Modified modulated wave acquisition method and model predictive control method for single-phase cascaded H-bridge rectifier

Abstract

A modified modulated wave acquisition method includes: obtaining a modulated wave u.sub.aba; calculating a difference between the given value i.sub.Nq* and the actual value i.sub.Nq of the q-axis component of a grid side current, inputting the result to a proportional integral (PI) controller, and multiplying an output of the PI controller by cos ωt to obtain a modulated wave offset Δu.sub.aba; and calculating a difference between the modulated wave u.sub.aba and the modulated wave offset Δu.sub.aba to obtain a modified modulation wave u.sub.aba′, where ωt is a grid voltage phase in a sinusoidal case. The MPC method for a single-phase cascaded H-bridge rectifier includes: obtaining the modified modulated wave u.sub.aba′, where the component i.sub.Nq* is 0; and replacing the modulated wave u.sub.aba with the modified modulated wave u.sub.aba′ to perform MPC for the single-phase cascaded H-bridge rectifier.

Claims

1. A modified modulated wave acquisition method, comprising: obtaining a modulated wave u.sub.aba; calculating a difference between a given value i.sub.Nq* and an actual value i.sub.Nq of the q-axis component of a grid side current, and inputting a result of the difference to a proportional integral (PI) controller; multiplying an output of the PI controller by cos ωt to obtain a modulated wave offset Δu.sub.aba; and calculating a difference between the modulated wave u.sub.aba and the modulated wave offset Δu.sub.aba to obtain a modified modulation wave u.sub.aba′, wherein ωt is a grid voltage phase in a sinusoidal case.

2. The modified modulated wave acquisition method according to claim 1, wherein a method for obtaining a proportional coefficient of the PI controller and an integral coefficient of the PI controller comprises: after setting the integral coefficient to 0, gradually increasing the proportional coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis oscillates, then gradually reducing the proportional coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis does not oscillate, and updating the proportional coefficient of the PI controller to a current proportional coefficient; and setting an initial value of the integral coefficient based on the proportional coefficient of the PI controller, gradually reducing the integral coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis oscillates, then gradually increasing the integral coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis does not oscillate and i.sub.Nq equals i.sub.Nq*, and updating the integral coefficient of the PI controller to the current integral coefficient.

3. The modified modulated wave acquisition method according to claim 1, wherein a method for obtaining the modulated wave u.sub.aba comprises: obtaining voltage components u.sub.abd and u.sub.abq of an input-side voltage u.sub.ab of a rectifier in a dq coordinate system; and performing direct-quadrature (d-q) inverse transformation on the voltage components u.sub.abd and u.sub.abq to obtain the modulated wave u.sub.aba.

4. The modified modulated wave acquisition method according to claim 2, wherein a method for obtaining the modulated wave u.sub.aba comprises: obtaining voltage components u.sub.abd and u.sub.abq of an input-side voltage u.sub.ab of a rectifier in a dq coordinate system; and performing d-q inverse transformation on the voltage components u.sub.abd and u.sub.abq to obtain the modulated wave u.sub.aba.

5. The modified modulated wave acquisition method according to claim 3, wherein a method for obtaining the voltage components u.sub.abd and u.sub.abq comprises: obtaining a relationship between a voltage and a current on an AC side of the rectifier in a stationary αβ coordinate system according to a topology of a rectifier circuit and Kirchhoff s voltage law; obtaining an expression of the voltage components u.sub.abd and u.sub.abq of the input-side voltage u.sub.ab of the rectifier in the dq coordinate system according to the relationship between the voltage and the current on the AC side of the rectifier; and converting the expression of the voltage components u.sub.abd and u.sub.abq of the input-side voltage u.sub.ab of the rectifier in the dq coordinate system into an expression containing a switching period T.sub.s to obtain the voltage components u.sub.abd and u.sub.abq.

6. A model predictive control (MPC) method for a single-phase cascaded H-bridge rectifier, comprising: obtaining a modified modulated wave u.sub.aba′ by using the method according to claim 1, wherein a component i.sub.Nq* is 0; and replacing a modulated wave u.sub.aba with the modified modulated wave u.sub.aba′ to perform MPC for the single-phase cascaded H-bridge rectifier.

7. The model predictive control (MPC) method for a single-phase cascaded H-bridge rectifier according to claim 6, wherein a method for obtaining a proportional coefficient of the PI controller and an integral coefficient of the PI controller comprises: after setting the integral coefficient to 0, gradually increasing the proportional coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis oscillates, then gradually reducing the proportional coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis does not oscillate, and updating the proportional coefficient of the PI controller to a current proportional coefficient; and setting an initial value of the integral coefficient based on the proportional coefficient of the PI controller, gradually reducing the integral coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis oscillates, then gradually increasing the integral coefficient until the component i.sub.Nq of the instantaneous grid-side current on the q-axis does not oscillate and i.sub.Nq equals i.sub.Nq*, and updating the integral coefficient of the PI controller to the current integral coefficient.

