Power converter and its control method
By introducing auxiliary switching circuits and control devices into the bridgeless PFC circuit, the hard turn-on and reverse recovery problems of high-frequency switching transistors are solved, zero-voltage turn-on and reverse recovery losses are reduced, the efficiency and performance of the converter are improved, and the cost is reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- MORNSUN GUANGZHOU SCI & TECH
- Filing Date
- 2026-01-04
- Publication Date
- 2026-06-02
AI Technical Summary
The hard turn-on and reverse recovery losses of high-frequency switching transistors in existing bridgeless PFC circuits result in high cost and low efficiency, making it difficult to meet the requirements of high performance and high power.
By introducing an auxiliary switching circuit and control device into the PFC circuit, the turn-on and turn-off sequence of the auxiliary switching transistor is controlled, so that the current of the magnetizing transistor and the freewheeling transistor is reduced to zero before the high-frequency switching transistor is turned on, thereby achieving zero-voltage turn-on and reducing reverse recovery losses.
It reduces the losses of high-frequency switching transistors, reduces heat dissipation costs, improves converter efficiency and power density, simplifies control logic, and reduces device costs.
Smart Images
Figure CN122137226A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power electronics technology, and in particular to power converters and their control methods. Background Technology
[0002] In AC / DC systems, driven by energy conservation and emission reduction policies, the requirements for system efficiency are becoming increasingly stringent. Furthermore, regulations mandate that AC / DC power supplies above 75W require the addition of a Power Factor Correction (PFC) circuit to achieve better Power Generation and Total Discharge (THD), improve energy utilization, and reduce harmonic pollution to the power grid. Traditional bridged PFC outputs a flat-wave voltage through a rectifier bridge. This voltage has a fixed polarity, making control relatively simple. However, because the power path of a bridged PFC requires passing through the rectifier bridge, its efficiency is relatively low and cannot meet the high-performance demands of power supplies.
[0003] To address the issue of high rectifier bridge losses in bridged PFC, various bridgeless PFC structures have evolved. Among the many Boost-PFC topologies, Totem bridgeless PFC is favored for its high efficiency and low component count, such as... Figure 1 The diagram shown is the circuit diagram of Totem Bridgeless PFC.
[0004] In the application of totem bridgeless PFC, there are two main current modes. For ease of description, high-frequency power transistors can be divided into magnetizing transistors and freewheeling transistors according to the magnetization / freewheeling (demagnetization) path of the inductor.
[0005] The first current mode is the inductor current critical mode (CRM), where the current is zero when the magnetizer is turned on, resulting in zero turn-on losses. The current is also zero when the freewheeling diode is turned off, thus the reverse recovery losses are essentially zero. Based on these characteristics, Si-MOS transistors are typically used in this mode. However, in medium to high power applications, due to the large peak inductor current, the power transistors require a large current-carrying capacity, making transistor selection difficult and costly. An interleaved parallel structure is usually adopted, but this doubles the number of PFC inductors and high-frequency power transistors, significantly increasing cost and size.
[0006] Another type is continuous current mode (CCM), where the inductor current is non-zero when the transistor is turned on, and also non-zero when the freewheeling diode is turned off. Therefore, when using Si-MOS power transistors, the magnetizer suffers from significant turn-on losses, and the freewheeling diode suffers from significant reverse recovery losses. In low-power applications, these losses are not significant, but they limit converter performance in medium-to-high power applications and increase heat dissipation costs. To address these issues, current technologies generally employ high-frequency wide-bandgap devices such as silicon carbide (SiC) or gallium nitride (GaN). SiC offers faster switching speeds and better reverse recovery characteristics compared to Si-MOS, but the turn-on losses of the magnetizer and the reverse recovery losses of the freewheeling diode are still considerable. Therefore, GaN is still required for high-performance or higher power applications. Inevitably, the use of both SiC and GaN leads to a significant increase in product costs and reduced competitiveness. Summary of the Invention
[0007] This invention provides a power converter and related devices that can solve the problems of hard turn-on and reverse recovery of high-frequency switching transistors, improve performance, and reduce costs.
[0008] In a first aspect, the present invention provides a power converter, including a PFC circuit, an auxiliary switching circuit, and a control device, wherein the PFC circuit is connected to the auxiliary switching circuit, and the control device is connected to both the PFC circuit and the auxiliary switching circuit. The control device is used to control the switching timing of the PFC circuit and the auxiliary switching circuit, thereby generating a drive signal for the auxiliary switching transistor in the auxiliary switching circuit based on the drive signal of the switching transistor in the PFC circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit. The auxiliary switching circuit is used to control the auxiliary switching tube to turn off for a period of time after it is turned on, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the PFC circuit is turned on.
