An LLC resonant converter control circuit and method

Abstract

The application provides an LLC resonant converter control circuit and method. The control circuit comprises a main control loop, an LLC resonant converter, and a compensation control loop. The main control loop comprises an output current loop, an output voltage loop and a resonant current loop. The output results of the output current loop and the output voltage loop are input into the resonant current loop. The output signals of the LLC resonant converter are fed back to the output current loop, the output voltage loop and the resonant current loop of the main control loop. The input end of the compensation control loop is connected with the LLC resonant converter, and is used for receiving the output signals of the LLC resonant converter and feeding back to the main control loop. The application can not affect the gain of a high frequency band, greatly improve the gain of a low frequency band, and effectively reduce the low frequency ripple of an output end.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of charging, in particular to an LLC resonant converter control circuit and method. BACKGROUND

[0002] The direct current charging module includes an AC-DC converter and a DC-DC converter, the AC-DC converter is to rectify three-phase alternating current input into direct current output, providing a direct current bus for the DC-DC converter, and the DC-DC converter is to provide corresponding direct current voltage and current according to the demand of the load. The direct current charging module needs not only high efficiency characteristics during the charging process, but also small current harmonics to reduce the additional loss of the battery caused by the current harmonics, so as to not only improve the charging efficiency but also prolong the service life of the battery. Although the LLC resonant converter can solve the problem of high efficiency of the direct current charging module, it has the problem of insufficient suppression ability of low frequency harmonics. Most of the low frequency ripples come from the power grid, are multiplied by the front-stage three-phase rectification module, and are superimposed on the direct current bus, so the voltage and current output by the rear-stage converter contain low frequency ripples, which will affect the charging quality during the charging process, and the frequency of the low frequency ripple is about 300 Hz.

[0003] The existing scheme adopts the LLC resonant converter in the rear-stage module, and utilizes the resonance of inductance and capacitance to make the voltage and current realize zero-crossing switching, so as to make the power tube realize zero-voltage turn-on, reduce the switching loss, and improve the working efficiency of the converter. In terms of control, the LLC resonant converter adopts PI as the control loop of the system, so that the LLC resonant converter can better stabilize the output. However, the LLC resonant converter has the problem of insufficient low-frequency gain, and only by continuously increasing the low-frequency gain in the PI control loop can the low-frequency harmonics be suppressed. Although the low-frequency harmonics can be weakened to a certain extent, the gain of the high-frequency band is also correspondingly increased, which will cause high-frequency oscillation and affect the stability of the LLC resonant converter. SUMMARY

[0004] To solve the above-mentioned defects, the purpose of the present application is to provide an LLC resonant converter control circuit and method, which can improve the gain of the low-frequency band without affecting the gain of the high-frequency band, and effectively reduce the low-frequency ripple at the output end.

[0005] The application provides an LLC resonant converter control circuit, which comprises a main control loop, an LLC resonant converter and a compensation control loop.

[0006] Preferably, the compensation control loop comprises a band-pass filter, a phase-locked loop module, a ripple amplitude closed-loop control module and a compensation alternating current integration module connected in sequence, the band-pass filter extracts a sinusoidal signal of a specific frequency from an output end of the LLC resonant converter, the phase-locked loop module and the ripple amplitude closed-loop control module obtain an amplitude of superimposed alternating current, and the compensation alternating current integration module obtains a compensation alternating current.

[0007] Preferably, the compensation control loop further comprises a second-order generalized integral module between the band-pass filter and the phase-locked loop module, and the sinusoidal signal passes through the second-order generalized integral module to obtain a standard sinusoidal wave with a phase difference of 90° and the same amplitude.

[0008] Preferably, the band-pass filter is a 300 Hz band-pass filter.

[0009] The application further provides an LLC resonant converter control method, which adopts the control circuit in the above claim, and comprises the following steps: obtaining an output signal at an output end of an LLC resonant converter; obtaining a ripple sinusoidal signal of a preset frequency through a band-pass filter of the preset frequency; obtaining a standard sinusoidal wave with a phase difference of 90° and the same amplitude through a second-order generalized integral module; obtaining a phase and an amplitude through a phase-locked loop module, αβ / dq conversion and phase locking; obtaining an amplitude of superimposed alternating current through a ripple amplitude closed-loop control module, and obtaining a compensation alternating current through a compensation alternating current integration module.

