Wide input and output range soft switching DC-DC converter and control method

Abstract

This invention relates to the field of DC-DC converters, and particularly to a wide input / output range soft-switching DC-DC converter and its control method. It includes an input circuit, a transformer, and an output circuit; the input circuit is a half-bridge circuit; the primary winding of the transformer is connected to the midpoint of the bridge arm of the half-bridge circuit via an inductor Lr; switches BS1 and BS2 are connected between the first end and the middle end of the secondary winding of the transformer; switches SR1 and SR2 are connected between the first end and the second end of the secondary winding of the transformer; a load and a capacitor CD2 are connected between the second end and the middle end of the secondary winding of the transformer. This invention achieves ZVS soft switching over a wide input / output range and under wide load conditions. It has multiple operating modes, effectively improving converter gain, power rating, and power density, and limiting voltage stress on the output-side power devices.

Description

Technical Field

[0001] This invention relates to the field of DC-DC converters, and particularly to a wide input / output range soft-switching DC-DC converter and its control method. Background Technology

[0002] A high-voltage DC-DC converter is a high-frequency power conversion device that mainly utilizes the periodic control of high-frequency switching devices to achieve functions such as voltage transformation and voltage stabilization. It is widely used in aerospace, new energy vehicles, industrial control and other fields.

[0003] Transformer-isolated circuit structures are common topologies for high-voltage DC-DC input DC-DC converters, such as flyback converters and forward converters. Under high-voltage DC input conditions, the switching voltage of the primary-side MOSFETs is high, resulting in large switching losses. This severely limits the power rating of hard-switching converters and makes it difficult to improve power density. Therefore, in such conditions, phase-shifted full-bridge converters and LLC converters, which can achieve ZVS soft switching, are more commonly used. However, the conditions for achieving ZVS soft switching in the rear bridge arm of a phase-shifted full-bridge converter are quite demanding, and the voltage stress on the secondary-side rectifier diodes or synchronous rectifier MOSFETs is high, limiting the potential for improving converter efficiency and power density. For LLC converters, the output voltage gain is adjusted using resonance, but the gain adjustment range is quite limited, making it difficult to adapt to wide input / output range applications. Therefore, traditional ZVS soft-switching converters have relatively low efficiency, power rating, and power density under high-voltage, wide input / output range conditions. Summary of the Invention

[0004] The purpose of this invention is to solve the aforementioned problems by designing a wide input / output range soft-switching DC-DC converter and its control method. To achieve the above objective, this invention provides the following solution: A wide input / output range soft-switching DC-DC converter includes an input circuit, a transformer, and an output circuit. The input circuit is a half-bridge circuit composed of switches S1 and S2, capacitor C1, and capacitor C2. The primary winding of the transformer is connected to the midpoint of the bridge arm of the half-bridge circuit via an inductor Lr. Switches BS1 and BS2 are connected in series between the first end of the transformer secondary winding and the middle end of the transformer secondary winding; switches SR1 and SR2 are connected in series between the first end of the transformer secondary winding and the second end of the transformer secondary winding; a load and a capacitor CD2 are connected in parallel between the second end of the transformer secondary winding and the middle end of the transformer secondary winding. The wide input / output range DC-DC converter determines its operating mode based on the highest operating frequencies of switches S1 and S2, and the volt-second product of the transformer.

[0005] As a further improvement to this technical solution, a capacitor CD1 is connected in parallel across the two ends of the input circuit.

[0006] As a further improvement to this technical solution, a capacitor Cr1 is connected in parallel across the two ends of the switch S1, and a capacitor Cr2 is connected in parallel across the two ends of the switch S2.

[0007] As a further improvement to this technical solution, the capacitance of capacitor Cr1 and capacitor Cr2 is smaller than the capacitance of capacitor C1 and capacitor C2.

[0008] As a further improvement to this technical solution, the switches S1, S2, SR1, SR2, BS1, and BS2 are all MOSFETs; the switches S1, S2, SR1, SR2, BS1, and BS2 each contain body diodes VD1 to VD6.

[0009] As a further improvement to this technical solution, the S pole of switch BS1 is connected to the S pole of switch BS2; the D pole of switch BS1 is connected to the first end of the secondary winding of the transformer; and the D pole of switch BS2 is connected to the middle end of the secondary winding of the transformer. The S pole of switch SR1 is connected to the S pole of switch SR2; the D pole of switch SR1 is connected to the second end of the secondary winding of the transformer; the D pole of switch SR2 is connected to the first end of the secondary winding of the transformer.

[0010] As a further improvement to this technical solution, the wide input / output range DC-DC converter has three operating modes: operating mode one when the operating frequency exceeds the maximum operating frequency of switches S1 and S2; operating mode two when the operating frequency is lower than the maximum operating frequency of switches S1 and S2 and the volt-second product of the transformer is lower than the set value; and operating mode three when the operating frequency is lower than the maximum operating frequency of switches S1 and S2 and the volt-second product of the transformer exceeds the set value.

