A dual active bridge converter secondary side self-powered driving power supply circuit, starting control method and transformer device

Abstract

This invention discloses a self-powered secondary-side drive power supply circuit, a startup control method, and a transformer device for a dual active bridge converter. The circuit includes a primary-side H-bridge, a transformer, a secondary-side H-bridge, a supporting capacitor, an energy harvesting circuit, and a secondary-side H-bridge drive circuit. The energy harvesting circuit draws power from the output of the secondary-side H-bridge, eliminating the need for an external low-voltage auxiliary power supply and enabling self-powered secondary-side operation. Furthermore, it eliminates the need for a separate isolation power supply module for each secondary-side switch, reducing wiring complexity. Since the secondary-side H-bridge and supporting capacitor are inherent to the dual active bridge converter structure, the energy harvesting circuit only needs to be connected in parallel across the supporting capacitor. Compared to adding auxiliary windings, this invention does not require transformer modification. The energy harvesting circuit utilizes the uncontrolled rectification stage of the secondary-side H-bridge as the power source for the startup stage, achieving self-powered operation of the secondary-side H-bridge drive circuit with a simple structural design.

Description

Technical Field

[0001] This invention relates to the field of power electronics, and in particular to a self-powered drive circuit for the secondary side of a dual active bridge converter, a start-up control method, and a transformer device. Background Technology

[0002] Dual active bridge converters are high-efficiency power conversion devices in the field of power electronics. Their core function is to achieve efficient, high-frequency, and bidirectional controllable DC power transmission under the premise of electrical isolation. In dual active bridge converters, the secondary H-bridge drive circuit requires a stable isolated power supply. The mainstream power supply solutions in the industry include independent isolated power supply modules, external auxiliary power supply, and auxiliary winding power supply.

[0003] External auxiliary power supply solutions require introducing low-voltage auxiliary power from outside the system, increasing system wiring complexity. Furthermore, in distributed power supply scenarios, the reliability of the auxiliary power supply becomes a new bottleneck. Independent isolated power module solutions require equipping each switch of the secondary-side H-bridge with an independent isolated DC-DC power module, which is expensive, and multiple modules occupy a large amount of PCB space, hindering power density improvement. Auxiliary winding power supply solutions require adding an auxiliary winding to the high-frequency transformer of the dual active bridge converter, utilizing magnetic coupling to obtain energy, which is then rectified and regulated to power the drive circuit. While this solution achieves self-powering on the secondary side by using magnetic component reuse, the introduction of the auxiliary winding requires redesigning the high-frequency transformer of the dual active bridge converter, and the insulation process between the auxiliary winding and the main power winding is difficult, increasing the overall design and manufacturing complexity of the dual active bridge converter. Summary of the Invention

[0004] The purpose of this invention is to provide a self-powered drive circuit, a start-up control method, and a transformer device for the secondary side of a dual active bridge converter, which solves the problem of high complexity in the design and manufacture of the power supply circuit for the secondary side H-bridge drive circuit of a dual active bridge converter.

[0005] To solve the above-mentioned technical problems, the present invention provides a self-powered drive circuit for the secondary side of a dual active bridge converter, comprising: Primary H-bridge, transformer, secondary H-bridge, supporting capacitor, energy extraction circuit and secondary H-bridge drive circuit; The input terminal of the primary-side H-bridge is connected to an external power supply, and the output terminal of the primary-side H-bridge is connected to the primary side of the transformer; the secondary side of the transformer is connected to the input terminal of the secondary-side H-bridge; the first output terminal of the secondary-side H-bridge is connected to the first terminal of the supporting capacitor and the first input terminal of the energy harvesting circuit, and the second output terminal of the secondary-side H-bridge is connected to the second terminal of the supporting capacitor and the second input terminal of the energy harvesting circuit; the output terminal of the energy harvesting circuit is connected to the secondary-side H-bridge drive circuit. The first, second, third, and fourth controllable switches of the secondary H-bridge each correspond to a diode, which are used to form an uncontrolled rectifier network.

