CN113098013A - Electrolytic capacitor-free parallel active power filter system and control method - Google Patents

Electrolytic capacitor-free parallel active power filter system and control method Download PDF

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CN113098013A
CN113098013A CN202110382440.8A CN202110382440A CN113098013A CN 113098013 A CN113098013 A CN 113098013A CN 202110382440 A CN202110382440 A CN 202110382440A CN 113098013 A CN113098013 A CN 113098013A
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active power
voltage
controller
axis component
current
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周娟
徐高祥
王莉
原亚雷
钊翔坤
王梅鑫
李京泽
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China University of Mining and Technology CUMT
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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
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1582—Buck-boost converters
    • 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
    • Y02E40/20—Active power filtering [APF]

Abstract

The invention discloses an electrolytic capacitor-free parallel active power filter system and a control method, and belongs to the field of power electronic control. The system comprises: the system comprises a three-phase power grid, a harmonic load, a filter inductor, a two-level converter and a bidirectional Boost active power decoupling circuit. The control method of the system comprises the following steps: step 1: the two-level converter is controlled to complete the power exchange of the AC side and the DC side so as to realize the load harmonic compensation; step 2: by controlling the bidirectional Boost active power decoupling circuit, the low-frequency fluctuation power of the direct current side of the active power filter is transferred to the auxiliary capacitor, so that the low-frequency ripple of the voltage of the direct current side of the active power filter is suppressed, the traditional electrolytic capacitor can be replaced by the thin-film capacitor with a small capacitance value under the condition that the voltage fluctuation of the direct current side is small, and the reliability of the system is improved. In addition, a low-pass filter of a direct-current side voltage control link of the active power filter is omitted, and the corresponding speed of the system is improved.

Description

Electrolytic capacitor-free parallel active power filter system and control method
Technical Field
The invention relates to the field of power electronic control, in particular to an electrolytic capacitor-free parallel active power filter system and a control method.
Background
With the development of power electronic technology, a plurality of nonlinear loads such as a rectifier, an inverter, an uninterruptible power supply and an arc furnace in a power distribution system are increased, and the harmonic pollution of a power grid is increased. Harmonic waves can cause problems of transformer overheating, protection equipment failure, harmonic resonance, communication network interference and the like, and in addition, with the development of science and technology and industry, large-capacity reactive equipment such as high-power motors and transformers appear in an electric power system, so that the power factor of a power grid is low. The low power factor can cause the problems of increased line loss, reduced power grid efficiency, even grid breakdown and the like. The parallel active power filter (SAPF) can effectively solve the harmonic pollution of a power grid, improve the power factor of the power grid, improve the electric energy quality of the power grid, can be easily disconnected from the power grid when a fault occurs, does not influence the operation of other equipment, and is widely applied to a power system at present.
Load harmonics in a three-phase symmetric power grid mainly include 6k +1(k is 1,2, … (natural number)) positive sequence harmonics and 6k +5(k is 0,1, … (natural number)) negative sequence harmonics, and when the harmonics are compensated, the SAPF causes 6k (k is 1,2, … (natural number)) order fluctuation of the direct-current side voltage of the SAPF. The quality of the output current of the SAPF is greatly influenced by the voltage fluctuation amplitude of the direct current side, in order to inhibit the voltage fluctuation of the direct current side, the traditional method is that an electrolytic capacitor with a large capacitance value is connected in parallel on the direct current side of the SAPF to slow down the fluctuation, but the electrolytic capacitor has the defects of easy volatilization of electrolyte and short service life, particularly when the fluctuation voltage is large, the fluctuation current repeatedly charges and discharges the electrolytic capacitor, the aging of the capacitor is accelerated, the electrolytic capacitor needs to be frequently replaced, the reliability of the device is influenced, and meanwhile, the response speed of the voltage of the direct current side is greatly influenced by the electrolytic capacitor with the large capacitance value. In addition, in order to avoid the influence of the DC side ripple voltage on the SAPF output current, a low-pass filter with a low cut-off frequency needs to be added, which further reduces the response speed of the system.
