CN112510712A - Inductance current proportion feedforward control hybrid filtering system based on RDFT - Google Patents

Inductance current proportion feedforward control hybrid filtering system based on RDFT Download PDF

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CN112510712A
CN112510712A CN202011337841.3A CN202011337841A CN112510712A CN 112510712 A CN112510712 A CN 112510712A CN 202011337841 A CN202011337841 A CN 202011337841A CN 112510712 A CN112510712 A CN 112510712A
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current
harmonic
circuit
rdft
filter
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张家亮
赵宇恒
赵子龙
魏心炜
熊仪
余佳傲
张磊
钟嘉俪
强雪
余千依
夏定元
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Wuhan University of Technology WUT
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Power Conversion In General (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

The invention relates to a mixed filtering system based on inductance current proportion feedforward control of RDFT, which comprises a harmonic detection circuit, a passive filter, an active filter, an inverter current control circuit and a power compensation circuit. The filtering of harmonic waves adopts a novel parallel mixed type filtering structure combining active filtering and passive filtering, an inductive current proportion feedforward control mode is used, the passive filter is used for bearing most of harmonic waves and reactive compensation tasks, the capacity of the active power filter is reduced, the filtering characteristic of the passive filter is improved by the active filter, and the excellent filtering effect with low cost and low energy consumption is realized. The harmonic detection and compensation in the system adopts a sliding window iteration DFT algorithm which is suitable for an Active Power Filter (APF) and has high operation speed and tracking precision, and the operation delay is reduced. The inverter current control circuit of the system adopts an inductive current proportion feedforward control algorithm to predict and compensate circuit current and reduce the harmonic distortion rate of a power grid.

Description

Inductance current proportion feedforward control hybrid filtering system based on RDFT
Technical Field
The invention relates to the technical field of power systems, in particular to a mixed filtering system based on inductance current proportion feedforward control of RDFT.
Background
Ideally, the voltage and current in the power grid are both sine waves. However, a large number of nonlinear loads exist in the actual electrical appliance, and the sinusoidal voltage is applied to the nonlinear loads, so that the fundamental current is distorted, and thus, harmonic waves are generated.
In recent years, various high-power nonlinear electronic devices (such as refrigerators and air conditioners in civil buildings) of power consumers are increasing, and a great burden is imposed on a power grid. When current flows through the nonlinear electronic equipment, the current and the applied voltage are not in a linear relation, a non-sinusoidal current is formed, and therefore harmonic waves are generated. Harmonic pollution in the current power system is increasingly serious, harmonic interference is a large 'public nuisance' which influences the quality of electric energy, the safe and stable operation of the power system is seriously threatened, and countermeasures are urgently needed to be taken.
The harmonic damage is very serious. In civil buildings, the harmonic wave reduces the efficiency of the production, transmission and utilization of electric energy, and increases the expenditure of electric charges; secondly, the harmonic wave can cause the transformer to be overheated, accelerate the insulation aging, shorten the service life of the transformer and reduce the reliability of power supply; for the outside of the power system, the harmonic waves can generate serious interference on communication equipment and electronic equipment, and the normal work of the equipment is influenced.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a mixed filtering system based on the inductance current proportion feedforward control of the RDFT, aiming at solving the problem of external harmonic interference of a power system and meeting the requirements of harmonic treatment and reactive compensation of a high-voltage high-power system.
In order to achieve the above object, the present invention provides a hybrid filter system based on inductor current proportional feedforward control of RDFT, which is characterized in that the hybrid filter system comprises:
the harmonic detection circuit: the device is used for collecting and analyzing transmission current signals in a three-phase power grid and monitoring harmonic components of the power grid; the harmonic detection circuit outputs harmonic current by adopting a sliding window iteration DFT algorithm;
a passive filter: for filtering out harmonics;
an active filter: the passive filter is used for improving the filtering characteristic of the passive filter and inhibiting the resonance between the power grid and the passive filter;
the inverter current control circuit predicts a compensation value of circuit current based on an inductance current proportion feedforward control algorithm, disperses a circuit state equation by adopting backward Euler approximation, constructs a prediction model and controls output compensation current.
Further, the harmonic detection circuit calculates a recursive formula of the harmonic current component by using a sliding window iterative DFT algorithm as follows:
Figure BDA0002797689450000021
in the formula An、BnFor the currently calculated nth harmonic component, An'、Bn' the N harmonic components from the previous calculation, N being the number of samples per cycle, NcT is the period and w is the fundamental angular frequency for the latest sampling point.
