Power converter startup control method, device and power converter startup system

Abstract

The present application relates to a power converter startup control method, device, and power converter startup system. The method includes: outputting a pulse width modulation signal to a power converter, the pulse width modulation signal being used to drive the power tube of the power converter; obtaining the operating frequency of the power converter; and when the operating frequency of the power converter is greater than a set operating frequency, gradually reducing the frequency of the pulse width modulation signal to reduce the operating frequency of the power converter. When the operating frequency of the power converter is greater than the set operating frequency, gradually reducing the frequency of the pulse width modulation signal to reduce the operating frequency of the power converter. The power converter is started using a time domain frequency conversion method. The startup process does not require switching and does not generate hardware overcurrent, software overcurrent, or overvoltage faults. The method is safe and reliable, and improves the control reliability of the power converter startup.

Description

Technical Field

[0001] The present application relates to the field of power conversion technology, and in particular to a power converter startup control method, device, and power converter startup system. Background Art

[0002] With the development of science and technology and the continuous progress of society, various types of electronic devices are becoming increasingly common in people's daily work and life. Currently, most electronic devices only have power converters. These converters convert the voltage or current input to the electronic device to generate output power suitable for different circuit modules, thus providing power to the different circuit modules of the electronic device.

[0003] The traditional power converter startup method involves first varying the pulse width and then switching to frequency modulation. While this method can start the power converter, the switchover point from pulse width variation to frequency modulation during startup is prone to hardware overcurrent failures. If fault protection isn't implemented in a timely manner, this can damage the circuit board, posing a significant safety hazard. This traditional power converter startup method also suffers from low control reliability. Summary of the Invention

[0004] Based on this, it is necessary to provide a power converter startup control method, device and power converter startup system that can improve control reliability in order to address the problem of low control reliability of traditional power converter startup methods.

[0005] A power converter startup control method, comprising:

[0006] Outputting a pulse width modulation signal to a power converter, wherein the pulse width modulation signal is used to drive a power tube of the power converter;

[0007] Obtaining an operating frequency of the power converter;

[0008] When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter.

[0009] The above-mentioned power converter startup control method monitors the operating frequency of the power converter after outputting a pulse width modulation signal to drive the power tube of the power converter. When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter. The power converter is started by using a time domain frequency conversion method. No switching is required during the startup process, and no hardware overcurrent, software overcurrent, or overvoltage faults will occur. The method is safe and reliable, thereby improving the control reliability of the power converter startup.

[0010] In one embodiment, the set operating frequency includes a first set frequency and a second set frequency, and when the operating frequency of the power converter is greater than the set operating frequency, gradually reducing the frequency of the pulse width modulation signal to reduce the operating frequency of the power converter includes:

[0011] When the operating frequency of the power converter is greater than the first set frequency, the frequency of the pulse width modulation signal is gradually reduced so that the operating frequency of the power converter is between the first set frequency and the second set frequency; wherein the first set frequency is greater than the second set frequency.

[0012] In one embodiment, gradually reducing the frequency of the pulse width modulation signal includes: gradually reducing the frequency of the pulse width modulation signal through PID regulation control.

[0013] In one embodiment, the step of gradually reducing the frequency of the pulse width modulation signal through PID regulation control includes: updating the PID limit value and / or register value according to a set update rate so that the frequency of the pulse width modulation signal gradually decreases and the duty cycle remains unchanged.

[0014] In one embodiment, after obtaining the operating frequency of the power converter, the method further includes:

[0015] When the operating frequency of the power converter is less than or equal to the set operating frequency, obtaining the output voltage of the power converter;

[0016] When the output voltage does not reach the set output voltage, the pulse width variation frequency of the pulse width modulation signal is adjusted according to the difference between the output voltage and the set output voltage until the output voltage reaches the set output voltage.

[0017] In one embodiment, after obtaining the output voltage of the power converter, the method further includes:

[0018] When the output voltage reaches the set output voltage, the power converter is controlled to perform synchronous rectification.

[0019] In one embodiment, if the operating frequency of the power converter is less than or equal to the set operating frequency, before obtaining the output voltage of the power converter, the method further includes:

[0020] Check whether the power converter is faulty;

[0021] When no fault is detected, the step of obtaining the output voltage of the power converter is performed.

[0022] A power converter startup control device, comprising:

[0023] A signal output module, configured to output a pulse width modulation signal to a power converter, wherein the pulse width modulation signal is used to drive a power transistor of the power converter;

[0024] A frequency detection module, configured to obtain the operating frequency of the power converter;

[0025] The frequency adjustment module is used to gradually reduce the frequency of the pulse width modulation signal when the operating frequency of the power converter is greater than the set operating frequency, so as to reduce the operating frequency of the power converter.

