Soft-switching high-gain DC-DC converter based on Sepic

Abstract

The invention relates to a soft switching high-gain DC-DC (Direct Current-Direct Current) converter based on Sepic (Sepic). The proposed converter utilizes a quasi-resonance (QR) technique to implement a soft switching condition and mitigate a diode reverse recovery problem. In addition, the converter is also integrated with a Y-source network, so that the voltage gain adjustment is more flexible. The steady state and the voltage and current stress of the element are analyzed in detail. And the design process of the device is fully considered. Finally, the effectiveness of the converter is verified by a 200W prototype manufactured in a laboratory. When the output power reaches 200W, the efficiency of the converter is 95.238%.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics and control thereof, in particular to a soft-switching high-gain DC-DC converter based on Sepic. Background Art

[0002] Since the output voltage of photovoltaic, fuel cell and wind power is low, usually 24V-48V, a high boost DC-DC converter is required to boost the low voltage to 400V DC bus voltage. Then an inverter is needed to complete the grid connection. Therefore, it has become an urgent task to develop a DC-DC converter with high voltage gain and high efficiency to boost low voltage to high voltage. In renewable energy applications, electrical isolation is not essential. Therefore, non-isolated converters have attracted much attention in recent years due to their small size and low cost.

[0003] Traditional non-isolated boost converters (such as BOOST and SEPIC) have low boost capability, large voltage stress, and high diode reverse recovery current, so it is urgent to study new high boost converters. Traditional boost technologies include switched inductors, switched capacitors, multiple cascades, etc. However, converters developed using these technologies usually operate under hard switching conditions. The application of coupled inductors is a good choice to improve the boost capability of the converter. However, the voltage spikes generated by leakage inductance are a major challenge facing switching devices. Therefore, active or passive clamping technology is needed to suppress voltage spikes. In addition, the application of soft switching technology is also an effective way to improve efficiency.

[0004] In recent years, improved converters based on SEPIC have become a hot topic of research. Such converters usually have the advantages of continuous input current and high efficiency. In addition, all such converters contain a switch, which simplifies the control complexity and improves the system stability. However, the boost capability of these converters still needs to be further improved. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a soft-switching high-gain DC-DC converter based on Sepic, which can achieve high boost capability and high conversion efficiency with fewer components and lower manufacturing cost.

[0006] To achieve the above object, the present invention adopts the following technical solution: a soft switching high gain DC-DC converter based on Sepic, comprising an inductor L, a switch tube S, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a capacitor C O, a first diode D1, a second diode D2, a third diode D3, a diode Do, a first transformer, a second transformer and a third transformer; the drain of the switch tube S is connected to one end of the inductor L, the negative electrode of the second capacitor C2 and the positive electrode of the first diode D1, and the source of the switch tube S is grounded; the negative electrode of the first diode D1 is connected to the positive electrode of the first capacitor C1 and one end of the first transformer, and the negative electrode of the first capacitor C1 is grounded; one end of the second transformer is connected to the other end of the first transformer and the negative electrode of the third capacitor C3, and the other end of the second transformer is connected to the positive electrode of the second capacitor C2; the positive electrode of the third capacitor C3 is connected to one end of the third transformer and the positive electrode of the third diode D3; the negative electrode of the fourth capacitor C4 is connected to the other end of the third transformer; the positive electrode of the fourth capacitor C4 is connected to the negative electrode of the third diode D3 and the positive electrode of the diode Do; the negative electrode of the diode Do is connected to the capacitor C O The positive electrode of capacitor C O The negative pole of is grounded; the voltage of inductor L is used as the input voltage.

[0007] In a preferred embodiment, when the switch tube S is turned on, Kirchhoff's voltage law is written for the converter equivalent circuit to obtain:

[0008]

[0009]

[0010] When the switch tube S is turned off, Kirchhoff's voltage law is written for the converter equivalent circuit to obtain:

[0011]

[0012] In a preferred embodiment, the turn ratio relationship of the first transformer, the second transformer and the third transformer is n2=N2 / N1, n3=N3 / N1, N1, N2, N3 are the turns of the transformer windings respectively; the following equation is obtained according to the transformer turn ratio relationship:

[0013] VN2=n2VN1, VN3=n3VN1 (3).

