Comparative Evaluation of Multi-Loop Control Schemes for a High-Bandwidth AC Power Source with a Two-Stage LC Output Filter

This paper presents a comparative evaluation of four different multi-loop control schemes for a high-bandwidth AC power source. The power source considered in this work is based on a three-level T-type inverter with a two-stage LC output filter. The control schemes evaluated in this paper have an output voltage controller in the outer loop. For the inner control loop the following options are evaluated: capacitor current feedbacks, proportional-integral and proportional inverter output current control in combination with reference voltage and load current feedforward, and first LC stage capacitor voltage and inverter output current feedback. The reference tracking capabilities as well as the power source output impedance are evaluated. Analytical and simulation results are shown to be in very good agreement, and the frequency and step responses for the different control schemes are compared. The results show that a cascaded structure consisting of a proportional-integral controller for the output voltage and a proportional controller for the inverter output current allows to achieve the best dynamic behavior in terms of output voltage control bandwidth and output impedance.