A Low-Voltage-Stress Three-Winding Coupled Inductor-Switched-Capacitor Boost Converter

Abstract

The present invention discloses a three-winding coupled-inductor switched-capacitor Boost converter with low voltage stress, belonging to the technical field of power electronic converters. The converter in the present invention is composed of a boosting unit, two passive clamping circuits, and two voltage-doubling units. The clamping diode D1 and the clamping capacitor C1 form the clamping absorption unit 1; the clamping diode D2 and the clamping capacitor C2 form the clamping absorption unit 2. The diode D3, the capacitor C3, and the secondary winding L of the coupled inductor b form the voltage-doubling unit 1, and the diode D4, the capacitor C4, and the secondary winding L of the coupled inductor c form the voltage-doubling unit 2. The present invention increases the control freedom of voltage gain. The two secondary windings form a double voltage-doubling unit. In one switching cycle, the output capacitors of the two voltage-doubling units alternately supply power to the load to provide a stable DC output. The present invention can also smooth the current on the secondary winding and reduce the reverse recovery loss of the diode by designing the leakage inductance of the coupled inductor.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a DC-DC converter which combines coupled inductor and switched capacitor technologies to achieve high efficiency, ultra-high gain and low voltage stress of all switch devices. Background Art

[0002] High-gain DC-DC converters play an indispensable role in situations where the input side is low-voltage DC and the load side is high-voltage DC. For example, in an uninterruptible power supply, the voltage of the acid battery (48V) is low, but the inverter bus voltage is 380V; in the automotive high-intensity discharge lamp electronic ballast system, a DC-DC converter is required to boost the low voltage (12V) of the car battery to a higher voltage (100V). Another important application is in some renewable energy systems, such as photovoltaic arrays and fuel cells, where the output voltage is low and a boost DC-DC converter is required as an integrated interface between the low-voltage power supply and the output load to provide a safe and reliable constant high voltage for the load.

[0003] At present, domestic and foreign scholars have conducted a lot of research on high-gain DC-DC converter technology. Among them, the coupled inductor converter adds a variable, the ratio of the primary and secondary windings of the coupled inductor, in addition to the duty cycle. While further improving the voltage gain, it also increases the flexibility of the converter's adjustment range, and is a hot topic in the current research of a type of high-gain converter. However, due to the presence of leakage inductance, this type of converter achieves high gain while reducing the converter's operating efficiency. In addition, the traditional single coupling structure will resonate with the parasitic capacitance of the power switching device, causing an instantaneous excessive voltage at both ends of the switching device, increasing the voltage stress of the switching device, and exacerbating the switching loss of the device, thereby affecting the overall stability of the converter and even the power generation system.

[0004] Li Hongzhu and others published the paper "A New Magnetic Integrated High-Gain Coupled Inductor Voltage Doubler Boost Converter" in Volume 35, Supplement 2 of the Transactions of the Chinese Society of Electrotechnical Engineering, published in December 2020. They proposed a new magnetic integrated high-gain coupled inductor voltage doubler Boost converter composed of two coupled inductors. The converter has the advantages of high voltage gain, low switching tube voltage stress, and small inductor current ripple. However, the solution proposed in this article still has shortcomings, mainly in the following aspects: 1) The use of two sets of coupled inductors will increase the size of the converter and reduce the power density of the converter; 2) Due to the existence of leakage inductance, the two switching tubes will generate voltage spikes at the turn-off moment, resulting in large switching losses; 3) The output voltage gain level is improved compared to the traditional Boost circuit, but the gain is still limited. Summary of the invention

[0005] 1. Technical problem to be solved by the invention

[0006] In order to improve the voltage gain, reduce the voltage stress of the switch tube, and solve the reverse recovery problem of the diode; the present invention provides a three-winding coupled inductor switched capacitor Boost converter with low voltage stress; using the technical solution provided by the present invention, the voltage gain can be further improved, and the voltage stress problem of the switching device caused by leakage inductance is effectively suppressed.