8. The model predictive control (MPC) method for a single-phase cascaded H-bridge rectifier according to claim 6, wherein a method for obtaining the modulated wave u.sub.aba comprises: obtaining voltage components u.sub.abd and u.sub.abq of an input-side voltage u.sub.ab of a rectifier in a dq coordinate system; and performing d-q inverse transformation on the voltage components u.sub.abd and u.sub.abq to obtain the modulated wave u.sub.aba.

9. The model predictive control (MPC) method for a single-phase cascaded H-bridge rectifier according to claim 8, wherein a method for obtaining the voltage components u.sub.abd and u.sub.abq comprises: obtaining a relationship between a voltage and a current on an AC side of the rectifier in a stationary αβ coordinate system according to a topology of a rectifier circuit and Kirchhoff s voltage law; obtaining an expression of the voltage components u.sub.abd and u.sub.abq of the input-side voltage u.sub.ab of the rectifier in the dq coordinate system according to the relationship between the voltage and the current on the AC side of the rectifier; and converting the expression of the voltage components u.sub.abd and u.sub.abq of the input-side voltage u.sub.ab of the rectifier in the dq coordinate system into an expression containing a switching period T.sub.s to obtain the voltage components u.sub.abd and u.sub.abq.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a topology diagram of a single-phase cascaded H-bridge seven-level rectifier;

(2) FIG. 2 is a principle block diagram of voltage components u.sub.abd and u.sub.abq of an input-side voltage of the single-phase cascaded H-bridge seven-level rectifier shown in FIG. 1 in a dq coordinate system;

(3) FIG. 3 is a principle block diagram of a modified modulated wave u.sub.aba′ in an MPC method for the single-phase cascaded H-bridge seven-level rectifier shown in FIG. 1;

(4) FIG. 4 is a principle block diagram of an MPC method for a single-phase cascaded H-bridge seven-level rectifier of a specific embodiment;

(5) FIG. 5 is a diagram of grid-side voltage and current waveforms before inductance error compensation;

(6) FIG. 6 is a diagram of grid-side voltage and current waveforms after inductance error compensation;

(7) FIG. 7 is a harmonic content graph obtained through FFT analysis before inductance error compensation in steady state;

(8) FIG. 8 is a harmonic content graph obtained through FFT analysis after inductance error compensation in steady state;

(9) FIG. 9 is a diagram of waveforms of a d-axis component and a q-axis component of a grid-side current before and after inductance error compensation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(10) The specific embodiments of the present invention will be described in detail below with reference to the drawings, so that those skilled in the art can understand the present invention. The described embodiments are only a part rather than all of the examples of the present invention. Without departing from the spirit and scope of the present invention defined by the appended claims, all other embodiments obtained by those skilled in the art without creative work shall fall within the protection scope of the claims.

(11) A modified modulated wave acquisition method includes:

(12) obtaining a modulated wave u.sub.aba;

(13) calculating a difference between the given value i.sub.Nq* and the actual value i.sub.Nq of the q-axis component of a grid side current, and inputting the result of the difference to a PI controller;

(14) multiplying an output of the PI controller by cos ωt to obtain a modulated wave offset Δu.sub.aba; and

(15) calculating a difference between the modulated wave u.sub.aba and the modulated wave offset Δu.sub.aba to obtain a modified modulation wave u.sub.aba′, where ωt is a grid voltage phase in a sinusoidal case.

(16) During implementation, a preferred method for obtaining a proportional coefficient and an integral coefficient of the PI controller includes:

(17) after setting the integral coefficient to 0, gradually increasing the proportional coefficient until the component i.sub.Nq oscillates, then gradually reducing the proportional coefficient until the component i.sub.Nq does not oscillate, and updating the proportional coefficient of the PI controller to the current proportional coefficient; and

(18) setting an initial value of the integral coefficient based on the proportional coefficient of the PI controller, gradually reducing the integral coefficient until the component i.sub.Nq oscillates, then gradually increasing the integral coefficient until the component i.sub.Nq does not oscillate and i.sub.Nq equals i*.sub.Nq, and updating the integral coefficient of the PI controller to the current integral coefficient. Specifically, after the proportional coefficient of the PI controller is determined, the initial value of the integral coefficient is: 100×proportional coefficient of the PI controller.

