Space Vector Modulation Scheme with Direct Vector Quantization for any N-level Voltage Source Inverter Biji Jacob, M. R. Baiju College of Engineering, Trivandrum, India biji@ece.cet.ac.in, mrbaiju@cet.ac.in Abstract—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 0 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. Keywords—Sigma Delta Modulator, Space Vector, Spread Spectrum Modulation, Vector Quantisation. I. INTRODUCTION Multilevel inverters are extensively used for medium- voltage high-power industrial drive applications. Voltage operation above classic semiconductor limits, lower common mode voltages, near sinusoidal outputs, reduced voltage derivatives (dv/dt), voltages with reduced harmonic content, increased efficiency are the main characteristics that have made multilevel inverters more popular [1 – 5]. The recent development of multilevel inverters has led to the introduction of many new simpler and flexible modulation schemes [6 – 15]. The modulation and control strategies in multilevel inverters can be broadly classified into Voltage Level based algorithm and Space Vector based algorithm [13], [14]. The space vector modulation schemes have wider linear modulation range, lower baseband harmonics and convenience for digital implementation [13], [14]. Compared with conventional orthogonal coordinate system, the representation of space vector in 60 0 Coordinate system reduces the computational complexity by eliminating fractional arithmetic [6 – 8]. In addition to the desired fundamental component, converters employing conventional deterministic modulation schemes have power spectrum concentrated around the switching frequency and its harmonics [16], [17]. This results in radiation of the electromagnetic interference and acoustic noise [16]– [22]. In two level inverters, to spread the harmonic energy over a large frequency range, variable frequency switching schemes such as random modulation of the switching frequency, sigma- delta modulation, chaotic control and hysteresis control are used [18]–[45]. In Adjustable Speed Drives the analog control signal is modulated and amplified by the voltage source inverter which is then demodulated by the high impedance offered by inductance of the motor. Hence in motor drive application, the inverter acts as transmission medium and motor act as the demodulator analogous to the communication system with modulation [35]. The voltage source inverter has a discrete state output like a digital systems and it tries to approximate the input signal, which is a set of three phase analog signals, by switching its discrete states at a high frequency. Therefore, inverter’s behavior is similar to an oversampling analog-to- digital converter (ADC) [40 – 41]. Hence induction motor drive system can be considered as a communication system with digital modulation. This understanding prompts us to explore the possibility of adopting the techniques used in the context of digital communication system, to control multilevel inverters. In digital communication, sigma delta modulators are used to achieve higher resolution with lesser number of bits by spreading the quantization noise out of the signal bandwidth [46 – 48]. The switching frequency in the sigma delta converters varies randomly resulting in spreading of output power spectrum. This will eliminate the concentration of energy at switching frequency harmonics which are present in the fixed frequency switching [46 – 48]. Instead of processing the N different bits of the ADC separately, as a Scalar Quantity, they can be treated as a single Vector Quantity with a magnitude and phase value for better result [49], [50]. By Shannon’s rate- distortion theory, better result can always be achieved by coding vectors instead of scalars. For efficient quantization in digital communication and data compression, the concept of Vector Quantization is used instead of scalar quantization [49], [50]. This principle of vector quantization has been used in space vector based sigma delta modulation for multilevel voltage source inverters after mapping the reference space vector into the 2-level space vector plane [51 – 55]. This paper proposes a space vector modulation scheme which directly Vector Quantize the reference space vector of the multilevel voltage source inverters in the sigma delta modulator without mapping. The inverter voltage space vectors are represented in 60° coordinate system having integer values for Vector Quantization of the instantaneous reference 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. 2012 IEEE International Conference on Power Electronics, Drives and Energy Systems December16-19, 2012, Bengaluru, India 978-1-4673-4508-8/12/$31.00 ©2012 IEEE