Power quality adaptive comprehensive treatment method for low-voltage cabinet

Abstract

The application relates to the technical field of power quality treatment, and discloses a power quality adaptive comprehensive treatment method for a low-voltage cabinet. The method obtains the harmonic content, the power factor and the three-phase unbalance degree of a power grid side, calculates the distortion contribution degree of each frequency interval through spectrum decomposition, dynamically allocates the compensation capacity and the priority of a static reactive power generation module and an active power filter module in the cabinet by using a multi-target constraint optimization model, controls the collaborative output of the two modules, and realizes integrated adaptive control of reactive power compensation, harmonic suppression and three-phase unbalance treatment.

Description

Technical Field

[0001] This invention relates to the field of power quality management technology, and specifically to an adaptive integrated power quality management method for low-voltage switchgear. Background Technology

[0002] With the increasing automation and electronic sophistication of industrial processes, the number of nonlinear devices such as frequency converters and rectifiers in the loads of low-voltage switchgear has increased significantly. This has led to a combination of power quality problems on the grid side, including harmonic pollution, low power factor, and three-phase imbalance. As the end-point connection facing users, the power quality of the low-voltage distribution network directly determines the operating efficiency and safety of equipment.

[0003] Traditional capacitor compensation devices use mechanical switches for fixed switching, which has drawbacks such as slow response speed, over-compensation or under-compensation, and difficulty in matching rapid load changes. While active power filter modules and static var generator modules can respectively manage harmonics and reactive power, in the case of a common DC bus in the cabinet, if there is no unified capacity scheduling and priority coordination mechanism, it is difficult to dynamically allocate compensation resources according to real-time operating conditions. This results in low capacity utilization of the treatment device, unsatisfactory residual indicators, and even deterioration of the treatment effect due to control conflicts.

[0004] Therefore, there is an urgent need for a comprehensive governance method that can adaptively identify harmonic spectrum characteristics, coordinate and optimize reactive power compensation and harmonic suppression, and achieve synergistic output of both. Summary of the Invention

[0005] To address the aforementioned technical shortcomings, the purpose of this invention is to provide an adaptive comprehensive management method for power quality in low-voltage switchgear, solving the problem of the difficulty in adaptively and collaboratively managing harmonics, reactive power, and three-phase imbalance within low-voltage switchgear.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: In a first aspect, the present invention provides an adaptive integrated power quality management method for low-voltage switchgear, the method comprising: Step S1: Obtain the harmonic content, power factor, and three-phase imbalance of the low-voltage switchgear grid side; Step S2: Based on the harmonic content, the frequency spectrum is divided into multiple frequency ranges through spectral decomposition, and the distortion contribution of each frequency range is calculated. Step S3: Based on the distortion contribution, power factor, and three-phase imbalance, use a multi-objective constraint optimization model to dynamically allocate the compensation capacity and priority of the static var generator module and the active power filter module in the cabinet. Step S4: Based on the allocated compensation capacity and priority, control the static var generator module and the active power filter module to perform coordinated output of reactive power compensation, harmonic suppression and three-phase imbalance management.

[0007] Preferably, in one possible implementation of the first aspect, step S1 includes: Synchronous sampling of the three-phase voltage and three-phase current on the grid side of the low-voltage switch is performed. The sampling clock is output after the fundamental phase is locked by the phase-locked loop, and the fundamental frequency dynamically tracks the grid frequency. RMS value of harmonic current Defined as ,in For the first RMS value of subharmonic current For harmonic order, The highest harmonic order; The power factor is obtained by the ratio of fundamental active power to fundamental apparent power; The three-phase unbalance is the ratio of the effective value of the negative-sequence fundamental component to the effective value of the positive-sequence fundamental component. The negative-sequence fundamental component and the positive-sequence fundamental component are obtained by symmetrical component transformation of the three-phase quantities.

[0008] Preferably, in one possible implementation of the first aspect, the calculation of the distortion contribution in step S2 includes: Variational mode decomposition is performed on the three-phase harmonic current within the sampling window to obtain several intrinsic mode functions, each of which corresponds to a center frequency; The number of decomposition layers K is preset so that the center frequency of each intrinsic mode function covers the fundamental frequency and each integer multiple of the harmonic frequency; The intrinsic mode functions are grouped into multiple frequency intervals in ascending order of center frequency, and each interval contains one or more adjacent consecutive center frequencies. Within each frequency range, the equivalent harmonic current of that range. Defined as ,in For the th interval The instantaneous amplitude of each intrinsic mode function, This represents the number of intrinsic mode functions within this interval. Frequency range index; The equivalent harmonic current quantity With total equivalent harmonic current The ratio is used as the distortion contribution rate for that interval. ,Right now ,in , This represents the total number of frequency ranges.

