An LLC resonant converter

Abstract

This invention discloses an LLC resonant converter, comprising an inverter circuit, an LLC resonant cavity, a transformer, a rectifier network, and a filter output circuit connected sequentially from input to output. The LLC resonant cavity includes a resonant inductor Lr, a magnetizing inductor Lm, a resonant capacitor Cr, a switching transistor S5, a switching transistor S6, and a clamping resonant capacitor Cs. One end of the resonant capacitor Cr is connected to the inverter circuit, and the other end of the resonant capacitor Cr is connected to one end of the resonant inductor Lr and the drain of the switching transistor S5. The other end of the resonant inductor Lr is connected to one end of the magnetizing inductor Lm and one end of the primary winding Np of the transformer T. The other end of the magnetizing inductor Lm is connected to the other end of the primary winding Np of the transformer T, the drain of the switching transistor S6, and the inverter circuit. The source of the switching transistor S6 is connected to one end of the capacitor Cs, and the other end of the capacitor Cs is connected to the source of the switching transistor S5. This invention solves the problem of non-monotonic output voltage gain caused by the resonance of the resonant inductor Lr and the parasitic capacitance of the transformer during the clamping process in PWM mode.

Description

Technical Field

[0001] This invention relates to the field of switching converter technology, and more specifically to an LLC resonant converter. Background Technology

[0002] With the rapid development of power electronics, switching converters are being used more and more widely, and people are placing higher demands on them: high power density, high reliability, and small size. LLC resonant converters, as a type of resonant converter, have many advantages, such as low noise, low stress, and low switching losses. However, traditional LLC resonant converters generally require changing the switching frequency to regulate the output voltage. When the load or input voltage fluctuates, the switching frequency needs to vary over a wide range, which brings great difficulties to the design, analysis, and control of the converter. When the required voltage gain is wide, the efficiency of traditional frequency converter-controlled LLC resonant converters decreases significantly.

[0003] For fixed-frequency controlled LLC resonant converters, the traditional control method is phase-shift control. However, because the current flowing through the switches on the leading and lagging arms of the primary side is different when they are turned on, it is difficult to achieve soft switching in the lagging arm. This is an inherent drawback of traditional phase-shift control. Under this control method, it is necessary to consider whether the lagging arm can still achieve soft switching at the maximum phase shift angle. A larger phase shift angle results in a wider gain range. Due to the aforementioned concerns, the phase shift angle is limited. Therefore, the gain range of traditional fixed-frequency phase-shift controlled LLC resonant converters cannot be widened.

[0004] Application No. 201911006674.1, entitled "A Wide Gain Control Method for a Variable Topology LLC Resonant Converter", hereinafter referred to as Background Document 1, illustrates an LLC resonant converter, such as... Figure 1 As shown, a step-down circuit is constructed by adding a bidirectional switch within the primary resonant cavity. Three operating modes are defined based on the input voltage level: in the low-voltage range, a variable frequency control (FBLLC) structure is used, changing the output voltage gain by altering the switching frequency; in the medium-voltage range, a fixed-frequency PWM control (FBLLC) structure is used, changing the output voltage gain by altering the duty cycle of the inverter circuit's switching transistor S1; and in the high-voltage range, a fixed-frequency PWM control (HBLLC) structure is used, again changing the output voltage gain by altering the duty cycle of the inverter circuit's switching transistor S1. However, due to parasitic parameters such as the transformer's parasitic capacitance, resonance occurs between the resonant capacitor and the transformer's parasitic capacitance during the clamping transistor's turn-on phase of the PWM control process. This resonance causes energy transfer to the secondary side during the clamping transistor's turn-off phase. Furthermore, the uncertainty of the resonant state at the end of the clamping phase, corresponding to the main transistor's turn-on, leads to non-monotonicity in the output voltage gain, negatively impacting the converter design. Summary of the Invention

[0005] The present invention aims to overcome at least one of the defects in the prior art and provide an LLC resonant converter with a wide gain range, thereby solving the problem of gain non-monotonicity in existing LLC resonant converters.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, an LLC resonant converter is provided, comprising an inverter circuit, an LLC resonant cavity, a transformer, a rectifier network, and a filter output circuit connected sequentially from input to output; the LLC resonant cavity includes a resonant inductor Lr, a magnetizing inductor Lm, a resonant capacitor Cr, a switching transistor S5, a switching transistor S6, and a clamping resonant capacitor Cs.

[0008] One end of the resonant capacitor Cr is connected to the inverter circuit, and the other end of the resonant capacitor Cr is connected to one end of the resonant inductor Lr and the drain of the switching transistor S5. The other end of the resonant inductor Lr is connected to one end of the magnetizing inductor Lm and one end of the primary winding Np of the transformer T. The other end of the magnetizing inductor Lm is connected to the other end of the primary winding Np of the transformer T, the drain of the switching transistor S6, and the inverter circuit. The source of the switching transistor S6 is connected to one end of the clamping resonant capacitor Cs, and the other end of the clamping resonant capacitor Cs is connected to the source of the switching transistor S5.

