A transport refrigeration system comprising: a vehicle ; a container ; a transportation refrigeration unit TRU comprising: a compressor configured to compress a refrigerant, the compressor having 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 /76); a return air temperature RAT sensor disposed in the return airflow and configured to measure the temperature RAT of the return airflow ; and a TRU controller operably connected to the RAT sensor and configured to execute a process to determine an alternating current AC power requirement for the TRU based on at least the RAT; and a power management system , wherein the power management system directs power to the TRU based at least in part on the AC power requirement, and characterised in that , the power management system is configured to receive at least one of: a first three phase AC power from an AC generator operably coupled to an axle or wheel hub of a tractor or trailer portion of the vehicle; and a second three phase AC power from a generator power converter that converts the first three phase AC power . a vehicle ; a container ; a transportation refrigeration unit TRU comprising: a compressor configured to compress a refrigerant, the compressor having 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 /76); a return air temperature RAT sensor disposed in the return airflow and configured to measure the temperature RAT of the return airflow ; and a TRU controller operably connected to the RAT sensor and configured to execute a process to determine an alternating current AC power requirement for the TRU based on at least the RAT; and a power management system , wherein the power management system directs power to the TRU based at least in part on the AC power requirement, and characterised in that , the power management system is configured to receive at least one of: a first three phase AC power from an AC generator operably coupled to an axle or wheel hub of a tractor or trailer portion of the vehicle; and a second three phase AC power from a generator power converter that converts the first three phase AC power . a compressor configured to compress a refrigerant, the compressor having 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 /76); a return air temperature RAT sensor disposed in the return airflow and configured to measure the temperature RAT of the return airflow ; and a TRU controller operably connected to the RAT sensor and configured to execute a process to determine an alternating current AC power requirement for the TRU based on at least the RAT; and a power management system , wherein the power management system directs power to the TRU based at least in part on the AC power requirement, and characterised in that , the power management system is configured to receive at least one of: a first three phase AC power from an AC generator operably coupled to an axle or wheel hub of a tractor or trailer portion of the vehicle; and a second three phase AC power from a generator power converter that converts the first three phase AC power . a first three phase AC power from an AC generator operably coupled to an axle or wheel hub of a tractor or trailer portion of the vehicle; and a second three phase AC power from a generator power converter that converts the first three phase AC power . <EOS>