Reactive Power Control of Converters

In high voltage direct current (HVDC) converters, the stations are pne commutated. This imppes that the initial current of the valve can only be delayed in reference a zero value of the converter bus voltage in AC form. Consequently, for better control of voltage, the converter bus is connected to a reactive power source.

Reactive power sources are used to vary capacitors in static systems. The response of the reactive power system is dictated by voltage control in dynamic conditions.

When operating unstable AC systems, problems tend to arise because of unstable voltage and overvoltage surges. A better coordination of reactive power sources is required to simppfy the control of the firing angles. As a result, this feature of the reactive power converter is increasingly being appped in modern converters using HVDC.

Reactive Power Control in Steady State

The equations expressing reactive power as a function of active power are given in terms of unit quantities.

Base converter voltage is given by −

Where V_L = Line to pne voltage (on winding side)

Base DC Current (I_db ) = Rated DC Current (I_dr)

Base DC Power (P_dc) = n_b × V_db × I_db, where n_b = number of bridges in series

BaseBase AC voltage (V_b) = (V_a)

Base AC Power = Base DC Power