An adaptive soft start power control method and system for thick film heaters

Abstract

This invention relates to the field of thermal management system technology for new energy vehicles, and particularly to an adaptive soft-start power control method and system for a thick-film heater. The method includes the following steps: the controller receives a target power P_set from a host computer and initializes an internal dynamic target power P_target; it distinguishes between initial cold starts and non-initial cold starts, gradually increasing P_target using small and large step sizes respectively, and clamping the P_target once it reaches the target power P_set; then, it uses the smoothed P_target as the PI setpoint, and adjusts the PWM duty cycle based on the real-time sampled power of the heater to complete the closed-loop power control. This invention, by replacing the step input with a stepped, gradual setpoint, can effectively suppress cold-start surge current, reduce the impact stress on power devices, alleviate power overcharging and output jitter caused by PI regulation, and balance start-up stability with normal power response speed, thereby improving the stability of the heater control system and the lifespan of the devices.

Description

Technical Field

[0001] This invention relates to the field of thermal management system technology for new energy vehicles, and in particular to an adaptive soft-start power control method and system for a thick film heater. Background Technology

[0002] A thick-film heater is a heating device that coats a conductive thick-film layer onto the surface of a metal substrate. When electricity is applied, the thick-film resistor heats up, transferring heat to the liquid cooling circuit. Compared to traditional PTC heaters, thick-film heaters offer advantages such as high heat transfer efficiency, small size, and fast response, and can be integrated with closed-loop control for precise power control. With the rapid development of the new energy vehicle industry, thick-film heaters have gradually become one of the core components of new energy vehicle thermal management systems.

[0003] In existing technologies, thick-film heaters typically employ a control architecture combining a PI proportional-integral control algorithm with a PWM pulse width modulation duty cycle to control output power. The vehicle control unit (VCU) sends the real-time target power via the CAN bus. The controller directly uses this target power as its input, collects the voltage and current of the thick-film heater, calculates the actual output power as feedback, and adjusts the PWM duty cycle of the IGBT switching devices in real time to stabilize the output power. This architecture is simple in structure and has low hardware modification costs, making it widely adopted in the industry. However, considering the inherent temperature resistance characteristics of the thick-film resistor and the complex operating conditions in vehicles, the following drawbacks still exist during implementation: 1. Inrush current issue during cold start: The resistance of a thick-film heater is significantly lower when cold than when hot, typically only 1 / 2 to 1 / 5 of its hot resistance. If started directly at full power, it will generate an inrush current far exceeding the rated value, reaching 2 to 4 times the steady-state current. This inrush current can easily lead to power supply protection tripping, overstress damage to IGBT switching devices, or contact welding, severely impacting system reliability and device lifespan.

[0004] 2. Large deviation and overshoot caused by fixed PI parameters: Thick-film heaters have a wide power range, such as 100W to 7000W. When the target power is set much higher than the actual power, the error is large. Even if the PI control parameters are set appropriately, overcharging and continuous jitter can easily occur during rapid convergence. This is especially pronounced during the initial cold start, when the thick-film resistance is at its lowest point.

[0005] 3. Existing soft-start solutions are insufficient: Currently, there are some soft-start technologies for thick-film heaters, such as dividing the PTC heater's total heating element into multiple columns and starting them sequentially, or using a target value ramp function to generate a target value that changes in a ramp-like manner to smooth the control response. However, these solutions mainly use open-loop control with a fixed power ramp rate, and cannot adaptively adjust based on the startup state and the distance between the current power and the target power. Therefore, they are insufficient in balancing the smoothness of the initial cold start and the rapid response during normal operation. Summary of the Invention

[0006] The purpose of this invention is to address the technical problems of excessive surge current, overcharging, and continuous fluctuations during cold start-up of thick film heaters in the prior art, and to provide an adaptive soft-start power control method and system for thick film heaters.

