A resonant converter and control method

Abstract

The application discloses a resonant converter and a control method. The resonant converter comprises a primary side inverter switching circuit (II), a primary side resonant cavity (III), a transformer (IV), a secondary side rectifier circuit (V) and a filter output circuit (VI) connected in sequence. The primary side resonant cavity (III) comprises a resonant capacitor, a resonant inductor, an excitation inductor and two switch tubes connected in reverse series. The secondary side rectifier circuit (V) comprises two power tubes and two switch tubes. In the control, when the resonant converter outputs a low voltage, a PWM control is adopted to adjust the output voltage; when the resonant converter outputs a high voltage, a phase shift control is adopted to adjust the output voltage. The resonant converter can adjust the output voltage from a low voltage to a high voltage, and the voltage adjustment range is wide. Compared with the traditional technology, the frequency adjustment range is obviously reduced, the optimization design of magnetic devices such as transformers and inductors is facilitated, and the power density and efficiency of the resonant converter are improved.

Description

Technical Field

[0001] This invention relates to the field of converter technology, and in particular to a resonant converter and its control method. Background Technology

[0002] In recent years, resonant converters have attracted the attention of scholars, researchers and engineers due to their soft switching, high efficiency and high power density, and are increasingly widely used in engineering applications such as data centers, aerospace power supplies, server power supplies and automotive power supplies.

[0003] Resonant converters include structures such as series LC resonant converters, parallel LC resonant converters, series-parallel LCC resonant converters, series-parallel LLC resonant converters, and series-parallel LCLC resonant converters. The performance of resonant converters with different structures is not the same, and their applications also differ to some extent.

[0004] Conventional DC-DC converters use pulse width modulation (PWM) control to regulate the output voltage, while resonant DC-DC converters typically use pulse frequency modulation (PFM) control. In wide-voltage applications, PFM-controlled resonant converters generally have a wide frequency adjustment range but limited gain adjustment capability, which is detrimental to the optimal design of magnetic components and reduces the converter's power density. In particular, when the switching frequency is much lower than the series resonant frequency, a large circulating current exists on the primary side of the resonant converter, severely reducing the converter's conversion efficiency. Furthermore, the resonant converter is prone to entering the capacitive region, causing the converter's soft-switching performance to fail, resulting in power system instability.

[0005] To overcome the shortcomings of PFM control, improve the voltage regulation capability of resonant converters, and narrow the frequency regulation range, scholars and technicians in this field have studied various improvement schemes. Among them, Li Ju, Ruan Xinbo, and others from Nanjing University of Aeronautics and Astronautics published a paper in 2013 entitled "Hybrid Control Strategy for Full-Bridge LLC Resonant Converters," proposing a frequency conversion-phase shift hybrid control strategy that can narrow the frequency regulation range. However, in phase-shift control mode, the soft-switching performance of the primary-side switching transistors is limited. To ensure the efficiency performance of the converter, the gain regulation capability of the resonant converter under this hybrid control strategy is limited.

[0006] In addition, inventors Wu Hongfei, Sun Wenjin, Ge Hongjuan, and Xing Yan from Nanjing University of Aeronautics and Astronautics applied for a Chinese patent in 2016 entitled "A Resonant Converter and Its Control Method." This invention discloses a resonant converter with a secondary-side active Boost rectifier circuit, which uses fixed-frequency phase-shift control or frequency-conversion-phase-shift hybrid control to regulate the output voltage. However, the resonant converter disclosed in this invention requires two auxiliary active switching transistors on the secondary side, increasing the circuit design cost and control complexity. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a resonant converter and its control method. This effectively narrows the frequency regulation range of the resonant converter under PFM control, which is beneficial for optimizing transformer design and improving the voltage regulation capability of the resonant converter, making it suitable for wide voltage applications and improving the conversion efficiency and power density of the resonant power supply system.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] In a first aspect, a resonant converter is provided, the resonant converter comprising a primary-side inverter switching circuit (II), a primary-side resonant cavity (III), a transformer (IV), a secondary-side rectifier circuit (V), and a filter output circuit (VI) connected in sequence;

[0010] The primary-side inverter switching circuit (Ⅱ) includes a primary-side first switch (S1) and a primary-side second switch (S2);

[0011] The secondary rectifier circuit (V) includes a first power transistor, a second power transistor, a fifth secondary switch transistor (S5), and a sixth secondary switch transistor (S6);

