The two hysteresis thresholds must both be higher than the nominal voltage as, based on the equivalent model of the system presented in Figure 6.6, the bus voltage can never be lower than U 0: calibration at U off < U 0 would mean that the brake chopper would never be switched off once it has been switched on (this is clearly not desirable). As the nominal voltage U 0 is 538 V, we may fix a chopper switch-on voltage at U max = 1.1 × U 0 = 592 V (conserving a safety margin greater than 2 with regards to the rated voltage of the components) and a switch-off voltage of U off = 1.05 × U 0 = 565 V.
Classically, hysteresis control (see Figure 6.5) of the voltage at the capacitor terminals enables robust and simple control. We should begin by determining the operating mode of the chopper. Details on the implementation of the method and simulated results were provided, incentivizing its future experimental validation. Finally, a new hysteresis voltage control method was introduced and explained, providing an alternative to reduce the commutation of semiconductors. After that, the use of the hysteresis technique to control the output voltage was discussed, reviewing two approaches, one regulating the amplitude or the RMS voltage and the other forming the shape of the voltage waveform. The three most relevant hysteresis current control techniques were described in a tutorial manner, showing their mode of operation and discussing their advantages and drawbacks. The possibility of using this technique to control the output current or output voltage of the inverters was also discussed, showing that this flexibility enlarges its application to both grid-connected and stand-alone cases. The main advantages of this nonlinear control technique are related to its simple implementation, performing time response, and robustness. Torres-Pinzón, in Multilevel Inverters, 2021 2.8 ConclusionsĪ review of hysteresis control methods applied to multilevel inverters was presented in this chapter.
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