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An Insight into Electric Vehicle Charging Systems: A Closer Look at the Floor-Mounted EV Charging Pile



Electric Vehicle Charging Systems play a crucial role in the energy supply for power batteries. Essentially, these are power conversion devices that draw energy from power supply systems to charge car batteries. The two main forms of charging systems are Alternating Current (AC), or slow, charging system and Direct Current (DC), or fast, charging system.

AC charging and DC charging

In this article, we will shift our focus toward the Floor-Mounted EV Charging Pile, or named EV Charging Station, a commonly used charging method for new energy vehicles.

A Deeper Dive into the Floor-Mounted EV Charging Pile

The floor-mounted EV Charging Pile, or named EV Charging Station, are broadly divided into two categories: the Integrated Charging Pile and the Distributed Charging Pile.

Floor-Mounted EV Charging Pile-Distributed Charging Pile
Floor-Mounted EV Charging Pile-Integrated Charging Pile

The Integrated Charging Pile has its main control and module amalgamated into a single machine. This results in charging speeds that are faster. However, it comes with a drawback: its power is fixed and unupgradable which makes repairs and replacements a challenge.

On the other hand, the Distributed Charging Pile operates without a main control board module. These charging piles function merely as information inputs as all main control modules are integrated within the centralized control box. This type of charging pile provides flexibility in power distribution and convenience concerning repairs and replacements. However, due to the independent operation of its charging equipment and power distribution equipment, its charging speed is slower compared to the integrated version.

An Overview of AC Charging Pile

The AC Charging Pile provides AC slow charging for electric vehicles. It integrates power conversion, charging control, human-computer interaction control, communication, billing, and metering. It is constructed with various components which we shall delve into.

1. LCD Display

LCD Display of EV charging pile

The LCD display primarily demonstrates the relevant information about the charging pile and ensures the real-time status information of the charging process is shared with the user. Additionally, it allows users to choose different modes of charging and allows maintenance personnel to access the charging post for inquiries, settings, record clearings, executing other tasks.

2. Card-reader

The card-reader exists to initiate charging and charging settlements. It uses RFID to interact with the user card and relay information to the main control board via the RS232 serial interface.

3. Main Control Module (AC Control Module)

Main Control Module of EV Charging pile

The main control module acts as the core of the charging pile. It facilitates communication with the touch screen LED and relays important information during the charging process.

4. Terminal Block

The terminal block functions as an interface for the 220V input power supply, necessary for distributing the input 220V AC power to the single-phase circuit breaker.

5. Single-phase circuit breaker (Air Switch)

A single-phase circuit breaker, also known as an air switch, is a type of switch that automatically breaks the circuit whenever the current in the circuit exceeds the rated current.

Air switch is a very important electrical appliance in low-voltage power distribution network and electric power traction system, which integrates control and various protection functions in one, in addition to contacting and breaking the circuit, it also protects the circuit or electrical equipment from short circuit, serious overload and under voltage.

It mainly distributes the 220V voltage transmitted from the terminal block to the surge protector (lightning protector) and smart meter through closing.

The downstream of the single-phase circuit breaker is connected in parallel with the surge protector (lightning protector) and in series with the smart meter.

6. Surge Protector (Lightning Protector)

Surge protector, also known as lightning protector, usually connected in parallel in the circuit system.

When lightning occurs, lightning into the building of various types of metal pipes, wires, resulting in high-intensity electromagnetic induction, thus generating a large amount of impulse energy, the role of the surge protector is to overcurrent into the earth, reduce the potential difference between the various ports of the equipment.

It is suitable for 220/380V power supply and distribution system transient over-voltage protection, can effectively inhibit the induction over-voltage and system operation over-voltage caused by the tube power, to protect the safety of the equipment, and to protect the normal operation of the system.

7. Smart Meter

Smart meter is the intelligent terminal of smart grid, it is not the traditional sense of the power meter.

