CN112928757A - Periodic frequency modulation APF variable carrier frequency digital PI control system and control method thereof - Google Patents

Periodic frequency modulation APF variable carrier frequency digital PI control system and control method thereof Download PDF

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CN112928757A
CN112928757A CN202110160165.5A CN202110160165A CN112928757A CN 112928757 A CN112928757 A CN 112928757A CN 202110160165 A CN202110160165 A CN 202110160165A CN 112928757 A CN112928757 A CN 112928757A
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voltage
digital
control circuit
controller
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CN112928757B (en
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陈楠
姜春霞
高丽辉
陈仁辉
黄勇
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Jilin Boan Fire Fighting Equipment Co ltd
Jilin Boan Intelligent Technology Co ltd
Changchun University of Technology
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Jilin Boan Fire Fighting Equipment Co ltd
Jilin Boan Intelligent Technology Co ltd
Changchun University of Technology
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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
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • 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
    • 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
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • 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]

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Abstract

The invention discloses a periodic frequency modulation APF variable-carrier frequency digital PI control system and a control method thereof, belonging to the field of active power filter control. The invention discloses a period frequency modulation APF variable carrier frequency digital PI control system and a control method thereof, wherein the period frequency modulation APF expands the energy of each harmonic to a certain frequency band by modulating the original constant clock frequency, reduces the peak value of carrier frequency harmonic, achieves the purpose of inhibiting electromagnetic interference, can enhance the performance of the period frequency modulation APF control system and reduce the total harmonic distortion of compensated network measurement current while improving the robustness and adaptability of the control method.

Description

Periodic frequency modulation APF variable carrier frequency digital PI control system and control method thereof
Technical Field
The invention discloses a periodic frequency modulation APF variable carrier frequency digital PI control system and a control method thereof, belonging to the field of active power filter control.
Background
An Active Power Filter (APF) fits the compensation current through the high frequency action of the Power electronic switch to neutralize the reactive and harmonic components in the nonlinear load current, keeping the grid current in phase with the grid voltage and sinusoidal. It should be noted that in the fixed switching frequency mode, the high-frequency action of the switching device may cause the converter to generate higher harmonics with larger amplitude at the carrier frequency of the integer multiple of the output waveform, so that the APF introduces carrier frequency harmonics while compensating the lower harmonics of the nonlinear load. The electromagnetic noise energy of the carrier frequency harmonic waves forms EMI (electro-magnetic interference) through near-field coupling and far-field coupling, so that the APF performance is reduced, the service life of nearby sensitive electronic equipment devices and the APF is influenced, and the safe and stable operation of the smart grid is seriously threatened.
Disclosure of Invention
The invention aims to solve the technical problem of providing a period frequency modulation APF variable carrier frequency digital PI control system and a control method thereof, wherein the system can inhibit electromagnetic interference and enhance the performance of an APF control system.
The invention aims to solve the problems and is realized by the following technical scheme:
a periodic frequency modulation APF variable carrier frequency digital PI control system comprises: the voltage outer ring control circuit comprises a current inner ring control circuit, the triangular wave generator is a variable frequency triangular wave generator, the current inner ring control circuit comprises a current inner ring digital PI controller, the voltage outer ring control circuit comprises a voltage outer ring digital PI controller, and a second output end of the triangular wave generator is respectively connected with second input ends of the current inner ring digital PI controller and the voltage outer ring digital PI controller;
corresponding to the kth triangular carrier wave, k is 0,1,2,3, and the proportionality coefficient k of the current inner loop digital PI controllerpi(k) And integral coefficient kii(k) Respectively calculating according to a formula (1) and a formula (2);
Figure BDA0002935154040000021
Figure BDA0002935154040000022
wherein, L is the energy storage inductance, R is the internal resistance of the energy storage inductance, zeta is the damping ratio of the inner loop control circuit, kpwmFor PWM loop gain, fc(k) Is the kth triangular carrier frequency;
the proportionality coefficient k of the voltage outer loop digital PI controllerpv(k) And integral coefficient kiv(k) Respectively calculating according to a formula (3) and a formula (4);
Figure BDA0002935154040000023
Figure BDA0002935154040000024
wherein, C wave-stabilizing capacitance value, h is the bandwidth in the outer loop control circuit, TsIs the grid voltage cycle.
