CN109698616B - Working method of voltage fluctuation absorption circuit on direct current side of active power filter - Google Patents
Working method of voltage fluctuation absorption circuit on direct current side of active power filter Download PDFInfo
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- CN109698616B CN109698616B CN201910028261.7A CN201910028261A CN109698616B CN 109698616 B CN109698616 B CN 109698616B CN 201910028261 A CN201910028261 A CN 201910028261A CN 109698616 B CN109698616 B CN 109698616B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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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
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
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- 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
- Y02E40/20—Active power filtering [APF]
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Abstract
The invention relates to the field of power technology application, in particular to a working method of an active power filter direct-current side voltage fluctuation absorbing circuit for effectively absorbing direct-current side voltage fluctuation of an active power filter and enabling the active power filter system to stably run.
Description
Technical Field
The invention relates to the field of power technology application, in particular to a working method of a voltage fluctuation absorption circuit on a direct current side of an active power filter.
Background
When a conventional active power filter compensates a three-phase balanced harmonic load, the direct-current side fluctuation is small, but with the development of the active power filter, the requirement on the compensation effect is higher and higher, so that the active power filter needs to compensate the reactive and unbalanced load under certain conditions, and in addition, the active power filter also needs to have the capability of unbalanced compensation due to the split-phase control of a three-phase four-wire system. At this moment, when the active power filter normally works, the problem of direct-current side voltage pulsation inevitably occurs, for asymmetric loads, the direct-current side voltage pulsation can generate great influence at this moment, a double-ring nested mode of current tracking inner ring and direct-current side voltage outer ring control is adopted in the active power filter control, the control mode that the control output of the direct-current voltage outer ring is directly superposed on the given control output of the current inner ring cannot play a role in inhibiting the direct-current side current, on the contrary, the pulsation of a harmonic wave can be superposed on the output current, the compensation performance of the active power filter is influenced, and even the active power filter device is damaged in serious cases.
As shown in fig. 1, since the load imbalance may exist, the parallel active power filter system compensates for the negative sequence, the zero sequence, and the harmonic of the fundamental wave, and the compensation of different currents will have different effects on the system.
In order to analyze the voltage fluctuation on the dc side, the power flow on the ac side and the dc side can be analyzed by power conservation, and at this time, since the capacitor branch in the LCL filter can be neglected and omitted during analysis due to the high frequency ripple flowing through, the equivalent circuit thereof is as shown in fig. 2: where L is the equivalent inductance including the LCL filter inductance and transformer leakage inductance, R represents the equivalent resistance of the reactor, capacitor and inverter losses on the line, CdcThe capacitor is a capacitor of a direct current bus of the voltage source type inverter. vj (j ═ a, b, c) is the grid voltage, ij (j ═ a, b, c) is the compensation current, i isdcIs a direct side current. The instantaneous power of each part is:
wherein:
at this time, the energy consumed on the output filter and the equivalent resistor is small and can be ignored, so that p is available1≈p3. Because the parallel active power filter system needs to compensate three-phase unbalanced current, the symmetrical component method shows that each harmonic current of compensation can be divided into positive and negative zero sequences, namely:
in the formula ipk，ink，izkThe positive and negative zero sequence current effective values of k harmonics respectively. The influence of the positive and negative zero sequences of each harmonic on the direct current side fluctuation is analyzed respectively.
When the output current is k positive sequence currents, the alternating-current side power is as follows:
according to the three-phase symmetry, the sum of three phases containing a three-phase angle relationship in the formula is necessarily 0, the fluctuation caused by the three-phase positive sequence current is the superposition of the positive sequence current every time, and the total power fluctuation is as follows:
it can be seen that the power of the fundamental positive sequence is a constant power, which causes the dc-side voltage to deviate in a fixed direction, and the deviation can be eliminated by injecting reverse power into the dc-side regulation loop.
In particular, when the compensated positive sequence current is reactive, then
The fixed power offset caused by the fundamental positive sequence current is 0, i.e. the fundamental positive sequence reactive current does not cause a dc side change.