[0009] The LLC resonant converter uses a frequency conversion PFM control with an FBLLC structure in the low-voltage input range, and changes the output voltage gain by changing the switching frequency.

[0010] The LLC resonant converter uses fixed-frequency PWM control with an FBLLC structure in the high-voltage input voltage range, and changes the output voltage gain by changing the duty cycle of the inverter circuit switching transistors.

[0011] Preferably, the resonant capacitor Cr is greater than or equal to 5 times the clamping resonant capacitor Cs.

[0012] Preferably, the inverter circuit is a full-bridge inverter circuit, including four switching transistors S1, S2, S3, and S4. The drain of switching transistor S1 is connected to the drain of switching transistor S2 and is used to connect to the positive terminal of the input power supply Vin. The source of switching transistor S1 is connected to the drain of switching transistor S3 and one end of the resonant capacitor Cr. The source of switching transistor S2 is connected to the drain of switching transistor S4, the drain of switching transistor S6, the other end of the magnetizing inductor Lm, and the other end of the primary winding Np of transformer T. The source of switching transistor S4 is connected to the source of switching transistor S3 and is used to connect to the negative terminal of the input power supply Vin.

[0013] Preferably, the inverter circuit is a half-bridge inverter circuit, including a switch S1 and a switch S2. The drain of switch S1 is used to connect to the positive terminal of the input power supply Vin. The source of switch S1 is connected to the drain of switch S2 and one end of the resonant capacitor Cr. The source of switch S2 is connected to the other end of the magneto-inductance Lm, the other end of the primary winding of transformer T, and the drain of switch S6, and then connected to the negative terminal of the input Vin.

[0014] Preferably, the rectifier network is a bridge rectifier network, including four power transistors D1, D2, D3, and D4. The first end of power transistor D1 is connected to the second end of power transistor D3 and one end of the secondary winding Ns of transformer T. The second end of power transistor D1 is connected to the second end of power transistor D2 and one end of the filter output circuit. The first end of power transistor D2 is connected to the second end of power transistor D4 and the other end of the secondary winding Ns of transformer T. The first end of power transistor D3 is connected to the first end of power transistor D4 and the other end of the filter output circuit.

[0015] Preferably, the four power transistors D1, D2, D3, and D4 are all diodes, with their first terminals being anodes and their second terminals being cathodes.

[0016] Preferably, the four power transistors D1, D2, D3, and D4 are all MOSFETs, with their first terminals being the source and their second terminals being the drain.

[0017] Preferably, the rectifier network is a full-wave rectifier network, including diode D1 and diode D2. The anode of diode D1 is connected to one end of the secondary winding Ns of transformer T, and the cathode of diode D1 is connected to one end of the filter output circuit. The anode of diode D2 is connected to the other end of the secondary winding Ns of transformer T, and the cathode of diode D2 is connected to one end of the filter output circuit. The center tap of the secondary winding Ns of transformer T is connected to the other end of the filter output circuit.

[0018] Secondly, an LLC resonant converter is provided, comprising an inverter circuit, an LLC resonant cavity, a transformer, a rectifier network, and a filter output circuit connected sequentially from input to output; the inverter circuit includes four switching transistors S1 to S4; the LLC resonant cavity includes a resonant inductor Lr, a magnetizing inductor Lm, a resonant capacitor Cr, a switching transistor S5, a switching transistor S6, and a clamping resonant capacitor Cs; the rectifier network includes four power transistors D1, D2, D3, and D4;

[0019] The drain of switch S1 is connected to the drain of switch S2 to connect to the positive terminal of the input power supply Vin. The source of switch S1 is connected to the drain of switch S3 and one end of resonant capacitor Cr. The other end of resonant capacitor Cr is connected to one end of resonant inductor Lr and the drain of switch S5. The other end of resonant inductor Lr is connected to one end of magnetizing inductor Lm and one end of primary winding Np of transformer T. The source of switch S2 is connected to the drains of switch S4 and S6, the other end of magnetizing inductor Lm, and the other end of primary winding Np of transformer T. The source of switch S6 is connected to the clamping resonant... One end of capacitor Cs and the other end of clamping resonant capacitor Cs are connected to the source of switching transistor S5. The source of switching transistor S4 is connected to the source of switching transistor S3 and then used to connect to the negative terminal of input power supply Vin. The first end of power transistor D1 is connected to the second end of power transistor D3 and one end of the secondary winding Ns of transformer T. The second end of power transistor D1 is connected to the second end of power transistor D2 and one end of the filter output circuit. The first end of power transistor D2 is connected to the second end of power transistor D4 and the other end of the secondary winding Ns of transformer T. The first end of power transistor D3 is connected to the first end of power transistor D4 and the other end of the filter output circuit.

