Bidirectional dc-dc converter and control method thereof

Abstract

This disclosure relates to a bidirectional DC-DC converter configured as a current-isolated circuit, comprising on the secondary side: a freewheeling switch, a rectifier switch, a first active clamping switch, a first clamping capacitor, a second active clamping switch, and a second clamping capacitor. The series circuit of the first active clamping switch and the first clamping capacitor is connected in parallel with the freewheeling switch, and the conduction direction of the first active clamping switch is opposite to that of the freewheeling switch. The series circuit of the second active clamping switch and the second clamping capacitor is connected in parallel with the rectifier switch, and the conduction direction of the second active clamping switch is opposite to that of the rectifier switch. Furthermore, this disclosure also relates to a control method for the bidirectional DC-DC converter.

Description

Technical Field

[0001] This disclosure relates to a bidirectional DC-DC converter and a control method for the bidirectional DC-DC converter. Background Technology

[0002] When using a vehicle's high-voltage battery to power other components, it is necessary to convert the high voltage of the high-voltage battery to a low voltage, a process known as forward operation. Existing technologies, such as buck circuits or boost-buck circuits (DC chopper circuits) and active clamp forward converter circuits, as well as active clamp flyback converter circuits, can all achieve forward operation.

[0003] However, in some cases, reverse operation is required. For example, before charging a vehicle's high-voltage battery, it is preferable to precharge the capacitors connected to the high-voltage battery to avoid large inrush currents caused by a large voltage difference between the high-voltage battery voltage and the charging voltage, thus preventing damage to related switching devices and / or capacitors. However, existing DC-DC converter circuits cannot achieve reverse operation. Summary of the Invention

[0004] This disclosure provides a bidirectional DC-DC converter and a control method for the bidirectional DC-DC converter, which enables bidirectional DC voltage variation. The bidirectional DC-DC converter according to this disclosure is an improvement over the prior art, featuring a simple structure and lower design and manufacturing costs.

[0005] This disclosure provides a bidirectional DC-DC converter configured as a current-isolated circuit, which converts a first DC voltage to a second DC voltage in a first operating mode and converts the second DC voltage to the first DC voltage in a second operating mode. The bidirectional DC-DC converter includes, on its secondary side, a freewheeling switch and a rectifier switch; and further includes a first active clamping switch, a first clamping capacitor, a second active clamping switch, and a second clamping capacitor. The series circuit of the first active clamping switch and the first clamping capacitor is connected in parallel with the freewheeling switch, and the conduction direction of the first active clamping switch is opposite to that of the freewheeling switch. The series circuit of the second active clamping switch and the second clamping capacitor is connected in parallel with the rectifier switch, and the conduction direction of the second active clamping switch is opposite to that of the rectifier switch.

[0006] In an embodiment according to this disclosure, the bidirectional DC-DC converter includes, on the primary side: a first switch, a second switch, a first capacitor, and a primary winding, wherein the first switch, the second switch, and the first capacitor form a series circuit, the two ends of the series circuit form a first DC voltage terminal, and the primary winding is connected in parallel to the series circuit formed by the second switch and the first capacitor.

[0007] In an embodiment according to this disclosure, the bidirectional DC-DC converter is configured as an active clamp forward converter circuit, the bidirectional DC-DC converter including on the secondary side: a secondary winding, a second capacitor and a first inductor, wherein the series circuit consisting of the secondary winding and the freewheeling switch is connected in parallel with the rectifier switch, the parallel circuit is connected to a second DC voltage terminal via the first inductor, and the second capacitor is connected in parallel to the second DC voltage terminal.

[0008] In an embodiment according to this disclosure, the bidirectional DC-DC converter is configured as an active clamp flyback converter circuit, the bidirectional DC-DC converter including on the secondary side: a second capacitor, a secondary winding and a tertiary winding, wherein a series circuit consisting of the secondary winding and the freewheeling switch is connected to a second DC voltage terminal, a series circuit consisting of the tertiary winding and the rectifier switch is connected to the second DC voltage terminal, and the second capacitor is connected in parallel to the second DC voltage terminal.

