A current feedforward type single-stage PFC fast charging application converter based on an active clamp flyback circuit

Abstract

This invention relates to the field of charging and discharging equipment, specifically to a current-feedforward single-stage PFC fast charging converter based on an active clamp flyback circuit. The topology of this invention includes an EMI filter circuit, a rectifier bridge, and a BUS capacitor C. bus Isolated resonant converter, PFC inductor L pfc The output half-wave rectifier circuit; the EMI filter circuit is used to filter out harmonics; the PFC inductor is used to achieve AC input current tracking of voltage; the rectifier bridge provides a return path for the PFC inductor and a connection to the BUS capacitor C. bus The charging of the circuit; the isolated resonant converter is used to achieve primary-secondary side isolation and soft switching of the switching transistor; the isolated resonant converter includes a resonant capacitor C. r Isolation transformer, transformer leakage inductance L r Switches Q1 and Q2, where L r and C r The resonant cavity is formed; the output half-wave rectifier circuit includes an SR transistor located on the secondary side of the isolation transformer and an output capacitor C. o .

Description

Technical Field

[0001] This invention relates to the field of charging and discharging equipment, specifically to a current-feedforward single-stage PFC fast charging converter based on an active clamp flyback circuit. Background Technology

[0002] With the rapid development of the global economy, energy and environmental issues have become particularly severe. Traditional non-renewable resources will be gradually replaced by renewable energy to achieve dual-carbon goals. Furthermore, with the widespread adoption of portable mobile devices, there is a growing demand for high-power fast charging with wide gain range, high efficiency, and high power density. Traditional high-power fast charging uses a two-stage structure, with the front stage implementing PFC and the rear stage implementing isolated DC / DC conversion. However, this two-stage solution has certain disadvantages in terms of topology and efficiency. Traditional single-stage fast charging, lacking PFC, cannot achieve an input power greater than 75W, and the converter operates in a hard-switching state, limiting further efficiency improvements.

[0003] Specifically, on the one hand, traditional two-stage fast charging solutions require all energy to pass through two power conversion stages, and their efficiency depends on the product of the efficiency of the front-end PFC stage and the rear-end isolated DC / DC stage. Furthermore, two-stage solutions require more components and control ICs than single-stage solutions. On the other hand, traditional single-stage fast charging solutions lack PFC functionality, limiting input power to below 75W. Single-stage fast charging solutions with PFC functionality, however, suffer from a mismatch between input and output power, resulting in a large double-frequency ripple at the output, and the converter operates in hard-switching mode, leading to lower energy conversion efficiency.

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

[0005] The purpose of this 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 an active clamp flyback circuit, the original topology achieves PFC functionality without adding switching transistors or increasing control complexity, and without affecting the original soft-switching operation. This improves the power density and efficiency of the converter.

[0006] This invention is achieved using the following technical solution: a current-feedforward single-stage PFC fast charging converter based on an active clamp flyback circuit, the topology of which includes an EMI filter circuit, a rectifier bridge, and a BUS capacitor C. bus Isolated resonant converter, PFC inductor L pfcThe output half-wave rectifier circuit; the EMI filter circuit is used to filter out harmonics; the PFC inductor is used to achieve AC input current tracking of voltage; the rectifier bridge provides a return path for the PFC inductor and a connection to the BUS capacitor C. bus The charging of the circuit; the isolated resonant converter is used to achieve primary-secondary side isolation and soft switching of the switching transistor; the isolated resonant converter includes a resonant capacitor C. r Isolation transformer, transformer leakage inductance L r Switches Q1 and Q2, where L r and C r The resonant cavity is formed; the output half-wave rectifier circuit includes an SR transistor located on the secondary side of the isolation transformer and an output capacitor C. o .

[0007] The active clamp flyback circuit combines the advantages of both flyback and LLC resonant circuits. It not only enables soft switching on both the primary and secondary sides, but also allows for wide gain range control via PWM. By adding current feedforward to the active clamp flyback circuit, efficiency can be further improved and converter size reduced without increasing the number of power switches or control complexity.

