MTPV Flux-Weakening Strategy for PMSM High Speed Drive

High speed permanent magnet synchronous motors (PMSMs) are used in electric vehicles because of their intense power density. The high speed implies a significant electromotive force and requires flux weakening. The usual control algorithms realize flux weakening by adding a negative Id current component when the voltage required by the current regulation exceeds the maximum voltage depending on the battery. If the magnet can be totally defluxed, then it is better to use a maximum torque per volt strategy. Furthermore, there is no speed regulation in the control and the driver gives a torque reference. This reference value has to be limited by the attainable operating points; therefore, the battery power limit has to be taken into account in addition to the voltage and current limits. The d-q current references are calculated to minimize the total current magnitude required to reach the reference torque. This paper proposes a strategy to control a PMSM operating continuously since the speed zero up to the maximum speed without the switching algorithm, in order to take into account the different limitations (current, voltage, and power) and to expand the overspeed zone. In order to validate the proposed strategy, experimental results are shown for a low power machine.