A power distribution network end three-phase voltage imbalance treatment method and device
Patent Information
- Application Number
- CN202611300945.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-26
- Publication Date
- 2026-10-27
AI Technical Summary
硬件架构简化，安装运维便捷。装置仅需接入三相四线一次线路，省去了电流互感器与二次电流布线，大幅降低现场施工难度与成本，同时消除了 CT 二次开路的安全隐患，尤其适合配网末端分散台区的批量改造。
Smart Images
Figure CN122992875A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of power quality management technology for low-voltage distribution networks, specifically relating to a three-phase voltage imbalance management method and corresponding compensation management device based on voltage sampling closed-loop control without the need for external current transformers. Background Technology
[0002] Low-voltage distribution networks commonly suffer from uneven single-phase load distribution and highly random load switching at the end, which easily leads to three-phase voltage imbalance. Three-phase voltage imbalance exacerbates transformer losses, increases line active power losses, and causes some phase voltages to be too high or too low, affecting the normal operation of electrical equipment and, in severe cases, causing equipment damage and shortened lifespan.
[0003] Currently, most mainstream three-phase imbalance active mitigation equipment adopts a current compensation architecture. It collects the three-phase current signals of the line load through current transformers, calculates the negative-sequence and zero-sequence compensation components, and then controls the converter to output the corresponding current to achieve imbalance mitigation. This type of technical solution has the following drawbacks in engineering applications: First, on-site construction requires the installation of multiple current transformers and the laying of secondary control cables, resulting in a large workload, complex wiring, and high overall construction costs. Furthermore, current transformers pose a safety hazard of secondary open circuits, requiring a high level of expertise from on-site maintenance personnel, which is not conducive to the batch transformation of distributed network endpoints. Second, the control strategy is relatively simple and cannot flexibly set mitigation priorities according to the actual operating conditions of the distribution area. The core requirement for some distribution areas is to suppress single-phase voltage exceeding limits, allowing for slight three-phase imbalance; the core requirement for other distribution areas is to control the three-phase imbalance within the assessment indicators, allowing for slight voltage fluctuations within the acceptable range. Existing equipment struggles to accommodate multiple mitigation objectives, resulting in insufficient scenario adaptability. Third, conventional voltage closed-loop PI controllers suffer from integral accumulation drift problems. When the actual voltage is already within the acceptable range, the integral of the PI controller cannot automatically return to zero. The equipment will continue to output unnecessary compensation current, generating additional line losses and device losses, failing to achieve both the treatment effect and the energy saving and loss reduction target. Fourth, traditional negative-sequence and zero-sequence current compensation schemes are primarily designed to offset unbalanced currents. However, they are not targeted enough for voltage amplitude imbalances caused by differences in line impedance voltage drops at the end of the distribution network, resulting in limited voltage regulation effects.
[0004] Therefore, developing a three-phase voltage imbalance mitigation solution that only collects three-phase four-wire voltage signals, requires no external current transformers, has multiple selectable control strategies, and can automatically converge to the minimum compensation power in steady state has high engineering application value. Summary of the Invention
[0005] Purpose of the invention The purpose of this invention is to address the shortcomings of existing technologies and provide a method and device for managing three-phase voltage imbalance at the end of a distribution network. On the one hand, it simplifies on-site installation by eliminating the need for current transformers and secondary wiring through a pure voltage sampling architecture. On the other hand, it adapts to the management needs of different distribution areas through a multi-mode control strategy and optimizes the PI control logic to achieve steady-state minimum power output, thereby reducing line and device losses while managing three-phase voltage imbalance.