[0007] The technical solution adopted by this invention to solve its technical problem is: On one hand, the present invention provides an adaptive soft-start power control method for a thick film heater, comprising the following steps: Step 1. The controller receives the target power P_set from the host computer and initializes the dynamic internal target power P_target within the controller. Step 2. The controller determines whether the current operating condition is the first cold start. If it is the first cold start, the internal target power P_target increases with a step size S1 in a step period. If it is not the first cold start, the internal target power P_target increases with a second step size S2 in a step period, where S2 > S1. Step 3. In each step cycle, the controller increases the internal target power P_target by one step until P_target ≥ P_set, and then limits P_target to P_set, that is: P_target = P_set; Step 4. Use the real-time internal target power P_target as the given input of the PI controller, and use the actual sampled power of the heater P_actual as the feedback input of the PI controller. Adjust the PWM duty cycle by outputting the control quantity through PI calculation, and control the actual output power of the thick film heater in a closed loop.

[0008] Furthermore, in step 2, the conditions for determining the first cold start are: the controller receives the target power P_set for the first time after power-on reset, and / or the heater temperature is lower than a preset temperature threshold.

[0009] Further, in step 3, the single stepping formula is: P_target(n) = P_target(n-1) + S, where S is the first step length S1 or the second step length S2, and n is the serial number of the current stepping cycle.

[0010] Further, after the thick film heater enters a stable operation state, the controller receives a new target power P_set_new according to the control cycle.

[0011] Further, after the controller receives P_set_new, it calculates the deviation ΔP between P_target and P_set_new as ΔP = |P_set_new - P_target|, and selects different step lengths according to the magnitude of ΔP: When ΔP is greater than the first threshold D1, S_big is adopted; When ΔP is between the first threshold D1 and the second threshold D2, S_mid is adopted; When ΔP is less than the second threshold D2, S_small is adopted; Wherein D1>D2>0, and S_big>S_mid>S_small.

[0012] Further, when P_set_new>P_target, the internal target power P_target is stepped up by one step length in each stepping cycle until P_set_new is reached, that is: P_target(n) = P_target(n-1) + S_, where S_ is one of S_big, S_mid and S_small.

[0013] Further, when P_set_new<P_target, the internal target power P_target is stepped down by one step length in each stepping cycle until P_set_new is reached, that is: P_target(n) = P_target(n-1) - S_, where S_ is one of S_big, S_mid and S_small.

[0014] Further, when P_set_new<P_target, the internal target power P_target is stepped down by one step length in each stepping cycle until P_set_new is reached, that is: P_target(n) = P_target(n-1) - S_, where S_ is a fixed step length for constant-speed downward adjustment.

[0015] Further, the stepping cycle and the control cycle have the same duration and are synchronized in time sequence.

[0016] On the other hand, the present invention also provides an adaptive soft-start power control system for a thick film heater, comprising: Thick film heater body; A power switching device is used to control the power-on and power-off of the thick film heater; The current and voltage sampling circuit is used to collect the voltage and current signals of the thick film heater in real time and convert them into the actual sampling power P_actual. The controller is electrically connected to both the power switching device and the sampling circuit.

[0017] The beneficial effects of this invention are: This invention differentiates the power step rate between initial cold start and non-initial start, progressively generates the internal target power, and completes closed-loop power control in conjunction with PI controller and PWM duty cycle adjustment. On the one hand, it slows down the power input rise rate in cold conditions, effectively suppresses the surge current generated by the thick film heater at low temperature, reduces the instantaneous stress on IGBT switching devices, and avoids the risk of device damage and power tripping. On the other hand, it abandons the mode of direct step input of target power, smooths the PI controller setpoint, and fundamentally alleviates the power overcharging and output jitter problems caused by large power deviation. At the same time, the design of different start-up and start-up timings balances the stability of cold start operation and the power ramp-up speed of regular restart. Moreover, relying on the mature PI-PWM closed-loop architecture, it is easy to program and implement on-board controllers, thus improving the overall stability and reliability of the thick film heater control system for new energy vehicles. Attached Figure Description

[0018] Figure 1 This is a flowchart of an adaptive soft-start power control method for a thick film heater according to an embodiment of the present invention.