[0009] Preferably, in one possible implementation of the first aspect, the multi-objective constrained optimization model in step S3 includes a set of objective functions and a set of constraint conditions; The objective function set simultaneously includes the capacity occupancy of the static var generator module, the capacity occupancy of the active power filter module, and the residual index after treatment. The residual index is obtained by aggregating the three-phase unbalance residual, reactive power residual and harmonic residual according to a preset weight. The constraint set covers the upper and lower limits of single-phase and three-phase output of the static var generator module, the upper and lower limits of frequency output of the active power filter module, the power coupling relationship between the static var generator module and the active power filter module in the cabinet sharing the DC bus, and the upper limit of single-phase current in the phase compensation scenario. The multi-objective constrained optimization model is solved using a non-dominated sorting genetic algorithm. After outputting the Pareto front, the optimal solution is selected according to the current working conditions as the basis for capacity and priority allocation.

[0010] Preferably, in one possible implementation of the first aspect, in the set of objective functions, Static Var Generator Module Capacity Usage Defined as ,in , , These represent the three-phase output reactive power within the sampling window. This refers to the rated reactive power capacity of the static var generator module. Capacity usage of active power filter module Defined as ,in For the first Effective value of subharmonic compensation current The highest harmonic order, This is the rated compensation current of the active power filter module; The residual indicators after treatment are the weighted aggregate values ​​of three-phase imbalance, power factor deviation and total harmonic distortion value predicted under the distribution scheme for the next sampling window. The weights of the three items are dynamically updated within a preset historical time window according to the load type on the grid side.

[0011] Preferably, in one possible implementation of the first aspect, in the set of constraints, the upper and lower limits of the single-phase output of the static var generator module are given according to the rated value of each phase bridge arm in the cabinet. The upper and lower limits of the frequency output of the active power filter module are given according to the switching frequency and inductance parameters inside the cabinet; The common DC bus power coupling relationship is expressed as follows: the sum of the active power fluctuations on the DC side of the static var generator module and the active power filter module is kept in balance through closed-loop control of the DC side capacitor voltage. In a phase-splitting compensation scenario, the upper limit of the output current of each phase is taken as the rated current value of the phase bridge arm.

[0012] Preferably, in one possible implementation of the first aspect, the dynamic allocation process of compensation capacity and priority includes: When the three-phase imbalance exceeds the first threshold, the static var generator module independently gives three-phase reactive power output commands for each phase, and the active power filter module superimposes in-phase harmonic compensation commands on each phase. The two work together to perform phase-by-phase compensation. When the three-phase imbalance does not exceed the first threshold and the power factor is lower than the second threshold, the static var generator module obtains the highest compensation priority, and the output command is dominated by the reactive power deficit. The output command of the active power filter module covers all frequency ranges under the condition of meeting the capacity limit, and its capacity occupancy is allocated according to the proportion of distortion contribution of each frequency range. When the three-phase imbalance does not exceed the first threshold and the power factor is not lower than the second threshold, the frequency range with the highest distortion contribution obtains the highest compensation priority in the active power filter module, and the static var generator module outputs a command to switch to three-phase balanced reactive power fine-tuning.

[0013] Preferably, in one possible implementation of the first aspect, the dynamic allocation process further includes: When the single-phase or three-phase aggregated capacity of the optimized static var generator module or active power filter module exceeds the rated upper limit of the corresponding module in the cabinet, the allocation quantity is scaled according to the currently determined priority order. During the scaling process, priority is given to ensuring that the allocation of imbalance management channels in phase compensation scenarios is not reduced, while the remaining channels are reduced proportionally. The power balance on the DC side between the static var generator module and the active power filter module is rechecked according to the common DC bus power coupling relationship. The final allocation value is output after iterating until the capacity constraint is met.

[0014] Preferably, in one possible implementation of the first aspect, the collaborative output process in step S4 includes: The static var generator module employs a dual closed-loop control system consisting of an outer voltage loop and an inner current loop. The inner current loop... After decoupling in the coordinate system, the signal is fed into the space vector pulse width modulation stage to generate the driving signal. The active power filter module uses a harmonic current detection stage to extract compensation commands for each frequency. In the coordinate system, the fundamental component is separated by decoupling the active and reactive power of the fundamental wave. The harmonic components of each frequency are tracked by the resonant controller and then sent to the current prediction and tracking stage to generate the driving signal. The static var generator module and the active power filter module share a DC bus. The DC side voltage is actively maintained by the voltage outer loop of the static var generator module, and the reference value of the DC side capacitor voltage switches depending on whether the phase compensation is engaged or not.

[0015] Preferably, in one possible implementation of the first aspect, the collaborative output process further includes: Because the switching frequencies of the static var generator module and the active power filter module are not synchronized with the modulation wave, dead zone compensation components are superimposed on the bridge arm drive output by the space vector pulse width modulation stage. The dead zone compensation component is given by looking up the preset compensation timing table based on the phase current polarity and the current voltage sector; When multiple active power filter modules are connected in parallel within the cabinet, a damping term is injected into the inner current loop command of each active power filter module. The damping term is... ,in This is the instantaneous current of the active power filter module. For the instantaneous current of other active power filter modules, These are preset coefficients.