Smart meter in addition to the traditional power meter basic power consumption measurement function, in order to adapt to the use of smart grid and new energy sources, it also has a two-way multiple rate measurement function, the user side control function, a variety of data transmission modes since the two-way data communication function, anti-electricity theft function, and other intelligent functions.

Smart meter represents the future of energy-saving smart meter, smart meter, smart meter is the future of energy-saving smart meter, smart meter is the future of energy-saving smart meter, smart meter is the future of energy-saving smart meter. Smart meter represents the development direction of future energy-saving smart grid end-user intelligent terminal.

Single-phase circuit breaker, smart meter, AC contactor three in series in the circuit (mainly in series with the L line in the AC circuit), through the RS485 communication line to communicate with the main control module, the main control module to calculate its current, power.

8. AC Contactor

The role of the AC contactor is to output 220V AC power to the charging gun after the 220V voltage lost from the smart meter is controlled and closed by the relay module.

Electrical schematic diagram of AC charging pile

The electrical schematic diagram of AC charging pile is centered on the AC control box, connecting all electrical components of the charging pile together.

Door control switch, emergency stop switch, circuit breaker, contactor, etc. are connected to the input terminal of the AC control box; the charging gun is connected to the output terminal of the AC control box; and the display screen and status indicator are connected to the upper terminal of the AC control box, as shown in the figure.

Electrical schematic diagram of AC charging pile

Charging Strategy of AC Charging Pile

The charging plug is resistance coded, e.g. CC indicates the power level (maximum current loading capacity per phase) of the vehicle’s charging cable can be recognized. For this purpose it is necessary to determine the Rc resistance between CC and PE in the charging plug (as shown in the figure), through which the charger recognizes the rated charging current. the CC also serves to confirm the connection.

Charging Strategy of AC Charging Pile

The communication is carried out through the contact CP. In case the operating unit is activated, there is a voltage of 12V between CP and PE;

in the charger, the signal is reduced to about 9V by the resistor R3 in case the plug is recognized and locked;

after confirming the connection, the charger further closes the resistor R2, and the signal is reduced to about 6V, and the charging pile next closes the power contactor to start charging;

at this time, the signal generator in the charging unit sends out a 1000Hz PV signal to the charger, generator in the charging unit sends a PWM signal of 1000Hz, which specifies the maximum charging current currently available.

Process of AC Charging Pile for Electric Vehicles

Process of AC Charging Pile

Connection and AC Wake-up Phase:

  • Initially, the AC charging gun is inserted, and upon successful connection, the On-Board Charger (OBC) is woken up by the Control Pilot (CP) and Charging Connection Confirmation (CC) signals sent by the AC charging pile.
  • After verifying the normality of CC and CP signals, the OBC outputs a 12V voltage signal through a hardwire to wake up the Vehicle Control Unit (VCU).

VCU Wake-up and Power-up Phase:

  • Once woken up, the VCU first closes the Main Power Relay to awaken various E-CAN controllers and the main display.
  • The VCU then controls the high-voltage system to power up and assesses if the conditions are suitable for charging. If so, it sends a charging enable signal to the Battery Management System (BMS).

BMS and OBC Interaction Phase:

  • Upon receiving the charging enable signal from the VCU, the BMS sends a charging enable signal to the OBC.
  • Based on the current battery status and the charging pile’s output capability, the BMS also sends a requested charging current and voltage to the OBC.

Charging Phase:

  • With the charging enable signal from the BMS, the OBC initiates the charging process.
  • According to the requests from the BMS, the OBC converts the 220V AC power from the grid into DC power and charges the battery.

This entire process represents a typical AC charging workflow for electric vehicles, commencing with the insertion of the charging gun and culminating in the charging of the battery through a series of interactions and assessments among various control units. This ensures the safety and efficiency of the charging process.

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Leo Chen

Leo has rich experience in the field of EV charger industry.

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