensate for unbalanced power in transformer substation I.

[0040] Reference Figure 2 According to the generalized instantaneous power theory of single phase, the single-phase power of the system can be solved as shown in the following equation. In the formula: , These are the two orthogonal components of a single-phase voltage in the αβ stationary coordinate system, typically constructed by delaying the original single-phase voltage by 90°. In phase with the original voltage, Lag 90°; , These are the two orthogonal components of a single-phase current in the αβ coordinate system, constructed similarly to those of a voltage. In phase with the original current, Lag 90°; P is instantaneous active power, Q is instantaneous reactive power.

[0041] The three-phase unbalanced current can be decomposed into positive, negative, and zero-sequence currents. The positive-sequence current and positive-sequence voltage of phases A, B, and C can be calculated using the above formula. The active and reactive components generated by the positive-sequence components of phases A, B, and C are the same, and the average active (or reactive) power generated by the positive-sequence voltage and current of each phase is equal. The imbalance of three-phase power (i.e., the unequal average power of each phase) is caused by the negative-sequence and zero-sequence voltage and current components. According to the mathematical model of the three-phase four-arm converter in the dq-0 coordinate system, the current component on the d-axis of the positive-sequence component corresponds to the active component of the output current. A DC quantity is given through the d-axis to maintain the stability of the DC network. Therefore, the converter VSC1 maintains the stability of the DC bus voltage through the positive-sequence power component, realizes the power mutual assistance between transformer substations, and thus solves the problem of voltage exceeding the limit in the transformer substation; by compensating for the negative-sequence and zero-sequence power in the transformer substation, it solves the problem of three-phase imbalance in the transformer substation.

[0042] Furthermore, in this embodiment, when the rated voltage level is not reached in step S4, the power of each of the three phases at the end is calculated, and the difference between this power and the power of each phase when the load voltage is at the rated voltage is obtained to obtain the active and reactive power commands to be compensated. The specific steps include: Reference Figure 3The system measures and calculates the unbalanced power at the beginning of the transformer substation in real time. The sum of the active and reactive power of the three-phase unbalanced power at the beginning of the substation is multiplied by the active and reactive power balance coefficients to obtain the compensation power reference value for each phase. The reference value and the actual value are then compared with the actual value to obtain the dq component of the current reference value. The reference values ​​of the three-phase current are obtained through coordinate transformation. A modulation signal is generated through the MPC current inner loop and PWM modulation to achieve three-phase power balance at the beginning of transformer substation II.

[0043] Assume the three-phase power output by the system is as follows: in, denoted as complex power for phases A, B, and C, respectively, where j is the imaginary unit.

[0044] The total three-phase power output by the system is: in, This represents the total power of the three phases.

[0045] To achieve a balanced three-phase load, compensation is needed for the unbalanced three-phase loads to ensure a balanced three-phase power output from the system. The balanced three-phase power output of the system is given by the following formula: Where: m is the active power mutual assistance coefficient between stations, n is the reactive power mutual assistance coefficient, and P sa P sb P sc These represent the target active power (Q) of phases A, B, and C of the compensated system side. sa Q sb Q sc These are the target reactive power of phases A, B, and C on the system side after compensation.

[0046] Therefore, the converter compensation reference value for three-phase imbalance is: Among them, P xref Q is the active power compensation reference command for phase X (phase A, B, or C). xref For the reactive power compensation reference command of phase X (phase A, B, or C), the values ​​of m and n are subject to the following constraints: Capacity constraints: Transformer capacity constraints: In the formula: This is the sum of the three-phase active power output of the transformer substation; S is the sum of the three-phase reactive power of the transformer area. N This is the rated apparent power of the transformer.

[0047] Converter VSC capacity constraints: In the formula: This is the sum of the three-phase active power output by the converter; This is the sum of the three-phase reactive power of the converter. This represents the rated apparent power capacity of the converter VSC.

[0048] Furthermore, in this embodiment, step S5, based on the active and reactive power control commands, selects the corresponding control to achieve self-regulation of three-phase imbalance and low voltage management in the transformer area, as well as power coordination between transformers. Specific steps include: Measure the voltage at the end of transformer area I and calculate the power at the end of the transformer area, comparing it with their respective rated voltages (U). ref Power compensation reference values ​​are generated through power calculation. and A phase-separated power control strategy is adopted, and the reference voltages of the three phases A, B, and C are obtained through the outer power loop, voltage loop, and inner current loop. The modulation signal of the converter VSC3 is generated by 3D-SVPWM modulation, and the dynamic voltage boost of the I end of the transformer area is realized through VSC3.

[0049] Reference Figure 4 By measuring the three-phase voltages (A, B, and C) at the series connection point and comparing them with the rated phase voltages, if one or more of the measured three-phase voltages (A, B, and C) are lower than the rated phase voltages, due to series compensation, there will be no difference in the phase currents before and after the series connection point. This is achieved through the following formula: The active and reactive power of each of the three phases A, B, and C is calculated and compared with the active and reactive power calculated from the actual voltage to obtain the reference values ​​for active and reactive power of each phase. Specifically, the power loop tracks the active and reactive power reference values ​​and active and reactive power compensation values ​​using a PI controller to obtain the d-axis and q-axis reference values ​​for the voltage loop. The voltage loop then decouples the d and q voltage reference values ​​from the actual d and q voltage values ​​using a PI controller to obtain the d and q current reference values ​​for the current loop. The current loop then decouples the d and q current reference values ​​from the actual d and q current values ​​using a PI controller to obtain the d and q values ​​for each of the three phases A, B, and C. Reference signals for each of the three phases A, B, and C are obtained through coordinate transformation, and the drive signal for VSC3 is obtained through 3DSVPWM modulation.

