PDOC

The precharge discharge over current circuit (PDOC) monitors the high-voltage (HV) system, ensuring the pre-charge and discharge processes (like turning the car on/off) happen at safe, controlled rates, preventing rapid current spikes that could damage componentsthe ortractive createsystem. hazards.The PDOC's job is to measure the tractive system voltage and accumulator voltages to ensure that the precharge is adequate before closing the accumalator isolation relays (AIRs). The TS voltage should be within 95% of the accumulator voltage when the AIRs close to ensure there isn't a insane amount of inrush current which can damage the tractive system.

 

The precharge process

When precharging occurs, the main contactor is open and the precharge contactor is closed, meaning that all the current must flow through the precharge resistor, limiting the inrush current. This means that the TS voltage is bought up to the accumulator voltage at a safe rate. Once the precharge is complete and the TS voltage is at 95% of the accumulator voltage the main contactor can be opened and the precharge contactor can be closed. This is the normal operation state where the precharge resistor is bypassed, meaning that now the current has a low resistance path to flow. 

 

During this process, the PDOC monitors the accumulator voltage, before and after the precharge resistor. 

 

Timer-based precharge systems are extremely effective but unable to diagnose and respond to wiring faults, which can still result in faults. The