Control method, device and vehicle power system for starting onboard computer (OBC)

Abstract

This application relates to the field of power control and discloses a control method, device, and vehicle power system for starting an on-board power supply (OBC). In this OBC system, the first bridge arm of the OBC secondary side is multiplexed with the primary bridge arm of the DC-DC converter to form a shared bridge arm. The second bridge arm of the OBC secondary side is a non-shared bridge arm. When the DC-DC converter receives an OBC start command, the following steps are executed: S1, increasing the switching frequency of the DC-DC converter from a first switching frequency to the OBC operating frequency; S2, activating the non-shared bridge arm and controlling the phase shift angle between the non-shared and shared bridge arms to 0°, making the equivalent output voltage of the OBC secondary side zero; S3, maintaining this for a first preset time to allow charge discharge on the primary DC bus capacitor; S4, after the primary DC bus voltage drops below a safe voltage threshold, executing the OBC soft-start process at the zero-crossing point. This application can suppress the overshoot risk during OBC start-up.

Description

Technical Field

[0001] This application relates to the field of power control, and in particular to a control method, device and vehicle power system for starting an on-board power supply (OBC). Background Technology

[0002] With the rapid development of new energy vehicles, the vehicle's power system is facing higher requirements in terms of conversion efficiency and power density. To achieve higher power density and smaller size, the industry is gradually evolving from physically independent OBC (On-Board Charger) and DCDC (Direct-to-DC Converter) architectures to a two-in-one integrated topology using bridge arm reuse. By reusing the secondary bridge arm of the OBC and the primary bridge arm of the DCDC, hardware sharing can be achieved at the circuit level, directly reducing the number of power devices and drive circuits, thereby reducing system costs and improving PCB utilization.

[0003] Currently, some basic cooperative control strategies have been proposed in the prior art for the aforementioned bridge arm multiplexing integrated topology. For example, existing technologies (such as the multiplexed bridge arm control method disclosed in application number CN121791692A) propose adjusting the switching frequency of the DC-DC circuit to match the operating frequency of the OBC circuit when the OBC start signal is received, and aligning the start time to the zero-crossing point of the AC input voltage. However, the above-mentioned existing strategies only remain at the level of macroscopic frequency synchronization and external timing coordination, and do not address the coupling mechanism inside the integrated topology.

[0004] In practical engineering applications, the aforementioned existing collaborative control strategies still have significant safety hazards and limitations. Specifically, when the system is in DC-DC operation mode, the multiplexed bridge arm is in a high-frequency switching state, and a high-voltage battery is directly connected to the OBC output side, resulting in a high-voltage DC bus on the OBC secondary side. Because existing technology lacks active intervention mechanisms for the phase shift state within the multiplexed bridge arm and a bus energy management mechanism, when the multiplexed bridge arm is in a high-frequency switching state, the high-voltage DC bus on the secondary side will generate parasitic coupling through the junction capacitance of the switching transistors, causing the primary side DC bus voltage to be "pumped up" to a high voltage close to the transformer turns ratio of the secondary side bus. At the moment of OBC startup, because the input voltage instantaneously approaches 0, the huge voltage difference between the input voltage and the primary side bus voltage will induce a resonant cavity current overshoot much greater than that in steady-state operation, which in severe cases will trigger system overcurrent protection or even directly damage power devices. Therefore, existing technology cannot mitigate the electrical surge risk generated during startup of the integrated topology under specific operating conditions. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a control method, device, and vehicle power supply system for starting the vehicle's on-board power supply (OBC).

[0006] Firstly, the control method for starting the on-board power supply (OBC) provided in this application adopts the following technical solution: A control method for starting an on-board power supply (OBC) is disclosed. In the OBC, the first bridge arm of the OBC secondary side is multiplexed with the primary bridge arm of the DC-DC converter to form a shared bridge arm. The second bridge arm of the OBC secondary side is a non-shared bridge arm. When the DC-DC converter is in operation and receives an OBC start command, the following steps are executed: S1, increasing the switching frequency of the DC-DC converter from a first switching frequency to a second switching frequency, the second switching frequency being consistent with the operating frequency of the OBC; S2, activating the non-shared bridge arm and controlling the non-shared bridge arm to... The phase shift angle between the shared bridge arms is 0°, making the equivalent output voltage of the secondary side of the OBC zero, thereby blocking the coupling path from the secondary high-voltage DC bus to the primary side; S3, the state of the phase shift angle being 0° is maintained for a first preset time, so that the charge accumulated on the primary side DC bus capacitor due to parasitic coupling is discharged through the body diode of the primary side switch until the primary side DC bus voltage drops below the safe voltage threshold; S4, after the primary side DC bus voltage is lower than the safe voltage threshold, the soft start process of the OBC is executed at the zero crossing point of the AC input voltage.

[0007] By adopting the above technical solution, this application does not directly jump to conventional phase-shifted power transmission control after receiving the OBC start command. Instead, it innovatively inserts a buffer stage of "zero phase-shift blocking and energy discharge". By controlling the phase shift angle to 0° to make the equivalent output voltage zero, the parasitic coupling path from the secondary high-voltage DC bus to the primary side is blocked from a physical mechanism. At the same time, the primary-side switching diode is used for charge discharge, and soft start is performed under the dual conditions of AC zero crossing and bus voltage safety threshold. This reduces the risk of resonant cavity current overshoot caused by the huge voltage difference between the input voltage and the primary DC bus at the moment of OBC start-up, and improves the safety and stability of the integrated topology under complex operating conditions.

[0008] Optionally, the first switching frequency is 70kHz to 90kHz, and the second switching frequency is 140kHz to 160kHz; during the frequency boosting process in step S1, the shared bridge arm maintains 50% complementary duty cycle modulation.

[0009] By adopting the above technical solution, the specific parameter range of frequency switching is clarified, and the 50% complementary duty cycle modulation of the shared bridge arm is maintained during the frequency increase process, which helps to maintain the output stability of the DC-DC converter during the frequency switching transition and reduce system disturbances caused by sudden changes in modulation mode.

