Starting method of resonant converter and LLC resonant converter

Abstract

The invention relates to the technical field of resonant converters, and discloses a starting method of a resonant converter and an LLC resonant converter, and the method comprises the steps: in the starting process of the resonant converter, obtaining an output electrical parameter value of the resonant converter, and obtaining a PWM signal of each power electronic switch of a bridge inverter circuit according to the electrical parameter value; for each bridge arm of the bridge inverter circuit, the charging time of the bootstrap circuit connected with the power electronic switch of the upper half bridge arm is adjusted by adjusting the duty ratio of the PWM signal of the power electronic switch of the lower half bridge arm, so that the charging time of the bootstrap circuit connected with the power electronic switch of the upper half bridge arm is ensured when the power electronic switch of the lower half bridge arm is turned off. And the voltage of the bootstrap capacitor can normally drive the electronic power switch of the upper half bridge arm to be switched on, so that the resonant converter can be normally started.

Description

Technical Field

[0001] The present invention relates to the technical field of resonant converters, and in particular to a starting method of a resonant converter and an LLC resonant converter. Background Art

[0002] It is necessary to design a power circuit in the product to provide a stable power supply for the operation of the equipment. As a commonly used switching power supply topology, LLC resonant converter is suitable for use with power requirements ranging from 100W to about 300W. LLC resonant converter utilizes the resonant characteristics of the LLC circuit, which can make the square wave voltage formed by the periodic switching of the MOS tube form an approximate sine waveform, so that during the state switching process of the MOS tube, the voltage at both ends is close to zero, and zero voltage shutdown is achieved, thereby reducing the switching loss of the MOS tube, improving the conversion efficiency, and avoiding overheating of the MOS tube.

[0003] However, when the LLC resonant converter in the related art is started under light load, the upper tube loses drive and cannot be turned on, causing a sudden increase in the primary current and triggering the overcurrent protection, resulting in failure to start normally. Summary of the invention

[0004] In view of this, the present invention provides a resonant converter startup method and an LLC resonant converter to solve the problem that the LLC resonant converter cannot start normally due to overcurrent protection being triggered when starting with a light load.

[0005] In a first aspect, the present invention provides a method for starting a resonant converter, wherein the resonant converter includes a bridge inverter circuit, and the power electronic switches of the upper bridge arm of the bridge inverter circuit are respectively connected to a bootstrap circuit. The starting method includes: during the startup process of the resonant converter, obtaining the output electrical parameter value of the resonant converter, and obtaining a PWM signal of each power electronic switch of the bridge inverter circuit according to the electrical parameter value; for each bridge arm of the bridge inverter circuit, adjusting the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm to adjust the charging time of the bootstrap circuit connected to the power electronic switch of the upper bridge arm.

[0006] The present invention aims at the phenomenon that the power electronic switch of the upper half bridge arm is easy to lose driving when the resonant converter is lightly loaded. By adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm, the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm is adjusted, so as to ensure that when the power electronic switch of the lower half bridge arm is turned off, the voltage of the bootstrap capacitor can normally drive the power electronic switch of the upper half bridge arm to turn on, thereby ensuring that the resonant converter can be started normally.

[0007] In a specific embodiment, the process of obtaining the PWM signal of each power electronic switch of the bridge inverter circuit includes: subtracting the output voltage value of the resonant converter from the reference voltage value to obtain a voltage difference; and performing proportional-integral-differential control on the voltage difference to obtain the PWM signal of each power electronic switch.

[0008] In a specific implementation, the process of adjusting the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm includes: determining the period of the PWM signal of the power electronic switch of the lower half bridge arm according to the PWM signal of the power electronic switch of the lower half bridge arm; determining the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm according to the period of the PWM signal of the power electronic switch of the lower half bridge arm and the high level conduction time and the low level conduction time; judging the power electronic switch of the lower half bridge arm. Whether the duty cycle of the PWM signal of the sub-switch is less than a preset threshold; when the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is less than the preset threshold, the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is increased by the preset compensation duty cycle, and the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is updated; the on-off state of the power electronic switch of the upper bridge arm and the power electronic switch of the lower bridge arm are controlled by using the duty cycle of the PWM signal of the power electronic switch of the upper bridge arm and the updated duty cycle of the PWM signal of the power electronic switch of the lower bridge arm.

[0009] In a specific implementation, the duty cycle of the updated PWM signal of the power electronic switch of the lower half bridge arm is less than 0.5.