[0012] The drain of the primary-side first switching transistor (S1) is used to connect to the DC input source V. in (I) is electrically connected to the positive terminal. The source of the primary-side first switch (S1) is connected to the drain of the primary-side second switch (S2). The source of the primary-side second switch (S2) is used to connect to the DC input source V. in (Ⅰ) Negative terminal electrical connection;

[0013] The first terminal of the first power transistor and the second terminal of the second power transistor are electrically connected to the same-name terminal of the secondary winding of the transformer (Ⅳ). The source of the fifth secondary switch transistor (S5) and the drain of the sixth secondary switch transistor (S6) are electrically connected to the non-same-name terminal of the secondary winding of the transformer (Ⅳ). The second terminal of the first power transistor is electrically connected to the drain of the fifth secondary switch transistor (S5). The first terminal of the second power transistor is electrically connected to the source of the sixth secondary switch transistor (S6).

[0014] When the resonant converter outputs a low voltage, PWM control is used to adjust the output voltage. The PWM control is used to adjust the duty cycle of the primary-side switching transistor.

[0015] When the resonant converter outputs a high voltage, phase-shift control is used to adjust the output voltage. There is a phase shift angle θ between the driving pulse of the fifth switch (S5) on the secondary side and the driving pulse of the second switch (S2) on the primary side. There is the same phase shift angle θ between the driving pulse of the sixth switch (S6) on the secondary side and the driving pulse of the first switch (S1) on the primary side. The value range of the phase shift angle θ is 0°≤θ≤180°. The phase shift control is used to adjust the phase shift angle θ. The output voltage is positively correlated with the phase shift angle, and the output voltage increases with the increase of the phase shift angle.

[0016] Preferably, both the first power transistor and the second power transistor are diodes, with the first end of both the first power transistor and the second end being the anode and the second end being the cathode.

[0017] Preferably, both the first power transistor and the second power transistor are MOSFETs, with the first terminal of both the first power transistor and the second terminal being the source.

[0018] Preferably, the primary-side resonant cavity (Ⅲ) includes a resonant capacitor (C). r ), primary-side third switch (S3), primary-side fourth switch (S4), resonant inductor (L) r Magnetizing inductance (L) m );

[0019] Resonant capacitor (C) r One end of the resonant capacitor (C) is connected to the source of the first primary-side switch (S1) and the drain of the second primary-side switch (S2), and the resonant capacitor (C) is connected to the source of the first primary-side switch (S1) and the drain of the second primary-side switch (S2). r The other end of the circuit is connected to the drain of the third primary-side switch (S3) and the resonant inductor (L). r One end of the resonant inductor (L) is electrically connected. r The other end of the circuit is connected to the magnetizing inductor (L). m One end of the magnetizing inductor (L) is electrically connected to the corresponding terminal of the primary winding of transformer (Ⅳ), and the magnetizing inductor (L) m The other end of the primary winding of the transformer (Ⅳ) is electrically connected to the drain of the primary fourth switch (S4) and the source of the primary second switch (S2). The source of the primary third switch (S3) is electrically connected to the source of the primary fourth switch (S4).

[0020] Preferably, the filter output circuit (VI) includes an output filter capacitor (C). o ) and load (R o Output filter capacitor (C) o One end of the transistor is electrically connected to the drain of the fifth secondary switch (S5), and the output filter capacitor (C) is connected to the drain of the fifth secondary switch (S5). o The other end of the transistor is electrically connected to the source of the sixth secondary switch (S6), and the load (R) o The two ends of the capacitor are connected to the output filter capacitor (C).o One end and the other end.

[0021] Secondly, a control method for a resonant converter is provided, including:

[0022] When the resonant converter outputs a low voltage, PWM control is used to adjust the output voltage. The PWM control is used to adjust the duty cycle of the primary-side switching transistor.

[0023] When the resonant converter outputs a high voltage, phase-shift control is used to adjust the output voltage. There is a phase shift angle θ between the driving pulse of the fifth switch (S5) on the secondary side and the driving pulse of the second switch (S2) on the primary side. There is the same phase shift angle θ between the driving pulse of the sixth switch (S6) on the secondary side and the driving pulse of the first switch (S1) on the primary side. The value range of the phase shift angle θ is 0°≤θ≤180°. The phase shift control is used to adjust the phase shift angle θ. The output voltage is positively correlated with the phase shift angle, and the output voltage increases with the increase of the phase shift angle.