[0020] The LLC resonant converter uses a frequency conversion PFM control with an FBLLC structure in the low-voltage input range, and changes the output voltage gain by changing the switching frequency.

[0021] The LLC resonant converter uses fixed-frequency PWM control with an FBLLC structure in the high-voltage input voltage range, and changes the output voltage gain by changing the duty cycle of the inverter circuit switching transistor S1.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] In this invention, switching transistors S5 and S6 are located on the primary side of the transformer, eliminating the need to consider isolation drive issues. Furthermore, by connecting the clamping resonant capacitor Cs in series between switching transistors S5 and S6, the existing step-down circuit is modified, reducing the influence of parasitic parameters such as transformer parasitic capacitance. This solves the problem of non-monotonic output voltage gain caused by the resonance between the resonant inductor Lr and the transformer parasitic capacitance during clamping in PWM mode.

[0024] This invention combines variable frequency PFM control with fixed frequency PWM control, thereby enabling the circuit to achieve a wider voltage gain range and higher efficiency, making the converter suitable for applications requiring a wider gain range.

[0025] The control method of this invention has a small frequency conversion range, low requirements for magnetic components such as transformers and inductors, and no leading or lagging bridge arms. Compared with single frequency conversion control, this control method has a wide voltage gain range and high efficiency. Attached Figure Description

[0026] Figure 1 The schematic diagram of the LLC resonant converter shown in background document 1;

[0027] Figure 2 The actual gain curve of the LLC resonant converter is shown in background document 1;

[0028] Figure 3 This is a schematic diagram of an LLC resonant converter according to a preferred embodiment of the present invention;

[0029] Figure 4 The actual gain curve of the LLC resonant converter in a preferred embodiment of the present invention;

[0030] Figure 5 The main operating waveforms of the LLC resonant converter in the preferred embodiment of the present invention when operating in FBLLC frequency conversion mode;

[0031] Figures 6-11 The equivalent circuit diagrams of each switching mode of the LLC resonant converter in the preferred embodiment of the present invention when it operates in FBLLC frequency conversion mode;

[0032] Figure 12 The main operating waveforms of the LLC resonant converter in the preferred embodiment of the present invention when operating in the FBLLC variable duty cycle mode;

[0033] Figures 13-18 The equivalent circuit diagrams of each switching mode of the LLC resonant converter in the preferred embodiment of the present invention when it operates in the FBLLC variable duty cycle mode. Detailed Implementation

[0034] like Figure 3 As shown, the LLC resonant converter in this embodiment includes an inverter circuit 10, an LLC resonant cavity 20, a transformer T, a rectifier network 30, and a filter output circuit 40 connected sequentially from input to output. In the figure, Vin is the input power supply of the converter, and Ro is the output load Ro of the converter.

[0035] LLC resonant cavity 20 includes resonant inductor Lr, magnetizing inductor Lm, resonant capacitor Cr, switching transistor S5, switching transistor S6, and capacitor Cs.

[0036] The rectifier network 30 can be a full-bridge rectifier circuit, including four power transistors D1, D2, D3, and D4. The first terminal of power transistor D1 is connected to the second terminal of power transistor D3 and one end of the secondary winding Ns of transformer T. The second terminal of power transistor D1 is connected to the second terminal of power transistor D2 and one end of the filter output circuit 40. The first terminal of power transistor D2 is connected to the second terminal of power transistor D4 and the other end of the secondary winding Ns of transformer T. The first terminal of power transistor D3 is connected to the first terminal of power transistor D4 and the other end of the filter output circuit 40. Alternatively, it can be a full-wave rectifier circuit, including diode D1 and diode D2. 2. The anode of diode D1 is connected to one end of the secondary winding Ns of transformer T, and the cathode of diode D1 is connected to one end of the filter output circuit 40. The anode of diode D2 is connected to the other end of the secondary winding Ns of transformer T, and the cathode of diode D2 is connected to one end of the filter output circuit 40. The center tap of the secondary winding Ns of transformer T is connected to the other end of the filter output circuit 40. Specifically, all four power transistors D1 to D4 are diodes, with the first end being the anode and the second end being the cathode; or all four power transistors D1 to D4 are MOSFETs, with the first end being the source and the second end being the drain.