[0008] Furthermore, the fast charging application converter operates in seven phases according to time periods: a, b, c, d, e, f, and g. The operating modes of each phase are as follows: Phase a [t1, t2]: In this phase, Q2 is turned on, Q1 remains off, and L... pfc The equivalent magnetizing inductance L on the primary side of the isolation transformer m The current on the transformer increases linearly. At this time, the SR transistor on the secondary side of the isolation transformer is clamped by the primary voltage and is in a reverse turn-off state, controlled by the output capacitor C. o Energy is supplied to the load R, and the resonant capacitor C r It does not participate in resonance;

[0009] Operating phase b[t2, t3]: During this phase, Q2 is turned off, Q1 remains off, and the excitation current is related to L. pfc The current simultaneously charges and discharges the junction capacitance of Q1 and Q2, and this process ends when the body diode of Q1 turns on.

[0010] Operating phase c[t3, t4]: During this phase, Q1 achieves zero-voltage switching (ZVS) turn-on, C r With L r Resonance occurs, and energy is transferred to the secondary side simultaneously, L pfc Due to the reverse voltage applied, the current begins to decrease, at which point the AC input simultaneously flows to C. bus Energy is transferred to the secondary side;

[0011] Operating phase d[t4, t5]: At t4, the resonant current reverses direction, Cr The stored energy is released to the secondary side;

[0012] Working phase e[t5, t6]: In this phase, L pfc The inductor current drops to 0, C r With L r To achieve resonance, C bus The capacitor will no longer be charged;

[0013] Operating phase f[t6, t7]: At time t6, the resonant current equals the magnetizing current, the primary side stops transferring energy to the secondary side, and the current of the SR transistor on the secondary side drops to 0, achieving zero-voltage switching (ZCS) turn-off. During this phase, the magnetizing inductance L... m With resonant capacitor C r When they resonate together, the output is converted to C. o Provide energy to the load;

[0014] Operating phase g[t7, t8]: At time t7, switch Q1 is turned off, and the reverse current charges and discharges the junction capacitance of the switch. This phase ends when the body diode of Q2 turns on. At the beginning of the next cycle, Q2 will turn on to achieve zero voltage switching (ZVS).

[0015] Furthermore, the positive and negative terminals of the output side of the EMI filter circuit are each connected to the inductor L via a diode. pfc Connect one end to L pfc The other end is connected to the primary side of the isolation transformer; the rectifier bridge includes two pairs of parallel connections and connected to C. bus The diodes connected in parallel with the capacitors are connected to the midpoints of the two pairs of parallel diodes on the output side of the EMI filter circuit.

[0016] Resonant capacitor C r After the switching transistors Q1 and Q2 are connected in series with C bus In the parallel capacitor configuration, the cathode of the first diode in the rectifier bridge is connected to the anode of the second diode, and the anode of the first diode is connected to transistor Q2. The cathode of the second diode is connected 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 switching transistors Q1 and Q2.

[0017] Furthermore, L pfc The other end is connected to the center tap on the primary side of the isolation transformer. By adjusting the position of the center tap, the PFC effect and C are balanced. bus Voltage stress problem.

[0018] This invention incorporates a current feedforward branch into the active clamp flyback topology, enabling the active clamp flyback circuit to shape the input current without affecting its original soft-switching capability. It also simplifies the topology and control, allowing for simultaneous output voltage regulation and automatic tracking of the input current to the input voltage using traditional PWM control. This single-stage topology, due to the wide gain range of the active clamp flyback circuit, is suitable for wide input and output power supplies. Furthermore, the inherent resonance of the active clamp flyback circuit allows both primary and secondary side switches to operate in soft-switching mode. This contributes to further improving converter efficiency and power density while simplifying system complexity. Attached Figure Description

[0019] Figure 1 One of the schematic diagrams of the converter topology described in this invention.

[0020] Figure 2 The second schematic diagram of the converter topology described in this invention.

[0021] Figure 3 The waveform diagram of the converter described in this invention.

[0022] Figure 4 One of the schematic diagrams of the working modes of the converter described in this invention (working phase a).

[0023] Figure 5 The second schematic diagram of the converter's operating mode (operating stage b) of the present invention.

[0024] Figure 6 The third schematic diagram of the converter's operating modes according to the present invention (operating stage c).

[0025] Figure 7 The fourth schematic diagram of the converter's working mode (working stage d) of the present invention.

