A Three-Phase Voltage Balancing Control Method and System Based on Power Quality Manager

Abstract

This invention relates to the field of power quality management devices, and provides a three-phase voltage balancing control method and system based on a power quality manager. The method includes: sampling the DC-side voltage and three-phase current, load current, and grid-side three-phase voltage of the power quality manager; obtaining phase information through phase-locked loop and combining it with the obtained load current to obtain the harmonic reactive power signal to be compensated; calculating the current value that needs to be adjusted for voltage balancing based on a ramp-up algorithm, and obtaining the reference current of the inner loop by combining the output of the outer voltage loop and the harmonic reactive power signal; obtaining the modulation value after repeated control, and then obtaining the three-phase PWM wave required for the switching transistor control in the power quality manager, thereby achieving the control objectives of grid voltage balancing and harmonic reactive power compensation. This invention solves the problems of insufficient grid-side voltage balancing control performance and current harmonic control management performance during the operation of the power quality manager.

Description

Technical Field

[0001] This invention relates to the field of power quality management device technology, specifically to a three-phase voltage balancing control method and system for a power quality manager. Background Technology

[0002] With the rapid increase in distributed power sources, electric vehicle charging stations, power electronic loads, and single-phase high-power loads, the three-phase load imbalance in distribution networks is becoming increasingly serious, leading to significant asymmetry in the three-phase voltage on the grid side and severely impacting the power quality of the distribution network. This is particularly true in rural power grids, where electricity loads are significantly affected by seasonality, and the dispersed nature of users results in complex wiring. Three-phase imbalance often stems from improper phase sequence allocation during meter connection, causing single-phase loads to concentrate on a single phase, resulting in severe three-phase load imbalance and generating harmonic and reactive currents. Three-phase load imbalance easily leads to transformer overload, line burnout, and false tripping of low-voltage switches, seriously threatening the safe and reliable power supply for residential and industrial users. To achieve comprehensive power quality management, power quality managers capable of harmonic compensation, reactive current management, and three-phase voltage balancing are widely used.

[0003] In existing technologies, power quality managers need to control the DC-side voltage and grid-side current quality, mainly employing a dual-loop control method combining voltage and current loops. For example, the paper "Research on Three-Phase Unbalanced Regulator with Harmonic Suppression Function" details the specific system structure of the three-phase unbalanced regulator and basic control methods such as harmonic suppression. In the three-phase unbalanced regulator system, the inner current control loop primarily ensures grid current quality, while the outer loop is a "signal preprocessing unit" that implements harmonic compensation. This signal is transmitted to the voltage loop and combined with the DC-side voltage stability control target of the voltage loop to jointly generate reference commands for the inner current loop, ensuring that the three-phase unbalanced regulator can achieve good power quality management and control functions. Although this paper analyzes the DC bus voltage and harmonic detection and control methods, the problem of three-phase voltage imbalance on the grid side remains unresolved, leading to increased neutral current and subsequent midpoint potential imbalance. Therefore, the control performance of the power quality regulator needs further improvement. Summary of the Invention

[0004] The technical problem to be solved by this invention is to improve the grid-side voltage balance control and current harmonic control management performance of the power quality manager, and to provide a three-phase voltage balance control method and system based on the power quality manager.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] This invention provides a three-phase voltage balancing control method based on a power quality manager, the method comprising the following steps:

[0007] S1, DC side voltage U of the power quality manager dc and three-phase current i a i b i c Sampling is performed on the three-phase load current i La i Lb i Lc Sampling was performed on the three-phase voltage e on the grid side. a e b e c Perform sampling;

[0008] S2, Based on the three-phase voltage e on the grid side a e b e c Phase-locked loop (PLL) calculations are performed to obtain the phase information ωt of the three-phase voltage on the grid side and the three-phase load current i. La i Lb i Lc By combining the grid phase information ωt, the three-phase harmonics and reactive current signals i that need to be compensated are obtained. ha i hb i hc ;