[0037] Specifically, the inverter circuit 10 can be a full-bridge inverter circuit, including switching transistors S1, S2, S3, and S4. The drain of switching transistor S1 is connected to the drain of switching transistor S2 and then used to connect to the positive terminal of the input power supply Vin. The source of switching transistor S1 is connected to the drain of switching transistor S3 and one end of the resonant capacitor Cr. The source of switching transistor S2 is connected to the drain of switching transistor S4, the drain of switching transistor S6, the other end of the magnetizing inductor Lm, and the other end of the primary winding Np of transformer T. The source of switching transistor S4 is connected to the source of switching transistor S3 and then used to connect to the input power supply Vi. The negative terminal of n; it can also be a half-bridge inverter circuit (not shown in the figure), which only includes switching transistors S1 and S2. The drain of switching transistor S1 is used to connect to the positive terminal of the input power supply Vin. The source of switching transistor S1 is connected to the drain of switching transistor S2 and one end of the resonant capacitor Cr. The source of switching transistor S2 is connected to the other end of the magneto-inductance Lm, the other end of the primary winding of transformer T, and the drain of switching transistor S6, and then connected to the negative terminal of the input Vin. When a half-bridge inverter circuit is used on the primary side, the number of switching transistors on the primary side is reduced from 6 to 4, saving the number of components, which is suitable for small and medium power applications.

[0038] Specifically, the filter output circuit 40 is the output filter capacitor Co.

[0039] In the specific implementation, inverter circuit 10 is a full-bridge inverter circuit, and switching transistors S1-S4 are all MOSFETs. Rectifier network 30 is a full-bridge rectifier circuit, and power transistors D1, D2, D3, and D4 are all diodes, hereinafter referred to as diodes D1, D2, D3, and D4. The drain of switching transistor S1 is connected to the drain of switching transistor S2 and the positive terminal of the input power supply Vin. The source of switching transistor S1 is connected to the drain of switching transistor S3 and one end of resonant capacitor Cr. The other end of resonant capacitor Cr is connected to one end of resonant inductor Lr and the drain of switching transistor S5. The other end of resonant inductor Lr is connected to one end of magnetizing inductor Lm and the same-name terminal of the primary winding Np of transformer T. The opposite-name terminal of transformer T is connected to the other end of magnetizing inductor Lm and the same-name terminal of switching transistor S2. The source of the transistor, the drain of the switching transistor S4, the drain of the switching transistor S6, the source of the switching transistor S4 is connected to the source of the switching transistor S3 and the negative terminal of the input power supply Vin, the source of the switching transistor S6 is connected to one end of the capacitor Cs, and the other end of the capacitor Cs is connected to the source of the switching transistor S5; the same-name terminal of the secondary winding Ns of the transformer T is connected to the anode of the diode D1 and the cathode of the diode D3, the cathode of the diode D1 is connected to the cathode of the diode D2, one end of the secondary output filter capacitor Co and one end of the output load Ro, the other end of the output load Ro is connected to the other end of the secondary output filter capacitor Co, the anode of the diode D3 and the anode of the diode D4, the cathode of the diode D4 is connected to the anode of the diode D2 and the opposite-name terminal of the secondary winding Ns of the transformer T.

[0040] The input voltage range is divided into two voltage segments, high and low, corresponding to two operating modes. The LLC resonant converter adopts frequency conversion control with an FBLLC structure in the low input voltage segment, and changes the output voltage gain by changing the switching frequency.

[0041] The resonant converter uses a fixed-frequency PWM control with an FBLLC structure in the middle voltage range of the input voltage, and changes the output voltage gain by changing the duty cycle of the inverter circuit switching transistor S1.

[0042] In this embodiment, the LLC resonant converter has a resonant capacitor Cr that is greater than or equal to 5 times the clamping resonant capacitor Cs. Specifically, the resonant capacitor Cr can be equal to 5 times the clamping resonant capacitor Cs, or it can be equal to 10 times the clamping resonant capacitor Cs, or it can be greater than 10 times the clamping resonant capacitor Cs; no limitation is made here. When the switches S5 and S6 are turned on, the resonant current stores energy in the loop during the circulating current phase in the circuit composed of the transformer magnetizing inductance Lm, the resonant inductance Lr, the clamping resonant capacitor Cs, and the switches S5 and S6. Since the capacitance Cs is much smaller than the resonant capacitance Cr, the current will hardly flow through the resonant capacitance Cr. At the same time, due to the presence of the clamping resonant capacitance Cs, the turn-off DS voltage of the switching transistors S1, S2, S3, S4, S5, and S6 is lower, which significantly reduces the turn-off loss and weakens the influence of parasitic parameters such as transformer parasitic capacitance. This solves the problem of non-monotonic output voltage gain caused by the resonance of the resonant inductor Lr and the transformer parasitic capacitance during the clamping process in PWM mode. Therefore, the LLC resonant converter described in this embodiment can further improve the circuit's operating efficiency.

