Control method and system of LLC resonant converter

Abstract

The invention relates to the field of resonant converters, in particular to a control method of an LLC resonant converter, which comprises the following steps: acquiring the input current of the LLC resonant converter, the voltage of a resonant capacitor and the output voltage; starting integration of the input current at the valley moment of the voltage of the resonant capacitor to obtain a first voltage; after the output voltage and the reference voltage pass through an operational amplifier loop compensation circuit, third voltage is obtained; enabling the first voltage and the third voltage to pass through a comparator to obtain a first reset signal; and copying the first reset signal to obtain an HG signal for controlling a first driving switch tube Q1 of the LLC resonant converter and an LG signal for controlling a second driving switch tube Q2 of the LLC resonant converter. The LLC resonant converter has the advantages that the input power of the LLC resonant converter is accurately controlled, the dynamic response speed is increased, output ripples are reduced, overload and short-circuit protection control is easily achieved until the output is a single-pole point system, and the design of the loop compensator is simpler.

Description

Technical Field

[0001] This application relates to the field of resonant converters, and in particular to a control method and system for an LLC resonant converter. Background Technology

[0002] Currently, LLC resonant converters have attracted much attention due to their soft-switching, high efficiency, and low EMI characteristics, and have been widely used in various power supply applications. However, existing LLC resonant converters typically use frequency modulation to directly control the switching frequency through output voltage negative feedback to achieve output voltage control. This method, known as voltage-mode control, suffers from drawbacks such as slow load response, multiple poles at the output, complex loop compensation due to load variations, and inaccurate control of input power. Summary of the Invention

[0003] To accurately control the input power, this application provides a control method and system for an LLC resonant converter.

[0004] This application provides a control method for an LLC resonant converter, which adopts the following technical solution: Firstly, a control method for an LLC resonant converter is provided, including: The input current, the voltage of the resonant capacitor, and the output voltage Vout of the LLC resonant converter are obtained respectively. At the moment when the voltage of the resonant capacitor is at its lowest point or when the input current first increases, the integration of the input current is initiated to obtain the first voltage V1. The output voltage Vout and the reference voltage Vref are passed through an operational amplifier loop compensation circuit to obtain a third voltage Vc; The first voltage V1 and the third voltage Vc are passed through a comparator to obtain the first reset signal RST1; The first reset signal RST1 is copied to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

[0005] Preferably, the step of copying the first reset signal RST1 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter includes: Using the initial pulse as the SET signal of the RS flip-flop and the first reset signal RST1 as the RESET signal of the RS flip-flop, the initial HG signal and the initial LG signal are obtained. The initial HG signal is sent to the second integration unit to obtain at least N triangular waves; The triangular wave is subjected to zero-reset detection to obtain at least N pulse waves; Using the at least N pulse waveforms as the SET signal of the RS flip-flop and the first reset signal RST1 as the RESET signal of the flip-flop, the HG signal and the LG signal are obtained.

[0006] Preferably, after initiating the integration of the input current at the valley of the voltage of the resonant capacitor or at the moment when the input current first rises to obtain the first voltage V1, the method further includes: The sawtooth wave signal is superimposed on the first voltage V1 to obtain the second voltage V2; The second voltage V2 and the third voltage Vc are passed through a comparator to obtain the second reset signal RST2; The second reset signal RST2 is copied to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

[0007] Preferably, the step of copying the second reset signal RST2 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter includes: Using the initial pulse as the SET signal of the RS flip-flop and the second reset signal RST2 as the RESET signal of the RS flip-flop, the initial HG signal and the initial LG signal are obtained. The initial HG signal is sent to the third integration unit to obtain at least N sawtooth waves Vs; the at least N sawtooth waves are superimposed on the first voltage V1 to obtain the second voltage V2; The initial HG signal is sent to the second integration unit to obtain at least N triangular waves; The triangular wave is subjected to zero-reset detection to obtain at least N pulse waves; Using the at least N pulse waveforms as the SET signal of the RS flip-flop and the second reset signal RST2 as the RESET signal of the flip-flop, the HG signal and the LG signal are obtained.