Thus, when compensating for all positive sequence currents, the current on the dc side should be:
from the power balance, the dc side voltage fluctuation caused by the positive sequence current is:
similarly, the voltage fluctuation on the direct current side caused by the negative sequence current can be deduced as follows:
the zero sequence current is three-phase symmetrical voltage, so the instantaneous power of the zero sequence current is always 0, namely the symmetrical zero sequence current only flows among three phases and does not cause voltage change at the direct current side.
The total voltage fluctuation on the dc side is:
from the above equation, the dc-side voltage fluctuation value due to the k-th harmonic is related to the harmonic order, and the higher the order, the smaller the fluctuation range, under the same output current effective value.
The influence of the DC side ripple on the control loop is analyzed below using phase A as an example.
As shown in fig. 3, the dc-side voltage loop control takes the double-frequency fluctuation caused by the negative sequence current as an example, and as can be seen from the above analysis, when the double-frequency fluctuation exists on the dc side, the generated command current is:
i.e. the dc side voltage ripple will inject an extra 3 rd harmonic current amount to the compensation current, which will affect the output compensation accuracy.
Similarly, the voltage fluctuation at the direct current side caused by other subharmonics can inject extra harmonic current into the output current through the voltage stabilizing ring at the direct current side, and when the current is serious, the parallel active power filter system can not compensate the load harmonic, but can inject extra harmonic into the power grid, so that the parallel active power filter system becomes a harmonic source needing to be controlled.
In addition, assuming that the parallel active power filter system is modulated by the SPWM, when the modulation wave is per-unit, the dc-side voltage reference value is generally used for per-unit modulation, and at this time, due to the existence of dc-side fluctuation, a fluctuation error exists between the inverter output voltage and the ideal output voltage, and the accumulation of the error will cause the reduction of the control precision, even cause the generation of overmodulation, and affect the stable operation of the parallel active power filter system.
Disclosure of Invention
In order to solve the technical problems, the invention provides a working method of the active power filter direct-current side voltage fluctuation absorption circuit, which can effectively absorb the direct-current side voltage fluctuation of the active power filter and ensure that an active power filter system stably operates.
In order to solve the above technical problems, the present invention provides an active power filter dc side voltage ripple absorption circuit, which includes an active power filter system, a dc side ripple circuit of the active power filter system, each dc side ripple compensation circuit, and a control loop circuit for controlling each dc side ripple compensation circuit, wherein the active power filter system includes a three-phase balancing circuit, a filter circuit, and a nonlinear load connected to each other.
Preferably: the active power filter system is a parallel active power filter system.
Preferably: the direct-current side fluctuation compensation circuit is a non-isolated buck-boost PWM DC/DC conversion circuit.
Preferably: the direct current side fluctuation compensation circuit is a direct current ripple compensation circuit, and the direct current ripple compensation circuit comprises a half bridge, a filter inductor and an absorption capacitor.
Preferably: the control loop circuit comprises a parallel active power filter system direct current side fluctuation repetitive control outer loop, a direct current side fluctuation compensation circuit capacitance mean value voltage stabilizing loop, a PI current inner loop and a parallel active power filter system direct current side voltage feedforward.
The working method of the voltage fluctuation absorbing circuit on the direct current side of the active power filter is provided: the direct-current side fluctuation quantity of the active power filter system is obtained by subtracting the direct-current side instantaneous voltage value of the active power filter system from the direct-current side of the active power filter system calculated by the average filter and is used as the input of the repeated control outer ring, so that a fluctuation compensation value is obtained, the voltage fluctuation of the active power filter system is absorbed by the fluctuation of a direct-current side fluctuation compensation circuit capacitor, the direct-current side fluctuation compensation circuit voltage stabilization quantity is a direct-current quantity, so that the voltage stabilization of the direct-current side fluctuation compensation circuit capacitor can be realized by directly controlling a reference signal by a current inner ring PI, the PI current inner ring controls the direct-current side fluctuation compensation circuit capacitor to absorb or release energy from the active power filter system by tracking an inductive current, and the control result that the direct-current side fluctuation compensation circuit capacitor absorbs the voltage fluctuation of the active power filter system capacitor is realized.