[0010] Optionally, in step S2, controlling the phase shift angle to 0° specifically includes: controlling the non-shared bridge arm and the shared bridge arm to output high-frequency square waves in phase, so that the voltage difference across the secondary winding of the OBC is zero, thereby blocking the LC resonant coupling of the secondary high-voltage DC bus to the primary side through the junction capacitance of the switching transistor.

[0011] By adopting the above technical solution, the non-shared bridge arm and the shared bridge arm are kept in phase and driven at high frequency, which can make the voltage difference across the secondary winding of the OBC zero. This eliminates the condition for the secondary high-voltage DC bus to excite LC resonance to the primary side through the junction capacitance of the switching transistor, thereby blocking the parasitic coupling path from the secondary high voltage to the primary bus, preventing abnormal voltage rise of the primary bus, and further improving the voltage stability and current controllability of the OBC startup process.

[0012] Optionally, the safety voltage threshold is 40V to 80V; the capacitance of the primary DC bus capacitor is 1μF to 5μF.

[0013] By limiting the safe voltage threshold to the range of 40V to 80V, it is ensured that the primary-side DC bus voltage drops to the safe operating range before OBC soft start, preventing excessive stress on devices due to excessive bus voltage during startup. Simultaneously, limiting the primary-side DC bus capacitance value to a relatively small range of 1μF to 5μF allows the accumulated charge on the bus capacitor to be fully discharged in a short time via the body diode of the primary-side switch, improving the response speed and reliability of startup control.

[0014] Optionally, the first preset time is 5s to 15s.

[0015] By adopting the above technical solution, the duration of bus capacitor charge discharge is limited to the range of 5s to 15s. This ensures that the accumulated charge from parasitic coupling is fully discharged, while avoiding excessive discharge time that could lead to delayed OBC startup response. This achieves a better balance between safety and rapid response in the startup control process.

[0016] Optionally, the OBC adopts a unipolar full-bridge topology or a unipolar matrix converter topology; the phase-shifting control is performed using the shared bridge arm as a fixed reference bridge arm.

[0017] By adopting the above technical solutions, the startup control method can be compatible with both unipolar full-bridge topology and unipolar matrix converter topology, thereby improving the applicability and versatility of the solution. At the same time, using a shared bridge arm as a fixed reference bridge arm for phase shift control can ensure that phase shift within the secondary bridge and phase shift between bridges have a unified phase reference, thereby improving the consistency and stability of the overall control timing under the multiplexed topology.

[0018] Secondly, the on-board power supply system provided in this application adopts the following technical solution: An on-board power supply system includes an OBC circuit and a DC-DC converter, wherein the OBC circuit and the DC-DC converter adopt an integrated architecture with bridge arm multiplexing; the secondary side of the OBC has a first bridge arm and a second bridge arm, wherein the first bridge arm is multiplexed with the primary side bridge arm of the DC-DC converter to form a shared bridge arm, and the second bridge arm is a non-shared bridge arm of the OBC secondary side; the DC bus of the OBC primary side is provided with a DC bus capacitor; the system further includes a controller, the controller being configured to execute the on-board power supply OBC startup control method as described in any of the first aspects.

[0019] By adopting the above technical solutions, an on-board integrated power supply hardware architecture that reuses the OBC circuit and DC-DC converter bridge arm is constructed. By setting up shared and non-shared bridge arms and configuring appropriate DC bus capacitors, complete hardware support is provided for achieving safe and low-impact OBC start-up control. The controller can execute the aforementioned start-up control method to suppress parasitic coupling from the secondary high voltage to the primary side and bus voltage pumping, thereby improving the system's start-up reliability and operational safety.

[0020] Optionally, the capacitance of the primary DC bus capacitor is 1μF to 5μF; the body diode of the switching transistor in the primary bridge arm of the OBC constitutes the charge discharge circuit of the primary DC bus capacitor.

[0021] By adopting the above technical solution, the primary DC bus capacitor is limited to a small capacitance range, which ensures that the accumulated charge on the bus capacitor can be discharged in a short time. At the same time, the body diode of the OBC primary-side switch is used to form a dedicated discharge circuit, eliminating the need for additional discharge devices, simplifying the hardware structure and improving the reliability and efficiency of the discharge process.

[0022] Thirdly, the control device for starting the vehicle power supply (OBC) provided in this application adopts the following technical solution: A control device for starting an on-board power supply (OBC) includes: a frequency switching unit for increasing the switching frequency to a second switching frequency consistent with the OBC operating frequency when the DC-DC converter is running and an OBC start command is received; a zero-phase-shift control unit for controlling the phase shift angle between the non-shared bridge arm and the shared bridge arm on the OBC secondary side to be 0°, so that the equivalent output voltage on the OBC secondary side is zero; a voltage monitoring and discharge management unit for monitoring the primary side DC bus voltage during a first preset time period while maintaining the phase shift angle at 0°; and a zero-crossing start unit for triggering the OBC soft-start process at the zero-crossing point of the AC input voltage when the primary side DC bus voltage drops below a safe voltage threshold.

[0023] By adopting the above technical solution, and utilizing the coordinated operation of functional units such as frequency switching, zero-phase shift control, voltage monitoring and zero-crossing start, low-impact start control of OBC is achieved under DC-DC operation. This blocks the coupling path from the secondary high voltage to the primary side, ensuring the bus voltage is safe before performing soft start, thus reducing start-up impact and device stress.

[0024] Optionally, the OBC is a unipolar OBC topology, which includes a unipolar full-bridge topology or a unipolar matrix converter topology; the shared bridge arm is a phase-shift controlled reference bridge arm.