[0010] In a specific embodiment, the process of adjusting the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm also includes: when the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is greater than or equal to a preset threshold, the duty cycle of the PWM signal of the power electronic switch of the upper bridge arm and the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm are used to control the on-off state of the power electronic switch of the upper half bridge arm and the power electronic switch of the lower half bridge arm.

[0011] In a second aspect, the present invention provides a starting device for a resonant converter, the device comprising: a parameter acquisition module, used to acquire the output electrical parameter value of the resonant converter, and obtain the PWM signal of each power electronic switch of the bridge inverter circuit according to the electrical parameter value; a duty cycle adjustment module, used to adjust the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm for each bridge arm of the bridge inverter circuit.

[0012] In a third aspect, the present invention provides an LLC resonant converter, comprising: a bridge inverter circuit, a resonant circuit, a rectifier circuit, a bootstrap circuit and a controller, wherein the DC side of the bridge inverter circuit is connected to a DC power supply, the AC side of the bridge inverter circuit is connected to the input end of the resonant circuit, and the power electronic switches of the upper bridge arm of the bridge inverter circuit are respectively connected to a bootstrap circuit; the output end of the resonant circuit is connected to the AC side of the rectifier circuit; the direct side of the rectifier circuit is connected to the load; and the controller is used to control the on-off state of each power electronic switch of the bridge inverter circuit by applying the starting method of the resonant converter of any one of claims 1 to 5.

[0013] In a specific embodiment, the bridge inverter circuit includes a first power electronic switch, a second power electronic switch, a third power electronic switch and a fourth power electronic switch, wherein the first end of the first power electronic switch is connected to a DC power supply and a first end of the third power electronic switch, the second end of the first power electronic switch is connected to the first end of the second power electronic switch and an input end of a resonant circuit; the second end of the second power electronic switch is connected to the second end of the fourth power electronic switch; the second end of the third power electronic switch is connected to the first end of the fourth power electronic switch and an input end of the resonant circuit; and the first power electronic switch and the third power electronic switch are respectively connected to a bootstrap circuit.

[0014] In a specific embodiment, the bootstrap circuit includes: a bootstrap capacitor and a bootstrap diode, wherein the cathode of the bootstrap diode is connected to the first end of the power electronic switch, the anode of the bootstrap diode is connected to the control end of the first power electronic switch and the first end of the bootstrap capacitor; the bootstrap capacitor is connected to the second end of the power electronic switch.

[0015] In a specific embodiment, the resonant circuit includes: a resonant inductor, a resonant capacitor, an excitation inductor and a transformer, wherein the first end of the resonant inductor is connected to the second end of the first power electronic switch, and the second end of the resonant inductor is connected to the first end of the resonant capacitor; the second end of the resonant capacitor is connected to the first end of the excitation inductor and the first end of the primary winding of the transformer; the second end of the excitation inductor is connected to the second end of the third power electronic and the second end of the primary winding of the transformer; and the secondary winding of the transformer is connected to the AC side of the rectifier circuit.

[0016] In a specific embodiment, the rectifier circuit includes: a first diode, a second diode, and a DC support capacitor, wherein the anode of the first diode is connected to the first end of the secondary winding of the transformer, and the cathode of the first diode is connected to the first end of the DC support capacitor; the anode of the second diode is connected to the second end of the secondary winding of the transformer, and the cathode of the second diode is connected to the cathode of the first diode; the second end of the DC support capacitor is connected to the tap of the secondary winding of the transformer, the second end of the DC support capacitor is also grounded, and both ends of the DC support capacitor are connected to the load.

[0017] In a fourth aspect, the present invention provides an electronic device, comprising: a memory and a processor, the memory and the processor are communicatively connected to each other, computer instructions are stored in the memory, and the processor executes the method for starting the resonant converter of the first aspect or any corresponding embodiment thereof by executing the computer instructions.