[0006] Optionally, the energy extraction circuit is a DC-DC conversion circuit, with the first input terminal of the DC-DC conversion circuit connected to the first terminal of the supporting capacitor, and the second input terminal of the DC-DC conversion circuit connected to the second terminal of the supporting capacitor.

[0007] Optionally, the first controllable switch is a first SiC MOSFET, the second controllable switch is a second SiC MOSFET, the third controllable switch is a third SiC MOSFET, and the fourth controllable switch is a fourth SiC MOSFET; the diodes corresponding to the first SiC MOSFET, the second SiC MOSFET, the third SiC MOSFET, and the fourth SiC MOSFET are their respective body diodes.

[0008] Optionally, the DC-DC conversion circuit is a BUCK circuit or a SEPIC circuit.

[0009] To address the aforementioned technical problems, the present invention also provides a startup control method applied to the aforementioned self-powered drive power supply circuit on the secondary side of a dual active bridge converter. The startup control method includes: Upon receiving a power-on signal, the first, second, third, and fourth controllable switches in the secondary H-bridge are turned off. The switching transistors in the primary-side H-bridge are turned on so that the energy harvesting circuit and driver are activated when the voltage across the supporting capacitor reaches the activation threshold of the energy harvesting circuit.

[0010] Optionally, controlling the conduction of the switching transistors in the primary-side H-bridge includes: The switching transistors in the primary-side H-bridge are controlled by gradually increasing pulse widths to achieve soft start.

[0011] Optional, also includes: Set the maximum soft boot time; After power is received from the input terminal of the primary H-bridge, timing begins. When the duration for which the voltage across the supporting capacitor is less than the start-up threshold reaches the maximum soft-start time, the power harvesting circuit is stopped and a fault is reported.

[0012] Optionally, the maximum soft-start time is 1 to 2 seconds.

[0013] Optionally, the activation threshold is 20 volts.

[0014] To solve the above-mentioned technical problems, the present invention also provides a transformer device, including a high-voltage DC power supply and the above-mentioned dual active bridge converter secondary self-powered drive power supply circuit.

[0015] This invention provides a dual active bridge secondary-side self-powered drive power supply circuit, including a primary-side H-bridge, a transformer, a secondary-side H-bridge, a supporting capacitor, a power extraction circuit, and a secondary-side H-bridge drive circuit. The input terminal of the primary-side H-bridge is connected to an external high-voltage DC power supply, converting the high-voltage DC into a high-frequency AC square wave, and outputting it to the primary winding of the transformer. The transformer transmits the high-frequency AC signal to its secondary winding via magnetic coupling, which is then connected to the secondary-side H-bridge. The secondary-side H-bridge includes four controllable switches, each connected in parallel with a diode, forming an uncontrolled rectifier network. During the initial power-on phase, the secondary side has not yet established a working voltage, the power extraction circuit is not activated, the secondary-side H-bridge drive circuit is in a non-operating state, and all four controllable switches are off. At this time, the high-frequency AC current charges the supporting capacitor through the uncontrolled rectifier network composed of the four diodes, causing the voltage across the capacitor to gradually rise. When the voltage across the supporting capacitor reaches the startup threshold of the energy harvesting circuit, the energy harvesting circuit starts working, drawing power from the output of the secondary H-bridge and supplying power to the secondary H-bridge drive circuit. The secondary H-bridge drive circuit then outputs a drive signal, controlling the four controllable switches to turn on and off in a synchronous rectification sequence, allowing the main current to flow through the controllable switches instead of the diodes. The system enters synchronous rectification mode, and the energy harvesting circuit continuously draws stable power from the output of the secondary H-bridge, maintaining the normal operation of the drive circuit. Since this scheme draws power from the output of the secondary H-bridge, there is no need to introduce a low-voltage auxiliary power supply from an external source, achieving self-powered secondary operation. Furthermore, it eliminates the need for an independent isolation power supply module for each secondary switch, reducing wiring complexity. Simultaneously, because the secondary H-bridge and supporting capacitor form the inherent structure of a dual active bridge converter, the energy harvesting circuit only needs to be connected in parallel across the supporting capacitor. Compared to schemes that add auxiliary windings, this scheme does not require transformer modification. The energy harvesting circuit utilizes the uncontrolled rectification stage of the secondary H-bridge as the source of power for the startup stage, achieving self-powered operation of the secondary H-bridge drive circuit with a simple structural design. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram illustrating the application of a dual active converter in a solid-state transformer. Figure 2This is a schematic diagram of a self-powered drive circuit for the secondary side of a dual active bridge converter, provided by the present invention. Detailed Implementation