[0008] Secondly, a control system for an LLC resonant converter is also provided, comprising: A resonant capacitor voltage sampling unit is used to acquire the voltage of the resonant capacitor of the LLC resonant converter; An input current sampling unit is used to acquire the input current of the LLC resonant converter; The operational amplifier loop compensation unit is used to obtain a third voltage Vc by passing the output voltage Vout and the reference voltage Vref of the LLC resonant converter through the operational amplifier loop compensation unit. The drive control unit is configured to initiate integration of the input current at the valley of the voltage of the resonant capacitor or at the moment when the input current first rises, to obtain a first voltage V1; pass the first voltage V1 and the third voltage Vc through a comparator to obtain a first reset signal RST1; copy the first reset signal RST1 to obtain an HG signal for controlling the first drive switch Q1 of the LLC resonant converter and an LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

[0009] Preferably, the drive control unit includes: The valley detection unit is used to obtain the valley value time of the voltage of the resonant capacitor of the LLC resonant converter; The first integration unit is used to start integrating the input current at the valley of the voltage of the resonant capacitor or at the moment when the input current first rises, so as to obtain the first voltage V1. A comparator is used to pass the first voltage V1 and the third voltage Vc through the comparator to obtain a first reset signal RST1; The drive replication unit is used to replicate the first reset signal RST1 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

[0010] Preferably, the drive replication unit includes: The initial pulse unit is used to generate an initial pulse for the SET port of the RS flip-flop; The second integration unit is used to integrate the HG signal to obtain at least N triangular waves; A zero-reset detection unit is used to perform zero-reset detection on the triangular wave to obtain at least N pulse waves; An OR gate is used to perform an OR operation on the initial pulse and the at least N pulse waves, and outputs the result to the SET port of the RS flip-flop; The third integration unit is used to integrate the HG signal to obtain at least N sawtooth waves Vs; An RS flip-flop is used to take the first reset signal RST1 as a RESET signal and at least N pulse waves as SET signals to obtain HG and LG signals.

[0011] Preferred options also include: A superimposed converter is used to superimpose the first voltage V1 and the at least N sawtooth waves to obtain a second voltage V2; the second voltage V2 and the third voltage Vc are compared by a comparator to obtain a second reset signal RST2.

[0012] In summary, this application includes at least one of the following beneficial technical effects: 1. The input power of the LLC resonant converter was accurately controlled; 2. Improve dynamic response speed and reduce output ripple; 3. Overload and short circuit protection can be easily implemented; 4. The control-to-output system is a single-pole system, making the loop compensator design simpler. Attached Figure Description

[0013] Figure 1 This is a step diagram of the first embodiment of a control method for an LLC resonant converter; Figure 2 This is a step diagram of the first embodiment of driving replication; Figure 3 This is a step diagram of a second embodiment of a control method for an LLC resonant converter; Figure 4 This is a step diagram of the second embodiment of driving replication; Figure 5 This is the logic block diagram of the control system for the LCC resonant converter; Figure 6 This is a logic block diagram of the first embodiment of the drive control unit; Figure 7 This is the logic block diagram of the driving replication unit; Figure 8 This is a logic block diagram of the second embodiment of the drive control unit; Figure 9 This is a detailed configuration diagram of the control system for an LCC resonant converter; Figure 10 This is the first detailed configuration diagram of the drive control unit; Figure 11 This is the first specific structural diagram of the driving replication unit; Figure 12 This is the second detailed configuration diagram of the drive control unit; Figure 13 This is the second specific structural diagram of the driving replication unit; Figure 14 These are the voltage sampling waveform and valley detection waveform of the resonant capacitor; Figure 15 This is the first sampled waveform of the input current; Figure 16 This is the second sampled waveform of the input current; Figure 17 The waveforms of V1, V1+Vs, and Vc are shown when the resonant frequency of the resonant cavity is higher than the local oscillator frequency of the LLC resonant frequency. Figure 18 The waveforms of V1, V1+Vs, and Vc are shown when the resonant frequency of the resonant cavity is lower than the local oscillator frequency of the LLC resonant frequency. Figure 19 This is the output waveform of the second integration unit; Figure 20 These are waveforms of the HG and LG signals.