[0026] The power converter startup control device monitors the operating frequency of the power converter after outputting a pulse width modulation signal to drive the power tube of the power converter. When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter. The power converter is started by using a time domain frequency conversion method. No switching is required during the startup process, and no hardware overcurrent, software overcurrent, or overvoltage faults will occur. The device is safe and reliable, thereby improving the control reliability of the power converter startup.

[0027] A power converter startup system includes a power converter, a drive adjustment device and a controller, wherein the controller is connected to the drive adjustment device, the drive adjustment device is connected to the power converter, and the controller is used to perform power converter startup control according to the above method.

[0028] The power converter startup system described above monitors the operating frequency of the power converter after outputting a pulse width modulation signal to drive the power tube of the power converter. When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter. The power converter is started by using a time domain frequency conversion method. No switching is required during the startup process, and no hardware overcurrent, software overcurrent, or overvoltage faults will occur. The system is safe and reliable, thereby improving the control reliability of the power converter startup.

[0029] In one embodiment, the power converter startup system further includes a sampling circuit connected to the controller and the power converter.

[0030] In one embodiment, the power converter includes a first conversion circuit, a transformer and a second conversion circuit, the drive regulation device includes a first drive regulation circuit and a second drive regulation circuit, the primary winding of the transformer is connected to the first conversion circuit, the secondary winding of the transformer is connected to the second conversion circuit, the first drive regulation circuit is connected to the controller and the first conversion circuit, and the second drive regulation circuit is connected to the controller and the second conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flow chart of a power converter startup control method in one embodiment;

[0032] Figure 2 is a flow chart of a power converter startup control method according to another embodiment;

[0033] Figure 3 is a structural block diagram of a power converter startup control device in one embodiment;

[0034] Figure 4 is a structural block diagram of a power converter startup control device in another embodiment;

[0035] Figure 5 is a structural block diagram of a power converter startup system in one embodiment;

[0036] Figure 6 is a structural block diagram of a power converter startup system in another embodiment;

[0037] Figure 7 is a schematic diagram of a power converter startup system in one embodiment;

[0038] Figure 8 A schematic diagram of complementary PWM waves in one embodiment;

[0039] Figure 9 A schematic diagram of adjusting a single PWM wave in one embodiment;

[0040] Figure 10 A schematic diagram of starting PID to adjust different variables in one embodiment;

[0041] Figure 11 FIG. 4 is a flow chart of frequency modulation startup of a power converter in one embodiment. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0043] In one embodiment, a power converter startup control method is provided, which is applicable to variable frequency startup of LLC frequency modulation converter, such as Figure 1 As shown, the method includes:

[0044] Step S110 : Outputting a pulse width modulation signal to a power converter.

[0045] Pulse Width Modulation (PWM) signals are used to drive the power transistors of the power converter. A controller can be connected to a drive and regulation device, which is connected to the power transistors in the power converter. After power-on initialization, the controller starts the power converter and disables synchronous rectification. The controller then outputs PWM signals to the power converter via the drive and regulation device to drive and control the power transistors. Specifically, the drive and regulation device outputs complementary PWM waves to the corresponding power transistors, controlling the on and off switching of the power transistors, thereby controlling the operation of the power converter. The PWM wave frequency is not unique; specifically, a high-frequency PWM wave can be output to drive the power transistors. This high-frequency PWM wave does not generate high currents when the power converter's main circuit is electrically connected, effectively preventing malfunctions. The high-frequency PWM wave can be in the range of 300kHz-700kHz; for example, a 500kHz PWM wave can be selected. Furthermore, the controller type is not unique; in this embodiment, the controller can be a microcontroller.

[0046] Step S120: Acquire the operating frequency of the power converter.

[0047] After the driving and regulating device outputs a pulse width modulation signal to drive the power tube of the power converter, the operating frequency of the power converter can be measured by an oscilloscope. The oscilloscope sends the measured operating frequency to the controller for subsequent time domain frequency conversion startup control of the power converter.

[0048] Step S130 : When the operating frequency of the power converter is greater than the set operating frequency, gradually reducing the frequency of the pulse width modulation signal to reduce the operating frequency of the power converter.

[0049] Among them, the set operating frequency is related to the circuit structure of the power converter. The set operating frequency can be determined in advance according to the structure of the power converter and saved. After receiving the operating frequency measured by the oscilloscope, the controller compares the set operating frequency with the measured operating frequency. When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter.

[0050] Specifically, the controller's frequency reduction control method is not unique. The controller can also select the amplitude by which it reduces the frequency of the pulse width modulation signal based on actual conditions, and the amplitude of each frequency reduction can be the same or different. By gradually reducing the frequency of the pulse width modulation signal, the operating frequency range is forced to decrease in each cycle, thereby forcing the operating frequency to decrease, thereby avoiding the power tube heating and causing failure when the high-frequency PWM wave drives the power tube. The method of gradually reducing the frequency of the pulse width modulation signal is not unique either. Taking the time-domain frequency modulation control using the PID (Proportion Integral Derivative) adjustment method as an example, it can be to modify the internal register value of the controller, or it can be to continuously modify and update the PID limit value, or it can be to perform frequency modulation control from both aspects simultaneously to ensure that the operating frequency of the power converter can be forced to decrease.

