Active Current Control of a Linear Generator for Energy Harvesting Applications

This paper presents an algorithm for automatic maximum power point tracking for linear generator drives used in Stirling or Thermoacoustic generators. The method adjusts the magnitude of the current command responsible for the active power set-point. The proposed approach combines a simple model-based feed-forward term with a slow but accurate correction based on the response of the output power to a lowfrequency modulation in the set-point current magnitude. The correction is derived from the phase of output power oscillations and used to adjust the power set-point and achieve activeload matching conditions. In the paper, the control principle is validated with simulations. As a basis for future experimental validation and to back part of the assumptions, the paper also includes experimental results on two-linear-machine test-rig showing the possibility to vary the internal equivalent damping of the prime-mover.