RET_2015-01-02-03-04_Flipbook

Grid voltage control with wind turbine inverters by using grid impedance estimation – Jonas De Kooning
The droop parameters are tuned to achieve a less fierce reactive power control as
depicted on Fig. 2 by the black circles. An opposite situation occurs as with the previous
tuning for lesser active power control. The voltage is controlled less for inductive grids
but remains almost the same for resistive grids. This is due to the fact that reactive
power control has little effect on the voltage for resistive grids. Although the voltage is
controlled less for inductive grids, also less reactive power is injected into the grid.
5 CONCLUSIONS
The grid voltage control as investigated in this article, is confirmed to improve the grid
voltage and avoid renewable energy sources to shut down when the voltage increases
too much. By reducing the active power output of a renewable energy source, a part of
the full potential of energy production is sacrificed to gain a grid voltage level closer to
its nominal value. This sacrifice is for the better: the alternative is to completely shut
down the energy source wherein the full potential of energy production is sacrificed.
The effectiveness of the grid voltage control is improved by estimating the grid
impedance ratio. This way, the grid voltage control can be applied for wind turbines
connected to any type of grid and it responds on changes in grid load and topology in
real-time.
The benefit of grid voltage control by wind turbine inverters is threefold. Because the
energy source does not completely shut down in the case of an overvoltage – but
reduces its power output, the total generated energy of a particular wind turbine on a
yearly basis will increase. Also, the grid voltage levels are improved because these are
controlled by the wind turbine inverter. Furthermore, the grid operator gains an
additional degree of freedom to manage the grid by controlling the droop parameters
of the voltage control of its wind turbines.
The presented method is explained with wind turbine applications in mind, but it can be
applied on any grid-connected converter of a DG-unit where the active power can be
regulated. Also, the method can be applied on both large and small wind turbines.
Although large wind turbines are typically connected to the transmission grid, the grid
impedance estimation makes sure the grid voltage control adapts itself to control by
using more reactive power.
RÉFÉRENCES
[1] [1] J. De Kooning, “Grid voltage control by wind turbine inverters by using grid impedance
estimation ”, Master's Dissertation, Ghent University, July 2014.
[2] L. Asiminoaei, R. Teodorescu, F. Blaabjerg and U. Borup, “Implementation and Test of an
Online Embedded Grid Impedance Estimation Technique for PV Inverters,” IEEE Trans. on
Industrial Electronics, vol. 52, pp. 1136–1144, August 2005.
Revue E Tijdschrift – 131 ste jaargang/131 e année – n° 1-2-3-4-2015 (publication mars/publicatie maart 2017) 6