Bridgeless sepic pfc converter based on switched-inductor-capacitor

Abstract

The application discloses a bridgeless Sepic PFC converter based on switched-inductor-capacitor, which mainly comprises switching tubes S1-S3, diodes D1-D4, inductors L1-L5, capacitors C1, C2 and C o . Wherein, the diodes D3 and D4, the capacitor C2 and the inductors L4 and L5 form a switched-inductor-capacitor structure. The voltage gain of the converter is D / 2(1-D), compared with the traditional Sepic PFC converter, the converter improves the step-down gain, and the output voltage is stable in the case of high step-down ratio. The bridgeless structure can realize lower on-state loss. The original output diode is replaced by the switched-inductor-capacitor structure, so that the output current is continuous, which is beneficial to filtering the output. All the switching tubes are common ground, and the control is convenient. The converter has rich practical value.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, specifically a bridgeless Sepic PFC converter based on switched inductors and capacitors. Background Technology

[0002] With the rapid expansion of the consumer electronics and electric vehicle markets, the demand for various power adapters has also surged. Since power adapters typically need to support a full voltage range (AC 85–265V) input and low DC voltage output, the wide input voltage range makes converter optimization difficult. For simplicity, a two-stage circuit consisting of a pre-stage PFC and a post-stage DC-DC converter is generally used. However, this two-stage circuit is not very efficient.

[0003] Traditional Sepic PFC converters can easily implement buck-boost functions and are suitable for a wide input voltage range. They are one of the most widely used topologies in power adapters. Compared to the two-stage structure of the aforementioned topologies, Sepic PFC converters significantly reduce the number of components. Furthermore, their input inductance ensures continuous input current, improving converter efficiency and power factor, reducing total harmonic distortion, and minimizing conduction losses. However, to achieve a high buck ratio, the conduction ratio of the switching devices becomes very low, and the severe reverse recovery problem of the switching transistors further reduces efficiency. In addition, the inherent on / off delay characteristics of the switching devices limit the increase in the converter's operating frequency. Therefore, a circuit that can solve these problems is needed. Summary of the Invention

[0004] To address the issues of low efficiency, discontinuous output current, and limited duty cycle range in buck mode inherent in existing Sepic PFC converters, this invention proposes a bridgeless Sepic PFC converter based on switched inductors and capacitors. The output diodes in the original Sepic PFC converter are replaced with a five-element switched inductor-capacitor unit. Compared to traditional Sepic PFC converters, this invention improves buck gain and ensures stable output voltage even at high buck ratios.

[0005] The technical solution adopted in this invention is as follows:

[0006] Bridgeless Sepic PFC converter based on switched inductors and capacitors, including AC power supply u s Switches S1-S3, diodes D1-D4, inductors L1-L5, capacitors C1, C2, C3 o ,

[0007] AC power supply u s One side is connected to the drain of the switching transistor S3 and one end of the inductor L1, and the other end of the inductor L1 is connected to the anode of the diode D1.

[0008] AC power supply u s On the other side, the drain of the switching transistor S2 and one end of the inductor L2 are connected respectively, and the other end of the inductor L2 is connected to the anode of the diode D2.

[0009] The positive terminal of capacitor C1 is connected to the cathodes of diodes D1 and D2, and the drain of switching transistor S1, respectively.

[0010] One end of inductor L3 is connected to the negative terminal of capacitor C1, the anode of diode D3, and one end of inductor L4, respectively.

[0011] The other end of inductor L3 is connected to the source of switching transistor S1, the source of switching transistor S2, the source of switching transistor S3, and the output capacitor C, respectively. o negative electrode;

[0012] The other end of inductor L4 is connected to the negative terminal of capacitor C2 and the anode of diode D4, respectively;

[0013] The positive terminal of capacitor C2 is connected to the cathode of diode D3 and one end of inductor L5; the other end of inductor L5 is connected to the cathode of diode D4 and the output capacitor C. o positive electrode;

[0014] Output capacitor C o With load R L in parallel.

[0015] In the converter, capacitor C2, inductors L4 and L5, and diodes D3 and D4 constitute a switching inductor-capacitor unit.

[0016] In the converter, the switching transistors S1, S2, and S3 share a common ground, and the power switching transistors S1, S2, and S3 are insulated gate bipolar transistors (IGBTs), integrated gate commutated thyristors (IGCTs), or power field-effect transistors (MOSFETs).

[0017] The voltage gain of the converter is D / 2(1-D).

