A power system architecture for powering a transportation refrigeration system comprising: a transport refrigeration unit TRU operable in a vapor compression cycle, the TRU having a compressor configured to compress a refrigerant, 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, the TRU also including a TRU controller configured to execute a process to determine an AC power requirement for the TRU; a generator power converter configured to receive a first generator three phase AC power from an alternating current AC generator operably coupled to an axle or wheel hub, and configured to provide a generator DC power; a grid power converter configured to receive a grid three phase AC power from a grid power source operable to provide the grid three phase AC power; the grid power converter operable to provide a grid DC power; an energy storage device, the energy storage device operable to provide a variable DC power and connected to a variable DC bus; a power management system operably connected to direct power to the TRU based at least in part on at least the AC power requirement; and characterised by an energy storage system including the energy storage device, a first energy storage system DC/DC converter configured to convert the variable DC power on the variable DC bus to a fixed DC power on a fixed DC bus to provide the fixed DC power to the power management system based at least in part on the AC power requirement, and a second energy storage system DC/DC converter configured to convert at least a portion of the fixed DC power on the fixed DC bus to supply the variable DC bus and the energy storage device. a transport refrigeration unit TRU operable in a vapor compression cycle, the TRU having a compressor configured to compress a refrigerant, 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, the TRU also including a TRU controller configured to execute a process to determine an AC power requirement for the TRU; a generator power converter configured to receive a first generator three phase AC power from an alternating current AC generator operably coupled to an axle or wheel hub, and configured to provide a generator DC power; a grid power converter configured to receive a grid three phase AC power from a grid power source operable to provide the grid three phase AC power; the grid power converter operable to provide a grid DC power; an energy storage device, the energy storage device operable to provide a variable DC power and connected to a variable DC bus; a power management system operably connected to direct power to the TRU based at least in part on at least the AC power requirement; and characterised by an energy storage system including the energy storage device, a first energy storage system DC/DC converter configured to convert the variable DC power on the variable DC bus to a fixed DC power on a fixed DC bus to provide the fixed DC power to the power management system based at least in part on the AC power requirement, and a second energy storage system DC/DC converter configured to convert at least a portion of the fixed DC power on the fixed DC bus to supply the variable DC bus and the energy storage device.