Full-bridge LLC resonant converter control circuit

Abstract

The utility model provides a full-bridge LLC resonant converter control circuit, which is characterized in that a full-bridge LCC resonant converter is provided with a frequency conversion controller, a phase shift controller and a mode switching module, the input end of the mode switching module is connected with an input voltage detection module, and when the input voltage of the full-bridge LCC resonant converter is lower than a preset threshold value, the phase shift controller is connected with the mode switching module. When the input voltage of the full-bridge LCC resonant converter is larger than or equal to a preset threshold value, the variable frequency controller controls a switching tube in the full-bridge LCC resonant converter to work through switching of the switch, and when the input voltage of the full-bridge LCC resonant converter is larger than or equal to the preset threshold value, the phase shift controller controls the switching tube in the full-bridge LCC resonant converter to work through switching of the switch. The full-bridge LLC resonant converter has the advantages that the variable-frequency controller and the phase-shift controller are arranged in the control circuit at the same time, switching of control modes can be achieved based on judgment of the magnitude of input voltage and through a simple switching circuit, the full-bridge LLC resonant converter has the advantages of variable-frequency control and phase-shift control, and the problems of voltage fluctuation and instability are solved.

Description

Technical Field

[0001] The utility model relates to power electronic technology, in particular to a full-bridge LLC resonant converter control circuit. Background Art

[0002] The LLC resonant converter is a resonant circuit composed of components such as an inductor, capacitor, and transformer. Its unique characteristic is that by adjusting the parameters of the inductor and capacitor in the circuit, it can achieve different power conversion requirements, such as rectification and inversion, while also achieving high power density and high energy conversion efficiency. Its basic operating principle is to indirectly control the output current and voltage by controlling the resonance of the inductor and capacitor. In the resonant state, the voltage and current of the inductor and capacitor reach their maximum values, achieving the highest circuit conversion efficiency. Precisely because of these excellent characteristics, the LLC resonant converter is increasingly widely used in power electronic devices such as frequency converters and inverters.

[0003] like Figure 1 As shown in Figure 1, a traditional full-bridge LLC resonant converter includes a DC power supply interface, a full-bridge inverter, an LLC resonant module, a transformer, a rectifier and filter circuit, and an electrical load interface. To precisely adjust the DC output voltage, a variable frequency control strategy is typically adopted, effectively controlling the output voltage by adjusting the converter's operating frequency. To achieve a wider DC voltage gain, the switching frequency adjustment range needs to be expanded. However, when the input voltage varies widely, the full-bridge converter faces two major problems:

[0004] 1) The output filter inductance is large: Analysis Figure 2 As the input voltage increases, the current ripple in the filter inductor increases accordingly. To meet this increased current ripple requirement, the filter inductor must be designed based on the system's highest input voltage. This design strategy leads to an increase in inductance value, which in turn increases the size of the converter's magnetic core, reducing the converter's power density and slowing down its dynamic response.

[0005] 2) Wide range of output duty cycle: Figure 2 Analysis shows that under high-voltage input conditions, the converter's duty cycle fluctuates widely and is generally small. This reduction in duty cycle significantly exacerbates current ripple in the filter inductor, leading to an increase in the effective value of the primary current. This effect negatively impacts the converter's overall efficiency under high-voltage input conditions, reducing its conversion efficiency.

[0006] Therefore, the traditional full-bridge LLC resonant converter has many performance deficiencies in scenarios with a wide input voltage range, and further design improvements are needed. Utility Model Content

[0007] In view of this, the purpose of the present invention is to provide a full-bridge LLC resonant converter control circuit, so that when the input voltage is low, the converter operates in a variable frequency control mode. At this time, the switch tube can operate at full duty cycle, and the output voltage can be precisely controlled by flexibly adjusting the switching frequency; when the input voltage increases, the converter can switch to a phase-shift control mode, and the switch tube operates at the highest frequency preset by the system, and optimizes the output voltage regulation by adjusting the phase shift angle. The combination of variable frequency control and phase-shift control can achieve the complementary advantages of various control modes under different input voltage conditions.

[0008] In order to achieve the above purpose, the specific technical solutions adopted by this utility model are as follows:

[0009] A full-bridge LLC resonant converter control circuit, the key of which is to configure a frequency conversion controller, a phase shift controller, and a mode switching module on a full-bridge LCC resonant converter. The input end of the mode switching module is connected to an input voltage detection module. When the input voltage of the full-bridge LCC resonant converter is lower than a preset threshold, the mode switching module causes the frequency conversion controller to control the operation of the switch tube in the full-bridge LCC resonant converter through switch switching. When the input voltage of the full-bridge LCC resonant converter is greater than or equal to the preset threshold, the mode switching module causes the phase shift controller to control the operation of the switch tube in the full-bridge LCC resonant converter through switch switching.

