Analysis on uncontrolled generation in electrical vehicles and a battery protection method

Interior permanent magnet synchronous motors often work under flux weakening state in electrical vehicles for higher speed but faults, such as overcurrent and overvoltage, might occur during that process, after which the power transistors are closed immediately and the battery packs are charged through three-phase uncontrolled rectifier composed of six fly-wheel diodes. It is called uncontrolled generation. The characteristics of uncontrolled generation, especially the output DC voltage and current quality of three-phase uncontrolled rectifier, need to be analyzed because they are relevant to the life and health of battery packs. At first, the model of uncontrolled generation is established. Then, analysis on the output properties of three-phase uncontrolled rectifier is carried out by means of mathematical calculation and simulation. Finally, a simple way to protect battery packs is described.