At present, some scholars suppress the fluctuation of the direct-current side voltage of the SAPF by introducing a resonant controller, but the effect is very little, and the SAPF output current is influenced to a certain extent. According to the invention, from the perspective of a topological structure, based on an active power decoupling technology, the fluctuation power of the SAPF direct current side is transferred to an auxiliary capacitor, so that the fluctuation suppression of the voltage of the SAPF direct current side is realized, the voltage of the SAPF direct current side only contains direct current components and higher harmonic components finally, and thus, a traditional large-capacitance electrolytic capacitor can be replaced by a small-capacitance film capacitor, and the reliability of the device is improved; meanwhile, a low-pass filter is eliminated in a direct-current side voltage control link, and the response speed of the system is increased.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides an electrolytic capacitor-free parallel active power filter system and a control method based on an active power decoupling technology. The specific technical implementation scheme is as follows:
an electrolytic capacitor-free parallel active power filter system and a control method thereof are provided, the system specifically comprises:
the power supply comprises a three-phase power grid, a harmonic load, a filter inductor, a two-level converter and a bidirectional Boost active power decoupling circuit; the DC side of the two-level converter adopts a film capacitor Cd(ii) a The bidirectional Boost active power decoupling circuit specifically comprises: two fully-controlled switching tubes T1 and T2 and a decoupling inductor LrAnd a thin film capacitor Cr(ii) a The T1 and the T2 are connected in series, the other end of the T2 is connected to the negative electrode of the direct current bus, and the other end of the T1 passes through an auxiliary capacitor CrIs connected to the negative electrode of the DC bus to decouple the inductor LrOne end of the direct current bus is connected with the midpoint of T1 and T2, and the other end of the direct current bus is connected with the positive electrode of the direct current bus to form a bidirectional Boost circuit.
Further, an electrolytic capacitor-free parallel active power filter system and a control method thereof are characterized in that the control method of the system comprises the following steps:
step 1: the two-level converter is controlled to complete the power exchange of the AC side and the DC side so as to realize the load harmonic compensation;
step 2: the bidirectional Boost active power decoupling circuit is controlled to transfer the low-frequency fluctuating power of the direct current side of the active power filter to the auxiliary capacitor, so that the low-frequency voltage ripple of the direct current side of the active power filter is restrained.
Further, the method for controlling the two-level converter in step 1 includes:
converting the d-axis component i of the grid currentsdWith a given value i thereofsd *Making a difference, and obtaining u after the difference value passes through a PI controllerd *(ii) a Obtaining a d-axis component u of the power grid voltage after the power grid voltage is subjected to Park conversionsdAnd q-axis component usq(ii) a D-axis component i of the grid currentsdAnd q-axis component isqMultiplying by ω L to obtain uLdAnd uLq(ii) a Q-axis component i of the grid currentsqWith a given value i thereofsq *Making a difference, and obtaining u after the difference value passes through a PI controllerq *(ii) a Will usdAnd uLqAdding the obtained result and subtracting ud *The difference is the d-axis component u of the reference output voltage of the active power filterod *(ii) a By usqMinus uLdSubtracting u from the resultq *The difference is the q-axis component u of the reference output voltage of the active power filteroq *(ii) a Will uod *And uoq *Obtaining a reference output voltage alpha axis component u of the active power filter after Clark conversionα *And a beta axis component uβ *(ii) a According to uα *And uβ *And driving the switching tube of the two-level converter based on the SVPWM technology.
Further, the given value i of the d-axis component of the grid current is obtainedsd *And q-axis component given value isq *The method comprises the following steps:
using voltage u on the DC side of an active power filterdcMaking difference with the given value, sending the difference value into a PI controller, and outputting the PI controller as the given value i of the d-axis component of the grid currentsd *(ii) a The active power filter simultaneously compensates harmonic and reactive in load current, and the given value i of q-axis component of grid currentsq *Is 0.
