Computationally efficient sphere decoding for long-horizon direct model predictive control

In this paper we present a computationally efficient implementation of the sphere decoder, which is employed to solve the integer least-squares (ILS) problem underlying direct model predictive control (MPC) for power electronic applications. The introduced modifications take advantage of the structure of the problem and, as a result, the required real-time operations can be reduced to a minimum. The efficacy of the developed algorithm is demonstrated with a variable speed drive system with a three-level voltage source inverter.