CN112928757B - 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 PDFInfo
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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
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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
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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
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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
- H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
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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 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
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 by the following technical scheme:
a kind of periodic frequency modulation APF changes the digital PI control system of carrier frequency, including: 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, k =1,2,3, ·. the proportionality coefficient k of the current inner loop digital PI controller pi (k) And integral coefficient k ii (k) Respectively calculating according to a formula (1) and a formula (2);
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, k pwm Gain of PWM link, f c (k) Is the kth triangular carrier frequency;
the proportionality coefficient k of the voltage outer loop digital PI controller pv (k) And integral coefficient k iv (k) Respectively calculating according to a formula (3) and a formula (4);
wherein C is the capacitance of the wave-stabilizing capacitor, h is the bandwidth of the outer loop control circuit, and T s Is 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 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 first output end of the triangular wave generator is connected with the second input port of the PWM generator, the four output ports of the PWM generator are connected with the four input ports of the driving circuit, the four output ports of the driving circuit are connected with the four input ports of the single-phase bridge full-control circuit, the alternating current side of the single-phase bridge full-control circuit is connected with the energy storage inductor in series, the compensating current collecting circuit is connected with the alternating current side of the bridge single-phase full-control circuit in series, the output port of the compensating current collecting circuit is connected with the third input port of the second adder, the nonlinear load is connected with the two ends of the grid-side input power grid in parallel, the load current collecting circuit is connected with the input port of the nonlinear load in series, the output port of the harmonic detector is connected with the second input port of the second adder, and the voltage inner ring control circuit of the second adder 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 variable carrier frequency digital PI control method is applied to the periodic frequency modulation APF variable carrier frequency digital PI control system; the method comprises the following steps:
step S10: corresponding to the kth triangular carrier starting time t k (ii) a The system is given a DC voltage E * d And rectified voltage E acquired by the direct-current voltage acquisition circuit d (t k ) After the difference is sent to a first adder, the first adder outputs a direct current voltage error signal e E (t k )；
Step S20: error of DC voltage e E (t k ) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generator c (k) Is sent intoIn the voltage outer ring digital PI controller, a voltage outer ring control signal u is obtained by calculation according to a formula (5) E (t k )；
Wherein e is E (t k ) Is t k The time DC voltage error signal is derived from the given DC voltage E * d And t k Rectified voltage E acquired by time direct-current voltage acquisition circuit d (t k ) Is calculated to obtain u E (t k ) Is t k Time voltage outer loop control signal, from t k Time of day DC voltage error signal e E (t k ) And the kth triangular carrier frequency f c (k) Calculating to obtain;
step S30: outer loop control signal u of voltage E (t k ) And the power grid voltage u acquired by the power grid voltage acquisition circuit s (t k ) Feeding into a multiplier, calculating a first given signal i of the current inner loop * s (t k )；
Step S40: load current i acquired by load current acquisition circuit l (t k ) Obtaining the reactive and harmonic components i of the load current after passing through a harmonic detector qh (t k )；
Step S50: current is injected into the loop to obtain a first given signal i * s (t k ) Load current reactive and harmonic components i qh (t k ) And the compensation current i acquired by the compensation current acquisition circuit c (t k ) Sending the signal to a second adder to calculate a compensation current error signal e i (t k )；
Step S60: compensating current error signal e i (t k ) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generator c (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 u i (t k )；
Wherein e is i (t k ) Is t k Compensating the current error signal by t k Time current inner loop first given signal i * s (t k )，t k Moment load current reactive and harmonic component i qh (t k ) And t k Compensating current i obtained by moment compensating current acquisition circuit c (t k ) Is calculated to obtain u i (t k ) Is t k Time current inner loop control signal, from t k Time of day compensating current error signal e i (t k ) And the kth triangular carrier frequency f c (k) Calculating to obtain;
step S70: PWM generator controls signal u by comparing current inner loop i (t k ) And a frequency conversion triangular carrier wave u output by the frequency conversion triangular wave generator c (k) Generating four control pulses P 1 、P 2 、P 3 、P 4 ；
Step S80: the obtained four control pulses generate four control signals S through a driving circuit 1 、S 2 、S 3 、S 4 Controlling a single-phase bridge full-control circuit, the single-phase bridge full-control circuit generating a compensation current i on the AC side c (t k ) 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 harmonic wave of the carrier frequency 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 according to the present invention.
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 controller pi (k) And integral coefficient k ii (k) Instantaneous value line graph.
FIG. 7 shows the proportionality coefficient k of the APF voltage outer loop digital PI controller pv (k) And integral coefficient k iv (k) A line graph of instantaneous values.
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 network side current frequency domain information after periodic frequency modulation APF compensation based on a 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 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 is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to 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 the 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.
