A switching method of a half-bridge / full-bridge LLC resonant converter

Abstract

The application discloses a switching method of a half-bridge / full-bridge LLC resonant converter, which mainly comprises the following steps: precisely modeling a circuit; calculating a switching frequency proportional relationship of two modes under the same voltage gain at a switching point; judging whether a maximum current can ensure that the two modes have a voltage gain coincidence point at the switching point; and if yes, adjusting closed-loop control parameters according to the obtained switching frequency proportional relationship of the two modes, and completing mode switching. The method can effectively reduce the overshoot of a resonant current and the fluctuation of an output voltage in the topology switching process, and realizes smooth and fast switching.

Description

Technical Field

[0001] This invention relates to the field of isolated high-frequency power conversion in power electronics, and particularly to a switching method for a half-bridge / full-bridge LLC resonant converter. Background Technology

[0002] The LLC resonant converter is a highly efficient high-frequency DC-DC converter circuit. It utilizes a resonant network formed by a magnetizing inductor, a resonant inductor, and a resonant capacitor to achieve zero-voltage turn-on of the transformer's primary-side switching device and zero-current turn-off of the secondary-side rectifier device, significantly reducing switching losses and thus achieving extremely high conversion efficiency. This converter exhibits excellent output voltage regulation performance and is widely applicable to applications requiring high efficiency and power density, such as chargers and server power supplies.

[0003] However, many applications require converters to operate over a wide input voltage range. Traditional half-bridge / full-bridge LLC resonant converters change the converter voltage gain by altering the switching frequency of the switching transistors to adapt to variations in the wide input voltage range and maintain output voltage stability. However, when switching between half-bridge and full-bridge topologies, the output voltage fluctuates significantly due to abrupt changes in voltage gain, and the voltage regulation process is slow. Summary of the Invention

[0004] To overcome the drawback of large output voltage fluctuations when switching between half-bridge and full-bridge topologies, this disclosure provides a switching method for half-bridge / full-bridge LLC resonant converters that enables smooth and fast switching.

[0005] This method first performs accurate circuit modeling, and then calculates the switching frequency relationship between the two topologies under the same voltage gain at the switching point. During switching, the switching frequency is directly switched, reducing the overshoot of resonant current and the fluctuation of output voltage during topology switching, thereby achieving smooth and fast switching.

[0006] Specifically, the switching method for half-bridge / full-bridge LLC resonant converters provided in this disclosure mainly includes the following steps: S1, to perform precise circuit modeling; S2, calculate the ratio of the switching frequencies of the two modes under the same voltage gain at the switching point; S3. Determine whether the maximum current can guarantee that the voltage gain coincides at the switching point between the two modes. If so, adjust the closed-loop control parameters according to the switching frequency ratio between the two modes obtained in step S2 to complete the mode switching.

[0007] Furthermore, the specific method of step S1 includes: The parameters of each component in the converter are measured. The leakage inductance of the transformer is obtained through a bridge circuit. The total resonant inductance is the sum of the series resonant inductance and the equivalent leakage inductance of the transformer primary side.

[0008] Further, according to the method of claim 1, in step S2, the switching frequency ratio of the two modes is calculated according to the following first method: S21, obtain the voltage gain based on the input voltage and output voltage at the switching point. M ; S22, Calculate the switching frequency at the switching point in full-bridge mode and half-bridge mode according to the following formula, and obtain the proportional coefficient of the switching frequency when switching between these two modes. k 1. k 2:

[0009] In the formula, f s For switching frequency, Q For quality factor, k Inductance ratio, f n Normalized frequency; L r , L k These are the series inductance that forms the resonant inductance in the resonant cavity of the half-bridge / full-bridge LLC resonant converter, and the equivalent leakage inductance on the primary side of the transformer, respectively. C r It is a resonant capacitor; L m The equivalent magnetizing inductance of the primary side of the transformer in the half-bridge / full-bridge LLC resonant converter is given, and the primary-to-secondary turns ratio of the transformer is 1: n ; V o For output voltage, V in Input voltage; k1 and k2 are the proportional coefficients of the switching frequency when switching between the two modes. Specifically, when switching from full-bridge mode to half-bridge mode, the relationship between the switching frequencies in the two modes is expressed as follows: , This refers to the switching frequency in half-bridge mode. This represents the switching frequency in full-bridge mode; when switching from half-bridge mode to full-bridge mode, the relationship between the switching frequencies in the two modes is expressed as follows: .

