Control method for grid-side rectification and corresponding control module thereof

Abstract

The invention provides a control method for grid-side rectification and a corresponding control module thereof, and belongs to the technical field of electric vehicle charging. The control method comprises the following steps: sampling an AC voltage signal, an inductive current signal and a rectified output voltage; converting the AC voltage signal into a sinusoidal signal through amplitude normalization; inputting an error between the rectified output voltage and an expected output voltage into a first proportional-integral controller, and converting the error into an expected current signal; multiplying the expected current signal by the sinusoidal signal to obtain a current instruction signal; subtracting the inductive current signal from the current instruction signal to obtain a current error signal; processing the current error signal through a second proportional-integral controller to obtain an output instruction signal with duty ratio information; the output command signal can be used to control the rectified output voltage. The power factor is improved, and the code complexity is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of electric vehicle charging, and in particular to a control method for grid-side rectification and a corresponding control module thereof. Background Art

[0002] With the popularity of electric vehicles, users' requirements for electric vehicles are gradually increasing. Energy replenishment efficiency is one of the important indicators for evaluating electric vehicles.

[0003] Electric vehicles convert the AC power of the grid into DC power through charging devices. Power factor is one of the important indicators for evaluating the efficiency of energy replenishment. Power factor is the ratio of active power to apparent power. During the energy replenishment process of electric vehicles, the grid-side current of the rectifier has a large difference with the grid voltage phase due to the different impedance properties of the connected load, thus generating a large amount of reactive power, resulting in a decrease in power factor, thereby reducing the efficiency of energy replenishment. At present, the mainstream technical solution is to extract the phase information of the grid-side AC power through a phase-locked loop (PLL), and then generate a current command based on the phase information extracted by the phase-locked loop. After passing through a proportional resonant (PR) controller, the grid voltage feedforward is introduced to obtain a modulation wave. Based on the modulation wave, the switch of the rectifier is controlled to output a DC voltage. However, the control strategy based on the phase-locked loop has a complex code structure during implementation and it is difficult to achieve the expected power factor.

[0004] Therefore, there is an urgent need for a control method for grid-side rectification to improve the power factor and reduce the code complexity during the implementation process. Summary of the invention

[0005] In order to solve the technical problems of low power factor and high code complexity of existing electric vehicle charging devices, an embodiment of the present application provides a control method for grid-side rectification, the control method comprising: Sampling AC voltage signal, inductor current signal and rectified output voltage; Converting the AC voltage signal into a sinusoidal signal by amplitude normalization; Inputting the error between the rectified output voltage and the desired output voltage into a first proportional-integral controller to convert it into a desired current signal; Multiplying the desired current signal by the sinusoidal signal to obtain a current command signal; Subtracting the inductor current signal from the current command signal to obtain a current error signal; The current error signal is processed by a second proportional-integral controller to obtain an output command signal having duty cycle information; the output command signal can be used to control the rectifier output voltage.

[0006] Optionally, the control method further comprises: performing feed-forward correction on the output command signal through an AC voltage signal, thereby obtaining a modulated wave; The switching action of the rectifier is controlled based on the modulation wave to obtain a rectified output voltage.

[0007] Optionally, the control method further includes: The feed-forward corrected current error signal is normalized.

[0008] Optionally, converting the AC voltage signal into a sinusoidal signal comprises: The AC voltage signal is multiplied by the inverse of the amplitude of the AC voltage.

[0009] Optionally, normalizing the current error signal after feedforward correction includes: The AC voltage signal and the current error signal are respectively multiplied by the inverse of the desired output voltage.

[0010] Optionally, the sinusoidal signal includes a frequency of the grid-side voltage and a phase of the grid-side voltage.

[0011] Optionally, the modulated wave contains duty cycle information.

[0012] Optionally, performing feed-forward correction on the current error signal through the AC voltage signal to obtain the modulation wave includes: Comparing the current error signal and the AC voltage signal by an operational amplifier, If the AC voltage signal is greater than the current error signal, a high level is output; otherwise, a low level is output.