[0051] The above-mentioned power converter startup control method monitors the operating frequency of the power converter after outputting a pulse width modulation signal to drive the power tube of the power converter. When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter. The power converter is started by using a time domain frequency conversion method. No switching is required during the startup process, and no hardware overcurrent, software overcurrent, or overvoltage faults will occur. The method is safe and reliable, thereby improving the control reliability of the power converter startup.

[0052] In one embodiment, the set operating frequency includes a first set frequency and a second set frequency. Step S130 includes: when the operating frequency of the power converter is greater than the first set frequency, gradually reducing the frequency of the pulse width modulation signal so that the operating frequency of the power converter is between the first set frequency and the second set frequency; wherein the first set frequency is greater than the second set frequency.

[0053] Specifically, taking an LLC power converter as an example, the first and second resonant frequencies of the LLC power converter are determined during circuit design. Once the circuit design is complete, these frequencies are fixed. The first and second resonant frequencies can be calculated using formulas based on the LLC power converter's circuit structure and stored as the first set frequency f1 and the second set frequency f2, respectively. The LLC power converter has three normal operating states: operating frequency greater than the first set frequency f1, operating frequency equal to the first set frequency f1, and operating frequency greater than the second set frequency f2 but less than the first set frequency f1. When operating between the first and second set frequencies f1 and f2, the LLC power converter can achieve zero voltage turn-on and zero current turn-off, effectively improving power converter efficiency and leveraging the advantages of the LLC power converter. However, when the LLC power converter is not operating between the first and second set frequencies f1 and f2, additional circuit regulators are required to achieve zero voltage turn-on and zero current turn-off, increasing hardware cost.

[0054] When it is detected that the operating frequency of the power converter is greater than the first set frequency f1, time-domain frequency modulation control is performed to gradually reduce the frequency of the pulse-width modulation signal, thereby forcibly reducing the operating frequency of the power converter. This prevents severe heating of the power tube caused by the high frequency of the driving PWM wave when the power converter is started. At the same time, by reducing the operating frequency of the power converter so that the power converter operates between the first and second resonant frequencies, zero-voltage turn-on and zero-current turn-off can be achieved without the need for additional circuit regulation components, effectively improving the efficiency of the power converter.

[0055] In one embodiment, gradually reducing the frequency of the pulse-width modulated signal in step S130 includes gradually decreasing the frequency of the pulse-width modulated signal through PID regulation. The controller uses PID regulation to gradually reduce the frequency of the pulse-width modulated signal, providing simple and reliable control. Specifically, in this embodiment, gradually decreasing the frequency of the pulse-width modulated signal through PID regulation includes updating a PID limit value and / or a register value according to a set update rate so that the frequency of the pulse-width modulated signal gradually decreases while maintaining a constant duty cycle.

[0056] The update rate can be selected and pre-saved based on actual needs. The controller cyclically updates the PID limiter and / or internal register value at this saved update rate, thereby implementing PWM wave frequency reduction to forcibly lower the power converter's operating frequency. Specifically, each time the controller updates the PID limiter and internal register value, the PWM wave frequency gradually decreases while maintaining a constant duty cycle of 50%. Maintaining a constant duty cycle during frequency reduction facilitates PWM wave regulation, ensuring that the output complementary PWM wave can properly drive the power transistors and avoid malfunctions.

[0057] In one embodiment, Figure 2 As shown, after step S120, when the operating frequency of the power converter is less than or equal to the set operating frequency, the method further includes steps S150 and S160.

[0058] Step S150: Acquire the output voltage of the power converter. Specifically, the output voltage of the power converter can be detected by a sampling circuit, and the detected output voltage is sent to the controller.

[0059] Step S160: When the output voltage does not reach the set output voltage, the pulse width variation frequency of the pulse width modulation signal is adjusted according to the difference between the output voltage and the set output voltage until the output voltage reaches the set output voltage.

[0060] The controller can pre-set the set output voltage of the power converter. After receiving the output voltage of the power converter detected by the sampling circuit, it compares the set output voltage with the sampled output voltage. If the output voltage has not yet reached the set output voltage, the controller adjusts the pulse width variation frequency of the pulse width modulation signal based on the difference between the output voltage and the set output voltage until the output voltage reaches the set output voltage. It can be understood that when the output voltage reaches the set output voltage, the controller can control the power converter to enable the synchronous rectification function.