Further, the control method of the bidirectional Boost active power decoupling circuit in the step 2 includes:
by decoupling inductor current iLrWith a given value i thereofLr *Making a difference, and obtaining u after the difference passes through a plurality of PR controllersLr(ii) a Using voltage u on the DC side of an active power filterdcMinus uLrObtaining the reference output voltage u of the bidirectional Boost circuitoc *(ii) a By uoc *Divided by the auxiliary capacitor voltage urObtaining a modulation wave u of the bidirectional Boost circuitrf(ii) a According to urfT1 and T2 are driven based on SPWM technology.
Further, the multi-PR controller of the decoupled inductor current control loop specifically includes:
a proportional controller, a resonance controller with a resonance frequency of 600 pi, a resonance controller with a resonance frequency of 1200 pi, a resonance controller with a resonance frequency of 1800 pi and a resonance controller with a resonance frequency of 2400 pi.
Further, obtaining a given value i of decoupling inductance currentLr *The specific method comprises the following steps:
the auxiliary capacitor voltage urMaking difference with its given value, after the difference value is passed through PI controller obtaining ir *(ii) a The DC side capacitance current i of the active power filterdcAfter passing through the resonance controller, i is obtainedd *(ii) a Will ir *And id *Adding the sum to obtain a given value i of decoupling inductance currentLr *。
Further, the resonance controller specifically includes:
a resonance controller with a resonance frequency of 600 pi, a resonance controller with a resonance frequency of 1200 pi, a resonance controller with a resonance frequency of 1800 pi and a resonance controller with a resonance frequency of 2400 pi.
Compared with the prior art, the invention has the following advantages:
1) the invention can well inhibit the low-frequency ripple of the voltage at the direct current side of the active power filter, thereby replacing the traditional electrolytic capacitor with large capacitance value by the thin-film capacitor with small capacitance value, improving the response speed of the system and increasing the reliability of the device;
2) the active power decoupling-based low-pass filter based on the active power decoupling technology carries out fluctuation suppression on the direct-current side voltage of the active power filter, eliminates the low-pass filter in the direct-current side voltage control link, and improves the response speed of the system. In addition, an independent active power decoupling circuit is adopted, the control of the independent active power decoupling circuit is separated from the control of the active power filter, and the independent active power decoupling circuit has the characteristics of simplicity in control and easiness in implementation.
Drawings
Fig. 1 is a control schematic diagram of an electrolytic capacitor-free parallel active power filter according to the present invention.
Fig. 2 is a diagram illustrating the overall circuit topology of the parallel active power filter without electrolytic capacitor according to the present invention.
Fig. 3 shows the voltage variation of the dc side before and after the active power decoupling circuit is turned on.
Fig. 4 shows the current change of the power grid before and after the active power decoupling circuit is put into operation.
Fig. 5 is a dc side voltage FFT analysis when no active power decoupling control is applied.
Fig. 6 is a dc side voltage FFT analysis when active power decoupling control is engaged.
Fig. 7 is a power grid current FFT analysis when active power decoupling control is not engaged.
Fig. 8 is a power grid current FFT analysis when active power decoupling control is engaged.
Detailed Description
The invention will be further described with reference to the accompanying drawings and specific embodiments. It is to be understood that the present invention may be embodied in various forms, and that there is no intention to limit the invention to the specific embodiments illustrated, but on the contrary, the intention is to cover some exemplary and non-limiting embodiments shown in the attached drawings and described below.
