2064 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 62, NO. 4, APRIL 2015 Space-Vector-Quantized Dithered Sigma–Delta Modulator for Reducing the Harmonic Noise in Multilevel Converters Biji Jacob, Member, IEEE , and M. R. Baiju, Senior Member, IEEE Abstract —Power converters using deterministic switch- ing frequency schemes have switching noise concentrated at harmonic frequencies, resulting in enhanced electro- magnetic emission. To suppress the harmonic spikes in three-phase multilevel voltage source converters, a digi- tal control scheme based on dithered sigma–delta mod- ulation (SDM) is proposed in this paper. Introducing a dithered sequence in an SDM varies the switching fre- quency randomly, resulting in the suppression of the spu- rious 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 quan- tizer, the quantizer in the proposed dithered sigma–delta converter uses the principle of space vector quantization. The proposed scheme is experimentally verified on a con- stant 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. Index Terms—Digital modulation, dithered sigma–delta modulator (DSDM), harmonic distortion, space vector quantization. I. I NTRODUCTION I N THE WORLD of depleting fossil fuel and stringent electromagnetic compatibility, efficient means of power conversion with emphasis on improved power quality is the need of the hour. The vast development of high-speed elec- trical machines and drives finds application in turbochargers, mechanical turbocompounding systems, aeroengine spools, he- licopter engines, racing engines, and fuel pumps [1]. The digital control of medium- and high-power converters is applied not only in industrial motor drives but also in renewable energy systems, electrical vehicles, and power systems [2]. Harmonic distortion and switching losses can be reduced by abolishing Manuscript received May 16, 2014; revised July 28, 2014; accepted August 31, 2014. Date of publication October 3, 2014; date of current version March 6, 2015. B. Jacob is with the Faculty of Electronics and Communication En- gineering, Government Engineering College, Thiruvananthapuram 695 035, India (e-mail: biji.jacob@rediffmail.com). M. R. Baiju is with the Department of Electronics and Communication Engineering, College of Engineering Trivandrum, Thiruvananthapuram 695 016, India (e-mail: mrbaiju@ieee.org). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2014.2361491 carrier modulation with its equidistant precalculated optimal pulse patterns for every steady-state operating point of the drive [3]. A concentrated harmonic spectrum in pulsewidth modulation (PWM) schemes will result in the radiation of electromagnetic interference (EMI) and acoustic noise in the electric machines driven by an inverter [4]. The IEEE Standard 1459-2010 gives guidelines in harmonic control over the power frequency range up to the 35th order resulting from the use of the static power converter in industry. This standard uses voltage distortion as the criterion of power system pollution and suggests voltage distortion limits for systems. The adverse effects of harmonics can be reduced by spreading the output spectrum of the inverter either by the time variation of a nominal switching pattern or by the time variation of the probability laws that govern the randomization [4], [5]. Spread-spectrum frequency modulation is used to suppress the EMI caused by high switching frequencies in a digitally controlled way [6]. A dithered PWM scheme is proposed to reduce the EMI in single-phase direct-current/alternating- current inverters [7]. The total harmonic distortion (THD) of the output voltage of the inverter can be improved by adding the right amount of harmonic voltage to the reference voltage to compensate for the harmonic voltage dropped on the output impedance [8]. The optimal control vectors and action time are calculated to minimize the weighted THD of the output voltage waveforms by an immune algorithm in a three-phase inverter under the space vector PWM (SVPWM) [9]. Switched capacitor filters are proposed for the harmonic elimination of the inverter-fed split-phase induction motor (IM) drive [10]. To modify the output spectrum, sigma–delta modulation (SDM) schemes have been proposed for two-level inverters [11]–[14]. The principle of vector quantization has been used in space- vector-based SDM to realize the spread-spectrum characteris- tics of voltage source inverters [15]–[17]. Discrete harmonic spikes appear at the output power spectral density of quantization noise even in a first-order SDM with a regular pattern input [18], [19]. By adding a 1-bit random sequence from an independent identically distributed process to the least significant bit of the input signal, harmonic spikes are suppressed in dithered SDM (DSDM) [20]–[22]. Harmonic spikes at a low modulation index are suppressed in a single- phase full-bridge converter and two-level inverter drives using DSDM [23], [24]. The inverter acts as a transmitter, and the motor acts as the demodulator analogous to the communication system with 0278-0046 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.