Improved single-zone overmodulation algorithm for space vector modulated inverters

Space vector modulated voltage-source inverters require an overmodulation algorithm for continuous control of line-side voltage during overmodulation and for a smooth transition from PWM to six-step mode. Overmodulation increases the dc bus utilisation of a voltage source inverter, but requires significantly higher computational effort than linear modulation. This paper proposes a novel single-zone overmodulation algorithm for two-level voltage-source inverters. The proposed algorithm treats the whole overmodulation zone as a single undivided zone for the purpose of voltage control. This overmodulation algorithm maintains proportionality between the reference voltage and applied voltage up to the six-step mode. The new algorithm is evaluated and compared, theoretically as well as experimentally, with the existing algorithms. The proposed single-zone algorithm decreases the computational effort significantly over the standard two-zone algorithm, but at the cost of moderate increase in harmonic distortion. Compared to the existing single-zone algorithm, the proposed algorithm is shown to reduce computational burden as well as harmonic distortion.