Fig. 2 shows an electrolytic capacitor-free parallel type SAPF system circuit topology of the present invention, which includes a three-phase power grid, a harmonic load, a filter inductor, a two-level converter, and a bidirectional Boost active power decoupling circuit; the DC side of the two-level converter adopts a film capacitor Cd(ii) a The bidirectional Boost active power decoupling circuit specifically comprises: two fully-controlled switching tubes T1 and T2 and a decoupling inductor LrAnd a thin film capacitor Cr(ii) a The T1 and the T2 are connected in series, the other end of the T2 is connected to the negative electrode of the direct current bus, and the other end of the T1 passes through an auxiliary capacitor CrIs connected to the negative electrode of the DC bus to decouple the inductor LrOne end of the direct current bus is connected with the midpoint of T1 and T2, and the other end of the direct current bus is connected with the positive electrode of the direct current bus to form a bidirectional Boost circuit. The bidirectional Boost active power decoupling circuit is connected in parallel to the direct current side of the SAPF, and the control of the bidirectional Boost active power decoupling circuit is independent of the control of the SAPF, so that the operation of the SAPF cannot be influenced.
The working principle of the invention is as follows:
the invention is based on an independent bidirectional Boost active power decoupling technology, and transfers 6-frequency, 12-frequency, 18-frequency and 24-frequency ripple power of the SAPF direct current side to an auxiliary capacitor C by controlling a bidirectional Boost active power decoupling circuitrTherefore, the fluctuation voltage of corresponding times in the SAPF direct-current side voltage is eliminated, and the SAPF direct-current side voltage only contains direct-current components and higher harmonic components with small amplitudes. Based on this, the traditional electrolytic capacitor with large capacitance value can be replaced by the thin film capacitor with small capacitance value, the reliability of the device is improved, and meanwhile, the low-pass filter is eliminated in the direct-current side voltage control link, so that the response speed of the system is improved.
The SAPF three-phase circuit equation obtained by kirchhoff's voltage law is as follows:
E1：
Figure BDA0003013543270000031
wherein u isN0Represents a zero sequence voltage, the value of which can be found according to the following formula:
E2：
Figure BDA0003013543270000032
transforming E1 from abc coordinate system to dq coordinate system, and obtaining the mathematical model of SAPF in dq coordinate system as follows:
E3：
Figure BDA0003013543270000033
the invention adopts the feedback closed-loop control of the power grid current, does not need a load harmonic detection link, and controls the power grid current into a sine wave, and the phase of the sine wave is the same as the power grid voltage.
Ideally, the grid-connected point voltage only contains a positive-sequence fundamental component, and assuming that the initial phase angle of the voltage of the a-phase grid is 0, the three-phase voltage of the grid-connected point can be represented as:
E4：
Figure BDA0003013543270000034
wherein, UsIs u ofsx(x is a, b, c). Considering only the 5, 7, 11, 13, 17, 19, 23, 25 th harmonics with larger harmonic amplitudes in the load current, the SAPF output three-phase current expression can be set as:
E5：
Figure BDA0003013543270000041
according to the instantaneous power theory, the three-phase instantaneous power output by the SAPF is as follows:
E6：pac＝pa+pb+pc＝usaioa+usbiob+uscioc
combining E1, E2 and E3, the instantaneous power on the AC side of SAPF can be calculated as:
E7：
Figure BDA0003013543270000042
it can be seen from E7 that the instantaneous power at the ac side of the SAPF includes the fluctuating powers of 6 times, 12 times, 18 times and 24 times, and according to the law of conservation of energy, there is also fluctuating power at the dc side of the SAPF by a corresponding number of times, resulting in low-frequency ripple at the dc side voltage by a corresponding number of times. In order to suppress voltage fluctuation on the direct current side, the fluctuation power needs to be transferred to an auxiliary capacitor by controlling a bidirectional Buck-Boost active power decoupling circuit.
Taking 6 frequency multiplication fluctuation voltage with maximum amplitude suppression as an example, the auxiliary decoupling capacitor CrThe upper voltage is modulated to:
E8：ur＝Ur0+Uc sin(6ωt+δ6)
wherein, Ur0Is an auxiliary capacitor voltage urD.C. component of (1), UcIs urDelta is urRelative to the initial phase angle of the a-phase grid voltage.
