A short-circuit protection control method and device for a three-phase resonant converter and a switching power supply

Abstract

This application relates to a short-circuit protection control method, device, and switching power supply for a three-phase resonant converter. By implementing step-by-step control of the three-phase resonant converter in both the soft-start and steady-state phases, this application features dual judgment logic in the soft-start phase and a pulse width gradual recovery mechanism in the steady-state phase. This effectively avoids false triggering, improves anti-interference capability, and ensures startup and operational stability. Simultaneously, it significantly reduces the bias voltage problem of the resonant capacitor during short-circuit protection, lowers device stress, and improves system reliability, thereby supporting short-circuit startup and long-term short-circuit operation of the three-phase resonant converter, adapting to harsh application scenarios. Furthermore, the hardware structure employing a sensing resistor combined with a comparator only requires sampling the input bus current, eliminating the need to detect the resonant cavity current, which simplifies the device structure and reduces design and material costs.

Description

Technical Field

[0001] This application relates to the field of converter technology, and in particular to a three-phase resonant short-circuit protection control method, control device and switching power supply. Background Technology

[0002] Three-phase interleaved resonant converters are widely used in high-current output applications due to their high efficiency and high power density. In some applications, due to structural limitations, efficiency, or cost considerations, it is not possible to directly sample the large output current; therefore, sampling the small input bus current for protection detection is preferred. However, the short-circuit protection scheme based on sampling the input bus current under output short-circuit conditions has the following drawbacks: Using a single-trigger shutdown PWM method is susceptible to current fluctuations, which can lead to false triggering, causing the converter to fail to start normally or to shut down abnormally during the steady-state phase. Figure 1 As shown; When using a cycle-by-cycle trigger turn-off scheme, the inconsistent output pulse widths of the three-phase PWM drive can lead to severe resonant capacitor bias, increased device stress, and safety risks. Figure 2 , Figure 4 As shown. Combined with Figure 3 Analysis reveals that the asymmetry in the three-phase drive caused by the cycle-by-cycle triggering of the turn-off drive results in the current and time for charging and discharging the resonant capacitor of a certain phase not meeting the charge balance requirement, thus forcing a voltage increase. Furthermore, the soft-start phase lacks a targeted short-circuit protection strategy, making it prone to false protection triggers due to bus current surges during startup, or device damage due to insufficient protection.

[0003] Existing solutions often require the detection of resonant cavity current, increasing circuit complexity and cost. Therefore, there is an urgent need for a short-circuit protection control scheme that can solve the above problems while balancing reliability, low cost, and low stress. Summary of the Invention

[0004] In view of the problems existing in the prior art, this application provides a short-circuit protection control method for high-power converters such as three-phase resonant converters, which solves the problems of weak anti-interference ability, severe resonant capacitor bias, high cost, and lack of effective protection in the soft start stage of the existing solution, and realizes short-circuit start-up and long-term short-circuit operation.

[0005] As a first aspect of this application, a short-circuit protection control method for a three-phase resonant converter is provided, comprising the following steps: S1. During the soft-start phase, the three-phase resonant converter starts outputting with a small first drive pulse width, and then the duty cycle gradually increases. S2. When the first driving pulse width reaches the preset threshold, maintain the current pulse width count for M cycles, and combine the output voltage Vout for short circuit judgment until the soft start is completed and the steady state pulse width is switched. S3. During the steady-state pulse width phase, the input bus current is detected by an external circuit to determine whether the short-circuit protection threshold has been reached. If the short-circuit protection threshold is reached, the current cycle is immediately shut down and cycle-by-cycle protection is performed. After triggering cycle-by-cycle protection, counting begins. During the counting process, the steady-state pulse width is reduced to a preset second driving pulse width. If the preset cycle-by-cycle counting number N is reached, it is determined to be a short-circuit fault, and the drive is immediately shut down. S4. If the input current detection signal does not reach the short-circuit protection threshold before the preset number of cycle counts N is reached, the count will be cleared and the drive pulse width will be gradually restored to the steady-state pulse width starting from the second drive pulse width.

[0006] In one alternative, the maintenance operation of the soft-start phase includes two methods: maintaining the duty cycle or maintaining the frequency.

[0007] In one alternative, in step S4, the process of gradually restoring the pulse width to the steady-state pulse width is either linear recovery or stepwise recovery.

[0008] In one alternative, the threshold value of the drive pulse width during the soft-start phase is set according to the converter's rated power and start-up stress requirements.