[0009] In embodiments according to this disclosure, one or more of the first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamping switch, and the second active clamping switch are configured as electronic switches, the electronic switches having diodes connected in antiparallel with them.

[0010] In embodiments according to this disclosure, one or more of the first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamp switch, and the second active clamp switch are configured as MOSFETs.

[0011] This disclosure also provides a control method for controlling a bidirectional DC-DC converter according to the above embodiments of this disclosure. The control method includes: in a first operating mode, controlling the first switch and the second switch to conduct alternately, such that the DC-DC converter converts the first DC voltage into the second DC voltage; in a second operating mode, controlling the first switch and the second switch to conduct alternately, the freewheeling switch and the first active clamping switch to conduct alternately, and the rectifier switch and the second active clamping switch to conduct alternately, such that the DC-DC converter converts the second DC voltage into the first DC voltage; wherein the second switch, the freewheeling switch, and the second active clamping switch are switched on and off synchronously, and the first switch, the rectifier switch, and the first active clamping switch are switched on and off synchronously.

[0012] In embodiments according to this disclosure, the first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamping switch, and the second active clamping switch have the same duty cycle and are less than 0.5.

[0013] In embodiments according to this disclosure, the first duty cycle of the second switch, the freewheeling switch, and the second active clamping switch is the same and less than 0.5, the second duty cycle of the first switch, the rectifier switch, and the first active clamping switch is the same and greater than 0.5, and the sum of the first duty cycle and the second duty cycle is less than or equal to 1.

[0014] In embodiments according to this disclosure, the on / off states of the first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamp switch, and the second active clamp switch are controlled by PWM.

[0015] This disclosure also provides an on-board charging device, which includes a bidirectional DC-DC converter according to the above embodiments of this disclosure.

[0016] This disclosure also provides an electric drive system including an on-board charging device according to the above embodiments of this disclosure.

[0017] This disclosure also provides a vehicle that includes an electric drive system according to the above embodiments of this disclosure. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some exemplary embodiments of this disclosure. For those skilled in the art, other embodiments can be obtained based on these embodiments without creative effort.

[0019] Figure 1 A schematic block diagram of a bidirectional DC-DC converter according to the present disclosure is shown.

[0020] Figure 2 A schematic circuit diagram of an active clamp forward converter circuit according to the prior art is shown.

[0021] Figure 3 A schematic circuit diagram of an active clamp flyback converter circuit according to the prior art is shown.

[0022] Figure 4 A schematic circuit diagram of an active clamp forward converter circuit according to an embodiment of the present disclosure is shown.

[0023] Figure 5 A schematic circuit diagram of an active clamp flyback converter circuit according to an embodiment of the present disclosure is shown, and

[0024] Figure 6 and Figure 7A schematic diagram of a switch control signal for a control method for a bidirectional DC-DC converter according to an embodiment of the present disclosure is shown. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this disclosure more apparent, exemplary embodiments according to this disclosure will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this disclosure, and not all embodiments of this disclosure. It should be understood that this disclosure is not limited to the exemplary embodiments described herein.

[0026] In this specification and accompanying drawings, substantially the same or similar steps and elements are indicated by the same or similar reference numerals, and repeated descriptions of these steps and elements will be omitted. Furthermore, in the description of this disclosure, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance or order.

[0027] In this specification and accompanying drawings, elements are described in singular or plural forms according to embodiments. However, the singular and plural forms are suitably chosen for the presented cases merely for ease of explanation and are not intended to limit the disclosure thereto. Thus, singular forms may include plural forms, and plural forms may include singular forms, unless the context clearly indicates otherwise. In embodiments of this disclosure, unless otherwise clearly stated, "connection" does not necessarily mean "direct connection" or "direct contact," but only requires electrical connection.

[0028] When using a vehicle's high-voltage battery to power other components, it is necessary to convert the high voltage of the high-voltage battery to a low voltage, a process known as forward operation. Existing technologies, such as buck circuits or boost-buck circuits (DC chopper circuits) and active clamp forward converter circuits, as well as active clamp flyback converter circuits, can all achieve forward operation.