[0018] The converter has the following four operating modes in CCM mode:

[0019] Operating mode 1: The circuit operates under AC power supply u s During the positive half-cycle, switches S1 and S2 are turned on, while switch S3 is turned off. Diode D1 is forward-biased and conducts, while the other diodes are reverse-biased and cut off. During this process, the AC power supply u... s Inductor L1 is charged, and capacitor C1 discharges to charge inductor L3, causing the current in inductors L1 and L3 to increase linearly. Inductors L4 and L5 then supply current to the output capacitor C via capacitor C2. o As the load discharges, the currents in inductors L4 and L5 decrease linearly.

[0020] Operating mode 2: The circuit operates under AC power supply us During the positive half-cycle, switch S2 is turned on, while switches S1 and S3 are turned off. Diodes D1, D3, and D4 are forward-biased and conduct, while the remaining diodes are reverse-biased and cut off. During this process, capacitors C1 and C2 are charged, and inductors L1 and L3 charge inductors L4 and L5, the load, and the output capacitor C. o Discharge.

[0021] Operating mode 3: At this time, the circuit operates under AC power supply u s During the negative half-cycle, switches S1 and S3 are turned on, while switch S2 is turned off. Diode D2 is forward-biased and conducts, while the other diodes are reverse-biased and cut off. During this process, the AC power supply u... s Inductor L2 is charged, and capacitor C1 discharges to charge inductor L3, causing the current in inductors L2 and L3 to increase linearly. Inductors L4 and L5 then flow through capacitor C2 to the output capacitor C. o As the load discharges, the currents in inductors L4 and L5 decrease linearly.

[0022] Operating mode four: The circuit operates under AC power supply u s During the negative half-cycle, switch S3 is turned on, while switches S1 and S2 are turned off. Diodes D2, D3, and D4 are forward-biased and conduct, while the remaining diodes are reverse-biased and cut off. During this process, capacitors C1 and C2 are charged, and inductors L2 and L3 charge inductors L4 and L5, the load, and the output capacitor C. o Discharge.

[0023] This invention discloses a bridgeless Sepic PFC converter based on switched inductors and capacitors, with the following technical advantages:

[0024] 1) Compared to the voltage gain of the traditional Sepic PFC converter, which is M = D / (1-D), the buck gain of the converter described in this invention is twice as high, at M = D / 2(1-D). In buck mode, the duty cycle range of the original Sepic PFC converter is extended from 0 to 0.5 to 0 to 0.67. With a high buck ratio, the converter described in this invention has a larger duty cycle, which is beneficial for solving the reverse recovery problem of the switching transistor, reducing current stress, and improving efficiency.

[0025] 2) The converter described in this invention introduces a switched inductor-capacitor unit, which makes the input power supply current and the output load current continuous and with small ripple, which is beneficial for filtering the input and output and improving the power factor.

[0026] 3) All switching transistors in the converter described in this invention share a common ground, and the switching transistors can be driven by a non-isolated driving circuit, which helps to reduce the design difficulty and cost of the converter.

[0027] 4) The converter described in this invention is a single-stage structure, which improves conversion efficiency compared to a two-stage converter structure. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Figure 1 This is a diagram of the main topology of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention.

[0030] Figure 2 This is a schematic diagram of the first operating mode of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention.

[0031] Figure 3 This is a schematic diagram of the second operating mode of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention.

[0032] Figure 4 This is a schematic diagram of the third operating mode of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention.

[0033] Figure 5 This is a schematic diagram of the fourth operating mode of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention.

[0034] Figure 6 This is a steady-state key waveform diagram of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention.

[0035] Figure 7 This is a schematic diagram comparing the voltage gain of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention with that of a conventional Sepic PFC converter.

[0036] Figure 8 The image shows the input voltage and current waveforms of a bridgeless Sepic PFC converter based on switched inductors and capacitors under steady-state conditions, according to the present invention.

[0037] Figure 9 The output voltage and current waveforms of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention are shown in the steady-state condition. Detailed Implementation

[0038] like Figure 1 As shown, the bridgeless Sepic PFC converter based on switched inductors and capacitors includes switching transistors S1-S3, diodes D1-D4, inductors L1-L5, and capacitors C1, C2, and C3. o ;

[0039] The converter inductors L4 and L5, capacitor C2, and diodes D3 and D4 form a switching inductor-capacitor unit.

[0040] AC power supply us One side is connected to the drain of switching transistor S3 and one end of inductor L1, and the other end of inductor L1 is connected to the anode of diode D1; AC power supply u s On the other side, the drain of the switching transistor S2 and one end of the inductor L2 are connected respectively, and the other end of the inductor L2 is connected to the anode of the diode D2.

[0041] The positive terminal of capacitor C1 is connected to the cathodes of diodes D1 and D2 and the drain of switching transistor S1, respectively.