(19) Taking a single-phase cascaded H-bridge rectifier shown in FIG. 1 as an example, a method for obtaining the modulated wave u.sub.aba includes:

(20) obtaining voltage components u.sub.abd and u.sub.abq of an input-side voltage of the rectifier in a dq coordinate system;

(21) obtaining a relationship between voltage and current on an AC side of the rectifier in a stationary αβ coordinate system according to a topology of a rectifier circuit and Kirchhoff s voltage law:

(22) $\hspace{1em}\{\begin{array}{c}{u}_{\mathrm{Nd}}=L_N\frac{{\mathrm{di}}_{\mathrm{Nd}}}{\mathrm{dt}}+\omega L_N{i}_{\mathrm{Nq}}+u_{\mathrm{abd}}\\ u_{\mathrm{Nq}}=L_N\frac{{\mathrm{di}}_{\mathrm{Nq}}}{\mathrm{dt}}-\omega L_N{i}_{\mathrm{Nd}}+u_{\mathrm{abq}}\end{array}$

(23) where u.sub.Nd and i.sub.Nd are components of grid-side voltage and current on a d-axis; u.sub.Nq and i.sub.Nq are components of the grid-side voltage and current on a q-axis; co is an angular frequency, and LN is an actual parameter of a grid-side inductance;

(24) obtaining an expression of the voltage components u.sub.abd and u.sub.abq of the input-side voltage u.sub.ab of the rectifier in the dq coordinate system according to the relationship between the voltage and current on the AC side of the rectifier;

(25) $\hspace{1em}\{\begin{array}{c}{u}_{\mathrm{abd}}=u_{\mathrm{Nd}}-L_N\frac{{\mathrm{di}}_{\mathrm{Nd}}}{\mathrm{dt}}-\omega L_N{i}_{\mathrm{Nq}}\\ u_{\mathrm{abq}}=u_{\mathrm{Nq}}-L_N\frac{{\mathrm{di}}_{\mathrm{Nq}}}{\mathrm{dt}}+\omega L_N{i}_{\mathrm{Nd}}\end{array}$

(26) converting the expression of the voltage components u.sub.abd and u.sub.abq into an expression containing a switching period T.sub.s to obtain the voltage components u.sub.abd and u.sub.abq (the switching period T.sub.s of the rectifier is fixed to facilitate filter design); the principles of the voltage components u.sub.abd and u.sub.abq are shown in FIG. 2:

(27) $\hspace{1em}\{\begin{array}{c}{u}_{\mathrm{abd}}=u_{\mathrm{Nd}}-\frac{L_N}{T_s}\left(i_{\mathrm{Nd}}^{*}-i_{\mathrm{Nd}}\right)-\omega L_N{i}_{\mathrm{Nq}}\\ u_{\mathrm{abq}}=u_{\mathrm{Nq}}-\frac{L_N}{T_s}\left(i_{\mathrm{Nq}}^{*}-i_{\mathrm{Nq}}\right)+\omega L_N{i}_{\mathrm{Nd}}\end{array}$

(28) performing inverse transformation (d-q) on the voltage components u.sub.abd and u.sub.abq to obtain the modulated wave u.sub.aba, wherein, the principle block diagram is shown in FIG. 3.

(29) In another aspect, the solution further provides an MPC method for a single-phase cascaded H-bridge rectifier, including: obtaining the modified modulated wave u.sub.aba according to the method provided in this solution, where the component i.sub.Nq* is 0, and replacing the modulated wave u.sub.aba with the modified modulated wave u.sub.aba to perform MPC for the single-phase cascaded H-bridge rectifier.

(30) In an embodiment, an MPC method for a single-phase cascaded H-bridge rectifier is shown in FIG. 4. Results obtained before and after inductance error compensation (that is, before and after the MPC method is used) are shown in FIG. 5 to FIG. 9. As seen from FIG. 5 to FIG. 9, the MPC method can eliminate the steady-state error caused by the mismatch of inductance parameters, increase the control precision, improve the accuracy of MPC, and improve the steady-state performance of a system, such as an electric vehicle for example, on which a single-phase cascaded H-bridge rectifier is mounted.

(31) For the purposes of promoting an understanding of the principles of the invention, specific embodiments have been described. It should nevertheless be understood that the description is intended to be illustrative and not restrictive in character, and that no limitation of the scope of the invention is intended. Any alterations and further modifications in the described components, elements, processes or devices, and any further applications of the principles of the invention as described herein, are contemplated as would normally occur to one skilled in the art to which the invention pertains.