[0029] However, in some cases, reverse operation is also necessary. For example, before charging the high-voltage battery of a vehicle, it is preferable to precharge the capacitor connected to the high-voltage battery to avoid a large inrush current caused by a large voltage difference between the high-voltage battery voltage and the charging voltage, thus preventing damage to related switching devices and / or capacitors. This precharging can be achieved, for example, by boosting the voltage of the low-voltage battery and supplying it to the capacitor connected to the high-voltage battery. In the prior art, the boost circuit is usually designed and arranged separately from the buck circuit, which results in an overly bulky and costly overall buck-boost circuit.

[0030] This disclosure improves upon the existing buck circuit to achieve bidirectional DC-DC voltage conversion. Therefore, the bidirectional DC-DC converter according to this disclosure can operate in both the forward direction (i.e., buck operation) and the reverse direction (i.e., boost operation).

[0031] Figure 1 A schematic block diagram of a bidirectional DC-DC converter 110 according to this disclosure is shown. Furthermore, Figure 1 The document also shows a first DC power supply 120 capable of outputting a first DC voltage U1 or being charged at the first DC voltage U1, and a second DC power supply 130 capable of outputting a second DC voltage U2 or being charged at the second DC voltage U2. It is assumed here that the first DC voltage U1 is greater than the second DC voltage U2. According to this disclosure, the bidirectional DC-DC converter 110 can step down the first DC voltage U1 to the second DC voltage U2 and output it to the second DC power supply 130 in a first operating mode, and step up the second DC voltage U2 to the first DC voltage U1 and output it to the first DC power supply 120 in a second operating mode.

[0032] In embodiments according to this disclosure, the bidirectional DC-DC converter 110 may be configured, for example, as an active clamp flyback converter circuit or an active clamp forward converter circuit. Figure 2 A schematic circuit diagram of an active clamp forward converter circuit 200 according to the prior art is shown. Figure 3 A schematic circuit diagram of an active clamp flyback converter circuit 300 according to the prior art is shown.

[0033] Existing active-clamp forward / flyback converter circuits or active-clamp forward converter circuits are constructed as current-isolation circuits based on transformers. The periodic switching on and off of switches in the converter circuit induces current changes and energy transfer. The desired voltage reduction operation can be achieved by adjusting the transformer turns ratio and the duty cycle of the switches. (See below for reference.) Figure 2 and Figure 3 Let's explain the first operating mode, namely the pressure reduction operation.

[0034] Both the active clamp forward converter circuit 200 and the active clamp forward-flyback converter circuit 300 have the same primary side structure. For example... Figure 2 and Figure 3 As shown, a first switch Q1, a second switch Q2, a first capacitor C1, and a primary winding P are arranged on the primary side. The first switch Q1, the second switch Q2, and the first capacitor C1 are connected in series and connected to a first DC power supply V1. The primary winding P is connected in parallel to the series circuit formed by the second switch Q2 and the first capacitor C1.

[0035] like Figure 2As shown, the existing active clamp forward converter circuit 200 has a third switch Q3 (i.e., a freewheeling switch), a fourth switch Q4 (i.e., a rectifier switch), a second capacitor C2, a secondary winding S, and a first inductor L1 on its secondary side. The series circuit formed by the secondary winding S and the third switch Q3 is connected in parallel with the fourth switch Q4, and the parallel circuit is connected to the second DC power supply V2 via the first inductor L1. The second capacitor C2 is connected to the second DC power supply V2.

[0036] like Figure 3 As shown, the existing active clamp flyback converter circuit 300 has a third switch Q3 (i.e., a freewheeling switch), a fourth switch Q4 (i.e., a rectifier switch), a second capacitor C2, a secondary winding S, and a tertiary winding T on its secondary side. The series circuit consisting of the secondary winding S and the third switch Q3 is connected to a second DC power supply V2. The series circuit consisting of the tertiary winding T and the fourth switch Q4 is also connected to the second DC power supply V2. The second capacitor C2 is connected to the second DC power supply V2.

