Improved load disturbance rejection method for 400 Hz GPU inverters

This paper presented an effective digital control method for a 400 Hz GPU inverter capable to maintain a low THD in presence of nonlinear loads without measuring inductor or capacitor filter current. The method uses a capacitor current observer and a new minor loop feedback term that compensates the computational delay and resonant controllers for both inner and outer loops. The resonant controllers are implemented as IIR fitters with a normal architecture to minimize the round-off errors in order to remove the third, fifth and seventh harmonics. The nonlinearities and the delay of the PWM stage are also compensated in order to maximize the bandwidth of the current loop. The solution has been tested on a single-chip 16-bit DSP-based controller from analog devices (ADMC401) that implements all the algorithms described. The proposed approach was experimented on both single-phase and three-phase inverters showing almost complete elimination of the third, fifth and seventh harmonics from the output voltage.