[0018] In a fifth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the method for starting a resonant converter according to the first aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 is a flow chart of a method for starting a resonant converter according to an embodiment of the present invention;

[0021] Figure 2 is a flow chart of another method for starting a resonant converter according to an embodiment of the present invention;

[0022] Figure 3 is a flow chart of a method for starting a resonant converter according to another embodiment of the present invention;

[0023] Figure 4 is a specific circuit structure diagram of an LLC resonant converter according to an embodiment of the present invention;

[0024] Figure 5 is a structural block diagram of a starting device of a resonant converter according to an embodiment of the present invention;

[0025] Figure 6 It is a schematic diagram of the hardware structure of the electronic device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0027] According to an embodiment of the present invention, an embodiment of a method for starting a resonant converter is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0028] LLC digital power supply is one of the current focuses of power supply research. It has a simple structure and can achieve soft switching at full load. It also has the characteristics of wide input range, convenient magnetic integration, and digital control flexibility. At present, LLC digital power supply based on LLC resonant converter is widely used in new energy vehicles, aviation power supply, server power supply and other fields. However, the design of LLC resonant converter is relatively complex. During the light load startup process, the primary current will suddenly increase, triggering OCP protection, resulting in failure to start normally, affecting the design and safety of the power supply. Therefore, it is of great significance to conduct in-depth research on the startup design of LLC resonant converter.

[0029] The LLC resonant converter has a topology that utilizes a combination of two inductors and one capacitor ("LLC") on the primary side of the converter. A switched (full or half) bridge on the primary side generates a square waveform that excites the LLC oscillating circuit, which in response outputs a resonant sinusoidal current that is scaled and rectified by the LLC converter's transformer and rectifier circuit. The output capacitor filters the rectified AC current and outputs a DC voltage.

[0030] The synchronous rectifier (SR) switch on the secondary side of the LLC converter is usually turned off during light load conditions when the output voltage is not regulated, and thus acts as a diode rectifier. Taking this approach simplifies PWM (pulse width modulation) pattern generation, avoids reverse power flow and reduces the possibility of hard commutation, but reduces the achievable efficiency due to the higher losses of the built-in FET (field effect transistor) diode.

[0031] A common driving scheme for the bridge switching devices on the primary side of an LLC converter uses a bootstrap capacitor. However, in order to apply the proper PWM mode, the bootstrap capacitor must be charged first. This applies not only to converter startup, but also to Burst Mode operation under light load conditions, as the off time can be long enough to discharge the bootstrap capacitor.

[0032] In the above-mentioned related technical solutions, in order to prevent the upper tube from losing drive when the LLC resonant converter is lightly loaded, causing a sudden increase in the primary current, triggering the overcurrent protection, and resulting in the problem of failure to start normally, most of the hardware is currently used to increase the capacitance of the bootstrap capacitor and increase the supply voltage. However, the hardware solution has certain limitations. The hardware equipment has restrictions on the supply voltage, and the capacitance of the bootstrap capacitor and the supply voltage cannot be too large.

[0033] In order to solve the above problem, a method for starting a resonant converter is provided in this embodiment. The resonant converter includes a bridge inverter circuit. The power electronic switches of the upper half bridge arm of the bridge inverter circuit are respectively connected to a bootstrap circuit, such as Figure 1 As shown, the startup method includes:

[0034] Step S1: During the startup process of the resonant converter, an output electrical parameter value of the resonant converter is obtained, and a PWM signal of each power electronic switch of the bridge inverter circuit is obtained according to the electrical parameter value.

[0035] Specifically, when the LLC resonant converter is started with a light load, the high level of the PWM signal output by the driving device (such as a DSP chip) of the LLC resonant converter accounts for a small proportion, that is, the duty cycle is small. When the power electronic switch of the upper bridge arm of the LLC resonant converter is turned off and the power electronic switch of the lower bridge arm is turned on, due to the small duty cycle, the power electronic turn-on time of the lower bridge arm is short, so the charging time of the bootstrap circuit connected to the power electronic switch of the upper bridge arm is short, and the voltage of the bootstrap circuit is small; when the power electronic switch of the lower bridge arm is turned off, the bootstrap circuit connected to the power electronic switch of the upper bridge arm starts to discharge, and the voltage across the capacitor in the bootstrap circuit gradually decreases. When the voltage across the capacitor of the bootstrap circuit cannot drive the power electronic switch of the upper bridge arm to turn on, it will eventually cause the power electronic switch of the upper bridge arm to lose drive, thereby causing the current of the LLC resonant converter to suddenly increase, and even trigger overcurrent protection.

[0036] Based on the above analysis, during the startup process of the resonant converter, the output electrical parameter values ​​of the resonant converter can be collected, and the PWM signal of each power electronic switch of the bridge inverter circuit can be obtained according to the electrical parameter values ​​to determine whether the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is too small.

