Goal of this project is to improve the control of this converter concept to operate the converter with a small number of commutations in order to minimize losses as well as to consider other optimization targets as the total harmonic distortion (THD) and the converter voltage utilization.
Methodological approach is the employment of space vector modulation which so far has not been applied to such converters, likely because of the large number of states to be handled (with N = 27 phases, N³ = 19683 states result), which are furthermore varying in time, and also because the commutations cannot be triggered arbitrarily with externally commutated converters. The implementation of a Direct Current Control in a rotor-fixed reference frame by means of Model Predictive Control (MPC) is a promising way to solve this complex task. Model Predictive Control will select the best switching state with help of an objective function that considers the control error, the rate of change of the predicted control variable (which is approximately proportional to THD) and the commutation voltage. In that way, the switching losses are expected to be reduced by about a factor of two.