Resonance suppression method for three-phase PWM rectifier with LCL filter

Abstract

The invention provides a resonance suppression method for a three-phase PWM (Pulse Width Modulation) rectifier with an LCL (Lower Control Limit) filter, which relates to a three-phase PWM rectifier control technology, and is characterized in that on the basis of vector control of power grid voltage orientation, voltage and current sampling is carried out at fixed time intervals, inner loop control is implemented, and on the premise of ensuring volt-second balance in a pulse width modulation process, namely, a PWM process, the voltage and current are sampled at fixed time intervals, so that the resonance suppression efficiency is improved. And the sampling period is minimized. According to the method, the sampling frequency is increased, the system bandwidth is improved, and resonance suppression can be achieved under the low carrier frequency when main circuit parameters are not matched.

Description

Technical Field

[0001] The invention relates to the technical field of three-phase PWM rectifier control systems, and in particular to a three-phase PWM rectifier resonance suppression method with an LCL filter. Background Art

[0002] Voltage-type three-phase PWM rectifier has the advantages of bidirectional energy flow, grid-side voltage and current maintaining unity power factor, and constant DC-side voltage, so it is widely used in high-power systems. At present, the control algorithms of three-phase PWM rectifier mainly include hysteresis current control, indirect current control, transient current control and voltage-oriented vector control.

[0003] Usually, in high-power rectification systems, in order to reduce losses and electromagnetic interference, only lower carrier frequencies can be used. If traditional L filters are used, larger inductance values ​​are required, which will not only increase the size of the filter, but also increase the inertia of the control system and reduce the current response speed. Therefore, LCL filters are usually used in high-power rectification systems. However, LCL filters lack damping and will inevitably have resonance problems.

[0004] In view of the shortcoming of LCL filter that it is easy to produce resonance, some scholars have proposed resonance suppression methods, including passive damping and active damping methods. The passive damping method usually increases the damping of the LCL filter by adding a series resistor to the filter capacitor branch, thereby achieving the purpose of suppressing the system resonance. However, the addition of damping will affect the filtering performance on the one hand, and increase the loss and reduce the efficiency on the other hand. The active damping method does not require actual damping resistors, but achieves damping through control algorithms, such as the virtual resistor method and the notch filter correction method. However, this method is complex to control and requires additional sensors, which increases the cost. In addition, the method of increasing the carrier frequency is usually adopted in engineering to keep the carrier frequency away from the resonant frequency to achieve resonance suppression, but the hardware cost will increase significantly. Summary of the invention

[0005] In view of the above problems, the present invention proposes a resonance suppression method for a three-phase PWM rectifier with an LCL filter, aiming to solve the resonance problem of the PWM rectifier with an LCL filter. The technical solution is as follows:

[0006] A resonance suppression method for a three-phase PWM rectifier with an LCL filter:

[0007] Step S1, in a PWM rectifier with an LCL filter, generating sampling pulses at equal time intervals within a triangular carrier cycle, and assuming that the number of samples generated at equal time intervals within a carrier cycle is N.

[0008] Step S2, performing voltage and current sampling: performing three-phase voltage and current sampling at each rising edge of the sampling pulse.

[0009] Step S3, performing phase-locked loop control according to the sampled voltage to obtain the sampled voltage phase angle θ, and at the same time performing coordinate transformation of the sampled voltage and current from the three-phase stationary coordinate system to the two-phase rotating coordinate system according to the phase angle, i.e., 3s / 2r transformation, to obtain the voltage e in the two-phase rotating coordinate system d 、e q and current i d 、i q ,

[0010] ,

[0011] Among them, C 3s / 2r is the coordinate transformation matrix of 3s / 2r transformation, θ is the voltage phase angle, cos is the cosine function operator, sin is the sine function operator, and [] is the matrix symbol.

[0012] Step S4, based on the sampled current i obtained in step S3 d 、i q Then the current given value i is obtained by combining with the voltage outer loop control dref 、i qref , perform current loop PI control, and then calculate the bridge arm voltage v d 、v q .

[0013] Step S5, update the modulation signal: after each sampling, calculate the modulation signal once; update the drive pulse at the vertex or valley of the triangular carrier using the most recent modulation signal, where the sampling time interval is the sampling period T c for:

[0014] ,

[0015] Among them, T c is the sampling period, T k is the triangular carrier period, and N is the number of samples.

