Sepic type power correction circuit based on switched inductor

Abstract

The application discloses a Sepic type power correction circuit based on a switched inductor, which comprises switching tubes S1-S3, diodes D1-D5, inductors L1-L5, capacitors C1 and C o The diodes D3-D5 and the inductors L4 and L5 form a switched inductor structure, and the voltage gain of the converter is D / (2-D). Compared with a conventional Sepic PFC converter, the Sepic type power correction circuit based on the switched inductor improves the step-down gain, ensures that the whole duty cycle range is in a step-down state, and has a larger duty cycle than the conventional Sepic PFC converter in the case of a high step-down ratio, thereby effectively avoiding the emergence of a limit duty cycle. The no-bridge structure can realize lower conduction loss. The original output diode is replaced by the switched inductor structure, so that the output current is continuous, and the output current can be filtered. All the switching tubes are common ground, and a lower-cost driving circuit can be used.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, specifically a Sepic-type power correction circuit based on a switching inductor. Background Technology

[0002] Traditional Buck PFC converters are widely used, but due to their discontinuous input current and current dead zone, their power factor is not high. However, according to the IEC 61000-3-2 standard, Class D appliances connected to the power grid with a rated power greater than 75W must meet certain harmonic current suppression requirements; otherwise, they will cause harmonic pollution to the power grid. Therefore, the application of Buck PFC converters is somewhat limited.

[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 small to medium power ratings. Sepic PFC circuits have an inductor at the input, resulting in continuous input current, which helps improve the converter's power factor and reduce THD. However, to achieve a high buck conversion ratio, the switching transistors need to operate at very low duty cycles, which can lead to converter instability and low conversion efficiency. Therefore, a circuit that can solve these problems is needed. Summary of the Invention

[0004] To address the issues of low efficiency in existing Sepic PFC converters, with a duty cycle range of only 0-0.5 in buck mode and extremely low duty cycle of the switching transistor at high buck ratios, this invention proposes a Sepic-type power correction circuit based on a switching inductor. The output diode in the original Sepic PFC converter is replaced with a switching inductor unit containing five components. Compared to traditional Sepic PFC converters, the power correction circuit of this invention improves the buck gain, ensures buck operation across the entire duty cycle range, and provides a higher duty cycle at high buck ratios than traditional Sepic PFC converters, effectively avoiding extreme duty cycle conditions.

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

[0006] Sepic-type power correction circuit based on switched inductors, including AC power supply u s Switches S1-S3, diodes D1-D5, inductors L1-L5, capacitors C1 and C2 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 sOn 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. 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. o negative electrode;

[0011] The other end of inductor L4 is connected to the anode of diode D4 and the anode of diode D5, respectively;

[0012] The cathode of diode D5 is connected to the cathode of diode D3 and one end of inductor L5, respectively.

[0013] The other end of inductor L5 is connected to the cathode of diode D4 and the output capacitor C, respectively. o Positive terminals connected;

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

[0015] In this power correction circuit, inductors L4 and L5, diodes D3, D4, and D5 constitute a switching inductor unit.

[0016] In this power correction circuit, 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 this power correction circuit is D / (2-D).

[0018] This power correction circuit 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, and switch S3 is turned off. Diodes D1 and D5 are forward-biased and conduct, while the remaining 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 discharge through diode D5 to the output capacitor C. 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, capacitor C1 is 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. Diodes D2 and D5 are forward-biased and conduct, while the remaining 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 discharge through diode D5 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, capacitor C1 is charged, and inductors L2 and L3 charge inductors L4 and L5, the load, and the output capacitor C. o Discharge.

[0023] The present invention discloses a Sepic-type power correction circuit based on a switching inductor, the technical effects of which are as follows:

[0024] 1) Compared to the traditional Sepic PFC converter, the power correction circuit described in this invention has a higher buck gain, M = D / (2-D). The duty cycle range of the original Sepic PFC converter in buck mode is expanded from 0-0.5 to 0-1. This ensures that the converter is in buck mode throughout the full duty cycle range. The high buck ratio allows the converter to operate at a larger duty cycle, which helps reduce current stress and improve efficiency.

[0025] 2) The power correction circuit of the present invention introduces a switching inductor 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 power correction circuit described in this invention share a common ground, and the drive circuit design is simple and reliable, which helps to reduce the overall cost of the circuit.

[0027] 4) The power correction circuit of the present invention adopts a bridgeless structure in the front-stage rectification section, which reduces the conduction loss of semiconductor devices. 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 schematic diagram of the main topology of a Sepic-type power correction circuit based on a switching inductor according to the present invention.

[0030] Figure 2 This is a schematic diagram of the first operating mode of a Sepic-type power correction circuit based on a switching inductor according to the present invention.

[0031] Figure 3 This is a schematic diagram of the second operating mode of a Sepic-type power correction circuit based on a switching inductor according to the present invention.

[0032] Figure 4 This is a schematic diagram of the third operating mode of a Sepic-type power correction circuit based on a switching inductor according to the present invention.

[0033] Figure 5 This is a schematic diagram of the fourth operating mode of a Sepic-type power correction circuit based on a switching inductor according to the present invention.

[0034] Figure 6 This is a key steady-state waveform diagram of a Sepic-type power correction circuit based on a switching inductor according to the present invention.

[0035] Figure 7 This is a schematic diagram comparing the voltage gain of a Sepic-type power correction circuit based on a switching inductor according to the present invention with that of a traditional Sepic PFC converter.