[0014] In a preferred embodiment, the following equation is obtained according to the volt-second balance law:

[0015] DV L_ON +(1-D)V L_OFF =0,DV N1_ON +(1-D)V N1_OFF =0 (4)

[0017] By combining equations (1)(2)(3)(4), we can solve the voltage gain formula and capacitor voltage stress of the proposed converter:

[0018]

[0019] In a preferred embodiment, the voltage stress of the switch tube and the diode is as follows:

[0020]

[0021] In a preferred embodiment, the input inductor and magnetizing inductor current ripple are

[0022]

[0023] When the input current is continuous, we get

[0024] 2I L ≥ΔI L (9) Combine (22) and (23) to determine the range of input inductance

[0025]

[0026] where f S is the switching frequency.

[0027] In a preferred embodiment, the relationship between the excitation inductance and the current satisfies formula (11):

[0028]

[0029] According to formula (8) (11), the range of inductance is

[0030]

[0031] in

[0032]

[0033] Calculate the capacitance range according to formula (13);

[0034]

[0035] In a preferred embodiment, the converters C3, C4, C O The capacitance value range is as follows:

[0036]

[0037] Since the first capacitor C1 and the second capacitor C2 are intermediate capacitors, their voltage ripple will not affect the output voltage; the first capacitor C1 and the second capacitor C2 also satisfy formula (15):

[0038]

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] By taking advantage of the continuous input current and common ground of the input and output voltage of the Sepic converter and mixing it with the characteristics of the Y-source step-down transformer, a new converter with the common advantages of the two converters is obtained to achieve a higher voltage gain. Quasi-resonance technology is applied to achieve soft switching of the switch tube and improve the conversion efficiency of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram (I) of the topology derivation of a soft-switching high-gain DC-DC converter based on Sepic according to a preferred embodiment of the present invention;

[0042] Figure 2 Schematic diagram (II) of the topology derivation of a soft-switching high-gain DC-DC converter based on Sepic according to a preferred embodiment of the present invention;

[0043] Figure 3 Schematic diagram (III) of the topology derivation of a soft-switching high-gain DC-DC converter based on Sepic according to a preferred embodiment of the present invention;

[0044] Figure 4 Schematic diagram (IV) of the topology derivation of a soft-switching high-gain DC-DC converter based on Sepic according to a preferred embodiment of the present invention;

[0045] Figure 5 This is an equivalent circuit diagram of a switch tube when conducting according to a preferred embodiment of the present invention;

[0046] Figure 6 This is an equivalent circuit diagram of a preferred embodiment of the present invention when the switch tube is turned off;

[0047] Figure 7 An experimental prototype of a preferred embodiment of the present invention;

[0048] Figure 8The experimental waveform diagram of the preferred embodiment of the present invention; wherein; (a) is the voltage of the switch tube S, the voltage of the inductor L, and the current of the inductor L; (b) is the voltage of the switch tube S, and the current of the switch tube S; (c) is the voltage of the diode D1, and the current of the diode D1; (d) is the voltage of the diode D2, and the current of the diode D2; (e) is the voltage of the diode D3, and the current of the diode D3; (f) is the voltage of the diode DO, and the current of the diode DO; (g) is the output voltage VO, the voltage of the coupled inductor N1, and the current of the leakage inductor Lk; (h) is the voltage of the capacitor C1, the current of the coupled inductor N2, the voltage of the coupled inductor N2, and the voltage of the capacitor C2; (i) is the voltage of the capacitor C3, the voltage of the capacitor C4, the voltage of the coupled inductor N3, and the current of the coupled inductor N3; (j) is the output current I O , output voltage V O . DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0050] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0051] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0052] A soft-switching high-gain DC-DC converter based on Sepic, reference Figure 1-8 , including an inductor L, a switch tube S, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a capacitor C O, a first diode D1, a second diode D2, a third diode D3, a diode Do, a first transformer, a second transformer and a third transformer; the drain of the switch tube S is connected to one end of the inductor L, the negative electrode of the second capacitor C2 and the positive electrode of the first diode D1, and the source of the switch tube S is grounded; the negative electrode of the first diode D1 is connected to the positive electrode of the first capacitor C1 and one end of the first transformer, and the negative electrode of the first capacitor C1 is grounded; one end of the second transformer is connected to the other end of the first transformer and the negative electrode of the third capacitor C3, and the other end of the second transformer is connected to the positive electrode of the second capacitor C2; the positive electrode of the third capacitor C3 is connected to one end of the third transformer and the positive electrode of the third diode D3; the negative electrode of the fourth capacitor C4 is connected to the other end of the third transformer; the positive electrode of the fourth capacitor C4 is connected to the negative electrode of the third diode D3 and the positive electrode of the diode Do; the negative electrode of the diode Do is connected to the capacitor C O The positive electrode of capacitor C O The negative pole of the power supply is grounded; the voltage of the inductor L is used as the input voltage. The input end of this solution contains an inductor, which can make the input current continuous and effectively increase the service life of the power supply; and the input voltage and the output voltage have a common ground, which is convenient for the control circuit design and reduces the common mode voltage; the built-in step-down transformer can use a smaller transformer volume to achieve a higher boost function; the output diode current stress is low, which can reduce losses; there are capacitive circuits at both ends of the switch tube, which can absorb the voltage spikes caused by the transformer leakage inductance and increase the service life of the switch tube; the parasitic parameters of the circuit device itself are used to achieve quasi-resonance, so as to achieve the purpose of soft switching of the switch tube, reduce switching losses, and have higher boost capability and power conversion efficiency.