[0018] The core of this invention is to provide a self-powered drive circuit for the secondary side of a dual active bridge converter, a start-up control method, and a transformer device.

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In dual active bridge converters, the secondary-side H-bridge drive circuit requires a stable, isolated power supply. Industry-standard power supply solutions include independent isolated power modules, external auxiliary power supplies, and auxiliary winding power supplies. External auxiliary power supplies require introducing a low-voltage auxiliary power source from outside the system, increasing wiring complexity. Furthermore, in distributed power supply scenarios, the reliability of the auxiliary power supply becomes a new bottleneck. On the other hand, if a centralized auxiliary power supply is used, the power supply for the secondary-side H-bridge drive circuit shares the same power source as the primary-side H-bridge drive circuit. This means the common-mode voltage on the high-voltage side will be directly conducted to the low-voltage secondary side through the power supply loop, not only compromising electrical isolation but also posing a serious threat to personal safety and equipment insulation. Independent isolated power modules require a separate isolated DC-DC power module for each switch in the secondary-side H-bridge, which is expensive, and multiple modules occupy a significant amount of PCB space, hindering power density improvement. The auxiliary winding power supply scheme requires adding an auxiliary winding to the high-frequency transformer of the dual active bridge converter. Energy is obtained through magnetic coupling and then rectified and regulated to power the drive circuit. Although this scheme achieves self-powered secondary side by using magnetic component reuse, the introduction of the auxiliary winding requires redesigning the high-frequency transformer of the dual active bridge converter. Furthermore, the insulation process between the auxiliary winding and the main power winding is quite difficult, which increases the design and manufacturing complexity of the entire dual active bridge converter.

[0021] For details, please see Figure 1 , Figure 1 This illustrates the application of dual active converters in solid-state transformers. For example... Figure 1As shown, in 10kV medium-voltage direct-connected solid-state transformer applications, a series-input, parallel-output topology combining cascaded H-bridges (CHBs) and dual active bridge converters (DABs) is commonly used. The high-voltage AC side employs multiple cascaded H-bridges, with a dual active bridge converter in the middle, and the output sides directly connect the DC output ports in parallel. In this topology, the ground potential of each cascaded H-bridge is different—the unit closest to the 10kV input can have a ground voltage as high as several kilovolts, varying with the number of cascaded stages. If the power supply for the secondary-side H-bridge drive circuit shares the same power supply as the primary-side H-bridge drive circuit, the common-mode voltage on the high-voltage side will be directly conducted to the low-voltage secondary side through the power supply loop, not only compromising electrical isolation but also posing a threat to personal safety and equipment insulation. While configuring an independent high-voltage isolated power supply for the secondary-side H-bridge circuit can avoid such safety hazards, introducing auxiliary power and adding extra power devices increases wiring complexity. In addition, the scheme of introducing auxiliary winding power supply realizes the self-powered power supply of the secondary H-bridge drive circuit, but it increases the design and manufacturing complexity of the entire dual active bridge converter.

[0022] To address the aforementioned technical problems, this invention provides a self-powered drive circuit for the secondary side of a dual active bridge converter.

[0023] For details, please see Figure 2 , Figure 2 This is a schematic diagram of a self-powered drive circuit for the secondary side of a dual active bridge converter, provided by the present invention.