[0009] S3. Based on the grid voltage and phase, the three-phase current i to be regulated is obtained through a ramp-up algorithm. eqa i eqb i eqc The three-phase harmonics and reactive current signal i are compensated. ha i hb i hc Superimposed and based on DC side voltage U dc The obtained external voltage loop output I outa,b,c The difference is used to obtain the three-phase reference current signal i of the inner current loop. aref i bref i cref The three-phase reference current signal serves as the input to the inner current loop and is used in conjunction with the three-phase current i of the power quality manager. a i b i c After repeated control calculations, the three-phase modulation value u is obtained. sa u sb u sc ;

[0010] S4, Three-phase modulation value u sa u sb u sc After comparison with the three-phase carrier wave, the three-phase PWM wave required for the switching transistor control in the power quality manager is obtained;

[0011] S5, the three-phase PWM wave controls the power quality manager, adjusting the target amplitude and phase required by the power quality manager to achieve the control objectives of grid voltage balance and harmonic reactive power compensation.

[0012] Furthermore, S1 describes the DC-side voltage U of the power quality manager. dc The sampling process is as follows:

[0013] The power quality manager uses a split capacitor structure on the DC side, with voltage U dc The voltage is obtained by sampling and superimposing the voltages of the two capacitors at the upper and lower ends of the DC side using a resistor voltage divider and a DC voltage Hall sensor structure.

[0014] Furthermore, the power quality manager in S1 uses a split capacitor structure on the DC side. The voltage Udc is obtained by sampling and superimposing the voltages of the two capacitors at the upper and lower ends of the DC side through a resistor voltage divider and a DC voltage Hall sensor structure.

[0015] Furthermore, S2 specifically includes:

[0016] After the three-phase voltages ea, eb, and ec on the grid side are converted from the three-phase stationary coordinate system to the two-phase rotating coordinate system, the two-phase rotating coordinate system voltage is ensured to track the voltage without steady-state error through proportional-integral control. The actual angular frequency of the grid is obtained by adding the grid's rated angular frequency with the proportional-integral control output. After integration, the real-time phase ωt of the grid voltage can be obtained, thereby realizing the phase-locked loop function and calculating the load current harmonics and reactive current components that need to be compensated.

[0017] Furthermore, the specific steps for calculating the load current harmonics and reactive current components that need to be compensated are as follows:

[0018] (1) Perform Fourier series decomposition on the three-phase load current to obtain the fundamental component and the second and above harmonic components. The fundamental component is further decomposed into active component and reactive component.

[0019] (2) Multiply the grid voltage signal and the load current signal to generate a product signal containing DC and AC components;

[0020] (3) Apply low-pass filtering to the product signal, extract the filtered DC component, and calculate the amplitude of the fundamental active current;

[0021] (4) Tracking the real-time phase of the grid voltage through the phase-locked loop: First, the grid voltage in the three-phase stationary coordinate system is converted to the two-phase rotating coordinate system. The voltage in the two-phase rotating coordinate system is tracked without static error through proportional-integral control. The output of proportional-integral control is added to the grid rated angular frequency to obtain the actual angular frequency of the grid. Then, the real-time phase of the grid voltage is obtained through integral calculation.

[0022] (5) Multiply the amplitude of the fundamental active current with the real-time phase of the grid voltage to generate a complete fundamental active current signal;

[0023] (6) Subtract the original load current from the fundamental active current signal to obtain the compensation command current containing reactive current and harmonic current.

[0024] Furthermore, the order of the Fourier series decomposition covers up to the 50th harmonic.

[0025] Furthermore, the cutoff frequency of the low-pass filter is set to 1 / 10 of the fundamental frequency of the power grid.

[0026] Furthermore, the proportional-integral control parameters of the phase-locked loop are tuned according to the dynamic response characteristics of the grid voltage. The proportional coefficient ensures the system response speed, while the integral coefficient eliminates steady-state error. The two work together to achieve zero steady-state error phase tracking.

[0027] Furthermore, the specific steps of S3 are as follows:

[0028] The algorithm employs a fixed step size and extreme value ramping algorithm. This algorithm is used by the power quality manager to adjust the reference values ​​of the current in each phase in real time when the three-phase voltage is unbalanced, thereby indirectly regulating the three-phase voltage drop and making the three-phase voltage tend to be balanced. The extreme value ramping algorithm detects the phases with the maximum and minimum values ​​of the three-phase voltage and gradually increases or decreases the active reference current of the corresponding phase, increasing the reference current of the phase with the lowest voltage.