[0011] A control method for a wide input / output range soft-switching DC-DC converter, when the operating frequency exceeds the maximum operating frequency of switches S1 and S2, includes the following stages: Phase a1: The time period from t10 to t11. At time t10, switches S1 and SR1 are turned on, while switches S2, SR2, BS1, and BS2 are turned off, and the current through inductor Lr increases. Phase a2: From t11 to t12, at time t11, switch SR1 is turned on, and switches S1, S2, SR2, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD2 is turned on. Phase a3: From t12 to t13, at time t12, switches S1 and S2 are off, switches BS1 and BS2 are on, switches SR1 and SR2 are off, and inductor Lr and capacitors Cr1 and Cr2 resonate. Stage a4: From t13 to t14, at time t13, during the resonance process of inductor Lr and capacitors Cr1 and Cr2, when the voltage at the connection point between inductor Lr and the midpoint of the bridge arm is 0, switch S1 is turned off, switch S2 is turned on, switches BS1, BS2 and SR1 are turned off, switch SR2 is turned on, and the current through inductor Lr increases. Phase a5: During the time period from t14 to t15, at time t14, switch SR2 is turned on, and switches S1, S2, SR1, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD1 is turned on. Phase a6: During the time period from t15 to t16, at time t15, switches S1 and S2 are turned off, switches BS1 and BS2 are turned on, switches SR1 and SR2 are turned off, and inductor Lr and capacitors Cr1 and Cr2 resonate. When the voltage at the connection point between inductor Lr and the midpoint of the bridge arm is the input voltage, phase a1 is repeated.

[0012] A control method for a wide input / output range soft-switching DC-DC converter, when the operating frequency is lower than the maximum operating frequency of switches S1 and S2, and the volt-second product of the transformer is lower than a set value, includes the following stages: Phase b1: The time period from t20 to t21. At time t20, switches S1 and SR1 are turned on, while switches S2, SR2, BS1, and BS2 are turned off, and the current through inductor Lr increases. Phase b2: During the time period from t21 to t22, at time t21, switch SR1 is turned on, and switches S1, S2, SR2, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD2 is turned on. Phase b3: During the time period from t22 to t23, at time t22, switches S2 and SR2 are turned on, while switches S1, SR1, BS1, and BS2 are turned off, and the current through inductor Lr increases. Phase b4: From t23 to t24, at time t23, switch SR2 is turned on, and switches S1, S2, SR1, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD1 is turned on. At time t24, phase b1 is repeated.

[0013] A control method for a wide input / output range soft-switching DC-DC converter, wherein the operating frequency is lower than the maximum operating frequency of switches S1 and S2, and the volt-second product of the transformer exceeds a set value, includes the following steps: Phase c1: The time period from t30 to t31. At time t30, switch S1 is turned on, switch S2 is turned off, switches BS1 and BS2 are turned on, and switches SR1 and SR2 are turned off. The current through inductor Lr increases. Phase c2: During the time period from t31 to t32, at time t31, switch S1 is turned on, switch S2 is turned off, switches BS1 and BS2 are turned off, switch SR1 is turned on, switch SR2 is turned off, and the current through inductor Lr decreases. Phase c3: From t32 to t33, at time t32, switch SR1 is turned on, and switches S1, S2, SR2, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD2 is turned on. Phase c4: During the time period from t33 to t34, at time t33, switch S1 is turned off, switch S2 is turned on, switches BS1 and BS2 are turned on, switches SR1 and SR2 are turned off, and the current through inductor Lr increases. Phase c5: From t34 to t35, at time t35, switch S2 is turned on, switch S1 is turned off, switches BS1 and BS2 are turned off, switch SR2 is turned on, switch SR1 is turned off, and the current through inductor Lr decreases. Phase c6: From t35 to t36, at time t35, switch SR2 is turned on, and switches S1, S2, SR1, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD1 is turned on. At time t36, phase c1 is repeated. Attached Figure Description

[0014] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Figure 1 This is a schematic diagram of the structure of a wide input / output range soft-switching DC-DC converter according to the present invention; Figure 2 The waveforms of the current iLr of inductor Lr and the voltage Vb at point B are shown in the operating mode of the wide input / output range soft-switching DC-DC converter of the present invention. Figure 3 This invention relates to a current loop for a wide input / output range soft-switching DC-DC converter operating mode. Figure 1 ; Figure 4This invention relates to a current loop for a wide input / output range soft-switching DC-DC converter operating mode. Figure 2 Figure 5 This invention relates to a current loop for a wide input / output range soft-switching DC-DC converter operating mode. Figure 3 Figure 6 This invention relates to a current loop for a wide input / output range soft-switching DC-DC converter operating mode. Figure 4 Figure 7 The waveforms of the current iLr of inductor Lr and the voltage Vb at point B for a wide input / output range soft-switching DC-DC converter in operating mode 2 of the present invention are shown. Figure 8 This is a current loop diagram for the second stage b2 of the operating mode of a wide input / output range soft-switching DC-DC converter according to the present invention. Figure 9 The waveforms of the current iLr of the three inductors Lr and the voltage Vb at point B are shown in the working mode of the wide input / output range soft-switching DC-DC converter of the present invention. Figure 10 This is a current loop diagram for the three-stage c1 of the operating mode of a wide input / output range soft-switching DC-DC converter according to the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” and “described” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the described features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0017] The present invention will now be described in detail with reference to the accompanying drawings.