An output port of the first adder 103 is connected with a first input port of a voltage outer ring digital PI controller 102, an output port of the voltage outer ring digital PI controller 102 is connected with a first input port of a multiplier 104, an output port of the multiplier 104 is connected with a first input port of a second adder 302, an output port of the second adder 302 is connected with a first input port of a current inner ring digital PI controller 301, an output port of the current inner ring digital PI controller 301 is connected with a first input port of a PWM generator 303, a second output port of a triangular generator 200 is connected with a second input port of the PWM generator 303, a second output port of the triangular generator 200 is respectively connected with second input ports of the current inner ring digital PI controller 301 and the voltage outer ring digital PI controller 102, a four-terminal output port of the PWM generator 303 is connected with a four-terminal input port of a driving circuit 304, a four-terminal output port of the driving circuit 304 is connected with a four-terminal input port of a single-phase full-control circuit 305, an energy storage inductor 310 is connected in series with an alternating current side of the single-phase full-control circuit 305, a wave stabilizing capacitor 106 is connected in parallel with a direct-current side of the single-phase full-control circuit 305, a direct-current voltage acquisition circuit 105 is connected with a direct-current side of the first input port of the 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 explaining the control method, two sets of coefficients are introduced, which are: proportional system of corresponding kth triangular carrier of current inner loop digital PI controller 301Number k pi (k) And integral coefficient k ii (k) And the proportionality coefficient k of the corresponding kth triangular carrier of the voltage outer loop digital PI controller 102 pv (k) And integral coefficient k iv (k) The APF current inner loop control block, k =0,1,2,3, ·, as shown in fig. 4, and the proportionality coefficient k of the current inner loop digital PI controller 301, as shown in fig. 5, according to the APF voltage outer loop control block, as shown in fig. 4 pi (k) And integral coefficient k ii (k) Expression and scaling factor k of voltage outer loop digital PI controller 102 pv (k) And integral coefficient k iv (k) The expression is shown in formulas (1) and (2);
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, k pwm For PWM gain, T c For the system closed loop control period, f c (k)＝1/T c ，f c (k) The k-th triangular carrier frequency, the capacitance of the C wave-stabilizing capacitor, h the bandwidth in the outer loop control circuit, T s Is the grid voltage cycle.
An example of solving for two sets of coefficients will be given below, where f c (k)＝[10000+800sin(200πt k )]Hz、L＝1.8mH、R＝0.1Ω、C＝9400μF、k pwm ＝1、ζ＝0.707、h＝0.707、T s K is taken in =20ms pi (k)、k ii (k) Expression and k pv (k)、k iv (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.
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 wave starting time t k (ii) a The system is given a DC voltage E * d =100V and rectified voltage E acquired by dc voltage acquisition circuit 105 d (t k ) After being subtracted by the first adder 103, the first adder 103 outputs a DC voltage error signal e E (t k )；
Step S20, converting the DC voltage error e E (t k ) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generator c (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 u E (t k )；
Wherein, t k Is the start time of the kth (k =0,1,2,3, ·) triangular carrier, e E (t k ) Is t k The time DC voltage error signal is derived from a given DC voltage E * d And t k Rectified voltage E acquired by time direct-current voltage acquisition circuit d (t k ) Is calculated to obtain u E (t k ) Is t k Time of day voltage outer loop control signal, from t k Time of day DC voltage error signal e E (t k ) And the kth triangular carrier frequency f c (k) Calculating to obtain;
step S30, the voltage outer ring control signal u E (t k ) And the grid voltage u acquired by the grid voltage acquisition circuit 101 s (t k ) The first given signal i is fed into the multiplier 104 and the current is calculated * s (t k )；
Step S40, the load current i acquired by the load current acquisition circuit 308 l (t k ) The load current reactive power and harmonic component i is obtained after passing through the harmonic detector 307 qh (t k )；
Step S50, a first given signal i of the current inner loop is processed * s (t k ) Load current reactive and harmonic components i qh (t k ) And the compensation current i acquired by the compensation current acquisition circuit 306 c (t k ) Sending the signal to a second adder 302 to calculate a compensation current error signal e i (t k )；
Step S60, compensating the current error signal e i (t k ) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generator c (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 u i (t k )；
Wherein e is i (t k ) Is t k Compensating the current error signal by t k Time current inner loop first given signal i * s (t k )，t k Moment load current reactive and harmonic component i qh (t k ) And t k Compensating current i obtained by moment compensating current acquisition circuit c (t k ) Is calculated to obtain u i (t k ) Is t k Time current inner loop control signal, from t k Time of day compensating current error signal e i (t k ) And the kth triangular carrier frequency f c (k) Calculating to obtain;
in step S70, the PWM generator 303 compares the current inner loop control signal u i (t k ) And the frequency conversion triangular wave generator outputs a frequency conversion triangular carrier u c (k) Generating four control pulses P 1 、P 2 、P 3 、P 4 ；
In step S80, the obtained four control pulses generate four control signals S through the driving circuit 304 1 、S 2 、S 3 、S 4 The 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 side c (t k ) 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, 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 an examination of fig. 8 and 10, the current time-domain waveforms shown in the two figures appear almost the same. However, as can be seen from observing fig. 9 and 11, the network 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 reduced by 0.37% compared with 4.86% of the network side current after the periodic frequency modulation APF compensation based on the fixed carrier frequency digital PI control method, and further optimization of the network 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. Therefore, the invention is not to be limited to the specific details and illustrations shown and described herein, without departing from the general concept as defined by the claims and their equivalents.