[0010] Optionally, the full-bridge LCC resonant converter includes a DC power supply interface, a full-bridge inverter, an LLC resonant module, a transformer, a rectifier filter circuit and an electrical load interface, and the LLC resonant module includes a resonant inductor L connected in series. r , excitation inductance L m and resonant capacitor C r , the excitation inductance L m The full-bridge inverter includes a switch tube Q1, a switch tube Q2, a switch tube Q3 and a switch tube Q4, which are connected in parallel to the primary winding of the transformer.

[0011] Optionally, each switch tube of the full-bridge inverter is provided with an anti-parallel diode and a switch tube junction capacitor.

[0012] Optionally, the frequency conversion controller is provided with a first reference voltage input terminal, a full-bridge LCC resonant converter output voltage acquisition terminal, an S14 signal output terminal and an S23 signal output terminal, the S14 signal output terminal is used to drive the switch tube Q1 and the switch tube Q4 in the full-bridge inverter, and the S23 signal output terminal is used to drive the switch tube Q2 and the switch tube Q3 in the full-bridge inverter.

[0013] Optionally, the phase-shift controller has a second reference voltage input terminal, a full-bridge LCC resonant converter output voltage acquisition terminal, and an S1 signal output terminal, an S2 signal output terminal, an S3 signal output terminal, and an S4 signal output terminal for correspondingly driving four switching tubes in the full-bridge inverter.

[0014] Optionally, the mode switching module includes a first switch switching circuit, a second switch switching circuit, a third switch switching circuit and a fourth switch switching circuit, the two signal input terminals of the first switch switching circuit are respectively connected to the S1 signal output terminal and the S14 signal output terminal, the output terminal of the first switch switching circuit is connected to the driving terminal of the switch tube Q1, the two signal input terminals of the second switch switching circuit are respectively connected to the S2 signal output terminal and the S23 signal output terminal, the output terminal of the second switch switching circuit is connected to the driving terminal of the switch tube Q2, the two signal input terminals of the third switch switching circuit are respectively connected to the S3 signal output terminal and the S23 signal output terminal, the output terminal of the third switch switching circuit is connected to the driving terminal of the switch tube Q3 The two signal input ends of the fourth switch switching circuit are respectively connected to the S4 signal output end and the S14 signal output end, the output end of the fourth switch switching circuit is connected to the driving end of the switch tube Q4, and the enable end of each switch switching circuit is connected to the input voltage detection module. When the input voltage of the full-bridge LCC resonant converter is lower than the preset threshold, the S14 signal output end and the S23 signal output end control the four switch tubes in the full-bridge inverter through the mode switching module. When the input voltage of the full-bridge LCC resonant converter is greater than or equal to the preset threshold, the S1 signal output end, the S2 signal output end, the S3 signal output end and the S4 signal output end control the four switch tubes in the full-bridge inverter through the mode switching module.

[0015] Optionally, the preset threshold is 360V.

[0016] The beneficial effects of the utility model are:

[0017] By configuring both a frequency conversion controller and a phase-shift controller in the control circuit, the control mode can be switched based on the input voltage and using a simple switching circuit. This allows the full-bridge LLC resonant converter to have the advantages of both frequency conversion control and phase-shift control to solve the problems of voltage fluctuation and instability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0019] Figure 1 This is the main circuit schematic of the traditional full-bridge LCC resonant converter;

[0020] Figure 2This is the waveform of the secondary rectifier voltage and filter inductor current of the traditional full-bridge LLC converter;

[0021] Figure 3 This is a circuit principle block diagram of the utility model;

[0022] Figure 4 yes Figure 3 Circuit schematic diagram of the mode switching module. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the preferred embodiments are only for illustrating the present invention and are not intended to limit the scope of protection of the present invention.

[0024] like Figure 3 As shown, the utility model provides a full-bridge LLC resonant converter control circuit, in which a frequency conversion controller, a phase shift controller and a mode switching module are configured on the full-bridge LCC resonant converter. The input end of the mode switching module is connected to an input voltage detection module. When the input voltage of the full-bridge LCC resonant converter is lower than a preset threshold value, the mode switching module causes the frequency conversion controller to control the switch tube in the full-bridge LCC resonant converter to operate through switch switching. When the input voltage of the full-bridge LCC resonant converter is greater than or equal to the preset threshold value, the mode switching module causes the phase shift controller to control the switch tube in the full-bridge LCC resonant converter to operate through switch switching.