[0061] Specifically, a correspondence between the difference between the output voltage and the set output voltage and the pulse width variation frequency can be pre-established. This correspondence can be either linear or non-linear. After calculating the difference between the output voltage and the set output voltage, the controller adjusts the pulse width variation frequency of the pulse width modulation signal based on the stored correspondence. For example, if the difference between the output voltage and the set output voltage is large, the pulse width variation frequency is increased, thereby increasing the output voltage and reducing the startup time. Conversely, if the difference is large, the pulse width variation frequency is decreased.

[0062] In this embodiment, the pulse width variation frequency of the PWM signal is adjusted according to the difference between the output voltage and the set output voltage, so that the output voltage curve changes more smoothly when the power converter starts, thereby improving the startup reliability of the power converter.

[0063] Furthermore, in one embodiment, after step S150, the method further includes step S170.

[0064] Step S170: When the output voltage reaches the set output voltage, control the power converter to perform synchronous rectification.

[0065] Specifically, when the output voltage of the power converter reaches the set output voltage, the controller controls the power converter to start the synchronous rectification function by driving the regulating device. While the power converter is connected to the external DC voltage and converted into AC power, it also rectifies the AC power to obtain a DC output voltage and outputs it.

[0066] Furthermore, after the power converter performs synchronous rectification, the sampling circuit can also collect the power converter's input voltage. The controller then controls the power converter's operational logic based on the relationship between the collected input voltage and a reference input voltage. Specifically, the controller uses the input voltage as one of the criteria to determine under what conditions to enable or disable synchronous rectification. For example, the controller can control the power converter to enable synchronous rectification when the input voltage is greater than the reference input voltage, and disable synchronous rectification when the input voltage is less than the reference input voltage.

[0067] In one embodiment, referring to Figure 2 If the operating frequency of the power converter is less than or equal to the set operating frequency, before step S150, the method further includes step S140.

[0068] Step S140: Detect whether the power converter has a fault. If no fault is detected, proceed to step S150.

[0069] There is no single method for detecting whether a power converter has failed. Specifically, the output voltage of the power converter can also be detected using a sampling circuit, and the detected output voltage can be sent to the controller. The controller can compare the collected output voltage with the set output voltage. When the difference between the collected output voltage and the set output voltage exceeds the set difference threshold, it can be considered that the power converter has failed; otherwise, no fault has occurred. If no fault is detected, step S150 is performed. If a fault is detected, the controller can activate the fault handling logic and cut off the power converter output to avoid a safety incident. When the fault is eliminated, the process is restarted, power-on initialization is performed, and synchronous rectification of the power converter is disabled, and then step S110 is entered.

[0070] In one embodiment, a power converter startup control device is also provided, which is suitable for variable frequency startup of LLC frequency modulation converter, such as Figure 3 As shown, the device includes a signal output module 110, a frequency detection module 120, and a frequency adjustment module 130. The signal output module 110 is used to output a pulse-width modulated signal to the power converter, which is used to drive the power transistors of the power converter. The frequency detection module 120 is used to obtain the operating frequency of the power converter. The frequency adjustment module 130 is used to gradually reduce the frequency of the pulse-width modulated signal to reduce the operating frequency of the power converter when the operating frequency of the power converter exceeds a set operating frequency.

[0071] In one embodiment, the set operating frequency includes a first set frequency and a second set frequency. When the operating frequency of the power converter is greater than the first set frequency, the frequency adjustment module 130 gradually reduces the frequency of the pulse width modulation signal so that the operating frequency of the power converter is between the first set frequency and the second set frequency; wherein the first set frequency is greater than the second set frequency.

[0072] In one embodiment, the frequency adjustment module 130 gradually reduces the frequency of the pulse width modulation signal through PID adjustment control.

[0073] In one embodiment, the frequency adjustment module 130 updates the PID limit value and / or register value according to a set update rate, so that the frequency of the pulse width modulation signal gradually decreases and the duty cycle remains unchanged.

[0074] In one embodiment, Figure 4 As shown, the power converter startup control device further includes a voltage regulating module 150. After the frequency detection module 120 obtains the operating frequency of the power converter, the voltage regulating module 150 is configured to obtain the output voltage of the power converter when the operating frequency of the power converter is less than or equal to a set operating frequency; and when the output voltage does not reach the set output voltage, the voltage regulating module 150 adjusts the pulse width variation frequency of the pulse width modulation signal according to the difference between the output voltage and the set output voltage until the output voltage reaches the set output voltage.

[0075] Furthermore, in one embodiment, the voltage regulation module 150 controls the power converter to perform synchronous rectification when the output voltage reaches a set output voltage.

