Loop control method and system with pre-charge soft start

Abstract

The present application relates to new energy charging technology field, especially to a kind of loop control method and system with pre-charge soft start, wherein, in pre-charge stage, close secondary side drive, to fixed duty ratio drive primary side switch tube, pre-charge active clamp capacitor, until its voltage is established to approach target platform voltage;In soft start stage, after the completion of clamping capacitor voltage platform establishment, with minimum duty ratio simultaneously open secondary side drive and active clamp drive, and gradually increase duty ratio, while gradually increasing output voltage reference value and current reference value;In closed-loop operation stage, using voltage outer loop and current inner loop cascade control architecture, combined with dynamic feedforward control, realize steady-state regulation and load mutation response.The method and system can realize zero overshoot start machine, improve device safety, have high dynamic response capability and high steady-state control precision, full working condition robustness is strong, from pre-charge, soft start to closed-loop operation realizes smooth seamless transition, improves system overall reliability.

Description

Technical Field

[0001] This invention relates to the field of new energy charging technology, and in particular to a loop control method and system with pre-charge soft start. Background Technology

[0002] Full-bridge DC-DC converters are widely used in electric vehicle charging, energy storage systems, and high-voltage DC-DC conversion due to their high efficiency and high power density. However, in practical engineering applications, converters face severe voltage stress and current surges during startup and load surges, which particularly affect the reliability of power devices and system lifespan.

[0003] In existing technologies, passive snubber circuits or active clamping circuits are commonly used to suppress voltage spikes generated by the secondary-side MOSFET during switching. While passive snubber circuits are simple in structure, they lead to decreased system efficiency and cannot completely absorb peak stress, making the MOSFET susceptible to avalanche breakdown due to voltage exceeding its maximum withstand voltage. Active clamping circuits are theoretically more effective at suppressing voltage stress, but at startup, because the secondary-side clamping capacitor has not yet established a plateau voltage, the active clamping MOSFET fails to turn on in time, causing the clamping function to fail. The secondary-side MOSFET then directly bears the high-voltage spike, posing a serious risk of avalanche breakdown.

[0004] Furthermore, traditional startup strategies directly switch to full closed-loop control after pre-charging, lacking a gradual voltage ramp-up and duty cycle smooth ramp-up mechanism. This is especially problematic under constant current load startup conditions, easily leading to severe voltage overshoot and current spikes. Additionally, existing control strategies fail to balance high-frequency dynamic response and steady-state accuracy in current sampling and PID regulation, resulting in sluggish response or system oscillations during sudden load changes.

[0005] Therefore, how to achieve safe, smooth, and high-performance control of a full-bridge DC-DC converter from startup to steady-state operation while ensuring high efficiency has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] The main objective of this invention is to overcome the shortcomings of the prior art and provide a loop control method and system with pre-charge soft start.

[0007] The technical solution adopted by this invention to achieve its technical objective is: a loop control method with pre-charge soft start, applied to an active clamp full-bridge DC-DC converter, comprising the following steps: S1. Pre-charge stage: The secondary side drive is turned off, and the primary side switch is driven with a fixed duty cycle to pre-charge the active clamping capacitor until its voltage is close to the target platform voltage. S2, Soft Start Phase: After the clamp capacitor voltage platform is established, the secondary drive and active clamp drive are started simultaneously with the minimum duty cycle, and the duty cycle is gradually increased while the output voltage reference value and current reference value are progressively increased. S3. Closed-loop operation stage: A control architecture with cascaded voltage outer loop and current inner loop is adopted, combined with dynamic feedforward control, to achieve steady-state regulation and load change response.

[0008] Preferably, during the pre-charge phase, the active clamp drive remains off to avoid affecting the voltage stress of the secondary MOSFET.

[0009] Preferably, during the soft start phase, the duty cycle increases by a target value of 3% with each interruption cycle until the closed-loop operation phase is entered.

[0010] Preferably, the calculation method for the dynamic feedforward control is as follows:

[0011] in, It is the duty cycle calculated by feedforward. This indicates the output voltage value. This indicates the input voltage value. This is expressed as the number of turns of the primary transformer. This represents the number of turns of the secondary transformer; The feedforward target voltage is determined based on the ratio of the output voltage to the input voltage; when the actual output voltage is greater than or equal to the target voltage, the feedforward value is calculated based on the reference voltage.

[0012] Preferably, the inner current loop employs fast and slow dual-channel sampling: Fast channels are used for instantaneous current monitoring and hardware protection; The slow channel is used to extract high-precision average current for loop control.

