Bidirectional Power Transfer (BPT)
ISO 15118 concept for charging and discharging where an EV and EVSE coordinate power flow in both directions (V2G/V2B), not just charging.
Technical Details
In ISO 15118-20, BPT is offered as dedicated services (AC BPT / DC BPT) with negotiated parameters and power schedules. Implementations align with IEC 61851-1 behavior for charging and similarly for discharging. Depending on the setup, discharging can be represented with negative power/current values and requires careful coordination of contactors and converter behavior.
Fleet Applications
Enables fleets to turn depot batteries into flexible energy assets: peak shaving, backup power, and grid services—while still meeting departure readiness and operational constraints.
Related Terms
Vehicle-to-Grid (V2G)
Bidirectional charging technology that enables electric vehicles to return digitally managed energy from their batteries back to the power grid during peak demand periods.
ISO 15118 (Plug & Charge)
Family of standards for high-level communication between an electric vehicle (EV) and a charging station (EVSE), enabling certificate-based "Plug & Charge" and advanced charging control (including bidirectional charging in newer editions).
BPT Channel (Unified vs Separated)
ISO 15118-20 parameter that describes whether bidirectional energy flow uses one shared channel (Unified) or two dedicated channels (Separated) for opposite directions.
Generator Mode (Grid-Following vs Grid-Forming)
ISO 15118-20 BPT parameter describing the inverter behavior during discharge: following the grid voltage/frequency (grid-following) or actively forming them (grid-forming).
Islanding Detection (Active vs Passive)
Techniques to detect an unintentional “island” where a site keeps energizing a local grid segment after it is disconnected from the main grid.
Bidirectional Charging
Charging that allows energy to flow both into the vehicle and back out to a building or the grid.