[0016] The beneficial effects of the present invention are as follows: The present invention performs variational mode decomposition on the harmonic current of the low-voltage switchgear grid side, divides the spectrum into multiple frequency intervals and calculates the distortion contribution of each interval, thereby identifying the characteristics of harmonic energy distribution.

[0017] Based on this, a multi-objective constrained optimization model is constructed, which covers module capacity occupancy and residual indicators after governance. The Pareto front is solved using a non-dominated sorting genetic algorithm, and the compensation capacity and priority of the static var generator module and the active power filter module are dynamically allocated accordingly.

[0018] The system automatically switches between phase compensation, reactive power priority, or harmonic priority management strategies based on the real-time status of three-phase imbalance, power factor, and distortion contribution, and checks the DC-side power balance according to the power coupling relationship of the common DC bus.

[0019] By employing dual closed-loop control of the voltage outer loop and the current inner loop, along with coordinated output methods such as resonance tracking and dead-zone compensation, this invention achieves integrated adaptive control of reactive power compensation, harmonic suppression, and three-phase imbalance management, thereby improving the capacity utilization of the modules within the cabinet and the comprehensive management effect under complex operating conditions. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. 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.

[0021] Figure 1 This application provides a flowchart of an adaptive integrated power quality management method for low-voltage switchgear. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0023] Example 1: As Figure 1 As shown, this invention provides an adaptive integrated power quality management method for low-voltage switchgear, comprising: Step S1: Obtain the harmonic content, power factor, and three-phase imbalance of the low-voltage switchgear grid side.

[0024] In this embodiment, synchronous sampling is performed on the three-phase voltage and three-phase current of the low-voltage switchgear on the grid side. The sampling clock is output after the fundamental phase is locked by a phase-locked loop (PLL), and the fundamental frequency dynamically tracks the grid frequency. The PLL adopts a PLL structure based on a synchronous reference coordinate system, which internally includes three basic components: a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). The phase detector converts the three-phase voltages through... Transformation and Transform to Extracting in a rotating coordinate system The axial component serves as the phase error signal. The loop filter employs a proportional-integral controller with a proportional coefficient... Take 180, integral coefficient Taking 3200, the corresponding closed-loop bandwidth is approximately The phase margin is approximately The transfer function of the proportional-integral controller is: Its output is the angular frequency increment. The voltage-controlled oscillator (VCO) obtains the output phase by adding the angular frequency increment from the loop filter output to the reference angular frequency and integrating the sum. This allows the phase-locked loop (PLL) output phase to track the phase of the grid's fundamental positive-sequence voltage in real time, ensuring that the sampling clock is synchronized with the grid's fundamental frequency. The sampling frequency is set to... 256 sampling points are collected in each power frequency cycle. The sampled data is preprocessed by an anti-aliasing filter and then stored in a circular buffer. The anti-aliasing filter is a Butterworth low-pass filter with a cutoff frequency set to [value missing]. The order is 4, and the passband ripple is less than 1. Stopband attenuation greater than .

[0025] RMS value of harmonic current Defined as ,in For the first RMS value of subharmonic current For harmonic order, The highest harmonic order is used in this embodiment. The effective values ​​of each harmonic current are taken as 50. These values ​​are calculated by performing a Fast Fourier Transform (FFT) on the sampled current data. The FFT uses a radix-2 decimation-time algorithm, and the Hanning window is chosen to reduce spectral leakage. The time-domain expression of the Hanning window is as follows: ,in In this embodiment, the window length is... We use 256, with a frequency resolution of 50 Hz. The Fast Fourier Transform outputs the amplitude and phase of each harmonic, and then calculates the effective value of each harmonic current.

[0026] The power factor is obtained by the ratio of fundamental active power to fundamental apparent power. Fundamental active power The fundamental active power is calculated by multiplying the in-phase components of the fundamental voltage and current. The fundamental voltage and current are obtained by extracting the fundamental components using a fast Fourier transform. The formula for calculating the fundamental active power is as follows: ,in This is the effective value of the fundamental voltage. This is the effective value of the fundamental current. This represents the phase difference between the fundamental voltage and the fundamental current. The fundamental apparent power... The calculation formula is Power factor Represented as .

[0027] The three-phase unbalance is the ratio of the effective value of the negative-sequence fundamental component to the effective value of the positive-sequence fundamental component. The negative-sequence and positive-sequence fundamental components are obtained from the three-phase quantities through a symmetrical component transformation. The symmetrical component transformation uses a complex transformation matrix, which is:

[0028] in , , These are the phasor representations of the three-phase fundamental voltages or currents, respectively. For rotation factor, These are positive-order component phasors. For negative-order component phasors These are the zero-sequence component phasors. The phasors of the three-phase fundamental voltage and current are obtained by extracting the fundamental components using a fast Fourier transform. The magnitude of each phasor is the effective value of the fundamental component for that phase, and the argument is the initial phase angle. Three-phase unbalance. The calculation formula is ,in This is the effective value of the negative sequence fundamental voltage. This is the effective value of the positive sequence fundamental voltage.