[0024] Preferably, when using PWM control to regulate the output voltage, the driving pulse of the primary side first switch (S1) is complementary to the driving pulse of the primary side third switch (S3), the driving pulse of the primary side second switch (S2) is complementary to the driving pulse of the primary side fourth switch (S4), and the driving pulse of the primary side second switch (S2) is 180° out of phase with the driving pulse of the primary side first switch (S1), and the driving pulse of the primary side fourth switch (S4) is 180° out of phase with the driving pulse of the primary side third switch (S3); the duty cycle of the driving pulse of the primary side first switch (S1) is D1, the duty cycle of the driving pulse of the primary side second switch (S2) is D2, the duty cycle of the driving pulse of the primary side third switch (S3) is D3, and the duty cycle of the driving pulse of the primary side fourth switch (S4) is D4, then D1=1-D3=D2=1-D3=D, where 0≤D≤0.5.

[0025] Preferably, when the output voltage is adjusted by phase-shift control, the duty cycle of the driving pulses of the primary side first switch (S1) and the primary side second switch (S2) is 0.5, that is, D1 = 1 - D3 = D2 = 1 - D3 = D = 0.5; the duty cycle of the secondary side fifth switch (S5) and the secondary side sixth switch (S6) is also 0.5, that is, D5 = D6 = D = 0.5.

[0026] Preferably, when the output voltage is regulated by PWM control, the fifth secondary switch (S5) and the sixth secondary switch (S6) are in the off state, and rectification is performed through the body diodes of the fifth secondary switch (S5) and the sixth secondary switch (S6).

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The circuit topology of this invention is simple, and the control method is simple and easy to implement. It can achieve both low and high output voltage regulation, improve the gain regulation capability of the resonant converter, and effectively narrow the frequency regulation range. This is beneficial for reducing the size of magnetic components and improving the efficiency and power density of the resonant converter. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the topology of the resonant converter described in this invention;

[0030] Figure 2 The driving waveform and key steady-state waveform of the resonant converter described in this invention when the output voltage is low;

[0031] Figure 3 The driving waveform and key steady-state waveform of the resonant converter described in this invention when it outputs high voltage;

[0032] Figure 4 This is another driving waveform and a key steady-state waveform when the resonant converter of the present invention outputs high voltage;

[0033] Figure 5 This is the soft-switching waveform of the primary-side switching transistor of the resonant converter described in this invention. Detailed Implementation

[0034] The technical solution of the present invention will now be described with reference to the accompanying drawings and embodiments to enable those skilled in the art to better understand the invention. However, the specific implementation of the technical solution of the present invention is not limited thereto.

[0035] like Figure 1 The diagram shown is a schematic diagram of the topology of an LLC resonant converter disclosed in this invention. The resonant converter includes a DC input source V. in (Ⅰ) Primary-side inverter switching circuit (Ⅱ) Primary-side resonant cavity (Ⅲ) Transformer (Ⅳ) Secondary-side rectifier circuit (Ⅴ) and filter output circuit (Ⅵ);

[0036] In practice, the components are as follows:

[0037] The primary-side inverter switching circuit (Ⅱ) includes a primary-side first switch (S1) and a primary-side second switch (S2);

[0038] The primary resonant cavity (Ⅲ) includes the resonant capacitor (C). r ), primary-side third switch (S3), primary-side fourth switch (S4), resonant inductor (L) r Magnetizing inductance (L) m );

[0039] Transformer (Ⅳ) is a high-frequency isolation transformer, which has the functions of voltage transformation and electrical isolation;

[0040] The secondary rectifier circuit (V) includes a first power transistor, a second power transistor, a fifth secondary switch transistor (S5), and a sixth secondary switch transistor (S6);

[0041] The filter output circuit (VI) includes the output filter capacitor (C). o ) and load (R o );

[0042] In practical implementation, both the first power transistor and the second power transistor are diodes, referred to as the first secondary rectifier diode (D1) and the second secondary rectifier diode (D2), respectively. The electrical connection relationships between the components of the resonant converter are as follows:

[0043] The drain of the primary-side first switching transistor (S1) of the primary-side inverter switching circuit (II) is connected to the DC input source V. in (Ⅰ) is electrically connected to the positive terminal, and the source of the primary-side first switch (S1) is connected to the drain of the primary-side second switch (S2) and the resonant capacitor (C). r One end of the primary side is electrically connected, and the source of the second primary-side switch (S2) is connected to the DC input source V. in (Ⅰ) Negative terminal electrical connection;

[0044] The resonant capacitance (C) of the primary resonant cavity (Ⅲ) r The other end is connected to the drain of the third primary-side switch (S3) and the resonant inductor (L). r One end of the resonant inductor (L) is electrically connected. r The other end of the circuit is connected to the magnetizing inductor (L). m One end of the magnetizing inductor (L) is electrically connected to the corresponding terminal of the primary winding of transformer (Ⅳ), and the magnetizing inductor (L) m The other end of the primary winding of the transformer (Ⅳ) is electrically connected to the non-same-name terminal of the primary winding and the source of the primary fourth switch (S4) and the source of the primary second switch (S4). The source of the primary third switch (S3) is electrically connected to the drain of the primary fourth switch (S4).

