Determining active power of RL-load e.g in resistance welding - involves measuring current peak valve and using sets of characteristic curves relating e.g. load and control angles and phase

摘要

Process for determining the active power of an RL load adjusted by means of an alternating current regulator (control angle alpha), e.g, in a resistance welding machine, has the novelty that the current peak value (iL) is measured, and two successive sets of characteristic curves are calculated and stored: (a) Load angle (psi L) as a function of the control angle (alpha) and the phase position (alpha S) of the current peak value (iL); (b) Relative active power (P/S50) as a function of the control angle (alpha) and the load angle (psi L). Subsequently the control angle (alpha) at the beginning of the control flow is measured, and from the characteristic curves is derived the relative fundamental frequency's active power (P/S50) for this control angle (alpha) and for a previously known load angle (psi L), which results from the characteristic for this control angle (alpha). Multiplication of the relative active power (P/S50) with the predetermined reference power S50 provides the active power value (P). ADVANTAGE - The process for determining the reactive power is made applicable to the predetermination of the active power in the case of RL-loads.