Further, the prediction model of the inverter current control circuit is:
Figure BDA0002797689450000022
in the formula uab(K +1) is the next beat of output voltage of the inverter circuit control circuit, L is the inductance value, T is the sampling period, K is the scaling factor, iL *(k +1) is the inductor current of the next beat,
Figure BDA0002797689450000023
the next beat of the grid voltage.
Furthermore, the passive filter is composed of a plurality of single tuning branches, and a pure tuning branch corresponding to the harmonic order to be compensated is arranged; the active filter and the additional inductor are connected in parallel through the coupling transformer and then connected in series into the passive filter.
Furthermore, the hybrid filter system further comprises a power compensation circuit which is connected with the three-phase power grid in parallel and used for compensating reactive power in the power grid, filtering harmonic current and balancing the three-phase power grid.
Further, the compensation capacity of the power compensation circuit is calculated by the following formula:
Figure BDA0002797689450000031
wherein Q is the compensation capacity, P is the active calculation power of the load,
Figure BDA0002797689450000032
is the current reactive phase angle.
Furthermore, the harmonic detection circuit comprises a voltage transformer, a hall sensor and a DFT computation module, wherein the voltage transformer is used for providing a power grid voltage signal, the hall sensor is used for measuring a direct current side capacitance voltage signal and measuring a load current signal, and the DFT computation module is used for computing a harmonic current.
Furthermore, an optical isolation driving circuit is arranged between the harmonic detection circuit and the active filter.
Furthermore, the inverter current control circuit comprises a semiconductor switching device, a grid-connected inductor L and a circuit equivalent series resistor r.
Compared with the prior art, the technical scheme of the invention can obtain the following beneficial effects:
1. the invention provides a sliding window iteration DFT algorithm with high operation speed and tracking precision, which is suitable for APF, so that the operation delay of harmonic circuit detection is greatly reduced, and the fast and accurate system of harmonic detection has extremely high real-time performance.
2. The hybrid filter circuit of the invention gives consideration to the advantages of the APF and the passive power filter, uses the passive filter to undertake most of the tasks of harmonic wave and reactive compensation, reduces the capacity of the active power filter, improves the filter characteristic of the passive filter and realizes the excellent filter effect with low cost and low energy consumption.
3. The inverter current control circuit provided by the invention adopts an inductive current proportion feedforward control algorithm to predict and compensate the circuit current and reduce the harmonic distortion rate of the power grid.
4. Based on the idea of traditional dead-beat predictive control, the invention adopts backward Euler approximation to disperse the state equation of the inverter control circuit, and constructs a new predictive model, thereby deriving an improved dead-beat predictive control.
5. The reactive power compensation provided by the invention can improve the power factor of a power grid, reduce the loss and improve the power supply efficiency.
Drawings
Fig. 1 is a block diagram of a hybrid filtering system according to the present invention.
Fig. 2 is a circuit diagram of a hybrid filtering system according to the present invention.
Fig. 3 is a single-phase equivalent circuit structure diagram of the hybrid filtering system according to the present invention.
FIG. 4 is a block diagram of the inverter current control circuit of FIG. 1
Fig. 5 is a block diagram of the power compensation module of fig. 1.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
As shown in fig. 1, the hybrid filtering system based on inductor current proportional feedforward control of RDFT according to the present invention includes: harmonic detection circuit, passive filter, active filter, inverter current control circuit, power compensation circuit.
The harmonic detection circuit: the device is used for collecting and analyzing transmission current signals in a three-phase power grid and monitoring harmonic components of the power grid; the harmonic detection circuit outputs harmonic current by adopting a sliding window iteration DFT algorithm.
A passive filter: for filtering out harmonics.
An active filter: for improving the filtering characteristics of the passive filter and for suppressing possible resonances between the network and the passive filter.
The inverter current control circuit predicts a compensation value of circuit current based on an inductance current proportion feedforward control algorithm, disperses a circuit state equation by adopting backward Euler approximation, constructs a prediction model and controls output compensation current.
And the power compensation circuit is connected with the three-phase power grid in parallel and is used for compensating reactive power in the power grid, filtering harmonic current, reducing THD (harmonic distortion) of the power grid and balancing the three-phase power grid.
