Sensorless control of a linear reciprocating switched-reluctance electric machine

Abstract

It is proposed to use a simple switched-reluctance electric machine that does not have windings or permanent magnets on a movable part to develop a linear reciprocating electric machine intended for use as an electric generator together with a free-piston internal-combustion engine. It is noted that one of the most difficult problems in the development of such a linear electric machine is the development of a control system. A sensorless control algorithm is considered. Information on the stator-phase inductance of the electric machine and its variation is used to determine the position of the movable part. For its estimation, probing voltage pulses of known duration are applied to the phase. The amplitude of the current pulses caused by them will be proportional to the phase inductance. A mathematical model of electromagnetic processes is used to test the efficiency of the proposed control algorithm and determine appropriate control parameters. Since stator phases have separate magnetic circuits and are not magnetically connected, the electromagnetic processes in each phase are considered independently. Model parameters are determined experimentally using an experimental prototype of the considered electric machine, for which the dependences of the phase flux linkage and the generated force on the phase current for different positions of the movable part are obtained. The results of the investigation of processes in the considered electric machine at different frequencies of the movable part are given. It is found that, at frequencies of the movable part close to the nominal frequency, the phase should be connected to the power supply even before the movable part reaches the extreme position. Control using probing pulses applied to the operating phase is impossible, because the level of these pulses does not reach the maximum value until the phase is switched on. In this case, it is necessary to use the probing pulses of another, nonoperating phase to determine the position of the movable part. Such an algorithm makes it possible to control a linear reciprocating switched-reluctance electric machine at both low and high frequencies of the movable part. The obtained results confirmed the correctness of the adopted approaches to the development of a sensorless control algorithm.