[0018] Example 1 like Figure 1 As shown.

[0019] This wide input / output range DC-DC converter comprises an input circuit, a transformer, and an output circuit, including a first half-bridge MOSFET S1, a second half-bridge MOSFET S2, a first common-open MOSFET BS1, a second common-open MOSFET BS2, a first synchronous rectifier MOSFET SR1, a second synchronous rectifier MOSFET SR2, a first resonant capacitor Cr1, a second resonant capacitor Cr2, a first bus capacitor C1, a second bus capacitor C2, an inductor Lr, a transformer T, a first electrolytic capacitor CD1, a second electrolytic capacitor CD2, and body diodes VD1 to VD6.

[0020] The first half-bridge MOSFET S1, the second half-bridge MOSFET S2, the first bus capacitor C1, and the second bus capacitor C2 form a half-bridge circuit. The first half-bridge MOSFET S1 and the second half-bridge MOSFET S2 form one bridge arm, and the first bus capacitor C1 and the second bus capacitor C2 form the other bridge arm. The source (S) terminal of the first half-bridge MOSFET S1 and the drain (D) terminal of the second half-bridge MOSFET S2 are connected together. The drain terminal of the first half-bridge MOSFET S1 is connected to the positive terminal of the input power supply, and the source terminal of the second half-bridge MOSFET S2 is connected to the negative terminal of the input power supply. The first electrolytic capacitor CD1 is connected in parallel with this half-bridge circuit.

[0021] The first half-bridge MOSFET S1 is connected in parallel with a first resonant capacitor Cr1. The anode of the body diode VD1 is connected to the source (S) terminal of the first half-bridge MOSFET S1, and the cathode of the body diode VD1 is connected to the drain (D) terminal of the first half-bridge MOSFET S1. The second half-bridge MOSFET S2 is connected in parallel with a second resonant capacitor Cr2. The anode of the body diode VD2 is connected to the source (S) terminal of the second half-bridge MOSFET S2, and the cathode of the body diode VD2 is connected to the drain (D) terminal of the second half-bridge MOSFET S2.

[0022] One end of the inductor Lr is connected to the midpoint of the bridge arm formed by the first half-bridge MOSFET S1 and the second half-bridge MOSFET S2, and the other end of the inductor Lr is connected to one end of the primary winding of the transformer T; the other end of the primary winding of the transformer T is connected to the midpoint of the other bridge arm formed by the first bus capacitor C1 and the second bus capacitor C2.

[0023] The secondary winding of the transformer T is a winding with a center tap.

[0024] The drain of the first common-open MOSFET BS1 is connected to the first terminal of the secondary side of transformer T. This first terminal and the connection terminal of the primary winding of transformer T to inductor Lr are of the same name. The source (S) terminal of the first common-open MOSFET BS1 is connected to the source (S) terminal of the second common-open MOSFET BS2. The drain (D) terminal of the second common-open MOSFET BS2 is connected to the center tap of the secondary side of transformer T. This center tap of the secondary side of transformer T and the connection terminal of the primary winding of transformer T to inductor Lr are of the same name. The body diode VD5 is connected in parallel with the first common-open MOSFET BS1. The cathode of the body diode VD5 is connected to the drain (D) terminal of the first common-open MOSFET BS1, and the anode of the body diode VD5 is connected to the source (S) terminal of the first common-open MOSFET BS1. The body diode VD6 is connected in parallel with the second common-open MOSFET BS2. The cathode of the body diode VD6 is connected to the drain (D) terminal of the second common-open MOSFET BS2, and the anode of the body diode VD6 is connected to the source (S) terminal of the second common-open MOSFET BS2.

[0025] The drain (D) of the first synchronous rectifier MOSFET SR1 is connected to the second terminal of the secondary winding of transformer T. This second terminal and the connection terminal of the primary winding of transformer T with inductor Lr are opposite terminals. The source (S) of the first synchronous rectifier MOSFET SR1 is connected to the negative output terminal. The drain (D) of the second synchronous rectifier MOSFET SR2 is connected to the first terminal of the secondary winding of transformer T. This first terminal and the connection terminal of the primary winding of transformer T with inductor Lr are the same terminal. The source (S) of the second synchronous rectifier MOSFET SR2 is connected to the negative output terminal. The body diode VD3 is connected in parallel with the first synchronous rectifier MOSFET SR1. The cathode of the body diode VD3 is connected to the drain (D) of the first synchronous rectifier MOSFET SR1, and the anode of the body diode VD3 is connected to the source (S) of the first synchronous rectifier MOSFET SR1. The body diode VD4 is connected in parallel with the second synchronous rectifier MOSFET SR2. The cathode of the body diode VD4 is connected to the drain (D) of the second synchronous rectifier MOSFET SR2, and the anode of the body diode VD4 is connected to the source (S) of the second synchronous rectifier MOSFET SR2.