[0013] Preferably, in the PID controllers of the voltage outer loop and the current inner loop: The integration path employs a large time constant RC filter to suppress low-frequency drift; The proportional and differential paths employ small time constant RC filtering to preserve high-frequency dynamic response capabilities.

[0014] This invention also provides a loop control system with pre-charge soft start, applied to an active clamp full-bridge DC-DC converter, comprising: The main control unit is used to execute the loop control method with pre-charge soft start described above; The drive logic unit is used to generate PWM signals for the primary-side main drive, active clamp drive, and secondary-side drive. Delay circuit, used to realize delayed turn-on and early turn-off of active clamp drive relative to main drive; The sampling unit is used to collect output voltage, output current, and clamping capacitor voltage. The state machine unit is used to manage the switching between the precharge phase, the soft start phase, and the closed-loop operation phase.

[0015] Preferably, in the driving logic unit: The primary drive H1 and L2 share one set of drives, while H2 and L1 share another set of drives. The two sets of drives are 180 degrees out of phase. The active clamp driver A is turned on and turned off early based on the timing delays of H1 and L2; The active clamp driver B is turned on and turned off early based on the timing delays of H2 and L1; Secondary driver A is complementary to H1 and L2, and secondary driver B is complementary to H2 and L1.

[0016] Preferably, the delay circuit uses a resistor-capacitor charging and discharging circuit to control the turn-on delay and turn-off advance of the main drive signal.

[0017] Preferably, in the sampling unit, the current channel is configured as a fast and slow dual-channel structure, which is respectively connected to a hardware comparator and an ADC controller.

[0018] The working principle of the loop control method and system with pre-charge soft start is as follows: The system adopts a dual-loop control architecture with a cascaded voltage outer loop and current inner loop, combined with a dynamic feedforward control strategy, to achieve precise regulation of output voltage and current. By introducing active clamping technology, the voltage stress generated by the secondary MOSFET during switching is effectively suppressed, preventing avalanche breakdown of the device. Simultaneously, the system is designed with a fast and slow dual-channel sampling mechanism. The integral path uses a large time constant RC filter to improve steady-state accuracy, while the proportional and derivative paths use a small time constant RC filter to retain high-frequency dynamic signals, ensuring rapid response to current surges. Furthermore, to address the problem of excessive stress caused by the failure of the active clamping capacitor platform voltage to establish during startup, the system innovatively incorporates a pre-charge soft start composite control strategy.

[0019] Compared with the prior art, the beneficial effects of the present invention are: This loop control method and system with pre-charge soft start can achieve zero overshoot start-up and improve device safety: through a three-level progressive timing control strategy of pre-charge, soft start, and closed-loop operation, a secondary clamping capacitor voltage platform is pre-established before start-up to avoid the secondary MOSFET being subjected to high voltage spikes at the moment of start-up, completely eliminating current spikes and voltage overshoots under CC load start-up conditions, and significantly reducing the risk of MOSFET avalanche breakdown.

[0020] This loop control method and system with pre-charge soft start has high dynamic response capability: it adopts a fast and slow dual-channel sampling mechanism, combined with small time constant RC filtering of proportional and differential paths, to retain high-frequency dynamic signal components, thereby achieving microsecond-level fast response to load changes, and improving the dynamic response speed by more than 30%.

[0021] The loop control method and system with pre-charge soft start can achieve high steady-state control accuracy: the integral path adopts a large time constant RC filter, which effectively suppresses switching noise and low-frequency drift, eliminates loop oscillation, and significantly improves the steady-state control accuracy of current and voltage.

[0022] The loop control method and system with pre-charge soft start exhibit strong robustness under all operating conditions: the cascaded architecture of the voltage outer loop and the current inner loop, combined with a dynamic feedforward control strategy, can maintain stable system operation under input voltage fluctuations, large dynamic load changes, and a wide temperature range, adapting to complex operating conditions.

[0023] This loop control method and system with pre-charge soft start can achieve comprehensive suppression of device stress: the pre-charge establishment of the active clamp capacitor voltage platform, combined with precise current control and drive timing management, comprehensively reduces the switching stress of the secondary MOSFET during startup and steady-state operation, and extends the service life of power devices.

[0024] This loop control method and system with pre-charge soft start can achieve seamless transition control and high system reliability: it achieves a smooth and seamless transition from pre-charge and soft start to closed-loop operation, avoiding the impact and protection malfunction caused by mode switching in traditional solutions, and improving the overall system reliability. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0026] Figure 1 This is a flowchart illustrating the steps of a loop control method with pre-charge soft start.

[0027] Figure 2 This is the control logic diagram for a loop control method with pre-charge soft start.

