Bilateral modulation control method capable of realizing reverse operation of LLC resonant converter of ZCS

Abstract

The invention relates to the technical field of switching power supplies, and discloses a bilateral modulation control method capable of realizing reverse operation of an LLC resonant converter of a ZCS. Comprising the following steps: deducing time domain expressions of converter operation stages Pr and Or under the influence of parasitic inductance Ls, calculating by using a time domain model to obtain zero current turn-off of a primary side switch of the converter in a full working frequency and load range, and designing a bilateral modulation controller. According to the method, zero-current turn-off of a primary side switching tube is realized; from the perspective of a steady-state simulation waveform, the turn-off current error is less than 1A, so that the switching loss is effectively reduced, the energy loss of the converter in the reverse operation process is reduced, and the overall operation efficiency is further improved; the voltage peak of a primary side switching tube can be reduced; by reducing the voltage spike, the risk that the switch tube is damaged due to overvoltage is reduced, the operation safety and stability of the converter are improved, and reliable operation of the whole system is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, specifically to a bilateral modulation control method for realizing reverse operation of a ZCS LLC resonant converter. Background Technology

[0002] LLC resonant converters are widely used in battery chargers due to their advantages such as wide voltage gain, high power density, zero-voltage switching, and narrow switching frequency range. When the battery needs to discharge, if an LLC converter can still be used, additional circuitry can be omitted, reducing costs.

[0003] However, when the LLC resonant converter operates in reverse, the regular reverse structure is essentially a SRC (Short-Range Resonant Converter) because the magnetizing inductor is always clamped by the input voltage, resulting in less than ideal voltage regulation capability. When the converter operates under light load, the switching frequency range becomes very wide. Therefore, this scheme is often used as a DC transformer to provide a constant voltage gain. To overcome this drawback, the literature [Al Attar H, Hamida M, Ghanes M, et al. Model Free Control design of DC-DC LLC converter with phase shift modulation in V2X mode for EV chargerapplication[C]. Trieste: 2022 IEEE Conference on Control Technology and Applications, 2022: 734-739.] proposes a control strategy based on the resonant variable state plane diagram to meet the requirements of wide voltage range applications. However, this control strategy is complex because the accurate turn-on times of the primary and secondary switches need to be precisely calculated.

[0004] The literature [Su M, Ouyang Q, Deng G, et al. Modified topology and PWMmodulation for bidirectional LLC-DCX Converter with center-tapped transformer[J]. IEEE Transactions on Transportation Electrification, 2022, 8(3): 3907-3920.] introduces a bidirectional GaN AC switch on the secondary side of the transformer. By controlling the phase shift of the primary-side switch and the duty cycle of the GaN AC switch, the converter can achieve buck or boost functions, thus realizing a wide voltage range. However, the controller needs to select different control methods according to the voltage range. In addition, the additional GaN AC switch results in a floating drive ground. The use of GaN devices also increases the cost; therefore, we propose a bilateral modulation control method for reverse operation of an LLC resonant converter that can achieve ZCS. Summary of the Invention

[0005] The purpose of this invention is to provide a bilateral modulation control method for an LLC resonant converter that can achieve reverse operation of ZCS, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a bilateral modulation control method for reversing an LLC resonant converter capable of ZCS, wherein the LLC resonant converter consists of an input capacitor... C L Inverter circuit, turns ratio 1:1: n The transformer T with center tap, resonant cavity, rectifier circuit and output capacitor C H composition; The inverter circuit is a push-pull structure consisting of primary-side MOSFETs S3 and S4, with the sources of S3 and S4 connected. C L The negative terminal of S3 is connected to the leakage inductance of the transformer. L s1 , L s1 Connect the external terminals of the transformer; the external terminals of the transformer are connected to the transformer leakage inductance. L s2 , L s2 Connect the drain of S4 and the center tap of the transformer. C L The positive electrode; The resonant cavity is composed of a resonant inductor Lr Magnetizing inductance of transformer T L m and resonant capacitor C r The resonant cavity is sequentially connected, with one end connected to the source S1 and the other end connected to the source S2. The modulation control method includes the following steps: S1, Deriving the parasitic inductance L s The influence of the converter operation phase P r and O r The time-domain expression is obtained, and the unknowns in the time-domain expression are solved based on the boundary conditions, establishing a system that considers parasitic inductance. L s The time-domain model of the LLC resonant converter running in reverse; S2. Calculate the theoretical turn-on time required for the converter to achieve zero-current switching (ZCS) on the primary side across the entire operating frequency and load range using a time-domain model. t ZCS ;Will t ZCS This is converted into the configuration value of the CMPA register used to control the dead time in the digital processing chip. C mpa ; switch frequency f s This is converted into the configuration value of the TBPRD register in the digital processing chip, which is used to control the frequency of the PWM signal. T bprd ; By using a piecewise fitting method to C mpa about T bprd and load resistance R o The relationship is transformed into a function expression; S3. Design a bilateral modulation controller; the controller includes a duty cycle calculation module and a voltage regulation PI controller.

