The control method uses voltage as first controlled variable, current as second controlled variable, power factor as third controlled variable, reactive current as fourth controlled variable, number of loop as fifth controlled variable. Comparing voltage, current, power factor, reactive current, and number of loop with their threshold values setup in advance, the method carries out voltage control, current control, power factor control, reactive current control, and number of loop control in sequence. Whole procedure is a large circulation. Based on ever changing parameter such as voltage, current, power factor, reactive current, and number of loop of product, the method does corresponding handling to implement synthetical and stable control.