This paper presents a solution to the control of a unified power quality (PQ) conditioner (UPQC) for Power Quality improvement in power distribution systems. The problem formulation allows not only harmonic compensation but also voltage sags/swells, load demand changes, and power factor correction to be tackled in a unified framework. The proposed controller combines the multivariable regulator theory with H^, loop shaping, so that zero steady-state error and insensitivity to supply frequency variations can be accomplished simultaneously. The effectiveness of the proposed controller is, in practice, verified by experimental studies on a single-phase power distribution system.