[0043] The aforementioned wide-gain-range LLC resonant converter can be controlled using the following frequency conversion method:

[0044] When the input voltage is in the low voltage range, the inverter circuit operates in the frequency conversion PFM control mode (FBLLC frequency conversion mode). Switches S5 and S6 are continuously off, while switches S1, S2, S3, and S4 maintain a fixed duty cycle of 0.5. Switches S1 and S2 are complementary in conduction, while switches S1 and S4 are simultaneously turned on and off, and switches S2 and S3 are simultaneously turned on and off. The output voltage V0 is controlled by adjusting the switching frequency of switches S1 to S4. The smaller the switching frequency, the greater the output voltage gain.

[0045] The aforementioned wide-gain-range variable-topology LLC resonant converter can be controlled using the following fixed-frequency PWM method:

[0046] When the input voltage is in the high-voltage range, the inverter circuit operates in fixed-frequency PWM control mode (FBLLC variable duty cycle mode). The switching frequencies of switches S1 to S6 are equal and fixed. Switches S1 and S5 conduct complementaryly, as do switches S2 and S6. Switches S1 and S4 are simultaneously turned on and off, as are switches S2 and S3. The duty cycle of switch S1 is equal to that of switch S2, both not greater than 0.5 and with a phase difference of 180°. The duty cycle of switch S5 is equal to that of switch S6, both not less than 0.5 and with a phase difference of 180°. The output voltage V0 is controlled by adjusting the duty cycle of switch S1 (the conduction time of switches S5 and S6 changes synchronously with the change in the duty cycle of switch S1). The larger the duty cycle of switch S1, the greater the output voltage gain.

[0047] In practical implementation, a reasonable dead time must be set between the switching signals of switching transistors S1 and S5 to achieve soft switching of switching transistors S1, S4, and S5; a reasonable dead time must also be set between the switching signals of switching transistors S2 and S6 to achieve soft switching of switching transistors S2, S3, and S6. Coss1 to Coss6 represent the output capacitances up to the sixth switching transistor S1 to S6, respectively.

[0048] The following is combined Figure 5 The working process of the LLC resonant converter when using variable frequency PFM control and fixed frequency PWM control is described in detail.

[0049] In this embodiment, the parameters are selected as follows: Lr = 45uH, Lm = 315uH, Cr = 100nF, Cs = 20nF, input voltage range 280~500VDC, and transformer primary-secondary turns ratio is 46:3.

[0050] When the input voltage of the converter is between 280V and 370V, the converter operates in FBLLC inverter mode, at which time the switching transistors S5 and S6 remain off. Figure 4 This is a waveform diagram showing the main operating waveforms of this resonant converter when frequency conversion control is used. Vgs1 / 4 is the drive signal for switches S1 and S4, Vgs2 / 3 is the drive signal for switches S2 and S3, and Vc, iLr, iLm, iD1 / 4, and iD2 / 3 represent the voltage across Cr, the current through Lr, the current through Lm, the current through rectifier diodes D1 and D4, and the current through rectifier diodes D2 and D3, respectively. The converter has six switching modes within half a cycle, as shown below. Figures 6-11 As shown in the waveform diagram, the operating modes of the second half of the LLC resonant converter are symmetrical with those of the first half of the cycle. Generally, the description of an LLC resonant converter only needs to describe half a cycle.

[0051] Switching mode 1 [t0, t1]: as shown in the appendix Figure 6 As shown, at time t0, switching transistors S1 and S4 are turned on with zero voltage; rectifier diodes D1 and D4 are turned on, and the current flowing through the diodes is proportional to the difference between the resonant current and the magnetizing current; the voltage across the magnetizing inductor Lm is clamped to nV by the output. O (n is the transformer turns ratio); the primary resonant inductor Lr and the resonant capacitor Cr participate in the resonance, the resonant current iLr is a standard sine wave and is negative, the excitation inductor current iLm increases linearly, but is less than the resonant current iLr;

[0052] Switching mode 2 [t1, t2]: as attached Figure 7 As shown, at time t1, the resonant current iLr crosses zero; rectifier diodes D1 and D4 continue to conduct; the voltage across the magnetizing inductor Lm is clamped to nVo by the output; the primary resonant inductor Lr and the resonant capacitor Cr participate in resonance, the resonant current iLr is a standard sine wave and is positive, the magnetizing inductor current iLm increases linearly, but is still less than the resonant current iLr;

[0053] Switching mode 3 [t2, t3]: as attached Figure 8 As shown, at time t2, switches S1 and S4 remain on, and the magnetizing current ILm becomes positive at the zero point; rectifier diodes D1 and D4 continue to conduct; the voltage across the magnetizing inductor Lm is clamped to nVo by the output; the primary resonant inductor Lr and resonant capacitor Cr participate in resonance, and the resonant current iLr is a standard sine wave and is positive; the magnetizing inductor current iLm increases linearly, but is still less than the resonant current iLr.

