A transportation refrigeration unit and power system (20, 26) comprising: a compressor configured to compress a refrigerant, the compressor having a compressor motor configured to drive the compressor; an evaporator heat exchanger operatively coupled to the compressor; an evaporator fan configured to provide return airflow from a return air intake and flow the return airflow over the evaporator heat exchanger; a return air temperature sensor disposed in the return airflow and configured measure the temperature of the return airflow; a transportation refrigeration unit controller operably connected to the return air temperature sensor and configured to execute a process to determine an AC power requirement for the transportation refrigeration unit based on at least the return air temperature; a power management system the power management system configured to receive a second three phase AC power from a generator power converter that coverts a first DC power; and at least one energy storage system configured to receive a three phase AC power from the power management system; wherein the power management system directs power to the transportation refrigeration unit based at least in part on the AC power requirement; wherein the energy storage system comprises an energy storage device and an AC/DC converter configured to convert at least a portion of the three phase power to DC power to supply the energy storage device; characterised in that, the energy storage system is configured to provide another three phase AC power to the power management system and comprises a DC/AC converter configured to provide the another three phase AC power to the power management system based at least in part in the AC power requirement. a compressor configured to compress a refrigerant, the compressor having a compressor motor configured to drive the compressor; an evaporator heat exchanger operatively coupled to the compressor; an evaporator fan configured to provide return airflow from a return air intake and flow the return airflow over the evaporator heat exchanger; a return air temperature sensor disposed in the return airflow and configured measure the temperature of the return airflow; a transportation refrigeration unit controller operably connected to the return air temperature sensor and configured to execute a process to determine an AC power requirement for the transportation refrigeration unit based on at least the return air temperature; a power management system the power management system configured to receive a second three phase AC power from a generator power converter that coverts a first DC power; and at least one energy storage system configured to receive a three phase AC power from the power management system; wherein the power management system directs power to the transportation refrigeration unit based at least in part on the AC power requirement; wherein the energy storage system comprises an energy storage device and an AC/DC converter configured to convert at least a portion of the three phase power to DC power to supply the energy storage device; characterised in that, the energy storage system is configured to provide another three phase AC power to the power management system and comprises a DC/AC converter configured to provide the another three phase AC power to the power management system based at least in part in the AC power requirement.