Hello, guys. In field oriented control of ac machines, the electromagnetic torque is proportional to the q-axis current. We can control instantaneous torque by control the q-axis current. If the torque we want is a constant value,with PI controller, no problem, no steady error. But if we want to have sinusoidal torque, with PI controller, there would be a steady error. What can we do about that? Any other method? Thank you!