A Novel Position Sensorless Control Approach for Synchronous Electrical Machines for Aerospace Applications 2008-01-2872

This paper presents a novel sensorless control topology called floating frame controller (FFC) for driving synchronous electrical machines using an inverter. Position sensorless control of electrical machines used in aerospace applications is increasingly becoming important due to many system advantages including reducing cost and weight, increasing reliability, and the capability of working in harsh environments.

A conventional synchronous machine typically uses rotor position sensors to provide information regarding the position of the machine's rotor with respect to the machine's stator windings. Rotor position sensors such as Hall Effect devices are typically mounted on the stator in close proximity of the stator windings. The rotor position sensors provide rotor position information, which allows for proper control for the conversion of power that is supplied to the stator windings of an electrical machine [1].

Traditionally rotor position sensors can be unreliable due to mechanical alignment problems (e.g., problems caused by bearings) and temperature incompatibility problems (e.g., problems between the stator windings and electronic components such as the Hall effect devices). Alignment problems in multi-pole machines are made worse, as the electrical misalignment angle is equivalent to the angular mechanical misalignment angle multiplied by the number of pairs of poles. Moreover, the rotor position sensors can be difficult to mount to the machine during machine assembly.

In response to the problems with rotor position sensors, position “sensorless” control techniques have been developed and used for controlling the speed of the synchronous machines. In this paper, a floating frame controller is presented for controlling an inverter that drives a synchronous machine. The method includes the steps of delivering an initial voltage command to the machine; determining whether an initial torque is negative and, if the initial torque is negative, reversing the polarity of voltage command. The method can also be expanded to include the steps of measuring at least two machine phase currents, determining a current Park vector based on those phase currents, estimating a position of the current Park vector, estimating an angular velocity of the current Park vector (which is approximately equal to rotor velocity), and finally generating a decoupled voltage command based on a floating frame current Park vector and the estimated angular velocity.