[0025] In specific implementation, the main circuit of the full-bridge LLC resonant converter is as follows: Figure 1 As shown, Q1~Q4 are the four switching tubes of the full-bridge inverter, D1~D4 are the four anti-parallel diodes of the switching tubes, C1~C4 are the four junction capacitors of the switching tubes, and the LLC resonant module includes a resonant inductor L r , resonant capacitor C r (also has filtering function) and excitation inductance L m (In parallel with the transformer, so the transformer excitation inductance can also be used to achieve), D in the rectifier filter circuit r1 ~D r4 is the output rectifier diode, C f is the output filter capacitor, R d is the output load.

[0026] For LLC resonant module, the resonant inductor L r and resonant capacitor C r The frequency that participates in resonance together is called the series resonant frequency (abbreviated as binary frequency), denoted as f r ; When the primary resonant inductor current i p and the magnetizing inductance current i Lm When the excitation inductance L is equal,m , the resonant inductor Lr and the resonant capacitor Cr work together to produce this special resonant frequency, which is called the series-parallel resonant frequency, or more simply called the ternary resonance, recorded as f m .f r , f r The expression is as follows:

[0027]

[0028] In this embodiment, the frequency conversion controller can change the operating frequency of the switch tube in the full-bridge inverter through the existing frequency conversion control technology, so that the LLC resonant converter can maintain a higher voltage gain under low-voltage full-load working conditions. Figure 3 It can be seen that the frequency conversion controller is provided with a first reference voltage input terminal Vref1, a full-bridge LCC resonant converter output voltage acquisition terminal Vo, an S14 signal output terminal and an S23 signal output terminal. The S14 signal output terminal is used to drive the switch tubes Q1 and Q4 in the full-bridge inverter, and the S23 signal output terminal is used to drive the switch tubes Q2 and Q3 in the full-bridge inverter.

[0029] In addition, the phase-shift controller can also realize the driving of Q1 to Q4 through the existing phase-shift control technology, where Q1 and Q3 together form the leading bridge arm, while Q2 and Q4 form the lagging bridge arm. By adjusting the phase difference between the leading bridge arm and the lagging bridge arm, that is, the phase shift angle, the output voltage can be effectively adjusted. At the same time, by adjusting the duty cycle, the converter can effectively realize the output voltage control in the buck mode under the high voltage input state. Therefore, combined with Figure 3 It can also be seen that the phase-shift controller has a second reference voltage input terminal Vref2, a full-bridge LCC resonant converter output voltage acquisition terminal Vo, and an S1 signal output terminal, an S2 signal output terminal, an S3 signal output terminal, and an S4 signal output terminal for correspondingly driving the four switching tubes in the full-bridge inverter.

[0030] Combine Figure 4It can be seen that in order to realize the switching of different control modes, the mode switching module includes a first switch switching circuit, a second switch switching circuit, a third switch switching circuit and a fourth switch switching circuit. The two signal input terminals of the first switch switching circuit are respectively connected to the S1 signal output terminal and the S14 signal output terminal, and the output terminal of the first switch switching circuit is connected to the driving terminal of the switch tube Q1. The two signal input terminals of the second switch switching circuit are respectively connected to the S2 signal output terminal and the S23 signal output terminal, and the output terminal of the second switch switching circuit is connected to the driving terminal of the switch tube Q2. The two signal input terminals of the third switch switching circuit are respectively connected to the S3 signal output terminal and the S23 signal output terminal, and the output terminal of the third switch switching circuit is connected The driving end of the switch tube Q3, the two signal input ends of the fourth switch switching circuit are respectively connected to the S4 signal output end and the S14 signal output end, the output end of the fourth switch switching circuit is connected to the driving end of the switch tube Q4, and the enable end of each switch switching circuit is connected to the input voltage detection module. When the input voltage of the full-bridge LCC resonant converter is lower than the preset threshold, the S14 signal output end and the S23 signal output end control the four switch tubes in the full-bridge inverter through the mode switching module. When the input voltage of the full-bridge LCC resonant converter is greater than or equal to the preset threshold, the S1 signal output end, the S2 signal output end, the S3 signal output end and the S4 signal output end control the four switch tubes in the full-bridge inverter through the mode switching module.

[0031] In specific implementation, the output voltage Vo is set to 360V, the input voltage Vin range is 250V~500V, the preset threshold is 360V, and the rated power W RP The maximum switching frequency is 3kW. smax The frequency is 120kHz. The simulation verifies that within the wide input voltage range of 250V to 500V, the converter can flexibly switch between frequency conversion and phase shift control modes, and accurately adjust the switching frequency or phase shift angle to achieve a stable 360V voltage output.

