The selection and analysis of precharge resistors mainly involves calculating the pulse energy at startup, then selecting an appropriate resistor scheme. The role of the precharge resistor is to limit the surge current when the battery is connected to a capacitive load, thus protecting the system from damage. The selection of the precharge resistor is based on calculations involving factors such as the load capacitance, battery voltage, and precharge time.

 

1. Calculating the energy of a single pulse: For a single pulse, the energy calculation is based on the load capacitance and battery voltage. If the pulse interval is very short (e.g., less than 1 second), the proportion of energy dissipated in practical applications is very small, and the total pulse energy can be calculated by linearly accumulating the energy dissipated.

 

Total energy calculation: The total energy equals the product of the single pulse energy and the number of consecutive pulses.

 

Calculation of resistor value: The formula for calculating the resistor value is R = xn16, where x is the precharge time, and n is the load end capacitance. For example, if the total voltage is 700V, the load capacitance is 2000uF, and the maximum precharge time is set to 300ms, when the capacitor voltage reaches 95% of the power supply voltage, the energy of a single pulse is 442J. If there are 5 consecutive pulses within a short period of time, the total pulse energy is approximately 2210J. Based on these data, the resistor value can be calculated to be 65.20.

 

Precharge circuit principle: The precharge circuit includes a precharge resistor used to limit the surge current, and a precharge relay used to prevent the load from being powered by the precharge resistor when the system is turned off. The selection of the precharge resistor design considers factors such as cost stability, resistance value, average power, pulse power, and precharge energy.

 

Resistor selection design: Consideration factors include input voltage, the voltage to be precharged, precharge capacitan