[0025] By adopting the above technical solutions, the control device can be compatible with both unipolar full-bridge topology and unipolar matrix converter topology, expanding the applicable scenarios and versatility of the device; at the same time, using a shared bridge arm as a fixed reference bridge arm for phase shift control ensures uniform phase shift timing and stable control logic, improving the consistency and robustness of start-up control under different topologies.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. This application solves the problems of bus voltage surge and excessive resonant current in the reused topology by using zero phase shift control to block parasitic coupling from the secondary side high voltage to the primary side before OBC startup and actively discharging the bus capacitor, thereby reducing startup impact and device stress. 2. This application achieves an optimal balance between safety, response speed, and control stability in startup control by reasonably configuring key parameters such as discharge time, safety voltage, and bus capacitance, making it applicable to a wider range of working conditions; 3. The system and device provided in this application are compatible with unipolar full-bridge and unipolar matrix converter topologies, have strong versatility, require little hardware modification, and can be directly applied to existing automotive integrated power supply products, thus possessing high practicality and engineering value. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the vehicle power system provided in the embodiments of this application; Figure 2 This invention provides an embodiment of another vehicle power system with respect to the OBC circuit and DC-DC converter. Figure 3 This is a flowchart of the control method for starting the vehicle power supply OBC provided in the embodiments of this application; Figure 4 This is a timing flowchart of the OBC startup control strategy provided in the embodiments of this application; Figure 5 This is a block diagram of a control device for starting an on-board power supply (OBC) according to an embodiment of this application.

[0028] Explanation of reference numerals in the attached figures: 10. OBC circuit; 20. DC-DC converter; 30. Controller. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1-5 This application will be described in further detail.

[0030] It should be noted that, in the description of this application, "primary side" refers to the side of the OBC circuit connected to the AC mains side, and "secondary side" refers to the side of the OBC circuit connected to the high-voltage battery side. "Shared bridge arm" refers to the bridge arm formed by multiplexing the first bridge arm of the OBC secondary side with the primary side bridge arm of the DC-DC converter, and "non-shared bridge arm" refers to the second bridge arm of the OBC secondary side that does not participate in bridge arm multiplexing. "Phase shift angle" refers to the phase offset of the drive signal of the non-shared bridge arm relative to the drive signal of the shared bridge arm. "Zero crossing point" refers to the moment when the instantaneous value of the AC input voltage crosses zero when it crosses from the positive half-cycle to the negative half-cycle or from the negative half-cycle to the positive half-cycle.

[0031] With the increasing power density requirements of new energy vehicles, the bridge arm multiplexing integrated architecture of OBC and DC-DC converter has become the mainstream technology direction for vehicle power systems. In this integrated architecture, the first bridge arm of the OBC secondary side and the primary bridge arm of the DC-DC converter share the same set of power switches, realizing the functions of the two converters through time-division multiplexing or cooperative control. Although this architecture reduces the number of power devices, lowers system costs, and increases power density, it also introduces a key engineering challenge: how to safely start the OBC when the system is in DC-DC standalone operation mode.

[0032] Specifically, in the standalone operation mode of the DC-DC converter, the shared bridge arm is in a high-frequency switching state to maintain the normal output of the DC-DC converter. At this time, the secondary side of the OBC is directly connected to a high-voltage battery (typically 200V to 800V), and a high voltage is always present on the secondary high-voltage DC bus. Although the OBC has not yet started, due to the inherent junction capacitance (parasitic capacitance) of the switching transistor, the secondary high-voltage DC bus will be parasiticly coupled to the high-frequency switching action of the shared bridge arm through these junction capacitances. During each switching cycle, the charging and discharging process of the junction capacitance will couple the high-voltage energy of the secondary side to the primary side through the transformer, causing the primary DC bus capacitor to gradually accumulate charge, thus gradually "pumping" the primary DC bus voltage to a high voltage level close to the transformer turns ratio of the secondary bus.

[0033] When the controller receives the OBC start command, if the non-shared bridge arm is directly activated and normal phase-shifted power transfer control is applied, the high voltage accumulated on the primary DC bus capacitor will be superimposed on the AC input voltage, causing a severe voltage surge. This voltage surge generates a current overshoot much greater than the steady-state operating value through the LC resonant network composed of the resonant inductor and transformer. In severe cases, it can trigger the system overcurrent protection or even directly damage power devices due to overstress. Although existing technologies have proposed strategies for frequency synchronization and zero-crossing start-up, they have not solved the problem of primary bus voltage surge at the level of parasitic coupling physical mechanisms, nor have they provided means to actively manage bus energy before OBC start-up. Therefore, significant start-up impact risks still exist in practical engineering applications.

[0034] To address the aforementioned issues, this application provides a control method, device, and vehicle power supply system for starting an on-board power supply (OBC). By inserting a buffer phase of "zero-phase-shift blocking and energy discharge" before the OBC is officially started, the parasitic coupling path from the secondary high voltage to the primary side is eliminated from a physical mechanism perspective. The accumulated charge on the primary bus capacitor is actively discharged. After confirming that the bus voltage has dropped to a safe range, soft start is performed in conjunction with the AC zero-crossing point, thereby suppressing the risk of voltage overshoot and current surge at the moment of startup.

[0035] Reference Figure 1 , Figure 1 A schematic diagram of an on-board power system provided in an embodiment of this application is shown. The on-board power system includes an OBC circuit 10 and a DC-DC converter 20, wherein the OBC circuit 10 and the DC-DC converter 20 adopt an integrated architecture with bridge arm multiplexing.

[0036] Specifically, the vehicle power system includes the following components: The primary-side circuit of the OBC is connected to the AC grid side and includes an EMI filter, a rectifier bridge or PFC power factor correction circuit, a primary-side full-bridge (or half-bridge) inverter, and a resonant network. A DC bus capacitor Cbus is provided on the DC bus of the OBC primary side. This DC bus capacitor Cbus is used for energy storage, filtering, and maintaining bus voltage stability. In this embodiment, the capacitance value of the primary-side DC bus capacitor Cbus is 1μF to 5μF, preferably 3μF.

