A transformer-less unified power quality conditioner having fast dynamic control

Apart from high power density, unified power quality conditioner (UPQC) offers a cost-effective and energy-efficient way to deal with power quality issues. A single-phase transformer-less unified power quality conditioner (TL-UPQC) utilizing four switching devices only is presented. The proposed UPQC consists of two voltage source inverters, one is connected in parallel with the load and another one is connected in series with the AC mains. The parallel inverter, which is controlled by a hysteresis current controller, is used to shape the current drawn from the AC mains and regulate the DC-link voltage. The series inverter, which is controlled by a boundary controller with second-order switching surface, is used to regulate the load voltage, eliminate voltage distortion and provide voltage sag / swell ride-through. The operating principle of the whole system will be described. A 1kVA, 110V, 60Hz prototype has been built and evaluated on a testing setup with nonlinear loads and simulated voltage sag / swell conditions.