[0013] In a second aspect, an embodiment of the present application further provides a control module for grid-side rectification, the control module comprising: A sampling unit, used for sampling AC voltage signal, input inductor current and rectified output voltage; A voltage error unit, used to calculate the error between the rectified output voltage and the expected output voltage; A first proportional-integral controller, configured to convert an error between the rectified output voltage and a desired output voltage into a desired current signal; A first normalization unit, configured to convert the AC voltage signal into a sinusoidal signal by amplitude normalization; A current command signal generating unit, used for multiplying the desired current signal by the sinusoidal signal to obtain a current command signal; A current error calculation unit, used for obtaining a current error signal by subtracting the inductor current signal from the current command signal; A second proportional-integral controller, used for processing the current error signal to obtain an output command signal; the output command signal can be used to control the rectifier output voltage; A rectifier is used to rectify an output voltage based on the modulated wave output.

[0014] Optionally, the control module further includes: The feedforward correction unit is used to perform feedforward correction on the output command signal through an AC voltage signal to obtain a modulated wave.

[0015] The control method for grid-side rectification provided in the embodiment of the present application and its corresponding control module convert the AC voltage signal into a sinusoidal signal by amplitude normalization, multiply the sinusoidal signal with the expected current signal to obtain a current command signal, perform feed-forward correction on the error between the inductor current signal and the current command signal to obtain a modulation wave, and control the switching action of the rectifier based on the modulation wave to output a DC voltage. The control method provided in the present application omits the phase-locked loop to reduce the code complexity in the implementation process, and by converting the AC voltage signal into a sinusoidal signal, multiplying the sinusoidal signal with the expected current signal to obtain a current command signal, thereby directly obtaining the phase information of the grid-side voltage to avoid the error caused by the phase-locked loop control strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the background technology, the drawings required for use in the embodiments of the present application or the background technology will be described below.

[0017] Figure 1 An optional schematic diagram of a conventional control method for grid-side rectification is shown; Figure 2 An optional schematic diagram of a conventional strategy simulation for a control method for grid-side rectification is shown; Figure 3 An optional schematic diagram showing a circuit corresponding to a conventional control method for grid-side rectification; Figure 4 An optional schematic diagram of a control method for grid-side rectification provided in an embodiment of the present application is shown; Figure 5 An optional schematic diagram of a strategy simulation of a control method for grid-side rectification provided in an embodiment of the present application is shown; Figure 6 An optional schematic diagram of a circuit corresponding to a control method for grid-side rectification provided in an embodiment of the present application is shown; Figure 7 It shows that Figure 1 Output voltage waveform diagram corresponding to the control method shown; Figure 8 It shows that Figure 1 The waveform diagram of the grid-side voltage and the inductor current corresponding to the control method shown; Fig. 9 It shows that Figure 4 Output voltage waveform diagram corresponding to the control method shown; Fig.10 It shows that Figure 4 The waveform diagram of the grid-side voltage and inductor current corresponding to the control method shown. DETAILED DESCRIPTION

[0018] In order to make the purpose, features and advantages of the invention more obvious and easy to understand, the technical solutions in the embodiments of the invention will be clearly and completely described below in combination with the drawings in the embodiments of the invention. Obviously, the embodiments described below are only part of the embodiments of the invention, not all of the embodiments. Based on the embodiments of the invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the invention. The embodiments of the present application describe the methods, devices, and electronic devices provided by the flowcharts and / or block diagrams.

[0019] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0020] Figures 1 to 3 The control block diagram, simulation diagram and corresponding circuit diagram of the conventional control method for grid-side rectification are shown respectively. Figures 1 to 3 Taking a single-phase pulse width modulation (PWM) rectifier as an example, the traditional control method for grid-side rectification is as follows: Extracting the phase information of the AC voltage through a phase-locked loop; Based on the error between the output voltage and the desired output voltage, the desired output current is obtained through a proportional-integral controller (PI). The desired output current is multiplied by the phase information extracted by the phase-locked loop to obtain a current command signal; The current error is obtained by subtracting the current command signal from the inductor current signal; The current error is fed forward by the grid voltage through the proportional resonant (PR) controller to obtain the modulation wave. The output current and voltage are obtained by controlling the rectifier based on the modulation wave.