[0007] 2. Technical solution

[0008] In order to achieve the above object, the technical solution provided by the present invention is:

[0009] The present invention discloses a three-winding coupled inductor switch capacitor Boost converter with low voltage stress. The power supply V in The positive pole and the primary winding inductance L of the coupled inductor a Same-name terminal connection; coupled inductor primary winding inductance L a The non-identical ends of are connected to the drain of the switch tube S, the anode of the diode D1 and the positive electrode of the capacitor C2 respectively; the source of the switch tube S is connected to the power supply V in The cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the anode of the capacitor C1 and the anode of the diode D3; the secondary winding inductance L of the coupled inductor is connected to the cathode of the capacitor C1, the anode of the capacitor C6 and the cathode of the diode D2; the ... cathode of the capacitor C6 and the cathode of the diode D2; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode b The same-name end is connected to the positive electrode of capacitor C3, and the non-same-name end is connected to the cathode of diode D3 and the anode of diode D5; the cathode of diode D6 is connected to the negative electrode of capacitor C2 and the anode of diode D2, and the anode of diode D6 is connected to the positive electrode of capacitor C4 and the cathode of diode D4; the secondary winding inductance L of the coupled inductor c The same-name end of the diode D5 is connected to the negative electrode of the capacitor C4; finally, the cathode of the diode D5 and the positive electrode of the capacitor C5 are connected to one end of the load, and the secondary winding inductance L of the coupling inductor is connected to the load. c The non-same-name end of the load, the cathode of capacitor C6 and the anode of diode D4 are connected to the other end of the load.

[0010] Furthermore, the two secondary windings of the coupled inductor form two sets of voltage doubling units. In one switching cycle, the output capacitors of the two voltage doubling units alternately supply power to the load to achieve a high gain effect. The voltage gain of the converter during the entire duty cycle is:

[0011]

[0012] Where n is the coupled inductor turns ratio (n = N S1 / N p =N S2 / N p ), k is the coupling coefficient of the coupled inductor (k = L m / (L m +L k1 +L k2 +L k3 )).

[0013] Furthermore, the circuit adopts passive clamping technology, which has a simple structure and is easy to control. It can not only reduce the voltage stress of the switch tube, but also realize the recovery of leakage inductance energy. The voltage stress of the switch tube S is:

[0014]

[0015] The voltage stresses of diodes D1 to D6 are:

[0016]

[0017]

[0018]

[0019] 3. Beneficial effects

[0020] Compared with the existing known technologies, the technical solution provided by the present invention has the following significant effects:

[0021] (1) A three-winding coupled inductor switched capacitor Boost converter with low voltage stress of the present invention uses two secondary windings of a coupled inductor to form two groups of voltage doubling units, and the output capacitors of the two voltage doubling units are connected in series to achieve high voltage gain output;

[0022] (2) A three-winding coupled inductor switched capacitor Boost converter with low voltage stress of the present invention, after the switch tube is turned off, two groups of passive clamping circuits composed of diodes and capacitors synchronously absorb the leakage inductance current, realizing lossless transfer of leakage inductance energy and improving conversion efficiency;

[0023] (3) A three-winding coupled inductor switched capacitor Boost converter with low voltage stress of the present invention can smooth the current on the secondary winding and reduce the reverse recovery loss of the diode by reasonably designing the leakage inductance;

[0024] (4) The three-winding coupled inductor switched capacitor Boost converter with low voltage stress of the present invention has greatly reduced voltage stress of the switch tube. Meanwhile, voltage stress of all diodes is also less than the output voltage. High-performance switching devices and diodes with low withstand voltage rating and low on-resistance can be used, thereby improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a circuit structure diagram of the present invention;

[0026] Figure 2is an equivalent circuit structure diagram of the present invention;

[0027] Figure 3 This is the main working waveform diagram of the present invention;

[0028] Figure 4 is an equivalent circuit diagram of mode 1 of the present invention;

[0029] Figure 5 is the equivalent circuit diagram of mode 2 of the present invention;

