A BPM or SRM electric motor (M) is supplied bus current. A PWM inverter (I) uses bus current to commutate the motor by Systematically energizing and de-energizing the motor's windings (W) with the current. The resultant bus current waveshape has characteristics that are a function of a commutation angle between a rotor (T) of the machine and its windings. The waveshape includes the effects of bus ripple or transients. A commutation controller (10) samples the waveshape during each commutation interval to obtain commutation angle information. The controller provides control inputs to an inverter (I) to control commutation angle in response to the sample information. Commutation angle control includes calculating a control variable (I.sub.curve) which is a function of commutation angle. This variable is comprised of sampled data values which are additively combined according to a prescribed formula and which provide a high degree of linearity over a wide range of commutation angles. The controller is further responsive to the motor's impulse response (H.sub.motor (t)) to reject bus ripple effects on the waveshape samples. By employing the control variable and impulse response, the controller provides appropriate frequency (f.sub.out) and voltage (V.sub. out corrected) inputs to the inverter to achieve an optimum commutation angle relationship between the rotor and windings.