[0026] The positive terminal of the second electrolytic capacitor CD2 is connected to the positive terminal of the output and to the center tap of the secondary side of the transformer T. The negative terminal of the second electrolytic capacitor CD2 is connected to the negative terminal of the output and forms a common terminal with the source terminal of the first synchronous rectifier MOSFET SR1 and the source terminal of the second synchronous rectifier MOSFET SR2.

[0027] The output circuit uses a synchronous rectifier diode, which is connected in parallel with the second electrolytic capacitor CD2. There is no series inductor, so no voltage spikes are generated during the switching period, effectively reducing voltage stress.

[0028] Example 2 like Figures 2 to 6 As shown.

[0029] A control method for a wide input / output range soft-switching DC-DC converter, wherein MOSFETs S1, S2, BS1, BS2, SR1, and SR2 are all MOSFETs with identical parameters. When the converter's operating frequency exceeds the maximum operating frequency of the MOSFETs designed to limit switching losses, the wide input / output range DC-DC converter is in operating mode one. MOSFETs S1, S2, BS1, BS2, SR1, and SR2 are periodically turned on and off under the control of the control circuit, and the voltage at point B, the connection point between inductor Lr and the midpoint of the half-bridge circuit arm, changes periodically. The positive half-cycle begins at time t10, and the wide input / output range DC-DC converter operates in the following stages: Phase a1: From t10 to t11, at time t10, switches S1 and SR1 are turned on, while switches S2, SR2, BS1, and BS2 are turned off. In the primary winding circuit of transformer T, current flows from the positive terminal of the input power supply, through MOSFET S1, inductor Lr, the primary winding of transformer T, and capacitor C2, forming a loop. The current through inductor Lr increases, and capacitor C2 charges. The current in inductor Lr and the voltage at point B enter the positive half-cycle. Due to the increased current in the primary winding of transformer T, a current is induced in the secondary winding of transformer T. This current flows from one end of the secondary winding of transformer T, through switch SR1, the load, and the center tap of transformer T, forming a loop.

[0030] The conduction time Ton1 is determined based on the output of the PI closed-loop control of the control circuit, t11=t10+Ton1.

[0031] Phase a2: From t11 to t12, at time t11, switch SR1 is turned on, and switches S1, S2, SR2, BS1, and BS2 are turned off, reducing the current through inductor Lr. After switch S1 is turned off, the power supply to the primary side of transformer T is cut off. Since inductor current cannot change abruptly, the current flowing through inductor Lr continuously decreases. The current flowing through inductor Lr causes VD2 to conduct. A current is induced in the secondary winding of transformer T, which still forms a loop from one end of the secondary winding of transformer T, switch SR1, the load, and the center tap of transformer T.

[0032] The time it takes for the current in inductor Lr to recover from its highest value to 0 is Toff1, and t12 = t11 + Toff1.

[0033] Phase a3: From t12 to t13, at time t12, switches S1 and S2 are off, switches BS1 and BS2 are on, and switches SR1 and SR2 are off. At this time, a short circuit is formed between one end of the secondary winding of transformer T and the intermediate tap, and the circuit formed by switches BS1 and BS2. On the primary side of transformer T, the circuit formed by capacitors Cr1, Cr2, C1, C2, inductor Lr, and the primary winding of transformer T resonates, and the voltage at point B and the current in inductor Lr change periodically.

[0034] Phase a4: During the time interval t13 to t14, at time t13, during the resonance process of inductor Lr and capacitors Cr1 and Cr2, when the voltage at point B is 0, switch S1 is turned off and switch S2 is turned on. Since the voltage of switch S2 is the same as the voltage at point B, it turns on when the voltage at point B is 0, thus achieving ZVS (Zero-Voltage Switching).

[0035] With switches BS1, BS2, and SR1 off, and switch SR2 on, the current in the primary winding of transformer T flows through the positive terminal of the input power supply, capacitor C1, the primary winding of transformer T, inductor Lr, and MOSFET S2, forming a loop. The current through inductor Lr increases, flowing from the primary winding of transformer T towards point B. The current in inductor Lr and the voltage at point B enter the negative half-cycle, charging capacitor C1. Due to the increased current in the primary winding of transformer T, a current is induced in the secondary winding of transformer T. This current flows through one end of the secondary winding of transformer T, switch SR2, the load, and the center tap of transformer T, forming a loop.

[0036] The conduction time Ton1 is determined based on the output of the PI closed-loop control of the control circuit, t14 = t13 + Ton1.

[0037] Phase a5: From t14 to t15, at time t14, switch SR2 is turned on, and switches S1, S2, SR1, BS1, and BS2 are turned off, reducing the current through inductor Lr. After switch S2 is turned off, the power supply to the primary side of transformer T is cut off. Since inductor current cannot change abruptly, the current flowing through inductor Lr continuously decreases. The current flowing through inductor Lr causes VD1 to conduct. A current is induced in the secondary winding of transformer T, which still forms a loop from one end of the secondary winding of transformer T, switch SR2, the load, and the center tap of transformer T.

[0038] The time it takes for the current in inductor Lr to recover from its highest value to 0 is Toff1, and t15 = t14 + Toff1.

