LLC resonant converter control method and system based on output diode current detection

Abstract

The invention relates to the technical field of LLC resonant converters, in particular to an LLC resonant converter control method and system based on output diode current detection, and the method comprises the steps: conditioning the output current of an LLC resonant converter; designing a control outer ring, and calculating an error signal of the reference current and the diode conditioning current; the stability of the output current is maintained by using the offset and adjusting the integral slope; the compensation amount of the offset is adjusted, and the offset and the integral slope are given to the control inner ring, so that the control inner ring works in the optimal working interval; the control inner ring detects the conditioning current, integrates the conditioning current, compares the integral conditioning current with the error signals of the reference current and the offset, and outputs the switching frequency; and a switching tube of the converter is controlled by using the switching frequency to control the output current, so that the converter enters a new steady state. The problems that an existing control method of the converter cannot meet the requirements of small input filter capacitance, output voltage ripple suppression, input disturbance resistance and the like at the same time are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LLC resonant converter, and particularly relates to an LLC resonant converter control method and system based on output diode current detection. BACKGROUND

[0002] Compared with an isolated DC / DC converter, the LLC resonant converter is widely used in fields such as charging batteries, solar energy and LED drivers, because it has the advantages of high efficiency, high power density and low EMI; the front stage of the LLC resonant converter is usually a single power factor correction (PFC) rectifier, the input voltage of the LLC comes from the output of the PFC, and a voltage ripple with a frequency of twice the power frequency is introduced, so that a low-frequency ripple appears in the LLC output voltage.

[0003] The traditional solutions include: increasing the filter capacitor between LLC and PFC, direct frequency control method, optimized trajectory control method, simplified trajectory control method, etc.; the method of increasing the filter capacitor reduces the power density of the circuit, and the electrolytic capacitor is prone to aging, which reduces the reliability of the circuit; the direct frequency control method adjusts the switching frequency by detecting the output voltage of the circuit, but the circuit has the characteristics of double poles, which limits the bandwidth of the circuit; the trajectory control method combines transient trajectory control and steady-state PI control to improve the dynamic response capability of the control circuit, but it needs to detect multiple state variables, and the cost is high, and the PI control method cannot suppress the output voltage ripple in the steady state. SUMMARY

[0004] In view of the deficiencies of the existing method, the present application solves the problem that the existing control method of the LLC resonant converter cannot simultaneously meet the requirements of small input filter capacitance, suppression of output voltage ripple and resistance to input disturbance.

[0005] The technical solution adopted by the present application is: an LLC resonant converter control method based on output diode current detection includes the following steps: Step one, sampling the output current of the LLC resonant converter I out and the output diode current I D1 ; then performing current conditioning to obtain the corresponding conditioned current i out and i D1 ; As a preferred embodiment of the present application, TMCS1100 is used for sampling and conditioning.

[0006] Step two, designing a control outer loop and calculating a reference current i ref and iout error signal e ; Using proportional-integral control e offset q out and regulation i ref integral slope K i3 maintain i out Stability; Regulation q out The amount of compensation will q out and K i3 Configure the inner control loop to operate within its optimal operating range; As a preferred embodiment of the present invention, offset q out The formula is: ,in, K p The coefficient of the proportional element. K i1 is the coefficient of the integral.

[0007] As a preferred embodiment of the present invention i ref The integral formula is: ,in, is the coefficient of the integral.

[0008] Step 3: Control Inner Ring Detection i D1 ,right i D1 After integration, and with integration i ref and q out error signal m Compare and output switching frequency f sw ;use f sw Controlling the switching transistors of the LLC resonant converter to achieve... I out The control enables the LLC resonant converter to enter a new steady state; In a preferred embodiment of the present invention, the MCU is used to... f sw The switching transistors of the LLC resonant converter are switched to PWM wave control.

[0009] In a preferred embodiment of the present invention, the integration is performed using an integrating circuit.

[0010] In a preferred embodiment of the present invention, a comparator is used for comparison.

[0011] As a preferred embodiment of the present invention, an LLC resonant converter control system based on output diode current detection includes: a memory for storing instructions executable by a processor; and a processor for executing the instructions to implement the LLC resonant converter control method based on output diode current detection.

[0012] In a preferred embodiment of the present invention, a computer-readable medium storing computer program code implements an LLC resonant converter control method based on output diode current detection when executed by a processor.