[0024] like Figure 2 As shown, the self-powered drive circuit for the secondary side of the dual active bridge converter includes: Primary H-bridge, transformer T, secondary H-bridge, supporting capacitor C, energy extraction circuit U1, and secondary H-bridge drive circuit U2; The input terminal of the primary H-bridge is connected to an external power supply, and the output terminal of the primary H-bridge is connected to the primary side of the transformer T; the secondary side of the transformer T is connected to the input terminal of the secondary H-bridge; the first output terminal of the secondary H-bridge is connected to the first terminal of the supporting capacitor C and the first input terminal of the energy harvesting circuit U1, and the second output terminal of the secondary H-bridge is connected to the second terminal of the supporting capacitor C and the second input terminal of the energy harvesting circuit U1; the output terminal of the energy harvesting circuit U1 is connected to the secondary H-bridge drive circuit U2. The first controllable switch Q1, the first controllable switch Q2, the first controllable switch Q3 and the fourth controllable switch Q4 of the secondary H-bridge each correspond to a diode, which are used to form an uncontrolled rectifier network.

[0025] Specifically, the primary-side H-bridge of the dual active converter consists of four controllable switches, which convert the input DC voltage into a high-frequency AC square wave voltage. Transformer T provides electrical isolation and voltage conversion; its primary winding receives the square wave voltage from the primary-side H-bridge and induces a corresponding voltage in the secondary winding through magnetic coupling. The secondary-side H-bridge also consists of four controllable switches, which synchronously rectify the AC square wave voltage from the secondary side of transformer T into a DC voltage output. The secondary-side H-bridge is equipped with a drive circuit that controls the on / off state of each controllable switch in the secondary-side H-bridge to achieve the rectification function. The two input terminals of the energy harvesting circuit U1 are connected in parallel across the supporting capacitor C to harvest the electrical energy output from the secondary-side H-bridge and power the secondary-side H-bridge drive circuit U2. The first controllable switch Q1, the first controllable switch Q2, the first controllable switch Q3, and the fourth controllable switch Q4 of the secondary H-bridge each correspond to a diode. The conduction direction of these four diodes is opposite to the conduction direction of their corresponding controllable switches, and the four diodes together form an uncontrolled rectifier network. When electrical energy is first transmitted to the secondary H-bridge through the transformer T, the energy harvesting circuit U1 has not yet obtained electrical energy to supply to the secondary H-bridge drive circuit U2. The secondary H-bridge drive circuit U2 is not working, so the four controllable switches of the secondary H-bridge are open. The square wave AC current transmitted from the secondary winding of the transformer T cannot flow through the controllable switches, but instead flows through the uncontrolled rectifier network composed of the four diodes, thereby converting the square wave AC current into DC current, providing the initial DC voltage for the subsequent start-up of the energy harvesting circuit U1. It should be noted that the diodes corresponding to the four controllable switches can be independent diodes packaged inside the controllable switches, or they can be parasitic diodes inherent in the controllable switches themselves. For example, when MOSFETs are selected as controllable switches, there is a naturally anti-parallel body diode between the drain and source of the MOSFET. Therefore, when the four MOSFETs form a secondary H-bridge, the four body diodes will also form an uncontrolled rectifier network.

[0026] Specifically, during the initial power-up phase of the system, the secondary side has not yet established a working voltage, the energy harvesting circuit U1 is not activated, the secondary H-bridge drive circuit U2 is in a non-operating state, and all four controllable switches are turned off. At this time, high-frequency AC current charges the supporting capacitor C through the uncontrolled rectifier path composed of four diodes, causing its voltage to gradually rise. When the voltage across the supporting capacitor C reaches the activation threshold of the energy harvesting circuit U1, the energy harvesting circuit U1 starts working, obtaining power from the output of the secondary H-bridge and supplying power to the secondary H-bridge drive circuit U2. The secondary H-bridge drive circuit U2 then outputs a drive signal to control the four controllable switches to turn on and off in a synchronous rectification sequence. At this time, the main current flows through the four controllable switches, the four diodes are reverse-biased and cut off, and the uncontrolled rectifier circuit composed of the four diodes also stops working. The system enters synchronous rectification mode, and the energy harvesting circuit U1 continues to stably draw power from the output of the secondary H-bridge to maintain the normal operation of the drive circuit.