[0037] In the active clamp forward converter circuit 200 or the active clamp forward-flyback converter circuit 300, the number of turns of the primary winding P is greater than that of the secondary winding S or the tertiary winding T. In other words, the turns ratio of the corresponding transformers is greater than 1.

[0038] In the active clamp forward converter circuit 200 or the active clamp forward-flyback converter circuit 300, during forward operation (i.e., buck conversion), the first DC power supply V1 outputs DC power. The first switch Q1 and the second switch Q2 on the primary side are alternately turned on to generate a changing current, thereby transferring energy from the primary side to the secondary side. The third switches Q3 and Q4 on the secondary side are alternately turned on to achieve rectification, thereby supplying power to the load or charging the second DC power supply V2.

[0039] The circuit consisting of the first switch Q1 and the first capacitor C1 is used to absorb the energy released by the primary winding P when the second switch Q2 is turned off, so as to minimize the peak voltage applied to the second switch Q2 and thus prevent the second switch Q2 from being damaged or broken down.

[0040] The forward operation principle of the active clamp forward converter circuit 200 is similar to that of a Buck circuit. When the third switch Q3 (freewheeling switch) is on and the fourth switch Q4 (rectifier switch) is off, the current induced in the secondary winding S charges the first inductor L1 and supplies power to the load or the second DC power supply V2. When the third switch Q3 (freewheeling switch) is off and the fourth switch Q4 (rectifier switch) is on, the fourth switch Q4 (rectifier switch) forms a circuit, and the first inductor L1 supplies power to the load or the second DC power supply V2. At the same time, the off of the third switch Q3 prevents the secondary winding S from being short-circuited.

[0041] During the forward operation of the active-clamped forward and flyback conversion circuit 300, the third switch Q3 (freewheeling switch) and the fourth switch Q4 (rectifying switch) conduct and disconnect alternately. When the third switch Q3 conducts, the secondary winding S supplies power to the load or the second DC power supply V2. When the fourth switch Q4 is turned on, the tertiary winding T supplies power to the load or the second DC power supply V2.

[0042] Through the alternating conduction between the first switch Q1 and the second switch Q2, and between the third switch Q3 and the fourth switch Q4, the voltage V of the first DC power supply V1 in is bucked down to V out and provided to the load or the second DC power supply V2, that is

[0043]

[0044] where D represents the duty cycle of the second switch Q2, and 0 < D < 1. n represents the turns ratio of the primary winding P to the secondary winding S / tertiary winding T, and n > 1.

[0045] According to the prior art, the active-clamped forward conversion circuit 200 or the active-clamped forward and flyback conversion circuit 300 cannot achieve reverse operation, that is, the second DC power supply V2 supplies power to the first DC power supply V1. The reason is that in the reverse operation, that is, the second operation mode, the third switch Q3 and the fourth switch Q4 conduct and disconnect alternately. The voltage applied by the second DC power supply V2 to the secondary winding S or the tertiary winding T is either the power supply voltage (the second DC voltage) or zero. Based on the current-holding effect of the secondary winding S or the tertiary winding T as an inductive element, the current in the winding cannot change abruptly. Therefore, when the power supply voltage is applied to the secondary winding S or the tertiary winding T, the current in the winding gradually increases. When the voltage is not applied, although the voltage is zero, the magnitude of the current in the winding remains unchanged or gradually decreases. When the power supply voltage is applied to the winding again in the next cycle, the current in the winding will continue to increase.

[0046] To avoid this situation, the present disclosure proposes a bidirectional DC converter, which is an improvement over the active-clamped forward conversion circuit 200 or the active-clamped forward and flyback conversion circuit 300 according to the prior art. The bidirectional DC converter according to the present disclosure can apply a reverse voltage to the inductive element in the circuit through the switching of the switches so as to quickly drop and reset the current of the inductive element, thereby ensuring the periodic change of the current.

