The wind of new energy vehicles has swept the world, and my country has begun to gradually support the manufacture of new energy vehicles and the construction of supporting facilities. Therefore, the current stage can be said to be the outbreak period of charging piles and new energy vehicles. Some traditional technologies have also joined this emerging market. Taking optocoupler isolation as an example, using optocoupler isolation circuit can achieve better security. This article describes this technique.
Charging piles can provide charging services for new energy vehicles, similar to fuel dispensers at gas stations. It can be fixed on the ground or wall, installed in public buildings (public buildings, shopping malls, public parking lots, etc.) and residential parking lots or charging stations, and can charge various types of electric vehicles according to different voltage levels. The input end of the charging pile is directly connected to the AC power grid, and the output end is equipped with a charging plug to charge the electric vehicle. Charging piles generally provide two charging methods: conventional charging and fast charging. People can use a specific charging card to swipe the card on the human-computer interaction interface on the charging pile to perform corresponding charging methods, charging time, cost data printing and other operations. The display screen of the charging pile can display data such as charging capacity, cost, and charging time.
The AC current is rectified and converted to DC, boosted by PFC, and then isolated and converted by DCTODC to obtain an output voltage for charging the car. The main control MCU samples and monitors the voltage and current information of the high-voltage side, controls the power supply equipment to be turned on and off, and ensures the safe and reliable operation of the system.
In addition to providing insulation and isolation, optocouplers also ensure signal integrity. In the charging pile, it is necessary to collect external information and then communicate with the external system of the charging pile. In this case, a digital isolation optocoupler is needed. The digital isolation optocoupler isolates the weak part of the charging pile (including the control part) from the external port and insulation. On the one hand, it prevents the weak part of the charging pile (including the control part) from being disturbed. On the other hand, it prevents the communication information from being disturbed and ensures the integrity of the information signal.
In product design, industrial products have high requirements on reliability, and products need to pass various safety certifications and electromagnetic compatibility test certifications. The interference on the strong current side is generally large, and it is easy to interfere with the weak current. In more serious cases, it will interfere with the main control part of the system, causing the system to fail to work normally. In order to prevent the interference from the strong current side from affecting the weak current side, designers need to isolate the strong and weak currents. In the charging pile system, it is necessary to monitor the voltage and current of the busbar and the voltage and current of the output port. In this case, an isolated voltage and current sampling device is required. Optocoupler isolation is a good choice.
Second, the traction inverter system in an electric vehicle is likely to operate at a DC voltage of around 800V. This high DC voltage is converted to AC to drive the traction motors. However, the traction battery in an EV does not simply connect multiple 12V batteries in series to generate 800V, it is a sealed unit. The addition of this high voltage system and its role in the vehicle means that 12V systems are now often treated as auxiliary systems. It provides power to all auxiliary equipment of the traction system, including the traction control system.
The main high voltage battery is now responsible for powering the 12V auxiliary system to keep the battery charged. For safety reasons, operation requires electrical isolation between the two voltage domains.
Isolation is crucial
A typical EV has many functional units, including traction inverters, climate control and heating systems, and on-board chargers. These systems operate at completely different voltage levels and must be electrically isolated. Galvanic isolation prevents current from flowing between different voltage domains while still supporting data transfer and power flow.
