Power Conversion using Indirect Matrix to Reactive Power by Third-Harmonic Injection & Voltage Transfer Ratio

Due to the merits of sinusoidal input currents and excellent conversion efficiency, buck-type active third-harmonic injection converters have received increasing attention in recent years. However, three major problems of these converters still exist in theory and practice. First, the existence of the dc-link capacitor, utilized by early researchers, causes inrush transient and distorts the input currents. Second, in some specific situations, such as wind energy conversion system and flexible ac transmission system, these converters' capabilities of generating input reactive power need sufficient improvements. Third, proper selection of the third-harmonic injection inductor is the key challenge to implement these converters, since the inductor affects not only the current ripple but also the tracking performance of the third-harmonic current. To solve these problems, this paper studies the two-stage matrix converter with third harmonics injection and demonstrates that the dc-link capacitor can be removed by bidirectional implementation and proper control of the rectifier. Then, an algorithm enhancing the input reactive power capability is developed. Thus, sinusoidal input currents are achieved and the reactive power control range is extended significantly. Moreover, the design criteria of the third harmonic injection inductor are discussed. Finally, the proposed method is verified by simulation and experimental results.