[0016] Furthermore, in step S1, the specific method for generating the sampling pulse is: generating a system triangular carrier by a microcontroller, dividing the time interval into equal intervals according to the number of pulses N in a carrier cycle, and generating sampling pulses with equal time intervals.

[0017] Furthermore, in step S2, the sampled voltage is the filter capacitor voltage e a 、e b 、e c , the sampling current is the inductor current i on the bridge arm side a 、i b 、ic .

[0018] Furthermore, in step S3, the sampling voltage e a 、e b 、e c By transforming the matrix C 3s / 2r Get e d 、e q , e q Perform PI regulation control at 0, plus the grid angular frequency base value ω 0 , and integrate the result to get the voltage phase angle θ:

[0019] ,

[0020] Where θ is the voltage phase angle, is the integral symbol, e q is the quadrature axis component of the sampled voltage in the two-phase rotating coordinate system, G PI (s) is the transfer function of the phase-locked loop PI controller, ω 0 is the grid angular frequency base value, d is the differential operator, and t is the time.

[0021] Further, in step S4, when the current i d 、i q With the current given value i dref 、i qref After PI control, the voltage feedforward decoupling is added, and the voltage on the bridge arm side is obtained as follows:

[0022] ,

[0023] Among them, v d 、v q is the voltage on the bridge arm side, i dref 、i qref is the given current value, G PI (s) is the transfer function of the current loop PI controller, ω is the grid voltage angular frequency, i d 、i q is the current feedback value, L is the inductance on the bridge arm side, e d 、e q are the quadrature and direct axis components of the sampled voltage in the two-phase rotating coordinate system.

[0024] Furthermore, in step S5, N voltage and current samples are taken within one triangular carrier cycle, but the modulation signal is updated only at the apex or valley of the carrier. When the modulation signal is greater than the triangular carrier, a high level is output, and when the modulation signal is lower than the triangular carrier, a low level is output to form a corresponding drive pulse.

[0025] The beneficial effects of the present invention are as follows: the present invention increases the sampling frequency by performing multiple sampling within a triangular carrier, which not only improves the system bandwidth and dynamic performance, but also avoids the aliasing phenomenon caused by the resonant frequency introduced by sampling in the control system, and effectively suppresses the resonance caused by parameter mismatch of the LCL filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A sampling and updating strategy diagram of a resonance suppression method for a three-phase PWM rectifier with an LCL filter provided by the present invention;

[0027] Figure 2 A hardware system topology diagram of a three-phase PWM rectifier resonance suppression method with an LCL filter provided by the present invention;

[0028] Figure 3 A phase-locked loop control structure block diagram of a three-phase PWM rectifier resonance suppression method with an LCL filter provided by the present invention;

[0029] Figure 4 A current inner loop feedforward decoupling control block diagram of a three-phase PWM rectifier resonance suppression method with an LCL filter provided by the present invention;

[0030] Figure 5 A simulation waveform diagram of a three-phase PWM rectifier resonance suppression method with an LCL filter provided by the present invention in a conventional sampling mode;

[0031] Figure 6 A simulation waveform diagram of a resonance suppression method for a three-phase PWM rectifier with an LCL filter provided by the present invention in a multi-sampling manner. DETAILED DESCRIPTION

[0032] The following is only a preferred embodiment of the present invention. The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can understand the present invention. It should be pointed out that for those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims without departing from the principle of the present invention, all inventions and creations using the concept of the present invention are protected.

[0033] Figure 1 A multi-sampling strategy for a three-phase PWM rectifier resonance suppression method with an LCL filter provided by the present invention. For a multi-sampling control system for a three-phase PWM rectifier resonance suppression method with an LCL filter proposed by the present invention, it mainly includes four processes: generating a triangular carrier of the system, voltage and current sampling, modulation signal calculation and update, and drive pulse generation:

[0034] (1) Generate a triangular carrier wave of the system: Generate a triangular carrier wave through a microcontroller, whose period is the switching period of the switch tube and whose amplitude is ±1.

[0035] (2) Voltage and current sampling: Sampling pulses are generated at equal time intervals within one cycle of the triangular carrier, and three-phase voltage and current sampling is performed at each rising edge of the sampling pulse.