[0037] It's understandable that the primary-side DC bus capacitor Cbus has a relatively small capacitance value (1μF~5μF) because in the bridge arm multiplexing integrated architecture, the amount of charge accumulated on this capacitor due to parasitic coupling is proportional to its capacitance value. A smaller capacitance value means that under the same parasitic coupling conditions, the total amount of charge accumulated on the capacitor is smaller, and the time required for subsequent discharge through the body diode is correspondingly shorter. If the capacitance value is too large, it will not only increase the discharge time but also release more stored energy at the moment of OBC startup, exacerbating the current overshoot.

[0038] Isolation transformer T1 serves as an electrical isolation and energy transfer bridge between the primary and secondary sides of the OBC. The primary winding of transformer T1 is connected to the output terminal of the OBC primary inverter, and the secondary winding is connected to the full-bridge rectifier / inverter circuit of the OBC secondary side.

[0039] The OBC secondary circuit is connected to the high-voltage battery side. The OBC secondary side has a first bridge arm (H7 and H8) and a second bridge arm (H5 and H6), each bridge arm consisting of two power switching transistors (usually MOSFETs) connected in series. The first bridge arm is multiplexed with the primary bridge arm of the DC-DC converter 20, forming a shared bridge arm. The second bridge arm is a non-shared bridge arm of the OBC secondary side and is only used when the OBC is operating.

[0040] The DC-DC converter 20 has a primary side bridge arm that is a common bridge arm (H7 and H8), and a secondary side connected to a low-voltage battery (a small battery, typically a 12V or 48V system) via transformer T2. The DC-DC converter 20 is used to convert the energy of the high-voltage battery into the voltage required by the low-voltage battery to power the low-voltage electrical appliances of the vehicle.

[0041] The controller 30 is connected to the drive terminals of the power switches of the OBC circuit 10 and the DC-DC converter 20, and is used to generate PWM drive signals for each bridge arm and execute the OBC startup control method of this application. The controller 30 integrates a signal acquisition and processing module to acquire real-time sampled values ​​of the primary DC bus voltage and AC input voltage, providing a data basis for frequency switching, voltage threshold judgment, and zero-crossing detection. The controller 30 can be selected from one or a combination of a DSP digital signal processor, an MCU microcontroller, or an FPGA.

[0042] It should be noted that in this embodiment, the OBC adopts a single-pole full-bridge topology. (Refer to...) Figure 1 The first bridge arm (shared bridge arm) and the second bridge arm (non-shared bridge arm) of the OBC secondary side constitute the secondary side full bridge. The shared bridge arm includes the upper tube H7 and the lower tube H8, and the non-shared bridge arm includes the upper tube H5 and the lower tube H6. The midpoints of the shared bridge arm and the non-shared bridge arm are respectively connected to the two ends of the secondary winding of transformer T1. In the DC-DC independent operation mode, the shared bridge arms (H7 and H8) perform high-frequency switching operation with a 50% complementary duty cycle, while the non-shared bridge arms (H5 and H6) are in the off state.

[0043] Reference Figure 2 , Figure 2 This illustration shows a schematic diagram of the architecture of another on-board power system provided in this application, regarding the OBC circuit 10 and the DC-DC converter 20. In this embodiment, the OBC adopts a unipolar matrix converter topology. Figure 1Unlike the unipolar full-bridge topology, the matrix converter topology uses a matrix switch array on the primary side of the OBC to directly achieve AC-AC conversion, eliminating the need for a rectifier bridge and a large-capacity DC bus capacitor. Although the unipolar matrix converter topology does not require a large-capacity DC bus energy storage capacitor on the primary side of the OBC, the DC side still has switch junction capacitance, PCB parasitic capacitance, and a small-capacity high-frequency buffer capacitor. During DCDC operation, the secondary high voltage will still couple to the primary side through parasitic paths, causing voltage pumping. Therefore, the zero-phase-shift blocking and charge discharge measures of this application are also required to ensure OBC startup safety. The bridge arm structure and multiplexing method of the secondary side are the same as those of the unipolar full-bridge topology. Specifically, the OBC secondary side still has a first bridge arm (shared bridge arm) and a second bridge arm (non-shared bridge arm), and the first bridge arm is multiplexed with the primary side bridge arm of the DCDC converter 20. The startup control method of this application is applicable to both topologies; the only difference is the power conversion method on the primary side of the OBC, while the bridge arm multiplexing architecture and startup control logic on the secondary side remain consistent.

[0044] It is understandable that, regardless of whether a unipolar full-bridge topology or a unipolar matrix converter topology is used, the shared bridge arm is used as the fixed reference bridge arm when performing the phase shift control of this application. This is because the shared bridge arm also undertakes the power transmission task of the DC-DC converter 20, and its drive signal needs to remain continuous and stable, so it is not advisable to adjust its phase during the OBC startup process. By using the shared bridge arm as the reference and only adjusting the phase of the drive signal of the non-shared bridge arm, the OBC startup control can be completed without interfering with the normal operation of the DC-DC converter, ensuring the coordinated stability of the two converters during the transition period.

[0045] In one embodiment, the body diodes of the switching transistors (H1-H4) in the primary-side bridge arm of the OBC constitute the charge discharge circuit for the primary-side DC bus capacitor. Specifically, the inherent body diodes (parasitic diodes) of the MOSFET power switching transistors can form a passive discharge path under certain conditions. When zero-phase-shift control is executed to block new parasitic coupling, the high voltage accumulated on the primary-side DC bus capacitor Cbus cannot be maintained. The charge flows back to the AC side circuit through the body diodes of the primary-side switching transistors (H1-H4) and the resonant inductor, and is gradually dissipated as heat in the equivalent resistance of the circuit, causing the voltage on the bus capacitor to decrease exponentially. This discharge circuit does not require additional discharge resistors or active discharge circuits; it directly utilizes the inherent characteristics of the primary-side power switching transistors and the resonant network, simplifying the hardware structure.