[0027] As can be seen, this embodiment draws power from the output of the secondary H-bridge, thus eliminating the need for an external low-voltage auxiliary power supply. This allows for self-powering of the secondary side and avoids the safety hazards caused by sharing a power supply with the primary H-bridge's drive circuit. Furthermore, it eliminates the need for a separate isolation power supply module for each secondary-side switch, reducing wiring complexity. Since the secondary H-bridge and supporting capacitor C form the inherent structure of a dual active bridge converter, the power extraction circuit U1 only needs to be connected in parallel across the supporting capacitor C. Compared to solutions that add auxiliary windings, this solution does not require modification of the transformer T. The power extraction circuit U1 utilizes the uncontrolled rectification stage of the secondary H-bridge as the source of power for the startup phase, achieving self-powering of the secondary H-bridge drive circuit U2 with a simple structural design.

[0028] Based on the above embodiments: As an optional embodiment, the energy harvesting circuit U1 is a DC-DC conversion circuit, with the first input terminal of the DC-DC conversion circuit connected to the first terminal of the supporting capacitor C, and the second input terminal of the DC-DC conversion circuit connected to the second terminal of the supporting capacitor C.

[0029] Specifically, the function of the power acquisition circuit U1 is to convert the acquired voltage into the operating voltage required by the secondary H-bridge drive circuit U2. The DC-DC conversion circuit is a power electronic device that converts a fixed DC voltage into a variable DC voltage. The operation of the DC-DC conversion circuit is based on high-frequency switching and pulse width modulation technology. When it is working, the semiconductor switches inside the circuit are turned on and off at extremely high frequencies. When the switch is on, the input power charges the inductor, converting electrical energy into magnetic energy for storage. When the switch is off, the inductor releases the stored magnetic energy to maintain a constant current and continues to supply power to the load. During this process, the inductor consumes little power, resulting in high conversion efficiency. Furthermore, the DC-DC converter has the advantage of a wide input voltage range. Through a feedback loop, the DC-DC converter monitors the output voltage in real time. When the input voltage fluctuates significantly, it quickly adjusts the duty cycle of the switching transistor. This timely dynamic adjustment allows the circuit to maintain a constant output voltage over a wide input range. Simultaneously, the DC-DC converter can also achieve low-voltage start-up. This wide input voltage range allows the DC-DC converter to adapt to the gradually increasing output voltage of the secondary H-bridge during the startup phase. Compared to linear regulator circuits and other DC regulation circuits, the wide input voltage range and high conversion efficiency of the DC-DC converter make it more suitable as an energy harvesting circuit U1.

[0030] As can be seen, this embodiment uses a DC-DC converter circuit as the power extraction circuit U1. By utilizing the wide input voltage range, low-voltage start-up, and high conversion efficiency of the DC-DC converter circuit, a stable power supply to the secondary H-bridge drive circuit U2 is achieved.

[0031] As an optional embodiment, the first controllable switch Q1 is a first SiC MOSFET, the first controllable switch Q2 is a second SiC MOSFET, the first controllable switch Q3 is a third SiC MOSFET, and the fourth controllable switch Q4 is a fourth SiC MOSFET; the diodes corresponding to the first SiC MOSFET, the second SiC MOSFET, the third SiC MOSFET, and the fourth SiC MOSFET are their respective body diodes.

[0032] Specifically, silicon carbide (SiC), as a third-generation semiconductor material, has a higher breakdown electric field strength and higher thermal conductivity compared to traditional silicon (Si). SiC MOSFETs exhibit lower switching losses; these extremely low losses allow SiC MOSFETs to easily operate at frequencies of hundreds of kHz or even MHz, while silicon-based IGBTs are typically limited to below 20 kHz. Furthermore, SiC MOSFETs inherently possess a body diode with extremely small reverse recovery charge and time. At the end of the dead time, the conducting SiC MOSFET applies a reverse voltage to the body diode, which has just completed its freewheeling. For silicon-based devices, this would generate a large reverse recovery current spike, overlapping with the high voltage and causing switching losses. However, the body diode of a SiC MOSFET almost completely lacks this current spike, thus reducing switching losses.

