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Comparative Study of NPC and Cascaded Converters Topologies - shoaibvv - 10-04-2017 Comparative Study of NPC and Cascaded Converters Topologies [attachment=17219] Introduction The interest for multilevel converters comes from their capacity to provide higher power, to generate good quality of waveforms, to operate at low switching frequency with low loss of energy and the low effort on statics devices [1], [2]. Among multilevel converters topologies, there are the Neutral Point Clamped (NPC) converter, the cascaded H-bridge multilevel converter and the imbricated cell multilevel converter [1], [3]. Theoretical Analysis A. NPC Converter Three phase NPC converter with five levels of voltage is shown on Figure 1. Each phase is made of eight controlled switches which are unidirectional in voltage and bidirectional in current and six maintaining diodes connected along the continued bus. The converter is powered by a DC source V, connected to four capacitors of equal values. Our study is limited to a leg of NPC converter with five levels. The voltage values vao are determined for different operating conditions and the switching sequences of the statics devices are presented. Five switching sequences can be identified: II. Generalization A. Multilevel Voltage NPC Converter The study of any multilevel NPC converters is derived from the analysis of three level and five level NPC converters. Figure 5 shows the configuration of a leg of the multilevel NPC converter. IV Principle of Control Many methods to generate pulse width modulation (PMW) signals for multilevel converter have been reported during the last two decades. There are two pulse width modulation technologies: the interceptive modulation and the space vector modulation (SVPWM) [5]. Recently, with the development digital technology, the SVPWM (Space Vector Pulse Width Modulation) is widely used, not only because of its easily implementation, but also for the quality of signals obtained by this method, in particular low displacement current factor [5] [6]. The major inconvenience of this method is that, the control algorithm to generate control signals are becoming increasingly complex for converters with voltage levels more than three [5]. V. Simulation Simulation study was carried out for two three phase topologies: the three levels and the five levels converters. The phase shifted (PS) PWM control method was used for power switches. The input voltage source is 110V, the load is a of a resistance R =1 W in series with an inductance L = 0.75 H . The power factor is cosj = 0.80 . |