Discrete Current Controller Design using Ragazzini Method for Active Damper

The capability of an active damper to suppress resonances in a wide range of harmonics frequencies and its stability depends heavily on the tracking performance of its inner current controller. Even though nowadays most of the current controllers are implemented digitally in a microcontroller or DSP, the conventional current controller design is still done in the continuous frequency domain. Later on, the current controller discretization is carried out using transformation techniques (e.g. Tustin transformation, forward rule, etc). The disadvantage of such methodology it that the current controller bandwidth is restricted to be ten times smaller than the PWM sampling frequency. This fact affects negatively the performance of the active damper and its stability especially at small values of the emulated resistance. In this paper, we present a current controller design that is carried out directly in the discrete domain using the Ragazzini method. The result is a current closed loop with a bandwidth three times higher than the bandwidth achieved by current controllers designed with traditional methods. The achieved higher bandwidth boosts the effectiveness of the active damper and pushes its stability limit forward.