[0006] Technical solution To achieve the above objectives, the present invention adopts the following technical solution: I. A method for mitigating three-phase voltage imbalance at the end of a distribution network
[0007] The method includes the following steps: S1, Voltage Sampling: Real-time acquisition of the three-phase four-wire instantaneous voltage signal at the common access point of the distribution network. S2, Parameter Calculation: Calculation of the effective value of the three-phase voltage based on the acquired instantaneous voltage signal. , , Simultaneously, calculate the current three-phase voltage imbalance. S3, Pattern Recognition and Target Voltage Calculation: Read the user-configured operating modes, which include four types: performance priority mode, voltage priority mode, balance priority mode, and compatibility mode; according to the calculation rules of the corresponding mode, solve for the voltage regulation target values of phases A, B, and C respectively. , , .
[0008] The specific calculation rules for the four types of working modes are as follows: Performance-priority mode: Calculate the average value of three-phase voltages The three-phase target voltage is automatically set to the average value, i.e. , , This mode aims for complete three-phase voltage balance as its ultimate goal, prioritizing the balance of the three-phase voltage.
[0009] Voltage priority mode: Reads the user-preset fixed voltage upper limit. Lower voltage limit Perform the determination phase by phase: if the current phase voltage is greater than... The target voltage for that phase is then taken as: If the current phase voltage is less than The target voltage for that phase is then taken as: If the current phase voltage is between and If the voltage is within the acceptable range, the target voltage for that phase is equal to the actual voltage of the current phase, and that phase does not actively perform adjustment. This mode prioritizes ensuring that the voltage of each phase is within the acceptable range, and allows for a certain degree of three-phase imbalance under the premise that the voltage meets the standard, so as to meet the voltage qualification requirements with the minimum compensation power.
[0010] Balance Priority Mode: Reads the user-preset three-phase imbalance limit. First, based on the current average three-phase voltage... Reverse driving state voltage threshold: , After obtaining the dynamic voltage upper and lower limits, the voltage regulation target for each phase is calculated phase by phase according to the judgment rules of the voltage priority mode described above. This mode prioritizes the control of the three-phase imbalance index, and the voltage threshold adaptively floats with the current voltage level, always keeping the imbalance within the set limit.
[0011] Compatibility mode: Reads user-defined fixed voltage upper and lower limits. , And the unbalance limit Kunb; first, according to the calculation logic of the balance priority mode, the dynamic voltage threshold is obtained. , Then, the two sets of thresholds are merged and filtered to determine the final effective voltage upper limit. The lower effective voltage limit is the minimum of the two upper limits. The maximum of the two lower limits is taken; after obtaining the combined upper and lower voltage limits, the target voltage of each phase is calculated phase by phase according to the judgment rules of the voltage priority mode. The compatibility mode satisfies both the single-phase voltage over-limit constraint and the three-phase imbalance index constraint, and takes the more stringent threshold of the two conditions as the control boundary, while ensuring that the voltage is qualified and the balance meets the standard.
[0012] S4. Closed-loop current command generation: Calculate the deviation between the actual voltage and the target voltage of each phase, denoted as... ,in ; to measure the voltage deviation of each phase The command is sent to the corresponding phase's PI controller to output the effective value of the compensation current. Current command The positive and negative signs represent the phase direction: When positive, the phase of the compensation current is the same as the phase of the grid voltage of this phase; When the value is negative, the phase of the compensation current is 180° out of phase with the phase of the grid voltage. The control cycle is synchronized with the grid voltage cycle.
[0013] S5. Instantaneous Current Decomposition and Output: This involves converting the current command in RMS form... The instantaneous current command for each sampling period is decomposed according to the voltage phase of the corresponding phase. The output amplitude of the control power converter unit is... Phase-matching compensation current. Depending on the phase direction, the compensation current can achieve bidirectional energy interaction, injecting active power into the grid or absorbing active power from the grid. It utilizes the inherent line transmission impedance at the end of the distribution network to generate an additional voltage drop, which in turn adjusts the three-phase voltage amplitude at the common access point, thereby achieving imbalance control.