[0037] Step S2: For each bridge arm of the bridge inverter circuit, the charging time of the bootstrap circuit connected to the power electronic switch of the upper bridge arm is adjusted by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm.

[0038] Specifically, since the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is too small, the charging time of the bootstrap circuit of the power electronic switch of the upper bridge arm will be too short, thereby causing the power electronic switch of the upper bridge arm to lose drive. Therefore, when the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is too small, the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm can be increased to increase the charging time of the bootstrap circuit.

[0039] Specifically, in the entire closed-loop control of the LLC resonant converter, the duty cycle adjustment method of steps S1 to S2 is implemented at each switching moment, wherein PID control is performed according to the output voltage value and the reference voltage value to adjust the PWM pulse width, which is not limited to PID control and can also be DF22 control. However, since PID is a simple and classic control method to implement in the control system, the general startup control adopts the PID control algorithm.

[0040] In some optional embodiments, such as Figure 2 As shown, the process of adjusting the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm includes:

[0041] Step S21: determining the period of the PWM signal of the power electronic switch of the lower half bridge arm according to the PWM signal of the power electronic switch of the lower half bridge arm.

[0042] Step S22: Determine the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm according to the period of the PWM signal of the power electronic switch of the lower half bridge arm and its high level on time and low level on time.

[0043] Specifically, for each bridge arm, when the power electronic switch of the upper bridge arm is turned off and the power electronic switch of the lower bridge arm is turned on, the power supply can charge the capacitor in the bootstrap circuit, that is, the high level time of the PWM signal of the power electronic switch of the lower bridge arm determines the charging time of the capacitor in the bootstrap circuit. Therefore, according to the PWM signal of the power electronic switch of the lower bridge arm, the period of the PWM signal of the power electronic switch of the lower bridge arm is determined, and the duty cycle is determined according to the high level time and the low level time.

[0044] Optionally, in this embodiment, the charging time of the bootstrap circuit can be adjusted by increasing the duty cycle of the PWM signal when using PWM signal control, but when the LLC resonant converter is controlled using a space vector, the charging time of the bootstrap circuit can be adjusted by adjusting the action time of the space vector.

[0045] Step S23: determine whether the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is less than a preset threshold.

[0046] Specifically, the size of the preset threshold is limited. If the preset threshold is too small, even if the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is adjusted, the conduction time of the power electronic switch of the lower half bridge arm may still be too short. Therefore, the preset threshold cannot be too small. At the same time, the preset threshold is too large. Since the duty cycle of the PWM signal of the power electronic switch is limited, that is, the maximum duty cycle of the PWM signal of the power electronic switch is 0.5, the preset threshold cannot be too large.

[0047] Optionally, the preset threshold may be 0.25, which may be selected through a large number of experimental adjustments and is not limited here.

[0048] Step S24: when the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is less than a preset threshold, the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is increased by a preset compensation duty cycle, and then the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is updated.

[0049] Specifically, when the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is less than the preset threshold value, it means that the charging time of the bootstrap circuit connected to the power electronic switch of the upper bridge arm is too short, which may cause the power electronic switch of the upper bridge arm to lose drive. Therefore, a preset compensation duty cycle is added on the basis of the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm. The preset compensation duty cycle is a fixed value, thereby increasing the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm and increasing the charging time of the bootstrap circuit.

[0050] Step S25: using the duty cycle of the PWM signal of the power electronic switch of the upper bridge arm and the updated duty cycle of the PWM signal of the power electronic switch of the lower bridge arm, control the on / off state of the power electronic switch of the upper bridge arm and the power electronic switch of the lower bridge arm.

[0051] Specifically, the on and off of the power electronic switch is controlled according to the cycle and duty cycle of the updated PWM signal, wherein the duty cycle of the PWM signal of the power electronic switch of the upper bridge arm remains unchanged. The specific duty cycle adjustment flow chart is as follows: Figure 3 shown.

[0052] In some optional implementations, the duty cycle of the updated PWM signal of the power electronic switch of the lower half bridge arm is less than 0.5.

[0053] Specifically, the LLC resonant converter is mostly composed of a voltage source inverter circuit, a resonant circuit, and a rectifier circuit connected in series in sequence. Since a dead time needs to be added between the PWM signals of the upper and lower bridge arm power electronic switches of the same bridge arm of the voltage source inverter circuit to prevent the bridge arm from being directly connected, when the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is less than a preset threshold, the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm not only needs to be increased by a preset compensation duty cycle, but also needs to ensure that the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm after the preset compensation duty cycle is increased still has a dead time with the PWM signal of the power electronic switch of the upper bridge arm, so the updated duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is less than 0.5.

