Design of a voltage sag generator based on impedance switching

Abstract

This paper describes an experimental setup of a voltage sag generator (VSG) based on impedance switching. Bidirectional switches with IGBTs, snubber and clamping circuits are adopted to obtain fast turn on, turn-off while avoiding undesirable voltages and currents stresses. In addition, with the proposed VSG it is possible to adjust the depth and duration of balanced and unbalanced voltage dips making it possible to observe the behavior of wind turbines (WT) under, for instance, voltage dips indicated in the IEC 61400-21.

4-wire Matrix Converter based voltage sag/swell generator to test LVRT in renewable energy systems

“…2. The current flow in the shunt impedance leads to the voltage sag, and the series impedance is designed to reduce the short circuit effects [7]. In order to generate grid-voltage sag with different depths a shunt impedance bank is required.…”

“…Plenty of university-built VSG have been reported [6]. [7], mainly using shunt impedance or transformer based VSG. Either commercially available or university built VSG are suitable for 3-phase 3-leg systems, but not attention have been paid to studied 3-phase 4-leg VSG.…”

Benchmarking of Voltage Sag Generators

“…Many voltage sag generator solutions have been reported in the literature [5]- [14]. There are mainly three different types of voltage sag generators: shunt impedance sag generator, transformer based voltage dip generator and fully controlled converter based voltage sag generator, as it is shown in Fig.…”

“…In order to generate voltage dips with different depths, a shunt impedance bank is used. The series impedance Zs is designed to reduce the short-circuit effects on the up-stream grid [2], [3], [5]. In the normal operation, the switch Sl should be closed and the shunt switches (S21, S22, ... , and S2n) should be open.…”

Inverter based test setup for LVRT verification of a full-scale 2 MW wind power converter

“…The transformer based VSG is a suitable solution for testing LVRT functionality but due to the fact of high costs and heavy weight of the transformer at higher power ratings it is not the preferred one. Another approach for emulating grid failures is an impedance based VSG similar to the one in [3]. The desired voltage sag is achieved by short circuiting the corresponding voltage phase of the three phase system through a shunt impedance which is also connected through bidirectional switches to the grid.…”