[0047] Figure 4 Fig. shows a schematic circuit diagram of an active-clamped forward conversion circuit 400 according to an embodiment of the present disclosure. Figure 5 Fig. shows a schematic circuit diagram of an active-clamped forward and flyback conversion circuit 500 according to an embodiment of the present disclosure. As Figure 4 and Figure 5As shown, the active clamp forward converter circuit 400 and active clamp forward-flyback converter circuit 500 according to embodiments of this disclosure differ from the prior art in that they include an additional fifth switch Q5 (first active clamp switch), a third capacitor C3 (first clamp capacitor), a sixth switch Q6 (second active clamp switch), and a fourth capacitor C4 (second clamp capacitor). The series circuit of the fifth switch Q5 and the third capacitor C3 is connected in parallel with the third switch Q3, and the conduction direction of the fifth switch Q5 is opposite to that of the third switch Q3. The series circuit of the sixth switch Q6 and the fourth capacitor C4 is connected in parallel with the fourth switch Q4, and the conduction direction of the sixth switch Q6 is opposite to that of the fourth switch Q4.

[0048] In an embodiment according to this disclosure, in reverse operation, i.e., the second operation mode, the third switch Q3 and the fifth switch Q5 are alternately turned on, the fourth switch Q4 and the sixth switch Q6 are alternately turned on, the first switch Q1 and the second switch Q2 are alternately turned on, and the second switch Q2, the third switch Q3 and the sixth switch Q6 are simultaneously turned on and off, and the first switch Q1, the fourth switch Q4 and the fifth switch Q5 are simultaneously turned on and off.

[0049] In embodiments according to this disclosure, the first switch Q1, the second switch Q2, the third switch Q3 (freewheeling switch), the fourth switch Q4 (rectifier switch), the fifth switch Q5 (first active clamping switch), and the sixth switch Q6 (second active clamping switch) may be configured as MOSFETs, especially N-MOSFETs.

[0050] In another implementation, the first switch Q1, the second switch Q2, the third switch Q3 (freewheeling switch), the fourth switch Q4 (rectifier switch), the fifth switch Q5 (first active clamping switch), and the sixth switch Q6 (second active clamping switch) may be configured as other electronic switches having diodes connected in antiparallel to the electronic switch.

[0051] For the active clamp forward converter circuit 400, if the voltage on the primary side is less than the voltage on the secondary side itself (i.e., the voltage on the high-voltage side is less than the voltage on the low-voltage side), then the operating mode with a duty cycle of less than 0.5 is adopted. If the voltage on the primary side is greater than the voltage on the secondary side itself (i.e., the voltage on the high-voltage side is greater than the voltage on the low-voltage side), then the operating mode with a sum of duty cycles equal to 1 is adopted. These two operating modes will be explained in detail later.

[0052] In the first stage, the second switch Q2, the third switch Q3, and the sixth switch Q6 are turned on; the first switch Q1, the fourth switch Q4, and the fifth switch Q5 are turned off. The second DC power supply V2 charges the secondary winding S and the first inductor L1, increasing the winding current. At the same time, the fourth capacitor C4 discharges, applying a reverse voltage to the first inductor L1, thus reducing the current flowing through the first inductor L1.

[0053] In the second stage, all switches are open, and the voltage applied to the secondary winding S is zero. For example, the sixth switch Q6, configured as a MOSFET, can conduct in reverse, and the fourth capacitor C4 can continue to discharge, applying a reverse voltage to the first inductor L1, causing the current flowing through the first inductor L1 to continue to decrease and reset. Similarly, for example, the fifth switch Q5, configured as a MOSFET, can conduct in reverse, and the third capacitor C3 can discharge, applying a reverse voltage to the secondary winding S, causing the current flowing through the secondary winding S to decrease and reset.

[0054] In the third stage, the second switch Q2, the third switch Q3, and the sixth switch Q6 are disconnected; the first switch Q1, the fourth switch Q4, and the fifth switch Q5 are connected. The second DC power supply V2 charges the first inductor L1. At the same time, the third capacitor C3 discharges, applying a reverse voltage to the secondary winding S, thereby reducing the current flowing through the secondary winding S.