[0054] In some optional implementations, the process of adjusting the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm further includes:

[0055] When the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is greater than or equal to a preset threshold, the on-off state of the power electronic switch of the upper bridge arm and the power electronic switch of the lower bridge arm are controlled by utilizing the duty cycle of the PWM signal of the power electronic switch of the upper bridge arm and the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm.

[0056] Specifically, when the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm is greater than or equal to the preset threshold, it indicates that the charging time of the bootstrap capacitor connected to the power electronic switch of the upper bridge arm is sufficient. Therefore, there is no need to adjust the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm.

[0057] In this embodiment, an LLC resonant converter is provided, including: a bridge inverter circuit, a resonant circuit, a rectifier circuit, a bootstrap circuit and a controller.

[0058] Specifically, the DC side of the bridge inverter circuit is connected to a DC power supply, the AC side of the bridge inverter circuit is connected to the input end of the resonant circuit, and the power electronic switches of the upper bridge arm of the bridge inverter circuit are respectively connected to a bootstrap circuit; the output end of the resonant circuit is connected to the AC side of the rectifier circuit; and the direct side of the rectifier circuit is connected to the load.

[0059] Specifically, LLC resonant converters have gained a lot of attention in industrial applications because of their ability to operate under wide input and load variations. In traditional PWM converters, the power switches operate in hard switching mode, with high switching losses and electromagnetic interference (EMI). But in LLC resonant converters, the switch tube can be turned on by zero voltage switching (ZVS), and the output rectifier diode can also be turned off by zero current switching (ZCS), thereby minimizing losses. Therefore, high-frequency, high-power density, and high-efficiency converters become feasible.

[0060] Specifically, the bridge inverter circuit can convert direct current into alternating current, the resonant circuit can realize functions such as AC frequency conversion, and the rectifier circuit can convert alternating current into direct current to supply power to the load, wherein the power electronic switch of each upper half bridge arm of the bridge inverter circuit is connected to a bootstrap circuit, which is a boost circuit using a bootstrap boost capacitor, thereby realizing voltage control of each power electronic switch.

[0061] Specifically, in order to prevent the upper tube from losing drive when the LLC resonant converter is lightly loaded, causing a sudden increase in the primary current, triggering the overcurrent protection, and causing the problem of being unable to start normally, most hardware is currently used to increase the capacitance of the bootstrap capacitor and increase the supply voltage. However, the hardware solution has certain limitations. The hardware equipment has restrictions on the supply voltage, and the bootstrap capacitor capacitance and supply voltage cannot be too large. Based on this, the controller uses the above embodiment and any optional implementation method of the resonant converter to control the on-off state of each power electronic switch in the bridge inverter circuit.

[0062] Specifically, at each switching moment, the controller obtains the output electrical parameter value of the resonant converter, and obtains the PWM signal of each power electronic switch of the bridge inverter circuit according to the electrical parameter value. The controller determines whether the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is less than a preset threshold value. When it is less than the preset threshold value, it indicates that the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm is insufficient. Therefore, the controller increases the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm to increase the charging time of the bootstrap circuit.

[0063] In some optional embodiments, such as Figure 4 As shown, the bridge inverter circuit includes a first power electronic switch S1, a second power electronic switch S2, a third power electronic switch S3 and a fourth power electronic switch S4.

[0064] Specifically, the first end of the first power electronic switch S1 is connected to the DC power supply Vd and the first end of the third power electronic switch S3, the second end of the first power electronic switch is connected to the first end of the second power electronic switch S2 and the input end of the resonant circuit; the second end of the second power electronic switch S2 is connected to the second end of the fourth power electronic switch S4; the second end of the third power electronic switch S3 is connected to the first end of the fourth power electronic switch S4 and the input end of the resonant circuit; the first power electronic switch S1 and the third power electronic switch S3 are respectively connected to a bootstrap circuit.