[0042] One end of inductor L3 is connected to the negative terminal of capacitor C1, the anode of diode D3, and one end of inductor L4. The other end of inductor L3 is connected to the source of switching transistors S1, S2, and S3, and the output capacitor C. o Negative terminals connected;

[0043] The other end of inductor L4 is connected to the negative terminal of capacitor C2 and the anode of diode D4, respectively;

[0044] The positive terminal of capacitor C2 is connected to the cathode of diode D3 and one end of inductor L5;

[0045] The other end of inductor L5 is connected to the cathode of diode D4 and output capacitor C. o Positive terminals connected;

[0046] Output capacitor C o With load R L in parallel.

[0047] The specific parameters of the circuit are as follows: the converter input AC voltage RMS value is 220V, the frequency is 50Hz, the switching frequency is 75kHz, the rated output power is 180W, and the DC side output voltage is V. o =48V, inductors L1=L2=2mH, L3=47uH, L4=L5=22uH, DC output capacitor C o =2000μF, capacitors C1=2μF, C2=63μF, load resistance R L =12.8Ω.

[0048] This invention relates to a bridgeless Sepic PFC converter based on switched inductors and capacitors, which includes the following operating modes under steady-state operation in CCM mode:

[0049] Working Mode 1: such as Figure 2 As shown, the circuit is currently operating with AC power supply u. s During the positive half-cycle, switches S1 and S2 are turned on, diode D1 is forward-biased and conducts, and all other semiconductor devices are turned off. In this process, the power supply charges inductor L1, capacitor C1 charges inductor L3, and inductors L4 and L5 charge the output capacitor C through capacitor C2. o and load discharge. This process corresponds to Figure 6During the time interval (t0 to t1), the voltage relationship across the inductor in this process is as follows:

[0050]

[0051] Among them, V C1 and V C2 These are the voltage stresses of capacitors C1 and C2, respectively, and V. S1 It is the voltage stress of the switching transistor S1, V g This is the drive signal for switch S1. It is assumed that all components are in ideal condition, the diode forward voltage drop is zero, the capacitor has a sufficiently large capacitance and no equivalent series resistance, and the inductor has no DC resistance.

[0052] Working Mode 2: such as Figure 3 As shown, the circuit operates under AC power supply u s During the positive half-cycle, switch S2 is turned on, diodes D1, D3, and D4 are forward-biased and conducting, and all other semiconductor devices are turned off. During this process, capacitors C1 and C2 are charged, and inductors L1 and L3 charge L4, L5, the load, and the output capacitor C. o Discharge. This process corresponds to... Figure 6 During the time interval (t1~t2), the voltage relationship across the inductor in this process is as follows:

[0053]

[0054] Working Mode 3: such as Figure 4 As shown, the circuit is currently operating with AC power supply u. s During the negative half-cycle, switches S1 and S3 are turned on, diode D2 is forward-biased and conducts, and all other semiconductor devices are turned off. In this process, the power supply charges inductor L2, capacitor C1 charges inductor L3, and inductors L4 and L5 charge the output capacitor C through capacitor C2. o and load discharge. This process corresponds to Figure 6 During the time interval (t0 to t1), the voltage relationship across the inductor in this process is as follows:

[0055]

[0056] Working Mode 4: such as Figure 5 As shown, the circuit operates under AC power supply u s During the negative half-cycle, switch S3 is turned on, diodes D2, D3, and D4 are forward-biased and conduct, and all other semiconductor devices are turned off. During this process, capacitors C1 and C2 are charged, and inductors L2 and L3 charge L4, L5, the load, and the output capacitor C. o Discharge. This process corresponds to... Figure 6 During the time interval (t1~t2), the voltage relationship across the inductor in this process is as follows:

[0057]

[0058] Voltage gain analysis when the converter is operating stably:

[0059] Let the switching period of the switching transistor S1 be T. S The duty cycle is D, which means the duration of the working mode is DT. S The duration of the second working mode is (1-D)T S Based on the volt-second balance characteristic of inductors, we can obtain:

[0060]

[0061] By combining equations (1) and (2), we can obtain:

[0062]

[0063] The voltage gain of the converter described in this invention is:

[0064]

[0065] The buck gain curve of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention is shown below. Figure 7 As shown. (Through) Figure 7 As can be seen, in buck mode, the duty cycle range of the converter described in this invention is wider than that of the traditional SepicPFC converter.

[0066] Figure 8 This diagram shows the steady-state input voltage and current waveforms of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention. For ease of comparison with the voltage waveform, the actual input current value is magnified by a factor of 30 without changing its phase. It can be seen that the input voltage and input current are in phase and the waveforms are undistorted, verifying the feasibility of power factor correction.