[0055] In the fourth stage, similarly, all switches are turned off, and the voltage applied to the secondary winding S is zero. For example, the sixth switch Q6, configured as a MOSFET, is reverse-biased, the fourth capacitor C4 discharges, and a reverse voltage is applied to the first inductor L1, causing the current flowing through the first inductor L1 to decrease and reset. Similarly, for example, the fifth switch Q5, configured as a MOSFET, is reverse-biased, the third capacitor C3 discharges, and a reverse voltage is applied to the secondary winding S, causing the current flowing through the secondary winding S to decrease and reset.

[0056] In the embodiments according to this disclosure, for the above four-stage operation, the second switch Q2, the third switch Q3 and the sixth switch Q6 that are switched on and off synchronously, as well as the first switch Q1, the fourth switch Q4 and the fifth switch Q5 that are switched on and off synchronously, can have the same duty cycle, and the duty cycle is less than 0.5.

[0057] In another embodiment, the reverse operation of the active clamp forward converter circuit 400 may, for example, consist only of the first and third stages described above. For this two-stage operation, the synchronously switched second switch Q2, third switch Q3, and sixth switch Q6 may have a first duty cycle, and the synchronously switched first switch Q1, fourth switch Q4, and fifth switch Q5 may have a second duty cycle. For example, the first duty cycle is less than 0.5, the second duty cycle is greater than 0.5, and the sum of the first and second duty cycles is 1. It should be noted that, theoretically, i.e., without considering dead time, the sum of the first and second duty cycles equals 1.

[0058] The desired boost operation can be achieved by adjusting the turns ratio between the windings and the duty cycle of the aforementioned switch.

[0059] Similarly, for the active clamp flyback converter circuit 500, if the voltage on the primary side is less than the voltage on the secondary side itself (i.e., the voltage on the high-voltage side is less than the voltage on the low-voltage side), then the operation mode with a duty cycle of less than 0.5 is adopted; if the voltage on the primary side is greater than the voltage on the secondary side itself (i.e., the voltage on the high-voltage side is greater than the voltage on the low-voltage side), then the operation mode with a sum of duty cycles equal to 1 is adopted. These two operation modes will be explained in detail later.

[0060] In the first stage, the second switch Q2, the third switch Q3, and the sixth switch Q6 are turned on; the first switch Q1, the fourth switch Q4, and the fifth switch Q5 are turned off. The second DC power supply V2 charges the secondary winding S, increasing the current in the secondary winding S. At the same time, the fourth capacitor C4 discharges, applying a reverse voltage to the tertiary winding T, thus reducing the current flowing through the tertiary winding T.

[0061] In the second stage, all switches are open, and the voltage applied to the secondary winding S and the tertiary winding T is zero. For example, the sixth switch Q6, configured as a MOSFET, can conduct in reverse, and the fourth capacitor C4 can continue to discharge, applying a reverse voltage to the tertiary winding T, causing the current flowing through the tertiary winding T to continue to decrease and reset. Similarly, for example, the fifth switch Q5, configured as a MOSFET, can conduct in reverse, and the third capacitor C3 can discharge, applying a reverse voltage to the secondary winding S, causing the current flowing through the secondary winding S to decrease and reset.

[0062] In the third stage, the second switch Q2, the third switch Q3, and the sixth switch Q6 are disconnected; the first switch Q1, the fourth switch Q4, and the fifth switch Q5 are connected. The second DC power supply V2 charges the third winding T. At the same time, the third capacitor C3 discharges, applying a reverse voltage to the secondary winding S, thus reducing the current flowing through the secondary winding S.

[0063] In the fourth stage, similarly, all switches are open, and the voltage applied to the secondary winding S and the tertiary winding T is zero. For example, the sixth switch Q6, configured as a MOSFET, is reverse-biased, the fourth capacitor C4 discharges, applying a reverse voltage to the tertiary winding T, reducing and resetting the current flowing through the tertiary winding T. Similarly, for example, the fifth switch Q5, configured as a MOSFET, is reverse-biased, the third capacitor C3 discharges, applying a reverse voltage to the secondary winding S, reducing and resetting the current flowing through the secondary winding S.