[0045] The primary winding terminal of transformer (Ⅳ) is connected to the magnetizing inductor (L) m One end of the transformer (Ⅳ) is electrically connected to the primary winding of the transformer (Ⅳ), and the non-identical terminal of the primary winding is connected to the magnetizing inductor (L). m The other end of the circuit is electrically connected, wherein the magnetizing inductor (L) m ) is the equivalent magnetizing inductance of the primary side of transformer (Ⅳ); the same-name terminal of the secondary winding of transformer (Ⅳ) is electrically connected to the anode of the first rectifier diode (D1) and the cathode of the second rectifier diode (D2) on the secondary side, and the non-same-name terminal of the secondary winding of transformer (Ⅳ) is electrically connected to the source of the fifth switch (S5) and the drain of the sixth switch (S6) on the secondary side;

[0046] In the secondary rectifier circuit (V), the anode of the first secondary rectifier diode (D1) and the cathode of the second secondary rectifier diode (D2) are electrically connected; the source of the fifth secondary switch (S5) and the drain of the sixth secondary switch (S6) are electrically connected; the cathode of the first secondary rectifier diode (D1) is electrically connected to the drain of the fifth secondary switch (S5); and the anode of the second secondary rectifier diode (D2) is electrically connected to the source of the sixth secondary switch (S6).

[0047] The output filter capacitor (C) of the filter output circuit (VI) o One end of the transistor is electrically connected to the drain of the fifth secondary switch (S5), and the output filter capacitor (C) is connected to the drain of the fifth secondary switch (S5). o The other end of the transistor is electrically connected to the source of the sixth secondary switch (S6), and the load (R) o The two ends of the capacitor are connected to the output filter capacitor (C). o One end and the other end.

[0048] In practical implementation, the resonant converter uses PWM control and phase-shift control to regulate the output voltage. The specific implementation method of the control scheme is as follows:

[0049] When the resonant converter outputs a low voltage, PWM control is used to adjust the output voltage. The driving pulse of the primary side first switch (S1) is complementary to the driving pulse of the primary side third switch (S3), the driving pulse of the primary side second switch (S2) is complementary to the driving pulse of the primary side fourth switch (S4), and the driving pulse of the primary side second switch (S2) is 180° out of phase with the driving pulse of the primary side first switch (S1), and the driving pulse of the primary side fourth switch (S4) is 180° out of phase with the driving pulse of the primary side third switch (S3). The duty cycle of the driving pulse for the first primary-side switch (S1) is D1, the duty cycle of the driving pulse for the second primary-side switch (S2) is D2, the duty cycle of the driving pulse for the third primary-side switch (S3) is D3, and the duty cycle of the driving pulse for the fourth primary-side switch (S4) is D4. Then, D1 = 1 - D3 = D2 = 1 - D3 = D, where 0 ≤ D ≤ 0.5. The PWM control is used to adjust the duty cycle of the primary-side switches. The output voltage is adjusted by adjusting the size of the duty cycle D. The output voltage is positively correlated with the duty cycle, and the output voltage increases as the duty cycle increases.

[0050] When the resonant converter outputs a high voltage, phase-shift control is used to adjust the output voltage. At this time, the duty cycle of the driving pulses of the first switch (S1) and the second switch (S2) on the primary side is 0.5, i.e., D1 = 1 - D3 = D2 = 1 - D3 = D = 0.5; the duty cycle of the fifth switch (S5) and the sixth switch (S6) on the secondary side is also 0.5, i.e., D5 = D6 = D = 0.5. There is a phase shift angle θ between the driving pulse of the fifth switch (S5) on the secondary side and the driving pulse of the second switch (S2) on the primary side, and there is also the same phase shift angle θ between the driving pulse of the sixth switch (S6) on the secondary side and the driving pulse of the first switch (S1) on the primary side. The value range of the phase shift angle θ is 0° ≤ θ ≤ 180°. The phase-shift control is used to adjust the phase shift angle θ. The output voltage is positively correlated with the phase shift angle, and the output voltage increases with the increase of the phase shift angle.