By adopting the technical scheme, the invention has the beneficial effects that: the invention firstly carries out modeling aiming at the direct current side voltage of the active power filter, analyzes the reason of the direct current side voltage fluctuation according to the instantaneous power balance theory, and designs a direct current side fluctuation absorption circuit based on the direct current side fluctuation absorption circuit.
Drawings
Fig. 1 is a block diagram of a parallel active power filter system according to an embodiment of the present invention;
fig. 2 is an equivalent circuit schematic diagram of a parallel active power filter system according to an embodiment of the present invention;
FIG. 3 is a block diagram of DC side voltage control according to an embodiment of the present invention;
FIG. 4 is a circuit topology diagram of the DC-side ripple compensation circuit according to the embodiment of the present invention;
FIG. 5 is a circuit control block diagram of the DC-side ripple compensation circuit according to an embodiment of the present invention;
FIG. 6 shows waveforms of the DC-side voltage and the DC-side ripple compensation circuit capacitor voltage before and after the DC-side ripple compensation circuit operates according to an embodiment of the present invention;
FIG. 7(a) shows the waveforms of the load current, the compensation current and the grid current before the input of the DC side ripple compensation circuit;
FIG. 7(b) shows the waveforms of the load current, the compensation current and the grid current after the DC side ripple compensation circuit is switched on;
fig. 7(c) is a power grid current FFT analysis result before the dc side ripple compensation circuit is put into operation;
fig. 7(d) is a power grid current FFT analysis result after the dc side ripple compensation circuit is put into use.
Detailed Description
The invention is described in further detail below with reference to the following figures and detailed description:
as shown in fig. 4 and 5, an active power filter DC side voltage fluctuation absorbing circuit includes an active power filter system, a parallel active power filter system DC side ripple circuit, each DC side ripple compensating circuit, and a control loop circuit for controlling each DC side ripple compensating circuit, the parallel active power filter system includes a three-phase balancing circuit, a filter circuit, and a non-linear load, the active power filter system is a parallel active power filter system, the DC side ripple compensating circuit is a non-isolated buck-boost PWM DC/DC converting circuit, the DC side ripple compensating circuit is a DC ripple compensating circuit, the DC ripple compensating circuit includes a half bridge, a filter inductor, and an absorbing capacitor, the control loop circuit comprises a parallel active power filter system direct current side fluctuation repetitive control outer loop, a direct current side fluctuation compensation circuit capacitance mean value voltage stabilizing loop, a PI current inner loop and a parallel active power filter system direct current side voltage feedforward.
The working method comprises the following steps: the direct-current side fluctuation quantity of the active power filter system is obtained by subtracting the direct-current side instantaneous voltage value of the active power filter system from the direct-current side of the active power filter system calculated by the average filter and is used as the input of the repeated control outer ring, so that a fluctuation compensation value is obtained, the voltage fluctuation of the active power filter system is absorbed by the fluctuation of a direct-current side fluctuation compensation circuit capacitor, the direct-current side fluctuation compensation circuit voltage stabilization quantity is a direct-current quantity, so that the voltage stabilization of the direct-current side fluctuation compensation circuit capacitor can be realized by directly controlling a reference signal by a current inner ring PI, the PI current inner ring controls the direct-current side fluctuation compensation circuit capacitor to absorb or release energy from the active power filter system by tracking an inductive current, and the control result that the direct-current side fluctuation compensation circuit capacitor absorbs the voltage fluctuation of the active power filter system capacitor is realized.
The working principle is as follows: regarding the design of the direct current side fluctuation compensation circuit:
as can be seen from the analysis of the background art, in order to reduce the fluctuation of the dc side voltage, the dc side capacitance needs to be increased, but the increase of the dc side capacitance is not favorable for the power density and the economy of the parallel active power filter system. In order to solve the problem of direct current side fluctuation of a parallel active power filter system, the invention designs a direct current fluctuation compensation direct current side fluctuation compensation circuit according to a common power decoupling circuit of a single-phase inverter so as to reduce direct current side voltage fluctuation:
as shown in fig. 4, in order to absorb the voltage fluctuation on the dc side, the dc side fluctuation compensation circuit topologies as shown in the figure are designed for the fluctuation of the upper and lower capacitors, respectively, and each circuit includes a half bridge, a filter inductor, and an absorption capacitor.