[0029] Step S2: Based on the harmonic content, divide it into multiple frequency intervals through spectral decomposition, and calculate the distortion contribution of each frequency interval.

[0030] In this embodiment, for , , The harmonic currents of the three phases are subjected to variational mode decomposition. For example, let's assume... The phase harmonic current signal is sampling frequency Sampling window length This corresponds to 2560 sampling points. Variational mode decomposition will... Decomposed into One intrinsic mode function Each mode corresponds to a center frequency. The augmented Lagrangian function for the variational problem is:

[0031] in The penalty factor is set to the preset number of decomposition layers. , For Lagrange multipliers, for Impulse function For time Partial derivatives, noise margin The frequency domain update formula is obtained by iteratively solving the problem using the alternating direction multiplier method:

[0032]

[0033]

[0034] in For the first The intrinsic mode function at the th ... Frequency domain value at the next iteration for Frequency domain of phase harmonic current signal Transformation, For the first Frequency domain values ​​of each mode Frequency domain of Lagrange multipliers Transformation, For angular frequency variables, For the first Lagrange multiplier frequency domain values ​​in the next iteration For the first The frequency domain values ​​of the Lagrange multipliers in the next iteration, and the iteration termination condition is... Preset number of decomposition layers This ensures that the center frequencies of each intrinsic mode function cover integer multiples of harmonic frequencies from the 2nd to the 50th order. to The initial center frequency is uniformly distributed in to Within the range. After decomposition, the 19 intrinsic mode functions are grouped into 5 frequency intervals in ascending order of their center frequencies: the first interval to It contains four intrinsic mode functions corresponding to the 2nd to 5th harmonics; the second interval to It contains five intrinsic mode functions corresponding to the 6th to 10th harmonics; the third interval to It contains 7 intrinsic mode functions corresponding to the 11th to 17th harmonics; the fourth interval to It contains eight intrinsic mode functions corresponding to the 18th to 25th harmonics; the fifth interval to It contains 25 intrinsic mode functions corresponding to the 26th to 50th harmonics.

[0035] For each intrinsic mode function Perform Hilbert transform to obtain analytic signal Take its modulus As instantaneous amplitude ,in for Transform operator. Within each sampling window, for each frequency range Calculate the square root of the sum of the squares of the instantaneous amplitudes of all intrinsic mode functions within the interval to obtain the equivalent harmonic current in that interval. ,in This represents the number of intrinsic mode functions within this interval. For the th interval indivual The instantaneous amplitude. Similarly, we obtain... Harmony Phase equivalent harmonic current and The equivalent harmonic currents of the three phases are combined into the comprehensive equivalent harmonic current for this interval using the following formula:

[0036] Total equivalent harmonic current The total number of frequency intervals Then the distortion contribution in this frequency range. To obtain a stable distortion contribution for subsequent optimization, the entire sampling window is used. The arithmetic mean of the values ​​is output as the distortion contribution of the sampling window, i.e. ,in The number of sampling points. For the first At each sampling time, after each sampling window, a set of distortion contribution values ​​for five frequency ranges is output. to .

[0037] Step S3: Based on the distortion contribution, power factor, and three-phase imbalance, dynamically allocate the compensation capacity and priority of the static var generator module and the active power filter module in the cabinet using a multi-objective constraint optimization model.

[0038] In this embodiment, the multi-objective constrained optimization model includes a set of objective functions and a set of constraints. The set of objective functions simultaneously covers the capacity occupancy of the static var generator (SVM), the capacity occupancy of the active power filter (APF) module, and the residual index after treatment. The capacity occupancy of the SVM module... Defined as ,in , , These represent the three-phase output reactive power within the sampling window, in var. In this embodiment, the rated reactive power capacity of the static var generator module is... Pick Capacity usage of the active power filter module Defined as ,in For the first Effective value of subharmonic compensation current The highest harmonic order, The rated compensation current of the active power filter module is specified in this embodiment. Pick The residual index after treatment is the weighted aggregate value of three-phase imbalance, power factor deviation, and total harmonic distortion in the next sampling window, predicted under the distribution scheme. Three-phase imbalance... The power factor deviation is defined as the ratio of the effective value of the negative-sequence fundamental component to the effective value of the positive-sequence fundamental component. Defined as the absolute value of the difference between the target power factor and the predicted power factor, with the target power factor set at 0.95, the total harmonic distortion value... Defined as the ratio of the square root of the sum of the squares of the effective values ​​of all harmonic currents to the effective value of the fundamental current. The three weights are dynamically updated within a preset historical time window based on the grid-side load type. The historical time window is 10 sampling windows long, and each sampling window is [length missing]. Load types are divided into two categories: linear loads and nonlinear loads. Linear loads refer to loads where current and voltage have a linear relationship and do not generate harmonics; nonlinear loads refer to loads containing power electronic devices that generate harmonic pollution. For linear loads, the weighting for three-phase unbalance is 0.3, the weighting for power factor deviation is 0.5, and the weighting for total harmonic distortion is 0.2; for nonlinear loads, the weighting for three-phase unbalance is 0.2, the weighting for power factor deviation is 0.3, and the weighting for total harmonic distortion is 0.5. The weighting is updated by statistically analyzing the frequency of occurrence of each load type within a historical time window, and taking the weight combination corresponding to the load type with the highest frequency as the current weight.