[0051] Specifically, in this embodiment, when the output voltage is less than the nominal output voltage of the resonant transformer, the resonant converter is determined to output a low voltage; when the output voltage is greater than the nominal output voltage of the resonant converter, the resonant converter is determined to output a high voltage. The nominal output voltage varies depending on the parameter design of the resonant converter, different component parameters, or application scenarios, and is not limited here. The output voltage of the resonant converter at the resonant frequency point is the rated output voltage, also known as the nominal output voltage. When the output voltage is lower than the rated output voltage, the primary-side PWM control method is used, called buck regulation, and the resonant converter outputs a low voltage with a gain adjustment range of (0,1). When the output voltage is higher than the rated output voltage, the secondary-side phase-shift control method is used, called boost regulation, and the resonant converter outputs a high voltage with a gain adjustment range of (1,2.5).

[0052] In a specific embodiment, Figure 1 Input voltage V in The voltage is 400V, and the resonant capacitor C is... r The resonant inductance L is 98.25nF. r The magnetizing inductance is 25.78uH. m The transformer has a power rating of 120uH, a turns ratio n of 25:3, a nominal output voltage of 24V, and a dead time of 200ns between drive pulses of the same bridge arm switching transistor. It should be noted that the specific circuit parameters above are merely for those skilled in the art to better understand the technical content of this invention, and are not intended to limit the technology of this invention. Those skilled in the art will clearly understand that the resonant converter can have different circuit parameters in different applications, but this will not affect the technology of this invention.

[0053] Figure 2The diagram shows the drive pulse waveform and the key steady-state operating waveform of the resonant converter when using PWM control in this embodiment. The fifth and sixth secondary-side switches (S5 and S6) are in the off state, forming a rectifier bridge through their body diodes. At this time, the resonant converter outputs a low voltage, less than the nominal output of 24V. Figure 2 In the middle, V gs1 V gs2 V gs3 V gs4 These represent the drive pulses for the primary-side first switch (S1), primary-side second switch (S2), primary-side third switch (S3), and primary-side fourth switch (S4), respectively; i Lr i Lm These represent the current flowing through the resonant inductor (L) r The resonant current and the current flowing through the magnetizing inductor (L) m The excitation current of ) i D1 i represents the current flowing through the first rectifier diode (D1) on the secondary side. D2 This represents the current waveform flowing through the second rectifier diode (D2) on the secondary side;

[0054] Figure 2 In the process, the driving pulse of the first primary switch (S1) is complementary to the driving pulse of the third primary switch (S3), the driving pulse of the second primary switch (S2) is complementary to the driving pulse of the fourth primary switch (S4), and the driving pulse of the second primary switch (S2) is 180° out of phase with the driving pulse of the first primary switch (S1), and the driving pulse of the fourth primary switch (S4) is 180° out of phase with the driving pulse of the third primary switch (S3). The duty cycle of the driving pulse for the first primary-side switch (S1) is D, the duty cycle of the driving pulse for the second primary-side switch (S2) is D, the duty cycle of the driving pulse for the third primary-side switch (S3) is 1-D, and the duty cycle of the driving pulse for the fourth primary-side switch (S4) is 1-D. The duty cycle D is positively correlated with the output voltage; the larger the duty cycle, the higher the output voltage. The output voltage is adjusted by regulating the size of the duty cycle D. When the duty cycle D is 0.335, the output voltage is 16.68V.

[0055] Figure 2 In the middle, the resonant current i Lr With excitation current i Lm The differential current transfers energy to the secondary side, realizing power transfer from the input to the output; when the resonant current i Lr Equal to the excitation current i Lm When the current in the secondary winding of the transformer drops to 0, the current flowing through the first rectifier diode (D1) and the second rectifier diode (D2) on the secondary side naturally drops to 0, and the secondary rectifier diodes achieve ZCS turn-off, which greatly reduces the reverse recovery loss of the rectifier diodes and helps to improve efficiency.

[0056] When the duty cycle D of the primary-side first switching transistor (S1) driving pulse is 0.5, the output voltage of the resonant converter is nominally 24V.