[0013] The beneficial effects of this invention are: 1. The control method of the present invention can not only resist input disturbances and realize rapid adjustment of output voltage, but also has good dynamic response capability, reduce output voltage ripple, reduce the requirement for input capacitor value, and improve the reliability of converter. 2. This invention achieves input ripple suppression, rapid dynamic response, and maintenance of steady-state accuracy through coordinated inner and outer loop control, as well as real-time compensation for load changes; the outer loop controls the input ripple through a reference current. i ref With output current i out Error signal obtained by subtraction e Offset adjusted by proportional-integral (PI) ratio q out The integral slope of the first integrator K i3 To maintain a stable output current (or output voltage); when the load changes or the input is disturbed, the outer loop adjusts the offset. q out Compensate for changes, output q out and K i3 The inner loop is configured to operate within its optimal operating range. The control of the inner loop involves detecting the output diode current, integrating it using a third integrator, and comparing this integrated signal with the integrated signal of the reference current. The comparator output signal triggers a switch, directly controlling the switching frequency. f sw The inner loop has a fast response speed and simplifies the high-order LLC control system into a single-pole system, thus improving the system's stability. 3. The capacitance of the filter capacitor between the LLC resonant converter and the preceding stage can be reduced, thereby increasing the power density of the system and improving the reliability of the converter. Attached Figure Description

[0014] Figure 1This is a flowchart of the LLC resonant converter control method and system based on output diode current detection of the present invention; Figure 2 This is the topology diagram of an LLC resonant converter circuit; Figure 3 This is a block diagram of the LLC resonant converter control system based on output diode current detection of the present invention. Figure 4 This is a block diagram of the integration and comparison operation control of the present invention; Figure 5 This is a schematic diagram illustrating the implementation of the second and third integrators of the present invention; Figure 6 This is a schematic diagram of the outer loop adjustment process when a sudden load current is applied; Figure 7 This is a schematic diagram of the coordinated adjustment process of the outer and inner loops when a sudden load current is applied. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments. The drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0016] like Figure 1 As shown, the LLC resonant converter control method based on output diode current detection includes the following steps: Step 1: Sample the output current of the LLC resonant converter I out and output diode current I D1 Then, current conditioning is performed to obtain the corresponding conditioning current. i out and i D1 ; like Figure 3 A system for controlling an LLC resonant converter based on output diode current sensing includes: The circuit includes an output diode current sampling and conditioning circuit, an output current sampling and conditioning circuit, an integration and comparison circuit, a main control circuit, and a drive circuit; among which... The output current of the LLC resonant converter I out The current signal is fed into the output current sampling and conditioning circuit to obtain the current signal. i out Output diode current of LLC resonant converter I D1 The current signal is fed into the output diode current sampling and conditioning circuit to obtain the current signal. i D1 ; It should be noted that output voltage can also be used. V out The voltage signal is fed into the output voltage sampling and conditioning circuit to obtain the voltage signal. v out Output diode voltage of LLC resonant converter V D1 The signal is fed into the output diode voltage sampling and conditioning circuit to obtain the current signal. v D1 Since the principle of voltage control is similar to that of current control, this embodiment only describes the current control process; the use of voltage control is also within the scope of protection of this invention.

[0017] Step 2: Adjust the diode current i D1 Perform integration; calculate i D1 and reference current signal i ref error value e ;right e Integrating to obtain q out ;right i ref Integrate and... q out Difference obtained m ; Will i D1 , i out The signal is fed into an integrator and comparator circuit to obtain the switching frequency. f sw ; Calculation result f sw The signal is transmitted to the main control circuit, which outputs four PWM drive waveforms to the switching transistors. Q 1~ Q 4.

[0018] The diode current sampling and conditioning circuit and the output current sampling and conditioning circuit can use the TMCS1100 chip.

[0019] like Figure 2 The circuit topology of an LLC resonant converter includes: input voltage. V in Switching transistor Q 1~ Q 4. The two arms that make up the full-bridge circuit; L r , C r , L m Constructing an LLC resonant cavity; transformerT 1. Outputs high-frequency alternating current; the high-frequency alternating current passes through diodes. D 1~ D 4. After forming a full-wave rectifier bridge, it outputs DC power.

[0020] like Figure 4 For the integrator and comparator circuit, the reference current signal i ref (If the output voltage) v out For the reference voltage signal v ref (Provided by the main control circuit MCU) i out and i ref Error value after subtraction e The output is obtained after integration by the first integrator. q out Signal, i ref The signal after the second integrator and q out The error signal is obtained by subtraction. m ; i D1 The signal after integration by the third integrator and m They are fed into the comparator respectively C After connecting the inverting and non-inverting inputs of 1, the output signal is... f sw The signal is sent to the main control circuit; the first integrator is a digital integrator circuit, which can be implemented by the calculation module inside the MCU; the second and third integrators can be implemented through, for example... Figure 5 The analog circuit shown is implemented using an RC integrator circuit; it includes: an operational amplifier. A 1. A 2. Resistors R1 to R3, capacitor C2, and switching transistor Q s , R 1.

