Initial voltage angle detection method of a PWM converter without any grid voltage measurement using conduction state of diodes for smooth starting

Accurate detection of the grid angle at the startup of a converter prevents the over-current trip and also reduces the commissioning time of the system. This paper presents a method to detect initial angle of the grid voltages by measuring the phase currents depending on conduction state of diodes. During the diode conduction, the source voltages are estimated and the estimated voltages are fed into phase locked loop (PLL). When all the diodes are turned off, the source voltage estimator and the PLL are bypassed and the voltage angle is calculated from the frequency of the estimated voltages. The feasibility of the proposed method has been verified by computer simulation and experimental results.