Preferably, the current inner loop control circuit further includes: the output port of the second adder is connected with the first input port of a current inner ring digital PI controller, the output port of the current inner ring digital PI controller is connected with the first input port of the PWM generator, the second output end of the triangular wave generator is connected with the second input port of the PWM generator, the four-end output port of the PWM generator is connected with the four-end input port of the driving circuit, the four-end output port of the driving circuit is connected with the four-end input port of the single-phase bridge full-control circuit, the alternating current side of the single-phase bridge full-control circuit is connected in series with the energy storage inductor, and the compensating current collecting circuit is connected in series with the alternating current side of the single-phase bridge full-control circuit, the output port of the voltage inner loop control circuit is connected with the third input end of the second adder, the nonlinear load is connected in parallel at two ends of a network side input power grid, the load current acquisition circuit is connected in series at the input end of the nonlinear load, the output port of the load current acquisition circuit is connected with the input port of the harmonic detector, the output port of the harmonic detector is connected with the second input end of the second adder, and the voltage inner loop control circuit further comprises: the output port of the first adder is connected with a first input port of a voltage outer ring digital PI controller, the output port of the voltage outer ring digital PI controller is connected with a first input port of the multiplier, the output port of the multiplier is connected with a first input port of a second adder, the wave stabilizing capacitor is connected with the direct current side of a single-phase bridge type full control circuit in parallel, the direct current side of the single-phase bridge type full control circuit is connected with the direct current voltage acquisition circuit in series, the output port of the direct current voltage acquisition circuit is connected with the input port of the first adder, the power grid voltage acquisition circuit is connected with two ends of a nonlinear load in parallel, and the output port of the power grid voltage acquisition circuit is connected with a second input port of the multiplier.
A periodic frequency modulation APF carrier frequency-variable digital PI control method comprises the following steps:
step S10: corresponding to the kth triangular carrier starting time tk(ii) a The system is given a DC voltage E* dAnd rectified voltage E acquired by the direct-current voltage acquisition circuitd(tk) After the difference is sent to a first adder, the first adder outputs a direct current voltage error signal eE(tk)；
Step S20: error of DC voltage eE(tk) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generatorc(k) Sending the signal into a voltage outer ring digital PI controller, and calculating according to a formula (5) to obtain a voltage outer ring control signal uE(tk)；
Figure BDA0002935154040000031
Wherein e isE(tk) Is tkThe time DC voltage error signal is derived from the given DC voltage E* dAnd tkRectified voltage E acquired by time direct-current voltage acquisition circuitd(tk) Is calculated to obtain uE(tk) Is tkTime of day voltage outer loop control signal, from tkTime of day DC voltage error signal eE(tk) And the kth triangular carrier frequency fc(k) Calculating to obtain;
step S30: outer loop control signal u of voltageE(tk) And the power grid voltage u acquired by the power grid voltage acquisition circuits(tk) Feeding into a multiplier for calculating a first given signal i of the current inner loop* s(tk)；
Step S40: load current i acquired by load current acquisition circuitl(tk) Obtaining the reactive and harmonic components i of the load current after passing through a harmonic detectorqh(tk)；
Step S50: current is injected into the loop to obtain a first given signal i* s(tk) Load current reactive and harmonic components iqh(tk) And the compensation current i acquired by the compensation current acquisition circuitc(tk) Sending the signal to a second adder to calculate a compensation current error signal ei(tk)；
Step S60: compensating current error signal ei(tk) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generatorc(k) Sending the signal into a current inner loop digital PI controller, and calculating according to a formula (6) to obtain a current inner loop control signal ui(tk)；
Figure BDA0002935154040000041
Wherein e isi(tk) Is tkCompensating the current error signal by tkTime current inner loop first given signal i* s(tk)，tkMoment load current reactive and harmonic component iqh(tk) And tkCompensating current i obtained by moment compensating current acquisition circuitc(tk) Is calculated to obtain ui(tk) Is tkTime current inner loop control signal, from tkTime of day compensating current error signal ei(tk) And the kth triangular carrier frequency fc(k) Calculating to obtain;
step S70: PWM generator controls signal u by comparing current inner loopi(tk) And a frequency conversion triangular carrier wave u output by the frequency conversion triangular wave generatorc(k) Generating four control pulses P1、P2、P3、P4；
Step S80: the obtained four control pulses generate four control signals S through a driving circuit1、S2、S3、S4Controlling a single-phase bridge full-control circuit, the single-phase bridge full-control circuit generating a compensation current i on the AC sidec(tk) And injecting the compensation current into the power grid.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a period frequency modulation APF variable carrier frequency digital PI control system and a control method thereof, which do not change the structure of the original control system and do not need any additional device, and parameters of a digital PI controller are adjusted in real time along with the change of a triangular carrier frequency in the period frequency modulation APF by changing a control algorithm program, and the period frequency modulation APF expands the energy of each harmonic wave to a certain frequency band by modulating the original constant clock frequency, thereby reducing the peak value of the carrier frequency harmonic wave and achieving the purpose of inhibiting electromagnetic interference.
