Influence of Freewheeling on Single Pulse Operation of a Switched Reluctance Generator

Switched reluctance generators (SRG) are a promising solution for back-up power generation for renewable energy or in electric vehicles. Classic approaches suggest choosing single pulse control angles to minimize dc-link rms current or excitation penalty to maximize system efficiency. Those publications only investigate the effect of turn-on angle theta(on) and turn-off angle theta(ff). The influence of an additional freewheeling period Delta theta(fw) (U-ph = 0 V) after the magnetization period..mag (U-ph = + U-dc) is only investigated in more recent publications, coming to the conclusion, that efficiency can be improved. However, these papers leave out eddy current losses in the machine coils as well as losses in the power source. Consequently, in this paper the effect of such a freewheeling period after phase-magnetization on the system losses of a 20kW 2-phase SRG (nominal speed 20 krpm) over a wide speed range down to 1/ 3 of the nominal speed by means of system simulations is investigated. It will be shown that introduction of Delta theta(fw) can lead to a more efficient use of the available co-energy loop and allows for optimization regarding different losses. A control strategy over a wide speed range will be derived from the analysis of the results.