[0054] Switching mode 4 [t3, t4]: as attached Figure 9 As shown, at time t3, the excitation current ILm is equal to the resonant current ILr, and the excitation inductor is no longer clamped (the transformer has no energy transfer); the current flowing through the rectifier diode D1 naturally passes 0, and the secondary rectifier diodes D1 and D4 are turned off with zero current, avoiding the diode reverse recovery problem; the primary resonant inductor Lr, resonant capacitor Cr, and excitation inductor Lm participate in resonance together, and the load energy is completely provided by the output capacitor Co;

[0055] Switching mode 5 [t4, t5]: as attached Figure 10 As shown, this period is the dead time, during which the magnetizing current and the resonant current iLr are equal and remain constant, and the secondary rectifier diodes are still in reverse cutoff state; all power transistors are turned off; the primary resonant inductor Lr, resonant capacitor Cr, and magnetizing inductor Lm participate in resonance together; the resonant current iLr supplies power to the output capacitors C of switching transistors S1 and S4. oss1 C oss4Charging is applied to the output capacitor C of switching transistors S2 and S3. oss2 C oss3 During discharge, the load energy is entirely provided by the output capacitor Co;

[0056] Switching mode 6 [t5, t6]: as attached Figure 11 As shown, this period is still the dead time, and the output capacitors C of switches S2 and S3 are... oss2 C oss3 When the voltage across the terminals drops to 0, the body diodes of switches S2 and S3 conduct, providing the conditions for switches S2 and S3 to achieve zero-voltage turn-on; at time t6, switches S2 and S3 achieve ZVS, and the circuit enters the second half of the cycle.

[0057] When the input voltage of the converter is between 370V and 500V, the converter operates in FBLLC variable duty cycle mode. Figure 12 This diagram shows the main operating waveforms of this resonant converter when using fixed-frequency PWM control. Vgs1 / 4 represents the drive signals for switches S1 and S4, Vgs2 / 3 represents the drive signals for switches S2 and S3, Vgs5 represents the drive signal for switch S5, and Vgs6 represents the drive signal for switch S6. Vcs, Vcr, iLr, and iLm represent the voltages across Cs, Cr, Lr, and Lm, respectively. Vds1 / 4 represents the DS voltages of switches S1 and S4, Vds2 / 3 represents the DS voltages of switches S2 and S3, Vds5 represents the DS voltage of switch S5, and Vds6 represents the DS voltage of switch S6. Id1 / d4 and Id2 / d3 represent the currents of rectifier diodes D1 and D4, and D2 and D3, respectively. Figure 10 It can be seen that when the switches S1, S2, S3, and S4 of this invention are turned off, the DS voltage rises more slowly, and the turn-off loss is lower. The converter also has six switching modes within this half-cycle, as follows: Figures 13-18 As shown.

[0058] Switching mode 1 [t0, t1]: as shown in the appendix Figure 13 As shown, before time t0, switch S6 is already turned on, switch S5 is turned off, and its body diode is reverse-biased and cut off; at time t0, switches S1 and S4 are turned on with zero voltage; rectifier diodes D1 and D4 are turned on, and the current flowing through the diodes is proportional to the difference between the resonant current and the magnetizing current; the voltage across the magnetizing inductor Lm is clamped to nV by the output. O (n is the transformer turns ratio); the primary resonant inductor Lr and the resonant capacitor Cr participate in the resonance, the resonant current iLr is a standard sine wave and is negative, the excitation inductor current iLm increases linearly, but is less than the resonant current iLr;

[0059] Switching mode 2 [t1, t2]: as attached Figure 14 As shown, at time t1, the resonant current iLr crosses zero; rectifier diodes D1 and D4 continue to conduct; the voltage across the magnetizing inductor Lm is clamped to nVO by the output; the primary resonant inductor Lr and the resonant capacitor Cr participate in resonance, the resonant current iLr is a standard sine wave and is positive, the magnetizing inductor current iLm increases linearly, but is less than the resonant current iLr;

[0060] Switching mode 3 [t2, t3]: as attached Figure 15 As shown, at time t2, switches S1 and S4 are turned off, and the resonant current iLr is still greater than the magnetizing inductor current iLm, so rectifier diodes D1 and D4 continue to conduct; the resonant current iLr supplies power to the output capacitor C of switches S1 and S4. oss1 C oss4 Charging, supplying power to the output capacitor C of switching transistors S2 and S3. oss2 C oss3 Discharge, to the output capacitor C of switch S5. oss5 Discharge, discharging capacitor Cs; when capacitor C... oss5 When the voltage across the two terminals drops to zero, the body diode of the switching transistor S5 turns on, providing the conditions for the switching transistor S5 to achieve zero-voltage turn-on;

[0061] Switching mode 4 [t3, t4]: as attached Figure 16 As shown, at time t3, switch S5 turns on with zero voltage, capacitor CS resonates with inductor Lr, capacitor Cs discharges, resonant current iLr decreases, switch S6 and rectifier diodes D1 and D4 continue to conduct; magnetizing inductor Lm is still clamped by output voltage, and magnetizing current iLm continues to increase linearly.

