previous welds the line voltage estimate v s n is used to scale the dig p values from the nominal line voltage to the estimated line voltage samples of the output of the power meter type a function 30 are used to generate an estimates such a voltage measurements v l1 p v l2 p and v l3 n of the rms line voltage furnished to the nominal firing angle generator 52 each pulse may have an initial estimate of the unloaded open circuit voltage at the beginning of the pulse v l1 p a loaded voltage obtained during the first cycle of the pulse v l2 p and a loaded voltage obtained during each subsequent cycle of the pulse v l3 n samples of the power meter type b 34 such as a current meter are used to generate an estimated sequence i u2212 n of the rms current for each negative half cycle furnished to both the nominal firing angle generator 52 and compensated firing angle generator 50 as well as furnishing the sequence of estimated positive half cycle current i n u2212 1 the negative conduction angle sequence u03b3 u2212 n and positive conduction angle sequence u03b3 n u2212 1 to the compensated firing angle generator 50 samples for power meters 30 and 34 are taken under control of the phase reference clock 28 with the inputs as given above the nominal firing angle generator 52 provides a sequence of nominal firing angles u03b1 nom n 1 a compensated target conduction angle sequence u03b3 t n 1 and a target current sequence i t.