[0029] Furthermore, S3 sets a dead zone threshold value under three-phase voltage imbalance. Only when the three-phase voltage difference exceeds the threshold value will it trigger real-time adjustment of the current reference value of each phase. The adjusted current command will be current-limited and clamped within the current-limiting threshold to prevent overcurrent of the compensation device.

[0030] Furthermore, the dead zone threshold value is set according to the allowable imbalance of the grid voltage, and is taken as 1% to 2% of the rated voltage.

[0031] The present invention also provides a system applicable to the above-mentioned three-phase voltage balancing control method based on power quality manager.

[0032] The advantages of this invention over the prior art are:

[0033] This invention employs a fixed step size and extreme value ramping algorithm. This algorithm detects the phases containing the maximum and minimum values ​​of the three-phase voltage. By gradually increasing or decreasing the active reference current of the corresponding phase, and increasing the reference current of the phase with the lowest voltage, this invention is used by the power quality manager to realize real-time adjustment of the reference values ​​of the current of each phase under the condition of three-phase voltage imbalance, thereby indirectly regulating the three-phase voltage drop and making the three-phase voltage tend to be balanced. Attached Figure Description

[0034] Figure 1 This is a flowchart of a three-phase voltage balancing control method based on a power quality manager, as an example of the present invention.

[0035] Figure 2 This is a block diagram of the overall control structure of an example of the present invention.

[0036] Figure 3 This invention presents voltage and current waveforms under voltage imbalance, along with the corresponding phase voltage values ​​and their THD values.

[0037] Figure 4 The voltage and current waveforms after voltage balancing control under voltage imbalance in this invention example, along with the corresponding phase voltage values ​​and their THD values, are shown. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] This embodiment provides a three-phase voltage balancing control method based on a power quality manager. The control structure flow is as follows: Figure 1 As shown, the method includes the following steps:

[0040] S1, DC side voltage U of the power quality manager dc and three-phase current i a i b i c Sampling is performed, with the power quality manager using a split capacitor structure on the DC side, and voltage U dc The voltage is obtained by sampling and superimposing the voltages of the upper and lower capacitors on the DC side using a resistive voltage divider and a DC voltage Hall sensor structure. This is used for the three-phase load current i. La i Lb i Lc Sampling was performed on the three-phase voltage e on the grid side. a e b e c Perform sampling;

[0041] S2, Three-phase voltage on the grid side e a e b e cAfter the three-phase stationary coordinate system is converted into a two-phase rotating coordinate system, the voltage of the two-phase rotating coordinate system is tracked without steady-state error through proportional-integral control. The actual angular frequency of the power grid is obtained by adding the rated angular frequency of the power grid with the output of proportional-integral control. After integration, the real-time phase ωt of the power grid voltage can be obtained, thereby realizing the phase-locked loop function.

[0042] The specific steps for calculating the load current harmonics and reactive current components that need to be compensated are as follows:

[0043] (1) Perform Fourier series decomposition on the three-phase load current. The order of the Fourier series decomposition covers the 50th harmonic. The decomposition yields the fundamental component and the harmonic components of the second and above. The fundamental component is further decomposed into active component and reactive component.

[0044] (2) Multiply the grid voltage signal and the load current signal to generate a product signal containing DC and AC components;

[0045] (3) Apply low-pass filtering to the product signal. Set the cutoff frequency of the low-pass filter to 1 / 10 of the fundamental frequency of the power grid. Extract the DC component after filtering and calculate the amplitude of the fundamental active current.

[0046] (4) Tracking the real-time phase of the grid voltage through the phase-locked loop: First, the grid voltage in the three-phase stationary coordinate system is converted to the two-phase rotating coordinate system. The voltage in the two-phase rotating coordinate system is tracked without static error through proportional-integral control. The output of proportional-integral control is added to the grid rated angular frequency to obtain the actual angular frequency of the grid. Then, the real-time phase of the grid voltage is obtained through integral calculation.

[0047] (5) Multiply the amplitude of the fundamental active current with the real-time phase of the grid voltage to generate a complete fundamental active current signal;

[0048] (6) Subtract the original load current from the fundamental active current signal to obtain the compensation command current containing reactive current and harmonic current.