[0019] Figure 2 This is a flowchart illustrating the step size selection when the deviation ΔP between the new CAN target power and the internal target power falls within different thresholds, as described in an embodiment of the present invention.

[0020] Figure 3 This is a flowchart of step size control during normal operation as described in an embodiment of the present invention. Detailed Implementation

[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] To address the technical problems of excessive surge current, overcharging, and continuous fluctuations during cold start-up of thick film heaters in existing technologies, this embodiment provides an adaptive soft-start power control method for thick film heaters.

[0023] like Figure 1 As shown, this embodiment specifically includes the following steps: Step 1. The controller receives the target power P_set from the host computer and initializes the dynamic internal target power P_target within the controller: In step 1, the controller receives the target power P_set sent by the thermal management host computer via the CAN bus. In this embodiment, the controller no longer directly uses P_set as the input setpoint for PI control, but instead uses it as the final target value. Simultaneously, it maintains a dynamically changing internal target power P_target, and uses P_target as the actual input setpoint for the PI controller. The internal target power P_target is a virtual, dynamically setpoint power within the controller, existing only in the control program memory, and is the only input setpoint used by the PI controller.

[0024] Step 2. The controller determines whether the current operating condition is a first cold start. If it is a first cold start, the internal target power P_target increases with a step size S1 in increments. If it is not a first cold start, the internal target power P_target increases with a second step size S2 in increments, where S2 > S1. In step 2, a cold start is determined when the controller receives the target power P_set from the thermal management host computer for the first time after power-on reset, or when the temperature of the heater temperature sensing element read by the MCU in real time is lower than the preset temperature threshold. When a cold start is determined, the power increment step is set to the first step size S1, and the internal target power P_target is gradually increased from the current value by the first step size S1. When a non-cold start is determined, the power increment step is set to the second step size S2, and the internal target power P_target is gradually increased from the current value by the second step size S2. Specifically, this embodiment uses a smaller power increment step S1, specifically 40W / 10ms, during the initial cold start, to allow the power of the thick film heater to slowly climb from 0 to the target value. In the low-power stage, preheating is completed first, allowing the thick film resistance to rise naturally, thereby effectively limiting the surge current during cold start and avoiding power protection tripping and IGBT switching device overstress damage. During non-initial cold starts, a larger power increment step S2, specifically 100W / 10ms, is used. At this time, the heater has residual heat and high resistance, with no strong surge risk, allowing the power to climb quickly and improving the system response speed.

[0025] Step 3. In each stepping cycle, the controller increases the internal target power P_target by one step until P_target ≥ P_set, then limits P_target to P_set, i.e.: P_target = P_set. In step 3, the controller sets a fixed stepping cycle. In this embodiment, a stepping cycle of 10ms is used. That is, every 10ms, the internal target power P_target is incremented once, i.e., P_target(n) = P_target(n-1) + S, where S is the first step size S1 or the second step size S2, and n is the current stepping cycle number. This continues until P_target reaches or exceeds P_set, at which point P_target is limited to P_set, i.e., P_target = P_set. At this point, the internal target power P_target no longer continues to increase, the given value remains fixed, and the thick film heater enters the steady-state constant power normal operation stage.