[0014] Explanation of reference numerals in the attached figures: 1. A control system for an LLC resonant converter; 11. Resonant capacitor voltage sampling unit; 12. Input current sampling unit; 13. Operational amplifier loop compensation unit; 14. Drive control unit; 141. Valley detection unit; 142. First integration unit; 143. Comparator; 144. Drive replication unit; 145. Superimposed unit; 1441. Initial pulse unit; 1442. Second integration unit; 1443. Zero-reset detection unit; 1444. OR gate; 1445. Third integration unit. Detailed Implementation

[0015] To make the purpose, technical solution, and advantages of this application clearer, the following description is provided in conjunction with the appendix. Figure 1 - Appendix Figure 20 The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the application.

[0016] Terminology Explanation: An LLC resonant converter mainly consists of four modules: a power switch, a resonant cavity, a transformer, and a diode rectifier. The resonant cavity includes two inductors (L) and a capacitor (C). One inductor is connected to the switching network, and the other is connected in parallel with the primary winding of the transformer. The power switch typically first converts the input DC voltage into a high-frequency square wave. This square wave then enters the resonant cavity, where harmonics are eliminated, and a fundamental frequency sine wave is output. This sine wave is then transmitted to the secondary side of the converter via the high-frequency transformer, where the voltage is boosted or bucked according to application requirements. Finally, the diode rectifier converts the sine wave into a stable DC output.

[0017] RS Flip-Flops: RS flip-flops, or reset / set flip-flops, are the simplest type of flip-flop and form the basis for various complex flip-flops. They are named after the abbreviations of "Reset" and "Set." Their working principle and basic function depend on the state of the input signal, specifically its "1" and "0" states. At any given moment, an RS flip-flop can only be in one state: either "reset" or "set."

[0018] To accurately control the input power, this application proposes a control method and system for an LLC resonant converter. The LLC resonant converter in this technical solution is a half-bridge LLC.

[0019] Firstly, such as Figure 1 As shown, a control method for an LLC resonant converter is provided, including: S101: Obtain the input current, the voltage of the resonant capacitor, and the output voltage Vout of the LLC resonant converter respectively; in the prior art, only the output voltage Vout is sampled; in this technical solution, the switching frequency of the two driving switches Q1 and Q2 in the LLC resonant converter is controlled by combining the input current of the LLC resonant converter and the voltage of the resonant capacitor.

[0020] S102: At the valley of the voltage of the resonant capacitor or at the moment when the input current first rises, integration of the input current is initiated to obtain the first voltage V1; when the resonant capacitor is in a resonant state, the voltage on the resonant capacitor is approximately a sine wave or a cosine wave; in this technical solution, when the input current first rises, integration of the input current can begin, that is, integration of the first rise of the input current caused by the rise of the HG signal due to the initial pulse signal, which causes the drive switch Q1 to turn on, to obtain the first voltage V1; After the input current rises for the first time, the valley detection method is used to obtain the moment when the voltage of the resonant capacitor is at its valley value. At this moment, the input current is integrated to obtain the first voltage V1. Due to the presence of the driving switches Q1 and Q2, the waveform of the input current is approximately a sine wave or a part of a cosine wave. After integrating the input current, the waveform of the first voltage V1 is approximately a cosine wave or a part of a sine wave.

[0021] S1031: The output voltage Vout and the reference voltage Vref are passed through an operational amplifier loop compensation circuit to obtain a third voltage Vc. In this technical solution, the reference voltage Vref is the level that the LLC resonant converter needs to reach. The reference voltage Vref is compared with the current output voltage Vout of the LLC resonant converter, and the operational amplifier loop compensation circuit is used to obtain the third voltage Vc. The third voltage Vc is used to control the input power limit of the LLC resonant converter, that is, the third voltage Vc is used for subsequent control, so that the opening and closing of the drive switches Q1 and Q2 of the LLC resonant converter controls the energy input to the resonant cavity.

[0022] S1041: Pass the first voltage V1 and the third voltage Vc through a comparator to obtain the first reset signal RST1; S1051: The first reset signal RST1 is copied to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle. To prevent the drive switches Q1 and Q2 from being turned on simultaneously, a dead time is set between the HG signal and the LG signal. During the dead time, both drive switches Q1 and Q2 are in the off state, that is, both the HG signal and the LG signal are at a low level, and drive switches Q1 and Q2 cannot be turned on.

