5.3 Linear Current Control Method with Pulse Width Modulation

Before presenting the predictive control method, a short review of classical current control applied to a three-phase NPC inverter is given to obtain suitable comparisons. The selected method involves linear controllers and a modulation strategy known as level shifted phase disposition pulse width modulation (LS-PD-PWM). This alternative was selected, among other PWM strategies, because it is widely used on this kind of inverter and provides the best harmonic profile [1].

The classical control scheme using PWM is shown in Figure 5.6. The load current is measured and compared to its reference value. Next, a PI controller generates the reference load voltages that enter a modulator. In this stage, each reference voltage is compared to two triangular carrier signals, superior and inferior, arranged in identical phase disposition. The switching state applied to the inverter is selected according to the results of the comparisons. For more details, see [2, 9–11].

Figure 5.6 Classical current control method for the NPC inverter (Vargas et al., 2007 © IEEE)