Practical field weakening current vector control calculations for PMSM in vehicle applications

Although the mathematics for defining field weakening expressions are relatively uncomplicated, the application of these expressions for practical field-weakening implementations is not well documented. This paper describes the derivation of simplified expressions for implementing field weakening in field-oriented control (FOC) algorithms for use in a high torque, permanent-magnet synchronous motor designed for automotive in-wheel applications. The formulae are based on modelled motor characteristics and take into account the varying states of the system in terms of rotational speed, torque demand, and supply voltage to produce a few uncomplicated expressions. The simplicity of the calculations makes them appealing for use in microcontroller applications, where a high processing overhead is already taken up with current control and safety-critical functionality.