Modeling, Analysis, and Attenuation of Uncontrolled Generation for IPMSM-Based Electric Vehicles in Emergency

Inevitable faults such as overcurrent might occur when interior permanent magnet synchronous machines (IPMSM) with high constant-power speed ratio in electric vehicles rotate over high-speed range, causing uncontrolled generation (UCG) phenomenon. In the process, the large current might be generated and then flow back to the battery through the uncontrolled rectifier, posing a great risk to the power devices. For a better understanding of UCG, this paper first explains the transient process by establishing a dynamic model of the uncontrolled rectifier (UR). Then, aiming at the steady-state generating stage, an enhanced UCG model is proposed for the analysis of motor parameter dependencies. Because it is found that the maximum UCG feedback current at high speed is inversely proportional to the d-axis inductance, an inductance design/optimization method for appropriate d-axis by changing the rotor structure is developed to attenuate the side effect of UCG. The proposed UCG model and the validity of the design/optimization approach are verified by experiments. The results have proved that the new model can be employed to estimate the working state of an IPMSM drive system under UCG operation and determine the optimal motor parameters in the course of machine design and optimization.