[0046] Reference Figure 3 , Figure 3A flowchart of the control method for starting the on-board power supply (OBC) according to an embodiment of this application is shown. This application discloses a control method for starting the on-board power supply (OBC), applied to the aforementioned on-board power supply system. In this on-board power supply, the first bridge arm of the OBC secondary side is multiplexed with the primary side bridge arm of the DC-DC converter 20 to form a shared bridge arm, while the second bridge arm of the OBC secondary side is a non-shared bridge arm. When the DC-DC converter 20 is in operation and receives an OBC start command, the following steps are executed: Step S1: Increase the switching frequency of the DC-DC converter 20 from the first switching frequency to the second switching frequency, which is consistent with the operating frequency of the OBC.

[0047] Specifically, in the DC-DC converter's standalone operation mode, the common bridge arm of the DC-DC converter 20 performs high-frequency switching at a first switching frequency. In one embodiment, the first switching frequency is 70kHz to 90kHz, preferably 80kHz. This frequency represents the optimal efficiency frequency of the DC-DC converter 20 under normal operating conditions, achieving a better balance between switching losses and magnetic component losses.

[0048] When the controller 30 receives the OBC start command, it first increases the switching frequency of the common bridge arm from the first switching frequency to the second switching frequency. In one embodiment, the second switching frequency is 140kHz to 160kHz, preferably 150kHz. This frequency is consistent with the switching frequency during normal OBC operation and is the optimal operating point of the OBC resonant network.

[0049] Understandably, the frequency ramp-up step is a prerequisite for subsequent OBC startup control. Since the shared bridge arm serves both the DC-DC converter and the OBC, the switching frequency of the shared bridge arm must be unified to the OBC's operating frequency before OBC startup to avoid resonant detuning and efficiency degradation caused by frequency mismatch. If frequency switching occurs after the non-shared bridge arm is turned on, the transient state during the frequency transition will be superimposed on the transient state during OBC startup, exacerbating system instability.

[0050] It should be noted that during the frequency increase process in step S1, the shared bridge arm maintains a 50% complementary duty cycle modulation. That is, the upper transistor H7 and the lower transistor H8 of the shared bridge arm always conduct alternately in a complementary manner, with each transistor's conduction time accounting for 50% of the entire switching cycle (excluding dead time). There is no simultaneous conduction between the upper and lower transistors. The reason for maintaining the 50% complementary duty cycle modulation is that this modulation method is the standard operating mode of resonant converters (such as LLC resonant converters). Maintaining this modulation method during frequency switching ensures a smooth transition of the output voltage and current waveforms of the DC-DC converter 20, preventing additional voltage ripple or current surges due to sudden changes in duty cycle.

[0051] In a preferred embodiment, the frequency ramp-up process is performed gradually, meaning the switching frequency increases linearly or piecewise from the first switching frequency to the second switching frequency, rather than a one-step jump. Gradual frequency ramp-up further reduces the transient oscillation amplitude of the resonant network during frequency switching. In another embodiment, when the system has high requirements for switching speed, a direct jump method can also be used, switching the frequency from the first switching frequency to the second switching frequency within one switching cycle. Although the direct jump method has slightly larger transient oscillations, the switching time is extremely short, making it suitable for applications with strict requirements for startup speed.

[0052] Step S2: Activate the non-shared bridge arm and control the phase shift angle between the non-shared bridge arm and the shared bridge arm to 0°, so that the equivalent output voltage of the OBC secondary side is zero, thereby blocking the coupling path from the secondary side high voltage DC bus to the primary side.

[0053] Specifically, after the switching frequency of the shared bridge arm has been increased to the second switching frequency, the controller 30 activates the drive signal of the non-shared bridge arm, causing the upper transistor H5 and lower transistor H6 of the non-shared bridge arm to begin 50% complementary duty cycle modulation at the second switching frequency. Simultaneously, the controller 30 controls the phase shift angle between the drive signal of the non-shared bridge arm and the drive signal of the shared bridge arm to be 0°.

[0054] It is understandable that controlling the phase shift angle to 0° physically means controlling the output of a high-frequency square wave that is in phase with the output of the non-shared bridge arm and the shared bridge arm. That is, at any given moment, when the upper transistor H7 of the shared bridge arm is turned on, the upper transistor H5 of the non-shared bridge arm is also turned on simultaneously; when the lower transistor H8 of the shared bridge arm is turned on, the lower transistor H6 of the non-shared bridge arm is also turned on simultaneously. Since the two ends of the secondary winding of transformer T1 are connected to the midpoints of the non-shared bridge arm and the shared bridge arm respectively, when the voltage at the midpoints of the two bridge arms is the same at any given moment, the voltage difference across the secondary winding is always zero.

[0055] The zero voltage difference across the secondary winding T1 means that the equivalent output voltage of the OBC secondary side is zero, and no power is transferred to the transformer primary side. More importantly, this zero voltage difference state physically blocks the LC resonant coupling caused by the secondary high-voltage DC bus to the primary side through the junction capacitance of the switching transistor.

[0056] It should be noted that the mechanism of the parasitic coupling described above is as follows: When the DC-DC converter is operating independently and the non-shared bridge arm is off, although the switching transistors H5 and H6 of the non-shared bridge arm are in the off state, their parasitic junction capacitances still exist. The voltage on the secondary high-voltage DC bus forms an LC resonant circuit through the junction capacitances of H5 and H6, the secondary winding of transformer T1, and the resonant inductor. Whenever the shared bridge arm switches, this LC resonant circuit is excited, generating an oscillating current that couples the high-voltage energy from the secondary side to the primary side, causing the voltage on the primary side DC bus capacitor Cbus to be gradually pumped up.

[0057] Step S3: Maintain the phase shift angle at 0° for a first preset time, so that the charge accumulated on the primary DC bus capacitor due to parasitic coupling is discharged through the body diode of the primary switch until the primary DC bus voltage drops below the safe voltage threshold.

[0058] Specifically, after step S2 is completed, the controller 30 continues to maintain a 0° phase shift angle between the non-shared bridge arm and the shared bridge arm for a first preset time. In one embodiment, the first preset time is 5s to 15s, preferably 10s.