[0049] Taking phase A as an example, the phase current i of the load La (t) is obtained by performing Fourier series decomposition:

[0050] (1)

[0051] The fundamental active current, fundamental reactive current, and harmonic current components in the phase A current of the load can be represented as follows:

[0052] (2)

[0053] Substituting equation (2) into equation (1) yields:

[0054] (3)

[0055] From equation (3), the load current i can be... La (t) is divided into several parts, namely: the load fundamental active current part i Lpa (t), reactive current part i Lqa (t) and harmonic current part i Lha (t). The load current i can then be calculated. La The fundamental active current component in (t) is then used to obtain the reactive and harmonic current components that need to be compensated by subtracting the load current from it.

[0056] Assume the initial phase of the A-phase grid voltage is zero, and for ease of calculation, assume u... La The peak value of (t) is 1, and the voltage signal u La (t) and current signal i La Multiplying (t) together, we get:

[0057] (4)

[0058] As can be seen from equation (4), the result obtained by multiplying the two variables includes both DC and AC components. By designing the LPF and selecting appropriate cutoff frequency parameters, the AC component is filtered out, leaving only the DC component. Combining equation (2), it can be seen that this DC component is the fundamental active current component i. Lpa If half of this DC component is obtained, then the magnitude of this DC component is equal to the fundamental active current i. Lpa Amplitude I Lpa Multiplying this by the phase sinωt obtained through the PLL phase-locked loop yields the fundamental active current i of the load current. Lpa .

[0059] The load current harmonics and reactive current that need to be compensated can be calculated by subtracting the load current from the fundamental active current. The current is:

[0060] (5)

[0061] S3. Based on the grid voltage and phase, the three-phase current i to be regulated is obtained through a ramp-up algorithm. eqa i eqb i eqcThis method employs a fixed step size and extreme value ramping algorithm. This algorithm is used by power quality managers to adjust the reference values ​​of the current in each phase in real time under three-phase voltage imbalance conditions, thereby indirectly regulating the three-phase voltage drop and bringing the three-phase voltages closer to equilibrium. The core idea of ​​the algorithm is to detect the phases with the maximum and minimum voltage values ​​and gradually increase or decrease the active power reference current of the corresponding phases, increasing the reference current for the phase with the lowest voltage. The reason is: assuming an unbalanced three-phase load, with many high-power single-phase loads connected to phase A, the current I in phase A will increase. a The voltage drop across the line resistance and transformer winding resistance is very large, resulting in a large voltage drop across phase A and a very low voltage across phase A. To make e... a To increase the voltage, the active current flowing through the line resistance must be reduced. The APF injects a positive active current ∆i into phase A, so the grid only needs to provide Ia-∆i, thereby reducing the line voltage drop and ultimately raising the voltage of phase A. Similarly, reducing the reference current for the phase with the highest voltage increases the line voltage drop, thus lowering its voltage.

[0062] (6)

[0063] Limit the current value obtained through the ramp-up algorithm:

[0064] (7)

[0065] This algorithm is in e max -e min >∆U th Effective at time, where ∆U th The threshold value representing the "dead zone" is a minimum operating voltage difference set to prevent malfunctions and avoid unnecessary back-and-forth climbing; in formulas (6) and (7), k∈{a,b,c}; in the formulas, i + eqk This represents the new current value of the k-th phase after adjustment using the ramp-up algorithm; i eqk Δi represents the current value that needs to be adjusted in the k-th phase at the previous moment; ∆i represents the magnitude of the current adjustment in each time cycle, adjusted according to the equipment capacity; argmin represents the index of the variable that minimizes the expression within the parentheses; argmax represents the index of the variable that maximizes the expression within the parentheses; i lim Representing i + eqk The amplitude limit value is set to avoid APF output overcurrent and ensure system stability.

[0066] Next, based on the obtained three-phase current i that needs to be adjusted eqa i eqb i eqc The compensated three-phase harmonics and reactive current signal iha i hb i hc External voltage loop output U outa U outb U outc Together, the three-phase reference current signal i of the inner current loop is obtained. aref i bref i cref The corresponding formula is as follows:

[0067] (8)

[0068] Where θ k This represents the initial phase angle corresponding to the k-th phase.

