Digital voltage and current controllers for three-phase PWM inverter for UPS applications

This paper proposes discrete time voltage and current controllers for three-phase PWM inverters used in UPS applications. An accurate state space discrete model of the PWM inverter-filter-load, which takes into account nonlinearities and propagation delays associated with a real time digital implementation, is derived for the controller design. The output voltages and inductors currents are dynamically limited by means of MIMO controllers designed using optimal servo linear quadratic regulators, which ensure stability for the system at all operating conditions. In order to ensure smooth transitions among the different modes of operation, a nonlinear MIMO anti-windup method is proposed to update the servo variables. A 15 kVA PWM inverter fully controlled by the DSP controller TMS320F241 has been used to validate the proposed approach. Simulations and experimental results show a good transient and steady state performances from no-load to short circuit operation.