[0009] Optionally, the PFC circuit includes a bridgeless PFC circuit and a bridged PFC circuit.
[0010] Optionally, the auxiliary switching circuit includes an auxiliary bridge arm and an auxiliary inductor, with a first end of the auxiliary inductor connected to the PFC inductor in the PFC circuit and a second end of the auxiliary inductor connected to the midpoint of the auxiliary bridge arm.
[0011] Optionally, the auxiliary switch in the auxiliary bridge arm includes a first auxiliary switch and a second auxiliary switch. The first end of the first auxiliary switch is connected to the output terminal of the power converter, the second end of the first auxiliary switch is connected to the first end of the second auxiliary switch and the second end of the auxiliary inductor, and the second end of the second auxiliary switch is connected to ground.
[0012] Optionally, the auxiliary bridge arm further includes an auxiliary diode, the cathode of which is connected to the output terminal of the power converter, and the anode of which is connected to the first terminal of the auxiliary switch and the second terminal of the auxiliary inductor, respectively. The second terminal of the auxiliary switch is connected to ground.
[0013] Optionally, the pulse width of the drive signal for the auxiliary switch is positively correlated with the input voltage or output power.
[0014] Secondly, the present invention also provides a control method for a power converter, the power converter including a PFC circuit and an auxiliary switching circuit, the PFC circuit being a bridgeless PFC circuit, and the control method comprising the following steps: The system detects the input voltage, average inductor current, and output voltage, and determines the polarity of the input voltage to determine the current input voltage cycle. Based on the current input voltage cycle, a drive signal for the corresponding auxiliary switch in the auxiliary switching circuit is generated based on the drive signal of the freewheeling diode in the bridgeless PFC circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit. After the auxiliary switch is turned on, it is turned off for a period of time, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the bridgeless PFC circuit is turned on.
[0015] Optionally, generating the drive signal for the corresponding auxiliary switching transistor in the auxiliary switching circuit based on the drive signal of the freewheeling transistor in the PFC circuit according to the current input voltage cycle includes: If the current input voltage period is determined to be a positive half-power frequency period, then the freewheeling transistor in the PFC circuit is the first switching transistor, and the excitation transistor is the second switching transistor. The driving signal of the corresponding auxiliary switching transistor in the auxiliary switching circuit is generated according to the falling edge of the driving signal of the first switching transistor. If the current input voltage period is determined to be the negative half-power frequency period, then the freewheeling transistor in the PFC circuit is the second switching transistor, and the excitation transistor is the first switching transistor. The driving signal of the corresponding auxiliary switching transistor in the auxiliary switching circuit is generated based on the falling edge of the driving signal of the second switching transistor.
[0016] Thirdly, the present invention also provides a control method for a power converter, the power converter including a PFC circuit and an auxiliary switching circuit, the PFC circuit being a bridged PFC circuit, and the control method comprising the following steps: The driving signal of the freewheeling diode in the PFC circuit is used to generate the driving signal of the corresponding auxiliary switching diode in the auxiliary switching circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit. After the auxiliary switch is turned on, it is turned off for a period of time, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the bridged PFC circuit is turned on.
[0017] After being turned on, a fixed pulse width signal or a variable pulse width signal is generated, so that the current of the rectifier diode in the bridged PFC circuit is zero before the high-frequency switching transistor in the PFC circuit is turned on.
[0018] Optionally, the pulse width of the variable pulse width signal is proportional to the output voltage of the rectifier bridge or the power output of the power supply in the bridged PFC circuit.
[0019] By implementing the embodiments of the present invention, the following beneficial effects can be achieved: This invention achieves near-zero reverse recovery for the high-frequency power transistors in a PFC circuit and zero-voltage turn-on for the high-frequency excitation switch, significantly reducing losses caused by reverse recovery and hard turn-on in existing solutions. Furthermore, the reduced losses in the high-frequency switch decrease its reliance on heat sinks, lowering heat dissipation costs; it also improves converter efficiency, contributing to increased power density. The circuit structure proposed in this invention is simple, and the control is straightforward and easy to implement. Compared to directly replacing the high-frequency bridge arm switch with GaN / SiC, this invention only requires a simple auxiliary circuit to solve the hard turn-on and reverse recovery problems, greatly reducing the cost of power devices. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly described below.