[0021] Among them, the phase-locked loop extracts the phase information of the AC voltage as follows: the phase detector in the phase-locked loop compares the phase difference between the input signal and the feedback signal (which is also the final output signal of the phase-locked loop) to obtain a signal that is proportional to the phase difference, usually an error signal; secondly, the low-pass filter in the phase-locked loop can filter out the high-frequency components in the phase difference information, retaining only the low-frequency error signal, reducing noise and fluctuations; then, the voltage-controlled oscillator in the phase-locked loop adjusts its output frequency according to the error signal output by the low-pass filter; finally, the output of the voltage-controlled oscillator is used as the feedback input of the phase detector to form a closed loop. After such operation, the phase-locked loop can obtain a signal of arbitrary amplitude with the same phase as the input signal.

[0022] It is not difficult to see that in the traditional control method, the phase-locked loop requires multiple links to extract phase information, and it is impossible to directly obtain phase information, which makes it difficult to realize the function of the phase-locked loop through code. Secondly, since the phase-locked loop itself is a closed-loop system, due to its inherent phase tracking error, the extracted phase always has errors, and after the transmission delay, the phase error is further amplified. In addition, in the above control method, in order to improve the voltage regulation accuracy of the output voltage, only a PR controller can be used. The PR controller has a high gain at the resonant frequency and a fixed gain at other frequencies. As a result, the PR controller is sensitive to parameter changes and needs to be adjusted and calibrated frequently, which is not suitable for the control of nonlinear systems (such as AC to DC). In summary, due to the inherent phase error of the phase-locked loop and the error caused by parameter changes in the PR controller, the inductor current error and the grid-side voltage error in the entire rectifier system are large, resulting in a decrease in the power factor.

[0023] In view of this, see Figures 4 to 6 , the embodiment of the present application provides a control method for grid-side rectification. Specifically, the control method at least includes: Sampling AC voltage signal V AC , inductor current signal I Lfdb and the rectified output voltage V fdb ; The AC voltage signal is normalized by amplitude V AC Convert to sinusoidal signal; The rectified output voltage V fdb The expected output voltage V ref The error is input into the first proportional integral (PI) controller and converted into the desired current signal I ref ; The expected current signal Iref Multiply with the sinusoidal signal to obtain the current command signal I cmd ; The inductor current signal I Lfdb With current command signal I cmd Make a difference to obtain a current error signal; The current error signal is converted into an output command signal including duty cycle information by a second PI controller, and the output command signal can be used to directly control the rectifier output voltage V fdb .

[0024] Among them, the AC voltage signal V AC is the grid-side voltage of AC power, and the inductor current signal I Lfdb is the current of the input inductor, and the rectified output voltage V fdb is the DC voltage output by the rectifier. Expected output voltage V ref is the ideal DC voltage output of the rectifier. And, the rectified output voltage V fdb is the voltage feedback signal, which is related to the desired output voltage V ref The voltage error signal can be converted into a retention current signal through the first PI controller.

[0025] Specifically, the rectified output voltage and the input voltage are coupled to each other. By adjusting the input current, the power of the system input can be changed, thereby indirectly changing the output voltage. The role of the loop that converts the AC voltage signal into a sinusoidal signal in the present application is to generate a current expected value related to the voltage error signal.

[0026] According to the implementation of the present application, the inductor current signal I Lfdb With current command signal I cmd The positive or negative value of the difference result affects the final control result. However, the order of difference between the two must be the inductor current signal. I Lfdb Current reduction command signal I cmd To avoid errors in the control direction of the system.

[0027] According to the implementation method of this application, see Figure 4 and Figure 5 , the collected AC voltage signal V ACMultiply by the inverse of its magnitude (i.e. ), thereby achieving amplitude normalization and obtaining a sinusoidal signal with an amplitude of 1 and only the frequency and phase characteristics of the grid-side voltage. This signal is used as a control signal for the inductor current signal, which can make the phase of the inductor current close to the phase of the grid-side voltage, thereby improving the power factor. The current command signal is obtained by multiplying the desired current signal with the sinusoidal signal. I cmd Optionally, the current command signal I cmd With the inductor current signal I Lfdb The current error signal is input as an input signal to the second PI controller. The second PI controller converts the current error signal into an output command signal including duty cycle information, and the output command signal can be used to directly control the output voltage. Optionally, the control method provided by the present application also includes: introducing an AC voltage signal V AC The output command signal is fed-forward corrected to improve the response speed of the system and eliminate the influence of low-order harmonics in the grid voltage on the grid-connected output current. After that, the output command signal after feed-forward correction is normalized using the desired output voltage. In this way, a modulation wave containing duty cycle information is obtained. Based on the modulation wave, the switching action of the rectifier is controlled to obtain the rectified output voltage. V fdb . This is used as the rectified output voltage V fdb Feedback is input to the first PI controller to form a closed loop.

