Pulse-Width-Modulation of Neutral-Point-Clamped Sparse Matrix Converter

Sparse matrix converter is an alternative "all- semiconductor" energy processor proposed recently for converting an ac source with fixed magnitude and frequency to a variable voltage and frequency supply that can meet the requirements of a particular industry application. In principle, sparse matrix converter is constructed by connecting a front-end bi-directional rectification stage to a conventional two-level inversion stage with no bulky capacitive or inductive energy storage connected to their intermediate dc-link. Through proper modulation and compensation of the resulting converter, sinusoidal input current and output voltage can be achieved with minimized rectification switching loss, rendering the sparse matrix converter as a competitive choice for interfacing the utility grid to (e.g.) defense facilities that require a different frequency supply. As an improvement, sparse matrix converter assembled using a three-level energy processing stage has briefly been mentioned in the literature, but has neither been tested in simulation nor experimentally because its operational principles, pulse-width modulation (PWM) control and index compensation have not yet been discussed in the existing literature. Addressing the afore-described issues, this paper focuses on the operational mode analysis of a three-level sparse matrix converter implemented using a neutral-point-clamped inversion stage, and the design of a number of PWM and modulation ratio compensation schemes for controlling the converter with improved waveform quality. Performances and practicalities of the designed schemes are verified in simulation and experimentally using an implemented laboratory prototype with some representative results captured and presented in the paper.