| Abstract |
Flicker has become an important power quality issue. One of the largest sources for flicker is the electric arc furnace, which due to its large time-varying load causes big voltage variations in the grid. Electric bulbs connected to this voltage produces a time-varying illumination, flicker, that is very annoying for humans.
In the paper, an analysis is done on what parts of the voltage spectrum that causes the flicker. It has been found that most parts of the flicker is generated by two narrow sidebands of the voltage fundamental. This has been verified in digital simulations with an arc furnace model containing a sinusoidally varied arc resistance. To mitigate the flicker, a voltage source converter (VSC) has been connected in parallel with the arc furnace and simulated. The converter control is performed in the synchronously rotating
dq-frame. Delays from measurement to realised converter current are of large importance for a well performing flicker mitigation. Measures have been taken in the control scheme to reduce the delay due to measurement filters and pulse width modulation (PWM). The flicker mitigation capability of a 60 MV A VSC is finally compared to that of a 120 MV A
SVC in a case with random arc length modulation. The PST is in this specific case reduced from 3,8 down to 2,4 with the SVC and to 1,2 with the VSC. |