Drawings
Fig. 1 is an electrical connection diagram of a period frequency modulation APF variable carrier frequency digital PI control system according to the present invention.
FIG. 2 is an electrical connection diagram of a voltage outer loop control circuit of a periodic frequency modulation APF variable carrier frequency digital PI control system.
Fig. 3 is an electrical connection diagram of a current inner loop control circuit of a periodic frequency modulation APF variable carrier frequency digital PI control system according to the present invention.
Fig. 4 is a block diagram of an APF current inner loop control.
Fig. 5 is a block diagram of the APF voltage outer loop control.
FIG. 6 shows the proportionality coefficient k of the APF current inner loop digital PI controllerpi(k) And integral coefficient kii(k) Instantaneous value line graph.
FIG. 7 shows the proportionality coefficient k of the APF voltage outer loop digital PI controllerpv(k) And integral coefficient kiv(k) Instantaneous value line graph.
Fig. 8 shows time domain information of the nonlinear load current, the periodic frequency modulation APF compensation current based on the variable carrier frequency digital PI control method, and the compensated network side current.
FIG. 9 is the frequency domain information of the grid current after the compensation of the periodic frequency modulation APF based on the variable carrier frequency digital PI control method
Fig. 10 shows time domain information of the nonlinear load current, the periodic frequency modulated APF compensation current based on the fixed carrier frequency digital PI control method, and the compensated network side current.
Fig. 11 is network-side current frequency domain information after periodic frequency modulation APF compensation based on a fixed-carrier-frequency digital PI control method.
Detailed Description
The invention is further illustrated below with reference to the accompanying figures 1-11:
the technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
As shown in fig. 1-3, a first embodiment of the present invention provides a system for controlling an APF carrier-frequency-variable digital PI based on a prior art, including: voltage outer loop control circuit 100 and triangular wave generator 200, voltage outer loop control circuit 1 includes: the current inner loop control circuit 300, the grid voltage acquisition circuit 101, the voltage outer loop digital PI controller 102, the first adder 103, the multiplier 104, the direct voltage acquisition circuit 105 and the wave stabilization capacitor 106, the current inner loop control circuit 300 includes: the current inner loop digital PI controller 301, the second adder 302, the PWM generator 303, the driving circuit 304, the single-phase bridge full-control circuit 305, the compensation current collection circuit 306, the harmonic detector 307, the load current collection circuit 308, the nonlinear load 309, and the energy storage inductor 310, wherein the triangular wave generator 200 is a variable frequency triangular wave generator, and the connection relationship of the above mentioned electronic devices will be described in detail below.
The output port of the first adder 103 is connected to the first input port of the voltage outer-loop digital PI controller 102, the output port of the voltage outer-loop digital PI controller 102 is connected to the first input port of the multiplier 104, the output port of the multiplier 104 is connected to the first input port of the second adder 302, the output port of the second adder 302 is connected to the first input port of the current inner-loop digital PI controller 301, the output port of the current inner-loop digital PI controller 301 is connected to the first input port of the PWM generator 303, the second output port of the triangular wave generator 200 is connected to the second input ports of the current inner-loop digital PI controller 301 and the voltage outer-loop digital PI controller 102, the four-port output port of the PWM generator 303 is connected to the four-port input port of the driving circuit 304, the four-port output port of, the energy storage inductor 310 is connected in series to the ac side of the single-phase bridge full-control circuit 305, the wave-stabilizing capacitor 106 is connected in parallel to the dc side of the single-phase bridge full-control circuit 305, the dc voltage acquisition circuit 105 is connected in parallel to the dc side of the single-phase bridge full-control circuit 305, and the output port of the dc voltage acquisition circuit 105 is connected to the input port of the first adder 103.