[0010] Preferably, the step of obtaining a phase and an amplitude through a phase-locked loop module, conversion and phase locking comprises the following steps: obtaining a phase θ and an amplitude U through dq conversion and phase locking. d , U d is an amplitude of the output end ripple.

[0011] Preferably, the step of obtaining an amplitude of superimposed alternating current through a ripple amplitude closed-loop control module, and obtaining a compensation alternating current through a compensation alternating current integration module comprises the following steps: obtaining an amplitude U of superimposed alternating current through a U d _PI closed-loop control module.* d, the compensated AC flow is integrated by the compensated AC flow integration module to obtain a compensated AC flow ac.

[0012] Preferably, the discrete transfer function of the band-pass filter is as follows:

[0013] y(n) = k1*y(n-1) + k2*y(n-2) + k3*x(n) + k4*x(n-2)

[0014] Preferably, the discrete transfer function of the second-order generalized integration module is as follows:

[0015] a 11 *y1(n) + a 21 *y1(n-1) + a 31 y1(n-2) = b 11 x(n) + b 21 x(n-1) + b 31 x(n-2)

[0016] a 12 *y2(n) + a 22 *y2(n-1) + a 32 y2(n-2) = b 12 x(n) + b 22 x(n-1) + b 32 x(n-2)

[0017] Preferably, the calculation formula of the ripple amplitude closed-loop control module is as follows:

[0018]

[0019] Beneficial effects:

[0020] Compared with the prior art, the LLC resonant converter control circuit and the control method thereof proposed in the application feed back the signal output by the LLC resonant converter to the main control loop through a compensation control loop. Since the output ripple is a low-frequency oscillation with a fixed period, the AC flow of the output ripple of the LLC resonant converter is extracted, compensation is performed to obtain a compensation amount, and the compensation amount is added to the given value of the outer loop of the main control loop, so that the system is compensated in advance, and the low-frequency ripple at the output end is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0021] The application will be further described below in combination with the drawings and embodiments:

[0022] Figure 1 Fig. 1 shows a structural schematic diagram of a charging module.

[0023] Figure 2 Fig. 3 shows a structural schematic diagram of an LLC resonant converter in the prior art.

[0024] Figure 3 Fig. 1 shows a schematic diagram of an LLC resonant converter control circuit according to an embodiment of the present application.

[0025] Figure 4 Fig. 2 shows a schematic diagram of a specific control circuit of the compensation control loop according to an embodiment of the present application.

[0026] Figure 5 Fig. 3 shows a flowchart of an LLC resonant converter control method according to an embodiment of the present application.

[0027] Figure 6 Fig. 4 shows a control flowchart of an LLC resonant converter control method according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] The above-mentioned schemes are further described in the following specific embodiments. It should be understood that these embodiments are used to illustrate the present application and do not limit the scope of the present application. The implementation conditions used in the embodiments can be further adjusted according to the specific manufacturer's conditions, and the implementation conditions not mentioned are usually the conditions in the conventional experiments.

[0029] The present application discloses an LLC resonant converter control circuit, which comprises: a main control loop, the main control loop comprising an output current loop, an output voltage loop and a resonant current loop, the output terminals of the output current loop and the output voltage loop being electrically connected to the input terminal of the resonant current loop, and the output results of the output current loop and the output voltage loop being input into the resonant current loop; an LLC resonant converter, which is electrically connected to the output terminal of the resonant current loop, and the output signals of the LLC resonant converter are respectively fed back to the output current loop, the output voltage loop and the resonant current loop of the main control loop; and a compensation control loop, which is connected to the LLC resonant converter, is used to receive the output signals of the LLC resonant converter and feed them back to the main control loop (and feed the compensation information back to the main control loop). The compensation control loop comprises a band-pass filter, a phase-locked loop module, a ripple amplitude closed-loop control module and a compensation alternating quantity integration module which are electrically connected in sequence, the band-pass filter is electrically connected to the output terminal of the LLC resonant converter and extracts a ripple signal of a specific frequency from the output terminal of the LLC resonant converter, the ripple amplitude closed-loop control module obtains the amplitude and phase of the superimposed alternating quantity through the phase-locked loop module and the ripple amplitude closed-loop control module, and the compensation alternating quantity integration module receives the amplitude and phase of the superimposed alternating quantity to obtain the compensation alternating quantity.