[0039] The constraint set covers the upper and lower limits of single-phase and three-phase output of the static var generator (SVM), the upper and lower limits of frequency output of the active power filter (APF), the power coupling relationship between the SVM and APF in the cabinet sharing a DC bus, and the upper limit of single-phase current in phase-by-phase compensation scenarios. The upper limit of single-phase output of the SVM is given based on the rated value of each phase arm in the cabinet; in this embodiment, the rated reactive power output of each phase arm is... The lower limit of single-phase output is The maximum output of the three-phase system is... The lower limit of three-phase output is The upper limit of the active power filter module's output frequency is calculated based on the switching frequency and inductor parameters within the cabinet. In this embodiment, the switching frequency is... The inductance parameters are Constrained by one-eighth of the switching frequency and the resonant frequency determined by the inductance, the smaller of the two values ​​is taken as the upper limit, and the calculated upper limit of the frequency output is: The lower limit of frequency output is The common DC bus power coupling relationship is expressed as follows: the sum of the active power fluctuations on the DC side of the static var generator (SGF) and the active power filter (APF) is maintained in balance through closed-loop control of the DC side capacitor voltage. The reference value for the DC side capacitor voltage is set as follows: The capacitance value of the DC side capacitor is In a phase-splitting compensation scenario, the upper limit of the output current of each phase is taken as the rated current value of the phase bridge arm. In this embodiment, the rated current of the phase bridge arm is... .

[0040] The multi-objective constrained optimization model was solved using a non-dominated sorting genetic algorithm. The population size was set to 100, the maximum number of generations to 200, the crossover probability to 0.8, and the mutation probability to 0.05. The decision variable was the three-phase reactive power output command of the static var generator module. , , and the harmonic compensation current commands of the active power filter module. arrive There are a total of 52 decision variables. The range of values ​​for the decision variables is restricted by a set of constraints. During population initialization, 100 individuals are randomly generated within the range of decision variable values, each corresponding to a set of decision variable values. Three objective function values ​​are calculated for each individual: the capacity occupancy of the static var generator module, the capacity occupancy of the active power filter module, and the residual index after treatment. Individuals in the population are non-dominated based on their objective function values, dividing all individuals into multiple non-dominated levels, with the first level being the Pareto optimal solution set. Within the same non-dominated level, the crowding degree of each individual is calculated, defined as the sum of the distances between adjacent individuals in each objective function direction within the same non-dominated level. The selection operation uses a tournament selection method, randomly selecting two individuals from the population each time and comparing their non-dominated levels; the individual with the lower non-dominated level wins; if the non-dominated levels are the same, the individual with the higher crowding degree wins. The crossover operation uses a simulated binary crossover method, with a crossover distribution exponent set to 15. The mutation operation uses a multinomial mutation method, with a mutation distribution exponent set to 20. After selection, crossover, and mutation operations, a progeny population is generated. The parent and progeny populations are merged to form a new population. The new population is then subjected to non-dominated sorting and crowding calculations again, retaining the top 100 individuals as the next generation. This process is repeated until the maximum number of generations (200) is reached. All individuals at the first non-dominated level in the final generation are output as the Pareto front. The optimal solution is selected from the Pareto front as the basis for capacity and priority allocation. The selection principle is to find the individual with the smallest residual index after governance on the Pareto front. If multiple individuals have the same residual index after governance, the individual with the smallest sum of the static var generator capacity occupancy and the active power filter capacity occupancy is selected.

[0041] The dynamic allocation process of compensation capacity and priority is executed based on the real-time status of three-phase imbalance, power factor, and distortion contribution. When the three-phase imbalance exceeds the first threshold (set to 2%), the static var generator (SVA) independently issues three-phase reactive power output commands for each phase, while the active power filter (APF) superimposes harmonic compensation commands on each phase, and the two jointly execute phase-by-phase compensation. The three-phase reactive power output commands of the SVA are directly taken from the solution results of the multi-objective constrained optimization model, and the harmonic compensation commands of the APF are allocated proportionally to the distortion contribution in each frequency range. When the three-phase imbalance does not exceed the first threshold and the power factor is lower than the second threshold (set to 0.90), the SVA receives the highest compensation priority, and the output commands are dominated by the reactive power deficit, which is the difference between the reactive power corresponding to the target power factor and the actual reactive power. The target power factor is 0.95. The output commands of the active power filter module cover all frequency ranges while meeting the upper limit of capacity. Its capacity is allocated according to the proportion of distortion contribution in each frequency range, with the frequency range with the highest distortion contribution receiving the largest proportion of compensation capacity. When the three-phase imbalance does not exceed the first threshold and the power factor is not lower than the second threshold, the frequency range with the highest distortion contribution receives the highest compensation priority in the active power filter module. The output commands of the static var generator module then revert to three-phase balanced reactive power fine-tuning. The adjustment amount of the three-phase balanced reactive power fine-tuning is the reactive power corresponding to the difference between the current power factor and the target power factor, and the adjustment range does not exceed 5% of the rated capacity of the static var generator module.