In this embodiment, the harmonic detection circuit is mainly composed of a voltage transformer and a hall sensor. The voltage transformer is used for providing a power grid voltage signal for the phase-locked loop. The direct current side capacitance voltage signal measured by the Hall sensor is used for stabilizing the direct current side capacitance voltage and measuring the load current signal for harmonic detection. The harmonic detection circuit adopts a main core chip STM32F407 and is provided with a chip ADE 7913. The ADE7913 direct current power supply is isolated by a DC/DC power supply converter, is a 2-order sigma-delta ADC, and has the sampling frequency of 1024MHz, 24-bit output and 1kHz output frequency. The RDFT harmonic detection algorithm based on wavelet denoising is completed in a main core chip STM32F407, the harmonic signals are subjected to wavelet decomposition, the obtained wavelet coefficients are subjected to thresholding treatment, and finally wavelet reconstruction is carried out to obtain denoised harmonic signals, so that errors caused by noise in the harmonic waves are reduced.
And on the basis of the known calculation value of the previous sampling moment, carrying out recursive operation to obtain a new current component, and adding the sine component and the cosine component obtained by RDFT to obtain the n-th harmonic current. The RDFT operation is simple, the operation delay is reduced, and the harmonic detection is fast and accurate.
For any periodic signal x (T), if the period is T, w is the fundamental angular frequency, and the sampling number per period is N, the sinusoidal component A of the fundamental current is calculated1And a cosine component B1For example, the following steps are carried out:
Figure BDA0002797689450000051
wherein N iscRepresenting the latest sample point, the current component A being calculated at the current sampling instant1、B1Calculating the current component A from the previous sampling time1'、B1' there is a recursive relationship between:
Figure BDA0002797689450000052
therefore, for any nth harmonic component, a new current value can be obtained by simple calculation on the basis of the calculated value at the previous sampling moment. The whole recursive computation process only needs to complete the summation operation in the whole period in one period of the initialization stage, and then the nth harmonic component A can be completed according to the recursive computation of the formulan、BnAnd (4) calculating.
The final nth harmonic current is calculated by the formula:
Figure BDA0002797689450000061
xnand (t) is the nth harmonic current.
And (3) performing a sliding window iteration DFT algorithm, enabling real-time sampling data to participate in load current calculation, storing the calculated new sum to an old sum data storage unit again, positioning the storage position of the current sampling data through a circular pointer, returning the pointer to the initial position of a storage space after completing the calculation of the sampling data of N points in a complete period, and starting the data cycle replacement of the next period. The RDFT algorithm greatly reduces the operation delay of the detection of the harmonic circuit, and the system has extremely high real-time performance.
The circuit structure of the hybrid filtering system proposed by the present invention is shown in fig. 2, USIs the grid voltage; zSIs the equivalent impedance of the power grid; i isS、IL、IFRespectively a power grid side current, a load side current and a filtering branch current; l isaAn additional inductor; t is a coupling transformer; l is a grid-connected inductor; u shapedcIs a direct current side energy storage capacitor.
In this embodiment, the passive filter is used to filter out most of the harmonics and compensate for some of the reactive power. The passive filtering is composed of a plurality of single tuning branches (including a high-pass filter), and pure tuning branches corresponding to harmonic orders to be compensated are arranged. The active power filter comprises a detection circuit, a control module, a PWM (pulse-width modulation) drive circuit and an IGBT (insulated gate bipolar transistor) module, and forms a current control closed loop. The detection circuit is used for detecting the current output by the passive power filter; and the PWM driving circuit is used for controlling the output current of the IGBT module according to the current data and the instruction current fed back and output by the detection circuit. The active filter is connected with the additional inductor in parallel through the coupling transformer, then connected with the passive filter in series, and then incorporated into the power grid. The active filter and the additional inductor are connected in parallel through the coupling transformer and then connected in series into the passive filter, and the coupling transformer plays a role in isolating and matching the voltage and current capacity of the PWM converter. Is provided withThe output current of source power filter (APF) is controlled by other network current and harmonic source current, and is controlled as a harmonic current source, and the fundamental reactive current is forced to flow through additional inductor LaOnly harmonic currents flow in the APF. Additional inductance LaThe fundamental impedance is small compared to the passive filter, so the fundamental voltage sustained by the APF is small. Therefore, the hybrid active filter can effectively reduce the capacity of the active part and is suitable for high-power occasions.
