A system for a hybrid electric vehicle comprising: a first inverter coupled to a generator, where the generator is mechanically couplable to an engine, the first inverter, when the generator is coupled to the engine, is configured to receive AC power from the generator and provide DC power for a DC link; an energy storage system selectively couplable to the DC link; a motor; a second inverter coupled to the DC link and configured to receive the DC power from the first inverter and the energy storage system when coupled and provide AC power to the motor; and a propulsion shaft coupled to the motor; characterized in that the vehicle further comprises: a switch configured to close to electrically couple the energy storage system to the DC link and open to electrically isolate the energy storage system from the DC link; and a processor configured to control the switch to open when a required propulsion output from the motor corresponding to a requested propulsion exceeds a power available to the motor or when an output from the motor which is producible from the power available to the motor is less than the required propulsion output from the motor corresponding to the requested propulsion, wherein when the switch is opened, the processor is configured to instruct an engine controller to cause the engine to boost engine output. a first inverter coupled to a generator, where the generator is mechanically couplable to an engine, the first inverter, when the generator is coupled to the engine, is configured to receive AC power from the generator and provide DC power for a DC link; an energy storage system selectively couplable to the DC link; a motor; a second inverter coupled to the DC link and configured to receive the DC power from the first inverter and the energy storage system when coupled and provide AC power to the motor; and a propulsion shaft coupled to the motor; characterized in that the vehicle further comprises: a switch configured to close to electrically couple the energy storage system to the DC link and open to electrically isolate the energy storage system from the DC link; and a processor configured to control the switch to open when a required propulsion output from the motor corresponding to a requested propulsion exceeds a power available to the motor or when an output from the motor which is producible from the power available to the motor is less than the required propulsion output from the motor corresponding to the requested propulsion, wherein when the switch is opened, the processor is configured to instruct an engine controller to cause the engine to boost engine output. a switch configured to close to electrically couple the energy storage system to the DC link and open to electrically isolate the energy storage system from the DC link; and a processor configured to control the switch to open when a required propulsion output from the motor corresponding to a requested propulsion exceeds a power available to the motor or when an output from the motor which is producible from the power available to the motor is less than the required propulsion output from the motor corresponding to the requested propulsion, wherein when the switch is opened, the processor is configured to instruct an engine controller to cause the engine to boost engine output.