Current feed-forward type single-stage PFC (Power Factor Correction) fast charging application converter based on active clamping flyback circuit

Abstract

The invention relates to the field of charging and discharging equipment, in particular to a current feed-forward type single-stage PFC (Power Factor Correction) fast charging application converter based on an active clamping flyback circuit. The topological structure comprises an EMI filter circuit, a rectifier bridge, a BUS capacitor Cbus, an isolated resonant converter, a PFC inductor Lpfc and an output half-wave rectifier circuit. The EMI filter circuit is used for filtering harmonic waves, the PFC inductor is used for realizing voltage tracking by alternating current input side current, and the rectifier bridge provides a backflow path for the PFC inductor and charges a BUS capacitor Cbus; the isolated resonant converter is used for realizing primary and secondary side isolation and soft switching of a switching tube; the isolated resonant converter comprises a resonant capacitor Cr, an isolation transformer, a transformer leakage inductor Lr, a switching tube Q1 and a switching tube Q2, and Lr and Cr form a resonant cavity; the output half-wave rectification circuit comprises an SR tube located on the secondary side of the isolation transformer and an output capacitor Co.

Description

Technical Field

[0001] The present invention relates to the field of charging and discharging equipment, and in particular to a current feedforward type single-stage PFC fast charging application converter based on an active clamp flyback circuit. Background Art

[0002] With the rapid development of the global economy, energy and environmental issues have become particularly severe. Traditional non-renewable resources will gradually be replaced by renewable energy to achieve the dual carbon goals. With the popularization of portable mobile devices, high-power fast charging with a wide gain range, high efficiency, and high power density is also in demand. The traditional high-power fast charging adopts a two-stage structure, with the front stage realizing the PFC function and the rear stage realizing the isolated DC / DC function, but the two-stage solution has certain disadvantages in topology and efficiency. The traditional single-stage fast charging does not have the PFC function, so the input power cannot be greater than 75W, and the converter operates in a hard switching state, and the efficiency cannot be further improved.

[0003] Specifically, on the one hand, the efficiency of the traditional two-stage fast charging solution depends on the product of the efficiency of the front-stage PFC stage and the rear-stage isolated DC / DC stage, because all the energy needs to go through two-stage power conversion links, and the two-stage solution uses more devices and control ICs than the single-stage solution. On the other hand, the traditional unipolar fast charging solution, because it does not have the PFC function, the input power can only be below 75W, and the single-stage fast charging solution with PFC function has a large double power frequency ripple on the output due to the mismatch between input and output power, and the converter switch is in hard switching mode, and the energy conversion efficiency is low.

[0004] In a single-stage resonant PFC converter, since the LLC cannot achieve a wide gain range, the resonant inductor usually needs to be added externally, which increases the overall complexity of the system. Therefore, its application in fast charging converters is limited. Summary of the invention

[0005] The purpose of the present invention is to provide a single-stage PFC fast-charging topology suitable for a wide input-output range and propose its control scheme, by combining the Boost PFC circuit structure with the active clamp flyback circuit, so that the original topology does not increase the switch tube, does not increase the complexity of the control, and has the PFC function without affecting the original soft switch working state. Thereby improving the power density of the converter and improving the converter efficiency.

[0006] The present invention is implemented by adopting the following technical scheme: a current feedforward type single-stage PFC fast charging application converter based on an active clamp flyback circuit, the topology structure includes an EMI filter circuit, a rectifier bridge, a BUS capacitor C bus , isolated resonant converter, PFC inductor L pfc, output half-wave rectifier circuit; EMI filter circuit is used to filter out harmonics, PFC inductor is used to realize the tracking of current to voltage on the AC input side, and the rectifier bridge provides a return path for the PFC inductor and the BUS capacitor C bus The isolated resonant converter is used to realize the primary and secondary isolation and the soft switching of the switch tube; the isolated resonant converter includes a resonant capacitor C r , isolation transformer, transformer leakage inductance L r , switch tube Q 1 and Q 2 , where L r and C r The output half-wave rectifier circuit includes an SR tube and an output capacitor C located on the secondary side of the isolation transformer. o .

[0007] The active clamp flyback circuit has the advantages of both the flyback circuit and the LLC resonant circuit. It can not only realize the soft switching of the primary and secondary sides, but also has a wide gain range through PWM control. On the basis of the active clamp flyback circuit, adding current feedforward can further improve the efficiency and reduce the size of the converter without increasing the power switch tube and the control complexity.