[0050] Example 3 is the third embodiment of the present invention, which differs from the previous two embodiments in that: This embodiment also provides an electronic device applicable to a situation of coordinated management of three-phase imbalance and low voltage in a low-voltage distribution area based on multiple converters, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the method for coordinated management of three-phase imbalance and low voltage in a low-voltage distribution area based on multiple converters as proposed in the above embodiment.

[0051] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements a method for the coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters, as proposed in the above embodiments.

[0052] The storage medium proposed in this embodiment and the method for co-managing three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0053] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0054] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for the coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters, characterized in that: include, By measuring the real-time phase current and voltage of the three phases at the beginning of the low-voltage distribution network, the real-time load of the three phases is calculated, and it is determined whether the real-time load of the three phases is balanced. When the load is unbalanced, the three-phase unbalanced current at the beginning of the three phases is separated into positive and negative zero sequence. The negative zero sequence power command is obtained by calculation. The load is balanced by reverse compensation, and the active and reactive power output commands of each phase line after balance are calculated. By measuring the real-time phase current and voltage at the end of the low-voltage distribution network of a long transmission line, it can be determined whether the phase voltage has reached the rated voltage level. When the rated voltage level is not reached, the power of each of the three phases at the end is calculated and the difference between the power of each phase when the load voltage is the rated voltage is obtained to obtain the active and reactive power command to be compensated. Based on the active and reactive power control commands, the corresponding control is selected to realize the self-control of three-phase imbalance and low voltage in the transformer area, as well as the coordinated power cooperation between transformer areas.

2. The method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters as described in claim 1, characterized in that: The low-voltage distribution network includes a parallel converter system, DC interconnection, and a series converter system. The parallel converter system consists of two three-phase four-bridge converters connected back-to-back via a common DC bus. In the parallel converter system, the two low-voltage distribution stations are flexibly interconnected via a common DC bus. The converter series system includes a converter connected in series with the end of the low-voltage distribution network via a coupling transformer, and the DC side of the converter is connected to a common DC bus. The flexible interconnection includes embedding parallel converter devices into two low-voltage distribution networks. The parallel converter devices are respectively connected to the starting ends of the two low-voltage distribution substations through LC filters. The series converter devices are connected to the end ends of the low-voltage distribution networks through LC filters and coupling transformers.

3. The method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters as described in claim 2, characterized in that: The determination of whether the three-phase real-time load is balanced includes calculating the three-phase real-time load by measuring the real-time phase current and real-time phase voltage of each phase at the beginning of the low-voltage distribution network. Three-phase real-time load balancing ensures that the power of the three phases A, B, and C at the beginning of the transformer substation is equal by injecting or absorbing power from the substation through the converter. in, These are the active power of phases A, B, and C, respectively. These are the reactive power values ​​for phases A, B, and C, respectively.

4. The method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters as described in claim 3, characterized in that: The flexible interconnection also includes designating the converter connected to the beginning of transformer area I as VSC1, the series converter connected to the end of transformer area I as VSC3, and the converter connected to the beginning of transformer area II as VSC2.

5. The method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters as described in claim 4, characterized in that: The converter connected to the beginning of transformer area I is VSC1. It measures and calculates the three-phase unbalanced power at the beginning of transformer area I in real time, separates the three-phase unbalanced current into positive, negative, and zero-sequence currents to obtain the negative-sequence and zero-sequence currents at the beginning of transformer area I, and controls the DC bus voltage U through a PI controller. dc The positive sequence current component is obtained, and the positive sequence, negative sequence, and zero sequence current components are transformed by coordinate transformation to obtain the reference values ​​of the three-phase current. The control signal for VSCI is obtained through MPC current inner loop control and PWM modulation, enabling the converter to stabilize the DC bus voltage and compensate for the unbalanced power in the transformer area I.

6. The method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters as described in claim 5, characterized in that: The converter connected to the beginning of transformer area II is VSC2. It measures and calculates the unbalanced power at the beginning of transformer area in real time. The sum of the active and reactive loads of the three-phase unbalanced power at the beginning of transformer area is multiplied by the active and reactive power balance coefficients to obtain the compensation power reference value of each phase. The reference value and the actual value are used to obtain the dq component of the current reference value through a PI controller. The reference value of the three-phase current is obtained through coordinate transformation. The modulation signal is generated by the MPC current inner loop and PWM modulation to achieve three-phase power balance at the head end of transformer area II.

7. The method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters as described in claim 6, characterized in that: The compensation power reference value includes the active and reactive power of each phase calculated based on the single-phase generalized instantaneous power theory. The summation of the calculated three-phase real-time loads yields the total active power of the three-phase loads. Total reactive load Then sum the active power of the three-phase load. Multiplying the active power balance factor m / 3 by the active power output of each phase line after balance is obtained. Sum of the three-phase loads Multiplying the reactive power output by the reactive power balance factor n / 3 yields the balanced reactive power output of each phase of the line. The balance coefficients m and n are related to the power limit of the converter.

8. The method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters as described in claim 7, characterized in that: The series converter connected to the end of transformer area I is VSC3. It measures the voltage at the end of transformer area I and calculates the power at the end of the transformer area, comparing it with their respective rated voltages U. ref Power compensation reference values ​​are generated through power calculation; A phase-separated power control strategy is adopted, and the reference voltages of the three phases A, B, and C are obtained through the outer power loop, voltage loop, and inner current loop. The modulation signal of converter VSC3 is generated by 3D-SVPWM modulation, and the dynamic voltage boost of the I terminal of the transformer area is realized by VSC3.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters, as described in any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for coordinated management of three-phase imbalance and low voltage in low-voltage distribution areas based on multiple converters, as described in any one of claims 1 to 8.

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