The grid voltage acquisition circuit 101 is connected in parallel to two sides of a grid voltage 400, an output port of the grid voltage acquisition circuit 101 is connected with a second input end of the multiplier 104, the compensation current acquisition circuit 306 is connected in series to an alternating current side of the single-phase bridge type full-control circuit 305, an output port of the compensation current acquisition circuit 305 is connected with a third input end of the second adder 302, and the nonlinear load 309 is connected in parallel to two ends of the grid side input grid 400; the power grid voltage acquisition circuit 101 is connected in parallel at two ends of the nonlinear load 309; the load current acquisition circuit 308 is connected in series to the input end of the nonlinear load 309, the output port of the load current acquisition circuit 309 is connected to the input port of the harmonic detector 307, and the output port of the harmonic detector 307 is connected to the second input end of the second adder 302.
The components of the system of the present invention are described above, and the control method will be described in detail below. Before describing the control method, two sets of coefficients are introduced, which are: proportionality coefficient k of corresponding kth triangular carrier of current inner loop digital PI controller 301pi(k) And integral coefficient kii(k) And the proportionality coefficient k of the corresponding kth triangular carrier of the voltage outer loop digital PI controller 102pv(k) And integral coefficient kiv(k) An APF current inner loop control block diagram, k ═ 0,1,2,3, ·, as shown in fig. 4, and a proportionality coefficient k of the current inner loop digital PI controller 301 according to the APF voltage outer loop control block diagram, as shown in fig. 5pi(k) And integral coefficient kii(k) Expression and scaling factor k of voltage outer loop digital PI controller 102pv(k) And integral coefficient kiv(k) The expression is shown in formulas (1) and (2);
Figure BDA0002935154040000081
Figure BDA0002935154040000082
wherein, L is the energy storage inductance, R is the internal resistance of the energy storage inductance, zeta is the damping ratio of the inner loop control circuit, kpwmFor PWM gain, TcFor system closed loop control period, fc(k)＝1/Tc，fc(k) Is the kth triangular carrier frequency, the capacitance value of the C wave-stabilizing capacitor, h is the bandwidth in the outer loop control circuit, TsIs the grid voltage cycle.
An example of solving two sets of coefficients will be given below, where fc(k)＝[10000+800sin(200πtk)]Hz、L＝1.8mH、R＝0.1Ω、C＝9400μF、kpwm＝1、ζ＝0.707、h＝0.707、Ts＝20ms into kpi(k)、kii(k) Expression and kpv(k)、kiv(k) The solution is performed in the expression, as shown in equations (3) and (4), and the variation graphs thereof are shown in fig. 6 and fig. 7.
Figure BDA0002935154040000083
Figure BDA0002935154040000084
The control method of the system will be described in detail below according to the above-listed embodiments, with the following steps:
step S10, corresponding to the k-th triangular carrier start time tk(ii) a The system is given a DC voltage E* d100V and the rectified voltage E acquired by the dc voltage acquisition circuit 105d(tk) After being subtracted by the first adder 103, the first adder 103 outputs a DC voltage error signal eE(tk)；
Step S20, converting the DC voltage error eE(tk) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generatorc(k) Sending the voltage outer ring control signal to a voltage outer ring digital PI controller 102, and calculating according to a formula (5) to obtain a voltage outer ring control signal uE(tk)；
Figure BDA0002935154040000091
Wherein, tkIs the start time of the kth (k ═ 0,1,2,3,. cndot.) triangular carrier, eE(tk) Is tkThe time DC voltage error signal is derived from the given DC voltage E* dAnd tkRectified voltage E acquired by time direct-current voltage acquisition circuitd(tk) Is calculated to obtain uE(tk) Is tkTime of day voltage outer loop control signal, from tkTime of day DC voltage error signal eE(tk) Andthe kth triangular carrier frequency fc(k) Calculating to obtain;
step S30, converting the voltage outer loop control signal uE(tk) And the power grid voltage u acquired by the power grid voltage acquisition circuit 101s(tk) The current is fed into a multiplier 104 and the calculated current is fed into an inner loop first given signal i* s(tk)；
In step S40, the load current i acquired by the load current acquisition circuit 308l(tk) The load current reactive power and harmonic component i is obtained after passing through the harmonic detector 307qh(tk)；
Step S50, the first given signal i of the current inner loop is processed* s(tk) Load current reactive and harmonic components iqh(tk) And the compensation current i acquired by the compensation current acquisition circuit 306c(tk) Sending the signal to a second adder 302 to calculate a compensation current error signal ei(tk)；