[0036] (3) Modulation signal calculation and update: The sampled voltage passes through a phase-locked loop to obtain the voltage phase angle, which is used for the 3s / 2r transformation of the voltage and current to obtain the current in the rotating coordinate system. PI control is then performed to obtain the voltage on the bridge arm side, and finally the most recent modulation signal is used to update the triangle carrier at the vertex or valley point.

[0037] (4) Driving pulse generation: When the amplitude of the modulated signal is greater than the triangular carrier, a high level is output; when the amplitude of the modulated signal is less than the triangular carrier, a low level is output, forming a corresponding driving pulse.

[0038] Under the multi-sampling strategy, combined with the proposed sampling method, the voltage and current sampling and control algorithm of the three-phase PWM rectifier with LCL filter are completed, which specifically includes the following steps:

[0039] Step S1, in a PWM rectifier with an LCL filter, such as Figure 1 As shown, sampling pulses are generated at equal time intervals within a carrier cycle, and the number of samples generated at equal time intervals within a carrier cycle is assumed to be N.

[0040] Here, the specific method for generating the sampling pulse is: generating a system triangular carrier through a microcontroller, dividing the time interval into equal intervals according to the number of samples N in a carrier cycle, and generating sampling pulses with equal time intervals.

[0041] Step S2, performing voltage and current sampling: performing three-phase voltage and current sampling at each rising edge of the sampling pulse.

[0042] Here, if Figure 2 As shown, the sampling voltage is the filter capacitor voltage e a 、e b 、e c , the sampling current is the inductor current i on the bridge arm side a 、i b 、i c .

[0043] Step S3, performing phase-locked loop control according to the sampled voltage to obtain the sampled voltage phase angle θ, and at the same time performing coordinate transformation of the sampled voltage and current from the three-phase stationary coordinate system to the two-phase rotating coordinate system according to the phase angle, i.e., 3s / 2r transformation, to obtain the voltage e in the two-phase rotating coordinate system d 、e qand current i d 、i q ,

[0044] ,

[0045] Among them, C 3s / 2r is the coordinate transformation matrix of 3s / 2r transformation, θ is the voltage phase angle, cos is the cosine function operator, sin is the sine function operator, and [] is the matrix symbol.

[0046] Here, if Figure 3 As shown, the sampling voltage e a 、e b 、e c By transforming the matrix C 3s / 2r Get e d 、e q , e q Perform PI regulation control at 0, plus the grid angular frequency base value ω 0 , integrate the result to get the grid voltage phase angle θ:

[0047] ,

[0048] Where θ is the voltage phase angle, is the integral symbol, e q is the quadrature axis component of the sampled voltage in the two-phase rotating coordinate system, G PI (s) is the transfer function of the phase-locked loop PI controller, ω 0 is the grid angular frequency base value, d is the differential operator, and t is the time.

[0049] Step S4, based on the sampled current i obtained in step S3 d 、i q Then the current given value i obtained by the voltage outer loop control is dref 、i qref ,like Figure 4 As shown, the current loop PI control is performed to calculate the bridge arm side voltage v d 、v q .

[0050] Here, at the current i d 、i q With the current given value i dref 、i qref After PI control, the voltage feedforward decoupling is added, and the voltage on the bridge arm side is obtained as follows:

[0051] ,

[0052] Among them, v d 、v qis the voltage on the bridge arm side, i dref 、i qref is the given current value, G PI (s) is the transfer function of the current loop PI controller, ω is the grid voltage angular frequency, i d 、i q is the current feedback value, L is the inductance on the bridge arm side, e d 、e q are the quadrature and direct axis components of the sampled voltage in the two-phase rotating coordinate system.

[0053] Step S5, update the modulation signal: after each sampling, calculate the modulation signal once; update the drive pulse at the vertex or valley of the triangular carrier using the most recent modulation signal, where the sampling time interval is the sampling period T c for:

[0054] ,

[0055] Among them, T c is the sampling period, T k is the triangular carrier period, and N is the number of samples.

[0056] Here, within one triangular carrier cycle, N voltage and current samples are taken, but the modulation signal is updated only at the carrier vertex or valley point. When the modulation signal is greater than the triangular carrier, a high level is output, and when the modulation signal is lower than the triangular carrier, a low level is output to form a corresponding drive pulse.

[0057] Figure 5 It is a simulation waveform diagram of a three-phase PWM rectifier with an LCL filter using conventional sampling method at a low carrier frequency.

[0058] Figure 6 It is a simulation waveform diagram of a three-phase PWM rectifier with an LCL filter using multi-sampling mode at a low carrier frequency.