Claims (2)
1. A kind of periodic frequency modulation APF changes the digital PI control system of carrier frequency, including: the voltage outer loop control circuit comprises a current inner loop control circuit, the current inner loop control circuit comprises a current inner loop digital PI controller, the voltage outer loop control circuit comprises a voltage outer loop digital PI controller, and a second output end of the triangular wave generator is connected with second input ports of the current inner loop digital PI controller and the voltage outer loop digital PI controller respectively;
corresponding to the kth triangular carrier, k =1,2,3, ·, the proportionality coefficient k of the current inner loop digital PI controller pi (k) And integral coefficient k ii (k) Respectively calculating according to a formula (1) and a formula (2);
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, k pwm For PWM loop gain, f c (k) Is the kth triangular carrier frequency;
the proportionality coefficient k of the voltage outer loop digital PI controller pv (k) And integral coefficient k iv (k) Respectively calculating according to a formula (3) and a formula (4);
wherein C is the capacitance value of the wave-stabilizing capacitor, h is the bandwidth in the outer loop control circuit, T s Is the grid voltage cycle;
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 first output end of the triangular wave generator is connected with the second input port of the PWM generator, the four output ports of the PWM generator are connected with the four input ports of the driving circuit, the four output ports of the driving circuit are connected with the four input ports 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, the compensating current collecting circuit is connected with the alternating-current side of the bridge single-phase full-control circuit in series, the output port of the compensating current collecting circuit is connected with the third input end of the second adder, the nonlinear load is connected with the two ends of the grid-side input power grid in parallel, the load current collecting circuit is connected with the input port of the nonlinear load in series, the output port of the harmonic detector is connected with the second input end of the second adder, and the voltage 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.
2. A periodic frequency modulation APF carrier frequency-variable digital PI control method is applied to the periodic frequency modulation APF carrier frequency-variable digital PI control system of claim 1, and is characterized by comprising the following steps:
step S10: corresponding to the kth triangular carrier starting time t k (ii) a The system is given a DC voltage E * d And rectified voltage E acquired by the direct-current voltage acquisition circuit d (t k ) Is sent intoAfter subtraction in the first adder, the first adder outputs a DC voltage error signal e E (t k )；
Step S20: error of DC voltage e E (t k ) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generator c (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 u E (t k )；
Wherein e is E (t k ) Is t k The time DC voltage error signal is derived from the given DC voltage E * d And t k Rectified voltage E acquired by time direct-current voltage acquisition circuit d (t k ) Is calculated to obtain u E (t k ) Is t k Time of day voltage outer loop control signal, from t k Time of day DC voltage error signal e E (t k ) And the kth triangular carrier frequency f c (k) Calculating to obtain;
step S30: outer loop control signal u of voltage E (t k ) And the grid voltage u acquired by the grid voltage acquisition circuit s (t k ) Feeding into a multiplier, calculating a first given signal i of the current inner loop * s (t k )；
Step S40: load current i acquired by load current acquisition circuit l (t k ) Obtaining the reactive and harmonic components i of the load current after passing through a harmonic detector qh (t k )；
Step S50: inner loop the current by a first given signal i * s (t k ) Load current reactive and harmonic components i qh (t k ) And the compensation current i acquired by the compensation current acquisition circuit c (t k ) Sending the signal to a second adder to calculate a compensation current error signal e i (t k )；
Step S60: compensating the current error signal e i (t k ) And the frequency conversion triangular carrier frequency f output by the frequency conversion triangular wave generator c (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 u i (t k )；
Wherein e is i (t k ) Is t k Compensating the current error signal by t k Time current inner loop first given signal i * s (t k )，t k Moment load current reactive and harmonic component i qh (t k ) And t k Compensating current i obtained by moment compensating current acquisition circuit c (t k ) Is calculated to obtain u i (t k ) Is t k Time current inner loop control signal, from t k Time of day compensating current error signal e i (t k ) And the kth triangular carrier frequency f c (k) Calculating to obtain;
step S70: PWM generator controls signal u by comparing current inner loop i (t k ) And the frequency conversion triangular wave generator outputs a frequency conversion triangular carrier u c (k) Generating four control pulses P 1 、P 2 、P 3 、P 4 ；
Step S80: the obtained four control pulses generate four control signals S through a driving circuit 1 、S 2 、S 3 、S 4 Controlling a single-phase bridge type full-control circuit, the single-phase bridge type full-control circuit generating a compensation current i on an alternating current side c (t k ) And injecting the compensation current into the power grid.
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