1306 Journal of Power Electronics, Vol. 16, No. 4, pp. 1306-1315, July 2016 http://dx.doi.org/10.6113/JPE.2016.16.4.1306 ISSN(Print): 1598-2092 / ISSN(Online): 2093-4718 JPE 16-4-7 Natural Balancing of the Neutral Point Potential of a Three-Level Inverter with Improved Firefly Algorithm M. Gnanasundari † , M. Rajaram * , and Sujatha Balaraman ** †,** Dept. of Electrical and Electronics Engineering, Govt. College of Engineering, Tirunelveli, Tamilnadu, India * Dept. of Electrical and Electronics Engineering, Anna University, Chennai, Tamilnadu, India Abstract Modern power systems driven by high-power converters have become inevitable in view of the ever increasing demand for electric power. The total power loss can be reduced by limiting the switching losses in such power converters; increased power efficiency can thus be achieved. A reduced switching frequency that is less than a few hundreds of hertz is applied to power converters that produce output waveforms with high distortion. Selective harmonic elimination pulse width modulation (SHEPWM) is an optimized low switching frequency pulse width modulation method that is based on offline estimation. This method can pre-program the harmonic profile of the output waveform over a range of modulation indices to eliminate low-order harmonics. In this paper, a SHEPWM scheme for three-phase three-leg neutral point clamped inverter is proposed. Aside from eliminating the selected harmonics, the DC capacitor voltages at the DC bus are also balanced because of the symmetrical pulse pattern over a quarter cycle of the period. The technique utilized in the estimation of switching angles involves the firefly algorithm (FA). Compared with other techniques, FA is more robust and entails less computation time. Simulation in the MATLAB/SIMULINK environment and experimental verification in the very large scale integration platform with Spartan 6A DSP are performed to prove the validity of the proposed technique. Keywords: Firefly Algorithm, FPGA, Natural Voltage Balancing, NPC Inverter, Selective Harmonic Elimination I. INTRODUCTION The advantages of multilevel inverters (MLIs), such as improved power quality and design flexibility, with components of low voltage ratings to handle or produce high voltage levels and hence high power levels have resulted in the extensive use of these inverters in high-power applications [1]. The three well-known configurations of MLI are diode clamped, flying capacitor, and cascaded H bridge type multilevel inverters. Among them, the NPC inverter is used more often in the high-voltage industrial sector at the voltage range of 2.3 KV to 4.16 KV. Several applications of the NPC inverter can even handle voltages up to 6 KV [2]. Its compactness, efficiency, and good performance make the NPC inverter useful in the drives industry. The increasing demand for electrical power could be satisfied only with appropriately designed high-power converters. If these converters are operated at a high switching frequency, then the harmonic content could be reduced at the cost of high switching losses. However, strict power quality and high switching frequency should be maintained. If the system is power efficiency conscious, then a low switching frequency should be opted for. Selective harmonic elimination pulse width modulation (SHEPWM) is an efficient scheme with a switching frequency in the order of a small integer multiple of the fundamental frequency. With SHEPWM, the strength of the dominant low-order harmonics is reduced drastically or nearly eliminated. Then, the high-order harmonics can be easily eliminated with small passive filters. To eliminate the low-order harmonics and improve the spectral with the required amplitude of the fundamental wave, a set of trigonometric Fourier series transcendental equations need to be solved. In addition, a set of switching angles need to be obtained. Such a set of Manuscript received Oct. 8, 2015; accepted Nov. 28, 2015 Recommended for publication by Associate Editor Lixiang Wei. † Corresponding Author: gnanasundari@gcetly.ac.in Tel: +91-4622552450, Govt. College of Engineering * Dept. of Electrical and Electronics Eng., Anna University, India ** Dept. of Electrical and Electronics Eng., Govt. College of Eng., India © 2016 KIPE