[0076] In one embodiment, the power converter startup control device further includes a fault detection module 140. Fault detection module 140 is configured to detect whether the power converter has a fault after the power converter's operating frequency is less than or equal to a set operating frequency and before the voltage regulation module 150 obtains the power converter's output voltage. If no fault is detected, the fault detection module 140 controls the voltage regulation module 150 to obtain the power converter's output voltage. Furthermore, if a fault is detected, fault detection module 140 can also shut down the power converter output to prevent safety incidents.

[0077] The specific definitions of the power converter startup control device can be found in the definitions of the power converter startup control method described above and will not be further elaborated here. Each module in the power converter startup control device described above may be implemented in whole or in part via software, hardware, or a combination thereof. Each of these modules may be embedded in or independent of a processor in a computer device in hardware form, or may be stored in a computer device memory in software form, allowing the processor to call and execute the corresponding operations of each module.

[0078] The power converter startup control device monitors the operating frequency of the power converter after outputting a pulse width modulation signal to drive the power tube of the power converter. When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter. The power converter is started by using a time domain frequency conversion method. No switching is required during the startup process, and no hardware overcurrent, software overcurrent, or overvoltage faults will occur. The device is safe and reliable, thereby improving the control reliability of the power converter startup.

[0079] In one embodiment, a power converter startup system is also provided. Figure 5 As shown, the system includes a controller 210, a drive adjustment device 220, and a power converter 230. The controller 210 is connected to the drive adjustment device 220, which is in turn connected to the power converter 230. The controller 210 is configured to perform power converter startup control according to the above-described method. Furthermore, the power converter startup system also includes an oscilloscope connected to the controller 210.

[0080] In one embodiment, Figure 6 As shown, the power converter startup system further includes a sampling circuit 240 , which is connected to the controller 210 and the power converter 230 .

[0081] Specifically, in one embodiment, Figure 7 As shown, the power converter 230 includes a first conversion circuit 232, a transformer T, and a second conversion circuit 234. The drive regulation device 220 includes a first drive regulation circuit 222 and a second drive regulation circuit 224. The primary winding of the transformer T is connected to the first conversion circuit 232, and the secondary winding of the transformer T is connected to the second conversion circuit 234. The first drive regulation circuit 222 is connected to the controller 210 and the first conversion circuit 232, and the second drive regulation circuit 224 is connected to the controller 210 and the second conversion circuit 234. In this embodiment, the controller 210 is a microcontroller 212.

[0082] The first conversion circuit 232 includes power transistors Q1, Q2, Q3, Q4, and a capacitor C. The control terminals of the power transistors Q1, Q2, Q3, and Q4 are all connected to the first drive regulation circuit 222. The first terminal of the power transistor Q1 and the first terminal of the power transistor Q3 are connected to the positive input electrode Vin+. The second terminal of the power transistor Q1 is connected to the first terminal of the power transistor Q2 and one end of the primary winding of the transformer T. The second terminal of the power transistor Q3 is connected to the first terminal of the power transistor Q4 and is connected to the other end of the primary winding of the transformer T via the capacitor C. The second terminal of the power transistor Q2 and the second terminal of the power transistor Q4 are connected to the negative input electrode Vin-. The sampling circuit 240 is connected to the positive input electrode Vin+ and the positive input electrode Vin+.

[0083] The power transistors Q1, Q2, Q3, and Q4 can be triodes or MOS transistors. In this embodiment, the power transistors Q1, Q2, Q3, and Q4 are all MOS transistors. The microcontroller 212 outputs complementary PWM waves to the corresponding power transistors in the first conversion circuit 232 via the first drive regulation circuit 222. The microcontroller 212 down-regulates the PWM waves based on the operating frequency captured by the oscilloscope to reduce the operating frequency of the power converter. The power transistors in the first conversion circuit 232 are switched on and off based on the PWM waves received by the control terminal. As a result, the first conversion circuit 232 converts the DC power received into AC power, which is then transmitted to the transformer T.

[0084] The second conversion circuit 234 includes power transistors Q5, Q6, Q7, and Q8. The control terminals of the power transistors Q5, Q6, Q7, and Q8 are all connected to the second drive regulation circuit 224. The first terminal of the power transistor Q5 and the first terminal of the power transistor Q7 are connected to the output positive electrode Vout+. The second terminal of the power transistor Q5 is connected to the first terminal of the power transistor Q6 and one end of the secondary winding of the transformer T. The second terminal of the power transistor Q7 is connected to the first terminal of the power transistor Q8 and the other end of the secondary winding of the transformer T. The second terminal of the power transistor Q6 and the second terminal of the power transistor Q8 are connected to the output negative electrode Vout-. The sampling circuit 240 is connected to the output positive electrode Vout+ and the output negative electrode Vout-.

