Dual Loop Control of 400 Hz Inverter for Ground Power Units

In this paper dual-loop control method is proposed for control of 400 Hz inverter. Resonant controllers are used in the outer loop to regulate the amplitude of fundamental harmonic and to remove the unwanted harmonics. To avoid phase delay and bandwidth degradation, proportional controller is used as the inner control loop. In this paper, hybrid digital design in discrete- and continuous-time domain is introduced to design the inner and outer control loops. To decouple the control system from the load current disturbances and to improve the dynamic performance, a feed-forward path is added to the dual-loop control structure. To reduce the noise of feed-forward path, a soft-derivative term is introduced which is optimized for 400 Hz frequency. To verify the system performance, several simulations have been carried out which shows satisfactory results under dynamic and steady state conditions. Finally, the experimental results of a 20 kVA hardware prototype is presented to confirm the validity of theoretical and simulation results.