Of the many loss-producing elements in motor control, total harmonic distortion or THD is probably the most overlooked. THD energy is a byproduct of the conversion of power process and causes eddy-current losses in the motor stator and rotor. Controlling a motor to run at 90,000 RPM, such as Power and Control Design has done, requires close attention to every detail.
In the 90,000 RPM motor example, what we would ideally like is a sinusoidal current at the motor’s fundamental frequency—completely void of any effects of PWM switching currents, i.e.,
current ripple, or sinusoidal approximations and errors produced by the power conversion device that don’t match the motor’s Id, Iq, Vd and Vq vectors.
Now back to reality. Of course this is the ideal situation. All we can do is question why we have so many harmonics and attack each source in order to better approximate the desired vectors.
The graphic to the right shows the actual spectral energy distribution achieved in Power and Control Design’s Automotive Motor Control program with a major automotive OEM. The net effect of our switching topology and other proprietary methods deployed to reduce harmonics resulted
in a superior spectral energy distribution and, in turn, reduced heat and power loss in the motor.