[0085] The power transistors Q5, Q6, Q7, and Q8 can be triodes or MOS transistors. In this embodiment, the power transistors Q5, Q6, Q7, and Q8 are all MOS transistors. After the output voltage collected by the sampling circuit 240 reaches the set output voltage, the microcontroller 212 controls the second drive regulation circuit 224 to output a PWM signal to drive the corresponding power transistors in the second conversion circuit 234, causing the second conversion circuit 234 to synchronously regulate the AC power output by the secondary winding of the transformer T to generate a DC voltage output.

[0086] The power converter startup system described above monitors the operating frequency of the power converter after outputting a pulse width modulation signal to drive the power tube of the power converter. When the operating frequency of the power converter is greater than the set operating frequency, the frequency of the pulse width modulation signal is gradually reduced to reduce the operating frequency of the power converter. The power converter is started by using a time domain frequency conversion method. No switching is required during the startup process, and no hardware overcurrent, software overcurrent, or overvoltage faults will occur. The system is safe and reliable, thereby improving the control reliability of the power converter startup.

[0087] To facilitate a better understanding of the power converter startup control method, device, and power converter startup system, the variable frequency startup control of an LLC frequency modulation converter is taken as an example for detailed explanation below.

[0088] The traditional startup method of the frequency-modulated LLC power converter is to first change the pulse width and then perform frequency switching. Although this startup method can start the LLC power converter, it has the following disadvantages:

[0089] ① During the startup process, the switching point from pulse width change to frequency modulation is prone to hardware overcurrent faults. If the fault protection is not timely, it is easy to damage the circuit board, causing great safety hazards;

[0090] ② The switching conditions need to be set. If the conditions are not set properly, the power converter will be difficult to start. This means that a lot of time and energy will be spent on debugging and finding the right conditions, which will increase the project cycle.

[0091] ③The output voltage establishment curve at startup does not change smoothly.

[0092] Based on this, the present application provides a time domain frequency conversion starting control solution. By adopting the time domain frequency conversion starting control method, it can effectively solve the problems of circuit board burning and uneven output voltage curve caused by failure during the startup of LLC variable frequency power converter, and can also reduce the startup debugging time of the power board and shorten the project cycle.

[0093] like Figure 7 As shown, the power converter startup system includes a microcontroller 212, a first drive regulation circuit 222, a second drive regulation circuit 224, a power converter, and a sampling circuit 240. The power converter includes a first conversion circuit 232, a transformer T, and a second conversion circuit 234. The microcontroller 212 outputs a PWM wave, which controls the operation of the power transistors in the power converter through the first drive regulation circuit 222 and the second drive regulation circuit 224.

[0094] like Figure 8 As shown, the microcontroller 212 outputs a complementary PWM wave, where DB is the dead time, which does not change, and the frequency of the PWM wave is constantly changing. During the startup process of the LLC power converter, the microcontroller 212 will first output a high-frequency PWM wave (such as a 500kHz PWM wave). Outputting a high-frequency PWM wave at the startup moment will not cause the LLC power converter to malfunction or burn out the circuit board. After that, it enters the time domain frequency modulation control link, and debugs and selects the appropriate amplitude to reduce the frequency according to the needs. The PWM wave conversion process is as follows Figure 8 As shown, the frequencies of p1 to p3 gradually decrease, but the duty cycle remains unchanged at 50%.

[0095] like Figure 9The figure shows the change of a single PWM wave during frequency modulation control. For example, at time t a When the PWM wave frequency is f a , the corresponding pulse width is h, at time t b The frequency f of the PWM wave a becomes frequency f b , the pulse width increases by d h .

[0096] Figure 10 The figure shows the startup diagram of different variables under PID regulation. a and b are the startup curves when different variables are regulated. Curve a is at time t a When the output voltage reaches the set output voltage Vset, curve b at time t b The factors that affect the startup curve are: PID parameters, PID limit value and dh / dt value. Among them, dh / dt (that is, the pulse width change frequency of the pulse width modulation signal) is used to measure the speed of change of the pulse width h during the PWM wave change process. When dh / dt changes greatly, Figure 10 The startup curve becomes very steep, otherwise it becomes flat.

[0097] Different loads have different requirements for the output voltage buildup of the power converter. A fast or slow output voltage buildup can cause load failure. You can select appropriate PID parameters based on actual needs, as well as a suitable update rate when updating the PID limit values. Furthermore, dh / dt is related to the difference between the output voltage and the set output voltage, and the relationship between the two can be set to either a linear or nonlinear relationship.

[0098] like Figure 11 This is a flowchart of the LLC frequency converter startup process. First, the LLC power converter performs initialization work immediately after power-on, such as bias calibration of the sampling circuit 240, configuration of the PWM register and ADC register, etc. After the microcontroller 212 determines that the power converter can operate normally according to the initialization logic, it outputs complementary PWM waves to the corresponding power transistors, starts the power converter, and disables synchronous rectification. This is because performing synchronous rectification during startup can cause malfunctions, and in severe cases, it can damage the power transistors and burn out the power converter. Figure 7 As shown, the power tubes Q1 and Q4 are driven by the same PWM wave, the power tubes Q2 and Q3 are driven by the same PWM wave; the power tubes Q1 and Q2 are driven by complementary PWM waves. Figure 8 As shown in FIG, there is a dead zone DB between PWM wave drives, and the dead zone time remains constant. Similarly, power transistors Q3 and Q4 are driven by complementary PWM waves with dead zones.