[0007] Optionally, S1 includes: S1.1, When the LLC converter is run in reverse, the operation phase of the primary side ZCS is divided into a dead-time phase O. r and conduction phase P r Derive the time-domain expressions for the per-unit values ​​of each state variable, including the resonant current. i rn Excitation current i mn Resonant capacitor voltage v rn Magnetizing inductor voltage v mnThe time-domain expression; P r The time-domain expression for the per-unit value of each state variable in the stage can be expressed as: ;

[0008] in, I rn , I mn , V rn yes i rn , i mn , v rn initial value, θ = wt, ，M = V o / nV L , k = L m / L r , h = L s / L r , ; benchmark value V base = nV L , , I base = V base / Z r ; O r The time-domain expression for the per-unit value of each state variable in the stage can be expressed as: ;

[0009] in ; S1.2, Let θ 1. θ 2 are O r and P r Phase end time; θ 1 corresponds to the dead time that can achieve ZCS. This corresponds to half a switching cycle; Solve for the unknown Irn , I mn , V rn , θ 1 and M ,in θ 1 corresponds to the dead time that enables ZCS. t ZCS The conversion formula is as follows: .

[0010] Optionally, S2 includes: S2.1, By adjusting θ 2. R on The value is used to obtain the theoretical on-time required to achieve ZCS under various load and frequency conditions of converter operation using the time-domain model established in S1. t ZCS ; S2.2 To facilitate the implementation of the proposed bilateral modulation control by the digital processing chip, the EPWM module in the chip is set to upward counting mode. t ZCS Configuration value converted to CMPA* register C mpa The conversion formula is as follows: C mpa = t ZCS *Counter frequency; The counter frequency is determined by the configuration of the digital processing chip; S2.3 To facilitate the implementation of the proposed bilateral modulation control by the digital controller, f s Configuration value converted into TBPRD register T bprd The conversion formula is as follows: ;

[0011] S2.4, load resistor R o Range of variation R min , R max Divide into 5 equal intervals, define R o and T bprd As the independent variable, C mpa As the dependent variable, a piecewise fitting method was used to obtain... C mpa about Ro and T bprd A quadratic polynomial in two variables.

[0012] Optionally, S3 specifically includes: S3.1: The duty cycle calculation module contains the function expression obtained from the piecewise fitting in S2.4; the input signals of the duty cycle calculation module include... V H , V L , I in and T bprd ,in T bprd Output from a voltage-regulated PI controller, V H , V L and I in Obtained through hardware sampling circuitry; according to V H , V L and I in Calculated using the following formula R o : ;

[0013] in, I in It is the converter input current; The duty cycle calculation module is based on R o and T bprd calculate C mpa ,Will C mpa Output to the EPWM module; S3.2, Voltage Reference Value V ref and output voltage V H The difference between the sampled values ​​is input to the PI controller to adjust the output signal. T bprd Enter the TBPRD register of the controller chip.

