Discrete-time internal model controller for three-phase PWM inverters with insulator transformer

A new digital voltage controller is proposed, derived in agreement with the internal model principle for three-phase inverters with ΔY transformer at the output. A dynamic model of the inverter, transformer, filter and load in stationary α-β co-ordinates is derived and a decoupling method is proposed. The proposed digital controller is not prone to amplify DC components, which can lead to output transformer saturation. Additionally, this digital controller results in a simple form and is well suited for fixed-point implementation. Experimental results, implemented in a 16-bit DSP controller, validate the theoretical developments and demonstrate the good steady-state performance of the proposed controller under both nonlinear balanced and unbalanced loads.