[0010] Furthermore, in step S2, the switching frequency ratio between the two modes can also be obtained using the following second method: Step S1 involves accurately modeling the converter, and the proportional gain of the switching frequency under the two modes is obtained through simulation in the simulation software. k 1. k 2.

[0011] Furthermore, in step S3, the method for determining whether the maximum current ensures that the voltage gain coincides at the switching point between the two modes includes: Maximum current I max The following formula must be satisfied: .

[0012] Furthermore, in step S3, the method for adjusting the closed-loop control parameters specifically includes: Assuming the half-bridge / full-bridge LLC resonant converter employs proportional-integral closed-loop control, then: S31. Adjust the output values ​​of the closed-loop control function in both modes to satisfy the proportional relationship obtained in step S2, as shown in the following formula: (8) (9) In equation (8), Pi output ( k -1) is the output value of the closed-loop control function corresponding to the full-bridge mode before switching. Pi output ( k () represents the output value of the closed-loop control function corresponding to the switching of the second half-bridge mode; In equation (9), Pi output ( k -1) is the output value of the closed-loop control function corresponding to the switching of the front half-bridge mode. Pi output ( k The output value of the closed-loop control function corresponding to the full-bridge mode after switching is ). S32, Based on the obtained closed-loop control function output value, calculate the new closed-loop control function output value. Pi output ( k The initial values ​​of the integral under the given conditions are shown in equations (10) and (11): (10) (11) Equation (10) represents the switch from full-bridge mode to half-bridge mode, and Equation (11) represents the switch from half-bridge mode to full-bridge mode. e ( k ) represents the error function.k i The integral coefficient is... I ( k ), I ( k -1) represents the term following and preceding the integral, respectively. Pi delta ( k () represents the output value of the control function before limiting. Pi output ( k The output value of the control function after limiting is ). k cor1 、k cor2 This represents the anti-saturation compensation gain under the two switching modes, which is the ratio of the integral coefficient to the proportional coefficient. During the switching process, it is only necessary to ensure that the period register value satisfies the relationship described in step S31, and then recalculate the initial integral value of the current loop control function based on the output value of the new current loop control function.

[0013] Furthermore, the method further includes the following steps: S4, set voltage hysteresis to avoid repeated switching.

[0014] Compared with the prior art, the advantages of this disclosure are: ① simple control, no need for a lot of calculation; ② smooth switching process, no resonant current overshoot; ③ maintaining stable output voltage; ④ fast voltage regulation process. Attached Figure Description

[0015] The above and other objects, features and advantages of this disclosure will become more apparent from the more detailed description of exemplary embodiments of this disclosure taken in conjunction with the accompanying drawings, in which the same reference numerals generally represent the same components.

[0016] Picture 1 This is a schematic diagram of an exemplary half-bridge / full-bridge LLC resonant converter circuit. Picture 2 The following is a flowchart of the switching process according to this disclosure. Detailed Implementation

[0017] Preferred embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0018] This disclosure provides a smooth and fast switching method for half-bridge / full-bridge LLC resonant converters. The main idea is as follows: first, the circuit is accurately modeled; then, by calculating the switching frequency relationship between the two topologies at the same voltage gain at the switching point, the switching frequency is directly switched during topology switching, reducing resonant current overshoot and output voltage fluctuations, thereby achieving smooth and fast switching.

[0019] In one exemplary implementation: A half-bridge / full-bridge LLC resonant converter consists of a power circuit and a control circuit, such as... Picture 1 As shown. Its power circuit topology includes: a primary-side inverter circuit, a resonant cavity, a transformer, and a secondary-side rectifier circuit. The primary-side inverter circuit is composed of a full-bridge circuit. When the input voltage is lower than the switching voltage... V switch When operating in full-bridge mode, S 1. S 4. Drive status is consistent. S 2. S 3. Drive states are consistent, duty cycle is 0.5, adjusted... S 1. S 2. S 3. S A switching frequency of 4 enables voltage gain regulation; when the input voltage is higher than the switching voltage... V switch When it is working in half-bridge mode, at this time, S 3. Shutdown S 4 conduction, S 1. S 2. The duty cycle is 0.5, adjusted by... S 1. S The switching frequency of 2 enables voltage gain regulation; The control circuit includes: a sampling circuit, a digital control circuit, and a drive circuit. The sampling circuit measures the input voltage. V in Output voltage V o Output current I o Perform sampling.

[0020] The half-bridge / full-bridge LLC resonant converter switching method in this embodiment is as follows: Picture 2 As shown, the main steps include the following: a) Measure the parameters of each component in the converter. The leakage inductance of the transformer is obtained through a bridge circuit. The total resonant inductance is the sum of the series resonant inductance and the equivalent leakage inductance of the transformer primary side.