[0028] Figure 3 This is a system framework diagram of a loop control system with pre-charge soft start.

[0029] Figure 4 This is a diagram of the drive control circuit in the drive logic unit.

[0030] Figure 5This is the circuit control diagram for the delay circuit. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0032] In the description of this invention, it should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to or indirectly connected to the other element.

[0033] In the description of this invention, it should be noted that the terms "center," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0034] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] Example 1: Please see Figures 1-2A loop control method with pre-charge soft start, applied to an active clamp full-bridge DC-DC converter, includes the following steps: S1. Pre-charge stage: The secondary side drive is turned off, and the primary side switch is driven with a fixed duty cycle to pre-charge the active clamping capacitor until its voltage is built up to close to the target platform voltage. The value of the target platform voltage is the ratio of the input voltage to the number of transformer turns. During the pre-charge phase, the active clamp drive remains off to avoid affecting the voltage stress of the secondary MOSFET.

[0036] S2, Soft start phase: After the clamp capacitor voltage platform is established, the secondary drive and active clamp drive are started simultaneously with the minimum duty cycle, and the duty cycle is gradually increased. Meanwhile, the ADC sample value corresponding to the target value is used as the reference target, and the output voltage and current sample values ​​during soft start are used as the reference starting values. Each control loop increments the reference value by 1 until the target value is reached, gradually increasing the output voltage reference value and current reference value. During the soft start phase, the duty cycle increases by 3% with each interruption cycle until the closed-loop operation phase is entered.

[0037] S3. Closed-loop operation stage: A control architecture with cascaded voltage outer loop and current inner loop is adopted, combined with dynamic feedforward control, to achieve steady-state regulation and load change response.

[0038] The calculation method for the dynamic feedforward control is as follows:

[0039] in, It is the duty cycle calculated by feedforward. This indicates the output voltage value. This indicates the input voltage value. This is expressed as the number of turns of the primary transformer. This represents the number of turns of the secondary transformer.

[0040] The feedforward coefficient is determined based on the PWM control frequency, transformer turns ratio, and input voltage sampling coefficient. The feedforward coefficient is then multiplied by the target feedforward voltage to obtain the voltage feedforward amount. This method allows the feedforward amount to increase with the target feedforward voltage and decrease with the input voltage, thus pre-compensating for input voltage fluctuations. The target feedforward voltage is determined based on the ratio of the output voltage to the input voltage. When the actual output voltage is greater than or equal to the target voltage, the feedforward value is calculated based on a reference voltage.

[0041] The purpose of feedforward is to compensate for the duty cycle of the output PWM in advance, enabling a rapid response when the input voltage changes. By adding dynamic switching, it prevents over-response of the PWM from causing output voltage fluctuations.

[0042] The inner current loop employs fast and slow dual-channel sampling: the fast channel is used for instantaneous current monitoring and hardware protection; the slow channel is used to extract high-precision average current for loop control.

[0043] In the PID controllers of the voltage outer loop and current inner loop: the integral path uses a large time constant RC filter to suppress low-frequency drift; the proportional path and derivative path use a small time constant RC filter to retain high-frequency dynamic response capability.

[0044] Specifically, in use, during the pre-charge phase, the system first shuts down the secondary-side drive to block the current backflow path, while simultaneously charging the bootstrap capacitor of the primary-side transistor to establish negative voltage operating conditions. Subsequently, the main circuit is driven with a fixed small duty cycle to pre-charge the secondary-side clamping capacitor, gradually raising its voltage plateau to near the target steady-state value. During this phase, the active clamping drive remains off to ensure that the voltage stress on the secondary-side devices is not affected.

[0045] During the soft-start phase, once the clamping capacitor voltage plateau is established, the system enters the soft-start phase. At this time, the secondary drive and active clamping drive are simultaneously activated with the minimum duty cycle, and the DC-DC working state machine switches to soft-start mode. The duty cycle gradually increases by 3% with each interrupt. Simultaneously, the output voltage reference value and current reference value also gradually increase with each interrupt, and the minimum value is compared with the duty cycle calculated by the PID algorithm to achieve a smooth start.

[0046] During the closed-loop operation phase, after soft start, the system switches to full closed-loop control. The voltage outer loop and current inner loop work together to sample the output voltage and current in real time and dynamically adjust the duty cycle through a PID controller. Dynamic feedforward control calculates the feedforward amount based on the ratio of output voltage to input voltage or a reference voltage to ensure that the system can respond quickly and maintain stable operation when there are sudden load changes or input voltage fluctuations.