[0067] Figure 9 This diagram shows the steady-state output voltage and current waveforms of a bridgeless Sepic PFC converter based on switched inductors and capacitors according to the present invention. The output voltage is stable at around 48V, and the output current waveform is continuous.

[0068] Compared to traditional Sepic PFC converters, the converter described in this invention improves the buck gain and maintains stable output voltage even at high buck ratios. The bridgeless structure achieves lower conduction losses. Replacing the original output diodes with a switched inductor-capacitor structure ensures continuous output current, which is beneficial for output filtering. Furthermore, all switches share a common ground, simplifying control implementation. The converter described in this invention has significant practical value.

Claims

1. A bridgeless Sepic PFC converter with switched inductors and capacitors, including AC power supply u s Switches S1~S3, diodes D1~D4, inductors L1~L5, capacitors C1, C2, C3 o Its features are: AC power supply u s One side is connected to the drain of the switching transistor S3 and one end of the inductor L1, and the other end of the inductor L1 is connected to the anode of the diode D1. AC power supply u s On the other side, the drain of the switching transistor S2 and one end of the inductor L2 are connected respectively, and the other end of the inductor L2 is connected to the anode of the diode D2. The positive terminal of capacitor C1 is connected to the cathodes of diodes D1 and D2, and the drain of switching transistor S1, respectively. One end of inductor L3 is connected to the negative terminal of capacitor C1, the anode of diode D3, and one end of inductor L4, respectively. The other end of inductor L3 is connected to the source of switching transistor S1, the source of switching transistor S2, the source of switching transistor S3, and the output capacitor C, respectively. o negative electrode; The other end of inductor L4 is connected to the negative terminal of capacitor C2 and the anode of diode D4, respectively; The positive terminal of capacitor C2 is connected to the cathode of diode D3 and one end of inductor L5; the other end of inductor L5 is connected to the cathode of diode D4 and the output capacitor C. o positive electrode; Output capacitor C o With load R L in parallel; The converter includes the following four operating modes: Operating mode 1: The circuit operates under AC power supply u s During the positive half-cycle, switches S1 and S2 are turned on, and switch S3 is turned off; diode D1 is forward-biased and conducts, while the other diodes are reverse-biased and cut off; during this process, the AC power supply u... s Inductor L1 is charged, capacitor C1 discharges and charges inductor L3, causing the current in inductors L1 and L3 to increase linearly; inductors L4 and L5 flow to the output capacitor C through capacitor C2. o As the load discharges, the currents in inductors L4 and L5 decrease linearly. Operating mode 2: The circuit operates under AC power supply u s During the positive half-cycle, switch S2 is turned on, while switches S1 and S3 are turned off; diodes D1, D3, and D4 are forward-biased and conduct, while the remaining diodes are reverse-biased and cut off; during this process, capacitors C1 and C2 are charged, and inductors L1 and L3 charge inductors L4 and L5, the load, and the output capacitor C. o Discharge; Operating mode 3: At this time, the circuit operates under AC power supply u s During the negative half-cycle, switches S1 and S3 are turned on, while switch S2 is turned off; diode D2 is forward-biased and conducts, while the other diodes are reverse-biased and cut off; during this process, the AC power supply u... s Inductor L2 is charged, capacitor C1 discharges and charges inductor L3, causing the current in inductors L2 and L3 to increase linearly; inductors L4 and L5 flow to the output capacitor C through capacitor C2. o As the load discharges, the currents in inductors L4 and L5 decrease linearly. Operating mode four: The circuit operates under AC power supply u s During the negative half-cycle, switch S3 is turned on, while switches S1 and S2 are turned off; diodes D2, D3, and D4 are forward-biased and conduct, while the remaining diodes are reverse-biased and cut off; during this process, capacitors C1 and C2 are charged, and inductors L2 and L3 charge inductors L4 and L5, the load, and the output capacitor C. o Discharge.

2. The bridgeless Sepic PFC converter with switched inductors and capacitors according to claim 1, characterized in that: In the converter, capacitor C2, inductors L4 and L5, and diodes D3 and D4 constitute a switching inductor-capacitor unit.

3. The bridgeless Sepic PFC converter with switched inductors and capacitors according to claim 1, characterized in that: In the converter, the switching transistors S1, S2, and S3 share a common ground, and the power switching transistors S1, S2, and S3 are insulated gate bipolar transistors (IGBTs), integrated gate commutated thyristors (IGCTs), or power field-effect transistors (MOSFETs).

4. The bridgeless Sepic PFC converter with switched inductors and capacitors according to claim 1, characterized in that: The voltage gain of the converter is D / 2(1-D).

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