[0059] Understandably, under the condition of maintaining a 0° phase shift angle, the parasitic coupling path from the secondary high voltage of the OBC to the primary side is blocked, and no new charge is injected into the primary side DC bus capacitor Cbus. Simultaneously, the charge accumulated on the primary side DC bus capacitor Cbus is gradually released through the discharge circuit formed by the body diode of the primary side switch. The body diode discharge process is an RC decay process; the bus voltage decreases exponentially, and the decay time constant depends on the capacitance of the bus capacitor and the equivalent resistance of the body diode circuit.

[0060] In one embodiment, the safe voltage threshold is 40V to 80V, preferably 60V. This safe voltage threshold is set based on the following: when the primary DC bus voltage is lower than this threshold, even if a transient overshoot occurs during OBC soft-start, the superimposed peak voltage will still be within the safe operating area (SOA) of the power device and will not cause overstress damage to the device. The specific value of the safe voltage threshold needs to be determined through comprehensive calculation based on the withstand voltage specifications of the power device used, the quality factor of the resonant network, and the maximum overshoot ratio that may occur during soft-start.

[0061] It should be noted that the specific value of the first preset time is related to the capacitance of the primary DC bus capacitor Cbus, the equivalent resistance of the discharge circuit, and the safety voltage threshold. When the capacitance of Cbus is 1μF to 5μF, in conjunction with the body diode discharge circuit, a first preset time of 5s to 15s can ensure that the bus voltage drops from the high voltage after parasitic coupling pump-up (which may be close to the secondary battery voltage) to below the safety voltage threshold. If the capacitance of Cbus is selected as a smaller value (e.g., 1μF), the discharge time can be shorter (e.g., 5s); if the capacitance of Cbus is selected as a larger value (e.g., 5μF), the discharge time should be longer (e.g., 15s) to ensure that the charge is fully discharged.

[0062] In one embodiment, while maintaining a 0° phase shift angle, the controller 30 monitors the primary DC bus voltage in real time via a voltage sampling circuit. When the primary DC bus voltage is detected to have dropped below the safe voltage threshold, the controller 30 can proceed to step S4 even before the upper limit of the first preset time has been reached. This method combines time and voltage conditions, prioritizing voltage conditions and supplementing them with time conditions, thus balancing safety and startup response speed. In another embodiment, the controller 30 can also use only the first preset time as the sole criterion for the discharge phase, directly proceeding to step S4 after the first preset time has been reached. This method has simple control logic and is suitable for applications with lower requirements for bus voltage sampling accuracy.

[0063] Step S4: After the primary DC bus voltage is lower than the safe voltage threshold, execute the OBC soft start procedure at the zero crossing point of the AC input voltage.

[0064] Specifically, once the controller 30 confirms that the primary DC bus voltage is below the safe voltage threshold, the controller 30 begins to detect the zero-crossing point of the AC input voltage. Upon detecting the next zero-crossing point, the controller 30 initiates the OBC soft-start procedure.

[0065] Understandably, the reason for choosing to perform OBC soft-start at the zero-crossing point of the AC input voltage is as follows: At the zero-crossing point, the instantaneous value of the AC input voltage is zero or close to zero, at which point the voltage excitation applied to the primary side of the OBC is minimal. If the OBC is started near the peak value of the AC voltage, the sudden high-voltage excitation applied to the primary side will generate a large transient current surge through the resonant network; while when starting at the zero-crossing point, the voltage excitation on the primary side of the OBC gradually increases from zero, and the current in the resonant network can build up smoothly as the voltage increases, minimizing the transient overshoot amplitude.

[0066] It should be noted that the OBC soft-start process refers to the transition process of the OBC gradually increasing from zero power output to rated power output. During the soft-start process, the controller 30 gradually increases the phase shift angle between the non-shared bridge arm and the shared bridge arm (starting from 0° and gradually increasing to the target operating phase shift angle), so that the equivalent output voltage on the secondary side of the OBC gradually increases from zero to the normal operating voltage, achieving a smooth power build-up. The duration of the soft-start is determined according to the system's power level and load characteristics, typically ranging from 100ms to 500ms.

[0067] Reference Figure 4 , Figure 4 The following is a timing flowchart of the OBC startup control strategy provided in an embodiment of this application. This flowchart is applicable to the startup control process after receiving the OBC power-on command when the DC-DC converter is in normal operation. The specific steps are as follows: First, during normal operation of the DC-DC converter, the controller 30 receives the OBC power-on command. Then, the controller 30 controls the switching frequency (common arm switch) of the DC-DC converter to increase from the original 80kHz to 150kHz, ensuring that the switching frequency of the DC-DC converter is consistent with the operating frequency of the OBC. After the frequency adjustment is complete, the non-common arm on the secondary side of the OBC is turned on, and the phase angle between the non-common arm and the common arm is controlled to be 0°, while all switches on the primary side of the OBC remain in the off state. This state is maintained for 10 seconds to provide discharge time for the primary bus capacitor. Finally, after the primary bus capacitor has completely discharged, the OBC soft-start process is executed normally.

[0068] The implementation principle of the control method for starting an on-board power supply (OBC) in this application embodiment is as follows: After receiving the OBC start command while the DC-DC converter 20 is running, the controller 30 does not directly put the OBC into normal power transmission state. Instead, it first performs frequency unification (step S1), then blocks the parasitic coupling path through zero-phase shift control (step S2), and then uses the body diode to discharge the accumulated charge on the bus capacitor to a safe voltage (step S3). Finally, at the AC zero-crossing point, the OBC is smoothly put into operation in a soft-start manner (step S4). These four steps constitute a complete "frequency synchronization - coupling blocking - energy discharge - safe start" control sequence, which systematically improves the problems of bus voltage pumping and resonant current overshoot faced by the bridge arm multiplexed integrated topology at the moment of OBC start-up from both timing arrangement and physical mechanism levels.

[0069] In one embodiment, the execution process of the above control method is described using a specific operating scenario. Assume the DC-DC converter 20 is operating normally at a first switching frequency of 80kHz, the high-voltage battery voltage is 400V, and the primary-side DC bus capacitor Cbus has a capacitance of 2μF. Due to parasitic coupling effects, the primary-side DC bus voltage is pumped up to approximately 350V.