[0028] According to an implementation of the present application, feedforward correction of the output command signal includes: superimposing the AC voltage signal on the output command signal. The output command signal after pre-correction contains the fluctuation information of the AC voltage signal, and can achieve a fast response, thereby reducing the working pressure of the current loop controller (i.e., the first PI controller). Specifically, feedforward correction of the output command signal to obtain a modulated wave includes: comparing the current error signal and the AC voltage signal through an operational amplifier, if the AC voltage signal is greater than the current error signal, then outputting a high level; otherwise, outputting a low level.

[0029] According to an embodiment of the present application, normalizing the output command signal after feedforward correction includes: multiplying the output command signal by the inverse of the desired output voltage.

[0030] Example 1 provides Figures 1 to 3 The control block diagram, simulation diagram and corresponding circuit diagram of the control method for grid-side rectification are shown. Figure 7 FIG. 1 shows a waveform diagram of the output voltage corresponding to the control method provided in Example 1 of the present application. Figure 7As shown, the output voltage stabilizes after 0.1 seconds, and the output voltage overshoots during the rectification process. Figure 8 The waveform diagram of the grid-side voltage and the inductor current corresponding to the control method provided in Example 1 of the present application is shown. Figure 8 Curve 1 is the inductor current waveform, and curve 2 is the grid-side voltage waveform. Figure 8 , after 0 to 0.1 seconds, the waveform of the inductor current tends to be stable, and correspondingly, the waveform of the output voltage is stable. Figure 8 As shown, in the time period from 0 to 0.1 seconds, the peaks and troughs of curve 1 and curve 2 are obviously not synchronized, which shows that there is a large phase difference between the inductor current and the grid-side voltage, and this phase difference will cause the power factor to decrease.

[0031] Example 2 provides Figures 4 to 6 The control block diagram, simulation diagram and corresponding circuit diagram of the control method for grid-side rectification are shown. Fig. 9 FIG. 2 shows a waveform diagram of the output voltage corresponding to the control method provided in Example 2 of the present application. Fig. 9 As shown in the figure, the output voltage stabilizes after 0.05 seconds. In addition, there is no overshoot in the output voltage during the rectification process. Fig.10 The waveform diagram of the grid-side voltage and the inductor current corresponding to the control method provided in Example 1 of the present application is shown. Fig.10 Curve 3 is the inductor current waveform, and curve 4 is the grid-side voltage waveform. Fig.10 , after 0 to 0.05 seconds, the waveform of the inductor current tends to be stable, and correspondingly, the waveform of the output voltage is stable. Fig.10 As shown, in the time period from 0 to 0.05 seconds, the peaks and troughs of curve 1 and curve 2 are synchronized, which shows that the phase difference between the inductor current and the grid-side voltage is small, thus avoiding the decrease in power factor caused by the phase difference.

[0032] In a second aspect, the present application further provides a control module for grid-side rectification. The control module includes: A sampling unit, used for sampling AC voltage signal, input inductor current and rectified output voltage; A voltage error unit, used to calculate the error between the rectified output voltage and the expected output voltage; A first proportional-integral controller, used for converting an error between the rectified output voltage and the desired output voltage into a desired current signal; A first normalization unit, used for converting the AC voltage signal into a sinusoidal signal by amplitude normalization; A current command signal generating unit, used for multiplying the desired current signal with the sinusoidal signal to obtain a current command signal; A current error calculation unit, used for obtaining a current error signal by subtracting the inductor current signal from the current command signal; A second proportional-integral controller, used for processing the current error signal to obtain an output command signal; A rectifier is used to rectify an output voltage based on the modulated wave output.

[0033] According to an embodiment of the present application, the control module further includes a feedforward correction unit for performing feedforward correction on the current error signal through an AC voltage signal to obtain a modulated wave.

