My PWM and sampling frequency is 10kHz and the frequency of the output current is 50Hz. I have applied a very simple digital low-pass filter with a cut-off at 1kHz to the measured voltages which has improved the performance of the controller significantly. However, I would prefer a filter with a sharper roll off since this introduces around 3deg phase shift around 50Hz and there is still some high frequency content getting by.

What would be the next step up the complexity scale in terms of filtering? I've thought about just cascading a few first order filters. I've also seen both FIR and IIR filters discussed in this context. It's a while since I did any sort of DSP class so I'm unsure how to proceed. What sorts of filter would be appropriate here?