Braking a Variable Flux-Intensifying IPMSM in Minimal Time

This paper proposes a method for braking the variable flux-intensifying interior permanent-magnet synchronous motor (FI IPMSM) under a minimal time condition while operating in the high-speed region. The rare-earth PMs retain its magnetization as the flux weakening current is decreased. This inherent feature of the PMs makes the braking torque maximization possible for IPMSMs, thus minimal-time braking can be achieved. In contrast, the low-coercive magnets utilized in variable-flux IPMSMs are partially demagnetized in the highspeed region. This means that the variable-flux IPMSM takes a longer time to stop if compared to the IPMSM. Supplying a magnetizing current that ranges from 1 to 3 p.u. in the highspeed region while the inverter is running out of voltage is quite challenging. In this paper, an analytical solution to the amount of magnetizing current required to maximize the braking torque based on the available voltage to ensure minimal-time braking is presented. The simulated and experimental results obtained using a 5-hp variable FI IPMSM show the validity of the proposed braking scheme. A front-end active rectifier is utilized to recuperate the braking energy and maintain the dc bus voltage constant.