[0057] Figure 3 The following are the drive pulse waveforms and key steady-state operating waveforms of the resonant converter when phase-shift control is used in this embodiment. At this time, the resonant converter is at high voltage output, and the output voltage is greater than the nominal output of 24V. Figure 3 In the middle, V gs1 V gs2 V gs3 V gs4 V gs5 V gs6 These represent the drive pulses for the primary-side first switch (S1), primary-side second switch (S2), primary-side third switch (S3), primary-side fourth switch (S4), secondary-side fifth switch (S5), and secondary-side sixth switch (S6), respectively; Lr i Lm These represent the current flowing through the resonant inductor (L) r The resonant current and the current flowing through the magnetizing inductor (L) m The excitation current of ) i D1 i represents the current flowing through the first rectifier diode (D1) on the secondary side. D2 This represents the current waveform flowing through the second rectifier diode (D2) on the secondary side;

[0058] Figure 3 In this circuit, the driving pulses of the first primary-side switch (S1) and the third primary-side switch (S3) are complementary, and the driving pulses of the second primary-side switch (S2) and the fourth primary-side switch (S4) are complementary. Furthermore, the driving pulses of the second primary-side switch (S2) and the first primary-side switch (S1) are 180° out of phase, and the driving pulses of the fourth primary-side switch (S4) and the third primary-side switch (S3) are also 180° out of phase. The duty cycle of the driving pulses of the first primary-side switch (S1), the second primary-side switch (S2), the third primary-side switch (S3), and the fourth primary-side switch (S4) is also 0.5. The sixth and fifth secondary switches (S6 and S5) are phase-shifted relative to the first and second primary switches (S1 and S2), respectively. The larger the phase shift angle θ, the greater the voltage gain of the resonant converter and the higher the output voltage. The output voltage is adjusted by adjusting the phase shift angle θ. When the phase shift angle is 36°, the output voltage is 30.17V.

[0059] Figure 3 In the middle, the resonant current i LrWith excitation current i Lm The differential current transfers energy to the secondary side, realizing power transfer from the input to the output; when the resonant current i Lr Equal to the excitation current i Lm When the current in the secondary winding of the transformer drops to 0, the first rectifier diode (D1) and the second rectifier diode (D2) on the secondary side achieve ZCS turn-off, eliminating the reverse recovery problem and improving the conversion efficiency.

[0060] Specifically, in order to further improve the conversion efficiency, the first rectifier diode (D1) and the second rectifier diode (D2) on the secondary side can be replaced with switching transistors, and synchronous rectification control can be adopted to further reduce rectification losses and improve conversion efficiency.

[0061] Figure 4 This is another driving pulse waveform and a key steady-state operating waveform of the resonant converter when phase-shift control is used in this embodiment. At this time, the resonant converter outputs a high voltage, with the output voltage exceeding the nominal output of 24V. Figure 4 In the middle, V gs1 V gs2 V gs3 V gs4 V gs5 V gs6 These represent the drive pulses for the primary-side first switch (S1), primary-side second switch (S2), primary-side third switch (S3), primary-side fourth switch (S4), secondary-side fifth switch (S5), and secondary-side sixth switch (S6), respectively; Lr i Lm These represent the current flowing through the resonant inductor (L) r The resonant current and the current flowing through the magnetizing inductor (L) m The excitation current of ) i D1 i represents the current flowing through the first rectifier diode (D1) on the secondary side. D2 This represents the current waveform flowing through the second rectifier diode (D2) on the secondary side;

[0062] Figure 4In this circuit, the drive pulses of the first primary-side switch (S1) and the second primary-side switch (S2) are complementary. The duty cycle of the drive pulses of the first primary-side switch (S1) and the second primary-side switch (S2) is 0.5. The drive signal of the third primary-side switch (S3) is a low-level signal with a duty cycle of 0. The duty cycle of the drive pulse of the fourth primary-side switch (S4) is also 0.5. There is a phase shift angle θ between the drive pulses of the sixth secondary-side switch (S6) and the second primary-side switch (S1), and the same phase shift angle θ exists between the drive pulses of the fifth secondary-side switch (S5) and the second primary-side switch (S2). The larger the phase shift angle, the higher the output voltage. The output voltage is adjusted by adjusting the phase shift angle θ. When the phase shift angle is 36°, the output voltage is 30.17V.

[0063] Figure 4 In the middle, the resonant current i Lr With excitation current i Lm The differential current transfers energy to the secondary side, realizing power transfer from the input to the output; when the resonant current i Lr Equal to the excitation current i Lm When the current in the secondary winding of the transformer drops to 0, the first rectifier diode (D1) and the second rectifier diode (D2) on the secondary side achieve ZCS turn-off, eliminating the reverse recovery problem and improving the conversion efficiency.