[0021] Figure 1 The diagram shows the existing bridgeless PFC circuit structure of Totem. Figure 2 Key waveform diagrams for bridgeless PFC in the existing CCM mode; Figure 3 The diagram shows the existing bridgeless PFC circuit structure of the interleaved CRM totem. Figure 4 This is a schematic diagram of the improved totem-style bridgeless PFC circuit according to the first embodiment of the present invention; Figure 5 This is a block diagram of the improved totem bridgeless PFC control logic of the first embodiment of the present invention; Figure 6 This is a key waveform diagram of the improved totem-style bridgeless PFC according to the first embodiment of the present invention; Figure 7 This is a schematic diagram of the improved bridged PFC circuit according to the second embodiment of the present invention. Detailed Implementation
[0022] To better understand the improvements made by this invention compared to the prior art, specific embodiments of the invention will be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention.
[0023] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "in an embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the accompanying drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
[0024] refer to Figure 4 and Figure 5 The present invention provides a power converter, including a PFC circuit, an auxiliary switching circuit 100 and a control device, wherein the PFC circuit is connected to the auxiliary switching circuit 100 and the control device is connected to both the PFC circuit and the auxiliary switching circuit 100. The control device is used to control the switching timing of the PFC circuit and the auxiliary switching circuit 100, thereby generating a driving signal for the auxiliary switching transistor in the auxiliary switching circuit 100 based on the driving signal of the switching transistor in the PFC circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit 100. The auxiliary switching circuit 100 is used to control the auxiliary switching tube to turn off for a period of time after it is turned on, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the excitation tube of the PFC circuit is turned on.
[0025] It should be noted that the PFC circuit can be a bridgeless PFC circuit or a bridged PFC circuit. The bridgeless PFC circuit can be a basic bridgeless circuit, a dual boost bridgeless circuit, or a totem bridgeless circuit structure.
[0026] The control device includes a sampling module and a drive control module. The sampling module samples the input voltage, output voltage, and average inductor current, obtaining the corresponding input voltage sampling signal Vin, output voltage sampling signal Vsense, and average inductor current sampling signal ILavg. The drive control module receives the sampling signals. Vin determines the polarity of the input power supply and turns on the corresponding high-frequency bridge arm power transistor and auxiliary bridge arm power transistor. ILavg is used for average current control and output power detection. Furthermore, the sampling signals Vin and ILavg are also used to compensate the pulse width of the auxiliary switching transistor.
[0027] Preferably, taking the positive half-power frequency cycle as an example, the auxiliary switch is turned on for a period of time before the first power transistor S1 is turned off, so that the output voltage excites the auxiliary inductor, thereby reversing the current of the first power transistor S1. No current flows through the body diode of the first power transistor S1, reducing the reverse recovery loss after the first power transistor S1 is turned off. At the same time, the pulse width of the auxiliary switch is controlled to achieve zero-voltage turn-on (ZVS) of the second power transistor S2.
[0028] Preferably, taking the positive half-cycle as an example, the auxiliary switch is turned on before the first power transistor S1 is turned off, and the turn-off time of the auxiliary switch is no later than the turn-off time of the second power transistor S2. Similarly, in the negative half-cycle, the corresponding auxiliary switch is turned on before the second power transistor S2 is turned off, and the turn-off time of the corresponding auxiliary switch is no later than the turn-off time of the first power transistor S1. Preferably, the auxiliary inductor can be a discrete inductor or the inductor winding can be wound onto the PFC inductor for magnetic coupling.
[0029] It should be noted that the PFC circuit includes a first bridge arm, a second bridge arm, and a PFC inductor. The power transistor in the first bridge arm can be a switching device such as a Si-MOS transistor, GaN, or SiC; the power transistor in the second bridge arm can be a switching device such as a Si-MOS transistor, GaN, or SiC, or it can be a diode.
[0030] In one embodiment, the auxiliary switching circuit 100 includes an auxiliary bridge arm and an auxiliary inductor. A first end of the auxiliary inductor is connected to the PFC inductor in the PFC circuit, and a second end of the auxiliary inductor is connected to the midpoint of the auxiliary bridge arm. The power transistor in the auxiliary bridge arm can be a switching device such as a Si-MOS transistor, GaN, or SiC, or it can be a diode.
