Control and Enslavement of Input DC Voltages of multilevel NPC inverter cascade F.Bouchafaa 1a , E.M.Berkouk 2 , M.S.Boucherit 2 1 Laboratory of Instrumentation, Faculty of Electronics and Computer, University of Sciences and Technology Houari Boumediene, BP 32 El-Alia 16111 Bab-Ezzouar Algiers, Algeria. 2 Laboratory of Process Control. Polytechnic National School Algiers. Street Hassen Badi, El Harrach, BP N°182, Algiers, Algeria. Fax:(213)21.52.29.73. Abstract- This paper describes the control and enslavement of input DC voltages of nine-level NPC voltage source inverter. The analysis and simulation of a cascade constituted by three phase’s three-level PWM rectifier-nine levels NPC voltage source inverter (VSI). This cascade is used to feed a permanent magnet synchronous machine with a speed control. In the first part, the authors present the speed control of the permanent magnet synchronous machine (PMSM) by using the field oriented control. Then, in the second part, we study the three-level PWM rectifier controlled by hysteresis strategy. After, we present a topology of nine levels NPC VSI for then they propose a model of this inverter and the PWM strategy which uses eight bipolar carriers to control it. The study of this cascade shows that the input DC voltages of the inverter are not stable and not equals. To remedy to this problem, the authors propose to introduce in the cascade a clamping bridge and regulation using PI regulator. The use of this strategy has let to stabilize the input DC voltages. The results obtained are full of promise to use the inverter in high voltage and great power applications as electrical traction. Key-Words: - NPC inverter, clamping bridge, rectifier multilevel, current hysteresis, PWM strategy, input DC voltages, power factor unit, regulation. 1 Introduction The apparition of new power components controllable in the opened and closed states (GTO and IGBT) has let to the conception of new and fast converters for high power applications. Thus, the speed variator (static converter-AC machines) has seen its cost decreasing considerably. The progress accomplished in the micro-computer tools has let the synthesis of more performant and robust control algorithms for sets of converter-machine [1]. The authors propose a new cascade constituted by three- level PWM rectifiers-nine-level NPC VSI. The performances of this cascade show the instability problem of the input DC voltages of the inverter. As solution to this problem, the authors propose the introduction of a clamping bridge and regulation of the input DC voltages of multilevel NPC inverter structure using PI regulator. This cascade lets to absorb, in network, sinusoidal currents with unity power factor. The results obtained confirm the good performances of the proposed solution. This cascade can find applications in high voltage and field’s great power [1,2]. 2 Permanent magnet synchronous machine drive The Park model of the permanent magnet synchronous machine, with P pairs of poles, is defined by the following equations system [2]. ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ 1 0 Φ ω I I dt d L 0 0 L I I Rs ω L ω L Rs V V f qs ds q d qs ds d q qs ds (1) The control strategy often used consists to maintain the current i ds to zero, and to control the speed by the current i qs via the voltage V qs . In this paper, we use the algorithm i ds =0 (fig.1) [3,4]. Fig.1. The speed control using the algorithm ids=0 + + + + + + − − dθ/dt i c i b i a V ds V qs I qsm I dsm I qsref I dsref Park T Current Regulator Decoupling Current Regulator Speed Regulator Position Sensor PWM Inverter Nine levels ω c θ m K T ω Park T -1 − − PMSM θ m + Proceedings of the 9th WSEAS International Conference on Applied Mathematics, Istanbul, Turkey, May 27-29, 2006 (pp157-162)