[0053] like Figure 1-4 As shown in Figure 1, the derivation process of the proposed converter topology is shown.

[0054] Figure 5 This is the equivalent circuit of the converter when the switch is turned on. Writing Kirchhoff's voltage law on it gives the following equation.

[0055]

[0056] The equivalent circuit when the switch is turned off is as follows Figure 6 As shown, writing Kirchhoff's voltage law gives the following equation.

[0057]

[0058] The transformer turns ratio relationship is n2 = N2 / N1, n3 = N3 / N1, N1, N2, N3 are the turns of the transformer winding respectively. According to the transformer turns ratio relationship, the following equation can be obtained.

[0059] VN2 =n2V N1 , V N3 =n3V N1 (3)

[0060] According to the volt-second balance law, the following equation can be obtained.

[0061] DV L_ON +(1-D)V L_OFF =0,DV N1_ON +(1-D)V N1_OFF =0 (4)

[0062] By combining equations (1)(2)(3)(4), we can solve the voltage gain formula and capacitor voltage stress of the proposed converter.

[0063]

[0064] The performance of a good converter depends on the accurate design of its components. The selection of diodes and switches is based on 1.5 times the voltage and current stress at the maximum operating point. Usually, switches and diodes can pass large currents, so their voltage stress is the main concern.

[0065] The voltage stress of the switch and diode can be easily calculated as follows.

[0066]

[0067] The input inductor and magnetizing inductor current ripple are

[0068]

[0069] When the input current is continuous, we can get

[0070] 2I L ≥ΔI L (9)

[0071] Combining (22) and (23), the range of input inductance can be determined

[0072]

[0073] where f S is the switching frequency

[0074] In order to avoid the converter operating in DCM mode, the relationship of the excitation inductor current should satisfy formula (11).

[0075]

[0076] According to formula (8) (11), the range of inductance is

[0077]

[0078] in

[0079]

[0080] The capacitance range can be calculated according to formula (13).

[0081]

[0082] Therefore, the proposed converters C3, C4, C O The capacitance value range is as follows.

[0083]

[0084] Since C1 and C2 are intermediate capacitors, their voltage ripple will not affect the output voltage. Therefore, capacitors with smaller capacitance values ​​can be selected. Therefore, the volume of the converter can be reduced. In addition, in order to achieve a quasi-resonant process. Therefore, capacitors C1 and C2 should also satisfy formula (15).

[0085]

[0086] In order to verify the feasibility of the proposed converter, a 200W experimental prototype was built in the laboratory. Figure 7 shown. Figure 8 This is the experimental waveform. Figure 8 As can be seen from (a), due to the use of a passive clamping loop, the voltage peak of the switch at the moment of turn-off is very small. The input current ripple is very small, with an average value of about 5.6A. When the switch is turned on, the voltage of the inductor L is equal to the input voltage. Figure 8 The voltage and current waveforms of the switch tube shown in (b) show that the switch tube can achieve ZVS at the moment of turn-on, thanks to the application of quasi-resonance technology. The voltage stress on the switch is about 60V, which is consistent with the calculation result of formula (7). The voltage and current waveforms of the diode are as follows Figure 8 Quasi-resonant technology helps D1 and D3 achieve ZCS and low reverse recovery (LRR) at the turn-off instant, while D2 and D O The diodes D1, D2, D3 and D OThe voltage stress of the output voltage, the voltage of N1 and the leakage inductance current are 62V, 210V, 170V and 280V respectively. The output voltage is 400V. When the duty cycle is 0.4, the turns ratio n2=0.5, n3=1.5, the theoretical voltage gain calculated according to formula (5) is 12. When the input voltage is 37.5V, the actual voltage gain is 400V / 37.5V=10.67, which is slightly lower than the theoretical value and within a reasonable range. The voltages of capacitors C1, C2, C3 and C4 are 62V, 25V, 140V and 100V respectively, which further verifies the correctness of formula (6). The voltage relationship of the coupled inductor is related to the turns ratio of the coupled inductor N1:N2:N3=1:0.5:1.5. When the output power changes between full load and half load, the output voltage can be stabilized quickly, which shows that the proposed converter has good stability.