[0062] Switching mode 5 [t4, t5]: as attached Figure 17 As shown, at time t4, the resonant current iLr is equal to the magnetizing current iLm. The current flowing through rectifier diode D1 naturally passes zero, and the secondary rectifier diodes D1 and D4 are turned off with zero current to avoid the diode reverse recovery problem. Switches S5 and S6 continue to conduct, the magnetizing current and the resonant current iLr are equal, and Lr, Lm and Cs resonate. Since the resonant frequency is low, the current change is not obvious.

[0063] Switching mode 6 [t5, t6]: as attached Figure 18 As shown, at time t5, switch S6 is turned off while switch S5 remains on; the resonant current iLr equals the magnetizing current iLm, and the secondary rectifier diode remains in reverse cutoff; the resonant current iLr supplies power to the output capacitor C of switches S1 and S4. oss1 C oss4Charging is applied to the output capacitor C of switching transistors S2 and S3. oss2 C oss3 Discharge, to the output capacitor C of switch S6. oss6 Charging; when capacitor C oss2 C oss3 When the voltage across the terminals drops to 0, the body diodes of switches S2 and S3 conduct, providing the conditions for switches S2 and S3 to achieve zero-voltage turn-on; at time t6, switches S2 and S3 achieve ZVS, and the circuit enters the second half of the cycle.

[0064] As can be seen from the above description of the converter's operation process, all switching devices in the converter can achieve zero-voltage turn-on, and the rectifier devices on the secondary side can also achieve zero-current turn-off. There is no problem of diode reverse recovery. All switching devices can achieve soft switching. The DS voltage rise of switching transistors S1, S2, S3, S4, and S5, S6 during turn-off is more slow, effectively reducing turn-off losses.

[0065] In this embodiment, the bidirectional switches (switching transistors S5 and S6) are located on the primary side of the transformer, eliminating the need to consider isolation drive issues and reducing the difficulty of circuit drive design. Therefore, overall, the LLC resonant converter structure of this invention reduces the design difficulty of LLC resonant converters.

[0066] This embodiment achieves output voltage regulation by controlling the duty cycle, realizing fixed-frequency PWM control, which facilitates the design of magnetic components such as transformers, reduces the difficulty of circuit drive design and device stress, realizes soft switching of all switching devices, reduces the turn-off losses of all switching transistors, and eliminates the leading and lagging bridge arms. It boasts a wide voltage gain range, high efficiency, and high power density. The inverter circuit can employ either a full-bridge or half-bridge configuration, achieving a wider voltage gain range than fixed-frequency phase-shift converters, meeting the needs of wide voltage gain range conversion applications. In summary, the converter of this invention exhibits excellent overall performance.

[0067] The above description of the embodiments is only for the purpose of helping to understand the inventive concept of this application and is not intended to limit the present invention. For example, the switching transistors S5 and S6 of the present invention can also be common-drain reverse series (each controlling the timing remains unchanged), the rectifier network can also be other full-wave rectifier circuits, and the above rectifier diodes can also be replaced with switching transistors, etc. In short, for those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made without departing from the principle of the present invention should be included within the protection scope of the present invention.

Claims

1. An LLC resonant converter, comprising an inverter circuit, an LLC resonant cavity, a transformer, a rectifier network, and a filter output circuit connected sequentially from input to output; characterized in that, The LLC resonant cavity includes a resonant inductor Lr, a magnetizing inductor Lm, a resonant capacitor Cr, a switching transistor S5, a switching transistor S6, and a clamping resonant capacitor Cs. One end of the resonant capacitor Cr is connected to the inverter circuit, and the other end of the resonant capacitor Cr is connected to one end of the resonant inductor Lr and the drain of the switching transistor S5. The other end of the resonant inductor Lr is connected to one end of the magnetizing inductor Lm and one end of the primary winding Np of the transformer T. The other end of the magnetizing inductor Lm is connected to the other end of the primary winding Np of the transformer T, the drain of the switching transistor S6, and the inverter circuit. The source of the switching transistor S6 is connected to one end of the clamping resonant capacitor Cs, and the other end of the clamping resonant capacitor Cs is connected to the source of the switching transistor S5. The LLC resonant converter uses frequency conversion PFM control in the low-voltage input range, and changes the output voltage gain by changing the switching frequency. The LLC resonant converter uses fixed-frequency PWM control in the high-voltage input range, and changes the output voltage gain by changing the duty cycle of the inverter circuit switching transistors.

2. The LLC resonant converter according to claim 1, characterized in that, The clamping resonant capacitor Cs is much smaller than the resonant capacitor Cr.