[0021] b. Method 1: First, obtain the voltage gain based on the input and output voltages at the switching point. Second, calculate the switching frequency in full-bridge and half-bridge modes at the switching point according to formula (1), and then obtain the proportional coefficient of the switching frequency in these two modes. k 1. k 2; Method Two: Accurately model the converter using step 1, and obtain the proportional coefficient of the switching frequency under the two modes through simulation in simulation software such as PSIM or MATLAB. k 1. k 2.

[0022] c. Closed-loop control parameter adjustment: The output value of the closed-loop control function is related to the switching frequency. In proportional-integral control, firstly, the output value of the closed-loop control function needs to be adjusted to satisfy the above proportional relationship; secondly, the initial integral value under the new closed-loop control function output value condition needs to be calculated.

[0023] d. Set a voltage hysteresis loop to avoid repeated switching.

[0024] e. In this switching method, it is necessary to ensure that the voltage gain of the two modes coincides at the switching point, so current judgment is introduced.

[0025] The steps are further detailed below: Step 1: Measure the parameters of each component in the converter. The leakage inductance of the transformer is obtained through a bridge circuit. The total resonant inductance is the sum of the series resonant inductance and the equivalent leakage inductance of the transformer primary side.

[0026] Step 2, Method 1: First, obtain the voltage gain based on the input voltage and output voltage at the switching point. M Secondly, according to formula (1), the switching frequencies at the switching points in full-bridge mode and half-bridge mode are calculated respectively. f full , f half This allows us to obtain the proportional coefficient of the switching frequency when switching between these two modes. k 1. k 2. In the formula, f s For switching frequency, Q For quality factor, k Inductance ratio, f n This is the normalized frequency.

[0027] (1) Method 2: Accurately model the converter using step 1, and obtain the scaling factor of the switching frequency under the two modes through simulation in simulation software such as PSIM or MATLAB. k 1. k2. When switching from full-bridge mode to half-bridge mode, the relationship between the switching frequencies in the two modes can be expressed as: (2) When switching from half-bridge mode to full-bridge mode, the relationship between the switching frequencies of the two modes can be expressed as: (3) Step 3, Current determination: It is important to note that to ensure sufficient gain and power output capability of the converter, the switching process described above needs to be performed within a certain power range; therefore, current judgment is introduced. The maximum switching frequency of the converter is also considered. f max The minimum value that determines its gain is the minimum switching frequency. f min This determines the maximum gain. To ensure successful switching between the two modes at the switching point, the voltage gain in both modes must be the same; therefore, the maximum current... I max The following formula must be satisfied: (4) Step 4, Closed-loop control parameter adjustment: The discrete form of proportional-integral control is shown in equations (5) to (7). Wherein, e ( k ) represents the error function. k p , k i These are the proportional coefficient and the integral coefficient, respectively. I ( k ), I ( k -1) represents the term following and preceding the integral, respectively. Pi delta ( k () represents the output value of the control function before limiting. Pi output ( k The output value of the control function after limiting is ). k cor To compensate for gain against saturation, an anti-saturation mechanism is introduced into the integral function to ensure a smooth transition and prevent saturation.

[0028] (5) (6) (7) The output value of the closed-loop control function is related to the switching frequency. In proportional-integral control, firstly, the output value of the closed-loop control function needs to be adjusted to satisfy the above proportional relationship, as shown in equation (8) or (9), where, Pi output ( k -1) represents the output value of the closed-loop control function corresponding to the mode before switching. Pi output ( k The output value of the closed-loop control function corresponding to the switched mode is 1; secondly, the output value of the new closed-loop control function needs to be calculated. Pi output ( k The initial values ​​of the integral under the condition are shown in equations (10) and (11).

[0029] (8) (9) (10) (11) In DSP-based voltage and current dual closed-loop control, the output value of the voltage loop control function is the input value of the current loop control function. The output value of the current loop control function is generally inversely proportional to the value of the period register. Therefore, during the switching process, it is only necessary to make the value of the period register satisfy the above relationship, and then recalculate the initial integral value of the current loop control function based on the output value of the new current loop control function.

[0030] Step 5: Set up voltage hysteresis to avoid repeated switching. Picture 2 middle V band It is half the width of the hysteresis loop.

[0031] The above technical solutions are merely exemplary embodiments of the present invention. For those skilled in the art, based on the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the methods described in the specific embodiments of the present invention. Therefore, the methods described above are merely preferred and not restrictive.

