Field Weakening Control of Interior Permanent Magnet Machine using Improved Current Interpolation Technique

An improved torque control under field weakening for interior permanent magnet machines (IPMM) is presented. The approach is founded on the recently proposed method to adjust d- and q-axis reference rotor current along constant torque curves using two-dimensional lookup tables. A new way of generating the reference current lookup tables based on machine data is presented. It allows to reduce complexity of the overall torque controller while maintaining all advantageous properties such as full torque linearity and highly dynamic behaviour. Normally invalid combinations of torque and flux linkage in the tables are replaced by operating points that are interpolated on the boundary of the operating area. This makes pre-limiting of the torque reference unnecessary. The scheme has been tested successfully on a 6 kW IPMM used in an ISG application