OPEN unified power quality conditioner (UPQC) offers different power quality levels with different electricity bill to their users. OPEN UPQC has more flexible modularity than traditional UPQC for field applications. OPEN UPQC consists of two controlled pulse-width modulated shunt and series inverters that have no common DC link. Shunt inverter eliminates current harmonics originating from non-linear load side and series inverter mitigates voltage sag/swell at the point of common coupling caused from faults on transmission system. In this study, controllers for both shunt and series inverters are based on enhanced phase locked loop (E-PLL) and non-linear adaptive filter. For the controller of shunt inverter, proportional integrator controller-based DC-link control strategy is adapted to E-PLL. A fast sag/swell detection method is also presented. Functionalities of OPEN-UPQC system is deeply analysed and tested through simulation studies with power system computer aided design/electromagnetic transients DC analysis program. The test results verify that OPEN UPQC achieves good performance for mitigating the effects of voltage sag/swell and suppressing the load current harmonics.