Claims

1. A soft-switching high-gain DC-DC converter based on Sepic, characterized in that: The circuit includes an inductor L, a switch tube S, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, and a capacitor C O , a first diode D1, a second diode D2, a third diode D3, a diode Do, a first transformer, a second transformer and a third transformer; the drain of the switch tube S is connected to one end of the inductor L, the negative electrode of the second capacitor C2 and the positive electrode of the first diode D1, and the source of the switch tube S is grounded; the negative electrode of the first diode D1 is connected to the positive electrode of the first capacitor C1 and one end of the first transformer, and the negative electrode of the first capacitor C1 is grounded; one end of the second transformer is connected to the other end of the first transformer and the negative electrode of the third capacitor C3, and the other end of the second transformer is connected to the positive electrode of the second capacitor C2; the positive electrode of the third capacitor C3 is connected to one end of the third transformer and the positive electrode of the third diode D3; the negative electrode of the fourth capacitor C4 is connected to the other end of the third transformer; the positive electrode of the fourth capacitor C4 is connected to the negative electrode of the third diode D3 and the positive electrode of the diode Do; the negative electrode of the diode Do is connected to the capacitor C O The positive electrode of capacitor C O The negative pole of is grounded; the voltage of inductor L is used as the input voltage.

2. A Sepic-based soft-switching high-gain DC-DC converter according to claim 1, characterized in that: When the switch tube S is turned on, write Kirchhoff's voltage law for the converter equivalent circuit to obtain: When the switch tube S is turned off, Kirchhoff's voltage law is written for the converter equivalent circuit to obtain:

3. A Sepic-based soft-switching high-gain DC-DC converter according to claim 2, characterized in that: The turns ratio relationship of the first transformer, the second transformer and the third transformer is n2=N2 / N1, n3=N3 / N1, N1, N2, N3 are the turns of the transformer winding respectively; according to the transformer turns ratio relationship, the following equation is obtained: VN2=n2VN1, VN3=n3VN1 (3).

4. A Sepic-based soft-switching high-gain DC-DC converter according to claim 3, characterized in that: According to the volt-second balance law, we get the following equation: DV L_ON +(1-D)V L_OFF =0,DV N1_ON +(1-D)V N1_OFF =0 (4) Combine equations (1)(2)(3)(4) to solve the voltage gain formula and capacitor voltage stress of the proposed converter:

5. A Sepic-based soft-switching high-gain DC-DC converter according to claim 4, characterized in that: The voltage stress of the switch tube and the diode is as follows:

6. A Sepic-based soft-switching high-gain DC-DC converter according to claim 5, characterized in that: The input inductor and magnetizing inductor current ripple are When the input current is continuous, we get <h2 style=";text-align:left;direction:ltr">2I<h2 style=";text-align:left;direction:ltr"> L <h2 style=";text-align:left;direction:ltr"> ≥ΔI<h2 style=";text-align:left;direction:ltr"> L <h2 style=";text-align:left;direction:ltr"> (9) Combining (22) and (23), we can determine the range of input inductance: where f S is the switching frequency.

7. A Sepic-based soft-switching high-gain DC-DC converter according to claim 6, characterized in that: The relationship between the excitation inductance current satisfies formula (11): According to formula (8) (11), the range of inductance is in Calculate the capacitance range according to formula (13); 8. The Sepic-based soft-switching high-gain DC-DC converter according to claim 7, characterized in that: The proposed converters C3, C4, C O The capacitance value range is as follows: Since the first capacitor C1 and the second capacitor C2 are intermediate capacitors, their voltage ripple will not affect the output voltage; the first capacitor C1 and the second capacitor C2 also satisfy formula (15):

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