Accurate torque control of saturated interior permanent magnet synchronous motors in the field-weakening region

This paper focuses on accurate torque control of saturated interior permanent magnet (IPM) synchronous motors operating in the field-weakening region, where the maximum torque per ampere strategy cannot be used. First, a simple-but yet accurate-torque calculation method that takes saturation effects into account is devised: the torque developed at an arbitrary (i_d, i_q) may be calculated using only six parameters, which makes the method well suited for DSP implementation. Next, a field-weakening strategy is suggested, which incorporates the new torque calculation method. In this way the torque is controlled accurately deep into the field-weakening region, where voltage and current limitations impose constraints on the allowable (i_d,i_q) excitation. Experimental results on a 15 kW low-voltage IPM motor are included to validate the practical usefulness of the work.