[0042] The dynamic allocation process also includes a capacity scaling mechanism. When the optimized single-phase or three-phase aggregated capacity of the static var generator (SVM) or active power filter (APF) exceeds the rated upper limit of the corresponding module in the cabinet, the allocation is scaled according to the currently determined priority order. During the scaling process, priority is given to ensuring that the allocation of the imbalance mitigation channel under the phase-by-phase compensation scenario is not reduced, while the allocation of other channels is reduced proportionally. The imbalance mitigation channel refers to the channel where the SVM and APF jointly perform phase-by-phase compensation when the three-phase imbalance exceeds the first threshold. The scaling factor for the remaining channels is the ratio of the rated upper limit to the actual allocation. The power balance on the DC side between the static var generator (SVR) and the active power filter (APF) is rechecked based on their common DC bus power coupling relationship. The check method is to calculate the sum of the active power on the DC side of the SVR and APF. If the sum exceeds the regulation capability of the DC side capacitor voltage closed-loop control, the three-phase reactive power output command of the SVR is adjusted to reduce active power fluctuations while meeting the upper and lower limits of single-phase output. The final allocation value is output after iterating until the capacity constraint is met.

[0043] Step S4: Based on the allocated compensation capacity and priority, control the static var generator module and the active power filter module to perform coordinated output of reactive power compensation, harmonic suppression and three-phase imbalance management.

[0044] In this embodiment, the static var generator module employs a dual closed-loop control strategy consisting of an outer voltage loop and an inner current loop. The input to the outer voltage loop is the reference value of the DC-side capacitor voltage. Compared with actual feedback value The difference is generated after being processed by the proportional-integral controller. Shaft current reference value The proportional coefficient of a proportional-integral controller Set to 2.5, integral coefficient The voltage outer loop bandwidth is set to 120. This ensures a rapid response to DC-side voltage fluctuations. The inner current loop... Decoupling control of three-phase current in a rotating coordinate system. Shaft current reference value From the voltage outer loop output, Shaft current reference value Determined according to the reactive power compensation instruction. shaft and The shaft current error is adjusted by a proportional-integral controller, with a proportional coefficient. Set to 0.8, integral coefficient The bandwidth of the inner current loop is set to 60. The output of the inner current loop. shaft and Shaft voltage command and After the reverse Transformation into voltage command in two-phase stationary coordinate system and The signal is then fed into the space vector pulse width modulation (SVM) stage to generate the drive signal. The SVM employs a seven-segment synthesis method with a switching frequency of... Set as carrier period for Voltage utilization is increased to 100%.

[0045] The active power filter module uses a harmonic current detection stage to extract compensation commands for each frequency. Harmonic current detection first synchronously samples the three-phase load current at a sampling frequency... Set as 256 sampling points are collected per power frequency cycle. The sampled data is filtered by a digital low-pass filter to remove high-frequency noise. The low-pass filter is a second-order Butterworth filter with a cutoff frequency set to [value missing]. Then the three-phase current is passed through Transform to a two-phase stationary coordinate system, then through Transform to Rotate the coordinate system. In the coordinate system, the fundamental active component is represented as a DC quantity, and the fundamental reactive component is also represented as a DC quantity, while the harmonic components are represented as AC quantities. The fundamental active and reactive DC quantities are extracted using a low-pass filter. The low-pass filter is a first-order inertial filter with a time constant of [missing information]. Set as The corresponding cutoff frequency is The original The harmonic components are obtained by subtracting the fundamental DC current from the shaft current. AC quantities in a coordinate system. The harmonic AC quantities are converted through an inverse... The system is transformed back to a two-phase stationary coordinate system to obtain the instantaneous values ​​of the harmonic currents. Based on the harmonic compensation commands, the amplitude and phase of each harmonic current are adjusted to generate compensation commands for each frequency. The harmonic components of each frequency are tracked by the resonant controller and then fed into the current prediction and tracking stage to generate drive signals. The transfer function of the resonant controller is... The resonant gain Set to 150, cutoff frequency Set as , Let be the center angular frequency of each harmonic. For the th harmonic... Second harmonic The resonant controller has infinite gain at the fundamental frequency, enabling zero steady-state error tracking of specific frequency harmonics. The current prediction tracking stage employs a deadbeat predictive control algorithm, predicting the output voltage command for the next switching cycle based on the current compensation current command and the system model. The system model includes a filter inductor. and equivalent resistance , Set as , Set as Sampling period of predictive control algorithm Set as ,correspond The sampling frequency. The output voltage command is processed by a space vector pulse width modulation stage to generate a drive signal, and the switching frequency of the active power filter module. Set as carrier period for .