[0069] The three-phase reference current signal serves as the input to the inner current loop and is used in conjunction with the three-phase current i of the power quality manager. a i b i c After repeated control calculations, the three-phase modulation value u is obtained. sa u sb u sc ;

[0070] S3 sets a dead zone threshold value under three-phase voltage imbalance. It triggers real-time adjustment of the current reference value of each phase only when the three-phase voltage difference exceeds the threshold value. It performs current limiting processing on the adjusted current command and clamps the current command within the current limiting threshold to prevent the compensation device from overcurrent.

[0071] The dead zone threshold value is set based on the allowable imbalance of the grid voltage, and is typically 1% to 2% of the rated voltage.

[0072] To further optimize dynamic performance, this invention introduces "voltage imbalance" as the basis for step size adjustment, specifically implemented as follows:

[0073] Voltage unbalance calculation:

[0074] The unbalance ε of three-phase voltage is defined as:

[0075]

[0076] in This is the arithmetic mean of the three-phase voltages. This represents the maximum value of the three-phase voltage. This is the minimum value of the three-phase voltage;

[0077] Adaptive step size adjustment rules:

[0078] Based on the magnitude of ε, the adjustment step size Δi is divided into multiple intervals, and corresponding step size values ​​are set:

[0079] when When there is a severe imbalance, a larger step size should be used. To quickly reduce the voltage difference;

[0080] when (For moderate imbalance) use a medium step size ;

[0081] when (For mild imbalance) use a smaller step size This allows for fine-tuning.

[0082] in, , For the set threshold, and Step size satisfies > > ;

[0083] Hysteresis control prevents oscillations:

[0084] To prevent adjustment oscillations caused by frequent step size switching near the threshold, hysteresis control is added during step size switching. For example, when ε changes from greater than... Descending to At that time, the step size remains unchanged. until ε continues to decrease to Switching to -Δh (Δh is the hysteresis width) only occurs when ;

[0085] Continuous function mapping of step size to voltage difference (optional advanced strategy):

[0086] To further achieve smooth adjustment, the step size Δi can also be designed as a continuous function of ε, such as:

[0087]

[0088] in This is the proportionality coefficient. This is the minimum step size, ensuring that regulation is still effective even when the voltage difference is extremely small.

[0089] S4, Three-phase modulation value u sa u sb u sc After comparison with the three-phase carrier wave, the three-phase PWM wave required for the switching transistor control in the power quality manager is obtained;

[0090] S5, the three-phase PWM wave controls the power quality manager, adjusting the target amplitude and phase required by the power quality manager to achieve the control objectives of grid voltage balance and harmonic reactive power compensation.

[0091] The present invention also provides a system applicable to the above-mentioned three-phase voltage balancing control method based on power quality manager.

[0092] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase voltage balancing control method for a power quality manager, characterized in that, The method includes the following steps: S1, sampling the voltage U at the DC side of the power quality manager dc and the three-phase current i a ,i b , i c , sampling the three-phase load current i La , i Lb , i Lc , sampling the grid-side three-phase voltage e a , e b , e c S2, based on the grid side three-phase voltage e a , b , c phase calculation, through the phase-locked loop to get the grid side three-phase voltage phase information ωt, three-phase load current i La , Lb , Lc combined with the grid phase information ωt to get the three-phase harmonic and reactive current signal i ha , hb , hc ; S3. Based on the grid voltage and phase, the three-phase current i to be regulated is obtained through a ramp-up algorithm. eqa i eqb i eqc , and the compensated three-phase harmonics and reactive current signal i ha i hb i hc Superimposed and based on DC side voltage U dc The obtained external voltage loop output I outa,b,c The difference is used to obtain the three-phase reference current signal i of the inner current loop. aref i bref i cref The three-phase reference current signal serves as the input to the inner current loop and is used in conjunction with the three-phase current i of the power quality manager. a i b i c After repeated control calculations, the three-phase modulation value u is obtained. sa u sb u sc ; S4, Three-phase modulation value u sa u sb u sc After comparison with the three-phase carrier wave, the three-phase PWM wave required for the switching transistor control in the power quality manager is obtained; S5, the three-phase PWM wave controls the power quality manager, adjusting the target amplitude and phase required by the power quality manager to achieve the control objectives of grid voltage balance and harmonic reactive power compensation.