The passive filter can filter out single harmonic of a high-voltage power grid, but can easily cause system resonance, and the requirement of power grid harmonic treatment is difficult to meet when the passive filter is used alone. Although an Active Power Filter (APF) can overcome the defects of a passive filter, the APF is difficult to independently hang on a high-power medium-high voltage power grid for operation. The hybrid filter circuit has the advantages of both the APF and the passive power filter, and has better performance in the aspects of resonance simulation, harmonic compensation and the like. Through the hybrid filter circuit, the limitations of the capacity, the cost and the like of a switch device can be effectively overcome, the requirements of harmonic suppression and reactive compensation of a high-voltage high-power system can be met, the advantages of active and passive filters are absorbed, and the performance-price ratio is high.
In the present embodiment, the inverter current control circuit is mainly composed of 4 semiconductor switching devices, S1 and S4 constitute one pair of arms, and S2 and S3 constitute another pair of arms. L is the grid-connected inductance, and r is the equivalent series resistance of the circuit.
In the embodiment, the inverter current control circuit adopts an inductance current proportion feedback-grid voltage prediction feedforward control strategy, so that a closed-loop discrete system can be established. The inverter current control circuit is used for controlling the on and off of the switching tube through a signal output by an inductor current proportion feedback-power grid voltage prediction feedforward control strategy. When the system gives alternating current inductive current, the inductive current proportional feedback-power grid voltage prediction feedforward control closed-loop system can accurately track the given inductive current without steady-state errors.
Based on the idea of traditional dead-beat predictive control, the invention adopts backward Euler approximation to disperse the state equation of the inverter control circuit, and constructs a new predictive model, thereby deriving an improved dead-beat predictive control:
Figure BDA0002797689450000071
uab(K +1) is the inverter control circuit output voltage, L is the inductance value, T is the sampling period, K is the scaling factor, iL *(k +1) is the inductor current of the next beat,
Figure BDA0002797689450000072
for the predicted value of the next beat of the grid voltage, the current grid voltage may be used
Figure BDA0002797689450000073
Alternatively, the control method can be directly controlled by the feedback current i at the present momentL(k) Obtaining the control quantity of the next beat
Figure BDA0002797689450000081
And the sensitivity to model parameters is reduced without extrapolating a beat of current through a prediction model.
iL *(k +1) the calculation formula is as follows:
Figure BDA0002797689450000082
uab(k) for the inverter bridge output voltage, iL(k) Is an inductive current ug(k) Is the grid voltage.
The single-phase equivalent circuit of the hybrid filtering system is shown in fig. 3. Ideally, the voltage and current in the power grid are both sine waves. However, a large number of nonlinear loads exist in the actual electrical appliance, and the sinusoidal voltage is applied to the nonlinear loads, so that the fundamental current is distorted, and harmonic current is generated. The nonlinear load in the single-phase equivalent circuit of the hybrid filter can be regarded as a current source IL. The active power filter comprises a detection circuit, a control module, a PWM (pulse-width modulation) drive circuit and an IGBT (insulated gate bipolar transistor) module, and forms a current control closed loop. A detection circuit for detectingCurrent output by the passive power filter; and the PWM driving circuit is used for controlling the output current of the IGBT module according to the current data and the instruction current fed back and output by the detection circuit. The output current of APF is controlled by other direct current, so that it is controlled as a harmonic current source IC；ZS、ZF、ZaRespectively the equivalent impedance of the power grid, the impedance of the passive filter and the impedance of the additional inductor; u shapeSAnd UTThe voltage of the power grid and the voltage of the filter access point are respectively; i isSAnd IFRespectively, the grid side current and the filter branch current.
A main circuit of the inverter current control circuit is shown in fig. 4, wherein L is a grid-connected inductor, r is a circuit equivalent series resistor, and S1, S2, S3 and S4 are semiconductor switching devices respectively; u. ofdIs a DC bus voltage uabFor the inverter bridge output voltage ugFor the mains voltage, iLIs the current flowing through the inductor and is also the grid-connected current.
In the embodiment, the power compensation circuit adopts a Mitsubishi SKMl50GBl2T4 type IGBT, the working current of the IGBT is 150A, the maximum withstand voltage is 1200V, and the frequency is 20 KHz. And a detection circuit in the compensation controller monitors the transmission current signal in the power grid in real time to obtain voltage and current information. And a DSP processor in a control circuit of the compensation controller respectively performs fast Fourier transform on the voltage and current information to calculate the current power factor. When the power factor is known, the reactive power compensation capacity required to be compensated can be determined.