[0014] Optionally, the rectifier circuit is a half-bridge structure composed of secondary-side MOSFETs S1 and S2, with the drain of S1 connected to... C HThe positive terminal of S1 is connected to the source terminal of S2, and the drain terminal of S2 is connected to the positive terminal of S2. C H The negative electrode; C L The voltage across the terminals is the input voltage. V L ; C H The voltage across the terminals is the output voltage. V H Define the output voltage of the resonant slot. v o It is the AC component of the drain-source voltage of S2, and its amplitude is... V o = V H / 2; v r yes C r The AC component of the terminal voltage.

[0015] Optionally, in S1.2, since the circuit waveform is symmetrical within the positive and negative half-cycles, the initial and final values ​​of the state variable within each half-cycle are opposites, thus the following constraints apply: ;

[0016] The initial values ​​of the resonant current and the excitation current satisfy the following equation: ;

[0017] Since the circuit must satisfy the charge conservation condition, the following constraints apply: ;

[0018] in R on This is the per-unit value of the load resistance.

[0019] Compared with the prior art, the present invention provides a bilateral modulation control method for realizing reverse operation of an LLC resonant converter with ZCS, which has the following beneficial effects: 1. This bilateral modulation control method enables zero-current turn-off (ZCS) of the primary-side resonant converter during reverse operation, achieving zero-current turn-off of the primary-side switch. Steady-state simulation waveforms show a turn-off current error of less than 1A, effectively reducing switching losses and lowering energy consumption during reverse operation, thus improving overall operating efficiency. It also reduces voltage spikes on the primary-side switch. Excessive voltage spikes can damage the switch and affect the converter's normal operation. By reducing voltage spikes, the risk of switch damage due to overvoltage is reduced, improving the safety and stability of the converter and ensuring reliable operation of the entire system.

[0020] 2. This bilateral modulation control method for reversing the LLC resonant converter with ZCS can achieve zero-current turn-off of the primary-side switch, improving the reverse operation efficiency of the converter; it can also reduce the voltage spike of the primary-side switch, improving the safety of converter operation.

[0021] 3. This bilateral modulation control method enables the reverse operation of the LLC resonant converter with ZCS. In the underresonant operating mode, traditional converters have insufficient voltage regulation capability, while this scheme enables the converter to have voltage reduction capability. This feature broadens the application range of the converter, enabling it to operate stably under different voltage demand scenarios and enhancing the practicality of the converter. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the LLC resonant converter topology of the present invention; Figure 2 The LLC converter P of this invention r Equivalent circuit diagram during operation; Figure 3 The LLC converter of this invention r Equivalent circuit diagram during operation; Figure 4 For the present invention C mpa about R o and T bprd Schematic diagram of the relationship surface of piecewise fitting; Figure 5 This is a schematic diagram of the bilateral modulation controller structure of the present invention; Figure 6 This is a schematic diagram of the steady-state simulation waveform of the bilateral modulation control of the present invention; Figure 7 This is a schematic diagram of the transient simulation waveform of the bilateral modulation control of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figures 1-7 As shown, this invention provides a technical solution: a bilateral modulation control method for reversing an LLC resonant converter capable of ZCS operation, wherein the LLC resonant converter consists of an input capacitor... C LInverter circuit, turns ratio 1:1: n The transformer T with center tap, resonant cavity, rectifier circuit and output capacitor C H Composition; Topology of LLC resonant converter as follows Figure 1 As shown; The inverter circuit is a push-pull structure consisting of primary-side MOSFETs S3 and S4, with the sources of S3 and S4 connected. C L The negative terminal of S3 is connected to the leakage inductance of the transformer. L s1 , L s1 Connect the external terminals of the transformer; the external terminals of the transformer are connected to the transformer leakage inductance. L s2 , L s2 Connect the drain of S4 and the center tap of the transformer. C L The positive electrode; The resonant cavity consists of a resonant inductor. L r Magnetizing inductance of transformer T L m and resonant capacitor C r The resonant cavity is connected sequentially, with one end connected to the source of S1 and the other end connected to the source of S2. The rectifier circuit is a half-bridge structure composed of secondary-side MOSFETs S1 and S2, with the drain of S1 connected to... C H The positive terminal of S1 is connected to the source terminal of S2, and the drain terminal of S2 is connected to the positive terminal of S2. C H The negative electrode; C L The voltage across the terminals is the input voltage. V L ; C H The voltage across the terminals is the output voltage. V H Define the output voltage of the resonant slot. v o It is the AC component of the drain-source voltage of S2, and its amplitude is... V o = V H / 2; v r yes C r The AC component of the terminal voltage.

