Method for determining the fundamental mode reactive power of an R-L load

摘要

In a method for the determination of the fundamental load reactive power of an R-L load controlled by means of an AC current controller (control angle alpha ), e.g. a resistance welding machine, the intention is for the reactive power measurement to be made without integration time (delay-free). This is achieved in that the peak current value îL is measured, that the following two families of characteristic curves are already previously calculated and stored: (1) load angle phi L as a function of the control angle alpha and the phase position alpha S of the peak current value îL (Fig. 1) (2) relative fundamental mode reactive power Q1/Smax as a function of the control angle alpha and the load angle phi L (Fig. 2) and that the control angle alpha at the start of current flow is measured and then the relative fundamental mode reactive power Q1/Smax for this control angle alpha and for a previously known load angle phi L, which is yielded by the family of characteristic curves (1) for this control angle is obtained from the family of characteristic curves (2), the multiplication of the relative reactive power with a predetermined reference power Smax yielding the fundamental mode reactive power Q1. IMAGE