[0047] Example 2: Please see Figures 3-5 Based on the above embodiments, this invention also provides a loop control system with pre-charge soft start, applied to an active clamp full-bridge DC-DC converter, including a main control unit, a drive logic unit, a delay circuit, a sampling unit, and a state machine unit.

[0048] In this embodiment, the main control unit is used to execute the loop control method with pre-charge soft start described above.

[0049] In this embodiment, the driving logic unit is used to generate PWM signals for the primary-side main drive, active clamp drive, and secondary-side drive.

[0050] In the driving logic unit: the primary side main driver H1 and L2 share a set of drivers, and H2 and L1 share another set of drivers, with the two sets of drivers having a phase difference of 180 degrees; the active clamp driver A is turned on and turned off early based on the timing delay of H1 and L2 (hundreds of nanoseconds); the active clamp driver B is turned on and turned off early based on the timing delay of H2 and L1 (hundreds of nanoseconds); the secondary side driver A is complementary to H1 and L2, and the secondary side driver B is complementary to H2 and L1.

[0051] In this embodiment, the delay circuit is used to realize the delayed turn-on and early turn-off of the active clamp drive relative to the main drive.

[0052] The delay circuit uses a resistor-capacitor charging / discharging circuit to control the turn-on delay and turn-off advance of the main drive signal. Specifically, the active clamp driver A is delayed (by hundreds of nanoseconds) to turn on and turned off early in the main drive H1 and L2 timing sequence; the active clamp driver B is delayed (by hundreds of nanoseconds) to turn on and turned off early in the main drive H2 and L1 timing sequence. The main drive signal passes through the delay circuit, generating a certain time delay for turn-on through R1 and C1 charging, and then discharging through R1, R2, and C1 to generate an early turn-off delay, ensuring that the active clamp MOS operates within a reasonable timing sequence.

[0053] In this embodiment, the sampling unit is used to collect the output voltage, output current, and clamping capacitor voltage.

[0054] In the sampling unit, the current channel is configured as a fast and slow dual-channel structure, which is respectively connected to the hardware comparator and the ADC controller.

[0055] In this embodiment, the state machine unit is used to manage the switching between the precharge phase, the soft start phase, and the closed-loop operation phase.

[0056] The solution in this embodiment can be selectively combined with solutions in other embodiments.

[0057] This loop control method and system with pre-charge soft start is applied to an active clamp full-bridge DC-DC converter, specifically as follows: Figures 1-5 As shown, it achieves safe, smooth, and high-performance control throughout the entire process from startup to steady-state operation through a three-level progressive timing control strategy, combined with a cascaded architecture of voltage outer loop and current inner loop, dynamic feedforward control, fast and slow dual-channel sampling, and differentiated PID filtering configuration. The specific usage process is as follows: The first stage, the pre-charge stage (establishing the clamping capacitor platform voltage); The system first shuts down the secondary-side drive to block the current backflow path; simultaneously, it drives the primary-side switch with a fixed small duty cycle to precharge the active clamping capacitor. During this stage, the active clamping drive remains off to avoid affecting the voltage stress of the secondary-side MOSFET. As the precharging progresses, the clamping capacitor voltage plateau gradually rises until it approaches the target steady-state value (i.e., the plateau voltage required by the secondary-side MOSFET). This solves the problem of the secondary-side MOSFET experiencing a high voltage spike and the risk of avalanche breakdown at startup due to the clamping capacitor not establishing voltage.

[0058] The second stage, the soft start stage (smooth entry into closed loop); Once the clamping capacitor voltage plateau is established, the system simultaneously activates the secondary drive and the active clamping drive at the minimum duty cycle. Subsequently, the duty cycle is gradually increased by 3% with each interrupt cycle, while the output voltage and output current reference values ​​are progressively increased. The system state machine switches to the soft-start phase, employing a segmented voltage soft-start mechanism to avoid voltage overshoot and current spikes caused by sudden changes in duty cycle, achieving a seamless transition from pre-charge to closed-loop operation and ensuring the safe operation of power devices during startup.

[0059] The third stage, closed-loop operation stage (high-performance steady-state control); The system enters a dual closed-loop cascaded control mode, which includes the following sub-mechanisms: (1) Cascaded control of voltage outer loop and current inner loop; the voltage outer loop generates a current command based on the output voltage error, limits it, and sends it to the current inner loop. The current inner loop generates a duty cycle control signal based on the current error to achieve precise adjustment of the output current.

