SLLSFV1 March 2025 MCF8329A-Q1
PRODUCTION DATA
PMSM or BLDC motors with magnetic saliency produces a reluctance torque from the difference between the direct-d axis inductance and the quadrature q-axis inductance. The maximum efficiency of the IPM motors can be achieved by proper selection of the current vector ratio between magnetic torque current and reluctance torque current in the total current. MCF8329A-Q1 provides the maximum torque per ampere control and in that, for a given bus current, it is possible to obtain the best torque performance by setting the d axis current reference as a function of the q axis current reference as per the equation below.
Ld and Lq are inductance of the d and q axis respectively. iq is the Q-axis current and ψm is the BEMF constant. In case of motors without saliency in the rotor, the inductances of d and q axis are the same and hence the point of maximum torque is always the one where d-axis current reference is 0. For motors with saliency, the d-axis reference can be set as a function of the q-axis reference as derived in the equation above so as to generate the maximum torque for any current drawn from the DC bus.