Reduction of the output impedance in single phase inverters for UPS combining conventional multi-loop and plug-in repetitive control

In this paper we propose a methodology for the design of the single-phase inverter control system for UPS applications, which allows to meet the performance requirements of the international power quality standards IEC62040-3 and IEC61000-2-2. The control system consists of a conventional multi-loop with Proportional-Integral-Derivative type controllers and a multi-rate Repetitive Controller in plug-in configuration (MR-OHRC). The proposal constitutes a conventional multi-loop design methodology with which the inverter output impedance is reduced and the performance of the MR-OHRC is complemented. In this way, variations in the output voltage are attenuated as a result of disturbances caused by sudden changes in the load current and non-linear loads. This strategy also allows to overcome the limitations of dynamic response and reduce the settling time of the MR-OHRC. The validity of the proposal is analyzed considering the requirements of international power quality standards in relation to the dynamic response, individual harmonic content and harmonic distortion, in an experimental 2kVA prototype.