Step S60, compensating the current error signal ei(tk) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generatorc(k) Sending the signal into a current inner loop digital PI controller 301, and calculating according to a formula (6) to obtain a current inner loop control signal ui(tk)；
Figure BDA0002935154040000092
Wherein e isi(tk) Is tkCompensating the current error signal by tkTime current inner loop first given signal i* s(tk)，tkMoment load current reactive and harmonic component iqh(tk) And tkCompensating current i obtained by moment compensating current acquisition circuitc(tk) Is calculated to obtain ui(tk) Is tkTime current inner loop control signal, from tkTime of day compensating current error signal ei(tk) And the kth triangular carrier frequency fc(k) MeterCalculating to obtain;
in step S70, the PWM generator 303 compares the current inner loop control signal ui(tk) And a frequency conversion triangular carrier wave u output by the frequency conversion triangular wave generatorc(k) Generating four control pulses P1、P2、P3、P4；
In step S80, the obtained four-way control pulse generates a four-way control signal S via the driving circuit 3041、S2、S3、S4The single-phase bridge full-control circuit 305 is controlled to ensure the voltage on the DC side to be stable, and simultaneously generate the compensation current i on the AC sidec(tk) As shown in fig. 8. After the compensation current is injected into the power grid 400, on one hand, harmonic current introduced by the nonlinear load is filtered out, and the sine degree of the power grid current is ensured; on the other hand, reactive components caused by the nonlinear load are counteracted, and the improvement of the power factor of the power grid is realized, as shown in fig. 9.
Fig. 10 shows a nonlinear load current, a periodic frequency modulation APF compensation current based on a fixed carrier frequency digital PI control method, and a compensated net side current. Fig. 11 is network-side current frequency domain information after periodic frequency modulation APF compensation based on a fixed-carrier-frequency digital PI control method. As can be seen from a review of fig. 8 and 10, the current time domain waveforms shown in both figures appear to be nearly identical. However, as can be seen from observing fig. 9 and 11, the grid-side current THD after the periodic frequency modulation APF compensation based on the variable carrier frequency digital PI control method is 4.49%, which is 0.37% lower than 4.86% of the grid-side current after the periodic frequency modulation APF compensation based on the fixed carrier frequency digital PI control method, and further optimization of the grid-side current THD is realized.
While embodiments of the invention have been disclosed above, it is not intended to be limited to the uses set forth in the specification and examples. It can be applied to all kinds of fields suitable for the present invention. Additional modifications will readily occur to those skilled in the art. It is therefore intended that the invention not be limited to the exact details and illustrations described and illustrated herein, but fall within the scope of the appended claims and equivalents thereof.

Claims (3)

1. A periodic frequency modulation APF variable carrier frequency digital PI control system comprises: the voltage outer ring control circuit comprises a current inner ring control circuit, the current inner ring control circuit comprises a current inner ring digital PI controller, the voltage outer ring control circuit comprises a voltage outer ring digital PI controller, and a second output end of the triangular wave generator is respectively connected with a second input port of the current inner ring digital PI controller and a second input port of the voltage outer ring digital PI controller;
corresponding to the kth triangular carrier wave, k is 0,1,2,3, and the proportionality coefficient k of the current inner loop digital PI controllerpi(k) And integral coefficient kii(k) Respectively calculating according to a formula (1) and a formula (2);
Figure FDA0002935154030000011
Figure FDA0002935154030000012
wherein, L is the energy storage inductance, R is the internal resistance of the energy storage inductance, zeta is the damping ratio of the inner loop control circuit, kpwmFor PWM loop gain, fc(k) Is the kth triangular carrier frequency;
the proportionality coefficient k of the voltage outer loop digital PI controllerpv(k) And integral coefficient kiv(k) Respectively calculating according to a formula (3) and a formula (4);
Figure FDA0002935154030000013
Figure FDA0002935154030000014
wherein, C wave-stabilizing capacitance value, hFor bandwidth, T, in the outer loop control circuitsIs the grid voltage cycle.