[0014] S6. Closed-Loop Feedback and Integral Convergence Optimization: Real-time acquisition and updating of three-phase voltage signals constitutes a voltage closed-loop control system. In non-performance-priority mode, when all three-phase voltages are within the upper and lower limits corresponding to the current mode and the system enters a steady-state qualified state, slow convergence processing is performed on the integral term of the PI controller. The convergence speed is much slower than the integral speed during PI dynamic adjustment. Without affecting the dynamic response performance, the steady-state compensation output current gradually converges to zero, maintaining the treatment effect with minimum compensation power and reducing line losses and device losses.
[0015] Furthermore, the PI controller's integral term converges in a proportional manner: in each control cycle, the integral value is multiplied by a decay coefficient that is less than 1 and infinitely close to 1, achieving slow decay.
[0016] Furthermore, the PI controller's integral term converges using a fixed-step convergence method: in each control cycle, the integral value is reduced by a fixed, tiny step towards zero, gradually eliminating the accumulated integral.
[0017] Furthermore, the operating mode, voltage upper and lower limits, and unbalance limits are also specified. It can be configured through a local human-machine interface or remote communication.
[0018] Furthermore, the power converter unit adopts a phase-independent control architecture, with decoupled adjustment of the compensation current of each phase, so that they do not interfere with each other.
[0019] II. A device for mitigating three-phase voltage imbalance at the end of a power distribution network
[0020] This device, used to implement the aforementioned governance method, includes a voltage sampling unit, a mode configuration unit, a main control and processing unit, and a power conversion unit. The voltage sampling unit's input terminal is directly connected to the three-phase four-wire primary power supply line, and it only collects voltage signals; the device itself does not have an external current transformer or an external secondary current sampling circuit. The mode configuration unit is used to receive and store the user-issued operating mode identifier, voltage upper and lower limit parameters, and three-phase imbalance limit values. The main control unit is used to perform voltage RMS calculation, three-phase unbalance calculation, target voltage calculation under four operating modes, PI closed-loop calculation, PI integral convergence algorithm, and output instantaneous current control commands. The power converter unit receives the instantaneous current commands from the main control unit, outputs phase-controllable compensation current, and uses the voltage drop across the distribution network line impedance to achieve three-phase voltage amplitude regulation. This unit has bidirectional energy transmission capability and can operate in both inverter and rectification modes, respectively realizing bidirectional regulation of injecting active power into the grid and absorbing active power from the grid.
[0021] Furthermore, the main control computing unit adopts a DSP or MCU microcontroller.
[0022] Furthermore, the mode configuration unit includes a local button display screen and / or a remote 485 or Ethernet communication interface.
[0023] Beneficial effects The hardware architecture is simplified, making installation and maintenance convenient. The device only needs to be connected to a three-phase four-wire primary circuit, eliminating the need for current transformers and secondary current wiring, which greatly reduces the difficulty and cost of on-site construction. At the same time, it eliminates the safety hazard of open circuit in the secondary circuit of the CT, making it particularly suitable for batch renovation of distributed transformer substations at the end of the distribution network.
[0024] Multi-mode adaptation and comprehensive scenario coverage. Four switchable working modes correspond to four types of governance needs: voltage priority, balance priority, dual compatibility, and extreme balance. Users can flexibly choose according to the assessment requirements of the transformer area and the characteristics of the load. One device can adapt to multiple working conditions.
[0025] The voltage regulation mechanism is highly targeted and offers flexible bidirectional adjustment. It employs independent power converter units for each phase, supporting bidirectional energy flow. By injecting in-phase or out-of-phase current to change the line voltage drop, it directly adjusts the voltage amplitude of each phase. For voltage imbalance caused by differences in line voltage drop, its mitigation effect is superior to traditional negative sequence current compensation schemes.
[0026] Significant steady-state loss reduction is achieved. A PI integral slow convergence mechanism is added, which automatically reduces the compensation output power after the voltage steady-state condition is met, avoiding invalid circulating current and unnecessary power output. This effectively reduces line losses and device losses while ensuring power quality. Attached Figure Description
[0027] Figure 1 is a block diagram of the overall hardware structure of the three-phase voltage imbalance mitigation device of the present invention; Figure 2 is a block diagram of the overall process of the three-phase voltage imbalance mitigation method of the present invention; Figure 3 is a logical schematic diagram of dual threshold merging in the compatible mode of the present invention; Figure 4 is a block diagram of the PI controller with integral convergence stage of the present invention. Detailed Implementation
[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.
