Fast connection /reconnection of the VSC to the power network

The problem of the connection of the voltage source converters to the network occurs when the converter transformer is energized from the converter side. This paper deals with the main problems of the transformer energizing, and proposes the procedure for the inrush elimination, simultaneously minimizing the connection period. When a transformer is connected to a circuit, under certain conditions magnetizing inrush currents may arise up to ten times the full load current of the transformer. These currents contain a large amount of harmonic components and cause some relays to trip out. When the transformer is energized with the power electronic devices, these currents could destroy them as well as the DC capacitor. In this paper, the compensation of the magnetizing inrush current using a PWM inverter was discussed. The magnetic condition of the transformer is estimated and the PWM inverter generates compensating voltage. Direct flux controllers are used for the fast response. The validity of analytically obtained results is investigated by using the process simulation. In addition, hardware implementation for the compensator is accomplished to verify the simulation results.