3. The LLC resonant converter according to claim 1, characterized in that, The inverter circuit is a full-bridge inverter circuit, including four switching transistors S1 to S4. The drain of switching transistor S1 is connected to the drain of switching transistor S2 and is used to connect to the positive terminal of the input power supply Vin. The source of switching transistor S1 is connected to the drain of switching transistor S3 and one end of the resonant capacitor Cr. The source of switching transistor S2 is connected to the drain of switching transistor S4, the drain of switching transistor S6, the other end of the magnetizing inductor Lm, and the other end of the primary winding Np of transformer T. The source of switching transistor S4 is connected to the source of switching transistor S3 and is used to connect to the negative terminal of the input power supply Vin.

4. The LLC resonant converter according to claim 1, characterized in that, The inverter circuit is a half-bridge inverter circuit, including switching transistor S1 and switching transistor S2. The drain of switching transistor S1 is used to connect to the positive terminal of the input power supply Vin. The source of switching transistor S1 is connected to the drain of switching transistor S2 and one end of the resonant capacitor Cr. The source of switching transistor S2 is connected to the other end of the magneto-inductor Lm, the other end of the primary winding of transformer T, and the drain of switching transistor S6, and then connected to the negative terminal of the input Vin.

5. The LLC resonant converter according to any one of claims 1-4, characterized in that, The rectifier network is a bridge rectifier network, including four power transistors D1 to D4. The first end of power transistor D1 is connected to the second end of power transistor D3 and one end of the secondary winding Ns of transformer T. The second end of power transistor D1 is connected to the second end of power transistor D2 and one end of the filter output circuit. The first end of power transistor D2 is connected to the second end of power transistor D4 and the other end of the secondary winding Ns of transformer T. The first end of power transistor D3 is connected to the first end of power transistor D4 and the other end of the filter output circuit.

6. The LLC resonant converter according to claim 5, characterized in that, The four power transistors D1 to D4 are all diodes, with the first end being the anode and the second end being the cathode.

7. The LLC resonant converter according to claim 5, characterized in that, The four power transistors D1 to D4 are all MOSFETs, with the first terminal being the source and the second terminal being the drain.

8. The LLC resonant converter according to any one of claims 1-4, characterized in that, The rectifier network is a full-wave rectifier network, including diodes D1 and D2. The anode of diode D1 is connected to one end of the secondary winding Ns of transformer T, and the cathode of diode D1 is connected to one end of the filter output circuit. The anode of diode D2 is connected to the other end of the secondary winding Ns of transformer T, and the cathode of diode D2 is connected to one end of the filter output circuit. The center tap of the secondary winding Ns of transformer T is connected to the other end of the filter output circuit.

9. An LLC resonant converter, comprising an inverter circuit, an LLC resonant cavity, a transformer, a rectifier network, and a filter output circuit connected sequentially from input to output; characterized in that, The inverter circuit includes four switching transistors S1 to S4; the LLC resonant cavity includes a resonant inductor Lr, a magnetizing inductor Lm, a resonant capacitor Cr, a switching transistor S5, a switching transistor S6, and a clamping resonant capacitor Cs; the rectifier network includes four power transistors D1 to D4. The drain of switch S1 is connected to the drain of switch S2 to connect to the positive terminal of the input power supply Vin. The source of switch S1 is connected to the drain of switch S3 and one end of resonant capacitor Cr. The other end of resonant capacitor Cr is connected to one end of resonant inductor Lr and the drain of switch S5. The other end of resonant inductor Lr is connected to one end of magnetizing inductor Lm and one end of primary winding Np of transformer T. The source of switch S2 is connected to the drains of switch S4 and S6, the other end of magnetizing inductor Lm, and the other end of primary winding Np of transformer T. The source of switch S6 is connected to the clamping resonant... One end of capacitor Cs and the other end of clamping resonant capacitor Cs are connected to the source of switching transistor S5. The source of switching transistor S4 is connected to the source of switching transistor S3 and then used to connect to the negative terminal of input power supply Vin. The first end of power transistor D1 is connected to the second end of power transistor D3 and one end of the secondary winding Ns of transformer T. The second end of power transistor D1 is connected to the second end of power transistor D2 and one end of the filter output circuit. The first end of power transistor D2 is connected to the second end of power transistor D4 and the other end of the secondary winding Ns of transformer T. The first end of power transistor D3 is connected to the first end of power transistor D4 and the other end of the filter output circuit. The LLC resonant converter uses frequency conversion PFM control in the low-voltage input range, and changes the output voltage gain by changing the switching frequency. The LLC resonant converter uses fixed-frequency PWM control in the high-voltage input voltage range, and changes the output voltage gain by changing the duty cycle of the inverter circuit switching transistor S1.

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