[0023] Preferred, such as Figure 2 As shown, the step of copying the first reset signal RST1 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter includes: S10511: Using the initial pulse as the SET signal of the RS flip-flop and the first reset signal RST1 as the RESET signal of the RS flip-flop, the initial HG and initial LG signals are obtained. In the initial stage of this technical solution, the RS flip-flop does not have an initial trigger signal. Using the initial pulse unit, an initial pulse signal is sent to the RS flip-flop at the beginning of the technical solution's execution. Simultaneously, the RESET terminal of the RS flip-flop receives the first reset signal RST1. At this time, the non-inverting and inverting output terminals of the RS flip-flop output symmetrical waveforms with a 50% duty cycle. This symmetrical waveform is used to control the on and off states of the drive switches Q1 and Q2.

[0024] S10512: The initial HG signal is sent to the second integration unit to obtain at least N triangular waves; the initial pulse waveform causes the initial HG signal in the symmetrical waveform output by the RS flip-flop to be used as a feedback signal and sent to the second integration unit to obtain at least N triangular waves; in this technical solution, the integration constant of the second integration unit can be set to 1 and -1. When HG is high, the input integration constant is 1, and when HG is low, the input integration constant is -1, so that the output of the second integration unit is at least N triangular waves.

[0025] S10513: Perform zero-reset detection on the triangular wave to obtain at least N pulse waves; by performing zero-reset detection using at least N output triangular waves, at least N pulse waves can be obtained; the zero-reset detection can be implemented using a Schmitt trigger.

[0026] S10514: Using the at least N pulse waveforms as the SET signal of the RS flip-flop, and the first reset signal RST1 as the RESET signal of the flip-flop, HG and LG signals are obtained. At this time, the zero-reset detection outputs at least N pulse waves as the SET signal of the RS flip-flop, eliminating the need for a single initial pulse. The RS flip-flop, combined with the at least N pulse waves used for the SET signal and the first reset signal RST1, can output at least N HG and LG signals. The dead time described above can be achieved by adding a delay circuit to both the inverting and non-inverting output terminals of the RS flip-flop.

[0027] Preferred, such as Figure 3 As shown, the step of initiating integration of the input current at the valley of the voltage of the resonant capacitor or at the moment of the first rise of the input current to obtain a first voltage V1, and then further includes: S1032: The sawtooth wave signal is superimposed on the first voltage V1 to obtain the second voltage V2; the integration constant of the third integration unit can be set to 1. When HG is high, the input integration constant is 1, and when HG is low, the integration output is reset, so that the output of the third integration unit is at least N sawtooth waves.

[0028] S1042: Pass the second voltage V2 and the third voltage Vc through a comparator to obtain the second reset signal RST2; S1052: Copy the second reset signal RST2 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

[0029] Preferred, such as Figure 4As shown, the step of copying the second reset signal RST2 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter includes: S10521: Using the initial pulse as the SET signal of the RS flip-flop and the second reset signal RST2 as the RESET signal of the RS flip-flop, the initial HG signal and the initial LG signal are obtained. S10522: Send the initial HG signal to the third integration unit to obtain at least N sawtooth waves Vs; superimpose the at least N sawtooth waves onto the first voltage V1 to obtain the second voltage V2; S10523: Send the initial HG signal to the second integration unit to obtain at least N triangular waves; S10524: Perform zero-reset detection on the triangular wave to obtain at least N pulse waves; S10525: Use the at least N pulse waveforms as the SET signal of the RS flip-flop, and the second reset signal RST2 as the RESET signal of the flip-flop to obtain the HG signal and the LG signal.

[0030] Secondly, such as Figure 5 As shown, a control system 1 for an LLC resonant converter is also provided, comprising: The resonant capacitor voltage sampling unit 11 is used to obtain the voltage of the resonant capacitor of the LLC resonant converter; The input current sampling unit 12 is used to acquire the input current of the LLC resonant converter. The operational amplifier loop compensation unit 13 is used to obtain a third voltage Vc by passing the output voltage Vout and the reference voltage Vref of the LLC resonant converter through the operational amplifier loop compensation unit. The drive control unit 14 is configured to initiate integration of the input current at the valley of the voltage of the resonant capacitor or at the moment when the input current first rises, to obtain a first voltage V1; pass the first voltage V1 and the third voltage Vc through a comparator to obtain a first reset signal RST1; copy the first reset signal RST1 to obtain an HG signal for controlling the first drive switch Q1 of the LLC resonant converter and an LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