[0033] It is evident that using SiC MOSFETs as controllable switches not only significantly reduces the size and weight of magnetic components by greatly increasing the switching frequency, thereby achieving high power density and miniaturized circuit design; at the same time, its built-in body diode enables uncontrolled rectification during system startup, and its excellent reverse recovery characteristics can effectively suppress high-frequency switching noise, thus ensuring stable operation of the system under high efficiency and high reliability conditions.

[0034] As an optional embodiment, the DC-DC conversion circuit is a BUCK circuit or a SEPIC circuit.

[0035] Specifically, Buck circuits or SEPIC circuits are both DC-DC voltage converters. Their core function is to convert a DC input voltage into a stable DC output voltage. Buck circuits or SEPIC circuits achieve voltage reduction through the high-speed switching of a transistor, combined with the energy storage and release of an inductor. When the switch is on, the input voltage is applied across the inductor through the transistor, causing the inductor current to rise linearly, storing energy and simultaneously charging the output capacitor and supplying power to the load. When the switch is off, the inductor generates a back electromotive force to maintain current, causing the freewheeling diode to conduct, forming a freewheeling circuit. The inductor releases the stored energy to continue supplying power to the load, and the current decreases linearly. Buck circuits or SEPIC circuits have a simple circuit structure, high energy conversion efficiency, and high reliability.

[0036] As can be seen, this embodiment selects a Buck circuit or a SEPIC circuit as the DC-DC conversion circuit, so that the voltage output by the secondary H-bridge can be reliably converted into the voltage required by the secondary H-bridge drive circuit U2, thereby achieving a stable power supply to the secondary H-bridge drive circuit U2.

[0037] To address the aforementioned technical problems, the present invention also provides a startup control method applied to the aforementioned self-powered drive power supply circuit on the secondary side of a dual active bridge converter. The startup control method includes: Upon receiving a power-on signal, the first controllable switch Q1, the first controllable switch Q2, the first controllable switch Q3, and the fourth controllable switch Q4 in the secondary H-bridge are turned off. The switching transistor in the primary H-bridge is turned on so that when the voltage across the supporting capacitor C reaches the start-up threshold of the energy harvesting circuit U1, the energy harvesting circuit U1 and the driver are started.

[0038] Specifically, there is a dead zone issue before the secondary-side H-bridge drive circuit U2 starts working. That is, during the initial power-up phase of the system, the secondary side has not yet established a working voltage, the power extraction circuit U1 is not activated, and the secondary-side H-bridge drive circuit U2 is in a non-working state. At this time, it is necessary to keep the first controllable switch Q1, the first controllable switch Q2, the first controllable switch Q3, and the fourth controllable switch Q4 in the secondary-side H-bridge all in the off state. Then, the switching transistors in the primary-side H-bridge are turned on, converting the input DC power into square wave AC power, which is then transmitted to the secondary-side H-bridge via transformer T. Since all four controllable switches in the secondary-side H-bridge are in the off state, current flows through the uncontrolled rectifier network composed of diodes, and after rectification, it is converted into DC power output. The supporting capacitor C is energized and begins to charge. The power extraction circuit U1 monitors the voltage value of the supporting capacitor C in real time. When the voltage value of the supporting capacitor C reaches the activation threshold of the power extraction circuit U1, the power extraction circuit U1 starts.

[0039] Specifically, during the initial power-on phase of the system, all four controllable switches of the secondary H-bridge remain off. The high-frequency AC current charges the supporting capacitor C through the uncontrolled rectifier network composed of four diodes, causing its voltage to gradually rise. When the voltage across the supporting capacitor C reaches the start-up threshold of the energy harvesting circuit U1, the energy harvesting circuit U1 starts working, obtaining power from the output of the secondary H-bridge and supplying power to the secondary H-bridge drive circuit U2. The secondary H-bridge drive circuit U2 then outputs a drive signal to control the four controllable switches to turn on and off in a synchronous rectification sequence. At this time, the main current flows through the four controllable switches, the four diodes are reverse-biased and cut off, and the uncontrolled rectifier circuit composed of the four diodes also stops working. The system enters the synchronous rectification mode, and the energy harvesting circuit U1 continues to stably draw power from the output of the secondary H-bridge to maintain the normal operation of the drive circuit.