[0065] Specifically, Figure 4 In the embodiment, the first power electronic switch S1 and the second power electronic switch S2 form a bridge arm, the third power electronic switch S3 and the fourth power electronic switch S4 form another bridge arm, the first power electronic switch S1 and the third power electronic switch S3 are both power electronic switches of the upper bridge arm, the second power electronic switch S2 and the fourth power electronic switch S4 are both power electronic switches of the lower bridge arm, and the first power electronic switch S1 and the third power electronic switch S3 are respectively connected to a bootstrap circuit.

[0066] Specifically, Figure 4 In the circuit, the on and off of the four power electronic switches are controlled by the PWM signals issued by the controller.

[0067] Optionally, Figure 4 The mid-bridge inverter circuit takes a full-bridge inverter circuit as an example, but it can also be a half-bridge inverter circuit, etc., which is not limited here.

[0068] In some optional embodiments, such as Figure 4 As shown, the bootstrap circuit includes: a bootstrap capacitor Cs and a bootstrap diode Ds, wherein the cathode of the bootstrap diode is connected to the first end of the power electronic switch, the anode of the bootstrap diode is connected to the control end of the first power electronic switch S1 and the first end of the bootstrap capacitor Cs; the bootstrap capacitor Cs is connected to the second end of the power electronic switch.

[0069] Figure 4 In the embodiment, the first power electronic switch S1 and the third power electronic switch S3 are respectively connected to a bootstrap circuit, and the on-off state of the first power electronic switch S1 and the third power electronic switch S3 is controlled by charging the bootstrap capacitor Cs.

[0070] Figure 4 In the circuit, the bootstrap circuit is a boost circuit using a bootstrap boost capacitor. In the circuit, a MOS tube is used to build a bridge inverter circuit. For the upper tube, if the gate G is to be driven directly, the condition of Vgs>Vgs(th) needs to be met. Then a high voltage needs to be added between the gate G and the ground, which is difficult to control. The bootstrap circuit can easily generate a high voltage on the gate G of the upper tube, thereby driving the upper tube MOS to turn on.

[0071] Figure 4 In the figure, taking the bridge arm formed by S1 and S2 as an example, when S2 is turned on, the voltage at point SW is 0, and the DC power supply Vd, bootstrap diode Ds, bootstrap capacitor Cs, and S2 form a loop. The DC power supply Vd charges the bootstrap capacitor Cs, and the voltage across the bootstrap capacitor Cs is approximately equal to the input V. At this time, the voltage at point A is also V. When S2 is disconnected, the voltage at point SW is not 0. Since the voltage V is stored across the bootstrap capacitor Cs, the voltage at point A is higher than the voltage at point SW after being raised, which is equivalent to the gate voltage of S1 and its source voltage being higher by V. At this point, S1 is turned on, and the voltage at point A becomes the sum of V and the voltage at point SW, achieving voltage raising.

[0072] Figure 4 In the process, the bootstrap circuit needs to continuously switch states to charge and discharge the bootstrap capacitor Cs to ensure that the voltage is raised for a long time. The voltage across the bootstrap capacitor Cs is constantly fluctuating relative to the voltage of the system GND, rising and falling, so that when needed, the voltage on the high side of the bootstrap capacitor Cs is high enough to drive the upper tube to turn on. However, when starting the machine under light load, since the duty cycle of the PWM signal output by the DSP is relatively small, the S2 turn-on time is very short, which makes the charging time of the bootstrap capacitor Cs short. When S2 is turned off, the voltage across the bootstrap capacitor Cs gradually decreases. When the voltage across the bootstrap capacitor Cs cannot drive the upper tube to turn on, S2 will be turned off, and S2 will lose drive, causing the primary current to suddenly increase, triggering the overcurrent P protection, and causing the LLC resonant converter to fail to work properly.

[0073] In some optional embodiments, such as Figure 4 As shown, the resonant circuit includes: a resonant inductor Lr, a resonant capacitor Cr, an excitation inductor Lm and a transformer T1, wherein a first end of the resonant inductor Lr is connected to a second end of the first power electronic switch S1, and a second end of the resonant inductor Lr is connected to a first end of the resonant capacitor Cr; a second end of the resonant capacitor Cr is connected to a first end of the excitation inductor Lm and a first end of a primary winding of the transformer T1; a second end of the excitation inductor Lm is connected to a second end of a third power electronic and a second end of the primary winding of the transformer T1; and a secondary winding of the transformer T1 is connected to an AC side of the rectifier circuit.

