SERIES-CONNECTED FIVE-PHASE TWO-MOTOR DRIVE WITH DECOUPLED DYNAMIC CONTROL Atif Iqbal School of Engineering Liverpool John Moores University Liverpool, UK ENGAIQBA@livjm.ac.uk Abstract Multi-phase ac machines are nowadays considered for various applications such as more electric aircrafts, ship propulsion, electric vehicles and textile mills etc due to numerous advantages that they offer when compared to their three-phase counterparts. In principle, vector control of ac machines requires only two stator d-q axis current components for independent flux and torque control. Thus in multi-phase machines there exist additional degrees of freedom in terms of extra non-flux/torque producing current components. The non-flux/torque producing current components which otherwise produces additional losses in machines are utilised in this paper to control other machine in a multi-motor drive system. The independent control of two or more multi-phase machines requires their stator windings to be connected in series with an appropriate phase transposition and supplying them from a single multi-phase VSI using vector control schemes. Originally this concept was introduced for an arbitrary phase number. This paper analyses a specific case of five-phase two-motor drive. The decoupled dynamic control of two five-phase induction machines, connected in series is presented by simulation and experimentation. A brief overview of the operating principles is presented first. This is followed by presentation of detailed simulation and experimental results for a number of transients. Key words Multi-phase machines, Variable speed drives, Five- phase machines, Two-motor drives, Vector control, ramp-comparison current control. 1 Introduction Numerous applications require more than one high- performance variable speed drive. These drives are often of different ratings and have to operate under different conditions. When three-phase machines are used in such applications, each machine is supplied from its own voltage source inverter (VSI) and inverter inputs are paralleled to the common DC link. This means that a set of k motors requires a total of 3k inverter legs. An entirely different concept, based on utilisation of multi-phase machines and multi-phase inverters, has been proposed recently [Levi et al 2003-2003d]. The idea stems from the fact that any n-phase AC machine requires only two currents for independent flux and torque control. Thus, in a multi-phase machine there are additional degrees of freedom, which can be used to control other machine [Gatric, 2000]. It has been shown that, by connecting multi-phase stator windings in series with an appropriate phase transposition, it is possible to control independently all the machines with supply coming from a single multi-phase VSI and using vector control scheme. The benefits of this concept, when compared to its three-phase counterpart, are a saving in the number of inverter legs, easiness of implementation within a single DSP and possibility of direct utilisation of the braking energy, which does not have to circulate through the inverter. Some specific system phase numbers have been studied in considerable detail in [Iqbal and Levi, 2004 and Jones et al, 2003-2003a] and some preliminary experimental results for a two-motor drive system are presented in [Levi et al, 2004]. However, all the available simulation studies have assumed either ideal current source or VSI controlled using hysteresis current control scheme. A two-motor drive system, consisting of two five- phase induction machines connected in series with an appropriate phase transposition, is considered. The concept of this system has been described in [Gatric, 2000 and Levi et al, 2003c-d], while detailed modeling procedure has been reported in [Levi et al, 2003d], where a model in the stationary reference frame had been developed. The simulation results reported in [Levi et al, 2003d] was obtained using hysteresis current control scheme. This article presents the simulation and experimental results obtained by exercising current control on inverter phase currents in the stationary reference frame using ramp-comparison current control technique. A brief overview of the operating principle of the five-phase two-motor drive is presented at first. This is followed by detailed simulation results for a number of transients. To fully verify the concept of decoupled dynamic control,