[0064] In the embodiments according to this disclosure, for the above four-stage operation, the second switch Q2, the third switch Q3 and the sixth switch Q6 that are switched on and off synchronously, as well as the first switch Q1, the fourth switch Q4 and the fifth switch Q5 that are switched on and off synchronously, can have the same duty cycle, and the duty cycle is less than 0.5.

[0065] In another embodiment, the reverse operation of the active clamp flyback converter circuit 500 may, for example, consist only of the first and third stages described above. For this two-stage operation, the synchronously switched second switch Q2, third switch Q3, and sixth switch Q6 may have a first duty cycle, and the synchronously switched first switch Q1, fourth switch Q4, and fifth switch Q5 may have a second duty cycle. For example, the first duty cycle is less than 0.5, the second duty cycle is greater than 0.5, and the sum of the first and second duty cycles is less than or equal to 1. In an alternative embodiment, for example, the first duty cycle may be greater than 0.5, the second duty cycle may be less than 0.5, and the sum of the first and second duty cycles is less than or equal to 1.

[0066] The desired boost operation can be achieved by adjusting the turns ratio between the windings and the duty cycle of the aforementioned switch.

[0067] Figure 6 and Figure 7 A schematic diagram of switch control signals for a control method for a bidirectional DC-DC converter according to an embodiment of the present disclosure is shown. In an implementation of the present disclosure, the control method can, for example, control the on / off states of the first switch Q1, the second switch Q2, the third switch Q3 (freewheeling switch), the fourth switch Q4 (rectifier switch), the fifth switch Q5 (first active clamping switch), and the sixth switch Q6 (second active clamping switch) using PWM, more specifically, control the duty cycles of the second switch Q2, the third switch Q3, and the sixth switch Q6, as well as the duty cycles of the first switch Q1, the fourth switch Q4, and the fifth switch Q5. Figure 6 and Figure 7 In the diagram, the vertical axis represents the level of the control signal for the corresponding switch; a high level indicates the switch is on, and a low level indicates the switch is off. The horizontal axis represents time, from which the duration of the on or off state can be determined. For example... Figure 6As shown, the second switch Q2, the third switch Q3, and the sixth switch Q6 are switched on and off synchronously, as are the first switch Q1, the fourth switch Q4, and the fifth switch Q5, and their duty cycles are basically the same, all less than 0.5. This corresponds to the four-stage operation described in detail above.

[0068] like Figure 7 As shown, the second switch Q2, the third switch Q3, and the sixth switch Q6 are switched on and off synchronously with a first duty cycle of less than 0.5; the first switch Q1, the fourth switch Q4, and the fifth switch Q5 are switched on and off synchronously with a second duty cycle of greater than 0.5, and the sum of the first duty cycle and the second duty cycle is close to 1. This corresponds to the two-stage operation described in detail above.

[0069] This disclosure also provides an on-board charging device, which includes a bidirectional DC-DC converter 110 according to the above embodiments of this disclosure, such as an active clamp forward converter circuit 400 or an active clamp forward-flyback converter circuit 500 according to the above embodiments of this disclosure.

[0070] This disclosure also provides an electric drive system including an on-board charging device according to the above embodiments of this disclosure.

[0071] This disclosure also provides a vehicle that includes an electric drive system according to the above embodiments of this disclosure.

[0072] The block diagrams of circuits, units, devices, apparatuses, devices, and systems disclosed herein are merely illustrative examples and are not intended to require or imply that connections, arrangements, or configurations must be made in the manner shown in the block diagrams. As those skilled in the art will recognize, these circuits, units, devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner that achieves the desired purpose. The circuits, units, devices, and apparatuses disclosed herein can be implemented in any suitable manner, such as using application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or using general-purpose processors in conjunction with programs.

[0073] Those skilled in the art should understand that the specific embodiments described above are merely examples and not limitations. Various modifications, combinations, partial combinations, and substitutions can be made to the embodiments of this disclosure according to design requirements and other factors, as long as they are within the scope of the appended claims or their equivalents, and thus fall within the scope of the rights to be protected by this disclosure.