Based on this, the decoupling capacitance current can be expressed as:
E9：icr＝6ωCrUc cos(6ωt+δ6)
in addition, the SAPF direct current can be expressed as:
E10：idc＝Idc0+idc-h
wherein, Idc0Is idcA direct current component of (1)dc-hIs idcHarmonic component of (1), i is considered to be stabledcAll harmonic components in (i) are suppresseddc-hWhen 0, then have idc＝Idc0Thus, according to kirchhoff's current law:
E11：iLr＝icr-idc＝6ωCrUc cos(6ωt+δ6)-Idc0
neglecting the loss of the switching device, the instantaneous power on the active power decoupling circuit can be obtained according to E8-E11 as follows:
E12：
Figure BDA0003013543270000051
it can be seen from E12 that there is also a 6-fold frequency ripple power on the decoupling circuit at this time, and this 6-fold frequency ripple power can be used to balance the 6-fold frequency ripple power in E4, thereby suppressing the 6-fold frequency ripple of the voltage on the direct current side of the SAPF. Similarly, when the bidirectional Boost circuit is controlled to enable the auxiliary capacitor voltage to contain 12-frequency, 18-frequency and 24-frequency ripple components, corresponding times of ripple power can be generated in the active power decoupling circuit, and the ripple power can be used for balancing 12-frequency, 18-frequency and 24-frequency ripple power in E4, so that 12-frequency, 18-frequency and 24-frequency ripple in the SAPF direct-current side voltage is inhibited.
Fig. 1 is a schematic diagram of an electrolytic capacitor-free parallel type SAPF control according to the present invention, which specifically includes the following steps:
step 1: the two-level converter is controlled to complete the power exchange of the AC side and the DC side so as to realize the load harmonic compensation;
step 2: the bidirectional Boost active power decoupling circuit is controlled to transfer the low-frequency fluctuating power of the direct current side of the active power filter to the auxiliary capacitor, so that the low-frequency voltage ripple of the direct current side of the active power filter is restrained.
Further, the method for controlling the two-level converter in step 1 includes:
converting the d-axis component i of the grid currentsdWith a given value i thereofsd *Making a difference, and obtaining u after the difference value passes through a PI controllerd *(ii) a Obtaining a d-axis component u of the power grid voltage after the power grid voltage is subjected to Park conversionsdAnd q-axis component usq(ii) a D-axis component i of the grid currentsdAnd q-axis component isqMultiplying by ω L to obtain uLdAnd uLq(ii) a Q-axis component i of the grid currentsqWith a given value i thereofsq *Making a difference, and obtaining u after the difference value passes through a PI controllerq *(ii) a Will usdAnd uLqAdding the obtained result and subtracting ud *The difference is the d-axis component u of the reference output voltage of the active power filterod *(ii) a By usqMinus uLdSubtracting u from the resultq *The difference is the activeReference output voltage q-axis component u of power filteroq *(ii) a Will uod *And uoq *Obtaining a reference output voltage alpha axis component u of the active power filter after Clark conversionα *And a beta axis component uβ *(ii) a According to uα *And uβ *And driving the switching tube of the two-level converter based on the SVPWM technology.
Further, the given value i of the d-axis component of the grid current is obtainedsd *And q-axis component given value isq *The method comprises the following steps:
using voltage u on the DC side of an active power filterdcMaking difference with the given value, sending the difference value into a PI controller, and outputting the PI controller as the given value i of the d-axis component of the grid currentsd *(ii) a The active power filter simultaneously compensates harmonic and reactive in load current, and the given value i of q-axis component of grid currentsq *Is 0.
Further, the control method of the bidirectional Boost active power decoupling circuit in the step 2 includes:
by decoupling inductor current iLrWith a given value i thereofLr *Making a difference, and obtaining u after the difference passes through a plurality of PR controllersLr(ii) a Using voltage u on the DC side of an active power filterdcMinus uLrObtaining the reference output voltage u of the bidirectional Boost circuitoc *(ii) a By uoc *Divided by the auxiliary capacitor voltage urObtaining a modulation wave u of the bidirectional Boost circuitrf(ii) a According to urfT1 and T2 are driven based on SPWM technology.