[0008] Furthermore, the fast charging application converter is divided into seven stages according to the time period: a, b, c, d, e, f, g, and the working mode of each stage is as follows: Working stage a[t 1 , t 2 ]: This stage Q 2 Tube opened, Q 1 The tube remains closed, L pfc and the primary equivalent excitation inductance L of the isolation transformer m The current on the secondary side of the isolation transformer increases linearly. At this time, the SR tube on the secondary side of the isolation transformer is clamped by the primary voltage and is in a reverse shutdown state. o Provide energy to the load R, the resonant capacitor C r Does not participate in resonance; Working stage b[t 2 , t 3 ]: At this stage, Q 2 Shutdown, Q 1 The tube remains in the off state, and the excitation current and L pfc The current flows to Q 1 and Q 2 The junction capacitance is charged and discharged, and this process ends at Q 1 The body diode of the tube is turned on; Working stage c[t 3 , t 4 ]: At this stage, Q 1 To achieve zero voltage switching (ZVS) turn-on, Cr With L r Resonance, while transferring energy to the secondary side, L pfc Due to the reverse voltage, the current begins to decrease. At this time, the AC input is simultaneously to C bus Transfer energy with the secondary side; Working stage d[t 4 , t 5 ]:t 4 When the resonant current reverses, C r The stored energy is released to the secondary side; Working stage 5 , t 6 ]:In this stage, L pfc The inductor current drops to 0, C r With L r Resonance, C bus The capacitor will no longer be charged; Working stage f[t 6 , t 7 ]:t 6 At this moment, the resonant current is equal to the excitation current, the primary side stops transferring energy to the secondary side, the SR tube current on the secondary side drops to 0, and zero voltage switching (ZCS) is achieved. In this stage, the excitation inductance L m With the resonant capacitor C r Resonate together, the output turns to C o Provide energy to the load; Working stage g[t 7 , t 8 ]:t 7 At this moment, the switch tube Q 1 When the switch is turned off, the reverse current charges and discharges the switch junction capacitance. This stage ends at Q 2 The body diode of the tube is turned on, and the next cycle starts. 2 The tube will achieve zero voltage switching (ZVS) turn-on.

[0009] Furthermore, the positive and negative electrodes at the output side of the EMI filter circuit are connected through a diode and an inductor L pfc One end of L pfc The other end is connected to the primary side of the isolation transformer; the rectifier bridge includes two pairs of parallel connected and C bus The diode connected in parallel with the capacitor, the positive and negative electrodes on the output side of the EMI filter circuit are connected to the midpoints of the two pairs of parallel diodes in the rectifier bridge respectively; Resonant capacitor C r , switch tube Q 1 and Q 2 After connecting in series with C busThe capacitors are connected in parallel. In the two pairs of diodes in the rectifier bridge, the cathode of the first diode is connected to the anode of the second diode, and the anode of the first diode is connected to Q 2 The cathode of the second diode is connected through L r Connected to one end of the primary side of the isolation transformer, and the other end of the primary side of the isolation transformer is connected to the switch tube Q 1 and Q 2 between.

[0010] Furthermore, L pfc The other end is connected to the center tap of the primary side of the isolation transformer. By adjusting the position of the center tap, the PFC effect and C bus Voltage stress problem.

[0011] The present invention reasonably adds a current feedforward branch to the active clamp flyback topology structure, so that the active clamp flyback circuit can realize the shaping function of the input current without affecting the original soft switch. At the same time, the topology structure and control are simplified, so that the output voltage regulation and the automatic tracking of the input current to the input voltage can be realized simultaneously through traditional PWM control. Due to the wide gain range of the active clamp flyback circuit, this single-stage topology is suitable for wide input and wide output power supply, and the resonance of the active clamp flyback itself can make the primary and secondary side switches work in soft switching. It helps to further improve the efficiency and power density of the converter and simplify the system complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 One of the schematic diagrams of the converter topology described in the present invention.

[0013] Figure 2 The second schematic diagram of the converter topology structure of the present invention.

[0014] Figure 3 Working waveform diagram of the converter described in the present invention.

[0015] Figure 4 One of the schematic diagrams of the working modes of the converter described in the present invention (working stage a).

[0016] Figure 5 The second schematic diagram of the working mode of the converter described in the present invention (working stage b).

[0017] Figure 6 The third schematic diagram of the working mode of the converter described in the present invention (working stage c).

[0018] Figure 7 The fourth schematic diagram of the working mode of the converter described in the present invention (working stage d).

