Optimum regulation of DC sources in cascaded multi‐level inverters

Abstract

If you would like to write for this, or any other Emerald publication, then please use our Emerald for Authors service information about how to choose which publication to write for and submission guidelines are available for all. Please visit www.emeraldinsight.com/authors for more information. About Emerald www.emeraldinsight.comEmerald is a global publisher linking research and practice to the benefit of society. The company manages a portfolio of more than 290 journals and over 2,350 books and book series volumes, as well as providing an extensive range of online products and additional customer resources and services.Emerald is both COUNTER 4 and TRANSFER compliant. The organization is a partner of the Committee on Publication Ethics (COPE) and also works with Portico and the LOCKSS initiative for digital archive preservation. AbstractPurpose -The purpose of this paper is to introduce a new concept in selecting the values of the DC source voltages in cascaded multi-level inverters in order to improve the output voltage THD. Design/methodology/approach -In cascaded multi-level inverters, it is usually assumed that the DC sources have the same constant voltage and output harmonics minimization is accomplished by applying proper switching angles. Employing different DC voltages with proper ratios can result in further reduction of the harmonics. After formulation of the system, i.e. describing the inverter's output voltage components in terms of the switching angles and unequal DC source voltages, a rule is applied to obtain the step heights of the staircase output waveform (DC source voltages), so that the output waveform becomes as close to the required fundamental sine wave as possible. Substituting the obtained DC source voltages into the harmonics elimination equations results in a set of equations, which are functions of switching angles only. Solving these equations leads to proper switching angles, which, regardless of the fundamental component's value, provide the specified harmonic conditions. The output voltage is then controlled by DC sources voltage regulation. Findings -Computer simulations show that employing the proposed concept results in substantial improvement in the harmonic minimization, as well as, extending the operating range of the inverter, compared to the conventional methods with equal DC source voltage multi-level inverters. Originality/value -The proposed concept according to which the ratio of the DC source voltages are determined, is original. IntroductionOwing to the limited ratings of the semiconductor switches and problems arising from their series connection, utilization of static converters in medium and high-voltage applications has been restricted for years. In recent decades, multi-level inverters have been proposed and widely utilized in various high voltage and high-power applications, such as flexible AC transmission systems (FACTS) devices, HVDC light transmission, AC drives and active filters, to overcome the aforementioned problems (Hammond

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