Speeds Estimation of Series-Connected Five-Phase Two- Motor Drive System using Adaptive Flux Observers

Utilization of multi-phase machines in variable speed drives is nowadays extensively considered for electric ship propulsion, ‘more-electric aircraft’ and traction applications, including EVs and HEVs. In addition to wellknown advantages, use of multi-phase machines enables independent control of a certain number of machines that are connected in series in an appropriate manner, with the supply coming from a single voltage source inverter (VSI). The concept was initially proposed for a five-phase seriesconnected two-motor drive, but is applicable to any system phase number greater than or equal to five. The number of connectable machines is a function of the VSI phase number and detailed theoretical and simulation studies have already been reported for various multi-phase multi-motor drive configurations of this type. Variable speed induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information of the rotor speed is extracted from measured stator currents and voltages at motor terminals. Open-loop estimators or closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. This paper analyses operation of an adaptive flux observer-based sensorless control of vector controlled series connected two motor five-phase drive system with current control in the stationary reference frame. Performance, obtainable with hysteresis current control, is illustrated for a number of operating conditions on the basis of simulation results. The purpose of this paper is to present, for the first time, simulation results on a sensorless control of a five-phase two-motor series-connected drive system. A brief overview of the operating principles is provided first. This is followed by a description of the sensorless technique.