[0019] Figure 8The fifth working mode diagram of the converter according to the present invention (working stage e).

[0020] Fig. 9 The sixth schematic diagram of the working mode of the converter described in the present invention (working stage f).

[0021] Fig.10 Schematic diagram of the seventh working mode of the converter described in the present invention (working stage g).

[0022] Fig.11 A schematic diagram of a topological structure in which the converter of the present invention adopts a current feedforward inductor connected to a center tap of a transformer.

[0023] Fig.12 Schematic diagram of the control scheme of the present invention.

[0024] Fig.13 Schematic diagram of energy transmission of the topology proposed in this invention. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings.

[0026] like Figure 1 , 2 As shown in the figure, a current feedforward single-stage PFC fast-charging application converter based on an active clamp flyback circuit has a topology including an EMI filter circuit, a rectifier bridge, a BUS capacitor, an isolated resonant converter, a PFC inductor, and an output half-wave rectifier circuit. The EMI filter circuit is used to filter out harmonics, the PFC inductor is used to track the voltage of the AC input side current, and the rectifier bridge provides a return path for the PFC inductor and charges the BUS capacitor. The isolated resonant converter is used to achieve isolation between the primary and secondary sides and soft switching of the switch tube. The isolated resonant converter is mainly composed of a resonant capacitor C r , isolation transformer, transformer leakage inductance L r , switch tube Q 1 and Q 2 Among them, L r and C r Form a resonant cavity.

[0027] by Figure 3-Figure 10 Take the working waveform as an example to analyze it. The working waveform is as follows: Working stage a[t 1 , t 2 ]: This stage Q 2 Tube opened, Q 1 The tube remains closed, L pfc and the magnetizing inductance L m The current on the upper side increases linearly. At this time, the secondary side SR is clamped by the primary side voltage and is in a reverse shutdown state. The output capacitor Co provides energy to the load R. The resonant capacitor C rDoes not participate in resonance.

[0028] Working stage b[t 2 , t 3 ]: At this stage, Q 2 Shutdown, Q 1 The tube remains in the off state, and the excitation current and L pfc The current flows to Q 1 and Q 2 The junction capacitance is charged and discharged, and this process ends at Q 1 The body diode of the tube is turned on.

[0029] Working stage c[t 3 , t 4 ]: At this stage, Q 1 To achieve ZVS, C r With L r Resonance, while transferring energy to the secondary side, L pfc Due to the reverse voltage, the current begins to decrease. At this time, the AC input is simultaneously to C bus Transfer energy to the secondary side.

[0030] Working stage d[t 4 , t 5 ]:t 4 When the resonant current reverses, C r The stored energy is released to the secondary side.

[0031] Working stage 5 , t 6 ]:In this stage, L pfc The inductor current drops to 0, C r Resonates with Lr. C bus The capacitor will no longer be charged.

[0032] Working stage f[t 6 , t 7 ]:t 6 At this moment, the resonant current is equal to the excitation current, the primary side stops transferring energy to the secondary side, the secondary side SR current drops to 0, and ZCS shutdown is achieved. In this stage, the excitation inductance and the resonant capacitor C r The output is converted to C o Provides energy to the load.

[0033] Working stage g[t 7 , t 8 ]:t 7 At this moment, the switch tube Q 1 When the switch is turned off, the reverse current charges and discharges the switch junction capacitance. This stage ends at Q 2 The body diode of the tube is turned on. At the beginning of the next cycle, Q 2The tube will achieve ZVS opening.

[0034] To alleviate C bus To solve the voltage stress problem, the current feed-forward inductor can be connected to the center tap of the transformer to reduce the voltage stress by pfc The volt-second value on the inductor to reduce C bus The voltage stress on the p1 With N p2 ratio, balancing the PFC effect and C bus Voltage stress problem. Fig.11 A center-tapped topology is shown.

[0035] Fig.12 The control scheme of the present invention is demonstrated, and only a simple voltage loop is required to achieve output voltage regulation and AC current shaping. bus The gain is the original gain of the active clamp flyback topology, that is: , therefore, this topology is conducive to achieving a wide gain range.

[0036] Fig.13 The energy transmission of the proposed topology is demonstrated, including three energy transmission paths: AC input to BUS capacitor, AC input to output, and BUS capacitor to output. There is a link in which energy is directly transferred from AC input to output, so the efficiency can be further improved and the power density can be optimized.