[0031] Preferred, such as Figure 6 As shown, the drive control unit 14 includes: Valley detection unit 141 is used to obtain the valley moment of the voltage of the resonant capacitor of the LLC resonant converter; The first integration unit 142 is used to start integrating the input current at the valley moment of the voltage of the resonant capacitor or at the moment when the input current first rises, so as to obtain the first voltage V1. Comparator 143 is used to pass the first voltage V1 and the third voltage Vc through the comparator to obtain a first reset signal RST1; The drive replication unit 144 is used to replicate the first reset signal RST1 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

[0032] Preferred, such as Figure 7 As shown, the drive copying unit 144 includes: The initial pulse unit 1441 is used to generate an initial pulse for the SET port of the RS flip-flop; The second integration unit 1442 is used to integrate the HG signal to obtain at least N triangular waves; The zero-reset detection unit 1443 is used to perform zero-reset detection on the triangular wave to obtain at least N pulse waves; OR gate 1444 is used to perform an OR operation on the initial pulse and the at least N pulse waves, and output the result to the SET port of the RS flip-flop; The third integration unit 1445 is used to integrate the HG signal to obtain at least N sawtooth waves Vs; RS flip-flop 1446 is used to take the first reset signal RST1 as a RESET signal and at least N pulse waves as SET signals to obtain HG signal and LG signal.

[0033] Preferred, such as Figure 8 The diagram shown is a logic block diagram of a second embodiment of the drive control unit; it also includes: The superimposed unit 145 is used to superimpose the first voltage V1 and the at least N sawtooth waves to obtain the second voltage V2; the second voltage V2 and the third voltage Vc are compared by a comparator to obtain the second reset signal RST2.

[0034] like Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 As shown, the working principle of a control system 1 for an LLC resonant converter is as follows: Figure 9 This is a detailed configuration diagram of the control system for an LCC resonant converter; Figure 10 This is the first detailed configuration diagram of the drive control unit; Figure 11 This is the first specific structural diagram of the driving replication unit; Figure 12 This is the second detailed configuration diagram of the drive control unit; Figure 13 This is the second specific structural diagram of the driving replication unit; and Figure 5 This is the logic block diagram of the control system for the LCC resonant converter; Figure 6 This is a logic block diagram of the first embodiment of the drive control unit; Figure 7 This is the logic block diagram of the driving replication unit; Figure 8 This is a logic block diagram of the second embodiment of the drive control unit; the above diagrams can be understood in combination.

[0035] The control system of the LLC resonant converter is applied between the input and output terminals of the LLC resonant converter; the input power supply of the LLC resonant converter is Vin, the driving switching transistors include Q1 and Q2, the resonant cavity includes two inductors L and a capacitor C, as well as a transformer T1 and a rectifier.

[0036] The input power supply Vin outputs a DC level. In the initial state, i.e., both drive switches Q1 and Q2 are off, the input current sampling unit obtains a DC level, and the resonant capacitor voltage sampling also obtains a DC level. At this time, under the action of the initial pulse, the initial HG signal output by the RS flip-flop is high. When the initial high-level HG signal reaches the drive switch Q1, the drive switch Q1 is turned on, the input current increases for the first time, causing the first integrator to start integrating; the integration result is sent to the non-inverting input of the comparator to obtain the initial reset signal RST0. The initial reset signal RST0 causes the HG signal output by the RS flip-flop to change from high level to low level. With energy input to the resonant cavity, it is then triggered to oscillate; therefore, subsequent input current sampling and harmonic capacitor voltage sampling both obtain waveforms that are approximately sine or cosine waves.

[0037] The sine or cosine wave obtained by sampling the resonant capacitor voltage is subjected to valley detection, i.e., differentiating using a differentiator to obtain the valley or peak value. At the valley value, a control command is issued to the first integrator unit, which then integrates the sine or cosine wave sampled from the input current to obtain a cosine or sine wave. At this time, the cosine or sine wave is directly sent to a comparator and compared with the third voltage Vc after processing the output voltage Vout, outputting a first reset signal RST1. The third voltage Vc is obtained by passing the reference voltage Vref and the output voltage Vout through an operational amplifier loop compensation unit. The third voltage Vc is also a DC level.

