Speed control of double stator synchronous machine supplied by two independent voltage source inverters NAZIH MOUBAYED Department of Electricity and Electronics Lebanese University El Arez Street, El-Kobbeh, Tripoli LEBANON Email: nmoubayed@ieee.org Abstract: - In high power applications, power division methods for AC high power converters and machines are used. The rated power of the elementary converters and/or machines becomes lower when the number of converters and/or machines increases. Therefore, power switches with high switching frequency can be used. Then, the current and torque ripples would have theoretically lower amplitude. The speed control of a double stator synchronous machine supplied by two independent voltage source inverters, which is an application of power division, is studied in this paper. After presenting the system under consideration, three strategies of current control are treated. The speed control method is also discussed. Key-Words: - Multi-converter, double stator machine, power division, current and speed control. 1 Introduction Electrical propulsion in embarked applications like ships and aircraft requires high power machines with variable speed drives. In this field, AC machines are increasingly used. These machines can be supplied by GTO Voltage-Source Inverter (VSI). The disadvantage is the low commutation frequency of the GTO and consequently the important current and torque ripples. In order to reduce these ripples, it is necessary to use high commutation frequency semi- conductor devices [1],[2]. Several solutions based on power division can be envisaged. Actually, in high power applications, association of multi-converters with multi-machines is developed. For economic reasons, these electric systems may share some resources in the energizing chain which imply some couplings between the various components. Taking into account these couplings, the system passes by a global approach of the set of the electric components connected to a same supplying source. The global system is defined then by the denomination ‘Multi-converter Multi- machine System (MMS)’ [3],[4]. It is composed of coupled subsystems which are going to interact between them. This paper treats the case of a magnetic coupling system which is the Double Stator Synchronous Machine (DSSM) supplied by two independent VSI. Switches with reduced power rating and higher switching frequency can therefore be used. The modularity of the used inverters, as well as the possibility of functioning with one or two inverters in service, makes this example attractive. The paper is organized as follows. Section 2 is devoted to present the open loop control of the DSSM supplied by two VSI. In section 3, three current control strategies are defined. Using these strategies, simulation results of currents and torque waveforms are presented and analyzed in section 4. Section 5 treats the speed control of the system. Finally, conclusions are given in section 6. 2 Open loop control of the DSSM The studied machine is composed of two stars; each one is formed of three Y connected windings. These stars can be shifted from each other by an electrical angle equal to ‘γ’ (Fig. 1). Each star is supplied by its own three phase VSI (Fig. 2). The rotor contains permanent magnets [5]. Fig. 1: Double stator of the studied machine. γ s2 s2’ s1’ s1 s3 s3’ WSEAS TRANSACTIONS on SYSTEMS and CONTROL Nazih Moubayed ISSN: 1991-8763 253 Issue 6, Volume 4, June 2009