[0060] (2) Dynamic feedforward control; the feedforward value is calculated based on the ratio of the output voltage to the input voltage. When the actual output voltage is greater than or equal to the reference voltage, it automatically switches to calculate the feedforward value based on the reference voltage to ensure that there is no overshoot protection when the CC (constant current) load is started, and at the same time, it responds quickly to load changes under closed-loop conditions.

[0061] (3) Fast and slow dual-channel sampling; Fast channel: used for instantaneous current monitoring, and works with hardware to achieve microsecond-level protection. Slow channel: used to extract high-precision average current for use in PID loop control.

[0062] (4) Differentiated PID filter configuration; Integral path: adopts a large time constant RC filter to effectively suppress switching noise and low-frequency drift, and improve steady-state accuracy. Proportional and derivative paths: adopt a small time constant RC filter to retain high-frequency dynamic signal components and ensure fast response and damping capability to current surges.

[0063] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of this invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of this invention, or equivalent structural, procedural, or functional transformations made using the description and drawings of this invention, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of protection of this invention.

Claims

1. A loop control method with pre-charge soft start, applied to an active clamp full-bridge DC-DC converter, characterized in that, Includes the following steps: S1. Pre-charge stage: The secondary side drive is turned off, and the primary side switch is driven with a fixed duty cycle to pre-charge the active clamping capacitor until its voltage is close to the target platform voltage. S2, Soft Start Phase: After the clamp capacitor voltage platform is established, the secondary drive and active clamp drive are started simultaneously with the minimum duty cycle, and the duty cycle is gradually increased while the output voltage reference value and current reference value are progressively increased. S3. Closed-loop operation stage: A control architecture with cascaded voltage outer loop and current inner loop is adopted, combined with dynamic feedforward control, to achieve steady-state regulation and load change response.

2. The loop control method with pre-charge soft start according to claim 1, characterized in that, During the pre-charge phase, the active clamp drive remains off to avoid affecting the voltage stress of the secondary MOSFET.

3. The loop control method with pre-charge soft start according to claim 1, characterized in that, During the soft start phase, the duty cycle increases by 3% with each interruption cycle until the closed-loop operation phase is entered.

4. The loop control method with pre-charge soft start according to claim 1, characterized in that, The calculation method for the dynamic feedforward control is as follows: ； in, It is the duty cycle calculated by feedforward. This indicates the output voltage value. This indicates the input voltage value. This is expressed as the number of turns of the primary transformer. This represents the number of turns of the secondary transformer; The feedforward target voltage is determined based on the ratio of the output voltage to the input voltage; when the actual output voltage is greater than or equal to the target voltage, the feedforward value is calculated based on the reference voltage.

5. The loop control method with pre-charge soft start according to claim 1, characterized in that, The inner current loop employs fast and slow dual-channel sampling: Fast channels are used for instantaneous current monitoring and hardware protection; The slow channel is used to extract high-precision average current for loop control.

6. The loop control method with pre-charge soft start according to claim 1, characterized in that, In the PID controllers of the voltage outer loop and current inner loop: The integration path employs a large time constant RC filter to suppress low-frequency drift; The proportional and differential paths employ small time constant RC filtering to preserve high-frequency dynamic response capabilities.

7. A loop control system with pre-charge soft start, applied to an active clamp full-bridge DC-DC converter, for executing the method according to any one of claims 1 to 6, characterized in that, include: The main control unit is used to execute the loop control method with pre-charge soft start described above; The drive logic unit is used to generate PWM signals for the primary-side main drive, active clamp drive, and secondary-side drive. Delay circuit, used to realize delayed turn-on and early turn-off of active clamp drive relative to main drive; The sampling unit is used to collect output voltage, output current, and clamping capacitor voltage. The state machine unit is used to manage the switching between the precharge phase, the soft start phase, and the closed-loop operation phase.

8. The loop control system with pre-charge soft start according to claim 7, characterized in that, In the driving logic unit: The primary drive H1 and L2 share one set of drives, while H2 and L1 share another set of drives. The two sets of drives are 180 degrees out of phase. The active clamp driver A is turned on and turned off early based on the timing delays of H1 and L2; The active clamp driver B is turned on and turned off early based on the timing delays of H2 and L1; Secondary driver A is complementary to H1 and L2, and secondary driver B is complementary to H2 and L1.

9. The loop control system with pre-charge soft start according to claim 7, characterized in that, The delay circuit achieves control over the turn-on delay and turn-off advance of the main drive signal through a resistor-capacitor charging and discharging circuit.

10. The loop control system with pre-charge soft start according to claim 7, characterized in that, In the sampling unit, the current channel is configured as a fast and slow dual-channel structure, which is respectively connected to the hardware comparator and the ADC controller.

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