Three-level NPC converter-based predictive direct power control of the doubly fed induction machine at low constant switching frequency

This paper presents a new application of the predictive direct power control (P-DPC) for the doubly fed induction machine. The P-DPC deals with several main characteristics which makes it very suitable for high power-medium voltage generation systems where total harmonic distortion of the generating power is relevant: a three-level NPC converter presenting low and constant switching frequency feeds the rotor by means of an intermediate inductive filter. The developed P-DPC takes into account the inductive filter in the prediction stage as a part of the plant model, deals with the different sectors and regions of converter available voltage vectors and the balancing of the bus capacitors voltages. This way, it creates a sequence of 3 + 3 vectors that generates an active and reactive power trajectory which minimizes the next sample time predicted error. In addition, the P-DPC is specially designed to maintain the real-time implementation structure and simplicity of the "classic" direct control strategies. Experimental results in a 15-kW test bench for the overall speed and power range are shown including synchronous speed, demonstrating that it is an attractive alternative to the conventional field-oriented control techniques.