[0038] The first reset signal RST1 is input to the drive replication unit to obtain the HG signal and the LG signal.

[0039] The driving replication unit, due to the presence of an initial pulse, first sends the initial HG signal to the second integration unit and the third integration unit respectively under the action of the generated initial HG signal. After being sent to the second integration unit, at least N triangular waves are obtained, and then at least N triangular waves are sent to the zero-reset detection unit to obtain at least N pulse waves. At this time, at least N pulse wave signals replace the initial pulse wave and serve as the input signal to the SET terminal of the RS flip-flop. Then, with the participation of the first reset signal RST1, the RS flip-flop continuously outputs HG and LG signals. At this time, the HG signal is at least N square wave signals, and the LG signal is at least N square wave signals; and the HG and LG signals are symmetrical waveforms with a 50% duty cycle. Since the HG signal is used to control the gate of the driving switch Q1, and the LG signal is used to control the gate of the driving switch Q2. To prevent the driving switches Q1 and Q2 from conducting simultaneously and causing a short circuit in the input power supply, it is necessary to set the conduction interval between the HG and LG signals, which is the dead time. Dead time can be achieved by setting delays at both the positive and negative output terminals of the RS flip-flop.

[0040] To avoid subharmonic oscillations in the resonant cavity, the HG signal is fed into the third integrator to obtain at least N sawtooth waves Vs. These sawtooth waves can be superimposed on the output voltage of the first integrator, i.e., superimposed on the first voltage V1, to obtain the second voltage V2. The second voltage V2 is then fed into a comparator and compared with the third voltage Vc to obtain the second reset signal RST2. Afterward, the same steps as described above are performed. In this technical solution, a superimposed unit and a third integrator are added to use the sawtooth waves Vs for slope compensation, thus avoiding subharmonic oscillations.

[0041] Finally, by adopting the control method and control system of this LLC resonant converter, the input power of the LLC resonant converter can be accurately controlled.

[0042] Figure 14 These are the resonant capacitor voltage sampling waveform and the valley detection waveform. It can be seen that the voltage at the resonant capacitor point is approximately a sine or cosine waveform. The valley detection waveform is a sine or cosine valley moment pulse, which is used to trigger the start of integration of the first integrator unit.

[0043] Figure 15 This is the first sampled waveform of the input current; at this time, the operating frequency of the LLC resonant converter is higher than the resonant frequency.

[0044] Figure 16 This is the second sampled waveform of the input current; at this time, the operating frequency of the LLC resonant converter is lower than the resonant frequency.

[0045] Figure 17This is a waveform diagram of V1, V1+Vs, and Vc when the operating frequency of the LLC resonant converter is higher than the resonant frequency. Figure 18 This is a waveform diagram of V1, V1+Vs, and Vc when the operating frequency of the LLC resonant converter is lower than the resonant frequency. Figure 19 This is the output waveform of the second integration unit; Figure 20 These are waveforms of the HG and LG signals.

[0046] In summary, this application includes at least one of the following beneficial technical effects: 1. The input power of the LLC resonant converter was accurately controlled; 2. Improve dynamic response speed and reduce output ripple; 3. Overload and short circuit protection can be easily implemented; 4. The control-to-output system is a single-pole system, making the loop compensator design simpler.

[0047] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any feature disclosed in this specification (including the abstract and drawings) may be replaced by other equivalent or similar features unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is only one example of a series of equivalent or similar features.

Claims

1. A control method for an LLC resonant converter, characterized in that, include: The input current, the voltage of the resonant capacitor, and the output voltage Vout of the LLC resonant converter are obtained respectively. At the moment when the voltage of the resonant capacitor is at its lowest point or when the input current first increases, the integration of the input current is initiated to obtain the first voltage V1. The output voltage Vout and the reference voltage Vref are passed through an operational amplifier loop compensation circuit to obtain a third voltage Vc; The first voltage V1 and the third voltage Vc are passed through a comparator to obtain the first reset signal RST1; The first reset signal RST1 is copied to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

2. The control method of the LLC resonant converter according to claim 1, characterized by, The step of copying the first reset signal RST1 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter includes: Using the initial pulse as the SET signal of the RS flip-flop and the first reset signal RST1 as the RESET signal of the RS flip-flop, the initial HG signal and the initial LG signal are obtained. The initial HG signal is sent to the second integration unit to obtain at least N triangular waves; The triangular wave is subjected to zero-reset detection to obtain at least N pulse waves; Using the at least N pulse waveforms as the SET signal of the RS flip-flop and the first reset signal RST1 as the RESET signal of the flip-flop, the HG signal and the LG signal are obtained.