[0021] in, R 1 = 500kΩ C 2 = 100 nF R 2 and R 3 is set to 1kΩ.

[0022] The main control circuit uses the TI TMS320F28379D digital controller; the driver circuit uses the IXDN609SI driver chip; and the second and third integrators use the LTC6229 operational amplifier.

[0023] Figure 2In the LLC resonant controller circuit, under steady state, the average current of the output diode is... I D1 equal to load current I out Therefore, the switching frequency can be adjusted. f sw This causes the output diode current to... i D1 The integral value is equal to the reference current. i ref The integral value is used to control the load current, satisfying: (1) in, T sw =1 / f sw .

[0024] e The formula is: (2) q out The formula is: (3) in, K p The coefficient of the proportional element. K i1 is the coefficient of the integral.

[0025] In this embodiment , .

[0026] If a given current i ref When a mutation occurs, the outer-loop regulatory process is as follows: Figure 6 As shown, i ref Increase to i ref_new ,but q out Increase to q out_new , T sw Increase to T sw_new The signal is sent to the main control circuit (MCU) to reduce the switching frequency. f sw Increase the voltage gain of the LLC to improve the output current. I out It begins to rise and reaches a new steady state.

[0027] Error signalm and i D1 The signal integrated by the third integrator is fed into the inverting and non-inverting inputs of the comparator for crossover, and the output signal after crossover is... f sw ( T sw The signal is sent to the main control circuit to directly control the switching transistor; that is, the frequency is... f sw of PWM 1- PWM 4. Input the corresponding switching transistor Q 1- Q 4; The control law is as follows: (4) In the example of the given load current sudden change, the outer loop is adjusted first. q out Simultaneous adjustment K i3 By reducing K i3 (increase) R 1 or C 2) Make i ref_new The slope further decreases to i ref_renew This slows down the rise rate of the reference integral signal, further increasing the intersection time. T sw_renew This significantly improves the gain of the LLC, resulting in increased output current. I out Rapid rise; such as Figure 7 As shown, when the diode current I D1 Further rise, making i D1 As the amplitude increases, the intersection time gradually increases, gradually reducing the slope of the reference current integral to avoid... f sw Too low a gain will result in too high a gain, and a new balance point will be reached.

[0028] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A control method for an LLC resonant converter based on output diode current detection, characterized in that, Includes the following steps: Step 1: Sample the output current of the LLC resonant converter I out and output diode current I D1 Then, current conditioning is performed to obtain the corresponding conditioning current. i out and i D1 ; Step 2: Design the control outer loop and calculate the reference current. i ref and i out error signal e ; Using proportional-integral control e offset q out and regulation i ref integral slope K i3 maintain i out Stability; Regulation q out The amount of compensation will q out and K i3 Configure the inner control loop to operate within its optimal operating range; Step 3: Control Inner Ring Detection i D1 ,right i D1 After integration, and with integration i ref and q out error signal m Compare and output switching frequency f sw ;use f sw Controlling the switching transistors of the LLC resonant converter to achieve... I out The control allows the LLC resonant converter to enter a new steady state.

2. The LLC resonant converter control method based on output diode current detection according to claim 1, characterized in that, q out The formula is: ,in, K p The coefficient of the proportional element. K i1 is the coefficient of the integral.

3. The LLC resonant converter control method based on output diode current detection according to claim 1, characterized in that, i ref The integral formula is: .

4. The LLC resonant converter control method based on output diode current detection according to claim 1, characterized in that, Using MCU f sw The switching transistors of the LLC resonant converter are switched to PWM wave control.

5. The LLC resonant converter control method based on output diode current detection according to claim 1, characterized in that, The integration uses an integrating circuit.

6. The LLC resonant converter control method based on output diode current detection according to claim 1, characterized in that, A comparator is used for comparison.

7. The LLC resonant converter control method based on output diode current detection according to claim 1, characterized in that, Sampling and conditioning were performed using TMCS1100.

8. A control system for an LLC resonant converter based on output diode current detection, characterized in that, include: Memory is used to store instructions that can be executed by the processor; A processor for executing instructions to implement the LLC resonant converter control method based on output diode current detection as described in any one of claims 1-7.

9. A computer-readable medium storing computer program code, characterized in that, The computer program code, when executed by a processor, implements the LLC resonant converter control method based on output diode current detection as described in any one of claims 1-7.

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