This paper presents averaging-based models of hybrid electric power systems for refrigeration units in delivery trucks. The model is intended to be used for a system-level power and energy flow study and eventually for a development of prototypes. Challenges unique to this hybrid application, including the thermal system interface, drive cycle response, and battery management, are introduced. The system topology is presented, including the hybrid power architecture, electrical-thermal system specifications, and the integrated model operation and controls. The modeling approach for each electrical component, including ac machines, the battery set, and converters, is discussed. An average modeling technique is used, because it can track system-level power and efficiency over a long time interval with fast simulation. Battery simulation is improved from previous literature to provide a more accurate and robust solution. The model, interfaced with the thermal system, is verified by simulation studies in MATLAB/Simulink. The average model is also validated through experiments, including an active front end test, a battery test, and a variable speed ac motor drive test. Using the model, energy and cost-effectiveness is analyzed and discussed.