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.