[0064] This embodiment describes a resonant converter and its control method. The control method is simple and easy to implement. It adopts PWM control and phase-shift control strategies to adjust the output voltage from low voltage to high voltage, which improves the voltage regulation capability of traditional resonant converters and significantly reduces the frequency regulation range. The effective reduction of the frequency range can optimize the design of magnetic devices, reduce the size of transformers, and thus improve the power density of the power supply system.

[0065] Figure 5 This is the soft-switching waveform of the primary-side switching transistor of the resonant converter described in this embodiment. Figure 5 In the middle, V gs1 V gs2 V gs3 V gs4 These represent the drive pulses for the primary-side first switch (S1), primary-side second switch (S2), primary-side third switch (S3), and primary-side fourth switch (S4), respectively; V DS1 V DS2 V DS3 V DS4These represent the drain-source voltages of the primary-side first switch (S1), second switch (S2), third switch (S3), and fourth switch (S4), respectively. Before the drive pulse of the primary-side first switch (S1) arrives, its drain-source voltage drops to 0, and ZVS is achieved. Before the drive pulse of the primary-side second switch (S2) arrives, its drain-source voltage drops to 0, and ZVS is achieved. Before the drive pulse of the primary-side third switch (S3) arrives, its drain-source voltage drops to 0, and ZVS is achieved. Before the drive pulse of the primary-side fourth switch (S4) arrives, its drain-source voltage drops to 0, and ZVS is achieved.

[0066] In combination with the above embodiments, the primary-side switch can achieve ZVS turn-on, and the secondary-side rectifier can achieve ZCS turn-off. The resonant converter described in this embodiment has good soft-switching performance, which can effectively reduce switching losses and improve conversion efficiency.

[0067] Furthermore, since the resonant converter and its control method described in this embodiment can achieve wide voltage regulation, the resonant converter can be applied to wide voltage applications such as server power supplies and on-board chargers, thus broadening the application range of the resonant converter.

[0068] The embodiments described above are merely illustrative examples of the technical solutions and content of the present invention. It should be noted that the above embodiments should not be considered as limitations on the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, but these will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims, and should also be considered within the protection scope of the present invention.

Claims

1. A resonant converter, characterized in that: The resonant converter includes a primary-side inverter switching circuit (II), a primary-side resonant cavity (III), a transformer (IV), a secondary-side rectifier circuit (V), and a filter output circuit (VI) connected in sequence. The primary-side inverter switching circuit (Ⅱ) includes a primary-side first switch (S1) and a primary-side second switch (S2); The secondary rectifier circuit (V) includes a first power transistor, a second power transistor, a fifth secondary switch transistor (S5), and a sixth secondary switch transistor (S6). The drain of the primary-side first switching transistor (S1) is used to connect to the DC input source. V in (I) is electrically connected to the positive terminal. The source of the primary-side first switch (S1) is connected to the drain of the primary-side second switch (S2). The source of the primary-side second switch (S2) is used to connect to the DC input source. V in (I) Negative terminal electrical connection; The first terminal of the first power transistor and the second terminal of the second power transistor are electrically connected to the same-name terminal of the secondary winding of the transformer (Ⅳ). The source of the fifth secondary switch transistor (S5) and the drain of the sixth secondary switch transistor (S6) are electrically connected to the non-same-name terminal of the secondary winding of the transformer (Ⅳ). The second terminal of the first power transistor is electrically connected to the drain of the fifth secondary switch transistor (S5). The first terminal of the second power transistor is electrically connected to the source of the sixth secondary switch transistor (S6). When the resonant converter outputs a low voltage, PWM control is used to adjust the output voltage. The PWM control is used to adjust the duty cycle of the primary-side switching transistor. When the resonant converter outputs a high voltage, phase-shift control is used to adjust the output voltage. There is a phase shift angle θ between the driving pulse of the fifth switch (S5) on the secondary side and the driving pulse of the second switch (S2) on the primary side. There is the same phase shift angle θ between the driving pulse of the sixth switch (S6) on the secondary side and the driving pulse of the first switch (S1) on the primary side. The value range of the phase shift angle θ is 0°≤θ≤180°. The phase shift control is used to adjust the phase shift angle θ. The output voltage is positively correlated with the phase shift angle. The output voltage increases with the increase of the phase shift angle. The duty cycles of the first switch (S1) and the second switch (S2) on the primary side are both 0.5, i.e., D1=1-D3=D2=1-D3=D=0.5; the duty cycles of the fifth switch (S5) and the sixth switch (S6) on the secondary side are also 0.5, i.e., D5=D6=D=0.

