Biji Jacob

A New Space Vector Modulation Scheme for Multilevel Inverters Which Directly Vector Quantize the Reference Space Vector

A new space-vector-based sigma delta modulation scheme for any general N-level voltage source inverter is proposed in this paper, which directly quantizes the reference space vector. The proposed scheme uses the sigma delta modulation with the quantizer implemented by the proposed space vector quantizer. A new scheme is proposed for directly quantizing the reference space vector to the multilevel inverter switching vectors without mapping it into two-level inverter vector space. Voronoi regions of the multilevel inverter vector space in the proposed space vector quantizer are defined as a parallelogram with the inverter switching vectors as its vertices. The property of the integer values of the inverter switching vectors in 60° coordinates is utilized for the direct vector quantization of the instantaneous reference voltage space vector. The proposed scheme is implemented for five-level inverters realized by an open-end-winding induction motor fed with two three-level inverters from either side having symmetrical dc-link voltages, and results are presented.

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° 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.

Space-Vector-Quantized Dithered Sigma–Delta Modulator for Reducing the Harmonic Noise in Multilevel Converters

Power converters using deterministic switching frequency schemes have switching noise concentrated at harmonic frequencies, resulting in enhanced electromagnetic emission. To suppress the harmonic spikes in three-phase multilevel voltage source converters, a digital control scheme based on dithered sigma-delta modulation (SDM) is proposed in this paper. Introducing a dithered sequence in an SDM varies the switching frequency randomly, resulting in the suppression of the spurious harmonic spikes in the output spectrum even with a regular control input. Although the switching frequency varies randomly, the minimum pulsewidth of the proposed scheme is the sampling time period, avoiding the minimum pulsewidth problem. Instead of a conventional scalar quantizer, the quantizer in the proposed dithered sigma-delta converter uses the principle of space vector quantization. The proposed scheme is experimentally verified on a constant v/f open-loop induction motor drive for a three-level inverter realized by cascading two two-level inverters. The performance of the proposed scheme is compared with different pulsewidth modulation schemes in the entire modulation index, including the overmodulation region.

Spread Spectrum Scheme for three-level inverters based on Space Vector Sigma Delta Modulator

A scheme for spreading the harmonic spectrum of Three-level Voltage Source Inverters is proposed in this paper. Space Vector based Sigma Delta Modulation is employed in the proposed scheme. The principle of Vector Quantization is applied for quantizing the reference Space Vector in the Sigma Delta Modulator. For the spatial quantization, the inverter voltage vector space is divided into different Voronoi regions. A method is proposed to code these Voronoi regions using instantaneous reference phase amplitudes without using lookup table. The proposed scheme naturally selects the outer vectors in the over-modulation condition and resulting in a smooth transition from linear to over-modulation region. The spectrum of inverter output is spread so that concentrations of power at switching frequency harmonics are avoided. The proposed scheme is implemented for 2-HP three phase induction motor in open-end winding configuration driven by dual 11.5 kVA two-level inverter driven from both ends. Experimental results of proposed scheme and comparison with Space Vector PWM are presented, including operation in over modulation region.

Vector quantized spread spectrum Pulse Density Modulation for four level inverters

A Pulse Density Modulation scheme based on Space Vector with Vector Quantization for four level inverter is proposed in this paper. The scheme disperses the power spectrum of the inverter output voltage as a wide-spectrum noise. The vector space of inverter reference space vector region is divided into voronoi regions to find out switching vectors. A new method is presented to code these voronoi regions using instantaneous reference phase amplitudes without using lookup table. To avoid fractional arithmetic sixty degree coordinate system is used. The space-vector diagram of four-level inverter is simplified to two-level space-vector diagram by the principle of mapping. The switching vectors are determined for two-level inverter using the proposed scheme and these switching vectors are then translated to the actual switching vectors of the four-level inverter by reverse mapping. The proposed scheme naturally selects the outer vectors in the over-modulation condition and hence results in a smooth transition from linear to over-modulation region. The scheme is implemented for 2-HP three phase open ended winding induction motor.

