Vehicle-to-Home (V2H)

V2H systems require galvanic isolation to physically separate the vehicle's high-voltage DC bus from the home's AC grid during backup mode. This prevents DC injection into the AC network, which can saturate distribution transformers and create shock hazards.

• A dedicated bidirectional inverter with an internal isolation transformer is mandatory.
• The system must comply with UL 9741 and IEEE 1547 anti-islanding standards.
• Automatic disconnect occurs within milliseconds of grid failure detection to prevent backfeeding.

A physical or solid-state transfer switch is the core of V2H integration. It physically disconnects the main service panel from the utility grid before the EV inverter can energize the home's circuits.

• Whole-home backup requires a service-entrance-rated transfer switch.
• Sub-panel backup isolates only critical loads (refrigerator, lights, medical devices).
• The switch must be rated for the EV's continuous export power, typically 9.6 kW to 19.2 kW for residential systems.

The vehicle's Battery Management System (BMS) supplies high-voltage DC (typically 400V or 800V) to an external inverter. The round-trip efficiency of converting DC to AC for home use is a critical performance metric.

• Modern silicon carbide (SiC) inverters achieve 96-98% peak efficiency.
• Efficiency drops at low loads; optimal operation is between 20-80% of rated power.
• Thermal management of the inverter is essential during sustained high-power discharge to prevent derating.

V2H relies on high-level digital communication between the EV and the stationary charger/inverter. The dominant standard is ISO 15118-20, which extends the basic charging protocol to manage bidirectional power flow.

• Plug & Charge (PnC) uses X.509 certificates for automatic authentication.
• The EV communicates its State of Charge (SoC) and maximum discharge power limits.
• The home energy management system (HEMS) sends dynamic setpoints for real and reactive power.

When the grid fails, the V2H system must transition to island mode without interrupting power to critical loads. This seamless transition is a key differentiator from backup generators.

• The inverter operates in grid-forming mode, establishing voltage and frequency references.
• A battery buffer or supercapacitor bank inside the inverter bridges the gap during the transfer switch's mechanical operation.
• The system must handle inrush currents from motor loads like HVAC compressors during black-start.

A V2H system is not a standalone device; it integrates with a Home Energy Management System (HEMS) to optimize self-consumption and arbitrage.

• During normal grid-connected operation, the HEMS can command V2H discharge to shave demand charges.
• Integration with rooftop solar allows the EV to store excess PV generation for evening use.
• The HEMS uses Model Predictive Control (MPC) to forecast load and solar generation, scheduling V2H discharge to minimize grid imports.