[0029] Example 1: Hardware Architecture of the Treatment Device As shown in Figure 1, the three-phase voltage imbalance mitigation device at the end of the distribution network provided in this embodiment mainly consists of four parts: a voltage sampling unit, a mode configuration unit, a main control and calculation unit, and a power converter unit. The three-phase four-wire primary circuit is directly connected to the voltage sampling unit; the device does not have any external current transformers or secondary current sampling circuits. The voltage sampling unit transmits the collected instantaneous voltage signal to the main control and calculation unit. The mode configuration unit communicates bidirectionally with the main control and calculation unit, responsible for sending user-configured parameters such as the operating mode, voltage upper and lower limits, and imbalance limits to the main control unit, while simultaneously transmitting the device's operating status back. The main control and calculation unit uses a DSP microcontroller to complete the calculation of the effective voltage value, imbalance degree calculation, target voltage generation, PI closed-loop control, integral convergence logic calculation, and finally outputs a PWM drive signal to the power converter unit. The power converter unit adopts a phase-independent full-bridge topology, supporting bidirectional energy flow: when the output current is in phase with the grid voltage of the same phase, the unit operates in inverter mode, injecting active power into the grid and raising the voltage at the end of that phase; when the output current is out of phase with the grid voltage of the same phase, the unit operates in rectification mode, absorbing active power from the grid and lowering the voltage at the end of that phase. By changing the voltage drop on the line, the voltage at the common access point of each phase is precisely adjusted, achieving three-phase voltage imbalance mitigation. The mode configuration unit supports local keypad and display screen operation, and also supports 485 and Ethernet remote communication, adapting to both local debugging and remote centralized control scenarios.
[0030] Example 2: Overall Process of Governance Method like Figure 2 As shown, the governance method described in this embodiment operates cyclically according to the following steps: First, the voltage sampling unit collects the instantaneous three-phase four-wire voltage in real time and sends it to the main control calculation unit. Second, the main control calculation unit calculates the effective value of the three-phase voltage using the root mean square algorithm. , , Simultaneously, the current three-phase voltage imbalance is calculated. The third step involves reading the operating mode stored in the mode configuration unit, executing the corresponding target voltage calculation logic based on the selected mode, and obtaining the voltage regulation target values for each of the three phases. , , The fourth step is to calculate the voltage deviation Uerr_x for each phase, input the deviation into the corresponding PI controller of the phase, and output the effective value command Iref of the compensation current. The fifth step is to combine the effective value current command with the grid voltage phase to decompose it into an instantaneous current command at each sampling moment, driving the power converter unit to output the compensation current, which acts on the distribution network lines through bidirectional energy interaction. The sixth step is to collect the adjusted three-phase voltage in real time and feed it back to the input of the PI controller, forming a voltage closed-loop control. The seventh step is to determine whether the current mode is non-performance priority mode and whether all three-phase voltages are within the acceptable range; if the conditions are met, the PI integral slow convergence loop is activated, and the convergence result is applied to the integral term of the PI controller; if not, the convergence loop is ineffective, and the PI controller operates normally. After completing one control cycle, the process returns to the first step and repeats.
[0031] Example 3: Specific Execution Process of Four Working Modes Performance-Priority Mode: The system uses the average three-phase voltage as a unified target. For example, if the current three-phase voltages are 230V, 220V, and 210V, then the average value Uavr is 220V, and the target voltage for all three phases is set to 220V. The PI controller adjusts the voltage of each phase individually: the voltage of phase A is reduced from 230V to 220V, and the voltage of phase C is increased from 210V to 220V, ultimately achieving complete three-phase voltage balance. This mode is suitable for scenarios with extremely high requirements for three-phase balance.