[0040] As can be seen, this embodiment first keeps the controllable switch of the secondary H-bridge open, then controls the primary H-bridge to start working, so that the AC power transmitted to the secondary side is first rectified by the uncontrolled rectifier network and converted into DC power before starting the energy harvesting circuit U1, thus realizing the self-powered secondary drive circuit of the dual active bridge converter.

[0041] As an optional embodiment, controlling the switching transistors in the primary-side H-bridge to turn on includes: The switching transistors in the primary-side H-bridge are controlled by gradually increasing pulse widths to achieve soft start.

[0042] Specifically, in a dual active bridge circuit, if the switching transistors are immediately put into full-speed operation upon power-up, inrush current will be generated. If the primary-side H-bridge immediately outputs full power at startup, the transformer T will instantly inject a huge current into the secondary side, several times or even tens of times the normal operating current, which can easily burn out the switching transistors. Therefore, a soft-start strategy is required. Initially, the drive pulse width is set to a very small value, causing each switching transistor in the primary-side H-bridge to operate with an extremely narrow conduction time. Subsequently, the drive pulse width gradually increases according to a set step size or pattern. This process allows the excitation current of the transformer T and the energy transferred to the secondary side to build up smoothly, effectively suppressing the current surge and voltage overshoot at startup, until the pulse width reaches a steady-state value, completing the soft start.

[0043] As can be seen, this embodiment avoids the safety hazards that would arise from directly running the primary H-bridge at full power by adopting a soft-start strategy.

[0044] As an optional embodiment, it also includes: Set the maximum soft boot time; After power is received from the input terminal of the primary H-bridge, timing begins. When the duration for which the voltage across the supporting capacitor C is less than the start-up threshold reaches the maximum soft-start time, the power harvesting circuit U1 is stopped from starting and a fault is reported.

[0045] When the primary-side H-bridge begins soft-start, the supporting capacitor C should receive electrical energy, and the voltage across capacitor C should gradually rise. When the voltage reaches the threshold for the power extraction circuit U1 to start, circuit U1 should begin operation. However, if, after the maximum soft-start time has elapsed since the primary-side H-bridge began soft-start, the voltage across capacitor C still fails to reach the threshold for the power extraction circuit U1, it indicates a circuit fault. The startup process should be stopped immediately, and the fault reported to alert the operator for inspection.

[0046] As can be seen, this embodiment achieves timely identification and reporting of circuit faults during the startup phase by setting a maximum soft-start time.

[0047] As an optional implementation, the maximum soft-start time is 1 to 2 seconds.

[0048] Specifically, to achieve the optimal balance between ensuring reliable system startup and preventing fault escalation, the maximum soft-start time setting must allow for a ramp-up margin. The essence of soft-start is to limit the rate of current change; to suppress inrush current, the voltage rises slowly. For the supporting capacitor C, charging from 0V to the startup threshold of the power extraction circuit U1 physically requires a certain integration time. An excessively short maximum soft-start time may lead to misjudgment. On the other hand, if the soft-start time is set too long, the circuit may remain in a fault state for an extended period upon power-up, creating a safety hazard. Therefore, this embodiment sets the maximum soft-start time to 1 to 2 seconds, thus balancing reliable system startup with preventing fault escalation.

[0049] As an optional implementation, the activation threshold is 20 volts.

[0050] Specifically, if the power harvesting circuit U1 is forcibly started when the voltage of the supporting capacitor C is low, the input voltage may be in the critical region of chip operation. Once the secondary H-bridge driver circuit U2 starts working, the voltage will be pulled down instantly, causing the power harvesting circuit U1 to shut down due to undervoltage; after shutdown, the voltage recovers, and it attempts to start again. Reaching 20V indicates that the capacitor has stored enough charge to support the startup of the power harvesting circuit U1. Meanwhile, if the startup threshold is set too high, it will affect the system response speed. Setting it to 20V can balance response speed and reliable system operation; alternatively, a 15V startup threshold can be set for higher operating efficiency.