[0025] In this embodiment, the modulation control method includes the following steps: S1, Deriving the parasitic inductanceL s The influence of the converter operation phase P r and O r The time-domain expression is obtained, and the unknowns in the time-domain expression are solved based on the boundary conditions, establishing a system that considers parasitic inductance. L s The time-domain model of the LLC resonant converter running in reverse; S1.1, When the LLC converter is run in reverse, the operation phase of the primary side ZCS is divided into a dead-time phase O. r and conduction phase P r Derive the time-domain expressions for the per-unit values ​​of each state variable, including the resonant current. i rn Excitation current i mn Resonant capacitor voltage v rn Magnetizing inductor voltage v mn The time-domain expression; P r The equivalent circuit of the stage is as follows Figure 2 As shown; P r The time-domain expression for the per-unit value of each state variable in the stage can be expressed as: ;

[0026] in, I rn , I mn , V rn yes i rn , i mn , v rn initial value, θ = wt, ，M = V o / nV L , k = L m / L r , h = L s / L r , ; benchmark value V base = nVL , , I base = V base / Z r ; O r The equivalent circuit of the stage is as follows Figure 3 As shown, O r The time-domain expression for the per-unit value of each state variable in the stage can be expressed as: ;

[0027] in ; S1.2, Let θ 1. θ 2 are O r and P r Phase end time; θ 1 corresponds to the dead time that can achieve ZCS. This corresponds to half a switching cycle; Since the circuit waveform is symmetrical within the positive and negative half-cycles, the initial and final values ​​of the state variables within each half-cycle are opposites. Therefore, the following constraints apply: ;

[0028] The initial values ​​of the resonant current and the excitation current satisfy the following equation: ;

[0029] Since the circuit must satisfy the charge conservation condition, the following constraints apply: ;

[0030] in R on This represents the per-unit value of the load resistance; Solve for the unknown I rn , I mn , V rn , θ 1 and M ,in θ 1 corresponds to the dead time that enables ZCS. t ZCS The conversion formula is as follows: .

[0031] S2. Calculate the theoretical turn-on time required for the converter to achieve zero-current switching (ZCS) on the primary side across the entire operating frequency and load range using a time-domain model. t ZCS ;Will t ZCS This is converted into the configuration value of the CMPA register used to control the dead time in the digital processing chip. C mpa ; switch frequency f s This is converted into the configuration value of the TBPRD register in the digital processing chip, which is used to control the frequency of the PWM signal. T bprd ; By using a piecewise fitting method to C mpa about T bprd and load resistance R o The relationship is transformed into a function expression; S2.1, By adjusting θ 2. R on The value is used to obtain the theoretical on-time required to achieve ZCS under various load and frequency conditions of converter operation using the time-domain model established in S1. t ZCS ; S2.2 To facilitate the implementation of the proposed bilateral modulation control by the digital processing chip, the EPWM module in the chip is set to upward counting mode. t ZCS Configuration value converted to CMPA* register C mpa The conversion formula is as follows: C mpa = t ZCS *Counter frequency; The counter frequency is determined by the configuration of the digital processing chip; S2.3 To facilitate the implementation of the proposed bilateral modulation control by the digital controller, f s Configuration value converted into TBPRD register T bprd The conversion formula is as follows: ;

[0032] Under full load and frequency range C mpa about R o and Tbprd Relationship such as Figure 4 As shown; S2.4, load resistor R o Range of variation R min , R max Divide into 5 equal intervals, define R o and T bprd As the independent variable, C mpa As the dependent variable, a piecewise fitting method was used to obtain... C mpa about R o and T bprd The bivariate quadratic polynomial is shown below:

[0033] The relevant parameters of the LLC resonant converter are shown in the table below: Parameter name numerical values <![CDATA[Resonant frequency f r > 100 kHz <![CDATA[Switching frequency f s > 60 kHz~100 kHz Transformer turns ratio 14：3 <![CDATA[Output voltage V dc > 400 V <![CDATA[Input voltage V bat > 40V~58V <![CDATA[Rated output power P nom > 1500 W <![CDATA[Resonant inductor L r > 16.18 μH <![CDATA[Field excitation inductance L m > 74.56 μH <![CDATA[Resonant capacitor C r > 164.38 nF S3. Design a bilateral modulation controller; the controller includes a duty cycle calculation module and a voltage regulation PI controller.