[0026] Step 4. Use the real-time internal target power P_target as the given input of the PI controller, and use the actual sampled power of the heater P_actual as the feedback input of the PI controller. Adjust the PWM duty cycle by outputting the control quantity through PI calculation to achieve closed-loop control of the output power of the thick film heater. In step 4, the real-time internal target power P_target, after adaptive step smoothing, is used as the expected value input to the PI controller. The actual sampled power P_actual of the heater, obtained by voltage and current sampling, is used as the feedback input. The controller compares the two to obtain the power deviation and performs PI calculation to generate an adjustment control quantity. This control quantity is then converted into a PWM duty cycle to drive the power switching device, continuously adjusting the average power supply to the thick film heater. At the same time, the actual power is continuously collected and refreshed to form a negative feedback closed loop, allowing the actual output power of the heater to stably follow the gradually changing internal target power P_target. The design of step 4 in this embodiment is the final execution step of converting the soft-start strategy into the actual output power of the heater. It completely abandons the original mode of directly sending the P_set step input to the PI from the vehicle CAN bus, eliminating the surge and power overshoot caused by large step inputs from the input source.

[0027] Furthermore, this embodiment also includes step size control during normal operation. Specifically, after the thick film heater enters a stable operating state, the CAN peripheral of the heater MCU is always in bus listening mode. The controller receives new target power P_set_new at a fixed PI control cycle. When new target power data is received, the controller calculates the deviation ΔP = |P_set_new - P_target| between the internal target power P_target and P_set_new, and selects different step sizes based on the magnitude of ΔP. Figure 2 As shown: When ΔP is greater than the first threshold D1, a large step size S_big is used; When ΔP is between the first threshold D1 and the second threshold D2, a medium step size S_mid is used; When ΔP is less than the second threshold D2, a small step size S_small is used; Where D1>D2>0, S_big>S_mid>S_small.

[0028] The first threshold D1 represents the internal target power P_target being far from the new target power P_set_new, and the second threshold D2 represents the internal target power P_target being close to the new target power P_set_new. Specifically, in this embodiment, the preferred values ​​are: first threshold D1 = 5000W, second threshold D2 = 2000W, large step size S_big = 100W / 10ms, medium step size S_mid = 60W / 10ms, and small step size S_small = 30W / 10ms. ΔP ≥ 5000W, use large step size; 2000W < ΔP < 5000W, use a medium step size; ΔP ≤ 2000W, using a small step size of 30W / 10ms; Specifically, such as Figure 3 As shown, in the implementation of this embodiment, when P_set_new > P_target, the internal target power P_target is increased by one step in each stepping cycle until P_set_new is reached, that is: P_target(n) = P_target(n-1) + S_, where S_ is one of S_big, S_mid, and S_small.

[0029] When P_set_new < P_target, the internal target power P_target is incremented by one step in each stepping cycle until P_set_new is reached, i.e.: P_target(n) = P_target(n-1) - S_, where S_ is one of S_big, S_mid, and S_small; alternatively, the internal target power P_target can be decreased at a constant speed with a fixed step size in each stepping cycle. In this embodiment, 100W / 10ms is preferred.

[0030] This invention distinguishes between the initial cold start and non-initial start of the thick film heater during the startup phase. It uses a differentiated step rate to smoothly generate the internal target power, avoiding the large deviation caused by a direct step input of the external target power. The small step size ramp-up in the cold state can significantly suppress the surge current under low temperature and low resistance conditions, effectively reducing the instantaneous stress on the IGBT switching devices and reducing the risk of device damage and circuit tripping. During the steady-state operation of the heater, a three-stage variable step size adjustment strategy is set for power command switching. Large step size is used for rapid ramp-up or ramp-down at long distances, and small step size is used for slow ramp-up or ramp-down near the target. This not only speeds up the power switching response speed, but also avoids the power overcharging and continuous jitter problems caused by the drastic adjustment of the PI controller from the source. Combined with synchronous timing PI and PWM closed-loop control, precise and stable power regulation is achieved. The entire control algorithm architecture is simple and easy to program and implement in the vehicle controller. Under the condition of frequent power changes in the thermal management of new energy vehicles, it greatly improves the stability of heater operation, system reliability and device life.

[0031] On the other hand, an adaptive soft-start power control system for a thick film heater specifically includes: Thick film heater body; A power switching device is used to control the power-on and power-off of the thick film heater; The current and voltage sampling circuit is used to collect the voltage and current signals of the thick film heater in real time and convert them into the actual sampling power P_actual. The controller is electrically connected to both the power switching device and the sampling circuit.