[0039] Phase a6: From t15 to t16, at time t15, switches S1 and S2 are off, switches BS1 and BS2 are on, and switches SR1 and SR2 are off. At this time, a short circuit is formed between one end of the secondary winding of transformer T and the intermediate tap, and the loop formed by switches BS1 and BS2. On the primary side of transformer T, the loop formed by capacitors Cr1, Cr2, C1, C2, inductor Lr, and the primary winding of the transformer resonates, and the voltage at point B and the current in inductor Lr change periodically. During the resonance process, when the voltage at point B is equal to the input voltage Vin, switch S1 is on. Since the voltage of switch S1 is the difference between the voltage at point B and the voltage of the power supply, it is on when the voltage at point B is equal to the voltage of the power supply, and the voltage value of switch S1 is 0. Switch S1 achieves ZVS (Zero-Voltage Switching).

[0040] Example 3 like Figure 7 and Figure 8 As shown.

[0041] A control method for a wide input / output range soft-switching DC-DC converter, where MOSFETs S1, S2, BS1, BS2, SR1, and SR2 are all MOSFETs with identical parameters. When the converter's operating frequency is lower than the maximum operating frequency of the MOSFETs designed to limit switching losses, but the transformer's volt-second product is lower than a set value, the wide input / output range DC-DC converter operates in operating mode two. The transformer's volt-second product is the product of the transformer winding voltage and half a working cycle time. Its set value, i.e., the maximum tolerable value, is nΔBAe, where n is the number of turns in the transformer's secondary winding T, ΔB is the maximum change in magnetic flux density determined based on transformer losses, and Ae is the effective cross-sectional area of ​​the transformer. MOSFETs S1, S2, BS1, BS2, SR1, and SR2 are periodically turned on and off under the control of the control circuit, and the voltage at point B, the connection point between inductor Lr and the midpoint of the half-bridge circuit arm, changes periodically. The positive half-cycle begins at time t20, and the wide input / output range DC-DC converter operates in the following stages: Phase b1: From t20 to t21, at time t20, switches S1 and SR1 are turned on, while switches S2, SR2, BS1, and BS2 are turned off. In the primary winding circuit of transformer T, current flows through the positive terminal of the input power supply, MOSFET S1, inductor Lr, the primary winding of transformer T, and capacitor C2, forming a loop. The current through inductor Lr increases, and capacitor C2 charges. The current in inductor Lr and the voltage at point B enter the positive half-cycle. Due to the increased current in the primary winding of transformer T, a current is induced in the secondary winding of transformer T. This current flows through one end of the secondary winding of transformer T, switch SR1, the load, and the center tap of transformer T, forming a loop.

[0042] The conduction time Ton2 is determined based on the output of the PI closed-loop control of the control circuit, t21=t20+Ton2.

[0043] Phase b2: From t21 to t22, at time t21, switch SR1 is turned on, and switches S1, S2, SR2, BS1, and BS2 are turned off. After switch S1 is turned off, the power supply to the primary side of transformer T is cut off. Since the inductor current cannot change abruptly, the current flowing through inductor Lr continuously decreases. A current is induced in the secondary winding of transformer T, which still forms a loop from one end of the secondary winding of transformer T, switch SR1, the load, and the center tap of transformer T.

[0044] Capacitor Cr2 discharges through inductor Lr. Since the capacitance of capacitor C2 is greater than that of Cr2, after all the charge on capacitor Cr2 is released, the current continues to flow from inductor Lr to capacitor C2. Because the capacitor voltage cannot change abruptly, and switch S2 is connected in parallel with capacitor Cr2, the voltage across switch S2 is clamped to 0. As the current continues to flow from inductor Lr to capacitor C2, the body diode VD2 conducts, forming a loop until the current through inductor Lr recovers from its highest value to 0. When switch S2 is open, the voltage across switch S2 remains clamped to 0, thus switch S2 achieves zero-voltage switching (ZVS).

[0045] The time it takes for the current in inductor Lr to recover from its highest value to 0 is Toff2, where t22 = t21 + Toff2.

[0046] Phase b3: From t22 to t23, at time t22, switches S2 and SR2 are turned on, while switches S1, SR1, BS1, and BS2 are turned off. In the primary winding circuit of transformer T, current flows from the positive terminal of the input power supply, through capacitor C1, the primary winding of transformer T, inductor Lr, and MOSFET S2, forming a loop. The current through inductor Lr increases, flowing from the primary winding of transformer T towards point B. The current in inductor Lr and the voltage at point B enter the negative half-cycle, and capacitor C1 charges. Due to the increased current in the primary winding of transformer T, a current is induced in the secondary winding of transformer T. This current flows from one end of the secondary winding of transformer T, through switch SR2, the load, and the center tap of transformer T, forming a loop.

[0047] Since the voltage of switch S2 is the same as the voltage at point B, when switch S2 is open, the voltage of switch S2 is still clamped to 0, so switch S2 achieves ZVS.

[0048] The conduction time Ton2 is determined based on the output of the PI closed-loop control of the control circuit, t23 = t22 + Ton2.