3. The control method of the LLC resonant converter according to claim 1, characterized by, The process involves initiating integration of the input current at the valley of the voltage across the resonant capacitor or at the moment of the first rise in the input current to obtain a first voltage V1. Following this, the process further includes: The sawtooth wave signal is superimposed on the first voltage V1 to obtain the second voltage V2; The second voltage V2 and the third voltage Vc are passed through a comparator to obtain the second reset signal RST2; The second reset signal RST2 is copied to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

4. The control method of the LLC resonant converter according to claim 3, characterized by, The step of copying the second reset signal RST2 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter includes: Using the initial pulse as the SET signal of the RS flip-flop and the second reset signal RST2 as the RESET signal of the RS flip-flop, the initial HG signal and the initial LG signal are obtained. The initial HG signal is sent to the third integration unit to obtain at least N sawtooth waves Vs; the at least N sawtooth waves are superimposed on the first voltage V1 to obtain the second voltage V2; The initial HG signal is sent to the second integration unit to obtain at least N triangular waves; The triangular wave is subjected to zero-reset detection to obtain at least N pulse waves; Using the at least N pulse waveforms as the SET signal of the RS flip-flop and the second reset signal RST2 as the RESET signal of the flip-flop, the HG signal and the LG signal are obtained.

5. A control system of an LLC resonant converter, characterized by, include: A resonant capacitor sampling unit is used to obtain the voltage of the resonant capacitor of the LLC resonant converter; An input current sampling unit is used to acquire the input current of the LLC resonant converter; The operational amplifier loop compensation unit is used to obtain a third voltage Vc by passing the output voltage Vout and the reference voltage Vref of the LLC resonant converter through the operational amplifier loop compensation unit. The drive control unit is configured to initiate integration of the input current at the valley of the voltage of the resonant capacitor or at the moment when the input current first rises, to obtain a first voltage V1; pass the first voltage V1 and the third voltage Vc through a comparator to obtain a first reset signal RST1; copy the first reset signal RST1 to obtain an HG signal for controlling the first drive switch Q1 of the LLC resonant converter and an LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

6. The control system of an LLC resonant converter according to claim 5, characterized in that, The drive control unit includes: The valley detection unit is used to obtain the valley value time of the voltage of the resonant capacitor of the LLC resonant converter; The first integration unit is used to start integrating the input current at the valley of the voltage of the resonant capacitor or at the moment when the input current first rises, so as to obtain the first voltage V1. A comparator is used to pass the first voltage V1 and the third voltage Vc through the comparator to obtain a first reset signal RST1; The drive replication unit is used to replicate the first reset signal RST1 to obtain the HG signal for controlling the first drive switch Q1 of the LLC resonant converter and the LG signal for controlling the second drive switch Q2 of the LLC resonant converter; the HG signal and the LG signal are symmetrical waveforms with a 50% duty cycle.

7. The control system of an LLC resonant converter according to claim 6, characterized in that, The drive copying unit includes: The initial pulse unit is used to generate an initial pulse for the SET port of the RS flip-flop; The second integration unit is used to integrate the HG signal to obtain at least N triangular waves; A zero-reset detection unit is used to perform zero-reset detection on the triangular wave to obtain at least N pulse waves; An OR gate is used to perform an OR operation on the initial pulse and the at least N pulse waves, and outputs the result to the SET port of the RS flip-flop; The third integration unit is used to integrate the HG signal to obtain at least N sawtooth waves Vs; An RS flip-flop is used to take the first reset signal RST1 as a RESET signal and at least N pulse waves as SET signals to obtain HG and LG signals.

8. The control system of an LLC resonant converter according to claim 7, characterized in that, Also includes: A superimposed converter is used to superimpose the first voltage V1 and the at least N sawtooth waves to obtain a second voltage V2; The second voltage V2 and the third voltage Vc are compared by a comparator to obtain a second reset signal RST2.

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