The most complete configuration of hybrid filters is the unified power quality conditioner (UPQC), which is also known as the universal active filter. UPQC is a multifunction power conditioner that can be used to compensate various voltage disturbances of the power supply, to correct voltage fluctuation, and to prevent the harmonic load current from entering the power system. It is a custom power device designed to mitigate the disturbances that affect the performance of sensitive and/or critical loads. UPQC has shunt and series compensation capabilities for harmonics, reactive power, voltage disturbances, and power-flow control. A UPQC consists of two voltage-source converters with a common DC link designed in single-phase, three-phase three-wire, or three-phase four-wire configurations. One converter is connected in series through a transformer between the source and the critical load at the PCC and operates as a voltage-source inverter. The other converter is connected in shunt at the PCC through a transformer and operates as a current-source inverter. The active series converter compensates for voltage supply disturbances, performs harmonic isolation, and damps harmonic oscillations. The active shunt converter compensates for load current waveform distortions and reactive power, and performs the DC link voltage regulation. UPQC is specifically designed to protect the critical load at the point of installation connected to distorted distribution systems by correcting the shortcomings, such as harmonic distortions at the utility–consumer PCC, voltage disturbances, voltage regulation, reactive power flow at fundamental and harmonic frequencies, neutral and negative-sequence currents, and harmonic isolation.
 
MATLAB Implementation of UPQC for Power quality Improvement in Power system