1. V2G Power Topology

The core of a bidirectional V2G charger is the AC/DC bidirectional converter, using a voltage-source PWM rectifier topology. Operation is reversible:

• Charging mode (rectification)： Grid AC → rectified to DC → charges vehicle battery

• Discharging mode (inversion)： Vehicle battery DC → inverted to AC → feeds back to grid

Key components include IGBT or SiC MOSFET H-bridge or T-type three-level structures with high-frequency PWM control, regulating grid-side current amplitude and phase for power factor correction (PFC) and bidirectional energy flow. In discharging mode, precise grid voltage phase/frequency synchronization (typically 50/60Hz) via Phase-Locked Loop (PLL) ensures power quality compliant with IEEE 519 harmonic standards.

2. V2G Impact on Battery Life

V2G increases battery cycling, affecting health. Key factors:

• Depth of Discharge (DOD)：Deep discharges (e.g., 100% to 20% SOC) accelerate aging; shallow cycles (SOC maintained at 40%-80%) have minimal impact

• C-rate：High currents accelerate lithium plating and SEI growth; recommended V2G discharge rate ≤0.5C

• Thermal management：Heat generation accelerates aging above 45°C; integrated thermal management required

Current research consensus: With moderate V2G dispatch strategies (shallow cycles, controlled C-rate), incremental battery degradation can be limited to ≤2% annual capacity loss, with annual V2G revenue covering depreciation costs and generating net positive returns.

3. Communication Protocol Stack (ISO 15118)

V2G relies on vehicle-charger-grid data exchange. ISO 15118 defines EV-charger communication protocols supporting:

• Plug & Charge：Automatic authentication and transaction initiation upon plug-in, eliminating cards or app operations

• Smart Charging：Grid load signals sent from charger to vehicle BMS for automatic power adjustment

• V2G Dispatch Commands：Grid operators send discharge instructions (time, power, duration) via chargers to vehicles; BMS executes upon confirmation

Physical layer communication uses PLC (Power Line Communication over CP pilot wire) or wireless (Wi-Fi/cellular), with application layer using V2GTP (Vehicle-to-Grid Transport Protocol) and EXI (Efficient XML Interchange) for data exchange.