Introduction to DC charging piles
DC charging piles can be carried out from different dimensions such as power size, number of charging guns, structure, installation method, etc. Classification. Among them, the mainstream classification according to the structural form is to divide the DC charging piles into two types: integrated DC charging piles and split DC charging piles.
The electrical part of the DC charging pile consists of a primary circuit and a secondary circuit. The input of the main circuit is three-phase alternating current. After passing through the input circuit breaker and the AC smart energy meter, the charging module (rectifier module) converts the three-phase alternating current into direct current that the battery can accept, and then connects the fuse and the charging gun to charge the electric vehicle. . The secondary circuit is composed of charging pile controller, card reader, display screen, DC meter, etc. The secondary circuit also provides “start-stop” control and “emergency stop” operation; signal lights provide “standby”, “charging” and “full” status indications; the display screen, as a human-computer interaction device, provides card swiping, charging mode setting and start-stop Control operation.
DC charging pile charging process
Load DC voltage at both ends of the battery, charge the battery with a constant high current, and the battery voltage gradually rises slowly , rise to a certain level, the battery voltage reaches the nominal value, the SoC reaches 95% (for different batteries, different), and the battery continues to be charged with a constant voltage and small current. “The voltage has gone up, but the power is not fully charged, that is, it is not full. If there is time, you can use a small current to fill it up.” In order to realize this charging process, the charging pile needs to have a “DC charging module” to provide DC power; a “charging pile controller” is required to control the “startup, shutdown, output voltage, and output current” of the charging module; The touch screen” is used as the man-machine interface to issue commands, and commands such as “start-up, shutdown, output voltage, and output current” are issued to the charging module through the controller. The simplest charging pile understood from the electrical level only needs a charging module, a control panel and a touch screen; if the commands such as power-on, power-off and output voltage, output current and other commands are made into several keyboards on the charging module, then one charging module can The battery is charged.
Detailed explanation of the charging process of the DC charging pile
The output of the DC charging pile consists of 9 wires, which are:
DC power line: DC+, DC-; equipment ground line: PE; charging communication line: S+, S-; charging connection confirmation line: CC1, CC2; low-voltage auxiliary power line: A+, A-.
The DC charging pile is to charge the electric vehicle through these 9 wires. The specific charging model is as follows:
Off-board charger (ie DC charging pile) and electric vehicle two connected through the vehicle socket. The S switch is a normally closed switch, which is associated with the button on the DC charging gun head (ie, the mechanical lock). When we press the button on the charging gun head, the S switch is turned on. U1 and U2 are a 12V pull-up voltage, R1~R5 are resistors with a resistance of about 1000 ohms, R1, R2, and R3 are on the charging gun, and R4 and R5 are on the vehicle socket.
Vehicle interface connection confirmation stage:
When we press the gun head button, insert the vehicle socket, and release the gun head button. The detection point 1 of the charging pile will detect the level change of 12V-6V-4V. Once 4V is detected, the charging pile will judge that the charging gun is successfully inserted, the vehicle interface is fully connected, and the electronic lock in the charging gun will be locked to prevent the gun head from falling off.
DC charging pile self-checking stage:
After the vehicle interface is fully connected, the charging pile will close K3 and K4 to make the low-voltage auxiliary power supply circuit conduct , supply power to the electric vehicle control device (some vehicles do not need power supply) (after the vehicle is powered, it will judge whether the vehicle interface is connected according to the voltage of monitoring point 2, if the voltage value is 6V, the vehicle device starts to periodically send communication handshake messages ), then close K1 and K2 to perform insulation detection. The so-called insulation detection is to detect the insulation performance of the DC line to ensure the safety of the subsequent charging process. After the insulation test is completed, the discharge circuit will be put into the discharge circuit to discharge the energy, and K1 and K2 will be disconnected, and at the same time, the communication handshake message will be sent periodically.
Charging ready stage:
Next, is the stage of mutual configuration between the electric vehicle and the DC charging pile. The vehicle controls K5 and K6 to close to make the charging The loop is turned on, the charging pile detects that the battery voltage at the vehicle end is normal (the voltage error of the battery described in the voltage and the communication message is ≤±5%, and within the range of the maximum and minimum voltage output of the charging pile), and then closes K1 and K2, then the DC The charging line is turned on, and the electric car is ready to start charging.
Charging stage:
In the charging stage, the vehicle sends the parameters of battery charging requirements to the charging pile in real time, and the charging pile will adjust the charging voltage in real time according to the parameters and current, and send their respective status information (charging pile output voltage and current, vehicle battery voltage and current, SOC, etc.) to each other.
End of charging stage:
The vehicle will be charged according to whether the BMS has reached a full state or received a “charging pile aborted charging message” sent by the charging pile. Determine whether to end charging (abnormal conditions will be introduced in subsequent articles). If the above charging end conditions are met, the vehicle will send a “vehicle stop charging message”, and disconnect K5 and K6 after confirming that the charging current is less than 5A. When the charging pile reaches the charging end condition set by the operator, or receives a “vehicle aborted charging message” from the car, it will send a “charging pile aborted charging message”, and control the charging pile to stop charging. After confirming the charging current When it is less than 5A, disconnect K1 and K2, put it into the bleeder circuit again, and then disconnect K3 and K4.