[0009] As another aspect of this application, a short-circuit protection control device for a three-phase resonant converter is provided, comprising: Sampling circuit, used to acquire output voltage signal; The current detection module consists of a detection resistor, a signal processing circuit, and an external comparator. The detection resistor is connected in series with the input bus of the three-phase resonant converter to collect the input bus current. The signal processing circuit amplifies the sampled input bus current, and the comparator converts the amplified current signal into a high or low level protection signal output. The controller is used to receive the protection signal output by the comparator and execute the short-circuit protection control method described above, including pulse width maintenance and voltage judgment logic in the soft-start phase and pulse width adjustment and recovery logic in the steady-state phase. And a drive module, used to receive the pulse width signal output by the controller, and then drive the switching devices of the three-phase resonant converter.

[0010] In one alternative, the sensing resistor is a high-precision sensing resistor, and the threshold voltage of the external comparator can be adjusted according to the short-circuit current threshold.

[0011] In one alternative, the controller is an MCU, DSP, or FPGA, with a built-in counting module and pulse width / frequency adjustment module.

[0012] As another aspect of this application, a switching power supply is provided, including a three-phase resonant converter, the three-phase resonant converter including: an inverter module, a resonant cavity module, a transformer module and a rectifier module; the three-phase resonant converter is controlled by the above-mentioned short-circuit protection control method and / or is provided with the above-mentioned short-circuit protection control device.

[0013] This application, by implementing step-by-step control of the three-phase resonant converter during the soft-start and steady-state phases, and combining this with a hardware structure employing a sensing resistor combined with a comparator, offers the following advantages over existing technologies: (1) Significantly reduces the bias voltage problem of the resonant capacitor during short-circuit protection, reduces device stress, and improves system reliability; (2) No need to detect the resonant cavity current, simplifying the hardware structure and reducing design and material costs; (3) Supports short-circuit start-up and long-term short-circuit operation, adapting to harsh application scenarios; (4) The dual judgment logic in the soft start phase and the pulse width gradual recovery mechanism in the steady state phase effectively avoid false triggering, improve anti-interference ability, and ensure startup and operation stability. Attached Figure Description

[0014] Figure 1 A schematic diagram of the driving logic for an existing single-time protection shutdown scheme; Figure 2 A schematic diagram of the driving logic for an existing cycle-by-cycle protection shutdown scheme; Figure 3 A schematic diagram illustrating the theoretical analysis of the resonant capacitor bias voltage.

[0015] Figure 4 This is a schematic diagram of the test waveform of the resonant capacitor bias voltage under short-circuit conditions. Figure 5 This is a schematic diagram of the steps of the short-circuit protection control method proposed in this application; Figure 6 This is a schematic diagram of the short-circuit protection control device proposed in this application; Figure 7 This is a schematic diagram of the driving logic in some embodiments of this application; Figure 8 This is a schematic diagram of the driving logic in some embodiments of this application; Figure 9 This is a flowchart illustrating the soft-start phase control logic proposed in this application; Figure 10 This is a flowchart illustrating the steady-state control logic proposed in this application. Detailed Implementation

[0016] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application. Similarly, the following examples are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0018] The terms "first," "second," etc., used in this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be used interchangeably where appropriate for the purposes of describing embodiments of this application herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0019] In some implementations, please refer to Figure 5 , Figures 7 to 10 This embodiment provides a short-circuit protection control method for a three-phase resonant converter, including: S1. During the soft-start phase, the three-phase resonant converter starts outputting with a small first drive pulse width, and then the duty cycle gradually increases. S2. When the first driving pulse width reaches the preset threshold, maintain the current pulse width count for M cycles, and combine the output voltage Vout for short circuit judgment until the soft start is completed and the steady state pulse width is switched. S3. During the steady-state pulse width phase, the input bus current is detected by an external circuit to determine whether the short-circuit protection threshold has been reached. If the short-circuit protection threshold is reached, the current cycle is immediately shut down and cycle-by-cycle protection is performed. After triggering cycle-by-cycle protection, counting begins. During the counting process, the steady-state pulse width is reduced to a preset second driving pulse width. If the preset cycle-by-cycle counting number N is reached, it is determined to be a short-circuit fault, and the drive is immediately shut down. S4. If the input current detection signal does not reach the short-circuit protection threshold before the preset number of cycle counts N is reached, the count will be cleared and the drive pulse width will be gradually restored to the steady-state pulse width starting from the second drive pulse width.

