Vector-Quantized Space-Vector-Based Spread Spectrum Modulation Scheme for Multilevel Inverters Using the Principle of Oversampling ADC

A generalized space-vector-based spread spectrum modulation scheme for multilevel inverters is proposed in this paper. The proposed scheme uses the principle of sigma-delta modulation as applied to analog-to-digital converters (ADCs), based on the view that a multilevel converter could be interpreted as an oversampling ADC. The principle of vector quantization is utilized for quantizing the instantaneous reference voltage space vector in the proposed space-vector-based sigma-delta converter. The switching vectors of the inverter are naturally selected without sector identification, ensuring optimum switching sequence under all conditions including the overmodulation region. As the sigma-delta converter results in a randomly varying switching frequency, the proposed scheme has spread spectrum characteristics. To avoid fractional arithmetic, a 60 degrees. coordinate system is used to represent the space vector in this paper. The proposed scheme can be used for any general n-level inverter, and experimental results are presented for four-, five-, and six-level inverters, driving a 2-hp three-phase induction motor in an open-end winding configuration. The experimental results of the proposed scheme are compared with the space-vector pulsewidth modulation (PWM) scheme and random PWM scheme.