[0030] Reference should be made to Figure 1The system structure diagram of the charging module is shown, the charging module includes a front stage module and a rear stage module, the front stage module 1 connects three-phase alternating current, converts the three-phase alternating current into direct current and then outputs the direct current to the rear stage module, and the rear stage module provides an output voltage in a corresponding range according to the requirement of a load. Specifically, the front stage module includes an AC-DC converter and a control module, the rear stage module includes a DC-DC converter and a control module, the AC-DC converter of the front stage module rectifies three-phase alternating current input into direct current output, and provides a direct current bus for the DC-DC converter of the rear stage module, and the DC-DC converter of the rear stage module provides a corresponding direct current voltage and current according to the requirement of the load.

[0031] The prior art rear stage module adopts an LLC resonant converter, please refer to Figure 2 As shown, the LLC resonant converter utilizes inductance and capacitance to generate resonance so that voltage and current realize zero-crossing switching, thereby making the power tube realize zero-voltage turn-on, reducing switching loss and improving the working efficiency of the converter. The control module includes a controller, a driving circuit, a resonant current sampling circuit, an output current sampling circuit and an output voltage sampling circuit, the controller samples the output current of the output current sampling circuit, the output voltage of the output voltage sampling circuit and the resonant current of the resonant current sampling circuit, performs closed-loop control according to the collected output voltage, output current and resonant current, and controls the output voltage and the output current as an outer ring and the resonant current as an inner ring respectively, thereby stabilizing the output voltage of the LLC resonant converter.

[0032] The above embodiment can weaken low-frequency harmonics to a certain extent, but also correspondingly raises the gain of the high-frequency band, which may cause high-frequency oscillation and thereby affect the stability of the LLC resonant converter.

[0033] Please refer to Figure 3As shown, this invention provides an LLC resonant converter control circuit, the circuit including: a main control loop 10, an LLC resonant converter 20, a compensation control loop 30, and a load 40. The main control loop 10 includes an output current loop 11, an output voltage loop 12, and a resonant current loop 13, which respectively perform closed-loop control on the acquired output current, output voltage, and resonant current. The LLC resonant converter 20 is connected to the resonant current loop of the main control loop 10 and receives the data transmitted by the resonant current loop. The input terminal of the compensation control loop 10 is connected to the output terminal of the LLC resonant converter 20 and is used to receive the output signal of the resonant converter 20. The output signal of the LLC resonant converter 20 is fed back to the output current loop 11 and the output voltage loop 12 respectively, and receives the compensation current and compensation voltage of the compensation control loop 30. In this embodiment, the signal at the output terminal of the LLC resonant converter 20 is fed back to the output current loop 11 and the output voltage loop 12 to form an outer loop, and the signal at the output terminal of the LLC resonant converter 20 is fed back to the resonant current loop 13 to form an inner loop. This invention can greatly improve the gain in the low-frequency band without affecting the gain in the high-frequency band, and effectively reduce the low-frequency ripple at the output terminal.

[0034] The main low-frequency ripple at the output of the LLC resonant converter of this invention is 300Hz. The compensation control loop mainly performs compensation control by extracting the AC quantity at the output of the LLC resonant converter, thereby obtaining the amplitude through phase locking and adding it to the given value of the outer loop formed by the LLC resonant converter, the output current loop, and the output voltage loop, thereby providing advance compensation to reduce the low-frequency ripple at the output.

