Predictive Control of Power Converters and Electrical Drives

5.1 Introduction

Three-level neutral-point clamped (NPC) inverters are widely used in industry for high-power, medium-voltage power conversion and drives [1, 2]. Topics related to power losses due to commutation and quality of the output current are relevant issues in this power range [3–5]. The neutral-point balancing problem in this topology is another subject that has been studied in recent years [6–8]. Among the most common control methods for this converter, the literature states, are non linear techniques, like hysteresis control, and linear methods, like the use of PI controllers in conjunction with pulse width modulation (PWM) [9–12].

The general predictive control scheme presented in Chapter 3 is applied here to the NPC inverter. The behavior of the system is predicted for each possible switching state of this kind of inverter. The switching state that minimizes a given cost function is selected to be applied during the next sampling interval following the same strategy presented in Chapters 3 and 4. The NPC inverter presents a high number of switching states, compared to the two-level inverter used in the previous chapter. The larger set of possible actuations allows for additional degrees of freedom and several compositions of the cost function can be considered. Considering the control requirements that are characteristic of this topology and its applications, several variations of the algorithm are studied and compared to classical linear control with PWM, including ...