I. Preparations before charging: A safe prelude to connection and self-test
The charging process of a DC charging station begins with a rigorous preparation phase, which is the first line of defense for ensuring safety. Users must first park and turn off their vehicles, then complete identity verification and payment authorization via the charging station's screen or app. For some devices, authorization is required before the charging gun can be unplugged to prevent risks caused by unauthorized cable movement. The national standard 9-pin charging gun is the key interface for energy transmission. Contacts 1 and 2 are responsible for DC positive and negative electrode transmission, capable of handling a maximum voltage of 1000V and a current of 600A, while contacts 5 and 6 are specifically used for communication with the vehicle.
After the charging gun is inserted, the mechanical and electronic locks immediately engage and lock, and the IP55-rated interface effectively isolates rainwater and dust. At this point, the charging station enters a full self-test mode: the insulation detection module performs an insulation test on the charging circuit to ensure there is no risk of leakage; the main controller activates the discharge resistor to discharge any residual high voltage from the capacitors to below 60V; simultaneously, the auxiliary power supply begins to power the vehicle's battery management system (BMS), establishing a "communication channel" between the charging station and the vehicle. This series of operations is typically completed within one minute, and the charging preparation phase is considered complete only after all indicators are normal.
II. Core Transformation: Two "Transformations" from Alternating Current to Direct Current
The core capability of DC charging piles is to efficiently convert AC power from the power grid into DC power that can be directly stored in batteries. This process is achieved through two-stage power conversion. The charging module, as the "energy heart," is the key to determining the conversion efficiency. It consists of a three-phase active power accelerator (PFC) and a DC/DC converter, which work together to reshape the electrical energy.
The first stage of conversion is completed by a three-phase active PFC circuit. After the charging pile is connected to 380V three-phase AC power, it first passes through an EMC filter to remove electromagnetic interference, and then the PFC circuit rectifies the AC power into pulsating DC power. More importantly, the PFC circuit is controlled by a DSP chip to ensure that the input current waveform closely follows the voltage waveform, raising the power factor to above 0.99, which reduces energy waste and avoids harmonic pollution to the power grid. Taking a 480kW liquid-cooled charging pile as an example, this step outputs a stable 750-850V high-voltage bus DC power, laying the foundation for subsequent conversion.
The second-stage conversion is performed by the DC/DC converter. After the high-voltage DC power enters this module, the high-frequency transformer first provides electrical isolation to ensure the safety of people and vehicles. Then, through PWM pulse width modulation technology, the voltage is precisely adjusted to the range required by the battery. Due to the significant voltage differences between batteries of different models (200V-1000V), the converter dynamically adjusts according to BMS commands, outputting a constant high current in the early stages of charging and automatically switching to a constant voltage later to adapt to the battery's charging characteristics. The multi-module parallel design allows for flexible power aggregation, achieving output power from 11kW to over 600kW.
III. Intelligent Control: BMS-led "On-Demand Supply"
The charging process is not a simple "feeding" of power, but rather a "cooperative operation" between the charging pile and the BMS, with the BMS acting as the "commander." The two communicate in real time via the CAN bus, exchanging dozens of data sets per second to ensure precise matching of charging parameters with battery status. The BMS continuously monitors parameters such as the battery's current state of charge (SOC), temperature, and individual cell voltage, dynamically sending commands for maximum allowable voltage and current.
When the battery level is low, the system enters the constant current charging phase, where the charging pile continuously supplies power at the set maximum current. During this phase, the voltage steadily increases, resulting in the highest charging efficiency. When the battery level reaches approximately 80%, the BMS issues a command to switch to the constant voltage phase, where the voltage remains stable while the current gradually decreases to prevent battery damage from overcharging. Taking a 600kW high-power charging pile as an example, its 1000V voltage and 600A current output combination is precisely through this dynamic adjustment to adapt to the battery needs of different car brands and models.
During charging, the main controller monitors various parameters in real time: voltage and current sensors ensure accurate output, and temperature sensors track the temperature of the module and cables. If the temperature exceeds 50°C, the liquid cooling + air cooling system is activated to reduce the temperature; if the temperature reaches 75°C, the system immediately shuts down for protection. This "dual monitoring" mechanism ensures that high-power charging is always within safe limits.
IV. Final Stage: Safe Power Off and Energy Recovery
There are typically three triggers for charging to end: user-initiated termination, battery fully charged, or detection of an anomaly. Regardless of the situation, the system follows a strict power-off procedure: the main controller first cuts off the output of the DC/DC converter, then shuts down the main relay, discharging the output voltage to a safe range. Once the voltage drops below 60V, the electronic lock automatically unlocks, at which point the user can remove the charging gun.
Smart meters accurately measure charging power with an accuracy level of 0.5, ensuring accurate billing. Charging stations upload charging data to the backend via Ethernet or 4G modules, simultaneously updating their status to standby mode. For devices equipped with bidirectional charging capabilities, surplus battery power can be fed back to the grid during peak hours, achieving peak shaving and valley filling for optimized energy utilization.
From AC power from the grid to DC power from the battery, DC charging piles achieve efficient energy replenishment through a two-stage conversion, ensure charging safety through intelligent communication, and adapt to diverse needs through modular design. With the popularization of supercharging technology above 600kW, and breakthroughs in technologies such as liquid cooling and wide voltage platforms, this "energy conversion station" is making the energy replenishment experience of electric vehicles almost as convenient as refueling a gasoline car.