[0032] It is understood that since the adaptive soft-start power control system for a thick film heater described in this invention is a system for implementing the adaptive soft-start power control method for the thick film heater, the description of the disclosed system is relatively simple because it corresponds to the disclosed method, and relevant parts can be referred to in the description of the method.

Claims

1. An adaptive soft-start power control method for a thick film heater, characterized in that, Includes the following steps: Step 1. The controller receives the target power P_set from the host computer and initializes the dynamic internal target power P_target within the controller. Step 2. The controller determines whether the current operating condition is the first cold start. If it is the first cold start, the internal target power P_target increases with a step size S1 in a step period. If it is not the first cold start, the internal target power P_target increases with a second step size S2 in a step period, where S2 > S1. Step 3. In each step cycle, the controller increases the internal target power P_target by one step until P_target ≥ P_set, and then limits P_target to P_set, that is: P_target = P_set; Step 4. Use the real-time internal target power P_target as the given input of the PI controller, and use the actual sampled power of the heater P_actual as the feedback input of the PI controller. Adjust the PWM duty cycle by outputting the control quantity through PI calculation to realize closed-loop control of the output power of the thick film heater.

2. The adaptive soft-start power control method for a thick film heater according to claim 1, characterized in that, In step 2, the conditions for determining the first cold start are: the controller receives the target power P_set for the first time after power-on reset, and / or the heater temperature is lower than the preset temperature threshold.

3. The adaptive soft-start power control method for a thick film heater according to claim 1, characterized in that, In step 3, the single step formula is: P_target(n) = P_target(n-1) + S, where S is the first step length S1 or the second step length S2, and n is the current step cycle number.

4. The adaptive soft-start power control method for a thick film heater according to claim 1, characterized in that, After the thick film heater enters a stable operating state, the controller receives a new target power P_set_new according to the control cycle.

5. The adaptive soft-start power control method for a thick film heater according to claim 4, characterized in that, After receiving P_set_new, the controller calculates the deviation ΔP = |P_set_new - P_target| between P_target and P_set_new, and selects different step sizes based on the magnitude of ΔP. When ΔP is greater than the first threshold D1, S_big is used; When ΔP is between the first threshold D1 and the second threshold D2, S_mid is used; When ΔP is less than the second threshold D2, S_small is used; Where D1 > D2 > 0, S_big > S_mid > S_small.

6. The adaptive soft-start power control method for a thick film heater according to claim 5, characterized in that, When P_set_new > P_target, the internal target power P_target is increased by one step in each stepping cycle until P_set_new is reached, that is: P_target(n) = P_target(n-1) + S_, where S_ is one of S_big, S_mid, and S_small.

7. The adaptive soft-start power control method for a thick film heater according to claim 5, characterized in that, When P_set_new < P_target, the internal target power P_target is stepped down by one step in each stepping cycle until P_set_new is reached, that is: P_target(n) = P_target(n-1) - S_, where S_ is one of S_big, S_mid, and S_small.

8. The adaptive soft-start power control method for a thick film heater according to claim 5, characterized in that, When P_set_new < P_target, the internal target power P_target is stepped down by one step in each stepping cycle until P_set_new is reached, that is: P_target(n) = P_target(n-1) - S_, where S_ is a fixed step size.

9. An adaptive soft-start power control method for a thick film heater according to any one of claims 1-8, characterized in that, The stepping cycle and the control cycle are of equal duration and synchronized in timing.

10. An adaptive soft-start power control system for a thick film heater, characterized in that, include: Thick film heater body; A power switching device is used to control the power-on and power-off of the thick film heater; The current and voltage sampling circuit is used to collect the voltage and current signals of the thick film heater in real time and convert them into the actual sampling power P_actual. The controller is electrically connected to both the power switching device and the sampling circuit.

Images