[0034] S3.1: The duty cycle calculation module contains the function expression obtained from the piecewise fitting in S2.4; the input signals of the duty cycle calculation module include... V H , V L , I in and T bprd ,in T bprd Output from a voltage-regulated PI controller, V H , V L and I in Obtained through hardware sampling circuitry; according to V H , V L and I in Calculated using the following formula R o : ;

[0035] in,I in It is the converter input current; The duty cycle calculation module is based on R o and T bprd calculate C mpa ,Will C mpa Output to the EPWM module; S3.2, Voltage Reference Value V ref and output voltage V H The difference between the sampled values ​​is input to the PI controller to adjust the output signal. T bprd Enter the TBPRD register of the controller chip.

[0036] The structure of the bilateral modulation controller is as follows Figure 5 As shown; The steady-state simulation waveform of the LLC resonant converter using a bilateral modulation control strategy during reverse operation is as follows: Figure 6 As shown, the turn-off current error is less than 1 A, indicating that the proposed control can enable the converter to achieve ZCS of the primary side switching transistor. The transient simulation waveform of the LLC resonant converter using a bilateral modulation control strategy during reverse operation is as follows: Figure 7 As shown, when the load switches from no load to 1500W, the voltage adjustment time is 15ms, indicating that the proposed control can take into account the dynamic adjustment of the output voltage.

[0037] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A bilateral modulation control method for realizing reverse operation of a ZCS LLC resonant converter, characterized in that: The LLC resonant converter consists of an input capacitor. C L Inverter circuit, turns ratio 1:1: n A center-tapped transformer T, resonant cavity, rectifier circuit, and output capacitor. C H composition; The inverter circuit is a push-pull structure consisting of primary-side MOSFETs S3 and S4, with the sources of S3 and S4 connected. C L The negative terminal of S3 is connected to the leakage inductance of the transformer. L s1 , L s1 Connect the external terminals of the transformer; the external terminals of the transformer are connected to the transformer leakage inductance. L s2 , L s2 Connect the drain of S4 and the center tap of the transformer. C L The positive electrode; The resonant cavity is composed of a resonant inductor L r Magnetizing inductance of transformer T L m and resonant capacitor C r The resonant cavity is connected sequentially, with one end connected to the source S1 and the other end connected to the source S2. The modulation control method includes the following steps: S1, Deriving the parasitic inductance L s The influence of the converter operation phase P r and O r The time-domain expression is obtained, and the unknowns in the time-domain expression are solved based on the boundary conditions, establishing a system that considers parasitic inductance. L s The time-domain model of the LLC resonant converter running in reverse; S2. Calculate the theoretical turn-on time required for the converter to achieve zero-current turn-off of the primary side switch across the entire operating frequency and load range using a time-domain model. t ZCS ;Will t ZCS This is converted into the configuration value of the CMPA register used to control the dead time in the digital processing chip. C mpa ; switch frequency f s This is converted into the configuration value of the TBPRD register in the digital processing chip, which is used to control the frequency of the PWM signal. T bprd ; By using a piecewise fitting method to C mpa about T bprd and load resistance R o The relationship is transformed into a function expression; S3. Design a bilateral modulation controller; the controller includes a duty cycle calculation module and a voltage regulation PI controller.

