## 4 Simulation and Experiment Results  
In order to verify validity of the proposed predictive control method, simulation and experimental results using the three-phase three-level NP rectifier are presented. In the simulations and experiments, the ac input voltage = 100 (V), the reference output voltage \(V_{dc}^{*}\) = 200 (V), the input resistance \(R_{i}\) = 3 (\(\Omega\)), the input inductance \(L_{i}\) = 15 (mH), the sampling period \(T_{s}\) = 50 (\(\mu\)s), the dc capacitance \(C\) = 2200 (\(\mu\)F) and the fundamental frequency of the input currents = 60 (Hz). Figure 5 shows simulation waveforms obtained by the NP rectifiers with the proposed control method. As shown in Figure 5a, the proposed control method with no weighting factors can produce sinusoidal input current waveforms in phase with the input voltage, leading to the unity power factor. In addition, the line-to-line rectifier voltage waveforms exhibit five levels. The frequency spectrum of the input current is depicted in Figure 5b, where the three-phase three-level NC rectifier yields spread frequency components due to the proposed predictive control algorithm. Figure 5c shows how the capacitor voltages are balanced by the proposed predictive control method with no weighting factor under a condition that the capacitor voltages were intentionally unbalanced, where the proposed control algorithm quickly eliminates capacitor voltage imbalance after the voltage balancing algorithm starts. Furthermore, Figure 5d shows the transient response waveform of the three-phase input currents and the capacitor voltages with a step change of the output reference voltage from 200 to 160 V.  
Figure 4: Capacitor current flow of sector 1 with switching status: (**a**) (ONN); (**b**) (PNN).  
Validity of the proposed algorithm was verified with a prototype of three-phase three-level NP rectifier built in the laboratory, operated with a Digital Signal Processor (DSP) board (TMS320F28335). Figure 6 shows experimental waveforms resulted from the proposed predictive control method employing no weighting factor. In Figure 6a, sinusoidal three-phase input currents are synthesized, which are in phase with the input voltage, leading to the unity power factor. Therefore, it is seen that the proposed method operating without the weighting factor generates sinusoidal input currents. Frequency analysis waveforms of the input currents of the proposed control method is also shown in Figure 6b. The experimental waveform in Figure 6c illustrates how quickly the capacitor voltages are balanced by the proposed method without a weighting factor to make the capacitor voltage balance when the capacitor voltages were intentionally unbalanced. As can be seen from Figure 6c, the proposed control method quickly eliminates capacitor voltage imbalance after the voltage balancing algorithm starts. Figure 6d shows transient response waveforms for the output voltage by the proposed algorithm, where the magnitude of the output voltage was exposed to a step-change from 200 to 160 V.  
Figure 5: Simulation results of (**a**) three-phase input currents, _a_-phase input voltage, and line-to-line rectifier voltage (**b**) frequency spectrum of input current (**c**) capacitor voltages under conditions with intentional voltage unbalances (**d**) input currents and capacitor voltages with step change of output reference voltage from 200 to 160 V.