[0030] Figure 6 is an equivalent circuit diagram of mode 3 of the present invention;

[0031] Figure 7 is an equivalent circuit diagram of mode 4 of the present invention;

[0032] Figure 8 is an equivalent circuit diagram of mode 5 of the present invention;

[0033] Fig. 9 Is the input and output voltage waveform;

[0034] Fig.10 is the magnetizing inductance L m With leakage inductance L k1 Current waveform diagram;

[0035] Fig.11 N is the secondary winding S1 、N S2 Current waveform diagram;

[0036] Fig.12 It is the voltage and current waveform of the switch tube S;

[0037] Fig.13 It is the voltage and current waveform of diode D1;

[0038] Fig.14 It is the voltage and current waveform of diode D2;

[0039] Fig.15 It is the voltage and current waveform of diode D3;

[0040] Fig.16 It is the voltage and current waveform of diode D4;

[0041] Fig.17 It is the voltage and current waveform of diode D5;

[0042] Fig.18 It is the voltage and current waveform of diode D6. DETAILED DESCRIPTION

[0043] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with the accompanying drawings and embodiments.

[0044] Example 1

[0045] like Figure 1 As shown, a three-winding coupled inductor switched capacitor Boost converter with low voltage stress in this embodiment, the power supply V in The positive pole and the primary winding inductance L of the coupled inductor a Same-name terminal connection; coupled inductor primary winding inductance L a The non-identical ends of are connected to the drain of the switch tube S, the anode of the diode D1 and the positive electrode of the capacitor C2 respectively; the source of the switch tube S is connected to the power supply V in The cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the anode of the capacitor C1 and the anode of the diode D3; the secondary winding inductance L of the coupled inductor is connected to the cathode of the capacitor C1, the anode of the capacitor C6 and the cathode of the diode D2; the ... cathode of the capacitor C6 and the cathode of the diode D2; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode of the diode D1 is connected to the cathode of the capacitor C3 and C5, the cathode of the capacitor C1 and the anode of the diode D3; the cathode b The same-name end is connected to the positive electrode of capacitor C3, and the non-same-name end is connected to the cathode of diode D3 and the anode of diode D5; the cathode of diode D6 is connected to the negative electrode of capacitor C2 and the anode of diode D2, and the anode of diode D6 is connected to the positive electrode of capacitor C4 and the cathode of diode D4; the secondary winding inductance L of the coupled inductor c The same-name end of the diode D5 is connected to the negative electrode of the capacitor C4; finally, the cathode of the diode D5 and the positive electrode of the capacitor C5 are connected to one end of the load, and the secondary winding inductance L of the coupling inductor is connected to the load. c The non-same-name end of the load, the cathode of capacitor C6 and the anode of diode D4 are connected to the other end of the load.

[0046] In this embodiment, the converter is composed of a boost unit, two passive clamping circuits and two voltage doubling units. The clamping diode D1 and the clamping capacitor C1 constitute the clamping absorption unit 1; the clamping diode D2 and the clamping capacitor C2 constitute the clamping absorption unit 2. The two secondary windings of the coupled inductor are used to form two voltage doubling units with the diode and the capacitor, respectively, which are composed of the diode D3, the capacitor C3 and the secondary winding L of the coupled inductor. b The voltage doubling unit 1 is composed of a diode D4, a capacitor C4 and a coupled inductor secondary winding L c The voltage doubling unit 2 is constituted.

[0047] This embodiment introduces a three-winding coupled inductor into the structure, which, on the one hand, increases the control freedom of the voltage gain and improves the utilization rate and power density of the magnetic core. On the other hand, the two secondary windings form a double voltage unit. In one switching cycle, the output capacitors of the two voltage doubler units alternately supply power to the load to provide a stable and constant DC output voltage. At the same time, when the switch tube S is turned off, the two sets of clamping circuits synchronously absorb the leakage current of the leakage inductance and output it to the load. This effectively suppresses the voltage spike on the switch tube S and also improves the output efficiency of the converter. In addition, by reasonably designing the size of the coupled inductor leakage inductance, the current on the secondary winding can be smoothed and the reverse recovery loss of the diode can be reduced.