As is clear from the analysis of the background art, the dc side ripple caused when the parallel active power filter system compensates the negative sequence current of the fundamental wave is the largest, so the following circuit design takes the ripple at the time of compensation of the negative sequence current with the largest ripple as the design basis.
The direct current side fluctuation compensation circuit is a buck-boost type circuit, the fluctuation on the direct current side of the parallel active power filter system is completely transferred to a direct current side capacitor of the direct current side fluctuation compensation circuit, and when the parallel active power filter system compensates the fundamental wave negative sequence current at full power, the voltage fluctuation on the direct current side fluctuation compensation circuit is as follows:
therefore, in order to reduce the total capacitance value of the DC side of the parallel active power filter system and the DC side of the DC side fluctuation compensation circuit and improve the power density of the system, the capacitance voltage drop on the absorption circuit can be improved, and the voltage fluctuation allowable value of the capacitance on the absorption circuit can be improved at the same time.
Therefore, the dc-side ripple compensation circuit is designed to operate in a boost operating mode, so as to increase the capacitance voltage drop on the dc-side ripple compensation circuit and simultaneously increase the allowable value of the capacitance voltage ripple on the dc-side ripple compensation circuit, but it should be noted that the voltage of the capacitor CR on the dc-side ripple compensation circuit should be ensured to be greater than the dc-side voltage value of the parallel active power filter system, and the dc-side ripple of the dc-side ripple compensation circuit may cause the peak value of the capacitance voltage to increase the voltage stress of the switching tube on the dc-side ripple compensation circuit, and the factor needs to be considered comprehensively during design.
The voltage value of the direct current side of the parallel active power filter system is set as VdcAllowable fluctuation is Δ VdcAnd the voltage value of the capacitor on the DC side fluctuation compensation circuit is VdcRAllowable fluctuation is Δ VdcRTheoretically, the maximum reduction factor of the total capacitance is:
the design idea of the filter inductance of the direct-current side fluctuation compensation circuit is consistent with that of the inductance of an output filter of a parallel active power filter system, the change rate of the inductive current needs to be considered in the inductance design, and if the designed inductance is too large, the change rate of the inductive current is reduced, and the change of the reference current cannot be accurately tracked; however, if the designed inductance is too small, the change rate of the inductor current is large, and the loss of the inductor and the switching tube will increase. Therefore, the inductance value needs to be designed by comprehensively considering the two relations.
When the dc side ripple compensation circuit completely absorbs the dc side ripple of the parallel active power filter system, the inductive current, i.e. the dc side voltage ripple current of the parallel active power filter system, can be expressed as:
by deriving the above formula, the change rate of the inductor current reference can be obtained
Because the direct current side fluctuation compensation circuit works in the boost mode, the rising slope of the filter inductance current in one boost switch action period is as follows:
the slope of the fall is:
in order to keep the inductor current tracking well with the reference current, the rising and falling speeds are required to exceed the rate of change of the dc side current, namely:
the selection conditions for obtaining the filter inductance are as follows:
regarding the design of a control loop of a direct-current side fluctuation compensation circuit:
the direct-current side fluctuation compensation circuit aims at absorbing the direct-current side fluctuation quantity of the parallel active power filter system into the energy storage capacitor of the circuit of the direct-current side fluctuation compensation circuit, and is different from the traditional power decoupling circuit, the direct-current side fluctuation of the parallel active power filter system is more complex, and the analysis shows that the direct-current side voltage fluctuation quantity contains fluctuation of a plurality of frequencies, and in order to track a plurality of fluctuation frequencies simultaneously and improve the tracking precision, a control loop adopts a PI + repetitive control double-loop control method:
the voltage fluctuation value of the direct current side of the parallel active power filter system can be obtained by utilizing the MAF filter and a sampling real-time value, and is used as a reference quantity output repetitive controller to track the change of the direct current side fluctuation, the obtained error and the output of a voltage stabilizing loop are input into a PI loop to be adjusted, a control quantity is generated to control the change of the half-bridge duty ratio of the direct current side fluctuation compensation circuit, the control of the whole direct current side fluctuation compensation circuit is completed, and meanwhile, the voltage feedforward control of the direct current side of the parallel active power filter system is introduced to eliminate the influence of the voltage of the direct current side of the parallel active power filter system on the control.
