Development and performance validation of an ISG diesel hybrid power-train for city buses - part II: Control strategy and road test

This is the second part of the two-part paper to illustrate the control system design and multi-energy strategy, it is the key to fulfill the fuel economy target for ISG hybrid bus. Based on a hierarchical structure, the control system is developed with the HCU (hybrid control unit) as the central controller to coordinate the motor, engine and CAN communication protocol. The multi-energy control strategy is consisted of the auxiliary strategy and the main strategy. The first one includes the finite state machine which decides the turning-point from one state to another state and the 2-quad tree of expert system which is adopted to realize the automatic start/stop function; the last one is called as the torque distribution strategy that satisfies the drive demand as well as implements the optimal torque distribution by fuzzy method. The parallel regenerative brake strategy and self-adaptive SOC balance strategy are all cooperated into the fuzzy based torque distribution strategy. The road tests are done to test the performance of ISG power-train and to validate the functions of the control system. The result shows that the fuel economy is 25% better than the traditional bus.