[0049] Phase b4: During the time period from t23 to t24, at time t23, switch SR2 is turned on, and switches S1, S2, SR1, BS1 and BS2 are turned off.

[0050] After switch S2 is closed, the power supply to the primary side of transformer T is cut off. Since the inductor current cannot change abruptly, the current flowing through inductor Lr continuously decreases. A current is induced in the secondary winding of transformer T, and this current still forms a loop from one end of the secondary winding of transformer T, switch SR2, the load, and the middle tap of transformer T.

[0051] Capacitor Cr1 discharges through inductor Lr. Since the capacitance of capacitor C1 is greater than that of Cr1, after all the charge on capacitor Cr1 is released, the current continues to flow from inductor Lr to capacitor C1. Because the capacitor voltage cannot change abruptly, and switch S1 and capacitor Cr1 are connected in parallel, the voltage across switch S1 is clamped to 0. As the current continues to flow from inductor Lr to capacitor C1, body diode VD1 conducts, forming a loop until the current through inductor Lr recovers from its highest value to 0. At time t24, phase b1 repeats. When switch S1 is open, the voltage across switch S1 remains clamped to 0, therefore switch S1 achieves ZVS (Zero-Voltage Switching).

[0052] The time it takes for the current in inductor Lr to recover from its highest value to 0 is Toff2, t24 = t23 + Toff2.

[0053] Example 4

[0054] like Figure 9 and Figure 10 As shown.

[0055] A control method for a wide input / output range soft-switching DC-DC converter, where MOSFETs S1, S2, BS1, BS2, SR1, and SR2 are all MOSFETs with identical parameters. When the converter's operating frequency is lower than the maximum operating frequency of the MOSFETs, and the volt-second product of the transformer exceeds a set value, the wide input / output range DC-DC converter is in operating mode three. MOSFETs S1, S2, BS1, BS2, SR1, and SR2 are periodically turned on and off under the control of the control circuit, and the voltage at point B, the connection point between the inductor Lr and the midpoint of the half-bridge circuit arm, changes periodically. The positive half-cycle begins at time t30, and the wide input / output range DC-DC converter operates in the following stages: Phase c1: The time period from t30 to t31. At time t30, switch S1 is turned on, switch S2 is turned off, switches BS1 and BS2 are turned on, and switches SR1 and SR2 are turned off.

[0056] In the primary winding circuit of transformer T, the current flows through the positive terminal of the input power supply, MOSFET S1, inductor Lr, the primary winding of transformer T, and capacitor C2, forming a loop. The current through inductor Lr increases, and capacitor C2 charges. The current in inductor Lr and the voltage at point B enter the positive half-cycle. Due to the increased current in the primary winding of transformer T, a current is induced in the secondary winding of transformer T. This current flows through one end of the secondary winding of transformer T, switch BS1, switch BS2, and the center tap of transformer T, forming a loop. Because of the short circuit on the secondary side of the transformer, the current flowing through inductor Lr is very large, and a large amount of energy accumulates in inductor Lr. At this time, transformer T is in a step-up operating state.

[0057] The conduction time Td of switches S1, BS1, and BS2 is determined according to the output of the PI closed-loop control of the control circuit, t31=t30+Td.

[0058] Phase c2: From t31 to t32, at time t31, switch S1 is on, switch S2 is off, switches BS1 and BS2 are off, switch SR1 is on, and switch SR2 is off. A current is induced in the secondary winding of transformer T, forming a loop from one end of the secondary winding, switch SR1, the load, and the center tap of transformer T. Because the current in the secondary winding of transformer T decreases, the current in the primary winding also decreases, resulting in a decrease in the current through inductor Lr. Capacitor Cr2 discharges through inductor Lr. Since the capacitance of capacitor C2 is greater than that of Cr2, after all the charge on capacitor Cr2 is released, the current continues to flow from inductor Lr to capacitor C2. Because capacitor voltage cannot change abruptly, and switch S2 and capacitor Cr2 are connected in parallel, the voltage across switch S2 is clamped to 0.

[0059] The conduction time Ton3 of switch S1 is determined according to the output of the PI closed-loop control of the control circuit, t32=t31+Ton3.

[0060] Phase c3: From t32 to t33, at time t32, switch SR1 is turned on, and switches S1, S2, SR2, BS1, and BS2 are turned off. After switch S1 is turned off, the power supply to the primary side of transformer T is cut off. Since the inductor current cannot change abruptly, the current flowing through inductor Lr decreases rapidly until it reaches zero. As the current continues to flow from inductor Lr to capacitor C2, body diode VD2 conducts, forming a loop. A current is induced in the secondary winding of transformer T, and this current still forms a loop from one end of the secondary winding of transformer T, switch SR1, the load, and the center tap of transformer T. The time for the current in inductor Lr to decrease rapidly from the beginning to return to zero is Toff3, and t33 = t32 + Toff3.

[0061] Phase c4: During the time period from t33 to t34, at time t33, switch S1 is off, switch S2 is on, switches BS1 and BS2 are on, and switches SR1 and SR2 are off.