Further, the multi-PR controller of the decoupled inductor current control loop specifically includes:
a proportional controller, a resonance controller with a resonance frequency of 600 pi, a resonance controller with a resonance frequency of 1200 pi, a resonance controller with a resonance frequency of 1800 pi and a resonance controller with a resonance frequency of 2400 pi.
Further, obtaining a given value i of decoupling inductance currentLr *The specific method comprises the following steps:
the auxiliary capacitor voltage urMaking difference with its given value, after the difference value is passed through PI controller obtaining ir *(ii) a The DC side capacitance current i of the active power filterdcAfter passing through the resonance controller, i is obtainedd *(ii) a Will ir *And id *Adding the sum to obtain a given value i of decoupling inductance currentLr *。
Further, the resonance controller specifically includes:
a resonance controller with a resonance frequency of 600 pi, a resonance controller with a resonance frequency of 1200 pi, a resonance controller with a resonance frequency of 1800 pi and a resonance controller with a resonance frequency of 2400 pi.
The control method is designed according to the process, Matlab/Simulink is used for carrying out simulation experiments, the effectiveness of the method is verified, and simulation parameters are shown in Table 1.
TABLE 1 simulation parameters
Figure BDA0003013543270000061
FIG. 3 shows the voltage u on the DC side of the SAPFdcIn the variation situation, no active power decoupling circuit is put in before 0.1s, the active power decoupling circuit is put in at 0.1s, only 6 frequency multiplication wave controllers are put in 0.1 s-0.2 s, 6 frequency multiplication and 12 frequency multiplication wave controllers are put in 0.2 s-0.3 s, and all the wave controllers are put in after 0.3 s. It can be seen that when the active power decoupling circuit is not put into use, the voltage at the direct current side has large fluctuation, and the fluctuation amplitude is about 30V; the voltage fluctuation is reduced within 0.1s to 0.2s, and the fluctuation amplitude is about 6V; the voltage fluctuation of the direct current side is further reduced within 0.2 s-0.3 s, and the fluctuation is about 1V; the DC side voltage of 0.3 s-0.4 s is almost a straight line, only contains some higher harmonics, and the fluctuation amplitude is about 0.5V. Therefore, the SAPF direct-current side voltage fluctuation suppression method can well suppress SAPF direct-current side voltage fluctuation and accelerate direct-current side voltage response speed. Furthermore, conventional SAPsF capacitance value, the direct current side capacitance value is about 5000 muF, the direct current side capacitance value in the SAPF system of the invention is only 50 muF, which is about 1% of the traditional SAPF capacitance value.
Fig. 4 shows the change situation of the power grid current, a low-pass filter is not added in the direct-current side voltage control link, and before 0.1s, due to the fact that the direct-current side voltage has large fluctuation, new harmonic current is injected into the power grid by the SAPF, and at the moment, the power grid current is seriously distorted; 0.1 s-0.2 s, and the current distortion of the power grid is reduced along with the reduction of the voltage fluctuation of the direct current side; the voltage fluctuation of the direct current side is further reduced by 0.2 s-0.3 s, and the current distortion of the power grid is further reduced; 0.3 s-0.4 s, the current of the power grid is almost close to sine wave. Therefore, the voltage fluctuation degree of the direct current side of the SAPF greatly influences the current quality of a power grid, and the voltage fluctuation suppression method of the direct current side of the SAPF can eliminate a low-pass filter of a voltage control link of the direct current side and ensure the current quality of the power grid.
Fig. 5 shows FFT analysis of the voltage on the direct current side of the SAPF when the active power decoupling circuit is not applied, and it can be seen that the voltage on the direct current side contains large harmonics of 6 th order, 12 th order, 18 th order and 24 th order, which is consistent with theoretical analysis.
