Initial Rotor Position Detection of Induction Machines Using Feedforward Sensorless Saliency Separation
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1
Institute of Energy Systems and Electrical Drives, Technische Universität Wien, Vienna, Austria
2
Rolling Stock Platform/Components Division, ALSTOM Transport Austria GmbH, Vienna, Austria
Power Electronics and Drives 2021;6 (41):301-313
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ABSTRACT
The use of induction machine spatial saliencies for sensorless vector control in the proximity of zero electrical frequency has been
extensively researched over the last few decades. A robust technique to extract machine saliencies is called voltage step excitation,
and it computes a saliency phasor out of phase current derivatives resulting from specific voltage steps generated by the inverter
switching. Within the saliency phasor, all machine saliencies appear superposed. For some machine constructions, multiple saliencies
are present, containing information about the spatial, magnetic and geometric state of the machine. Due to its direct relation with the
rotor angle and its high accuracy, rotor slotting saliency is often chosen as the sensorless control signal. In order to exclusively access
rotor slotting, saliency separation needs to be carried out, with the goal of eliminating all non-control saliencies from the saliency
phasor. In this research, feedforward harmonic compensation based on look-up tables (LUTs) is chosen. The idea is to estimate each
saliency in relation to amplitude and phase shift once, store such information in a torque-dependent LUT and use it for feedforward
compensation. Yet, several saliencies are linked to the rotor position and, thus, the stored phase shift in the LUT is fixed to a defined
rotor position at which the saliency estimation was performed. For the feedforward compensation to work during each sensorless
start-up, an initial rotor slot detection must be carried out. This paper presents a technique to estimate initial rotor angle based only on
the inherent characteristics of the induction machine multi-saliencies and an iterative feedforward compensation process that requires
no extra resources and only a few PWM (Pulse Width Modulation) periods to achieve initial slot rotor angle. Experimental results
measured at two different test benches prove the high accuracy of the method.