[0031] In one embodiment, the auxiliary switch in the auxiliary bridge arm includes a first auxiliary switch and a second auxiliary switch. The first end of the first auxiliary switch is connected to the output terminal of the power converter, the second end of the first auxiliary switch is connected to the first end of the second auxiliary switch and the second end of the auxiliary inductor, and the second end of the second auxiliary switch is connected to ground.
[0032] The first auxiliary switch and the second auxiliary switch can be switching devices such as Si-MOS transistors, GaN, SiC, or diodes. In this embodiment, both the first auxiliary switch and the second auxiliary switch are NMOS transistors. The first terminal of the first auxiliary switch is the drain and the second terminal of the first auxiliary switch is the source. The first terminal of the second auxiliary switch is the drain and the second terminal of the second auxiliary switch is the source.
[0033] In one embodiment, the auxiliary bridge arm further includes an auxiliary diode, the cathode of which is connected to the output terminal of the power converter, and the anode of which is connected to the first terminal of the auxiliary switch and the second terminal of the auxiliary inductor, respectively. The second terminal of the auxiliary switch is connected to ground.
[0034] In one embodiment, the pulse width of the drive signal for the auxiliary switch is positively correlated with the input voltage or the output power.
[0035] Furthermore, embodiments of the present invention also provide a control method for a power converter, the power converter including a PFC circuit and an auxiliary switching circuit 100, the PFC circuit being a bridgeless PFC circuit, and the control method including the following steps: S101. Detect the input voltage, average inductor current, and output voltage, and determine the polarity of the input voltage to determine the current input voltage cycle; When it is determined to be the positive half-power frequency cycle, that is, the first power transistor S1 of the first bridge arm is a freewheeling transistor, and the current flowing through S1 is ID1 (direction from source to drain), and the second power transistor S2 of the first bridge arm is a magnetizing transistor, and the current flowing through S2 is ID2 (direction from drain to source).
[0036] S102. Based on the current input voltage cycle, generate a drive signal for the corresponding auxiliary switch in the auxiliary switch circuit 100 based on the drive signal of the freewheeling transistor in the bridgeless PFC circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switch circuit 100. S103. Control the auxiliary switch to turn off after a period of time, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the bridgeless PFC circuit is turned on.
[0037] Among them, the auxiliary switch S4 is turned on and then turned off for a period of time, so that the current ID1 is less than zero and the current ID2 is also less than zero before S2 is turned on. This can reduce the reverse recovery of the body diode D1 after S1 is turned off, and at the same time, it can enable S2 to achieve zero voltage turn-on (ZVS). If the polarity of the input voltage VIN is detected to be the negative half-cycle of the power frequency, then S1 is the magnetizer and S2 is the freewheeling diode. The control method with the same positive half-cycle of the power frequency is used to control the pulse width of the auxiliary switch S3 to optimize the reverse recovery of the freewheeling diode S2 and the ZVS of the magnetizer S1.
[0038] It should be noted that the conduction time of the auxiliary switch S4 can be determined by pre-setting a base time, and then multiplying the detected input voltage and output power by coefficients k1 and k2 respectively for positive compensation. The total conduction time is base time + k1*Vin + k2*Iavg_pk (the coefficients are adjusted by external circuitry or internal chip); it can also be determined by detecting the current of the magnetizing tube and the demagnetizing tube.
[0039] Optionally, generating the drive signal for the corresponding auxiliary switch in the auxiliary switching circuit 100 based on the drive signal of the freewheeling transistor in the PFC circuit according to the current input voltage cycle includes: If the current input voltage period is determined to be a positive half-power frequency period, then the freewheeling transistor in the PFC circuit is the first switching transistor, and the excitation transistor is the second switching transistor. The driving signal of the corresponding auxiliary switching transistor in the auxiliary switching circuit 100 is generated according to the falling edge of the driving signal of the first switching transistor. If the current input voltage period is determined to be the negative half-power frequency period, then the freewheeling transistor in the PFC circuit is the second switching transistor, and the excitation transistor is the first switching transistor. The driving signal of the corresponding auxiliary switching transistor in the auxiliary switching circuit 100 is generated based on the falling edge of the driving signal of the second switching transistor.
[0040] Preferably, in the sampling step, the average inductor current and output voltage are also sampled to realize the output power detection and obtain an output power detection signal. When the detection signal is less than a set threshold, the drive signal of the first bridge arm switch is stopped, and the third bridge arm is controlled by PWM to transmit energy to the output, thereby reducing drive loss and switching loss. Preferably, during the positive half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S4 can be generated before the falling edge of the drive signal of the freewheeling diode S1, and during the negative half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S3 can be generated before the falling edge of the drive signal of the freewheeling diode S2.
