Dynamic voltage restorer-multilevel inverter based on predictive voltage controller

This paper introduces a predictive voltage controller for multilevel inverter used in Dynamic Voltage Restorer, which is able to protect a sensitive load against grid voltage sags dynamically. The compensated voltages are obtained by using Phase-Lock Loop to detect the phase and the magnitude of the grid voltage then compare to the load reference voltage. A three-phase NPC inverter with output LC filter is used to generate the ac voltage that will be injected to the load via injection transformer to compensate sag voltages. A new method to generate very high quality compensated voltages based on predictive controller will be presented. The model of the systems include NPC inverter and LC filter are built to establish the equations that can be applied to calculate the future values of the compensated voltage and the dc link voltage capacitor at the next sampling time. After that, the optimal voltage vectors that minimize both the compensated voltage and the dc link capacitor errors will be chosen for the next switching state of the NPC inverter. Obtained simulation results verified the theoretical analysis. The compensated voltage is almost sinusoidal and the load voltage is always constant with THD lower than 2% when facing voltage sags.