2. The bilateral modulation control method for realizing reverse operation of a ZCS LLC resonant converter according to claim 1, characterized in that: S1 includes: S1.1, When the LLC converter is run in reverse, the operation phase of the primary side ZCS is divided into a dead-time phase O. r and conduction phase P r Derive the time-domain expressions for the per-unit values ​​of each state variable, including the resonant current. i rn Excitation current i mn Resonant capacitor voltage v rn Magnetizing inductor voltage v mn The time-domain expression; P r The time-domain expression for the per-unit value of each state variable in the stage can be expressed as: ； in, I rn , I mn , V rn yes i rn , i mn , v rn initial value, θ = wt, , M = V o / nV L , k = L m / L r , h = L s / L r , ; benchmark value V base = nV L , , I base = V base / Z r ; O r The time-domain expression for the per-unit value of each state variable in the stage can be expressed as: ； in ; S1.2, Let θ 1. θ 2 are O r and P r Phase end time; θ 1 corresponds to the dead time that can achieve ZCS. This corresponds to half a switching cycle; Solve for the unknown I rn , I mn , V rn , θ 1 and M ,in θ 1 corresponds to the dead time that enables ZCS. t ZCS The conversion formula is as follows: .

3. The bilateral modulation control method for realizing reverse operation of an LLC resonant converter with ZCS according to claim 1, characterized in that: S2 includes: S2.1, By adjusting θ 2. R on The value is used to obtain the theoretical on-time required to achieve ZCS under various load and frequency conditions of converter operation using the time-domain model established in S1. t ZCS ; S2.2 To facilitate the implementation of the proposed bilateral modulation control by the digital processing chip, the EPWM module in the chip is set to upward counting mode. t ZCS Configuration value converted to CMPA* register C mpa The conversion formula is as follows: C mpa = t ZCS *Counter frequency; The counter frequency is determined by the configuration of the digital processing chip; S2.3 To facilitate the implementation of the proposed bilateral modulation control by the digital controller, f s Configuration value converted into TBPRD register T bprd The conversion formula is as follows: ； S2.4, load resistor R o Range of variation R min , R max Divide into 5 equal intervals, define R o and T bprd As the independent variable, C mpa As the dependent variable, a piecewise fitting method was used to obtain... C mpa about R o and T bprd A quadratic polynomial in two variables.

4. The bilateral modulation control method for realizing reverse operation of an LLC resonant converter with ZCS according to claim 1, characterized in that: Specifically, S3 is: S3.1: The duty cycle calculation module contains the function expression obtained from the piecewise fitting in S2.4; the input signals of the duty cycle calculation module include... V H , V L , I in and T bprd ,in T bprd Output from a voltage-regulated PI controller, V H , V L and I in Obtained through hardware sampling circuitry; according to V H , V L and I in Calculated using the following formula R o : ； in, I in It is the converter input current; The duty cycle calculation module is based on R o and T bprd calculate C mpa ,Will C mpa Output to the EPWM module; S3.2, Voltage Reference Value V ref and output voltage V H The difference between the sampled values ​​is input to the PI controller to adjust the output signal. T bprd Enter the TBPRD register of the controller chip.

5. A bilateral modulation control method for reversing an LLC resonant converter capable of ZCS operation according to claim 1, characterized in that: The rectifier circuit is a half-bridge structure composed of secondary-side MOSFETs S1 and S2, with the drain of S1 connected to... C H The positive terminal of S1 is connected to the source terminal of S2, and the drain terminal of S2 is connected to the positive terminal of S2. C H The negative electrode; C L The voltage across the terminals is the input voltage. V L ; C H The voltage across the terminals is the output voltage. V H Define the output voltage of the resonant slot. v o It is the AC component of the drain-source voltage of S2, and its amplitude is... V o = V H / 2; v r yes C r The AC component of the terminal voltage.

6. A bilateral modulation control method for reversing operation of an LLC resonant converter capable of ZCS according to claim 1, characterized in that: In S1.2, since the circuit waveform is symmetrical within the positive and negative half-cycles, the initial and final values ​​of the state variable within each half-cycle are opposites. Therefore, the following constraints apply: ； The initial values ​​of the resonant current and the excitation current satisfy the following equation: ； Since the circuit must satisfy the charge conservation condition, the following constraints apply: ； in R on This is the per-unit value of the load resistance.

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