[0041] Preferably, during the positive half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S4 can be generated after the falling edge of the drive signal of the freewheeling diode S1, and during the negative half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S3 can be generated after the falling edge of the drive signal of the freewheeling diode S2.
[0042] Preferably, in order to simplify control, the pulse width of the drive signal of the auxiliary switch S4 can be a fixed value during the positive half-cycle of the power frequency, and the pulse width of the drive signal of the auxiliary switch S3 can be a fixed value during the negative half-cycle of the power frequency. Preferably, in order to provide better control performance, during the positive half-cycle of the power frequency, the pulse width of the drive signal of the auxiliary switch S4 can be adjusted in a positive correlation with the magnitude of the input voltage and the magnitude of the output power. During the negative half-cycle of the power frequency, the pulse width of the drive signal of the auxiliary switch S3 can be adjusted in a positive correlation with the magnitude of the input voltage and the magnitude of the output power, thereby optimizing the reverse recovery of the freewheeling tube and the ZVS of the excitation tube across the entire voltage and load range.
[0043] Preferably, the power converter operates in constant frequency current continuous mode (CCM).
[0044] In addition, this embodiment of the invention also provides a control method for a power converter, the power converter including a PFC circuit and an auxiliary switching circuit 100, the PFC circuit being a bridged PFC circuit, and the control method including the following steps: The drive signal of the freewheeling transistor in the PFC circuit is used to generate the drive signal of the corresponding auxiliary switching transistor in the auxiliary switching circuit 100, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit 100. After the auxiliary switch is turned on, it is turned off for a period of time, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the bridged PFC circuit is turned on.
[0045] After being turned on, a fixed pulse width signal or a variable pulse width signal is generated, so that the current of the rectifier diode in the bridged PFC circuit is zero before the high-frequency switching transistor in the PFC circuit is turned on.
[0046] Optionally, the pulse width of the variable pulse width signal is proportional to the output voltage of the rectifier bridge or the power output of the power supply in the bridged PFC circuit.
[0047] First Embodiment Figure 4 The circuit diagram of the improved totem-style bridgeless PFC according to the first embodiment of the present invention is shown. The improved totem-style bridgeless PFC circuit adds an auxiliary switching bridge arm and an auxiliary inductor to the basic totem-style bridgeless PFC circuit. The improved totem-style bridgeless PFC includes an input power supply, a PFC inductor, a high-frequency bridge arm, a low-frequency bridge arm, an output load, an auxiliary bridge arm, an auxiliary inductor, and a control device, with the following connection relationships: The high-frequency bridge arm includes a first switch S1 and a second switch S2. The drain of the first switch S1 is connected to the positive terminal of the output load, and the source of the first switch S1 is connected to the drain of the second switch S2, forming the midpoint of the high-frequency bridge arm. The source of the second switch S2 is connected to the negative terminal of the output load. D1 and D2 are the body diodes of S1 and S2, respectively, and C1 and C2 are the output junction capacitances of S1 and S2, respectively. The low-frequency bridge arm includes a fifth diode and a sixth diode. The cathode of the fifth diode is connected to the positive terminal of the output load, and the anode is connected to the cathode of the sixth diode, forming the midpoint of the low-frequency bridge arm. The anode of the sixth diode is connected to the negative terminal of the output load. The auxiliary bridge arm includes a third switch S3 and a fourth switch S4. The drain of the third switch S3 is connected to the positive terminal of the output load, and the source of the third switch S3 is connected to the drain of the fourth switch S4, forming the midpoint of the auxiliary bridge arm. The source of the fourth switch S4 is connected to the negative terminal of the output load. D3 and D4 are the body diodes of S3 and S4, respectively, and C3 and C4 are the output junction capacitances of S3 and S4, respectively. The first end of the auxiliary inductor is connected to the midpoint of the auxiliary bridge arm, and the second end is connected to the midpoint of the high-frequency bridge arm and connected to the second end of the PFC inductor. The first end of the PFC inductor is connected to the first end of the input power supply, and the second end of the input power supply is connected to the midpoint of the low-frequency bridge arm.
[0048] The control device is used to control the switching timing of the high-frequency bridge arm and the auxiliary bridge arm. For the control of the high-frequency bridge arm, mature single-cycle control can be used. Taking fixed-frequency control as an example, the falling edge of the freewheeling diode is determined, so the drive of the auxiliary bridge arm switching transistor can be generated based on the falling edge of the freewheeling diode.