[0099] Microcontroller 212 controls first drive regulation circuit 222 to output a high-frequency PWM wave. Selecting a high-frequency PWM wave for driving prevents the instantaneous generation of high current in the power converter's main circuit, effectively preventing malfunctions. However, after the high-frequency PWM wave is activated, relying solely on PID output regulation without forced frequency reduction will still allow the output voltage to reach the set voltage value. However, the frequency of the driving PWM wave is very high, causing severe heating of the power tube, which is inconsistent with the circuit characteristics of the LLC power converter. Therefore, software-driven frequency reduction is required.

[0100] Specifically, the LLC power converter circuit's operating frequency fully enters discontinuous mode between the first and second resonant frequencies, achieving zero voltage turn-on and zero current turn-off, effectively improving the power converter's efficiency and leveraging the advantages of the LLC power converter circuit. After the power converter is designed, the first and second resonant frequencies are fixed and can be calculated using a formula based on the LLC power converter's structure. The LLC power converter has three normal operating states: operating frequency greater than the first resonant frequency, operating frequency equal to the first resonant frequency, and operating frequency greater than the second resonant frequency but less than the first resonant frequency. However, the LLC power converter can achieve zero voltage turn-on and zero current turn-off when operating between the first and second resonant frequencies, resulting in high efficiency.

[0101] The first resonant frequency and the second resonant frequency are respectively used as the first set frequency f1 and the second set frequency f2. When the circuit is working, the operating frequency of the LLC power converter can be measured with an oscilloscope. When it is detected that the operating frequency is higher than the first set frequency f1, the operating frequency of the power tubes Q1-Q4 is forced to be reduced. The operating frequency range of the LLC power converter is forced to be reduced in each cycle, so that the operating frequency is forced to decrease. The amount of each reduction can be selected according to the actual needs to select a suitable value to reduce the upper limit of the operating frequency. The forced reduction of the operating frequency is mainly achieved in two aspects. On the one hand, it is achieved by continuously modifying the internal register value of the microcontroller 212. On the other hand, it is achieved by continuously modifying and updating the limit value of the PID. From two aspects, it is ensured that the operating frequency can be forced to be reduced so that the operating frequency of the LLC power converter circuit is between the first resonant frequency and the second resonant frequency. As Figure 11 As shown, if it is detected that the operating frequency is less than the first resonant frequency, the operation of updating the PID limit value and the internal register value to reduce the operating frequency may no longer be performed, and the fault detection process is entered.

[0102] When PWM waves of different frequencies are output to drive the power tube, the main circuit of the LLC power converter generates voltage and current, and the output voltage value continues to increase, which can effectively solve the problems of failure and burning of circuit boards during the traditional startup process. For safety reasons, fault detection and processing are still performed.

[0103] Sampling circuit 240 and an external interrupt circuit can be used to determine if a power converter fault has occurred. For example, if a power converter is designed to maintain a stable output voltage of 400V, but due to some factors, the output voltage of the power converter reaches 450V, sampling circuit 240 will sample this high voltage of 450V and compare it with a set safety value (for example, 405V). If 450V is greater than 405V, microcontroller 212 will take action to cut off the voltage output to prevent a safety accident. Alternatively, an interrupt method can be used: when the external voltage exceeds 405V, an interrupt is triggered, and microcontroller 212 takes action to cut off the voltage output.

[0104] When no fault occurs, the ADC sampling is performed through the sampling circuit 240 to obtain the current output voltage value. From a macroscopic point of view, the voltage value continues to rise until it is the same as the set voltage value. When the output voltage is the same as the set value, the LLC power converter starts synchronous rectification and enters the normal operation logic. Otherwise, Figure 11 As shown, the startup time of the LLC power converter needs to be adjusted. When the difference between the detection voltage and the set voltage is large, dh / dt is increased. It can be a linear increase or a nonlinear increase. By increasing the pulse width change frequency of the PWM wave, the output voltage value is increased and the startup time is reduced; vice versa.

[0105] If a cycle does not enter the normal operating logic, it will enter the cycle again until the sampled output voltage reaches the set output voltage, enter the synchronous rectification and normal operating logic; if the startup process enters the fault logic, then after the fault is resolved and restored, the startup process will be restarted.