[0020] This application, through the aforementioned steps, implements step-by-step control of the three-phase resonant converter during the soft-start and steady-state phases. It features dual judgment logic in the soft-start phase and a pulse width gradual recovery mechanism in the steady-state phase, effectively preventing false triggering, improving anti-interference capabilities, and ensuring startup and operational stability. Simultaneously, it significantly reduces the bias voltage problem of the resonant capacitor during short-circuit protection, lowers device stress, and enhances system reliability. Thus, it supports short-circuit startup and prolonged short-circuit operation of the three-phase resonant converter, adapting to harsh application scenarios.

[0021] In some implementations, the maintenance operation during the soft-start phase can be either maintaining the duty cycle or maintaining the frequency.

[0022] As an example, please refer to Figure 8 During the soft-start phase, a frequency maintenance method is used, while protection is still achieved by adjusting the pulse width during the steady-state phase. In this way, by maintaining the frequency during the soft-start phase, the stress on the resonant cavity during startup is further reduced. Combined with the steady-state protection logic of pulse width adjustment, this also achieves the effects of reduced resonant capacitor bias voltage, error-free triggering, and support for short-circuit startup. This is suitable for applications with high requirements for startup frequency stability. In some implementations, the pulse width recovery process can be set to linear recovery or stepwise recovery.

[0023] In some implementations, the preset pulse width threshold for the soft-start phase can be set according to the converter's rated power and start-up stress requirements.

[0024] In some implementations, please refer to Figure 6 This application provides a short-circuit protection control device for a three-phase resonant converter, comprising: a sampling circuit for acquiring output voltage signals; The current detection module consists of a detection resistor, a signal processing circuit, and an external comparator. The detection resistor is connected in series with the input bus of the three-phase resonant converter to collect the input bus current. The signal processing circuit amplifies the sampled input bus current, and the comparator converts the amplified current signal into a high or low level protection signal output.

[0025] The controller is used to receive the protection signal output by the comparator and execute the short-circuit protection control method described above, including pulse width maintenance and voltage judgment logic in the soft-start phase and pulse width adjustment and recovery logic in the steady-state phase.

[0026] And a drive module, used to receive the pulse width signal output by the controller, and then drive the switching devices of the three-phase resonant converter.

[0027] This embodiment uses a hardware structure that combines a detection resistor with a comparator. It only needs to collect the input bus current and does not need to detect the resonant cavity current, which helps to simplify the structure of the device and reduce design and material costs.

[0028] In some implementations, a high-precision sensing resistor can be selected, and the threshold voltage of the external comparator can be adjusted according to the short-circuit current threshold.

[0029] In some implementations, the controller can be an MCU, DSP, or FPGA, with a built-in counting module and pulse width / frequency adjustment module.

[0030] In some implementations, please refer to Figure 6 An example of a short-circuit protection control device for a three-phase resonant converter is provided, and its parameter design is shown in the table below:

[0031] Based on the parameters in the table above, the first drive pulse width for the soft-start phase, with an initial duty cycle, is set to 10%. During the soft-start phase, the pulse width count M = 2 interrupt cycles are maintained, and the duty cycle is maintained at 20%. The Vout output short-circuit detection threshold is 2V. At the end of the soft-start phase, i.e., the steady-state phase, when cycle-by-cycle protection is triggered, the PWM is reduced to a duty cycle of 10%. If cycle-by-cycle protection reaches a count N = 4 interrupt cycles, the drive is shut down.

[0032] For the current detection module, a 15mΩ detection resistor was selected, and the comparator's reference threshold voltage was set to a 1.5V voltage signal corresponding to a 10A short-circuit current threshold. When the sampled voltage exceeds the threshold, the comparator outputs a high-level protection signal. The controller uses a TI TMS320F280025 (MCU), which has a built-in timer to generate three-phase PWM signals, receives the protection signal output by the comparator through an ADC interface, and has a built-in counting module to perform cycle-by-cycle counting. The drive module uses a driver chip to receive the PWM signal output by the MCU and drive the converter's MOSFETs to turn on or off.

[0033] The following is combined Figure 5 , Figure 6 and Figure 7The short-circuit control method of this embodiment further describes how this application performs step-by-step control of the converter during the soft-start and steady-state phases. The specific process is as follows: Soft start phase: Upon startup, the MCU controls the PWM pulse width to gradually increase from 10%. When the pulse width reaches a preset threshold of 20%, the MCU activates a pulse width maintenance mechanism to keep the current pulse width unchanged, while simultaneously acquiring the output voltage Vout via the ADC. Wherein: If Vout is lower than the preset voltage threshold of 2V, it is determined to be a real short circuit and the protection logic is activated. If Vout is greater than the preset voltage threshold of 2V, the protection operation will not be performed, and the pulse width will continue to increase.