[0074] Specifically, the resonant circuit part is obtained by connecting a resonant inductor Lr, a resonant capacitor Cr in series with the primary side of the transformer T1, and connecting an excitation inductor Lm in parallel with the primary side of the transformer T1. Figure 4 In the circuit, the output voltage is adjusted by changing the operating frequency of the pulse input to the resonant circuit.

[0075] In some optional embodiments, such as Figure 4As shown, the rectifier circuit includes: a first diode D1, a second diode D2, and a DC support capacitor Cd, wherein the anode of the first diode D1 is connected to the first end of the secondary winding of the transformer T1, and the cathode of the first diode D1 is connected to the first end of the DC support capacitor; the anode of the second diode D2 is connected to the second end of the secondary winding of the transformer T1, and the cathode of the second diode D2 is connected to the cathode of the first diode D1; the second end of the DC support capacitor Cd is connected to the tap of the secondary winding of the transformer T1, the second end of the DC support capacitor Cd is also grounded, and both ends of the DC support capacitor are connected to the load R1.

[0076] Specifically, Figure 4 The rectifier circuit in the figure takes a half-wave rectifier circuit as an example, but the specific structure is not limited here.

[0077] Optionally, in this embodiment, a separate charging device may be provided for each bootstrap capacitor. When the duty cycle of the power electronic switch of the lower half bridge arm is too small, the charging device may be used to charge the bootstrap capacitor separately.

[0078] In this embodiment, a resonant converter start-up device is also provided, which is used to implement the above-mentioned embodiments and preferred implementation modes, and will not be repeated hereafter. As used below, the term "module" may be a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0079] This embodiment provides a starting device for a resonant converter, such as Figure 5 As shown, the device comprises:

[0080] A parameter acquisition module, used to acquire the output electrical parameter value of the resonant converter, and obtain the PWM signal of each power electronic switch of the bridge inverter circuit according to the electrical parameter value;

[0081] The duty cycle adjustment module is used to adjust the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm for each bridge arm of the bridge inverter circuit.

[0082] The start-up device of the resonant converter in this embodiment is presented in the form of a functional unit, where the unit refers to an ASIC circuit, a processor and a memory that executes one or more software or fixed programs, and / or other devices that can provide the above functions.

[0083] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0084] The embodiment of the present invention also provides an electronic device having the above Figure 5 The starting device of the resonant converter is shown.

[0085] See also Figure 6 , Figure 6 is a schematic diagram of the structure of an electronic device provided by an optional embodiment of the present invention, such as Figure 6 As shown, the electronic device includes: one or more processors 10, a memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. The various components are connected to each other using different buses for communication, and can be installed on a common mainboard or installed in other ways as needed. The processor can process instructions executed in the electronic device, including instructions stored in or on the memory to display graphical information of the GUI on an external input / output device (such as a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple electronic devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 6 A processor 10 is taken as an example.

[0086] The processor 10 may be a central processing unit, a network processor or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0087] The memory 20 stores instructions executable by at least one processor 10, so that at least one processor 10 executes the method shown in the above embodiment.

[0088] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created by the use of an electronic device based on the presentation of a small program landing page, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely arranged relative to the processor 10, and these remote memories may be connected to the electronic device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0089] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid state drive; the memory 20 may also include a combination of the above types of memory.

[0090] The electronic device further comprises a communication interface 30 for the electronic device to communicate with other devices or a communication network.

[0091] The embodiment of the present invention also provides a computer-readable storage medium. The method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor, or hardware, the method shown in the above embodiment is implemented.

[0092] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for starting a resonant converter, characterized in that: The resonant converter includes a bridge inverter circuit, the power electronic switches of the upper half bridge arm of the bridge inverter circuit are respectively connected to a bootstrap circuit, and the startup method includes: During the startup process of the resonant converter, an output electrical parameter value of the resonant converter is obtained, and a PWM signal of each power electronic switch of the bridge inverter circuit is obtained according to the electrical parameter value; For each bridge arm of the bridge inverter circuit, the charging time of the bootstrap circuit connected to the power electronic switch of the upper bridge arm is adjusted by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower bridge arm.

2. The method for starting a resonant converter according to claim 1, characterized in that: The process of obtaining the PWM signal of each power electronic switch of the bridge inverter circuit includes: Subtract the output voltage value of the resonant converter from the reference voltage value to obtain a voltage difference value; The voltage difference is subjected to proportional-integral-differential control to obtain a PWM signal for each power electronic switch.

