Feedback Quantizer Improved With Simplified Discrete Space Vector Modulation for Power Converters

Abstract

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.