The whole controller comprises the following 4 parts:
1) the direct current side fluctuation of the parallel active power filter system is controlled repeatedly by an outer ring: and obtaining the direct current side fluctuation quantity of the parallel active power filter system by subtracting the direct current side voltage instantaneous value of the parallel active power filter system calculated by an average value filter (MAF) from the direct current side of the parallel active power filter system, and using the direct current side fluctuation quantity as the input of a repetitive control outer ring, thereby obtaining a fluctuation compensation value.
2) And (3) a capacitance mean value voltage stabilizing ring of the direct-current side fluctuation compensation circuit: in order to ensure the normal operation of the direct current side fluctuation compensation circuit, the mean value of the capacitance of the direct current side fluctuation compensation circuit is kept at a stable amount, the voltage fluctuation of the parallel active power filter system is absorbed by utilizing the fluctuation of the capacitance of the direct current side fluctuation compensation circuit, and the voltage stabilizing amount of the direct current side fluctuation compensation circuit is a constant flow, so that the voltage stabilization of the capacitance of the direct current side fluctuation compensation circuit can be realized by directly utilizing the control of a current inner loop PI by utilizing a reference signal.
3) The PI current inner loop controls the direct current side fluctuation compensation circuit capacitor to absorb or release energy from the parallel active power filter system by tracking the inductive current, so that the control result that the direct current side fluctuation compensation circuit capacitor absorbs the voltage fluctuation of the parallel active power filter system capacitor is achieved.
4) And introducing voltage feedforward at the direct current side of the parallel active power filter system to eliminate the influence of voltage fluctuation at the direct current side of the parallel active power filter system on the control effect.
It can be seen that, under the condition of reasonable design of control bandwidth, the control loop can control the direct-current side fluctuation of all sub-harmonics of the parallel active power filter system, and transfer the direct-current side fluctuation quantity of the parallel active power filter system to the direct-current side fluctuation compensation circuit.
And (3) testing: the load is set to be a resistive load with an A phase and a B phase connected by 2 ohms, the C phase is open, the parallel active power filter system only compensates three-phase unbalanced current, the analysis shows that the fluctuation of the direct current side current reaches the maximum, and after the parallel active power filter system operates for a period of time, the parallel active power filter system is put into the direct current side fluctuation compensation circuit and the parallel active power filter system to work for a period of time
As shown in fig. 6: under the condition that the direct current side fluctuation compensation circuit does not work, the direct current side of the parallel active power filter system has serious double-frequency fluctuation, the fluctuation peak value reaches 20V, after the direct current side fluctuation compensation circuit works, the direct current side fluctuation is absorbed by the direct current side fluctuation compensation circuit, the direct current side voltage of the parallel active power filter system basically does not fluctuate, and therefore after the direct current side fluctuation compensation circuit is adopted, the fluctuation of the direct current side voltage can be effectively inhibited.
As shown in fig. 7(a), 7(b), 7(c), and 7(d), the dc side ripple compensation circuit applies the load current waveform of the front-rear parallel active power filter system to compensate the current waveform.
It can be seen from the experimental results that, before the dc side ripple compensation circuit is put into operation, although the parallel active power filter system can normally output the negative sequence compensation current, the negative sequence compensation current has a large distortion, as can be seen from the above analysis, at this time, 3 times of harmonic waves are injected into the grid current by the output current, as can be seen from the grid current FFT analysis result, the 3 times of harmonic wave content of the grid reaches 3.66%, and after the dc side ripple compensation circuit is put into operation, because the dc side capacitance ripple is eliminated, the negative sequence compensation current waveform output by the parallel active power filter system is improved, the 3 times of harmonic waves injected into the grid current by the output current are basically eliminated, as can be seen from the grid current FFT analysis result, the 3 times of harmonic wave content of the grid current is only 0.24%.
The present invention has been described in detail with reference to the specific embodiments, but these should not be construed as limitations of the present invention. Many variations and modifications may be made by one of ordinary skill in the art without departing from the principles of the present invention, which should also be considered as within the scope of the present invention.
