Sensorless Control of a Linear Generator for Energy Harvesting Applications

Linear generators are key components for enabling power conversion from reciprocating prime movers such as Stirling and Thermoacoustic engines and wave energy convertors. The control of a linear generator is usually synchronized with instantaneous speed which sets a reference for optimal current - usually in phase with speed. Measuring speed, however, is often challenging because the linear alternator is located in a sealed pressurized vessel or operates in a harsh environment. This paper proposes a simple sensorless control based on a linear observer which estimates instantaneous velocity of the plunger to be used as a phase reference to synchronise the control. The performance and sensitivity of the proposed observer is studied and verified by means of both simulation and experiment. For the particular example the estimated position (from estimated speed integration) is lagging 6.8° towards the measured position, and their amplitudes are different by less then 1%.