Analysis of the internal structure of the on-board charger for new energy vehicles

OBC is a power electronic device for charging automobile power batteries, that is, an on-board charger, or OBC for short.

I. Definition

The on-board charger of electric vehicles adopts high-frequency switching power supply technology. Its main function is to convert AC 220V into high-voltage DC to charge the power battery to ensure the normal driving of the vehicle. At the same time, the on-board charger provides corresponding protection functions, including overvoltage, undervoltage, overcurrent, undercurrent and other protection measures. When the charging system is abnormal, the power supply will be cut off in time.

2. Internal Structure

The interior of the on-board charger can be divided into three parts: main circuit, control circuit, wiring harness and standard parts

Conversion principle:

220Vac is filtered by the EMI filter circuit, rectified by an AC-DC converter, rectified into DC, and then boosted by the PFC power factor calibration circuit. It is then sent to the switch and transformer for variable frequency boosting. After the LLC is rectified and filtered for the second time, high-voltage DC is output to charge the power battery (the first 220Vac is rectified to 310Vdc, the voltage is not enough, and it needs to be boosted and converted twice)

1. Main circuit: The main circuit can usually be divided into two stages. The front stage is the power factor correction PFC module, which improves the input power factor and suppresses high-order harmonics; the back stage is the DCDC converter, that is, the LLC module, which meets the current and voltage requirements of battery charging and realizes electrical isolation (PFC: power factor corrector, when converting AC power to DC power, improves the utilization rate of electricity. Reduce the energy loss in the conversion process and make the voltage and current phase frequency consistent)

2. Control circuit: The control circuit completes signal reception and charging control through sensors, ECU and IGBT driver.

Function: Control the switch of MOS tube, communicate with BMS, monitor the status of charger, shake hands with charging pile, etc.

3. Wiring harness and standard parts: used to connect the main circuit and control circuit, and fix components and circuit boards.

3. Charger indicator light

comminicate

Power indicator light, when connected to AC power, the power indicator light will light up

Work

When the charger is connected to the battery and enters the charging state, the charging indicator light turns on.

warn

Warning indicator light, lights up when there is a fault inside the charger or an incorrect operation

4. Vehicle charger fault signal:

The fault information of the on-board charger will be reported to the bus through the CAN bus, and the fault information can be found through the CAN bus.

Common faults:

1. 12V low voltage power supply is abnormal. When the 12V module of the charger is abnormal, the BMS, instrument, etc. cannot communicate with the charger because there is no wake-up signal.

Judgment method: When 12V is not powered, the easiest way to judge is that when AC power is on, the battery does not make a relay closing sound, which is generally 12V abnormal. It is necessary to check the charging wake-up fuse and relay in the low-voltage fuse box, and whether the charger terminal has a pin withdrawal situation.

2. The battery voltage detected by the charger does not meet the requirements. This problem occurs when the BMS can work normally during the charging process, but the charger needs to detect the power battery voltage before it starts working. When the power battery voltage is within the working range, the on-board charger can work normally, otherwise the charger thinks that the battery does not meet the charging requirements.

Judgment method: This situation is usually caused by the high-voltage plug-in terminal being pulled out or the high-voltage fuse being blown, or the battery voltage exceeding the operating range.

3. The handshake between the charger and the charging pile is abnormal. During the operation of the charger, the charger will detect the handshake signal between the charger and the charging pile. When it is determined that the CC switch is disconnected, the charger thinks that the charging gun is about to be unplugged, and it will stop working to prevent live plugging and unplugging, thereby increasing the life of the charging gun terminal.