[0026] Figure 8 The fifth schematic diagram of the converter's operating mode (operating stage e) of the present invention.

[0027] Figure 9 The sixth schematic diagram of the converter's operating modes (operating stage f) of the present invention.

[0028] Figure 10 The seventh schematic diagram of the converter's working modes according to the present invention (working stage g).

[0029] Figure 11 The converter described in this invention adopts a topology structure in which a current feedforward inductor is connected to the center tap of a transformer.

[0030] Figure 12 A schematic diagram of the control scheme of the present invention.

[0031] Figure 13 A schematic diagram of energy transmission in the topology proposed in this invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings.

[0033] like Figure 1 , 2 As shown, a current-feedforward single-stage PFC fast-charging converter based on an active clamp flyback circuit is illustrated. The topology includes 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 harmonics, the PFC inductor is used to achieve AC input current tracking of voltage, 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 primary-secondary isolation and soft switching of the switching transistor. The isolated resonant converter mainly consists of a resonant capacitor C. r Isolation transformer, transformer leakage inductance L r It consists of switching transistors Q1 and Q2. Wherein, L... r and C r It forms a resonant cavity.

[0034] by Figures 3-10 Taking this as an example, let's analyze its working waveform, which is as follows:

[0035] Operating phase a[t1, t2]: During this phase, transistor Q2 is turned on, transistor Q1 remains off, and L... pfc And excitation inductance L m The current increases linearly. At this time, the secondary side SR is clamped by the primary side voltage and is in a reverse turn-off state. Energy is supplied to the load R by the output capacitor Co. Resonant capacitor C r It does not participate in resonance.

[0036] Operating phase b[t2, t3]: During this phase, Q2 is turned off, Q1 remains off, and the excitation current is related to L. pfc The current simultaneously charges and discharges the junction capacitance of Q1 and Q2, and this process ends when the body diode of Q1 turns on.

[0037] Working phase c[t3, t4]: In this phase, Q1 achieves ZVS activation, C r With L r Resonance occurs, and energy is transferred to the secondary side simultaneously, L pfc Due to the reverse voltage applied, the current begins to decrease, at which point the AC input simultaneously flows to C. bus It transfers energy to the secondary side.

[0038] Operating phase d[t4, t5]: At t4, the resonant current reverses direction, C r The stored energy is released to the secondary side.

[0039] Working phase e[t5, t6]: In this phase, L pfc The inductor current drops to 0, C r It resonates with Lr. C bus The capacitor will no longer be charged.

[0040] Operating phase f[t6, t7]: At time t6, the resonant current equals the magnetizing current, the primary side stops transferring energy to the secondary side, and the secondary side SR current drops to 0, achieving ZCS turn-off. During this phase, the magnetizing inductance and resonant capacitor C... r They resonate together. The output is converted to C. o Provide energy to the load.

[0041] Operating phase g[t7, t8]: At time t7, switch Q1 is off, and the reverse current charges and discharges the junction capacitance of the switch. This phase ends when the body diode of Q2 turns on. At the start of the next cycle, Q2 will achieve ZVS turn-on.

[0042] To alleviate C bus To address voltage stress issues, the current feedforward inductor can be connected to the center tap of the transformer, thereby reducing L... pfc The volt-second value on the inductor, to reduce C bus The voltage stress is adjusted by changing the position of the center tap, i.e., N. p1 With N p2 The ratio of the two values ​​balances the PFC effect with C. bus Voltage stress problem. Figure 11 The topology scheme with a center tap is shown.

[0043] Figure 12 The control scheme of this invention is demonstrated, which can achieve output voltage regulation and AC current shaping with only a simple voltage loop. Output to C bus The gain is the original gain of the active clamp flyback topology, that is: Therefore, this topology is advantageous for achieving a wide gain range.

[0044] Figure 13 The energy transfer of the proposed topology is demonstrated, including three energy transfer paths: AC input to BUS capacitor, AC input to output, and BUS capacitor to output. The presence of a direct energy transfer link from AC input to output further improves efficiency and optimizes power density.

