Passive element-thyristor parallel connection for mitigating inrush current in static transfer switch
Disclosed herein is a static transfer switch and methods of operating the same. The static transfer switch includes a first switch between a first voltage source and a load, and a second switch between a second voltage source and the load. The first switch and the second switch are configured to alternate power to the load between the first voltage source or the second voltage source. The static transfer switch also includes a first parallel circuit branch coupled in parallel to the first switch, the first parallel circuit branch comprising a first passive element and a first auxiliary switch.
1 . A static transfer switch comprising:
a first silicon-controlled-rectifier-based (SCR-based) switch between a first voltage source and a load;
a second SCR-based switch between a second voltage source and the load, wherein the first SCR-based switch and the second SCR-based switch are configured to alternate power to the load between the first voltage source and the second voltage source; and
a first parallel circuit branch coupled in parallel to the first SCR-based switch, the first parallel circuit branch comprising a first inductor and a first auxiliary SCR-based switch, the first auxiliary SCR-based switch connected in series with the first inductor in the first parallel circuit branch,
wherein the first auxiliary SCR-based switch is configured to be closed while the first SCR-based switch is open during activation of the first voltage source.
2 . The static transfer switch of claim 1 , further comprising a second parallel circuit branch coupled in parallel to the second SCR-based switch, the second parallel circuit branch comprising a second inductor and a second auxiliary SCR-based switch, the second auxiliary SCR-based switch connected in series with the second inductor in the second parallel circuit branch.
3 . The static transfer switch of claim 2 , wherein the second auxiliary SCR-based switch is closed while the second SCR-based switch is open during activation of the second voltage source.
4 . The static transfer switch of claim 3 , wherein the second auxiliary SCR-based switch is open while the second SCR-based switch is closed.
5 . The static transfer switch of claim 1 , wherein the first SCR-based auxiliary switch is open when the first SCR-based switch is closed.
6 . The static transfer switch of claim 1 , wherein the first parallel circuit branch is coupled in parallel to the first SCR-based switch and the second SCR-based switch.
7 . The static transfer switch of claim 6 , wherein the first auxiliary SCR-based switch is closed while one of the first SCR-based switch or the second SCR-based switch is open.
8 . The static transfer switch of claim 7 , wherein the first auxiliary SCR-based switch is open when the one of the first SCR-based switch or the second SCR-based switch is closed.
9 . A method of operating a static transfer switch, the method comprising:
coupling a first silicon-controlled-rectifier-based (SCR-based) switch between a first voltage source and a load;
coupling a second SCR-based switch between a second voltage source and the load, wherein the first SCR-based switch and the second SCR-based switch are configured to alternate power to the load between the first voltage source and the second voltage source;
coupling a first parallel circuit branch in parallel to the first SCR-based switch, the first parallel circuit branch including a first inductor and a first auxiliary SCR-based switch, the first auxiliary SCR-based switch connected in series with the first inductor in the first parallel circuit branch;
closing the first auxiliary SCR-based switch to conduct current through the first parallel circuit branch during activation of the first voltage source until the first voltage source is ON; and
when the first voltage source is ON, closing the first SCR-based switch to conduct current through the first SCR-based switch to power the load using the first voltage source.
10 . The method of claim 9 , wherein said closing the first auxiliary SCR-based switch is initiated upon start-up of the load.
11 . The method of claim 9 , further comprising opening the first auxiliary SCR-based switch during said closing the first SCR-based switch.
12 . The method of claim 9 , further comprising:
coupling a second parallel circuit branch in parallel to the second SCR-based switch, the second parallel circuit branch including a second inductor and a second auxiliary SCR-based switch, the second auxiliary SCR-based switch connected in series with the second inductor in the second parallel circuit branch.
13 . The method of claim 12 , further comprising:
detecting a voltage disturbance between the first voltage source and the load;
closing the second auxiliary SCR-based switch to conduct current through the second parallel circuit branch during activation of the second voltage source until the second voltage source is ON; and
when the second voltage source is ON, closing the second SCR-based switch to conduct current through the second SCR-based switch to power the load using the second voltage source.
14 . The method of claim 13 , further comprising disconnecting the first voltage source from the load.
15 . The method of claim 13 , further comprising opening the second auxiliary SCR-based switch during said closing the second SCR-based switch.
16 . The method of claim 9 , wherein coupling the first parallel circuit branch in parallel to the first SCR-based switch further comprises coupling the first parallel circuit branch in parallel to the second SCR-based switch.