Dr. Espinosa-Neira, Eduardo

The use of advanced modulation and control schemes for power converters, such as a Feedback Quantizer and Predictive Control, is widely studied in the literature. This work focuses on improving the closed-loop modulation scheme called Feedback Quantizer, which is applied to a three-phase voltage source inverter. This scheme has the natural behavior of mitigating harmonics at low frequencies, which are detrimental to electrical equipment such as transformers. This modulation scheme also provides good tracking for the voltage reference at the fundamental frequency. On the other hand, the disadvantage of this scheme is that it has a variable switching frequency, creating a harmonic spectrum in frequency dispersion, and it also needs a small sampling time to obtain good results. The proposed scheme to improve the modulation scheme is based on a Discrete Space Vector with virtual vectors to obtain a better approximation of the optimal vectors for use in the algorithm. The proposal improves the conventional scheme at a high sampling time (200 μs), obtaining a THD less than 2% in the load current, decreases the noise created by the conventional scheme, and provides a fixed switching frequency. Experimental tests demonstrate the correct operation of the proposed scheme.

In-depth research has been done in the literature on applying sophisticated modulation and control systems for power converters, such as Feedback Quantizer and Predictive Control. This research aims to enhance the Feedback Quantizer, a closed-loop modulation technique used in three-phase voltage source inverters. This method naturally reduces harmonics at low frequencies, which harms electrical machinery like transformers and AC motors. This modulation technique achieves an excellent follow-up of the fundamental voltage reference. One of the disadvantages of Feedback Quantizer are the low sampling time to achieve a good waveform quality; in addition, as it is not a carrier-based method, the switching frequency is variable, resulting in a dispersed harmonic spectrum. The three-phase voltage source inverter has eight valid states to monitor the voltage reference; the proposal consists of modifying the feedback quantizer modulation using virtual vectors by discrete space vectors, which achieves a better follow-up. The proposal considers a simplified implementation of discrete space vectors in such a way as to reduce the computational cost to obtain voltage and current waveforms with low WTHD, THD distortion, and a defined harmonic spectrum but with a high sampling time. The proposed modulation scheme obtains a THD of less than 2% in the load current, reducing the noise produced by the traditional scheme of Feedback Quantizer and using a fixed switching frequency for a sampling time of ( 200 μ s). The above is an improvement compared to the conventional Feedback Quantizer. Additionally, it was possible to reduce the mathematical operations of the algorithm by a factor of 5.38 by using strategies to simplify the algorithm of the suggested scheme. The proposed technique operates correctly, according to experimental tests.INDEX TERMS Feedback quantizer, discrete space vector modulation, total harmonic distortion, weighted total harmonic distortion, voltage source converter, modulation scheme.