[0032] Voltage Priority Mode: The user sets the upper voltage limit to 235V and the lower limit to 205V. The system performs phase-by-phase judgment: If a phase voltage is 240V, higher than the upper limit, the target voltage is set to 235V, and the control device outputs a reverse current to lower the phase voltage; if a phase voltage is 200V, lower than the lower limit, the target voltage is set to 205V, and a current in the same direction is output to raise the phase voltage; if a phase voltage is 220V, within the range, the target voltage equals the current voltage, and no compensation current is output for this phase. This mode ensures that the voltage does not exceed the limit with minimum power, and is suitable for terminal areas with large voltage fluctuations.
[0033] Balance Priority Mode: User sets imbalance limits. The current average three-phase voltage is 220V. Therefore, the dynamic upper limit is 220×(1+2%)=224.4V, and the dynamic lower limit is 220×(1-2%)=215.6V. Subsequent adjustments are made phase-by-phase according to the voltage priority mode logic to ensure that the voltage of any phase does not exceed this dynamic range, thereby stabilizing the three-phase imbalance within 2%. In this mode, the voltage range adaptively fluctuates with the average value, always prioritizing ensuring that the imbalance index meets the standard.
[0034] Compatibility mode: such as Figure 3As shown, the user simultaneously sets a fixed voltage upper limit of 235V, a lower limit of 205V, and an imbalance limit of 2%. With the current average voltage at 220V, the dynamic upper limit is 224.4V, and the dynamic lower limit is 215.6V. The final effective upper limit is set to min(235V, 224.4V) = 224.4V, and the final effective lower limit is set to max(205V, 215.6V) = 215.6V. The system adjusts the voltage according to this composite range, simultaneously meeting the dual requirements of voltage not exceeding limits and imbalance not exceeding limits, making it suitable for the general governance scenarios of most conventional transformer substations.
[0035] Example 4: Specific Implementation of PI Integral Convergence like Figure 4 As shown, the PI controller consists of a proportional and an integral element connected in parallel, with the integral element connected in series with an integral convergence module. When the system is in a dynamic adjustment process and the voltage is not within the acceptable range, the convergence module does not operate, and the PI controller integrates normally to ensure a fast dynamic response. When the system enters steady state and all three-phase voltages are within the acceptable range, the convergence module starts. If a proportional convergence method is used, the integral value is multiplied by a decay coefficient of 0.999 in each control cycle to achieve extremely slow decay; if a fixed step size convergence method is used, the equivalent integral step size is corrected by 0.01A towards zero in each control cycle. Since the convergence speed is much lower than the integral response speed of the PI controller, it will not affect the dynamic adjustment performance of the system. It only gradually eliminates the integral accumulation in the steady state stage, making the compensated output current approach zero, achieving minimum power operation, and achieving energy saving and loss reduction.