Fig. 6 shows FFT analysis of the SAPF dc-side voltage after 0.3s input to all the ripple controllers, and it can be seen that the 6, 12, 18 and 24 ripples in the dc-side voltage are all suppressed at this time, which illustrates the effectiveness of the method for suppressing the low-frequency ripple of the SAPF dc-side voltage according to the present invention.
Fig. 7 shows FFT analysis of the grid current when the active power decoupling circuit is not put into the grid current before 0.1s, and it can be seen that, at this time, because there is large fluctuation in the dc side, the grid current contains a large amount of harmonics of 5, 7, 11, 13, 17, 19, 23, and 25, which is equivalent to that the SAPF loses the harmonic compensation capability, and the THD of the grid current is 14.14%.
Fig. 8 shows FFT analysis of the grid current after 0.3s of input to all the ripple controllers, and it can be seen that, at this time, since the dc side voltage ripple is suppressed, the SAPF does not inject harmonics into the grid current, and at the same time, the load harmonics can be compensated well, and the grid current THD is 0.46%. The ripple suppression method can well suppress voltage ripples on the direct current side of the SAPF, and a low-pass filter in the direct current side voltage control link is omitted.
The above-described embodiments are presently preferred, and are possible examples of implementations, provided solely for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the technology described herein, and it will be apparent to those of ordinary skill in the art that numerous changes and modifications may be made without departing substantially from the principles of the invention, and that such changes and modifications are to be considered as within the scope of the invention.

Claims (8)

1. An electrolytic capacitor-free parallel active power filter system and a control method thereof are characterized in that the system comprises:
the power supply comprises a three-phase power grid, a harmonic load, a filter inductor, a two-level converter and a bidirectional Boost active power decoupling circuit; the DC side of the two-level converter adopts a film capacitor Cd(ii) a The bidirectional Boost active power decoupling circuit specifically comprises: two fully-controlled switching tubes T1 and T2 and a decoupling inductor LrAnd a thin film capacitor Cr(ii) a The T1 and the T2 are connected in series, the other end of the T2 is connected to the negative electrode of the direct current bus, and the other end of the T1 passes through an auxiliary capacitor CrIs connected to the negative electrode of the DC bus to decouple the inductor LrOne end of the direct current bus is connected with the midpoint of T1 and T2, and the other end of the direct current bus is connected with the positive electrode of the direct current bus to form a bidirectional Boost circuit.
2. The parallel active power filter system without electrolytic capacitor and the control method thereof as claimed in claim 1, wherein the control method of the system comprises the steps of:
step 1: the two-level converter is controlled to complete the power exchange of the AC side and the DC side so as to realize the load harmonic compensation;
step 2: the bidirectional Boost active power decoupling circuit is controlled to transfer the low-frequency fluctuating power of the direct current side of the active power filter to the auxiliary capacitor, so that the low-frequency voltage ripple of the direct current side of the active power filter is restrained.
3. The parallel active power filter system without electrolytic capacitor and the control method thereof as claimed in claim 2, wherein the control method of the two-level converter in step 1 comprises:
converting the d-axis component i of the grid currentsdWith a given value i thereofsd *Making a difference, and obtaining u after the difference value passes through a PI controllerd *(ii) a Obtaining a d-axis component u of the power grid voltage after the power grid voltage is subjected to Park conversionsdAnd q-axis component usq(ii) a D-axis component i of the grid currentsdAnd q-axis component isqMultiplying by ω L to obtain uLdAnd uLq(ii) a Q-axis component i of the grid currentsqWith a given value i thereofsq *Making a difference, and obtaining u after the difference value passes through a PI controllerq *(ii) a Will usdAnd uLqAdding the obtained result and subtracting ud *The difference is the d-axis component u of the reference output voltage of the active power filterod *(ii) a By usqMinus uLdSubtracting u from the resultq *The difference is the q-axis component u of the reference output voltage of the active power filteroq *(ii) a Will uod *And uoq *Obtaining a reference output voltage alpha axis component u of the active power filter after Clark conversionα *And a beta axis component uβ *(ii) a According to uα *And uβ *And driving the switching tube of the two-level converter based on the SVPWM technology.