Space vector based Dithered Sigma Delta Modulator for two-level inverter to suppress the harmonic spikes

This paper proposes a Space Vector based Dithered Sigma Delta modulation scheme for three phase 2-level voltage source inverters. In the proposed scheme the instantaneous reference voltage space vector is synthesized by dithered sigma delta analog-to-digital converter. The spurious harmonic spikes at the output of the Sigma Delta Modulator with regular input are eliminated by introducing a dithered sequence in the Dithered Sigma Delta Modulator. The switching frequency of dithered sigma delta converter varies randomly resulting in the spreading of power spectrum of the inverter. The minimum pulse width of the output pulse train is the sampling time period, which prevents the inverter from missing switching operations. In the present work, the quantizer in the sigma delta converter uses the principle of Vector Quantization instead of conventional scalar quantizer. In this study the space vectors are represented in the 60° coordinate system to reduce the computational complexity compared to the conventional Cartesian coordinate system. Experimental results of proposed scheme are compared with Space Vector based Sigma Delta Modulator, SVPWM scheme and Random PWM scheme.

Spread spectrum modulation scheme for multilevel inverters using vector quantized sigma delta modulation

A generalized Space Vector based Spread Spectrum Modulation scheme for multilevel inverters is proposed in this paper. The proposed space vector based scheme is based on the view that a multilevel converter could be interpreted as an oversampling analog-to-digital converter. As the switching frequency of sigma delta modulator in the oversampling analog-to-digital converter varies randomly, the proposed scheme has spread spectrum characteristics. The principle of Vector Quantization is utilized for quantizing the instantaneous reference voltage space vector in the sigma delta converter. The switching vectors of the inverter are naturally selected without sector identification, ensuring optimum switching sequence under all conditions including the over-modulation region. To avoid fractional arithmetic, sixty degree coordinate system is used to represent the space vector in this paper. The proposed scheme is implemented for six-level inverter, driving 2-HP three phase induction motor and experimental results are presented. Experimental results of the proposed scheme are compared with Space Vector PWM scheme and Random PWM scheme.

Space Vector based pulse Density Modulation scheme for two level voltage source inverter

A Space Vector based Pulse Density Modulation scheme for spreading the spectra of Voltage Source Inverters is proposed in this paper. The proposed scheme employs first order Sigma-Delta Modulator. The principle of Vector Quantization is applied for quantizing the reference voltage Space Vector in the Sigma Delta Modulator. For the spatial quantization, the inverter voltage vector space is divided into seven Voronoi regions. In this paper, a method is proposed to code these Voronoi regions using instantaneous reference phase amplitudes without using lookup table. To avoid fractional arithmetic sixty degree coordinate system is used. The proposed scheme automatically selects the apex vectors in the over-modulation condition and hence results in a smooth transition from linear to over-modulation region. In Pulse Density Modulation, the switching frequency varies randomly, resulting in the spreading of harmonic spectra. The proposed scheme uses only instantaneous reference phase amplitudes to obtain switching vectors without using lookup table and timer. The proposed scheme is implemented and tested with 11.5 kVA two-level inverter driving 2-HP three phase induction motor. Experimental results of proposed scheme are compared with Space Vector PWM and Random Space Vector PWM.

Space Vector based Spread Spectrum Modulation scheme for three-level inverters

A Spread Spectrum Modulation scheme based on Space Vector for three level inverter is proposed in this paper. The scheme disperses the power spectrum of the inverter output voltage as a wide-spectrum noise. The vector space of inverter reference space vector region is divided into voronoi regions to find out switching vectors. A new method is presented to code these voronoi regions with Vector Quantization using instantaneous reference phase amplitudes without using lookup table. The space-vector diagram of three-level inverter is simplified to two-level space-vector diagram by the principle of mapping. The switching vectors are determined for two-level inverter using the proposed scheme and these switching vectors are then translated to the actual switching vectors of the three-level inverter by reverse mapping. The proposed scheme naturally selects the outer vectors in the over-modulation condition and hence results in a smooth transition from linear to over-modulation region. The scheme is implemented for 2-HP three phase induction motor driven by three-level cascaded inverter topology.

Space vector modulation scheme with direct Vector Quantization for any N-level voltage source inverter

A new space vector based spread spectrum modulation scheme for any general N-level voltage source inverter is proposed in this paper. The proposed scheme uses the sigma delta modulation with quantizer implemented by the principle of Vector Quantization. The N-level inverter vector space is divided into different Voronoi regions around the inverter switching vectors. A new method is proposed for directly quantizing the reference space vector to the inverter switching vectors. The property of integer values of the inverter switching vectors in 60° coordinates is utilized for the direct Vector Quantization of instantaneous reference voltage space vector. The proposed scheme is implemented for 5-level inverter realized by an open-end-winding induction motor fed with two 3-level inverter from either side having symmetrical dc-link voltages and results are presented.