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2. The resonant converter according to claim 1, characterized in that, Both the first power transistor and the second power transistor are diodes. The first end of both the first power transistor and the second end of both power transistors are anodes and cathodes.

3. The resonant converter according to claim 1, characterized in that, Both the first power transistor and the second power transistor are MOSFETs. The first terminal of both the first power transistor and the second terminal of both power transistors are drains, and the second terminal of both power transistors is the source.

4. The resonant converter according to any one of claims 1-3, characterized in that, The primary resonant cavity (Ⅲ) includes a resonant capacitor (C). r ), primary-side third switch (S3), primary-side fourth switch (S4), resonant inductor ( L r Magnetizing inductor ( L m ); Resonant capacitor (C) r One end of the resonant capacitor (C) is connected to the source of the first primary-side switch (S1) and the drain of the second primary-side switch (S2), and the resonant capacitor (C) is connected to the source of the first primary-side switch (S1) and the drain of the second primary-side switch (S2). r The other end of the circuit is connected to the drain of the third primary-side switch (S3) and the resonant inductor. L r One end of the resonant inductor is electrically connected to the resonant inductor. L r The other end of the circuit is connected to the magnetizing inductor ( L m One end of the magnetizing inductor is electrically connected to the corresponding end of the primary winding of transformer (Ⅳ), and the magnetizing inductor ( L m The other end of the primary winding of the transformer (Ⅳ) is electrically connected to the drain of the primary fourth switch (S4) and the source of the primary second switch (S2). The source of the primary third switch (S3) is electrically connected to the source of the primary fourth switch (S4).

5. The resonant converter according to claim 4, characterized in that, The filter output circuit (VI) includes an output filter capacitor ( C o ) and load ( R o Output filter capacitor (); C o One end of the capacitor is electrically connected to the drain of the fifth switching transistor (S5) on the secondary side, and the output filter capacitor ( C o The other end of the transistor is electrically connected to the source of the sixth secondary switch (S6), and the load ( R o The two ends of ) are respectively connected to the output filter capacitor ( C o One end and the other end.

6. A control method applied to the resonant converter according to any one of claims 1-5, characterized in that, The control method includes: When the resonant converter outputs a low voltage, PWM control is used to adjust the output voltage. The PWM control is used to adjust the duty cycle of the switching transistor on the primary side of the transformer. When the resonant converter outputs a high voltage, phase-shift control is used to adjust the output voltage. There is a phase shift angle θ between the driving pulse of the fifth switch (S5) on the secondary side and the driving pulse of the second switch (S2) on the primary side. There is the same phase shift angle θ between the driving pulse of the sixth switch (S6) on the secondary side and the driving pulse of the first switch (S1) on the primary side. The value range of the phase shift angle θ is 0°≤θ≤180°. The phase shift control is used to adjust the phase shift angle θ. The output voltage is positively correlated with the phase shift angle, and the output voltage increases with the increase of the phase shift angle.

7. The control method according to claim 6, characterized in that, When using PWM control to regulate the output voltage, the driving pulse of the first primary switch (S1) is complementary to the driving pulse of the third primary switch (S3), the driving pulse of the second primary switch (S2) is complementary to the driving pulse of the fourth primary switch (S4), and the driving pulse of the second primary switch (S2) is 180° out of phase with the driving pulse of the first primary switch (S1), and the driving pulse of the fourth primary switch (S4) is 180° out of phase with the driving pulse of the third primary switch (S3). The duty cycle of the driving pulse of the first primary switch (S1) is D1, the duty cycle of the driving pulse of the second primary switch (S2) is D2, the duty cycle of the driving pulse of the third primary switch (S3) is D3, and the duty cycle of the driving pulse of the fourth primary switch (S4) is D4. Then, D1 = 1 - D3 = D2 = 1 - D3 = D, where 0 ≤ D ≤ 0.

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8. The control method according to claim 6, characterized in that, When the output voltage is adjusted using phase-shift control, the duty cycles of the primary side first switch (S1) and the primary side second switch (S2) are both 0.5, i.e., D1=1-D3=D2=1-D3=D=0.5; the duty cycles of the secondary side fifth switch (S5) and the secondary side sixth switch (S6) are also 0.5, i.e., D5=D6=D=0.

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9. The control method according to claim 7, characterized in that, When the output voltage is regulated by PWM control, the fifth switch (S5) and the sixth switch (S6) on the secondary side are in the off state, and rectification is performed through the body diodes of the fifth switch (S5) and the sixth switch (S6).

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