[0048] Example 2

[0049] The structure of the three-winding coupled inductor switched capacitor Boost converter with low voltage stress in this embodiment is the same as that in embodiment 1, and its equivalent circuit structure is as follows: Figure 2 shown.

[0050] Figure 2 The structure shown introduces a three-winding coupled inductor, combined with Figure 1 , the coupled inductor has two secondary windings, and the same-name ends of the coupled inductor are indicated by "*". Among them, L a is the primary winding inductance of the coupled inductor, L b , L c They are the inductances of the two secondary windings of the coupled inductor, L a The number of turns is N P , L b , L c The number of turns is N s1 、N s2 , the turns ratio of the coupled inductor is n1=N p / N s1 , n2=N p / N s2 . Combined Figure 2 , L m is the magnetizing inductance of the coupled inductor, L k1 , L k2 , L k3 They are the equivalent leakage inductance of the primary side and the two secondary sides of the coupled inductor respectively; the clamping diode D1 and the clamping capacitor C1 constitute the clamping absorption unit 1, and the clamping diode D2 and the clamping capacitor C2 constitute the clamping absorption unit 2; the capacitor C3, the diode D3 and the secondary winding L of the coupled inductor b The voltage doubling unit 1, capacitor C4, diode D4 and the secondary winding L of the coupled inductor c Constitute voltage doubling unit 2; V C1 、V C2 、V C3 、V C4 、V C5 、VC6 are the voltages across capacitors C1, C2, C3, C4, C5, and C6, respectively, i D1 、i D2 、i D3 、i D4 、i D5 、i D6 is the current flowing through diodes D1, D2, D3, D4, D5, and D6, i C5 is the current flowing through capacitor C5; V ds and i ds are the voltage across the switch tube S and the current flowing through the switch tube S respectively; i in is the input current, V in is the input voltage, V o is the voltage across the load R, that is, the output voltage.

[0051] The Boost converter of this embodiment has five operating modes from the time the switch is turned on to the time it is turned on next time. The main operating waveforms are as follows: Figure 3 As shown, there are five working modes in one switching cycle, such as Figures 4 to 8 shown.

[0052] Mode 1[t0-t1]

[0053] like Figure 4 As shown in Figure 1, at time t0, the switch tube S and diodes D4 and D5 are turned on. The DC voltage source starts to pass through the switch tube S to the leakage inductor L. k1 Charging, flowing through the leakage inductance L k1 The current rises linearly. At the same time, the excitation inductance L m The capacitors C4 and C5 continue to be charged through the two secondary windings, so the current flowing through the two secondary windings and the excitation inductance current decrease linearly. In this mode, the load is powered by capacitors C1 and C6. Leakage inductance L k2 , L k3 The change rate of the secondary winding current is controlled, thereby controlling the drop rate of the output diode D5 turn-off current, thereby alleviating the reverse recovery problem of the diode D5. When the currents of the two secondary windings drop to 0 at time t1, the diodes D4 and D5 are turned off, and the mode ends.

[0054] Mode 2[t1-t2]

[0055] like Figure 5 As shown in Figure 1, at time t1, diodes D4 and D5 are turned off, and diodes D3 and D6 are turned on. The DC voltage source supplies the excitation inductor L through the switch tube S. m and leakage inductance L k1 Charging, flowing through the excitation inductor L m and leakage inductance L k1 The current in the secondary winding NS1 The capacitor C3 is charged through the diode D3; the secondary winding N S2 The capacitors C2 and C4 charge the capacitor C6 through the diode D6 and the switch tube S. The load is powered by the capacitors C1 and C5.