Claims

1. A bidirectional DC-DC converter configured as a current isolation circuit, wherein in a first operating mode, it converts a first DC voltage to a second DC voltage, and in a second operating mode, it converts the second DC voltage back to the first DC voltage, wherein, The bidirectional DC-DC converter includes, on the secondary side: a freewheeling switch and a rectifier switch; and It also includes: a first active clamping switch, a first clamping capacitor, a second active clamping switch, and a second clamping capacitor, wherein the series circuit of the first active clamping switch and the first clamping capacitor is connected in parallel with the freewheeling switch, and the conduction direction of the first active clamping switch is opposite to the conduction direction of the freewheeling switch; and the series circuit of the second active clamping switch and the second clamping capacitor is connected in parallel with the rectifier switch, and the conduction direction of the second active clamping switch is opposite to the conduction direction of the rectifier switch.

2. The bidirectional DC-DC converter according to claim 1, wherein, The bidirectional DC-DC converter includes, on the primary side: a first switch, a second switch, a first capacitor, and a primary winding. The first switch, the second switch, and the first capacitor form a series circuit, and the two ends of the series circuit form a first DC voltage terminal. The primary winding is connected in parallel to the series circuit formed by the second switch and the first capacitor.

3. The bidirectional DC-DC converter according to claim 2, wherein, The bidirectional DC-DC converter is configured as an active clamp forward converter circuit, and the bidirectional DC-DC converter includes, on the secondary side: a secondary winding, a second capacitor, and a first inductor. The series circuit consisting of the secondary winding and the freewheeling switch is connected in parallel with the rectifier switch. The parallel circuit is connected to the second DC voltage terminal via the first inductor element, and the second capacitor is connected in parallel to the second DC voltage terminal.

4. The bidirectional DC-DC converter according to claim 2, wherein, The bidirectional DC-DC converter is configured as an active clamp flyback converter circuit. The bidirectional DC-DC converter includes, on the secondary side: a second capacitor, a secondary winding, and a tertiary winding. The series circuit consisting of the secondary winding and the freewheeling switch is connected to the second DC voltage terminal, the series circuit consisting of the tertiary winding and the rectifier switch is connected to the second DC voltage terminal, and the second capacitor is connected in parallel to the second DC voltage terminal.

5. The bidirectional DC-DC converter according to claim 2, wherein, One or more of the first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamping switch, and the second active clamping switch are configured as electronic switches, the electronic switches having diodes connected in antiparallel with them.

6. The bidirectional DC-DC converter according to claim 2, wherein, One or more of the first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamp switch, and the second active clamp switch are configured as MOSFETs.

7. A control method for controlling a bidirectional DC-DC converter according to any one of claims 2 to 6, the control method comprising: In the first operating mode, the first switch and the second switch are controlled to be turned on alternately, so that the DC converter converts the first DC voltage into the second DC voltage; In the second operating mode, the first switch and the second switch are controlled to be turned on alternately, the freewheeling switch and the first active clamping switch are turned on alternately, and the rectifier switch and the second active clamping switch are turned on alternately, so that the DC converter converts the second DC voltage into the first DC voltage; The second switch, the freewheeling switch, and the second active clamping switch are switched on and off synchronously, as are the first switch, the rectifier switch, and the first active clamping switch.

8. The control method according to claim 7, wherein, The first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamp switch, and the second active clamp switch all have the same duty cycle and are less than 0.

5.

9. The control method according to claim 7, wherein, The first duty cycle of the second switch, the freewheeling switch, and the second active clamping switch is the same and less than 0.5; the second duty cycle of the first switch, the rectifier switch, and the first active clamping switch is the same and greater than 0.5; and the sum of the first duty cycle and the second duty cycle is less than or equal to 1.

10. The control method according to claim 7, wherein, The on / off state of the first switch, the second switch, the freewheeling switch, the rectifier switch, the first active clamp switch, and the second active clamp switch is controlled by PWM.

11. An on-board charging device, comprising a bidirectional DC-DC converter according to any one of claims 1 to 6.

12. An electric drive assembly system, comprising the on-board charging device according to claim 11.

13. A vehicle comprising the electric drive assembly system according to claim 12.

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