[0045] The active clamp flyback circuit described in this invention combines the advantages of both flyback circuits and LLC resonant circuits. It not only enables soft switching on both the primary and secondary sides, but also allows for wide gain range control via PWM. By adding current feedforward to the active clamp flyback circuit, efficiency can be further improved and converter size reduced without increasing the number of power switches or control complexity.

Claims

1. A current-feedback single-stage PFC fast charging converter based on an active clamp flyback circuit, characterized in that: The topology includes an EMI filter circuit, a rectifier bridge, and a BUS capacitor C. bus Isolated resonant converter, PFC inductor L pfc The output half-wave rectifier circuit; the isolated resonant converter includes a resonant capacitor C. r Isolation transformer, transformer leakage inductance L r Switches Q1 and Q2, where L r and C r The resonant cavity is formed; the output half-wave rectifier circuit includes an SR transistor located on the secondary side of the isolation transformer and an output capacitor C. o ; The positive and negative terminals of the output side of the EMI filter circuit are each connected to an inductor L via a diode. pfc Connect one end to L pfc The other end is connected to the primary side of the isolation transformer, with the contact located between switching transistors Q1 and Q2; the rectifier bridge includes two pairs of parallel circuits connected to C. bus The diodes connected in parallel with the capacitors are connected to the midpoints of the two pairs of parallel diodes on the output side of the EMI filter circuit. Resonant capacitor C r After the switching transistors Q1 and Q2 are connected in series with C bus In the parallel capacitor configuration, the cathode of the first diode in the rectifier bridge is connected to the anode of the second diode, and the anode of the first diode is connected to transistor Q2. The cathode of the second diode is connected 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 switching transistors Q1 and Q2; The fast charging converter operates in seven phases according to time periods: a, b, c, d, e, f, and g. The operating modes of each phase are as follows: Phase a [t1, t2]: In this phase, Q2 is turned on, Q1 remains off, and L... pfc The equivalent magnetizing inductance L on the primary side of the isolation transformer m The current on the transformer increases linearly. At this time, the SR transistor on the secondary side of the isolation transformer is clamped by the primary voltage and is in a reverse turn-off state, controlled by the output capacitor C. o Energy is supplied to the load R, and the resonant capacitor C r It does not participate in resonance; Operating phase b[t2, t3]: During this phase, Q2 is turned off, Q1 remains off, and the excitation current is related to L. pfc The current simultaneously charges and discharges the junction capacitance of Q1 and Q2, and this process ends when the body diode of Q1 turns on. Operating phase c[t3, t4]: During this phase, Q1 achieves zero-voltage switching on, C r With L r Resonance occurs, and energy is transferred to the secondary side simultaneously, L pfc Due to the reverse voltage applied, the current begins to decrease, at which point the AC input simultaneously flows to C. bus Energy is transferred to the secondary side; Operating phase d[t4, t5]: At t4, the resonant current reverses direction, 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 To achieve resonance, C bus The capacitor will no longer be charged; Operating phase f[t6, t7]: At time t6, the resonant current equals the magnetizing current, the primary side stops transferring energy to the secondary side, and the current of the SR transistor on the secondary side drops to 0, achieving zero-voltage switching off. During this phase, the magnetizing inductance L... m With resonant capacitor C r When they resonate together, the output is converted to C. o Provide energy to the load; Operating phase g[t7, t8]: At time t7, the switch Q1 is turned off, and the reverse current charges and discharges the junction capacitance of the switch. This phase ends when the body diode of Q2 turns on. At the beginning of the next cycle, Q2 will achieve zero-voltage switching.

2. The current-feedforward single-stage PFC fast-charging converter based on an active clamp flyback circuit as described in claim 1, characterized in that, The EMI filter circuit is used to filter out harmonics, the PFC inductor is used to enable AC input current to track voltage, and the rectifier bridge provides a return path for the PFC inductor and a connection to the BUS capacitor C. bus Charging; the isolated resonant converter is used to achieve primary-secondary isolation and soft switching of the switching transistor.

3. The current-feedforward single-stage PFC fast-charging converter based on an active clamp flyback circuit as described in claim 1, characterized in that, L pfc The other end is connected to the center tap on the primary side of the isolation transformer. By adjusting the position of the center tap, the PFC effect and C are balanced. bus Voltage stress problem.

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