In this paper a model predictive control (MPC) has been designed and implemented on the Packed U-Cell (PUC) inverter which has one isolated DC source and one capacitor as an auxiliary DC link. The MPC is designed to regulate the capacitor voltage at the desired magnitude to have seven voltage levels at the output of the inverter. Since grid-connected application is targeted by this application, the inverter should be capable of supplying requested amount of active and reactive power at the point of common coupling (PCC) as well. Therefore, MPC should also consider the line current control in order to monitor the exchange of reactive power with the grid while injecting appropriate active power at low THD. Various experimental tests including change in DC source voltage, active power variation and operation at different power factor (PF) have been performed on a laboratory prototype to validate the good performance obtained by the proposed MPC. The dynamic performance of the controller during sudden changes in dc capacitor voltage, supply current and PF demonstrates the fast and accurate response and the superior operation of the proposed controller.
Fig. 1. General Scheme for MPC
EXPECTED SIMULATION RESULTS:
Fig. 2. Steady state voltage and current waveforms for grid-connected PUC.
Fig. 3 Results during 20% grid voltage variation (from 140V to 110V peak).
Fig. 4. Response to transient DC bus voltage changes.
Fig. 5. Controller response to reactive power variations.
Fig. 6. Experimental results showing grid current reference amplitude 100%
increase and thereafter 50% decrease.
In this paper, a Model Predictive Control has been designed for the 7-level PUC inverter in grid-connected mode of operation, an excellent candidate for photovoltaic and utility interface application to deliver green power to the utility. MPC is a simple and intuitive method that does not have confusing gains to adjust as well as featuring fast response during any change in the system parameters. Experimental results have been provided to show the fast response of the implemented controller on the grid-connected multilevel PUC inverter. It has been demonstrated that the DC link capacitor voltage has been regulated at desired level and 7-level voltage waveform has been generated at the output of the inverter. The injected current to the grid was successfully controlled to have regulated amplitude and synchronized waveform with the grid voltage to deliver maximum power with unity power factor. Moreover, the PF has been controlled easily to exchange reactive power with the grid while injecting the available active power. Exhaustive experimental results including change in the grid current reference, DC source and AC grid voltages variations, as well as PF have been tested and results have been illustrated which ensured the good dynamic performance of the proposed controller applied on the grid connected PUC inverter.
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