[0070] When controller 30 receives the OBC start command: (1) Execute step S1 to increase the switching frequency of the common bridge arm from 80kHz to 150kHz, maintain 50% complementary duty cycle modulation of the common bridge arm, and keep the output voltage of the DC-DC stable. (2) Execute step S2 to open the non-common bridge arm and control the phase shift angle between it and the common bridge arm to be 0°. At this time, the voltage difference between the two ends of the secondary winding of OBC is zero, the parasitic coupling path is blocked, and the DC bus voltage of the primary side stops rising; (3) Execute step S3 to maintain the 0° phase shift angle. The accumulated voltage of 350V on the primary side DC bus capacitor Cbus begins to discharge through the body diode of the primary side switch. After about 8 seconds, the controller 30 detects that the primary side DC bus voltage has dropped to 55V, which is lower than the safe voltage threshold of 60V; (4) After executing step S4, the controller 30 detects the next zero-crossing point of the AC input voltage and begins the OBC soft-start process. The phase shift angle between the non-shared bridge arm and the shared bridge arm starts from 0° and gradually increases at a rate of 2° to 5° per power frequency cycle until the target operating phase shift angle is reached. The output power of the OBC is established smoothly, and there is no obvious voltage overshoot or current surge during the entire startup process.

[0071] Reference Figure 5 , Figure 5 A block diagram of a control device for starting an on-board computer (OBC) according to an embodiment of this application is shown. The control device includes: The frequency switching unit is used to increase the switching frequency to a second switching frequency that is consistent with the OBC operating frequency when the DC-DC converter 20 is running and receives the OBC start command.

[0072] Specifically, the frequency switching unit receives the OBC start command signal and, after confirming that the DC-DC converter 20 is in normal operating condition, generates a frequency control command to control the PWM generation module of the shared bridge arm to increase the switching frequency from the first switching frequency to the second switching frequency. The frequency switching unit can be internally configured with a frequency gradient algorithm module to achieve a linear or piecewise smooth transition of the switching frequency, reducing transient oscillations during frequency switching.

[0073] The zero-phase-shift control unit is used to control the phase shift angle between the non-common bridge arm and the common bridge arm on the secondary side of the OBC to be 0°, so that the equivalent output voltage on the secondary side of the OBC is zero.

[0074] Specifically, the zero-phase-shift control unit is triggered after the frequency switching unit completes the frequency boost. It outputs a drive signal to the gate drive circuits of each switch in the non-shared bridge arm, enabling the non-shared bridge arm to operate in complete phase with the shared bridge arm. The zero-phase-shift control unit ensures precise alignment of the rising edge of the non-shared bridge arm drive signal with the rising edge of the shared bridge arm drive signal through a phase-locked loop or direct digital synchronization, with the phase deviation controlled within ±1°.

[0075] The voltage monitoring and discharge management unit is used to monitor the primary DC bus voltage for a first preset time while maintaining a phase shift angle of 0°.

[0076] Specifically, the voltage monitoring and discharge management unit includes a voltage sampling submodule and a judgment logic submodule. The voltage sampling submodule acquires the real-time sampled value of the primary DC bus voltage through the signal acquisition and processing module inside the controller 30, with a sampling period that can be set from 100μs to 1ms. The judgment logic submodule compares the acquired bus voltage value with a preset safe voltage threshold. When the bus voltage drops below the safe voltage threshold, the voltage monitoring and discharge management unit outputs a "discharge complete" signal to the zero-crossing start unit. Simultaneously, the voltage monitoring and discharge management unit has a built-in timer to measure a first preset time. When the timer expires and the bus voltage has not yet dropped below the safe threshold, the voltage monitoring and discharge management unit can output an alarm signal, indicating that there is an abnormality in the discharge circuit of the system.

[0077] The zero-crossing start unit is used to trigger the OBC soft-start process at the zero-crossing point of the AC input voltage when the primary DC bus voltage drops below the safe voltage threshold.

[0078] Specifically, after receiving the "discharge complete" signal from the voltage monitoring and discharge management unit, the zero-crossing start-up unit continuously detects the zero-crossing point of the AC input voltage through the signal acquisition and processing module inside the controller 30. The zero-crossing start-up unit has an internal zero-crossing detection circuit, which accurately captures the zero-crossing moment by sampling the AC voltage and then using a comparator. After detecting the zero-crossing moment, the zero-crossing start-up unit triggers the OBC soft-start control program. This program controls the phase shift angle between the non-shared bridge arm and the shared bridge arm to gradually increase from 0° at a preset slope, completing a smooth transition of the OBC from zero power to rated power.

[0079] It is understood that the functional units in the aforementioned control device can be implemented in the processor of the controller 30 as software modules, or as hardware logic circuits (such as FPGA logic modules), or as a combination of software and hardware. The functional units communicate and coordinate with each other through internal data buses or signal lines.

[0080] It should be noted that the control device described in this application can also be integrated into the controller 30 of the above-mentioned vehicle power system. In one embodiment, the processor of the controller 30 runs an OBC startup control program, which includes frequency switching function, zero phase shift control function, voltage monitoring and discharge management function, and zero-crossing start function, respectively corresponding to the functional implementation of the above four functional units.

[0081] In one embodiment, the OBC is a unipolar OBC topology, which includes a unipolar full-bridge topology or a unipolar matrix converter topology. The shared bridge arm is the reference bridge arm for phase-shift control.

[0082] Understandably, in a unipolar full-bridge topology, the two arms of the OBC secondary side, together with the transformer secondary winding, form a full-bridge inverter or rectifier structure, achieving power regulation through phase shifting within the bridge. In a unipolar matrix converter topology, the OBC primary side uses a matrix switch array, while the secondary side structure is the same as the full-bridge topology. Under both topologies, the control device in this application uses a shared arm as the fixed reference arm for phase shift control, adjusting only the phase of the non-shared arm. This unified control reference allows the control device to adapt seamlessly to both topologies, improving its versatility.