2. The three-phase voltage balancing control method of the power quality manager according to claim 1, characterized in that, The power quality manager in S1 uses a split capacitor structure on the DC side, with voltage U dc The voltage is obtained by sampling and superimposing the voltages of the two capacitors at the upper and lower ends of the DC side using a resistor voltage divider and a DC voltage Hall sensor structure.

3. The three-phase voltage balancing control method of the power quality manager according to claim 1, characterized in that, S2 specifically includes: Three-phase voltage e on the grid side a e b e c After converting from a three-phase stationary coordinate system to a two-phase rotating coordinate system, proportional-integral control is used to ensure zero steady-state error tracking control of the voltage in the two-phase rotating coordinate system. The actual angular frequency of the power grid is obtained by adding the rated angular frequency of the power grid with the output of proportional-integral control. After integration, the real-time phase ωt of the power grid voltage can be obtained, thereby realizing the phase-locked loop function. The load current harmonics and reactive current components that need to be compensated are calculated.

4. The three-phase voltage balancing control method of the power quality manager according to claim 3, characterized in that, The specific steps for calculating the load current harmonics and reactive current components that need to be compensated are as follows: (1) Perform Fourier series decomposition on the three-phase load current to obtain the fundamental component and the second and above harmonic components. The fundamental component is further decomposed into active component and reactive component. (2) Multiply the grid voltage signal and the load current signal to generate a product signal containing DC and AC components; (3) Apply low-pass filtering to the product signal, extract the filtered DC component, and calculate the amplitude of the fundamental active current; (4) Tracking the real-time phase of the grid voltage through the phase-locked loop: First, the grid voltage in the three-phase stationary coordinate system is converted to the two-phase rotating coordinate system. The voltage in the two-phase rotating coordinate system is tracked without static error through proportional-integral control. The output of proportional-integral control is added to the grid rated angular frequency to obtain the actual angular frequency of the grid. Then, the real-time phase of the grid voltage is obtained through integral calculation. (5) Multiply the amplitude of the fundamental active current with the real-time phase of the grid voltage to generate a complete fundamental active current signal; (6) Subtract the original load current from the fundamental active current signal to obtain the compensation command current containing reactive current and harmonic current.

5. The three-phase voltage balancing control method of the power quality manager according to claim 4, characterized in that, The order of the Fourier series decomposition covers up to the 50th harmonic.

6. The three-phase voltage balancing control method for a power quality manager according to claim 5, characterized in that, The cutoff frequency of the low-pass filter is set to 1 / 10 of the fundamental frequency of the power grid.

7. The three-phase voltage equalization control method for a power quality manager according to claim 6, characterized in that, The proportional-integral control parameters of the phase-locked loop are tuned according to the dynamic response characteristics of the grid voltage. The proportional coefficient ensures the system response speed, while the integral coefficient eliminates steady-state error. The two work together to achieve zero steady-state error phase tracking.

8. The three-phase voltage balancing control method of the power quality manager according to claim 3, characterized in that, The specific steps for S3 are as follows: The algorithm employs a fixed step size and extreme value ramping algorithm. This algorithm is used by the power quality manager to adjust the reference values ​​of the current in each phase in real time when the three-phase voltage is unbalanced, thereby indirectly regulating the three-phase voltage drop and making the three-phase voltage tend to be balanced. The extreme value ramping algorithm detects the phases with the maximum and minimum values ​​of the three-phase voltage and gradually increases or decreases the active reference current of the corresponding phase, increasing the reference current of the phase with the lowest voltage.

9. The three-phase voltage balancing control method for a power quality manager according to claim 8, characterized in that, S3 sets a dead zone threshold value under three-phase voltage imbalance. It triggers real-time adjustment of the current reference value of each phase only when the three-phase voltage difference exceeds the threshold value. It performs current limiting processing on the adjusted current command and clamps the current command within the current limiting threshold to prevent the compensation device from overcurrent.

10. The three-phase voltage equalization control method for a power quality manager according to claim 9, characterized in that, The dead zone threshold value is set based on the allowable imbalance of the grid voltage, and is taken as 1% to 2% of the rated voltage.

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