[0056] Mode 3[t2-t3]

[0057] like Figure 6 As shown in the figure, at time t2, the switch tube S is turned off and the diodes D1 and D2 are turned on. At the moment when the switch tube S is turned off, the clamping diodes D1 and D2 are turned on, and the leakage inductance current is absorbed by the capacitors C1 and C2 through the diodes D1 and D2, respectively, reducing the switching loss. P And leakage inductance L k1 Capacitors C1 and C2 are charged through diodes D1 and D2 respectively, and current flows through leakage inductance L k1 The current decreases linearly. At the same time, in this mode, the leakage inductance L k2 , L k3 The current sudden change is suppressed, and the current flowing through the two secondary windings decreases linearly, which alleviates the reverse recovery problem of diode D6. S1 The capacitor C3 is charged through the diode D3; the secondary winding N S2 The series capacitor C4 charges the capacitor C6 through the diodes D2 and D6. At time t3, the current drops to 0, the diodes D3 and D6 are turned off, and the mode ends.

[0058] Mode 4[t3-t4]

[0059] like Figure 7 As shown, at time t3, diodes D4 and D5 are turned on, and the excitation inductance L m Through two secondary windings N S1 、N S2 The capacitors C4 and C5 are charged, and the current of the excitation inductor decreases linearly. At the same time, the DC voltage source and the primary side of the coupled inductor N P And leakage inductance L k1 The capacitors C1 and C2 are still charged through the diodes D1 and D2 respectively, and the leakage inductance current decreases linearly. At time t4, when the leakage inductance current decreases to 0, the diodes D1 and D2 are turned off, and the mode ends.

[0060] Mode 5[t4-t5]

[0061] like Figure 8 As shown, at time t4, diodes D1 and D2 are turned off, and the excitation inductance still charges capacitors C4 and C5 through two secondary windings, and the excitation inductance current decreases linearly. In this mode, capacitors C1 and C6 supply power to the load. When the switch tube S is turned on, this mode ends and enters the next cycle.

[0062] In order to simplify the analysis, the loss is not taken into account in the following analysis and the influence of the coupling inductor leakage inductance is ignored. Since the transient mode does not affect the voltage gain characteristics of the converter, only the two normal modes of the main switch on and off are considered in the analysis.

[0063] Voltage Gain

[0064] definition and They are respectively the excitation inductance in the charging state, the excitation inductance L m and secondary side N s1 、N s2 The voltage on and They are respectively the excitation inductance in the discharge state, the excitation inductance L m and secondary side N s1 、N s2 The voltage on the switch; d is the switch duty cycle; k is the coupling coefficient of the coupled inductor and (k = L m / (L m +L k1 +L k2 +L k3 )). ; n is the coupled inductor turns ratio (n1=N S1 / N p , n2=N S2 / N p , the following is a simplified analysis, let n1=n2=n).

[0065] When the converter operates in Figure 5 In mode 2 shown, the input power V in The excitation inductance L m Charge:

[0066]

[0067]

[0068] Work in Figure 7 In mode 4 shown, the voltage expressions of capacitors C1, C2, and C4 are:

[0069]

[0070]

[0071]

[0072] Combining equations (2) and (5), we get the voltage expression of capacitor C5:

[0073]

[0074] Combining equations (1), (4), and (6), we get the voltage expression of capacitor C6:

[0075]

[0076] Combining equations (4), (7), and (8), we get the expression of the converter output voltage:

[0077]

[0078] The voltage gain of the converter is:

[0079]

[0080] In summary, the voltage gain expression of the converter has four degrees of freedom, namely the duty cycle d, the coupling coefficient k of the coupled inductor, and the turns ratios n1 and n2 of the coupled inductor, which increases the flexibility of gain adjustment.

[0081] According to the above analysis, the voltage stress of the switch tube S can be derived:

[0082]

[0083] The voltage stresses of diodes D1 to D6 are:

[0084]

[0085]

[0086]

[0087] It can be seen from the voltage stress formula that the voltage stress of each power device is reduced and lower than the output voltage, which is conducive to the selection of low-power and high-performance switching devices.