[0106] After synchronous rectification is enabled and normal operation begins, microcontroller 212 uses the input voltage sampled by sampling circuit 240 as one of the criteria for determining when to enable or disable synchronous rectification. For example, synchronous rectification is enabled when the input voltage is greater than 380V. In actual operation, microcontroller 212 enables synchronous rectification when the input voltage is greater than 380V and disables it when the input voltage is less than 380V.

[0107] The time-domain variable frequency startup control solution provided in this application has the following beneficial effects:

[0108] ① The power tube changes regularly, and no hardware overcurrent, software overcurrent, overvoltage or other faults will occur during the startup process. It is safe and reliable, and increases the service life of the power converter;

[0109] ② There is no switching during the startup process, and the adjustment is smooth. There is no need to spend time looking for switching conditions, which reduces development time;

[0110] ③During the whole process, the output voltage establishment curve changes smoothly.

[0111] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0112] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A power converter startup control method, characterized in that: include: Outputting a pulse width modulation signal to a power converter, wherein the pulse width modulation signal is used to drive a power tube of the power converter; Obtaining an operating frequency of the power converter; When the operating frequency of the power converter is greater than a set operating frequency, gradually reducing the frequency of the pulse width modulation signal to reduce the operating frequency of the power converter; wherein the set operating frequency includes a first resonant frequency and a second resonant frequency, and the first resonant frequency is greater than the second resonant frequency; when the operating frequency of the power converter is greater than the first resonant frequency, gradually reducing the frequency of the pulse width modulation signal to make the operating frequency of the power converter between the first resonant frequency and the second resonant frequency; When the operating frequency of the power converter is less than or equal to the first resonant frequency, obtaining the output voltage of the power converter; When the output voltage does not reach the set output voltage, the pulse width variation frequency of the pulse width modulation signal is adjusted according to the difference between the output voltage and the set output voltage until the output voltage reaches the set output voltage.

2. The power converter startup control method according to claim 1, wherein: The step of gradually reducing the frequency of the pulse width modulation signal includes: gradually reducing the frequency of the pulse width modulation signal through PID regulation control.

3. The power converter startup control method according to claim 2, wherein: The step of gradually decreasing the frequency of the pulse width modulation signal by PID regulation control includes: updating the PID limit value and / or register value according to a set update rate, so that the frequency of the pulse width modulation signal gradually decreases and the duty cycle remains unchanged.

4. The power converter startup control method according to claim 1, wherein: After obtaining the output voltage of the power converter, the method further includes: When the output voltage reaches the set output voltage, the power converter is controlled to perform synchronous rectification.

5. The power converter startup control method according to claim 1, wherein: If the operating frequency of the power converter is less than or equal to the set operating frequency, before obtaining the output voltage of the power converter, the method further includes: Check whether the power converter is faulty; When no fault is detected, the step of obtaining the output voltage of the power converter is performed.

6. The power converter startup control method according to claim 5, wherein: After detecting whether the power converter is faulty, the method further includes: When a fault is detected, the fault handling logic is activated to cut off the output of the power converter.

7. A power converter startup control device, characterized in that: include: A signal output module, configured to output a pulse width modulation signal to a power converter, wherein the pulse width modulation signal is used to drive a power transistor of the power converter; A frequency detection module, configured to obtain the operating frequency of the power converter; a frequency adjustment module, configured to, when the operating frequency of the power converter is greater than a set operating frequency, gradually reduce the frequency of the pulse width modulation signal to reduce the operating frequency of the power converter; wherein the set operating frequency includes a first resonant frequency and a second resonant frequency, and the first resonant frequency is greater than the second resonant frequency; when the operating frequency of the power converter is greater than the first resonant frequency, gradually reduce the frequency of the pulse width modulation signal to make the operating frequency of the power converter between the first resonant frequency and the second resonant frequency; a voltage regulation module, which obtains the output voltage of the power converter when the operating frequency of the power converter is less than or equal to the first resonant frequency; and when the output voltage does not reach the set output voltage, adjusts the pulse width variation frequency of the pulse width modulation signal according to the difference between the output voltage and the set output voltage until the output voltage reaches the set output voltage.

8. A power converter starting system, characterized in that: It includes a power converter, a drive adjustment device and a controller, the controller is connected to the drive adjustment device, the drive adjustment device is connected to the power converter, and the controller is used to perform power converter startup control according to the method according to any one of claims 1-6.

9. The power converter startup system according to claim 8, wherein: It also includes a sampling circuit, which is connected to the controller and the power converter.

10. The power converter startup system according to claim 8, wherein: The power converter includes a first conversion circuit, a transformer and a second conversion circuit. The drive regulation device includes a first drive regulation circuit and a second drive regulation circuit. The primary winding of the transformer is connected to the first conversion circuit, and the secondary winding of the transformer is connected to the second conversion circuit. The first drive regulation circuit is connected to the controller and the first conversion circuit, and the second drive regulation circuit is connected to the controller and the second conversion circuit.

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