3. The method for starting a resonant converter according to claim 1, characterized in that: The process of adjusting the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm comprises: Determining the period of the PWM signal of the power electronic switch of the lower half bridge arm according to the PWM signal of the power electronic switch of the lower half bridge arm; Determine the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm according to the period of the PWM signal of the power electronic switch of the lower half bridge arm and its high level on time and low level on time; Determining whether the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is less than a preset threshold; When the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is less than a preset threshold, the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is increased by a preset compensation duty cycle, and then the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is updated; The on-off states of the power electronic switches of the upper bridge arm and the lower bridge arm are controlled by utilizing the duty cycle of the PWM signal of the power electronic switch of the upper bridge arm and the updated duty cycle of the PWM signal of the power electronic switch of the lower bridge arm.

4. The method for starting a resonant converter according to claim 3, characterized in that: include: The updated duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is less than 0.

5.

5. The method for starting a resonant converter according to claim 3, characterized in that: The process of adjusting the charging time of the bootstrap circuit connected to the power electronic switch of the upper half bridge arm by adjusting the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm also includes: When the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm is greater than or equal to a preset threshold, the on-off state of the power electronic switch of the upper half bridge arm and the power electronic switch of the lower half bridge arm are controlled by utilizing the duty cycle of the PWM signal of the power electronic switch of the upper half bridge arm and the duty cycle of the PWM signal of the power electronic switch of the lower half bridge arm.

6. An LLC resonant converter, characterized in that: include: A bridge inverter circuit, a resonant circuit, a rectifier circuit, a bootstrap circuit and a controller, wherein: The DC side of the bridge inverter circuit is connected to a DC power supply, the AC side of the bridge inverter circuit is connected to an input end of the resonant circuit, and the power electronic switches of the upper bridge arm of the bridge inverter circuit are respectively connected to a bootstrap circuit; The output end of the resonant circuit is connected to the AC side of the rectifier circuit; The direct side of the rectifier circuit is connected to the load; The controller is used to control the on-off state of each power electronic switch of the bridge inverter circuit by applying the starting method of the resonant converter described in any one of claims 1 to 5.

7. The LLC resonant converter according to claim 6, characterized in that: The bridge inverter circuit includes a first power electronic switch, a second power electronic switch, a third power electronic switch and a fourth power electronic switch, wherein: The first end of the first power electronic switch is connected to the DC power supply and the first end of the third power electronic switch, and the second end of the first power electronic switch is connected to the first end of the second power electronic switch and the input end of the resonant circuit; a second end of the second power electronic switch and a second end of the fourth power electronic switch; The second end of the third power electronic switch is connected to the first end of the fourth power electronic switch and the input end of the resonant circuit; The first power electronic switch and the third power electronic switch are respectively connected to a bootstrap circuit.

8. The LLC resonant converter according to claim 6, characterized in that: The bootstrap circuit includes: a bootstrap capacitor and a bootstrap diode, wherein: The cathode of the bootstrap diode is connected to the first end of the power electronic switch, and the anode of the bootstrap diode is connected to the control end of the first power electronic switch and the first end of the bootstrap capacitor; The bootstrap capacitor is connected to the second end of the power electronic switch.

9. The LLC resonant converter according to claim 7, characterized in that: The resonant circuit includes: a resonant inductor, a resonant capacitor, an excitation inductor and a transformer, wherein: The first end of the resonant inductor is connected to the second end of the first power electronic switch, and the second end of the resonant inductor is connected to the first end of the resonant capacitor; The second end of the resonant capacitor is connected to the first end of the excitation inductor and the first end of the primary winding of the transformer; The second end of the excitation inductor is connected to the second end of the third power electronic device and the second end of the primary winding of the transformer; The secondary winding of the transformer is connected to the AC side of the rectifier circuit.

10. The LLC resonant converter according to claim 9, characterized in that: The rectifier circuit includes: a first diode, a second diode, and a DC support capacitor, wherein: An anode of the first diode is connected to a first end of a secondary winding of the transformer, and a cathode of the first diode is connected to a first end of the DC support capacitor; An anode of the second diode is connected to the second end of the secondary winding of the transformer, and a cathode of the second diode is connected to the cathode of the first diode; The second end of the DC support capacitor is connected to the tap of the secondary winding of the transformer, the second end of the DC support capacitor is also grounded, and both ends of the DC support capacitor are connected to the load.

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