2. The system of claim 1, wherein the current inner loop control circuit further comprises: the output port of the second adder is connected with the first input port of the current inner ring digital PI controller, the output port of the current inner ring digital PI controller is connected with the first input port of the PWM generator, the second output end of the triangular wave generator is connected with the second input port of the PWM generator, the four-end output port of the PWM generator is connected with the four-end input port of the driving circuit, the four-end output port of the driving circuit is connected with the four-end input port of the single-phase bridge full control circuit, the energy storage inductor is connected with the alternating current side of the single-phase bridge full control circuit in series, and the compensating current collecting circuit is connected with the alternating current side of the single-phase bridge full control circuit in series, the output port of the voltage outer loop control circuit is connected with the third input end of the second adder, the nonlinear load is connected in parallel at two ends of a network side input power grid, the load current acquisition circuit is connected in series at the input end of the nonlinear load, the output port of the load current acquisition circuit is connected with the input port of the harmonic detector, the output port of the harmonic detector is connected with the second input end of the second adder, and the voltage outer loop control circuit further comprises: the output port of the first adder is connected with a first input port of a voltage outer ring digital PI controller, the output port of the voltage outer ring digital PI controller is connected with a first input port of the multiplier, the output port of the multiplier is connected with a first input port of a second adder, the wave stabilizing capacitor is connected with the direct current side of a single-phase bridge type full control circuit in parallel, the direct current side of the single-phase bridge type full control circuit is connected with the direct current voltage acquisition circuit in series, the output port of the direct current voltage acquisition circuit is connected with the input port of the first adder, the power grid voltage acquisition circuit is connected with two ends of a nonlinear load in parallel, and the output port of the power grid voltage acquisition circuit is connected with a second input port of the multiplier.
3. A periodic frequency modulation APF carrier frequency-variable digital PI control method is characterized by comprising the following steps:
step S10: corresponding to the kth triangular carrier starting time tk(ii) a The system is given a DC voltage E* dAnd rectified voltage E acquired by the direct-current voltage acquisition circuitd(tk) After the difference is sent to a first adder, the first adder outputs a direct current voltage error signal eE(tk)；
Step S20: error of DC voltage eE(tk) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generatorc(k) Sending the signal into a voltage outer ring digital PI controller, and calculating according to a formula (5) to obtain a voltage outer ring control signal uE(tk)；
Figure FDA0002935154030000031
Wherein e isE(tk) Is tkThe time DC voltage error signal is derived from the given DC voltage E* dAnd tkRectified voltage E acquired by time direct-current voltage acquisition circuitd(tk) Is calculated to obtain uE(tk) Is tkTime of day voltage outer loop control signal, from tkTime of day DC voltage error signal eE(tk) And the kth triangular carrier frequency fc(k) Calculating to obtain;
step S30: outer loop control signal u of voltageE(tk) And the power grid voltage u acquired by the power grid voltage acquisition circuits(tk) Feeding into a multiplier for calculating a first given signal i of the current inner loop* s(tk)；
Step S40: load current i acquired by load current acquisition circuitl(tk) Obtaining the reactive and harmonic components i of the load current after passing through a harmonic detectorqh(tk)；
Step S50: current is injected into the loop to obtain a first given signal i* s(tk) Load current reactive and harmonic components iqh(tk) And the compensation current i acquired by the compensation current acquisition circuitc(tk) Sending the signal to a second adder to calculate a compensation current error signal ei(tk)；
Step S60: compensating current error signal ei(tk) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generatorc(k) Sending the signal into a current inner loop digital PI controller, and calculating according to a formula (6) to obtain a current inner loop control signal ui(tk)；
Figure FDA0002935154030000032
Wherein e isi(tk) Is tkCompensating the current error signal by tkTime current inner loop first given signal i* s(tk)，tkMoment load current reactive and harmonic component iqh(tk) And tkCompensating current i obtained by moment compensating current acquisition circuitc(tk) Is calculated to obtain ui(tk) Is tkTime current inner loop control signal, from tkTime of day compensating current error signal ei(tk) And the kth triangular carrier frequency fc(k) Calculating to obtain;
step S70: PWM generator controls signal u by comparing current inner loopi(tk) And a frequency conversion triangular carrier wave u output by the frequency conversion triangular wave generatorc(k) Generating four control pulses P1、P2、P3、P4；
Step S80: the obtained four control pulses generate four control signals S through a driving circuit1、S2、S3、S4Controlling a single phaseA bridge type full-control circuit, wherein the AC side of the single-phase bridge type full-control circuit generates a compensation current ic(tk) And injecting the compensation current into the power grid.
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