[0049] The control method for the auxiliary bridge arm by the control device includes the following steps: Sampling steps: Detect the polarity of the input voltage VIN, detect the average inductor current, detect the output voltage, and determine the polarity based on the detection results. When it is determined to be the positive half-power frequency cycle, that is, the first power transistor S1 of the first high-frequency bridge arm is a freewheeling transistor, and the current flowing through S1 is ID1 (direction from source to drain), and the second power transistor S2 of the first high-frequency bridge arm is a magnetizing transistor, and the current flowing through S2 is ID2 (direction from drain to source).
[0050] Conduction control steps: The drive signal for the auxiliary tube S4 is generated based on the falling edge of the drive signal S1. During the turn-on period of S4, the output voltage VOUT excites the auxiliary inductor L2.
[0051] Turn-off control steps: After S4 is turned on, it is turned off for a period of time, so that the current ID1 is less than zero and the current ID2 is also less than zero before S2 is turned on. This can reduce the reverse recovery of the body diode D1 after S1 is turned off, and at the same time, it can enable S2 to achieve zero voltage turn-on (ZVS). If the polarity of the input voltage VIN is detected to be the negative half-cycle of the power frequency, then S1 is the magnetizer and S2 is the freewheeling diode. The control method with the same positive half-cycle of the power frequency is used to control the pulse width of the auxiliary tube S3 to optimize the reverse recovery of the freewheeling diode S2 and the ZVS of the magnetizer S1.
[0052] The waveform diagram of the improved totem-based bridgeless PFC according to the first embodiment of the present invention is shown below. Figure 5 As shown, taking the positive half-power frequency cycle as an example, the working process is as follows: 1) t0-t1: The high-frequency bridge arm switch S2 is turned on, the input voltage VIN excites the PFC inductor L1, the current IL1 rises linearly, and at the same time the auxiliary inductor L2 is quickly demagnetized to 0. 2) t1-t2: The auxiliary inductor L2 resonates with the output capacitor of the auxiliary bridge arm switch S4, VDS4 drops, and the auxiliary inductor is reverse-magnetized until the body diode of S4 is turned on. 3) t2-t3: At this time, L2 demagnetizes in reverse. The demagnetizing voltage is the voltage drop across the DC impedance + the conduction voltage drop of S2 + the voltage drop of the body diode of S4. Since the demagnetizing voltage is small, the demagnetizing process lasts for a long time and the demagnetizing process is not over until time t3. 4) t3-t4: The high-frequency bridge arm switch S2 is turned off, and the inductor currents IL1 and IL2 charge and discharge the output junction capacitances of S2 and S1. VDS2 rises to Vo, and the body diode of S1 turns on. At this time, VDS2 quickly demagnetizes L2. After demagnetizing to zero, it is re-magnetized in the reverse direction until time t4, when VDS4 rises to Vo. At this time, the high-frequency bridge arm S1 achieves ZVS. 5) t4-t5: During this stage, Vo-Vin demagnetizes the PFC inductor L1 to provide energy for the output load. At the same time, L2 is also demagnetized. The demagnetizing voltage is the voltage drop across the DC impedance - the on-state voltage drop of S1 + the voltage drop of the body diode of S3. 6) t5-t6: S1 continues to conduct. At this time, S4 is turned on, and Vo excites the auxiliary inductor L2. Since the inductance of the auxiliary inductor is small, the demagnetizing current IDS1 flowing through S1 decreases rapidly to zero. 7) t6-t7: At this time, IL2=IL1, ID1=0. After this, the high-frequency bridge arm switch S1 is turned off, so the body diode of S1 has no reverse recovery. 8) t7-t8: S4 continues to conduct for a period of time, IL2 is greater than IL1, the auxiliary bridge arm S4 is turned off, IL2-IL1 charges and discharges the parasitic capacitance of the high-frequency bridge arms S1 and S2. Before time t7, VDS2=0, so that the high-frequency bridge arm S2 can be turned on at time t7 to achieve ZVS. Preferably, during the positive half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S4 can be generated before the falling edge of the drive signal of the freewheeling diode S1, and during the negative half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S3 can be generated before the falling edge of the drive signal of the freewheeling diode S2. Preferably, during the positive half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S4 can be generated after the falling edge of the drive signal of the freewheeling diode S1, and during the negative half-cycle of the power frequency, the rising edge of the drive signal of the auxiliary switch S3 can be generated after the falling edge of the drive signal of the freewheeling diode S2. Preferably, in order to simplify control, the pulse width of the drive signal of the auxiliary switch S4 can be a fixed value during the positive half-cycle of the power frequency, and the pulse width of the drive signal of the auxiliary switch S3 can be a fixed value during the negative half-cycle of