Analysis of Power Converters for AC-Fed Traction Drives and Microcomputer-Aided On-Line Optimization of Their Line Response

The analysis of sector-controllable bridges shows the dependence of line responses on special circuit parameters and control methods. The line response of a line current is calculated in terms of the corresponding harmonic spectrum and the magnitudes of the power factor X and the psophometric current Ip4. Referring to the case of a drive model, it is shown how a microcomputer control system optimizes the line response of a particular power converter. This system evaluates the harmonics of line current and line voltage, using a fast FFT-computer. These harmonics are then expressed in terms of certain quantities which represent the line response of the system. A control algorithm makes use of these quantities to calculate a combination of firing angles for an optimum power factor, the minimum psophometric current or the suppression of certain harmonics. In this way, a traction drive can be operated by automatic control, causing little influence on the line side.