[0046] The static var generator (SGF) and active power filter (APF) share a DC bus, and the DC-side voltage is actively maintained by the SGF's outer voltage loop. (DC-side capacitor voltage reference value) Set as When phase compensation is applied, Switch to This is to improve the voltage support capability during phase-separated compensation. DC-side capacitor value. Set as Composed of four The electrolytic capacitors are connected in parallel. The fluctuation range of the DC side voltage is controlled within... Within, that is to between.

[0047] Because the switching frequencies of the static var generator module and the active power filter module are not synchronized with the modulation wave, a dead-time compensation component is superimposed on the bridge arm drive output by the space vector pulse width modulation stage. Dead time Set as The dead-zone compensation component is determined by looking up a preset compensation timing table based on the phase current polarity and the current voltage sector. The compensation timing table is pre-stored in the digital signal processor's read-only memory; the table size is 6 sectors multiplied by 2 current polarities, resulting in 12 compensation values. The phase current polarity is determined using a hysteresis comparison method, with the hysteresis width set to [value missing]. This prevents frequent polarity jumps when the current crosses zero. The voltage sector is determined by the angle of the reference voltage vector in space vector pulse width modulation, with an angle range of [missing information]. to It is divided into 6 sectors, each sector spanning For the static var generator module, the amplitude of the dead-zone compensation component... ,in This is the DC-side voltage. For active power filter modules, the amplitude of the dead-time compensation component... The dead-zone compensation components of the two modules are superimposed in their respective space vector pulse width modulation stages. The compensation timing tables are the same, but the compensation amplitude is calculated separately according to their respective carrier periods.

[0048] When multiple active power filter modules are connected in parallel within the cabinet, a damping term is injected into the inner current loop command of each active power filter module. The damping term is... ,in This is the instantaneous current of the active power filter module. This is the sum of the instantaneous currents of the remaining parallel modules. The preset coefficient is set to 0.15. The damping term injection is achieved by superimposing an additional component into the inner current loop command. This additional component is proportional to the inter-module circulating current, effectively suppressing circulating current oscillations between parallel modules. This ensures rapid attenuation of the high-frequency circulating current.

[0049] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for adaptive integrated power quality management for low-voltage switchgear, characterized in that, The method includes: Step S1: Obtain the harmonic content, power factor, and three-phase imbalance of the low-voltage switchgear grid side; Step S2: Based on the harmonic content, the frequency spectrum is divided into multiple frequency ranges through spectral decomposition, and the distortion contribution of each frequency range is calculated. Step S3: Based on the distortion contribution, power factor, and three-phase imbalance, use a multi-objective constraint optimization model to dynamically allocate the compensation capacity and priority of the static var generator module and the active power filter module in the cabinet. Step S4: Based on the allocated compensation capacity and priority, control the static var generator module and the active power filter module to perform coordinated output of reactive power compensation, harmonic suppression and three-phase imbalance management.

2. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 1, characterized in that, Step S1 includes: Synchronous sampling of the three-phase voltage and three-phase current on the grid side of the low-voltage switch is performed. The sampling clock is output after the fundamental phase is locked by the phase-locked loop, and the fundamental frequency dynamically tracks the grid frequency. RMS value of harmonic current Defined as ,in For the first RMS value of subharmonic current For harmonic order, The highest harmonic order; The power factor is obtained by the ratio of fundamental active power to fundamental apparent power; The three-phase unbalance is the ratio of the effective value of the negative-sequence fundamental component to the effective value of the positive-sequence fundamental component. The negative-sequence fundamental component and the positive-sequence fundamental component are obtained by symmetrical component transformation of the three-phase quantities.

3. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 1, characterized in that, The calculation of distortion contribution in step S2 includes: Variational mode decomposition is performed on the three-phase harmonic current within the sampling window to obtain several intrinsic mode functions, each of which corresponds to a center frequency; The number of decomposition layers K is preset so that the center frequency of each intrinsic mode function covers the fundamental frequency and each integer multiple of the harmonic frequency; The intrinsic mode functions are grouped into multiple frequency intervals in ascending order of center frequency, and each interval contains one or more adjacent consecutive center frequencies. Within each frequency range, the equivalent harmonic current of that range. Defined as ,in For the th interval The instantaneous amplitude of each intrinsic mode function, This represents the number of intrinsic mode functions within this interval. Frequency range index; The equivalent harmonic current quantity With total equivalent harmonic current The ratio is used as the distortion contribution rate for that interval. ,Right now ,in , This represents the total number of frequency ranges.

4. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 1, characterized in that, The multi-objective constrained optimization model in step S3 includes a set of objective functions and a set of constraint conditions. The objective function set simultaneously includes the capacity occupancy of the static var generator module, the capacity occupancy of the active power filter module, and the residual index after treatment. The residual index is obtained by aggregating the three-phase unbalance residual, reactive power residual and harmonic residual according to a preset weight. The constraint set covers the upper and lower limits of single-phase and three-phase output of the static var generator module, the upper and lower limits of frequency output of the active power filter module, the power coupling relationship between the static var generator module and the active power filter module in the cabinet sharing the DC bus, and the upper limit of single-phase current in the phase compensation scenario. The multi-objective constrained optimization model is solved using a non-dominated sorting genetic algorithm. After outputting the Pareto front, the optimal solution is selected according to the current working conditions as the basis for capacity and priority allocation.

5. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 4, characterized in that, In the set of objective functions Static Var Generator Module Capacity Usage Defined as ,in , , These represent the three-phase output reactive power within the sampling window. This refers to the rated reactive power capacity of the static var generator module. Capacity usage of active power filter module Defined as ,in For the first Effective value of subharmonic compensation current The highest harmonic order, This is the rated compensation current of the active power filter module; The residual indicators after treatment are the weighted aggregate values ​​of three-phase imbalance, power factor deviation and total harmonic distortion value predicted under the distribution scheme for the next sampling window. The weights of the three items are dynamically updated within a preset historical time window according to the load type on the grid side.

6. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 5, characterized in that, In the constraint condition group, the upper and lower limits of the single-phase output of the static var generator module are given according to the rated value of each phase bridge arm in the cabinet. The upper and lower limits of the frequency output of the active power filter module are given according to the switching frequency and inductance parameters inside the cabinet; The common DC bus power coupling relationship is expressed as follows: the sum of the active power fluctuations on the DC side of the static var generator module and the active power filter module is kept in balance through closed-loop control of the DC side capacitor voltage. In a phase-splitting compensation scenario, the upper limit of the output current of each phase is taken as the rated current value of the phase bridge arm.

7. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 6, characterized in that, The dynamic allocation process of compensation capacity and priority includes: When the three-phase imbalance exceeds the first threshold, the static var generator module independently gives three-phase reactive power output commands for each phase, and the active power filter module superimposes in-phase harmonic compensation commands on each phase. The two work together to perform phase-by-phase compensation. When the three-phase imbalance does not exceed the first threshold and the power factor is lower than the second threshold, the static var generator module obtains the highest compensation priority, and the output command is dominated by the reactive power deficit. The output command of the active power filter module covers all frequency ranges under the condition of meeting the capacity limit, and its capacity occupancy is allocated according to the proportion of distortion contribution of each frequency range. When the three-phase imbalance does not exceed the first threshold and the power factor is not lower than the second threshold, the frequency range with the highest distortion contribution obtains the highest compensation priority in the active power filter module, and the static var generator module outputs a command to switch to three-phase balanced reactive power fine-tuning.

8. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 7, characterized in that, The dynamic allocation process also includes: When the single-phase or three-phase aggregated capacity of the optimized static var generator module or active power filter module exceeds the rated upper limit of the corresponding module in the cabinet, the allocation quantity is scaled according to the currently determined priority order. During the scaling process, priority is given to ensuring that the allocation of imbalance management channels in phase compensation scenarios is not reduced, while the remaining channels are reduced proportionally. The power balance on the DC side between the static var generator module and the active power filter module is rechecked according to the common DC bus power coupling relationship. The final allocation value is output after iterating until the capacity constraint is met.

9. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 1, characterized in that, The collaborative output process in step S4 includes: The static var generator module employs a dual closed-loop control system consisting of an outer voltage loop and an inner current loop. The inner current loop... After decoupling in the coordinate system, the signal is fed into the space vector pulse width modulation stage to generate the driving signal. The active power filter module uses a harmonic current detection stage to extract compensation commands for each frequency. In the coordinate system, the fundamental component is separated by decoupling the active and reactive power of the fundamental wave. The harmonic components of each frequency are tracked by the resonant controller and then sent to the current prediction and tracking stage to generate the driving signal. The static var generator module and the active power filter module share a DC bus. The DC side voltage is actively maintained by the voltage outer loop of the static var generator module, and the reference value of the DC side capacitor voltage switches depending on whether the phase compensation is engaged or not.

10. The adaptive integrated power quality management method for low-voltage switchgear as described in claim 9, characterized in that, The collaborative output process also includes: Because the switching frequencies of the static var generator module and the active power filter module are not synchronized with the modulation wave, dead zone compensation components are superimposed on the bridge arm drive output by the space vector pulse width modulation stage. The dead zone compensation component is given by looking up the preset compensation timing table based on the phase current polarity and the current voltage sector; When multiple active power filter modules are connected in parallel within the cabinet, a damping term is injected into the inner current loop command of each active power filter module. The damping term is... ,in This is the instantaneous current of the active power filter module. For the instantaneous current of other active power filter modules, These are preset coefficients.

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