[0035] In one embodiment of the present invention, please refer to Figure 4 As shown, the compensation control loop 30 includes a bandpass filter 31, a second-order generalized integrator module 32, a phase-locked loop module 33, and a ripple amplitude closed-loop control module (U) connected in sequence. d The bandpass filter 31 extracts a sinusoidal signal of a specific frequency from the output of the LLC resonant converter 20. The sinusoidal signal is integrated by the second-order generalized integral module to obtain a pair of standard sine waves with a 90° phase difference and the same amplitude. The standard sine waves are then transformed and phase-locked in the phase-locked loop module 33 through αβ / dq transformation to obtain the corresponding position θ and amplitude U. d U d It is the amplitude of the output ripple, amplitude U d After the ripple amplitude closed-loop control module (U) d The closed-loop control of _PI)34 obtains the amplitude U*d of the superimposed AC quantity, and finally generates the compensation AC quantity ac.

[0036] In one embodiment of the present invention, the bandpass filter 31 is a 300Hz bandpass filter.

[0037] U in the above embodiments d In PI control, the controlled object is the amplitude U of the output ripple. d The goal is to reduce the output ripple to 0 for U d Perform closed-loop control and make U d Gradually track the given value of 0. The difference between the controlled object and the target value: err = 0 - U d .

[0038] Since the integral term is obtained by continuously accumulating the error err, when the ripple amplitude is large, U d The value of * also increases, resulting in a larger compensation amount, and the ripple at the output is well attenuated (U). d As the output decreases, err also gradually decreases, and Ud* reaches a constant value, eventually achieving a stable output with very small ripple.

[0039] Therefore, the compensation AC quantity ac is superimposed on the given Ref of the outer loop control, thereby improving the low-frequency gain of the system control. Without increasing the gain in the high-frequency range, the low-frequency gain is effectively reduced, thus reducing the low-frequency ripple at the output.

[0040] One embodiment of this application also provides a DC charging module including the above-described LLC resonant converter control circuit.

[0041] This invention also provides a control method for an LLC resonant converter; please refer to [reference needed]. Figure 5 , Figure 6 As shown, the method includes:

[0042] S10, obtain the output voltage at the output terminal of the LLC resonant converter. The main low-frequency ripple at the output terminal of the LLC resonant converter is 300Hz.

[0043] S20: The output voltage is passed through a bandpass filter of a preset frequency to obtain a sinusoidal signal of a preset frequency. The output voltage of the LLC resonant converter is passed through a 300Hz bandpass filter to extract a 300Hz sinusoidal signal from the output terminal. The discrete transfer function of the bandpass filter is as follows:

[0044] y(n)=k1*y(n-1)+k2*y(n-2)+k3*x(n)+k4*x(n-2)

[0045] S30, the sinusoidal signal is passed through a second-order generalized integrator to obtain a standard sine wave with a 90° phase difference and the same amplitude. The discrete transfer function is as follows:

[0046] a 11 *y1(n)+a 21 *y1(n-1)+a 31 y1(n-2)=b11 x(n)+b 21 x(n-1)+b 31 x(n-2)

[0047] a 12 *y2(n)+a 22 *y2(n-1)+a 32 y2(n-2)=b 12 x(n)+b 22 x(n-1)+b 32 x(n-2)

[0048] S40 transforms and locks in a standard sine wave through a phase-locked loop module to obtain its phase and amplitude.

[0049] S50 obtains the amplitude of the superimposed AC quantity through the ripple amplitude closed-loop control module, and obtains the compensated AC quantity through the compensated AC quantity integration module.

[0050] In the phase-locked loop module, the corresponding position θ and amplitude U are obtained through αβ / dq transformation and phase locking. d U d It is the amplitude of the output ripple. After U d The PI closed-loop control obtains the amplitude U*d of the superimposed AC quantity, and finally generates the compensation AC quantity ac.

[0051] Among them, in U d In PI control, the controlled object is the amplitude U of the output ripple. d The goal is to reduce the output ripple to 0 for U d Perform closed-loop control and make U d Gradually track the given value of 0. The difference between the controlled object and the target value: err = 0 - U d The closed-loop control calculation formula is as follows:

[0052]

[0053] Since the integral term is obtained by continuously accumulating the error err, when the ripple amplitude is large, U d The value of * also increases, resulting in a larger compensation amount, and the output ripple is well attenuated (U). d (It gets smaller), and err also gradually gets smaller. d *When the value is constant, the final output becomes stable and the ripple is very small.