4. The parallel active power filter system without electrolytic capacitor and the control method thereof as claimed in claim 3, wherein the given value i of d-axis component of the obtained grid current issd *And q-axis component given value isq *The method comprises the following steps:
using voltage u on the DC side of an active power filterdcIs different from its given valueThe difference value is sent to a PI controller, and the output of the PI controller is the given value i of the d-axis component of the grid currentsd *(ii) a The active power filter simultaneously compensates harmonic and reactive in load current, and the given value i of q-axis component of grid currentsq *Is 0.
5. The electrolytic capacitor-free parallel active power filter system and the control method according to claim 2, wherein the control method of the bidirectional Boost active power decoupling circuit in the step 2 comprises:
by decoupling inductor current iLrWith a given value i thereofLr *Making a difference, and obtaining u after the difference passes through a plurality of PR controllersLr(ii) a Using voltage u on the DC side of an active power filterdcMinus uLrObtaining the reference output voltage u of the bidirectional Boost circuitoc *(ii) a By uoc *Divided by the auxiliary capacitor voltage urObtaining a modulation wave u of the bidirectional Boost circuitrf(ii) a According to urfT1 and T2 are driven based on SPWM technology.
6. The parallel active power filter system without electrolytic capacitor and the control method thereof as claimed in claim 5, wherein the multi-PR controller of the decoupled inductor current control loop specifically comprises:
a proportional controller, a resonance controller with a resonance frequency of 600 pi, a resonance controller with a resonance frequency of 1200 pi, a resonance controller with a resonance frequency of 1800 pi and a resonance controller with a resonance frequency of 2400 pi.
7. The parallel active power filter system without electrolytic capacitor as claimed in claim 5, wherein the decoupling inductance current given value i is obtainedLr *The specific method comprises the following steps:
the auxiliary capacitor voltage urMaking difference with its given value, after the difference value is passed through PI controller obtaining ir *(ii) a Applying the DC side capacitance current of the active power filteridcAfter passing through the resonance controller, i is obtainedd *(ii) a Will ir *And id *Adding the sum to obtain a given value i of decoupling inductance currentLr *。
8. The parallel active power filter system without electrolytic capacitor and the control method thereof as claimed in claim 7, wherein the resonance controller comprises:
a resonance controller with a resonance frequency of 600 pi, a resonance controller with a resonance frequency of 1200 pi, a resonance controller with a resonance frequency of 1800 pi and a resonance controller with a resonance frequency of 2400 pi.
CN202110382440.8A 2021-04-09 2021-04-09 Electrolytic capacitor-free parallel active power filter system and control method Pending CN113098013A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113890051A (en) * 2021-09-29 2022-01-04 华东交通大学 Active capacitance control method, system, equipment, medium and terminal
CN114123203A (en) * 2021-10-28 2022-03-01 国网山西省电力公司电力科学研究院 Direct-current bus voltage ripple suppression strategy during voltage unbalance of alternating-current power grid

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113890051A (en) * 2021-09-29 2022-01-04 华东交通大学 Active capacitance control method, system, equipment, medium and terminal
CN113890051B (en) * 2021-09-29 2023-08-08 华东交通大学 Active capacitor control method, system, equipment, medium and terminal
CN114123203A (en) * 2021-10-28 2022-03-01 国网山西省电力公司电力科学研究院 Direct-current bus voltage ripple suppression strategy during voltage unbalance of alternating-current power grid
CN114123203B (en) * 2021-10-28 2023-08-29 国网山西省电力公司电力科学研究院 DC bus voltage ripple suppression strategy during unbalanced AC grid voltage

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