the power frequency. Preferably, in order to provide better control performance, during the positive half-cycle of the power frequency, the pulse width of the drive signal of the auxiliary switch S4 can be adjusted in a positive correlation with the magnitude of the input voltage and the magnitude of the output power. During the negative half-cycle of the power frequency, the pulse width of the drive signal of the auxiliary switch S3 can be adjusted in a positive correlation with the magnitude of the input voltage and the magnitude of the output power. This optimizes the reverse recovery of the freewheeling tube and the ZVS of the excitation tube across the entire voltage and load range. If the polarity of the input voltage VIN is negative half-cycle, then S1 is the magnetizing tube and S2 is the freewheeling tube. The pulse width optimization of S3 is used to control the reverse recovery of the freewheeling tube and the ZVS of the main tube, which are controlled by the same control method as the positive half-cycle. Because the auxiliary bridge arm switch has a short conduction time and a very small effective current, it is not sensitive to conduction losses. Therefore, a power transistor with a slightly larger conduction impedance and a smaller package can be selected to achieve greater results at a lower cost.
[0053] Second Embodiment Figure 6 The circuit schematic of an improved bridged PFC according to a second embodiment of the present invention is shown. This bridged PFC circuit, based on a Boost bridged PFC circuit, adds an auxiliary switching bridge arm and an auxiliary inductor. The Boost bridged PFC includes an input power supply, a rectifier bridge, a PFC inductor, a high-frequency switching transistor, a rectifier diode, an output load, an auxiliary bridge arm, an auxiliary inductor, and a control device. Its connection relationship is as follows: After the input power supply passes through the rectifier bridge, the positive output terminal is connected to the first terminal of the PFC inductor, and the negative output terminal is connected to the source of the high-frequency switching transistor. The second end of the PFC inductor is connected to the anode of the rectifier diode and to the drain of the high-frequency switching transistor, forming the midpoint of the high-frequency bridge arm. The auxiliary bridge arm includes an auxiliary switch S2 and an auxiliary diode D4. The cathode of the auxiliary diode D4 is connected to the positive terminal of the output load, and the anode of the auxiliary diode D4 is connected to the drain of the auxiliary switch S2, forming the midpoint of the auxiliary bridge arm. The source of the auxiliary switch S2 is connected to the negative terminal of the output load. D2 is the body diode of S2, and C2 is the output junction capacitance of S2. The first end of the auxiliary inductor is connected to the midpoint of the auxiliary bridge arm, and the second end is connected to the midpoint of the high-frequency bridge arm and connected to the second end of the PFC inductor. The first end of the PFC inductor is connected to the first end of the input power supply, and the second end of the input power supply is connected to the midpoint of the low-frequency bridge arm.
[0054] The control device is used to control the switching timing of the high-frequency switch and the auxiliary switch. For the control of the high-frequency switch, mature control technology can be used, such as single-cycle control. The rising edge of the high-frequency switch is determined, so the drive of the auxiliary switch can be generated based on the rising edge of the high-frequency switch.
[0055] The control method for the auxiliary switching transistor by the control device includes the following steps: A turn-on control step, generating a drive signal for the auxiliary switching transistor S2 based on the rising edge of the drive signal for the high-frequency switching transistor S1, with VOUT energizing the auxiliary inductor L2. A turn-off control step, generating a fixed pulse width signal or a variable pulse width signal after turn-on. The pulse width of the variable pulse width signal is proportional to the rectifier bridge output voltage and the power supply output power to achieve adjustable pulse width. This ensures that before the high-frequency switching transistor S1 is turned on, the rectifier diode current is zero, and the current direction of the high-frequency switching transistor S1 flows from the source to the drain, reducing the reverse recovery of the rectifier diode D1 after the high-frequency switching transistor S1 is turned on, and simultaneously enabling S1 to achieve zero-voltage turn-on.
[0056] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
[0057] Furthermore, all the terms "electrical connection" and "connection" mentioned in this patent application do not refer solely to the direct connection of components, but rather to the ability to form a better connection structure by adding or removing connecting accessories according to the specific implementation. The use of "electrical connection" in this invention is only to emphasize this meaning, but it does not preclude the use of "connection" and other terms from having the same meaning.