[0062] In the primary circuit of transformer T, the current flows through the positive terminal of the input power supply, capacitor C1, the primary winding of transformer T, inductor Lr, and MOSFET S2, forming a loop. The current through inductor Lr increases, charging capacitor C1. The current in inductor Lr and the voltage at point B enter the negative half-cycle. Due to the increased current in the primary winding of transformer T, a current is induced in the secondary winding, forming a loop from one end of the secondary winding, switch BS1, switch BS2, and the center tap of transformer T. Because of the short circuit on the secondary side of the transformer, the current flowing through inductor Lr is very large, and inductor Lr accumulates a large amount of energy. At this time, transformer T is in a boost operation state. When switch S2 is open, the voltage at switch S2 remains clamped to 0, so switch S2 achieves zero-voltage switching (ZVS).

[0063] The conduction time Td of switches S2, BS1, and BS2 is determined according to the output of the PI closed-loop control of the control circuit, t34 = t33 + Td.

[0064] Phase c5: From t34 to t35, at time t35, switch S2 is on, switch S1 is off, switches BS1 and BS2 are off, switch SR2 is on, and switch SR1 is off. A current is induced in the secondary winding of transformer T, forming a loop from one end of the secondary winding, switch SR2, the load, and the center tap of transformer T. Because the current in the secondary winding of transformer T decreases, the current in the primary winding also decreases, resulting in a decrease in the current through inductor Lr. Capacitor Cr1 discharges through inductor Lr. Since the capacitance of capacitor C1 is greater than that of Cr1, after all the charge on capacitor Cr1 is released, the current continues to flow from inductor Lr to capacitor C1. Because capacitor voltage cannot change abruptly, and switch S1 and capacitor Cr1 are connected in parallel, the voltage across switch S1 is clamped to 0.

[0065] The conduction time Ton3 of switch S2 is determined according to the output of the PI closed-loop control of the control circuit, t35=t34+Ton3.

[0066] Phase c6: From t35 to t36, at time t35, switch SR2 is turned on, and switches S1, S2, SR1, BS1, and BS2 are turned off. After switch S2 is turned off, the power supply to the primary side of transformer T is cut off. Since the inductor current cannot change abruptly, the current flowing through inductor Lr decreases rapidly until it reaches zero. As the current continues to flow from inductor Lr to capacitor C1, body diode VD1 conducts, forming a loop. A current is induced in the secondary winding of transformer T, which still forms a loop from one end of the secondary winding of transformer T, switch SR2, the load, and the center tap of transformer T. At time t36, phase c1 is repeated. When switch S1 is turned on, the voltage of switch S1 is still clamped to 0, so switch S1 achieves ZVS (Zero Voltage Switching). The time for the current in inductor Lr to decrease rapidly from the beginning to return to zero is Toff3, and t36 = t35 + Toff3.

[0067] In summary, this invention proposes a wide input / output range soft-switching DC-DC converter and control method. The output-side power devices are connected in parallel with the output capacitor, offering the advantage of low voltage stress. Multiple operating modes can be switched according to different loads, achieving ZVS soft switching over a wide input / output range and under wide load conditions. Different operating modes have different effects on the converter's gain. In operating mode three, due to the energy storage effect of the primary circuit inductance, the converter can operate in a boost state, increasing the gain. Therefore, this wide input / output range soft-switching DC-DC converter can effectively improve converter gain, power rating, and power density while limiting voltage stress on the output-side power devices.

Claims

1. A wide input / output range soft-switching DC-DC converter, characterized in that, It includes an input circuit, a transformer, and an output circuit; the input circuit is a half-bridge circuit composed of switch S1, switch S2, capacitor C1, and capacitor C2; the primary winding of the transformer is connected to the midpoint of the bridge arm of the half-bridge circuit via inductor Lr. Switches BS1 and BS2 are connected in series between the first end of the transformer secondary winding and the middle end of the transformer secondary winding; switches SR1 and SR2 are connected in series between the first end of the transformer secondary winding and the second end of the transformer secondary winding; a load and a capacitor CD2 are connected in parallel between the second end of the transformer secondary winding and the middle end of the transformer secondary winding. The wide input / output range DC-DC converter determines its operating mode based on the highest operating frequencies of switches S1 and S2, and the volt-second product of the transformer.

2. The wide input / output range soft-switching DC-DC converter according to claim 1, characterized in that, A capacitor CD1 is connected in parallel across the two ends of the input circuit.

3. A wide input / output range soft-switching DC-DC converter according to claim 1, characterized in that, A capacitor Cr1 is connected in parallel across the two ends of switch S1, and a capacitor Cr2 is connected in parallel across the two ends of switch S2.

4. A wide input / output range soft-switching DC-DC converter according to claim 3, characterized in that, The capacitance of capacitors Cr1 and Cr2 is less than the capacitance of capacitors C1 and C2.

5. A wide input / output range soft-switching DC-DC converter according to claim 1, characterized in that, The switches S1, S2, SR1, SR2, BS1, and BS2 are all MOSFETs; each of the switches S1, S2, SR1, SR2, BS1, and BS2 contains a body diode VD1 to VD6.