[0034] It is important to note that the detection and judgment logic of Vout exists throughout the entire process from the start of pulse width maintenance until the end of the soft start phase.

[0035] The soft-start duration is set to 2 interrupt cycles, or 40µs. After the duration ends, the pulse width continues to increase to the rated value, and the system switches to steady-state protection logic.

[0036] Steady-state phase: During normal operation, the MCU monitors the comparator output signal in real time. If a high-level protection signal is detected, it starts counting cycle by cycle (the preset number of protection cycles is 4). During the counting period, the PWM pulse width is reduced to the second drive pulse width (10%) and maintained. If the protection signal disappears (comparator outputs low level) before the count reaches 4, the MCU controls the pulse width to gradually recover to the normal pulse width at a rate of 2% of the rated pulse width per cycle to avoid current surges caused by sudden changes. If the protection signal still exists after the count reaches 4, the PWM output is shut down and short-circuit shutdown protection is executed.

[0037] In some embodiments, this application provides a switching power supply, including a three-phase resonant converter, which includes an inverter module, a resonant cavity module, a transformer module, and a rectifier module; the three-phase resonant converter is controlled by the above-mentioned short-circuit protection control method and / or is equipped with the above-mentioned short-circuit protection control device.

[0038] The control method and apparatus of this application are widely applicable to three-phase interleaved resonant topologies, including but not limited to LLC topology, CLLC topology, LCL topology and other related circuit structures.

[0039] The above are merely some embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, and substitutions to the above embodiments within the scope of this application.

Claims

1. A short-circuit protection control method for a three-phase resonant converter, characterized in that, Includes the following steps: S1. During the soft-start phase, the three-phase resonant converter starts outputting with a small first drive pulse width, and then the duty cycle gradually increases. S2. When the first driving pulse width reaches the preset threshold, maintain the current pulse width count for M cycles, and combine the output voltage Vout for short circuit judgment until the soft start is completed and the steady state pulse width is switched. S3. During the steady-state pulse width stage, the input bus current is detected by the external circuit to determine whether the short-circuit protection threshold has been reached. If the short-circuit protection threshold has been reached, the current cycle is immediately shut off and cycle-by-cycle protection is performed. After the cycle-by-cycle protection is triggered, counting begins. During the counting process, the steady-state pulse width is reduced to a preset second driving pulse width. If the preset number of cycles N is reached, a short circuit fault is identified, and the drive is immediately shut down. S4. If the input current detection signal does not reach the short-circuit protection threshold before the preset number of cycle counts N is reached, the count will be cleared and the drive pulse width will be gradually restored to the steady-state pulse width starting from the second drive pulse width.

2. The short-circuit protection control method according to claim 1, characterized in that: The maintenance operations during the soft-start phase include two methods: maintaining the duty cycle or maintaining the frequency.

3. The short-circuit protection control method according to claim 1, characterized in that: In step S4, the process of gradually restoring the pulse width to the steady-state pulse width is either linear recovery or stepwise recovery.

4. The short-circuit protection control method according to claim 1, characterized in that: The threshold value of the drive pulse width during the soft-start phase is set according to the converter's rated power and start-up stress requirements.

5. A short-circuit protection control device for a three-phase resonant converter, characterized in that, include: Sampling circuit, used to acquire output voltage signal; The current detection module consists of a detection resistor, a signal processing circuit, and an external comparator. The detection resistor is connected in series with the input bus of the three-phase resonant converter to collect the input bus current. The signal processing circuit amplifies the sampled input bus current, and the comparator converts the amplified current signal into a high or low level protection signal output. A controller is used to receive the protection signal output by the comparator and execute the short-circuit protection control method according to any one of claims 1-4, including pulse width maintenance and voltage judgment logic in the soft-start phase and pulse width adjustment and recovery logic in the steady-state phase. And a drive module, used to receive the pulse width signal output by the controller, and then drive the switching devices of the three-phase resonant converter.

6. The control device according to claim 5, characterized in that, The detection resistor is a high-precision detection resistor, and the threshold voltage of the external comparator can be adjusted according to the short-circuit current threshold.

7. The control device according to claim 5, characterized in that, The controller is an MCU, DSP, or FPGA, with a built-in counting module and pulse width / frequency adjustment module.

8. A switching power supply, characterized in that: The invention includes a three-phase resonant converter, comprising: an inverter module, a resonant cavity module, a transformer module, and a rectifier module; the three-phase resonant converter is controlled by a short-circuit protection control method as described in any one of claims 1 to 4 and / or is equipped with a short-circuit protection control device as described in any one of claims 5 to 7.

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