[0054] Therefore, the compensation AC quantity ac is superimposed on the given Ref of the outer loop control, thereby improving the low-frequency gain of the system control. Without increasing the gain in the high-frequency range, the low-frequency gain is effectively reduced, thus reducing the low-frequency ripple at the output.

[0055] The embodiments described in this invention enable the system to better reduce output ripple under steady-state conditions without introducing other high-frequency oscillations, and to better control the resonant current to achieve stable output under dynamic conditions.

[0056] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A control circuit for an LLC resonant converter, characterized in that, The circuit includes: The main control loop includes an output current loop, an output voltage loop, and a resonant current loop, and the output results of the output current loop and the output voltage loop are input into the resonant current loop; An LLC resonant converter, wherein the output signal of the LLC resonant converter is fed back to the output current loop, output voltage loop and resonant current loop of the main control loop respectively; The compensation control loop has its input connected to the LLC resonant converter, and is used to receive the output signal of the LLC resonant converter and feed it back to the main control loop. The compensation control loop includes a bandpass filter, a phase-locked loop module, a ripple amplitude closed-loop control module, and a compensation AC quantity integration module connected in sequence. The bandpass filter extracts a ripple signal of a specific frequency from the output of the LLC resonant converter, obtains the amplitude and phase of the superimposed AC quantity through the phase-locked loop module and the ripple amplitude closed-loop control module, and obtains the compensation AC quantity through the compensation AC quantity integration module. The compensation control loop also includes a second-order generalized integrator module, located between the bandpass filter and the phase-locked loop module. The sine signal passes through the second-order generalized integrator module to obtain a standard sine wave with a phase difference of 90° and the same amplitude, which is used by the phase-locked loop to lock the phase of the output ripple.

2. The LLC resonant converter control circuit according to claim 1, characterized in that, The bandpass filter is a 300Hz bandpass filter.

3. A control method for an LLC resonant converter, characterized in that, Using the control circuit described in claims 1-2, the method includes: Obtain the output voltage signal or output current signal at the output terminal of the LLC resonant converter; The output signal is passed through a bandpass filter of a preset frequency to obtain a sinusoidal signal of a preset frequency. The sinusoidal signal is passed through a second-order generalized integral module to obtain a standard sine wave with a phase difference of 90° and the same amplitude. The standard sine wave is passed through a phase-locked loop module, and its phase and amplitude are obtained through dq transformation and phase-locking. The amplitude is obtained by passing the ripple amplitude closed-loop control module to obtain the amplitude and phase of the superimposed AC quantity, and then the compensated AC quantity is obtained by passing the compensated AC quantity integration module.

4. The LLC resonant converter control method according to claim 3, characterized in that, The step of obtaining the phase and amplitude of the standard sine wave through a phase-locked loop module, after transformation and phase locking, includes: The standard sine wave is passed through a phase-locked loop module, and after dq transformation and phase-locking, the phase θ and amplitude U are obtained. d U d It is the amplitude of the output ripple.

5. The LLC resonant converter control method according to claim 3, characterized in that, The steps of obtaining the amplitude of the superimposed AC quantity by the ripple amplitude closed-loop control module and obtaining the compensated AC quantity by the compensated AC quantity integration module include: After U d The PI closed-loop control module obtains the amplitude U of the superimposed AC quantity. * d U*d, after being processed by the compensation AC quantity integration module, yields the compensation AC quantity ac.

6. The LLC resonant converter control method according to claim 3, characterized in that, The discrete transfer function of the bandpass filter is as follows: y(n)=k1*y(n-1)+k2*y(n-2)+k3*x(n)+k4*x(n-2).

7. The LLC resonant converter control method according to claim 3, characterized in that, The discrete transfer function of the second-order generalized integral module is as follows: a 11 *y1(n)+a 21 *y1(n-1)+a 31 y1(n-2)=b 11 x(n)+b 21 x(n-1)+b 31 x(n-2) a 12 *y2(n)+a 22 *y2(n-1)+a 32 y2(n-2)=b 12 x(n)+b 22 x(n-1)+b 32 x(n-2).

8. The LLC resonant converter control method according to claim 3, characterized in that, The calculation formula for the ripple amplitude closed-loop control module is as follows:

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