[0034] The control method for grid-side rectification provided in the embodiment of the present application and its corresponding control module convert the AC voltage signal into a sinusoidal signal by amplitude normalization, multiply the sinusoidal signal with the expected current signal to obtain a current command signal, perform feed-forward correction on the error between the inductor current signal and the current command signal to obtain a modulation wave, and control the switching action of the rectifier based on the modulation wave to output a DC voltage. The control method provided in the present application omits the phase-locked loop to reduce the code complexity in the implementation process, and by converting the AC voltage signal into a sinusoidal signal, multiplying the sinusoidal signal with the expected current signal to obtain a current command signal, thereby avoiding the error caused by the phase-locked loop control strategy by directly obtaining the phase information of the grid-side voltage. The control method provided by the present application directly converts the AC voltage into a sinusoidal signal by amplitude normalization to extract the phase information, thereby realizing PI control of the current error and avoiding the problem of unsatisfactory control effect of the PR controller in a nonlinear system.

[0035] The above is only a specific implementation of the embodiment of the present application, but the protection scope of the embodiment of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the embodiment of the present application, which should be included in the protection scope of the embodiment of the present application. Therefore, the protection scope of the embodiment of the present application shall be based on the protection scope of the claims.

Claims

1. A control method for grid-side rectification, characterized in that: The control method comprises: Sampling AC voltage signal, inductor current signal and rectified output voltage; Converting the AC voltage signal into a sinusoidal signal by amplitude normalization; Inputting the error between the rectified output voltage and the desired output voltage into a first proportional-integral controller to convert it into a desired current signal; Multiplying the desired current signal by the sinusoidal signal to obtain a current command signal; Subtracting the inductor current signal from the current command signal to obtain a current error signal; The current error signal is processed by a second proportional-integral controller to obtain an output command signal having duty cycle information; the output command signal can be used to control the rectifier output voltage.

2. The control method according to claim 1, characterized in that: The control method further includes: performing feed-forward correction on the output command signal through the AC voltage signal, thereby obtaining a modulated wave; The switching action of the rectifier is controlled based on the modulation wave to obtain a rectified output voltage.

3. The control method according to claim 2, characterized in that: The control method further comprises: Normalize the output command signal after feedforward correction.

4. The control method according to any one of claims 1 to 3, characterized in that: The converting the AC voltage signal into a sinusoidal signal comprises: The AC voltage signal is multiplied by the inverse of the amplitude of the AC voltage.

5. The control method according to claim 3, characterized in that: The normalizing of the output command signal after feedforward correction comprises: The output command signal is multiplied by the inverse of the desired output voltage.

6. The control method according to claim 1, characterized in that: The sinusoidal signal includes the frequency of the grid-side voltage and the phase of the grid-side voltage.

7. The control method according to claim 2, characterized in that: The modulated wave contains duty cycle information.

8. The control method according to claim 2, characterized in that: The method of performing feedforward correction on the output command signal by using the AC voltage signal to obtain the modulation wave comprises: Comparing the current error signal and the AC voltage signal by an operational amplifier, If the AC voltage signal is greater than the current error signal, a high level is output; otherwise, a low level is output.

9. A control module for grid-side rectification, characterized in that: The control module comprises: A sampling unit, used for sampling AC voltage signal, input inductor current and rectified output voltage; A voltage error unit, used to calculate the error between the rectified output voltage and the expected output voltage; A first proportional-integral controller, configured to convert an error between the rectified output voltage and a desired output voltage into a desired current signal; A first normalization unit, configured to convert the AC voltage signal into a sinusoidal signal by amplitude normalization; A current command signal generating unit, used for multiplying the desired current signal by the sinusoidal signal to obtain a current command signal; A current error calculation unit, used for obtaining a current error signal by subtracting the inductor current signal from the current command signal; A second proportional-integral controller, used for processing the current error signal to obtain an output command signal; the output command signal can be used to control the rectifier output voltage; A rectifier is used to rectify an output voltage based on the modulated wave output.

10. The control module according to claim 9, characterized in that: The control module also includes: The feedforward correction unit is used to perform feedforward correction on the output command signal through an AC voltage signal to obtain a modulated wave.

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