FPGA Implementation of Generalized Modulation for Hybrid Multilevel Inverter with fixed Ratio DC Link Voltage Shweta Gautam Dept. of Electrical Eng., Motilal Nehru National Institute of Technology, Allahabad, India Sombuddha Kundu Enterprise Accounts Manager, Tally Solutions Pvt. Ltd, Kolkata, India Pinaki Basu Supervisor, Radar Indian Air Force, Jaisalmer, India Rajesh Gupta Dept. of Electrical Eng., Motilal Nehru National Institute of Technology, Allahabad, India Abstract— In this paper, an FPGA implementation of generalized modulation for hybrid multilevel inverter, having fixed ratio dc voltage for each cell, has been proposed. A hybrid inverter consists of number of high voltage H-bridge cells, each operating at the fundamental frequency and a low voltage PWM operated H-bridge cell. The proposed modulation algorithm is independent of the actual dc link voltage of the cells. Also the templates for output voltage of each high voltage cells are generated internally without any need of inverter output voltage feedback for comparison with the reference. Verification of the proposed modulation algorithm is obtained for a seven level hybrid inverter using two cascaded H-bridge cells, both through the simulations and experiments. In experimental verification, the modulation algorithm is implemented using LabVIEW FPGA module programming on reconfigurable data acquisition board. Keywords — Asymmetrical multilevel inverters, fast Fourier transform (FFT), field programmable gate array (FPGA), total harmonic distortion (THD). I. INTRODUCTION The concept of utilizing multiple small voltage levels to perform power conversion was patented by an MIT researcher over twenty five years ago [1]. Advantages of the multilevel approach include improved output voltage quality, better electromagnetic compatibility (EMC), low switching losses, and high voltage capability. The main disadvantages of this technique is that a large number of switching semiconductor devices are required and the small voltage steps must be supplied on the dc side either by a capacitor bank or isolated voltage sources [1]-[4]. Use of voltage source converters (VSCs) in medium to high power conversion has led to the increased use of multilevel converters [3]-[5]. Multilevel converters finds its applications in active power conditioning, renewable energy conversion, industrial drives etc. because of the motivation for obtaining high quality output using limited rating power electronic devices [1], [4]. Its importance can also be attributed to the current energy scenario. The world is slowly moving from fossil fuels to renewable energy. This paradigm shift is effected partly due to concerns of rising global pollution levels but more so because of the inherent economic motivators. As energy prices rise and countries implement stricter environmental protection laws it provides incentives for the renewable energy market to flourish. The mainstream renewable energy market as of now consists of wind and solar power. Photovoltaic (PV) systems produce DC voltage and wind energy systems produces AC voltage but needs to be converted into DC and then reconverted to AC to provide constant frequency and amplitude output. In both cases conversion from DC to AC is a crucial part of the procedure. Use of Voltage source converters (VSC) in medium to high power conversion as in the previously cited examples has led to the increased use of multilevel converters [3]-[5]. The first paper which propounds the concept of multilevel PWM converters was back in the 1980’s. Before that the converters traditionally used in power systems were switched at fundamental frequency. Although these could be used on the distribution voltages directly, it had power quality issues. Therefore power quality enhancement using active power conditioning based on the multilevel converters became an important research area [4]. Recent advances in power electronics have made the multilevel concept practical. Furthermore, several papers explained about multilevel power conversion. It is evident that the multilevel concept will be a prominent choice for power electronic systems in future years, especially for medium- voltage operation. The use of commonly available power electronic devices, e.g., IGBT (660V, 80A to 2.5kV, 1.5 kA), at the distribution voltage levels of 440V-11kV are no longer restricted due to the available technology of multilevel inverters [9]. The asymmetrical multilevel inverters with unequal DC voltages is receiving increasing attention because it is possible to synthesize voltage waveforms with reduced harmonic content, even using a few series-connected cells. This advantage is achieved by using distinct voltage levels in different cells in fixed ratio, which can create more levels in the output voltage and minimize its total harmonic distortion (THD) without increasing the number of switching devices and isolated sources [4]–[19]. In this paper a generalized modulation for hybrid multilevel inverter, having fixed ratio dc voltage for each cell, has been proposed. The inverter consists of number of high voltage H- bridge cells and a single low voltage H-bridge cell. Each high voltage bridge operates at the fundamental frequency and the low voltage bridge operates at high frequency pulse width 2012 IEEE International Conference on Power Electronics, Drives and Energy Systems December16-19, 2012, Bengaluru, India 978-1-4673-4508-8/12/$31.00 ©2012 IEEE