Claims

1. A method for switching a half-bridge / full-bridge LLC resonant converter, characterized in that, Includes the following steps: S1, to perform precise circuit modeling; S2, calculate the ratio of the switching frequencies of the two modes under the same voltage gain at the switching point; S3. Determine whether the maximum current can guarantee that the voltage gain coincides at the switching point between the two modes. If so, adjust the closed-loop control parameters according to the switching frequency ratio between the two modes obtained in step S2 to complete the mode switching.

2. The method according to claim 1, characterized in that, The specific method of step S1 includes: The parameters of each component in the converter are measured. The leakage inductance of the transformer is obtained through a bridge circuit. The total resonant inductance is the sum of the series resonant inductance and the equivalent leakage inductance of the transformer primary side.

3. The method according to claim 1, characterized in that, In step S2, the switching frequency ratio between the two modes is calculated using the following first method: S21, derive the voltage gain based on the input voltage and output voltage at the switching point. M ; S22, Calculate the switching frequency at the switching point in full-bridge mode and half-bridge mode according to the following formula, and obtain the proportional coefficient of the switching frequency when switching between these two modes. k 1. k 2: In the formula, f s For switching frequency, Q For quality factor, k Inductance ratio, f n Normalized frequency; L r , L k These are the series inductance that forms the resonant inductance in the resonant cavity of the half-bridge / full-bridge LLC resonant converter, and the equivalent leakage inductance on the primary side of the transformer, respectively. C r It is a resonant capacitor; L m The equivalent magnetizing inductance of the primary side of the transformer in the half-bridge / full-bridge LLC resonant converter is given, and the primary-to-secondary turns ratio of the transformer is 1: n ; V o For output voltage, V in Input voltage; k1 and k2 are the proportional coefficients of the switching frequency when switching between the two modes. Specifically, when switching from full-bridge mode to half-bridge mode, the relationship between the switching frequencies in the two modes is expressed as follows: , This refers to the switching frequency in half-bridge mode. This represents the switching frequency in full-bridge mode; when switching from half-bridge mode to full-bridge mode, the relationship between the switching frequencies in the two modes is expressed as follows: .

4. The method according to claim 3, characterized in that, In step S2, the switching frequency ratio between the two modes is obtained using the following second method: Step S1 involves accurately modeling the converter, and the proportional gain of the switching frequency under the two modes is obtained through simulation in the simulation software. k 1. k 2.

5. The method according to claim 3 or 4, characterized in that, In step S3, the method for determining whether the maximum current ensures that the voltage gain overlaps at the switching point between the two modes includes: Maximum current I max The following formula must be satisfied: 。 6. The method according to claim 3 or 4, characterized in that, In step S3, the method for adjusting the closed-loop control parameters specifically includes: Assuming the half-bridge / full-bridge LLC resonant converter employs proportional-integral closed-loop control, then: S31. Adjust the output values ​​of the closed-loop control function in both modes to satisfy the proportional relationship obtained in step S2, as shown in the following formula: (8) (9) In equation (8), Pi output ( k -1) is the output value of the closed-loop control function corresponding to the full-bridge mode before switching. Pi output ( k () represents the output value of the closed-loop control function corresponding to the switching of the second half-bridge mode; In equation (9), Pi output ( k -1) is the output value of the closed-loop control function corresponding to the switching of the front half-bridge mode. Pi output ( k The output value of the closed-loop control function corresponding to the full-bridge mode after switching is ). S32, Based on the obtained closed-loop control function output value, calculate the new closed-loop control function output value. Pi output ( k The initial values ​​of the integral under the given conditions are shown in equations (10) and (11): (10) (11) Equation (10) represents the switch from full-bridge mode to half-bridge mode, and Equation (11) represents the switch from half-bridge mode to full-bridge mode. e ( k ) represents the error function. k i The integral coefficient is... I ( k ), I ( k -1) represents the term following and preceding the integral, respectively. Pi delta ( k () represents the output value of the control function before limiting. Pi output ( k () represents the output value of the control function after limiting. k cor1 、k cor2 The anti-saturation compensation gain is given by the integral coefficient and the proportional coefficient under the two switching modes, respectively. k 1 or k The ratio of 2; During the switching process, it is only necessary to ensure that the period register value satisfies the relationship described in step S31, and then recalculate the initial integral value of the current loop control function based on the output value of the new current loop control function.

7. The method according to claim 1, characterized in that, It also includes the following steps: S4, set voltage hysteresis to avoid repeated switching.

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