A Novel Proportional‐Integral Synergetic Controller for the Onboard Microgrids With Stability Analysis

ABSTRACT In hybrid electric vehicles (HEVs), the stability of the onboard microgrid is crucial as it directly affects the secure and dependable operation of all electrical equipment in the vehicle. However, the drive motors in HEVs are usually powered by tightly controlled inverters which absorb more current with lower voltage. This negative impedance characteristic may cause direct current (DC) bus voltage fluctuations or even impact the stability of the entire system. To address this issue, this paper develops a nonlinear system model of the onboard microgrid first. The negative impedance of the drive motors' inverters is incorporated in such a nonlinear system model. The inevitable parasitic resistances of the onboard microgrid are also modeled. Then, a novel proportional‐integral synergetic controller (PISC) is designed for the DC/DC converter by regulating a proper macro‐variable, which is composed of the DC bus voltage and inductor current. Under such a controller, the bus voltage is ensured to reach the reference voltage rapidly. The convergence rate is also configurable, and the system operates without chattering. Though the system is shown to be stable under the PISC, large fluctuations may still exist. Thus, a stability criterion for the whole nonlinear system is also formulated by utilizing the principles of mixed potential function (MPF) theory. The criterion shows how the circuit parameters and loads fluctuations impact the system stability under specific control. Then, it is shown that the criterion helps to predict large fluctuations under the PISC. Finally, various case studies are provided to validate the effectiveness of the proposed controller.