[0083] It should be noted that the parameter ranges defined in this application are all determined based on the actual engineering constraints and device characteristics of the vehicle power system, and have clear engineering significance: Regarding the switching frequency parameters, the first switching frequency of 70kHz to 90kHz is the typical operating frequency range of the DC-DC converter 20. Within this frequency range, the DC-DC converter 20 can achieve a better trade-off between the size of the magnetic components and the switching losses. The second switching frequency of 140kHz to 160kHz is the typical operating frequency range of the OBC resonant converter. This frequency range matches the resonant frequency of the OBC resonant network, which can achieve better soft-switching effect and conversion efficiency.

[0084] Regarding the safe voltage threshold parameter, the range of 40V to 80V was determined after comprehensively considering the voltage tolerance margin of mainstream automotive power MOSFETs (typically 650V or 1200V), the transient overshoot factor of the resonant network during OBC soft-start (typically 1.2 to 1.5 times), and the system safety margin. Starting the OBC within this voltage range ensures that even with the superimposed startup transient overshoot, the total voltage can still be controlled within the device's safe operating area.

[0085] Regarding the first preset time parameter, the range of 5s to 15s is determined based on the typical capacitance value of the primary DC bus capacitor (1μF to 5μF), the equivalent resistance of the body diode discharge circuit, and the RC time constant required for the voltage to decay from the maximum pump-up voltage to the safe voltage threshold. This time range ensures that even under the most unfavorable conditions (maximum capacitance, highest pump-up voltage), the charge on the bus capacitor can be fully discharged to a safe level.

[0086] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A control method of an OBC startup of an on-vehicle power supply, characterized by, The first bridge arm of the OBC secondary side in the vehicle power supply is multiplexed with the primary side bridge arm of the DC-DC converter (20) to form a shared bridge arm. The second bridge arm of the OBC secondary side is a non-shared bridge arm. When the DC-DC converter (20) is in operation and receives the OBC start command, the following steps are performed: S1. Increase the switching frequency of the DC-DC converter (20) from the first switching frequency to the second switching frequency, the second switching frequency being consistent with the operating frequency of the OBC; S2. Open the non-shared bridge arm and control the phase shift angle between the non-shared bridge arm and the shared bridge arm to 0°, so that the equivalent output voltage of the secondary side of the OBC is zero, thereby blocking the coupling path from the secondary side high voltage DC bus to the primary side. S3. Maintain the phase shift angle at 0° for a first preset time, so that the charge accumulated on the primary DC bus capacitor due to parasitic coupling is discharged through the body diode of the primary switch, until the primary DC bus voltage drops below the safe voltage threshold. S4. After the primary DC bus voltage is lower than the safety voltage threshold, the soft start procedure of the OBC is executed at the zero crossing point of the AC input voltage.

2. The control method of the vehicle-mounted power source OBC startup according to claim 1, characterized by, The first switching frequency is 70kHz to 90kHz, and the second switching frequency is 140kHz to 160kHz; during the frequency boosting process in step S1, the shared bridge arm maintains 50% complementary duty cycle modulation.

3. The control method for starting the vehicle-mounted power supply (OBC) according to claim 1, characterized in that, In step S2, controlling the phase shift angle to 0° specifically includes: controlling the non-shared bridge arm and the shared bridge arm to output high-frequency square waves in phase, so that the voltage difference across the secondary winding of the OBC is zero, thereby blocking the LC resonant coupling of the secondary high-voltage DC bus to the primary side through the junction capacitance of the switching transistor.

4. The control method of an OBC startup of a vehicle-mounted power supply according to claim 1, characterized by, The safe voltage threshold is 40V to 80V; the capacitance of the primary DC bus capacitor is 1μF to 5μF.

5. The control method of an OBC startup of a vehicle-mounted power supply according to claim 1, characterized by, The first preset time is 5s to 15s.

6. The control method of an OBC startup of a vehicle-mounted power supply according to claim 1, characterized by, The OBC adopts a unipolar full-bridge topology or a unipolar matrix converter topology; the phase shift control is performed using the shared bridge arm as a fixed reference bridge arm.

7. An on-board power supply system, comprising an OBC circuit (10) and a DC-DC converter (20), wherein the OBC circuit (10) and the DC-DC converter (20) adopt an integrated architecture with bridge arm multiplexing; characterized in that, The secondary side of the OBC has a first bridge arm and a second bridge arm. The first bridge arm is multiplexed with the primary side bridge arm of the DC-DC converter (20) to form a shared bridge arm. The second bridge arm is a non-shared bridge arm of the secondary side of the OBC. The primary side DC bus of the OBC is provided with a DC bus capacitor. The system also includes a controller (30) configured to perform the vehicle power supply OBC start-up control method as described in any one of claims 1 to 6.

8. The vehicle-mounted power supply system according to claim 7, characterized by The capacitance of the primary DC bus capacitor is 1μF to 5μF; the body diode of the switching transistor in the primary bridge arm of the OBC constitutes the charge discharge circuit of the primary DC bus capacitor.

9. A control device for an OBC startup of an in-vehicle power supply, characterized by, include: The frequency switching unit is used to increase the switching frequency to a second switching frequency that is consistent with the OBC operating frequency when the DC-DC converter (20) is running and receives the OBC start command; The zero-phase-shift control unit is used to control the phase shift angle between the non-common bridge arm and the common bridge arm on the secondary side of the OBC to be 0°, so that the equivalent output voltage on the secondary side of the OBC is zero. The voltage monitoring and discharge management unit is used to monitor the primary DC bus voltage during a first preset time period while maintaining the phase shift angle at 0°. The zero-crossing start unit is used to trigger the OBC soft-start process at the zero-crossing point of the AC input voltage when the primary DC bus voltage drops below the safe voltage threshold.

10. The OBC starting control device of claim 9, wherein The OBC is a unipolar OBC topology, which includes a unipolar full-bridge topology or a unipolar matrix converter topology; the shared bridge arm is a phase-shift controlled reference bridge arm.

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