[0036] Figure 8 The image shows the input voltage and current waveforms of a Sepic-type power correction circuit based on a switching inductor under steady-state conditions, according to the present invention.

[0037] Figure 9 The output voltage and current waveforms of a Sepic-type power correction circuit based on a switching inductor according to the present invention are shown in steady state. Detailed Implementation

[0038] like Figure 1 As shown, the Sepic-type power correction circuit based on a switching inductor includes switching transistors S1-S3, diodes D1-D5, inductors L1-L5, and capacitors C1 and C2. o ;

[0039] AC power supply u s 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.

[0040] The positive terminal of capacitor C1 is connected to the cathodes of diodes D1 and D2 and the drain of switching transistor S1, respectively.

[0041] 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;

[0042] The other end of inductor L4 is connected to the anodes of diodes D4 and D5, respectively;

[0043] The cathode of diode D5 is connected to the cathode of diode D3 and one end of inductor L5;

[0044] The other end of inductor L5 is connected to the cathode of diode D4 and output capacitor C. o Positive terminals connected;

[0045] Output capacitor C o With load R L in parallel.

[0046] The inductors L4 and L5, and diodes D3, D4 and D5 of the power correction circuit form a switching inductor unit;

[0047] The specific parameters of the converter are as follows: the effective value of the input AC voltage 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 =2200μF, intermediate connecting capacitor C1=2μF, load resistor R L =12.8Ω.

[0048] The Sepic-type power correction circuit based on a switched inductor, under steady-state operation in CCM mode, includes the following operating modes:

[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, diodes D1 and D5 are forward-biased and conducting, 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 output capacitor C through diode D5. 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:

[0050]

[0051] Among them, V C1 It is the voltage stress of capacitor C1, 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, capacitor C1 is charged, and inductors L1 and L3 charge L4, L5, the load, and 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, diodes D2 and D5 are forward-biased and conducting, 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 output capacitor C through diode D5. 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 conducting, and all other semiconductor devices are turned off. During this process, capacitor C1 is charged, and inductors L2 and L3 charge L4, L5, the load, and 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 of the power correction circuit during stable operation:

[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 power correction circuit described in this invention is:

[0064]

[0065] The step-down gain curve of a Sepic-type power correction circuit based on a switched inductor according to the present invention is shown below. Figure 7 As shown. (Through) Figure 7 As can be seen, the power correction circuit described in this invention operates in buck mode throughout the entire duty cycle range. Under high buck ratio conditions, the duty cycle range of the power correction circuit described in this invention is wider than that of the traditional Sepic PFC converter, effectively avoiding the occurrence of extreme duty cycle conditions for the switching transistors.

[0066] Figure 8 This is a steady-state input-side voltage and current waveform diagram of a Sepic-type power correction circuit based on a switched inductor according to the present invention. For a more intuitive comparison with the voltage waveform, Figure 8 The current waveform shown is the actual value multiplied by a gain of 30. It can be seen that the input voltage and input current are in phase and the waveforms are undistorted, thus achieving the power factor correction function.

[0067] Figure 9 This is a steady-state output voltage and current waveform diagram of a Sepic-type power correction circuit based on a switched inductor according to the present invention. It can be seen that the DC-side output voltage is stable at around 48V, and the output current is continuous.

[0068] Compared to traditional Sepic PFC converters, the power correction circuit described in this invention improves the buck gain, ensuring a buck state across the entire duty cycle range. It offers a larger duty cycle than traditional Sepic PFC converters at high buck ratios, effectively avoiding extreme duty cycle conditions. The bridgeless structure achieves lower conduction losses. Replacing the original output diodes with a switched inductor structure ensures continuous output current, facilitating output current filtering. Furthermore, all switches share a common ground, allowing for the use of lower-cost drive circuits. This Sepic power correction circuit based on switched inductors is highly practical.

Claims

1. A Sepic-type power correction circuit based on a switched inductor, including an AC power supply u s Switches S1~S3, diodes D1~D5, inductors L1~L5, capacitors C1, C 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. 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. o negative electrode; The other end of inductor L4 is connected to the anode of diode D4 and the anode of diode D5, respectively; The cathode of diode D5 is connected to the cathode of diode D3 and one end of inductor L5, respectively. The other end of inductor L5 is connected to the cathode of diode D4 and the output capacitor C, respectively. o Positive terminals connected; Output capacitor C o With load R L in parallel; This power correction circuit has 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; diodes D1 and D5 are forward-biased and conduct, while the remaining 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 supply current to output capacitor C through diode D5. 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, capacitor C1 is charged, and inductors L1 and L3 charge inductors L4 and L5, the load, and 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; diodes D2 and D5 are forward-biased and conduct, while the remaining 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 rise linearly; inductors L4 and L5 supply current to output capacitor C through diode D5. 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, capacitor C1 is charged, and inductors L2 and L3 charge inductors L4 and L5, the load, and output capacitor C. o Discharge.

2. The Sepic-type power correction circuit based on a switched inductor according to claim 1, characterized in that: In this power correction circuit, inductors L4 and L5, diodes D3, D4, and D5 constitute a switching inductor unit.

3. The Sepic-type power correction circuit based on a switched inductor according to claim 1, characterized in that: In this power correction circuit, 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 Sepic-type power correction circuit based on a switched inductor according to claim 1, characterized in that: The voltage gain of this power correction circuit is D / (2-D).

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