Mathematical description of sensorless pulse-vector control system of asynchronous motor at constant voltage supply

Sensorless control of Electric Drives is quite relevant according to the SciVal system data. Indirect determination of the rotor angular position in pulse-vector control systems with wound rotor induction motor (PVCS with WR IM) provides opportunity to enlarge application of these systems. Lack of appropriate mathematical description of electromagnetic processes in schemes with non-traditional windings connection of stator and rotor complicates design of sensorless pulse-vector control systems. The paper depicts operation of PVCS with WR IM as a complex multiphase asymmetric system. Dependencies of motor windings magnetomotive force (MMF) on the rotor angular position with a constant supply voltage are evaluated. These angular curves clearly explain the physics of the stator and rotor windings interaction when they are connected in series. The possibility to reckon a rotor angular position in PVCS with WR IM by angular curves of windings MMF or by electric variables proportional to MMF is defined. The paper illustrates the unique algorithm of indirect determination of the initial rotor position based on comparison of rotor and stator windings MMF. The advantages of this algorithm are simplicity and small demands of computer resources. It presents a functional scheme of the estimator based on stator winding and rotor rings voltages. The estimator implementation can calculate initial rotor position with a satisfactory accuracy (up to 60 electrical degrees). It is sufficient to perform control in PVCS with WR IM.