best value public electric car charging stations engineering technology

1. Charging station electrical system
The electrical system of the charging station includes three parts: power supply system, charging equipment and monitoring system. Its structural block diagram is shown in Figure 1. The power supply system provides power for charging equipment, and is mainly composed of primary equipment (including switches, transformers and lines, etc.) and secondary equipment (including detection, protection, control devices, etc.). The electric car charger is a nonlinear load, which will generate harmonics, which is a kind of pollution to the power grid. Effective measures must be taken, such as power factor correction or reactive power compensation technology, to limit the total spectral wave amount of the electric car charger entering the power grid.
The monitoring system consists of one or more workstations or servers, which can include monitoring workstations, data servers, etc., connected through the network. The monitoring workstation provides charging monitoring human-computer interaction interface for charging machine monitoring and data collection, query and other work; the data server stores the original data and statistical analysis data of the entire charging system, and provides data services and other application services.

2. Working principle of the charging pile
The charging equipment in the charging station is the core part of the electrical system of the entire charging station. Electric car charging piles are generally divided into DC charging piles and AC charging piles.

1) Working principle of DC charging pile
The three-phase alternating current of the electrical system of the charging station is rectified into direct current by the three-phase bridge uncontrollable rectifier circuit, filtered and supplied to the high-frequency DC/DC power converter, and the required direct current is output by the high-frequency DC/DC power converter. After filtering again, it charges the electric car power battery. The electrical system of the DC charging pile is shown in Figure 2.

The new DC charging pile adopts the fast charging method, which is different from the traditional charging pile. The continuous current charging and pulse current charging methods adopt the intelligent variable pulse charging method. The charging pulse current waveform is shown in Figure 3, including charging pulse T₁, intermittent pulse T₂ and discharge pulse T₃. By intermittently stopping charging, the oxygen and hydrogen produced by the chemical reaction of the lead-acid battery have time to recombine and be absorbed, so that the next round of constant current charging can be carried out more smoothly, so that the lead-acid battery can absorb more electricity .

2) Working principle of AC charging pile
The block diagram of the electrical system of the AC charging pile is shown in Figure 4. The main circuit is composed of input protection circuit breaker, AC smart energy meter, AC control contactor and charging interface connector; the secondary circuit is composed of control relay, emergency stop button, running status indicator, charging pile intelligent controller and human-computer interaction equipment ( display, input and swipe).

The main circuit input circuit breaker has overload, short circuit and leakage protection functions; the AC contactor controls the on-off of the power supply; the connector provides a charging interface connected to the electric car, with a locking device and an anti-misoperation function.
The secondary circuit provides “start-stop” control and “emergency stop” operation; signal lights provide “standby”, “charging” and “full” status indication; AC smart energy meter performs AC charging measurement; human-computer interaction equipment provides card swiping and charging methods Setup and start/stop control operations. Figure 5 shows the workflow of the AC charging column swiping transaction.

3. AC charger features
(1) The AC input side is equipped with a leakage protection switch, which has the functions of overload protection, short circuit protection and leakage protection on the output side.
(2) The AC input side is equipped with a D-level lightning arrester, which has the protection functions of anti-induction lightning and anti-operational overvoltage.
(3) The AC output side is equipped with an AC smart energy meter for AC charging measurement, and the metering information can be uploaded to the charging pile intelligent controller and the power consumption collection terminal through RS-485.
(4) The charging pile intelligent controller has the functions of comprehensive measurement, control and protection of the running status of the charging pile, such as running status monitoring, fault status monitoring, charging metering and billing, and linkage control of the charging process.
(5) Equipped with a color touch screen or LCD man-machine interface, the charging charging method can be set according to the amount of electricity, amount, time and automatic charging; the charging start method can choose immediate charging or scheduled charging; the charging method can be displayed in real time during the charging process, Time, power and billing information.
(6) Configure the running status indicator light bar, the green light is always on to indicate the “standby” state of the charging pile, the red light is always on to indicate the “charging” state of the charging pile, the yellow light is always on to indicate the “full” state of the charging pile, and the yellow light is flashing to indicate charging. Pile “fault” status, including interlock failure, circuit breaker tripping (overload protection, short circuit protection or leakage protection).
(7) Configure a radio frequency card reader, support IC card payment method, and adopt a combination of “withholding fee and actual checkout”.
(8) With perfect communication function, the charging pile intelligent controller obtains the metering information of the smart energy meter through RS-485, and completes the linkage control of charging billing and charging process; The information and equipment status information are uploaded to the background monitoring system, and the control commands of the background monitoring system are obtained and executed.