Current THD analysis in direct model predictive control

Direct model predictive control (MPDxC) appears to be a strong candidate for high-power applications, because it can achieve very low switching frequencies and keep variables of concern, such as power, current, torque and flux, within specified bounds. The width of bounds is observed to regulate THD of a current when MPDxC is used for controlling the current. This paper describes mathematically the linear relationship in between THD and width of the current bounds and, therefore, evaluates THD without running detailed and time consuming simulations. This mathematical function is valid over a range of bound widths for which the current ripple is approximated to be a piecewise linear function. In the case of a three phase system, the function specifies the upper bound of the THD values, whereas an optimized pulse patterns (OPP) specifies the lower bounds of the THD values. The feasibility of the function over a range of bound widths is demonstrated through simulations and experimental results of a 830-VA single phase converter, and simulations of a 6.78-MVA grid-connected three phase converter.