Claims
1. A power converter, characterized in that: It includes a PFC circuit, an auxiliary switching circuit, and a control device, wherein the PFC circuit is connected to the auxiliary switching circuit, and the control device is connected to both the PFC circuit and the auxiliary switching circuit. The control device is used to control the switching timing of the PFC circuit and the auxiliary switching circuit, thereby generating a drive signal for the auxiliary switching transistor in the auxiliary switching circuit based on the drive signal of the switching transistor in the PFC circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit. The auxiliary switching circuit is used to control the auxiliary switching tube to turn off for a period of time after it is turned on, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the PFC circuit is turned on.
2. The power converter according to claim 1, characterized in that: The PFC circuit includes a bridgeless PFC circuit and a bridged PFC circuit.
3. The power converter according to claim 1, characterized in that: The auxiliary switching circuit includes an auxiliary bridge arm and an auxiliary inductor. The first end of the auxiliary inductor is connected to the PFC inductor in the PFC circuit, and the second end of the auxiliary inductor is connected to the midpoint of the auxiliary bridge arm.
4. The power converter according to claim 3, characterized in that: The auxiliary switch in the auxiliary bridge arm includes a first auxiliary switch and a second auxiliary switch. The first end of the first auxiliary switch is connected to the output end of the power converter, and the second end of the first auxiliary switch is connected to the first end of the second auxiliary switch and the second end of the auxiliary inductor. The second end of the second auxiliary switch is connected to ground.
5. The power converter according to claim 1, characterized in that: The auxiliary bridge arm also includes an auxiliary diode, the cathode of which is connected to the output terminal of the power converter, and the anode of which is connected to the first terminal of the auxiliary switch and the second terminal of the auxiliary inductor, respectively. The second terminal of the auxiliary switch is connected to ground.
6. The power converter according to claim 1, characterized in that: The pulse width of the drive signal for the auxiliary switch is positively correlated with the input voltage or output power.
7. A control method for a power converter, characterized in that, The power converter includes a PFC circuit and an auxiliary switching circuit, wherein the PFC circuit is a bridgeless PFC circuit, and the control method includes the following steps: The system detects the input voltage, average inductor current, and output voltage, and determines the polarity of the input voltage to determine the current input voltage cycle. Based on the current input voltage cycle, a drive signal for the corresponding auxiliary switch in the auxiliary switching circuit is generated based on the drive signal of the freewheeling diode in the bridgeless PFC circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit. After the auxiliary switch is turned on, it is turned off for a period of time, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the bridgeless PFC circuit is turned on.
8. The control method according to claim 7, characterized in that: The step of generating a drive signal for the corresponding auxiliary switching transistor in the auxiliary switching circuit based on the drive signal of the freewheeling transistor in the PFC circuit according to the current input voltage cycle includes: If the current input voltage period is determined to be a positive half-power frequency period, then the freewheeling transistor in the PFC circuit is the first switching transistor, and the excitation transistor is the second switching transistor. The driving signal of the corresponding auxiliary switching transistor in the auxiliary switching circuit is generated according to the falling edge of the driving signal of the first switching transistor. If the current input voltage period is determined to be the negative half-power frequency period, then the freewheeling transistor in the PFC circuit is the second switching transistor, and the excitation transistor is the first switching transistor. The driving signal of the corresponding auxiliary switching transistor in the auxiliary switching circuit is generated based on the falling edge of the driving signal of the second switching transistor.
9. A control method for a power converter, characterized in that, The power converter includes a PFC circuit and an auxiliary switching circuit, wherein the PFC circuit is a bridged PFC circuit, and the control method includes the following steps: The driving signal of the freewheeling diode in the PFC circuit is used to generate the driving signal of the corresponding auxiliary switching diode in the auxiliary switching circuit, so that the output voltage excites the auxiliary inductor in the auxiliary switching circuit. After the auxiliary switch is turned on, it is turned off for a period of time, so that the current through the freewheeling tube and the excitation tube is less than or equal to zero before the magnetizing tube of the bridged PFC circuit is turned on. After being turned on, a fixed pulse width signal or a variable pulse width signal is generated, so that the current of the rectifier diode in the bridged PFC circuit is zero before the high-frequency switching transistor in the PFC circuit is turned on.
10. The control method according to claim 9, characterized in that: The pulse width of the variable pulse width signal is proportional to the output voltage of the rectifier bridge or the power output of the power supply in the bridged PFC circuit.