Power Transfer Maximization and Di/Dt Based Extremum Tracking for a Swing Engine Based Portable Power System

Several new distributed generation sources are being proposed today that feature variable frequency multiple unbalanced output voltages. One such example is a portable power system based on a permanent magnet generator (PMG) that is driven by a micro internal combustion swing engine (MICSE). Maximum power transfer in such systems can be challenging and reduces system efficiency by 15-30%. Unlike conventional rotating generators, this PMG rotor swings or oscillates through a fraction of a revolution, stops, and swings back to the starting position, where it stops again and so on. This motion is repeated and results in an unbalanced harmonic rich three-phase generator voltage. Discontinuous input currents are common in AC-DC power converters operating from such unbalanced voltages and as a consequence the rms value of the input currents becomes large, thereby limiting the amount of power that can be drawn without tripping the input protection devices. This paper describes power conversion techniques designed to draw the maximum power from such generators. Moreover, key engine controls such as ignition timing are based on the terminal electrical quantities of the PMG which are also simultaneously influenced by the functionality of the power converter. A novel input current di/dt tracker is proposed that indicates the extremum of the engine swings thereby allowing cycle-by-cycle ignition timing adjustments