Electrical safety monitoring of PTC heater
1 PCB Temperature Safety
The temperature sensor of the MCU is used to detect the temperature of the PCB, and when the PCB is over-temperature, it will be turned off and the power will be reduced. The protection logic is as follows:
When the PCB temperature is higher than 120°C, the heating power is reduced according to the 80% derating factor, and the heating power is restored when the temperature is lower than 115°C.
When the PCB temperature is higher than 125°C, the heating is stopped, and the heating is resumed when the temperature is lower than 110°C.
2 Media temperature safety
Two NTC temperature sensors are used to detect the temperature of the water inlet and outlet respectively. The MCU continuously detects the rationality of the temperature sensor signal. Once an abnormality is found, it will be identified as a temperature sensor failure, which can avoid the heating runaway event caused by the temperature sensor failure.
When the medium temperature is higher than 70°C, the heating is stopped, and when the medium temperature is lower than 60°C, the heating is resumed.
Note: The occurrence of this failure indicates that there may be a problem with the system, such as: the water pump failure causes the coolant flow to be interrupted, or there are air bubbles in the coolant system, or the coolant leaks, and a similar dry-burning condition occurs. Check and maintain the PTC electric heater in time, otherwise it may further lead to permanent failure of the PTC electric heater.
3 Current derating
When the PTC electric heater detects that the heating current is higher than 15A and the duration exceeds 3s, the current derating protection is performed, and the heating power is reduced according to the 80% derating factor.
4 Short circuit overcurrent detection
When the PTC electric heater detects that the heating current is higher than about 56A, the heating will be stopped immediately after the duration exceeds about 1us, and then the reset restart and start-up inspection will be performed after a delay of 2 seconds.
During the start-up inspection, if the short-circuit fault is removed, the system can automatically resume normal operation, otherwise the second short-circuit fault will be triggered, and the system will further identify which branch has failed.
If a short circuit fault occurs 3 times in a row, the system enters the protection lock state and stops heating.
5 Long time overcurrent detection
When the PTC electric heater detects that the heating current is higher than 18A, and the duration exceeds 15 seconds, the heating will be stopped immediately, and then the reset action will be executed after a delay of 2 seconds, and then the start-up inspection action will be executed.
After the long-term overcurrent is detected for 3 consecutive times, the system enters the lock protection state and stops heating.
6 High voltage power supply voltage detection
The PTC electric heater will continuously detect the voltage value of the high-voltage power supply. When the high-voltage power supply voltage is higher than 760V or lower than 440V, it will stop heating immediately, and report the abnormal fault of the high-voltage power supply voltage. When the high-voltage power supply voltage returns to lower than 750V or higher than 450V , the system automatically returns to normal working state.
7 Startup Check
When the PTC electric heater is powered on or reset and restarted, if the heating power requested by the upper computer is valid, the startup inspection process will be performed.
First, detect the total current of all heating branches in the off state. If this current exceeds the specified value, it indicates that there is a short circuit in the system hardware, or leakage current, or a fault in the current sensor detection circuit.
Then the system will supply power to each heating branch separately for a period of time, and detect whether the corresponding current exceeds the specified value. The road can continue to work normally.