[0037] The active clamp flyback circuit of the present invention has the advantages of both the flyback circuit and the LLC resonant circuit. It can not only realize the soft switching of the primary and secondary sides, but also can be controlled by PWM to have a wide gain range. On the basis of the active clamp flyback circuit, current feedforward is added, which can further improve the efficiency and reduce the volume of the converter without increasing the power switch tube and the control complexity.

Claims

1. A current feed-forward single-stage PFC fast-charging application converter based on an active clamp flyback circuit, characterized in that: The topology includes EMI filter circuit, rectifier bridge, BUS capacitor C bus , isolated resonant converter, PFC inductor L pfc , output half-wave rectifier circuit; EMI filter circuit is used to filter out harmonics, PFC inductor is used to realize the tracking of current to voltage on the AC input side, and the rectifier bridge provides a return path for the PFC inductor and the BUS capacitor C bus The isolated resonant converter is used to realize the primary and secondary isolation and the soft switching of the switch tube; the isolated resonant converter includes a resonant capacitor C r , isolation transformer, transformer leakage inductance L r , switch tubes Q1 and Q2, where L r and C r The output half-wave rectifier circuit includes an SR tube and an output capacitor C located on the secondary side of the isolation transformer. o .

2. A current feed-forward single-stage PFC fast-charging application converter based on an active clamp flyback circuit as claimed in claim 1, characterized in that: The fast charging application converter is divided into seven stages according to the time period: a, b, c, d, e, f, and g. The working modes of each stage are as follows: Working stage a [t1, t2]: In this stage, Q2 tube is turned on, Q1 tube remains off, and L pfc and the primary equivalent excitation inductance L of the isolation transformer m The current on the secondary side of the isolation transformer increases linearly. At this time, the SR tube on the secondary side of the isolation transformer is clamped by the primary voltage and is in a reverse shutdown state. o Provide energy to the load R, the resonant capacitor C r Does not participate in resonance; Working stage b[t2, t3]: In this stage, Q2 is turned off, Q1 tube remains off, and the excitation current and L pfc The current charges and discharges the junction capacitance of Q1 and Q2 at the same time, and this process ends when the body diode of Q1 tube is turned on; Working stage c[t3, t4]: In this stage, Q1 realizes zero voltage switching and C r With L r Resonance, while transferring energy to the secondary side, L pfc Due to the reverse voltage, the current begins to decrease. At this time, the AC input is simultaneously to C bus Transfer energy with the secondary side; Working stage d[t4, t5]: At t4, the resonant current reverses, C r The stored energy is released to the secondary side; Working phase e[t5, t6]: In this phase, L pfc The inductor current drops to 0, C r With L r Resonance, C bus The capacitor will no longer be charged; Working stage f[t6, t7]: At t6, the resonant current is equal to the excitation current, the primary side stops transferring energy to the secondary side, the SR tube current on the secondary side drops to 0, and the zero voltage switch is turned off. In this stage, the excitation inductance L m With the resonant capacitor C r Resonate together, the output turns to C o Provide energy to the load; Working phase g[t7, t8]: At t7, the switch tube Q1 is turned off, and the reverse current charges and discharges the junction capacitance of the switch tube. This phase ends when the body diode of Q2 tube is turned on. At the beginning of the next cycle, Q2 tube will realize zero voltage switching and turn on.

3. A current feed-forward single-stage PFC fast-charging application converter based on an active clamp flyback circuit as described in claim 1 or 2, characterized in that: The positive and negative electrodes on the output side of the EMI filter circuit are connected through a diode and an inductor L pfc One end of L pfc The other end is connected to the primary side of the isolation transformer; the rectifier bridge includes two pairs of parallel connected and C bus The diode connected in parallel with the capacitor, the positive and negative electrodes on the output side of the EMI filter circuit are connected to the midpoints of the two pairs of parallel diodes in the rectifier bridge respectively; Resonant capacitor C r , the switch tubes Q1 and Q2 are connected in series with C bus The capacitors are connected in parallel. In the two pairs of diodes in the rectifier bridge, the cathode of the first diode is connected to the anode of the second diode, the anode of the first diode is connected to the Q2 tube, and the cathode of the second diode is connected to the Q2 tube through L r It is connected to one end of the primary side of the isolation transformer, and the other end of the primary side of the isolation transformer is connected between the switch tubes Q1 and Q2.

4. A current feed-forward single-stage PFC fast-charging application converter based on an active clamp flyback circuit as claimed in claim 3, characterized in that: L pfc The other end is connected to the center tap of the primary side of the isolation transformer. By adjusting the position of the center tap, the PFC effect and C bus Voltage stress problem.

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