[0032] Through the above embodiments, it can be seen that the full-bridge LLC resonant converter control circuit proposed by the present invention selects the variable frequency control mode when the input voltage is low. At this time, the switch tube operates at a full duty cycle, and the output voltage is precisely controlled by flexibly adjusting the switching frequency. When the input voltage increases, the converter switches to the phase-shift control mode, and the switch tube operates at the highest frequency preset by the system, and optimizes the output voltage regulation by adjusting the phase shift angle.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not intended to limit it. The core concept of the present invention lies in the improvement of the circuit topology. The frequency conversion control and phase shift control themselves can adopt various existing mature control algorithms. Although the circuit mentions voltage determination and mode switching, there is no improvement in the method itself. Although the present invention is described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A full-bridge LLC resonant converter control circuit, characterized in that: A frequency conversion controller, a phase shift controller and a mode switching module are configured on the full-bridge LCC resonant converter. The input end of the mode switching module is connected to an input voltage detection module. When the input voltage of the full-bridge LCC resonant converter is lower than a preset threshold, the mode switching module causes the frequency conversion controller to control the switch tube in the full-bridge LCC resonant converter to operate through switch switching. When the input voltage of the full-bridge LCC resonant converter is greater than or equal to the preset threshold, the mode switching module causes the phase shift controller to control the switch tube in the full-bridge LCC resonant converter to operate through switch switching.

2. The full-bridge LLC resonant converter control circuit according to claim 1, characterized in that: The full-bridge LCC resonant converter includes a DC power supply interface, a full-bridge inverter, an LLC resonant module, a transformer, a rectifier filter circuit and an electrical load interface. The LLC resonant module includes a resonant inductor L connected in series. r , excitation inductance L m and resonant capacitor C r , the excitation inductance L m The full-bridge inverter includes a switch tube Q1, a switch tube Q2, a switch tube Q3 and a switch tube Q4, which are connected in parallel to the primary winding of the transformer.

3. The full-bridge LLC resonant converter control circuit according to claim 2, characterized in that: Each switch tube of the full-bridge inverter is provided with an anti-parallel diode and a switch tube junction capacitor.

4. The full-bridge LLC resonant converter control circuit according to claim 2 or 3, characterized in that: The frequency conversion controller is provided with a first reference voltage input terminal, a full-bridge LCC resonant converter output voltage acquisition terminal, an S14 signal output terminal and an S23 signal output terminal. The S14 signal output terminal is used to drive the switch tubes Q1 and Q4 in the full-bridge inverter, and the S23 signal output terminal is used to drive the switch tubes Q2 and Q3 in the full-bridge inverter.

5. The full-bridge LLC resonant converter control circuit according to claim 4, characterized in that: The phase shift controller has a second reference voltage input terminal, a full-bridge LCC resonant converter output voltage acquisition terminal, and an S1 signal output terminal, an S2 signal output terminal, an S3 signal output terminal, and an S4 signal output terminal for correspondingly driving the four switching tubes in the full-bridge inverter.

6. The full-bridge LLC resonant converter control circuit according to claim 5, characterized in that: The mode switching module includes a first switch switching circuit, a second switch switching circuit, a third switch switching circuit and a fourth switch switching circuit. The two signal input terminals of the first switch switching circuit are respectively connected to the S1 signal output terminal and the S14 signal output terminal, and the output terminal of the first switch switching circuit is connected to the driving terminal of the switch tube Q1. The two signal input terminals of the second switch switching circuit are respectively connected to the S2 signal output terminal and the S23 signal output terminal, and the output terminal of the second switch switching circuit is connected to the driving terminal of the switch tube Q2. The two signal input terminals of the third switch switching circuit are respectively connected to the S3 signal output terminal and the S23 signal output terminal, and the output terminal of the third switch switching circuit is connected to the driving terminal of the switch tube Q3. The two signal input ends of the fourth switch switching circuit are respectively connected to the S4 signal output end and the S14 signal output end, the output end of the fourth switch switching circuit is connected to the driving end of the switch tube Q4, and the enable end of each switch switching circuit is connected to the input voltage detection module. When the input voltage of the full-bridge LCC resonant converter is lower than the preset threshold, the S14 signal output end and the S23 signal output end control the four switch tubes in the full-bridge inverter through the mode switching module. When the input voltage of the full-bridge LCC resonant converter is greater than or equal to the preset threshold, the S1 signal output end, the S2 signal output end, the S3 signal output end and the S4 signal output end control the four switch tubes in the full-bridge inverter through the mode switching module.

7. The full-bridge LLC resonant converter control circuit according to claim 1 or 6, characterized in that: The preset threshold is 360V.

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