[0088] Parameter setting: Input voltage U in =40V, output voltage U o =400V, output power is 800W, switching frequency is 40kHz, excitation inductance L m =100μH, leakage inductance L k1 =L k2 =L k3 =2μH, coupled inductor turns ratio N S1 :N S2 :N p =1, output capacitor C5 = C6 = 460μF, clamp capacitor C1 = C2 = 460μF, voltage doubling unit capacitor C3 = C4 = 220μF. The simulation waveform is as follows Figure 9-18 .

[0089] Fig. 9 are input and output voltage waveforms; Fig.10 is the magnetizing inductance L m With leakage inductance L k1 Current waveform; Fig.11 N is the secondary winding S1 、N S2 Current waveform; Fig.12 The voltage and current waveform of the switch tube S; Fig.13 is the voltage and current waveform of diode D1; Fig.14 is the voltage and current waveform of diode D2; Fig.15 is the voltage and current waveform of diode D3; Fig.16 is the voltage and current waveform of diode D4; Fig.17 is the voltage and current waveform of diode D5; Fig.18 is the voltage and current waveform of diode D6. From the simulation results, the converter can still achieve a very high voltage gain under non-limit duty cycle, and the voltage stress of each switch device is much smaller than the output voltage, which is conducive to improving the output efficiency.

[0090] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. A three-winding coupled inductor switched capacitor boost converter with low voltage stress, characterized in that: It includes a boost unit, two clamping absorption units and two voltage doubling units, wherein the boost unit is connected to the clamping absorption unit and the voltage doubling unit respectively; wherein, Power Supply V in The positive pole and the primary winding inductance L of the coupled inductor a Same-name terminal connection; primary winding inductance L of coupled inductor a The non-identical ends of are connected to the drain of the switch tube S, the anode of the diode D1 and the positive electrode of the capacitor C2 respectively; the source of the switch tube S is connected to the power supply V in The cathode of the diode D1 is connected to the cathode of the capacitor C3, the cathode of C5, the anode of the capacitor C1 and the anode of the diode D3; the secondary winding inductance L of the coupled inductor is connected to the cathode of the capacitor C1, the anode of the capacitor C6 and the cathode of the diode D2; the cathode of the diode D1 is connected to the cathode of the capacitor C3, the anode of C5, the anode of the capacitor C1 and the anode of the diode D3; the secondary winding inductance L of the coupled inductor is connected to the cathode of the capacitor C3, the cathode ... b The same-name end is connected to the positive electrode of capacitor C3, and the non-same-name end is connected to the cathode of diode D3 and the anode of diode D5; the cathode of diode D6 is connected to the negative electrode of capacitor C2 and the anode of diode D2, and the anode of diode D6 is connected to the positive electrode of capacitor C4 and the cathode of diode D4; the secondary winding inductance L of the coupled inductor c The same-name end of the diode D5 is connected to the negative electrode of the capacitor C4; finally, the cathode of the diode D5 and the positive electrode of the capacitor C5 are connected to one end of the load, and the secondary winding inductance L of the coupling inductor is connected to the load. c The non-same-name end of the load, the cathode of capacitor C6 and the anode of diode D4 are connected to the other end of the load.

2. The three-winding coupled inductor switched capacitor Boost converter with low voltage stress according to claim 1, characterized in that: The clamping diode D1 and the clamping capacitor C1 constitute a clamping absorption unit 1 ; the clamping diode D2 and the clamping capacitor C2 constitute a clamping absorption unit 2 .

3. The three-winding coupled inductor switched capacitor Boost converter with low voltage stress according to claim 2, characterized in that: Diode D3, capacitor C3 and the secondary winding inductance L of the coupled inductor b The voltage doubling unit 1 is composed of a diode D4, a capacitor C4 and a secondary winding inductance L of a coupled inductor. c A voltage doubling unit 2 is formed.

4. A three-winding coupled inductor switched capacitor Boost converter with low voltage stress according to any one of claims 1 to 3, characterized in that: In one switching cycle of the converter, the capacitors of the two voltage doubler units supply power to the load alternately, and the voltage gain is: Where n is the turns ratio of the coupled inductor, k is the coupling coefficient of the coupled inductor, and d is the duty cycle.

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