13.6 Comparative Results
Simulations were performed for the three methods using MATLAB/Simulink, with nominal system parameters R = 10 Ω, L = 7 mH, and Vdc = 540 V. For the PI controller and deadbeat control, the frequency of the carrier wave is 5 kHz and the sampling time is 200 μs. These values have been used for adjustment of the PI controller and in the model of the deadbeat controller and MPC. Due to the absence of modulator and variable switching frequency in the MPC scheme, the sampling time T = 45 μs was chosen in order to reach an average switching frequency comparable to the fixed switching frequency of 5 kHz of the other methods.
To compare the performance of the system under parameter variability it is necessary to choose a performance index to evaluate significant aspects of the system under control [11]. According to [12], the RMS current error was chosen because this index is suitable for evaluating how exactly the real current follows the reference current instantaneously.
Simulations were carried out to investigate the steady state performance of the system under the three control methods. The current waveforms at steady state with nominal parameters are shown in Figure 13.8. The three methods show good results, even in the case of MPC where a small increment in the current ripple is noticeable, compared to the other two methods.
Figure 13.8 Steady state waveforms of the load current, with nominal values of the parameters
The performance of each control method ...
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