[0051] As can be seen, this embodiment sets the startup threshold to 20 volts while taking into account both response speed and reliable startup of the secondary H-bridge drive circuit U2.

[0052] To address the aforementioned problems, the present invention also provides a transformer device, including a high-voltage DC power supply and a self-powered secondary-side drive power supply circuit for a dual active bridge converter as described above. For a description of the transformer device provided by the present invention, please refer to the embodiment of the self-powered secondary-side drive power supply circuit for a dual active bridge converter described above; further details will not be repeated here.

[0053] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section. It should also be noted that in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0054] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A self-powered drive power supply circuit for the secondary side of a dual active bridge converter, characterized in that, include: Primary H-bridge, transformer, secondary H-bridge, supporting capacitor, energy extraction circuit and secondary H-bridge drive circuit; The input terminal of the primary-side H-bridge is connected to an external power supply, and the output terminal of the primary-side H-bridge is connected to the primary side of the transformer; the secondary side of the transformer is connected to the input terminal of the secondary-side H-bridge; the first output terminal of the secondary-side H-bridge is connected to the first terminal of the supporting capacitor and the first input terminal of the energy harvesting circuit, and the second output terminal of the secondary-side H-bridge is connected to the second terminal of the supporting capacitor and the second input terminal of the energy harvesting circuit; the output terminal of the energy harvesting circuit is connected to the secondary-side H-bridge drive circuit. The first, second, third, and fourth controllable switches of the secondary H-bridge each correspond to a diode, which are used to form an uncontrolled rectifier network.

2. The self-powered drive power supply circuit for the secondary side of a dual active bridge converter as described in claim 1, characterized in that, The energy extraction circuit is a DC-DC conversion circuit. The first input terminal of the DC-DC conversion circuit is connected to the first terminal of the supporting capacitor, and the second input terminal of the DC-DC conversion circuit is connected to the second terminal of the supporting capacitor.

3. The self-powered drive power supply circuit for the secondary side of a dual active bridge converter as described in claim 1, characterized in that, The first controllable switch is a first SiC MOSFET, the second controllable switch is a second SiC MOSFET, the third controllable switch is a third SiC MOSFET, and the fourth controllable switch is a fourth SiC MOSFET; the diodes corresponding to the first SiC MOSFET, the second SiC MOSFET, the third SiC MOSFET, and the fourth SiC MOSFET are their respective body diodes.

4. The self-powered drive power supply circuit for the secondary side of a dual active bridge converter as described in claim 2, characterized in that, The DC-DC conversion circuit is either a BUCK circuit or a SEPIC circuit.

5. A start-up control method, characterized in that, The startup control method, applied to a self-powered drive circuit on the secondary side of a dual active bridge converter according to any one of claims 1 to 4, includes: Upon receiving a power-on signal, the first, second, third, and fourth controllable switches in the secondary H-bridge are turned off. The switching transistors in the primary-side H-bridge are turned on so that the energy harvesting circuit and driver are activated when the voltage across the supporting capacitor reaches the activation threshold of the energy harvesting circuit.

6. The start-up control method as described in claim 5, characterized in that, Controlling the conduction of the switching transistors in the primary-side H-bridge includes: The switching transistors in the primary-side H-bridge are controlled by gradually increasing pulse widths to achieve soft start.

7. The start-up control method as described in claim 6, characterized in that, Also includes: Set the maximum soft boot time; After power is received from the input terminal of the primary H-bridge, timing begins. When the duration for which the voltage across the supporting capacitor is less than the start-up threshold reaches the maximum soft-start time, the power harvesting circuit is stopped and a fault is reported.

8. The start-up control method as described in claim 7, characterized in that, The maximum soft-start time is 1 to 2 seconds.

9. The start-up control method as described in claim 5, characterized in that, The activation threshold is 20 volts.

10. A transformer device, comprising a high-voltage DC power supply, characterized in that, It also includes a self-powered drive power supply circuit for the secondary side of the dual active bridge converter as described in any one of claims 1 to 4.

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