The control circuit part of the power compensation circuit mainly comprises a DSP processor, and the DSP processor respectively carries out fast Fourier transform on the value of the reactive phase angle in the voltage and current information and can calculate the current power factor. When the power factor is known, the reactive power compensation capacity required to be compensated can be determined. Assuming that the active computing power of the load is P (unit: W),
Figure BDA0002797689450000091
the compensated power factor is set to 0.95 for the current reactive phase angle (corresponding to a power factor angle of pi/10). Then the capacity Q is compensated (single)Bit: var) can be obtained by the following formula:
Figure BDA0002797689450000092
and comparing the current compensation capacity with the calculated compensation capacity, and if the current compensation capacity is smaller than the calculated compensation capacity, putting the capacitor bank into the power compensation circuit, otherwise, cutting off the capacitor bank.
The system firstly collects the harmonic current of the power grid through a harmonic detection circuit consisting of a voltage transformer and a Hall sensor, obtains each subharmonic component through an RDFT (remote data transfer) harmonic detection algorithm, inputs each harmonic component into an inverter control circuit, generates compensation current with the same size and opposite phase with each harmonic component through an inductance current proportional feedback-power grid voltage prediction feedforward control strategy, and injects the compensation current into the circuit. Then the current in the circuit (including harmonic current and compensation current) flows into Active Power Filter (APF) and passive filter, so as to reduce the distortion rate of the current and further optimize the filtering effect. And finally, before the filtered circuit current flows into the power grid, reactive power compensation is carried out, so that the power factor of the power grid can be improved, the loss is reduced, and the power supply efficiency is improved.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. A RDFT-based hybrid filter system for inductor current proportional feedforward control, the hybrid filter system comprising:
the harmonic detection circuit: the device is used for collecting and analyzing transmission current signals in a three-phase power grid and monitoring harmonic components of the power grid; the harmonic detection circuit outputs harmonic current by adopting a sliding window iteration DFT algorithm;
a passive filter: for filtering out harmonics;
an active filter: the passive filter is used for improving the filtering characteristic of the passive filter and inhibiting the resonance between the power grid and the passive filter;
the inverter current control circuit predicts a compensation value of circuit current based on an inductance current proportion feedforward control algorithm, disperses a circuit state equation by adopting backward Euler approximation, constructs a prediction model and controls output compensation current.
2. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 1, wherein: the recursive formula of the harmonic detection circuit for calculating the harmonic current component by using the sliding window iteration DFT algorithm is as follows:
Figure FDA0002797689440000011
in the formula An、BnFor the currently calculated nth harmonic component, An'、Bn' the N harmonic components from the previous calculation, N being the number of samples per cycle, NcT is the period and w is the fundamental angular frequency for the latest sampling point.
3. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 1, wherein: the prediction model of the inverter current control circuit is as follows:
Figure FDA0002797689440000012
in the formula uab(K +1) is the next beat of output voltage of the inverter circuit control circuit, L is the inductance value, T is the sampling period, K is the scaling factor, iL *(k +1) is the inductor current of the next beat,
Figure FDA0002797689440000013
the next beat of the grid voltage.
4. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 1, wherein: the passive filtering is composed of a plurality of single tuning branches, and pure tuning branches corresponding to harmonic orders needing to be compensated are arranged; the active filter and the additional inductor are connected in parallel through the coupling transformer and then connected in series into the passive filter.
5. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 1, wherein: the hybrid filter system further comprises a power compensation circuit which is connected with the three-phase power grid in parallel and used for compensating reactive power in the power grid, filtering harmonic current and balancing the three-phase power grid.
6. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 5, wherein: the compensation capacity calculation formula of the power compensation circuit is as follows:
Figure FDA0002797689440000021
wherein Q is the compensation capacity, P is the active calculation power of the load,
Figure FDA0002797689440000022
is the current reactive phase angle.
7. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 2, wherein: the harmonic detection circuit comprises a voltage transformer, a Hall sensor and a DFT calculation module, wherein the voltage transformer is used for providing a power grid voltage signal, the Hall sensor is used for measuring a direct-current side capacitance voltage signal and a load current signal, and the DFT calculation module is used for calculating harmonic current.
8. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 2, wherein: and an optical isolation driving circuit is arranged between the harmonic detection circuit and the active filter.
9. The RDFT-based hybrid filter system for inductor current proportional feed-forward control according to claim 3, wherein: the inverter current control circuit comprises a semiconductor switching device, a grid-connected inductor L and a circuit equivalent series resistor r.
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