Optimal Modulation Algorithm for Hybrid Clamped Three-Level Inverter

Abstract

The principle of a three phase hybrid clamped three-level inverter was presented. Taking Keywords: Optimization method, Hybrid clamped inverter, Pulse width modulation, DC-voltage balanceCopyright © 2016 Universitas Ahmad Dahlan. All rights reserved. IntroductionNowadays, in order to meet the demands of the high-voltage grades and high-power inverter, an important trend in power electronic has been the replacement of the traditional twolevel inverter by multilevel inverter [1][2][3]. With the development of power electronic technology, in [4][5][6][7], multilevel technology has been widely studied in the high-voltage and high-power system, grid-connected wind power system, active power filters, and many other fields. Currently, there is a large variety of such multilevel topologies available [8][9]. However, the three phase diode clamped three-level inverter is the most widely used topology. As an effective multilevel implementation, besides the characters of fewer power switching devices, lower input current harmonics, better sinusoidal and high adjustable power factor, diode clamped threelevel inverter also has the advantages of bi-directional energy transfer, lower switching frequency and higher system efficiency, which can satisfy the requirements of higher voltage grades, higher power and lower harmonic pollution trend of inverter [10]. The operation and the control of three phase diode clamped three-level inverter have been researched during the last decade and both control and modulation methods have been presented in [11][12].However, large-scale application of multilevel topology is subjected to the unbalance voltages of capacitors in DC-bus and the turn-off over-voltage for power switching devices [13][14][15], and diode clamped three-level inverter is no exception [16]. To solve the above problems, a variety of ideas have been put forward in many research papers [17][18][19]. Among these, the topology proposed by Korean scholar Young-Seok Kim in 1993, called the hybrid clamped three-level inverter (HCTLI) has the additional benefits of increased controlled switch states in addition to the general the benefits of diode clamped three-level inverter. Compared to three phased diode clamped three-level inverter, three clamped capacitors are added to three clamped legs. Thus, it can restrain the fluctuations of DC-bus neutral potential, realize the bidirectional current flow and restrain the over-voltages of the power switching devices by charging or discharging clamped capacitors and feasible modulation algorithms. Thereby, due to the opportunities of competitive advantages, HCTLI is generally considered attractive and applied as an inverter for the DC-AC converter. The research of HCTLI has focused so far on control schemes, fewer on the pulse width modulation (PWM) algorithms. Traditionally, in order to restrain the problem of DC-bus capacitor voltages unbalance, these modulation algorithms