A modified sphere decoder for online adjustment of the switching frequency

Abstract

In this paper we present a modified sphere decoder that can adjust the switching frequency in real time. To achieve this, the underlying integer least-squares (ILS) problem is reformulated and the lattice generator matrix is modified. By doing so, computational demanding operations required to be performed in real time are avoided altogether, rendering the proposed method computationally feasible. Moreover, the optimization process is kept computationally modest by appropriately manipulating the geometry of the ILS problem. The effectiveness of the introduced method is tested with a medium voltage variable speed drive system consisting of a three-level neutral point clamped (NPC) inverter and an induction machine.