A harmonic constrained minimum energy controller for a single-phase grid-tied inverter using model predictive control

This paper presents a decoupled power control method for a single-phase grid-tied inverter that uses model predictive control (MPC) to minimize the number of switch state changes required to control the output bridge while simultaneously constraining the output current harmonics. On one hand, minimizing the number of switch state changes in the output bridge of the inverter results in minimizing switching losses. On the other hand, lower switching frequencies typically result in larger harmonic currents. The proposed controller evaluates a cost function with an adjustable weight factor. Total harmonic distortion (THD) of grid side current is the constraint of the controller which seeks to minimize switch state changes to lower switching losses while meeting the THD constraint. Thus the MPC performs constrained multi-objective optimization. Because the controller is harmonic-constrained, the single-phase inverter has robust operation under pulsating dc-link voltage, which allows a smaller dc-link capacitor and higher bus ripple voltage. The weight factor can be chosen from an engineering tradeoff between the output current THD and the switching frequency. The simulation results are verified experimentally by implementing the controller using DS1007 platform by dSPACE.