IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 64, NO. 3, MARCH 2017 1807 A New High-Switching-Frequency Modulation Technique to Improve the DC-Link Voltage Utilization in Multilevel Converters Mohsen Aleenejad, Student Member, IEEE, Hamid Mahmoudi, Student Member, IEEE, Reza Ahmadi, Member, IEEE, and Hossein Iman-Eini, Member, IEEE Abstract—This paper presents a new high-frequency modulation method for multilevel converters. The proposed method provides a broad linear operating range and can be digitally implemented with minimal computational effort. This modulation method creates a phase voltage composed of a rectangular component superimposed on the top of a quasi-square-shaped reference function. The reference functions are defined such that the utilization of the dc- link voltage is maximized in any modulation index, while the dv/dt of the switches is always the minimum possible value. In order to implement the proposed method, an up- date time that is much shorter than the fundamental period is defined in the algorithm for updating the rectangular com- ponents of the reference voltage. The high-frequency rect- angular component can then be imposed on the reference function to generate the final switching function by switch- ing between two voltage levels during the time between two update instances. Several experimental results are provided to evaluate the performance of the proposed method and to compare its operation to conventional methods. Index Terms—DC-link voltage utilization, modulation strategies, multilevel converter (MLC), voltage stress over the switches. I. INTRODUCTION N OT LONG AFTER being conceptualized,the multilevel converters (MLCs) have successfully found their place in industrial applications with medium- to high-voltage and power conversion requirements. They offer improved charac- teristics such as lower total harmonic distortion (THD) [1], higher efficiency [2], and lower switching voltage stress com- pared to conventional two-level inverters [3]. The three main OT long after being conceptualized, the MLCs have success- fully found their place in industrial applications with medium- Manuscript received October 30, 2015; revised February 7, 2016, July 2, 2016, August 8, 2016, and September 5, 2016; accepted September 24, 2016. Date of publication October 31, 2016; date of current version February 9, 2017. M. Aleenejad, H. Mahmoudi, and R. Ahmadi are with the Depart- ment of Electrical Engineering and Computer Science, The Univer- sity of Kansas, Lawrence, KS 66045 USA (e-mail: aleenejad@ku.edu; Mahmoudi@ku.edu; Ahmadi@ku.edu). H. Iman-Eini is with the School of Electrical and Computer Engineer- ing, College of Engineering, University of Tehran, Tehran 14395-515, Iran (e-mail: Imaneini@ut.a.ir). 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.2016.2623256 to high-voltage and power conversion requirements [4], [5]. They offer improved characteristics MLC topologies are diode- clamped converter [6], flying capacitor converter [7], and cas- caded H-bridge (CHB) converter [8]. Thanks to the develop- ment of MLC topologies [9], many new modulation techniques have been introduced in the literature recently [10], [11]. These modulation methods can be classified based on their switch- ing frequency into two main groups: fundamental switching frequency methods and high-switching-frequency pulsewidth modulation (PWM) methods [12], [13]. Several categories of high-switching-frequency methods have been reported in the literature lately [14], [15]. However, switching techniques based on carrier-based PWM modulation and space vector modulation (SVM) are the most prevalent methods in industry [16], [17]. Carrier-based PWM techniques have drawn increasing in- terest in industrial applications recently [6], due to their simple structure and good performance [18]. Sinusoidal PWM (SPWM) technique, for instance, is widely used in modern industrial drives. This switching technique itself can be classified into two major subcategories: the phase-shifted PWM (PSPWM) [19] and level-shifted PWM (LSPWM) [20]. In PSPWM, the carri- ers are arranged with horizontal phase shifts, while in LSPWM, the carriers are displaced vertically [21], [22]. Similar to carrier- based PWM methods, the SVM-based techniques have found a special place in industrial applications as well [23]. The SVM- based techniques are particularly suited for digital implementa- tion and offer several advantages such as switching loss reduc- tion, higher dc-link voltage utilization, and lower THD genera- tion [24]–[26]. The fundamental switching frequency methods are well suited for high-power MLCs due to the decreased switching losses, leading to higher efficiencies [27], [28]. Among all the reported fundamental frequency methods in the literature, the two widely adopted techniques are selective harmonic elimination (SHE) [29] and space vector control [30]. Using SHE, switching angles are calculated at the fundamental frequency, such that the desired fundamental voltage is achieved while some specific low order harmonics of the voltage waveform are eliminated. By eliminat- ing some certain harmonic contents, the THD can be reduced or increased [31]. The SHE method requires complex off-line calculations and a large amount of storage space on the digital controller for storing the calculated switching angles [32]. One of the key targets of the researchers in the field of multilevel 0278-0046 © 2016 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.