[0059] contrast Figure 5 and Figure 6 It can be seen that the conventional sampling method has resonance and a divergent tendency, causing system instability; using a three-phase PWM rectifier resonance suppression method with an LCL filter in the present invention can effectively increase the sampling frequency, improve the system bandwidth, suppress the resonance in the grid-side voltage and current, and reduce the total harmonic distortion rate of the current.

[0060] Although the specific implementation of the invention is described in detail in conjunction with the drawings, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A resonance suppression method for a three-phase PWM rectifier with an LCL filter, characterized in that: The method is: Step S1, in a PWM rectifier with an LCL filter, generating sampling pulses at equal time intervals within a carrier cycle, assuming that the number of samples generated at equal time intervals within a carrier cycle is N; Step S2, sampling voltage and current: sampling three-phase voltage and current at each rising edge of the sampling pulse; Step S3, performing phase-locked loop control according to the sampled voltage to obtain the sampled voltage phase angle θ, and at the same time performing coordinate transformation of the sampled voltage and current from the three-phase stationary coordinate system to the two-phase rotating coordinate system according to the phase angle, i.e., 3s / 2r transformation, to obtain the voltage e in the two-phase rotating coordinate system d 、e q and current i d 、i q , ， Among them, C 3s / 2r is the coordinate transformation matrix of 3s / 2r transformation, θ is the voltage phase angle, cos is the cosine function operator, sin is the sine function operator, and [] is the matrix symbol; Step S4, based on the sampled current i obtained in step S3 d 、i q Then the current given value i obtained by the voltage outer loop control is dref 、i qref , perform current loop PI control, and then calculate the bridge arm voltage v d 、v q ; Step S5, update the modulation signal: after each sampling, calculate the modulation signal once; update the drive pulse at the vertex or valley of the triangular carrier using the most recent modulation signal, where the sampling time interval is the sampling period T c for: ， Among them, T c is the sampling period, T k is the triangular carrier period, and N is the number of samples.

2. A method for suppressing resonance of a three-phase PWM rectifier with an LCL filter according to claim 1, characterized in that: In the step S1, the specific method of generating the sampling pulse is: generating a system triangular carrier through a microcontroller, dividing the time interval into equal time intervals according to the number of samples N in a carrier cycle, and generating sampling pulses with equal time intervals.

3. The method for suppressing resonance of a three-phase PWM rectifier with an LCL filter according to claim 1, characterized in that: In step S2, the sampled voltage is the filter capacitor voltage e a 、e b 、e c , the sampling current is the inductor current i on the bridge arm side a 、i b 、i c .

4. The method for suppressing resonance of a three-phase PWM rectifier with an LCL filter according to claim 1, characterized in that: In step S3, the sampling voltage e a 、e b 、e c By transforming the matrix C 3s / 2r Get e d 、e q , e q Perform PI regulation control at 0, add the grid angular frequency base value ω0, and integrate the result to obtain the grid voltage phase angle θ: ， Where θ is the voltage phase angle, is the integral symbol, e q is the quadrature axis component of the sampled voltage in the two-phase rotating coordinate system, G PI (s) is the transfer function of the phase-locked loop PI controller, ω0 is the grid angular frequency base value, d is the differential operator, and t is time.

5. The method for suppressing resonance of a three-phase PWM rectifier with an LCL filter according to claim 1, characterized in that: In step S4, when the current i d 、i q With the current given value i dref 、i qref After PI control, the voltage feedforward decoupling is added, and the voltage on the bridge arm side is obtained as follows: ， Among them, v d 、v q is the voltage on the bridge arm side, i dref 、i qref is the given current value, G PI (s) is the transfer function of the current loop PI controller, ω is the grid voltage angular frequency, i d 、i q is the current feedback value, L is the inductance on the bridge arm side, e d 、e q are the quadrature and direct axis components of the sampled voltage in the two-phase rotating coordinate system.

6. A method for suppressing resonance of a three-phase PWM rectifier with an LCL filter according to claim 1, characterized in that: In step S5, N voltage and current samplings are performed within one triangular carrier cycle, but the modulation signal is updated only at the carrier vertex or valley point. When the modulation signal is greater than the triangular carrier, a high level is output, and when the modulation signal is lower than the triangular carrier, a low level is output to form a corresponding drive pulse.

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