Claims
1. A method for mitigating three-phase voltage imbalance at the end of a distribution network, characterized in that, Includes the following steps: S1. Real-time acquisition of three-phase four-wire voltage signals at the common access point of the power distribution network; S2. Calculate the effective value of the three-phase voltage based on the collected voltage signal. , , And calculate the current three-phase voltage imbalance; S3. Obtain the user-configured operating modes, including performance-priority mode, voltage-priority mode, balance-priority mode, and compatibility mode; according to the calculation rules of the corresponding operating mode, solve for the voltage regulation target values of phases A, B, and C respectively. , , ; in: Performance-priority mode: Calculate the average value of three-phase voltages Automatic settings , , ; Voltage priority mode: Reads a preset fixed voltage upper limit. Lower voltage limit ; Phase-by-phase judgment, if the current phase voltage is greater than Then the target voltage value of that phase is... If the current phase voltage is less than Then the target voltage value of that phase is... If the current phase voltage is between and If the voltage is between these values, then the target voltage for that phase is taken as the actual voltage for that phase. Balance Priority Mode: Reads the preset three-phase imbalance limit. Based on the current average three-phase voltage Reverse drive state voltage threshold: , Then, the voltage regulation target for each phase is calculated phase by phase according to the determination rules of the voltage priority mode. Compatibility mode: Reads user-defined fixed voltage upper and lower limits. , and imbalance limit First, calculate the dynamic voltage threshold according to the balance priority mode. , Take the final effective upper limit. Take the final effective lower bound. Then, according to the voltage priority mode determination rules, calculate the voltage regulation target for each phase one by one; S4. Calculate the difference between the actual voltage and the target voltage for each phase. , The voltage deviation ΔUx is sent to the PI controller of the corresponding phase, and the effective value command of the compensation current is output. Iref is the phase of the timing compensation current, which is the same as the phase of the grid voltage. When the phase is negative, the phase of the compensation current is 180° out of phase with the phase of the grid voltage. S5. Transmit the current command in RMS form. Decomposition yields the instantaneous current command for each sampling period. Control the output compensation current of the inverter unit; rely on the voltage drop generated by the transmission impedance of the distribution network terminal line to adjust the three-phase voltage amplitude at the common access point; S6. Real-time acquisition of three-phase voltage signals to form voltage closed-loop control; in non-performance priority mode, when all three-phase voltages are within the voltage upper and lower limit ranges corresponding to the current mode, slow convergence processing is performed on the integral term of the PI controller. The convergence speed is less than the integral speed during PI dynamic adjustment. Under steady-state conditions, the device output compensation current converges to the minimum power.
2. The method for addressing three-phase voltage imbalance at the end of a distribution network according to claim 1, characterized in that, The PI controller's integral term converges using proportional convergence. In each control cycle, the integral value is multiplied by a decay coefficient that is less than 1 and infinitely close to 1.
3. The method for addressing three-phase voltage imbalance at the end of a distribution network according to claim 1, characterized in that, The PI controller's integral term convergence method is fixed-step convergence, where a fixed small step is subtracted in the direction of integral zeroing during each control cycle.
4. The method for addressing three-phase voltage imbalance at the end of a distribution network according to claim 1, characterized in that, The control cycle is synchronized with the grid voltage cycle.
5. The method for addressing three-phase voltage imbalance at the end of a distribution network according to claim 1, characterized in that, The operating mode and voltage limits are controlled via a human-machine interface or remote communication. , and imbalance limit Parameter configuration.
6. The method for addressing three-phase voltage imbalance at the end of a distribution network according to claim 1, characterized in that, The inverter unit outputs compensation current independently for each phase, and the compensation current between each phase is decoupled and controlled.
7. A device for addressing three-phase voltage imbalance at the end of a distribution network, used to implement the treatment method described in any one of claims 1-6, characterized in that, It includes a voltage sampling unit, a mode configuration unit, a main control and processing unit, and an inverter output unit; The input terminal of the voltage sampling unit is directly connected to the three-phase four-wire primary power supply line, and only collects voltage signals. The device body does not have an external current transformer and does not have an external secondary current sampling circuit. The mode configuration unit is used to receive and store the operating mode identifier, voltage upper and lower limit parameters, and three-phase imbalance limit value issued by the user. The main control and computing unit is used to perform calculations of effective voltage value and three-phase unbalance, calculation of target voltage for each phase under four working modes, PI closed-loop operation, PI integral convergence algorithm, and output instantaneous current control commands. The inverter output unit receives instantaneous current commands from the main control unit and outputs phase-controllable compensation currents, thereby achieving three-phase voltage amplitude regulation by utilizing the voltage drop across the distribution network line impedance.
8. A three-phase voltage imbalance mitigation device at the end of a distribution network according to claim 7, characterized in that, The main control and processing unit is a DSP or MCU microcontroller.
9. A three-phase voltage imbalance mitigation device at the end of a distribution network according to claim 8, characterized in that, The mode configuration unit includes a local button display and / or a remote 485 or Ethernet communication interface.