6. A wide input / output range soft-switching DC-DC converter according to claim 1, characterized in that, The S pole of switch BS1 is connected to the S pole of switch BS2; the D pole of switch BS1 is connected to the first end of the secondary winding of the transformer; the D pole of switch BS2 is connected to the middle end of the secondary winding of the transformer. The S pole of switch SR1 is connected to the S pole of switch SR2; the D pole of switch SR1 is connected to the second end of the secondary winding of the transformer; the D pole of switch SR2 is connected to the first end of the secondary winding of the transformer.

7. A wide input / output range soft-switching DC-DC converter according to claim 1, characterized in that, The wide input / output range DC-DC converter has three operating modes: operating mode one when the operating frequency exceeds the maximum operating frequency of switches S1 and S2; operating mode two when the operating frequency is lower than the maximum operating frequency of switches S1 and S2 and the volt-second product of the transformer is lower than the set value; and operating mode three when the operating frequency is lower than the maximum operating frequency of switches S1 and S2 and the volt-second product of the transformer exceeds the set value.

8. A control method for a wide input / output range soft-switching DC-DC converter as described in any one of claims 5 to 7, characterized in that, When the operating frequency exceeds the maximum operating frequency of switches S1 and S2, the following stages are included: Phase a1: The time period from t10 to t11. At time t10, switches S1 and SR1 are turned on, while switches S2, SR2, BS1, and BS2 are turned off, and the current through inductor Lr increases. Phase a2: From t11 to t12, at time t11, switch SR1 is turned on, and switches S1, S2, SR2, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD2 is turned on. Phase a3: From t12 to t13, at time t12, switches S1 and S2 are off, switches BS1 and BS2 are on, switches SR1 and SR2 are off, and inductor Lr and capacitors Cr1 and Cr2 resonate. Stage a4: From t13 to t14, at time t13, during the resonance process of inductor Lr and capacitors Cr1 and Cr2, when the voltage at the connection point between inductor Lr and the midpoint of the bridge arm is 0, switch S1 is turned off, switch S2 is turned on, switches BS1, BS2 and SR1 are turned off, switch SR2 is turned on, and the current through inductor Lr increases. Phase a5: During the time period from t14 to t15, at time t14, switch SR2 is turned on, and switches S1, S2, SR1, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD1 is turned on. Phase a6: During the time period from t15 to t16, at time t15, switches S1 and S2 are turned off, switches BS1 and BS2 are turned on, switches SR1 and SR2 are turned off, and inductor Lr and capacitors Cr1 and Cr2 resonate. When the voltage at the connection point between inductor Lr and the midpoint of the bridge arm is the input voltage, phase a1 is repeated.

9. A control method for a wide input / output range soft-switching DC-DC converter as described in any one of claims 5 to 7, characterized in that, When the operating frequency is lower than the maximum operating frequency of switches S1 and S2, and the volt-second product of the transformer is lower than the set value, the following stages are included: Phase b1: The time period from t20 to t21. At time t20, switches S1 and SR1 are turned on, while switches S2, SR2, BS1, and BS2 are turned off, and the current through inductor Lr increases. Phase b2: During the time period from t21 to t22, at time t21, switch SR1 is turned on, and switches S1, S2, SR2, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD2 is turned on. Phase b3: During the time period from t22 to t23, at time t22, switches S2 and SR2 are turned on, while switches S1, SR1, BS1, and BS2 are turned off, and the current through inductor Lr increases. Phase b4: From t23 to t24, at time t23, switch SR2 is turned on, and switches S1, S2, SR1, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD1 is turned on. At time t24, phase b1 is repeated.

10. A control method for a wide input / output range soft-switching DC-DC converter as described in any one of claims 5 to 7, characterized in that, When the operating frequency is lower than the maximum operating frequency of switches S1 and S2, and the volt-second product of the transformer exceeds the set value, the following steps are included: Phase c1: The time period from t30 to t31. At time t30, switch S1 is turned on, switch S2 is turned off, switches BS1 and BS2 are turned on, and switches SR1 and SR2 are turned off. The current through inductor Lr increases. Phase c2: During the time period from t31 to t32, at time t31, switch S1 is turned on, switch S2 is turned off, switches BS1 and BS2 are turned off, switch SR1 is turned on, switch SR2 is turned off, and the current through inductor Lr decreases. Phase c3: From t32 to t33, at time t32, switch SR1 is turned on, and switches S1, S2, SR2, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD2 is turned on. Phase c4: During the time period from t33 to t34, at time t33, switch S1 is turned off, switch S2 is turned on, switches BS1 and BS2 are turned on, switches SR1 and SR2 are turned off, and the current through inductor Lr increases. Phase c5: From t34 to t35, at time t35, switch S2 is turned on, switch S1 is turned off, switches BS1 and BS2 are turned off, switch SR2 is turned on, switch SR1 is turned off, and the current through inductor Lr decreases. Phase c6: From t35 to t36, at time t35, switch SR2 is turned on, and switches S1, S2, SR1, BS1 and BS2 are turned off. The current through inductor Lr decreases, and VD1 is turned on. At time t36, phase c1 is repeated.

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