Claims (5)
1. Active power filter direct current side voltage fluctuation absorbing circuit, its characterized in that: the active power filter system comprises an active power filter system, a direct current side fluctuation circuit of the active power filter system, each direct current side fluctuation compensation circuit and a control loop circuit for controlling each direct current side fluctuation compensation circuit;
the active power filter system comprises a three-phase balance circuit, a filter circuit and a nonlinear load which are connected with each other;
the control loop circuit includes:
the method comprises the steps that an outer ring is controlled repeatedly through fluctuation of the direct current side of an active power filter system, the instantaneous value of the direct current side voltage of the active power filter system is input, the direct current component of the direct current side voltage of the active power filter system is obtained through an average value filter, the direct current side fluctuation quantity of the instantaneous value of the direct current side voltage of the active power filter system is obtained after the difference is made with an original input signal, and a fluctuation compensation value is obtained after the input of a repetitive controller;
the direct current side fluctuation compensation circuit capacitor mean value voltage stabilizing ring absorbs voltage fluctuation of an active power filter system by utilizing the fluctuation of a direct current side fluctuation compensation circuit capacitor, so that the voltage stabilizing quantity of the direct current side fluctuation compensation circuit is a direct current quantity, an actual direct current side fluctuation compensation circuit capacitor voltage instantaneous value is input, an actual mean value of the direct current side fluctuation compensation circuit capacitor voltage is obtained after passing through a mean value filter, and a direct current side fluctuation compensation circuit capacitor voltage error value is obtained after a difference is made between the actual mean value and a direct current side fluctuation compensation circuit capacitor voltage reference value;
the PI current inner loop controls the direct current side fluctuation compensation circuit capacitor to absorb or release energy from the active power filter system by tracking the inductive current, so that the direct current side fluctuation compensation circuit capacitor absorbs the control result of the voltage fluctuation of the active power filter system capacitor, the direct current side fluctuation compensation circuit capacitor voltage error value and the fluctuation compensation value are differed, the difference is made with the feedback inductive current value to obtain a current error value, and the current error value is input into the PI controller to obtain a current control instruction;
and the direct-current side voltage feedforward of the active power filter system is used for eliminating the influence of the direct-current side voltage fluctuation of the active power filter system on the control effect, and a modulation wave instruction output by the direct-current side voltage feedforward of the active power filter system is obtained after a current control instruction is input and a sampled direct-current side voltage instantaneous value of the active power filter system is subjected to difference.
2. The active power filter dc-side voltage fluctuation absorbing circuit according to claim 1, characterized in that: the active power filter system is a parallel active power filter system.
3. The active power filter dc-side voltage fluctuation absorbing circuit according to claim 1, characterized in that: the direct-current side fluctuation compensation circuit is a non-isolated buck-boost PWM DC/DC conversion circuit.
4. The active power filter dc-side voltage fluctuation absorbing circuit according to claim 3, characterized in that: the direct current side fluctuation compensation circuit is a direct current ripple compensation circuit, the direct current ripple compensation circuit comprises a half bridge, a filter inductor and an absorption capacitor, the filter inductor is connected with the midpoint of the half bridge, and the absorption capacitor is connected with the upper and lower points of the half bridge.
5. The operating method of the active power filter dc-side voltage fluctuation absorbing circuit according to claim 1, characterized in that: the direct-current side fluctuation quantity of the active power filter system is obtained by subtracting the direct-current side voltage instantaneous value of the active power filter system calculated by the average filter from the direct-current side voltage instantaneous value of the active power filter system calculated by the average filter and is used as the input of the repeated control outer ring, so that a fluctuation compensation value is obtained, the voltage fluctuation of the active power filter system is absorbed by the fluctuation of a direct-current side fluctuation compensation circuit capacitor, the direct-current side fluctuation compensation circuit regulated quantity is a constant current, and the PI current inner ring controls the direct-current side fluctuation compensation circuit capacitor to absorb or release energy from the active power filter system by tracking an inductive current, so that the control result that the direct-current side fluctuation compensation circuit capacitor absorbs the voltage fluctuation of the active power filter system capacitor is realized.
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