Power converter circuit and associated triggering method for generators with dynamically variable power output
A power converter circuit and associated triggering method for connecting a three-phase generator to an electrical network. The circuit includes a first direct connection of the generator to the network and a second connection of the generator to the network, through a four-quadrant converter which includes a first power converter, whose alternating voltage terminals are connected to the generator, and a second power converter, whose alternating voltage terminals are connected to the network. The triggering method for power compensation in the event of a short circuit is such that in a first period of time after the short, the second power converter outputs reactive power into the network; in a second period of time, the power converter feeds reactive power back into the network; and in a third period of time, the entire four-quadrant converter controls the gentle restarting, without loading the network with reactive power from the generator.
1. A power converter circuit for connecting a three-phase generator to an electrical network, said generator having a terminal for each of said three phases, said power converter circuit comprising:
three switches connected between said generator and said electrical network, each of said switches being connected to a respective one of said phases of said generator, and providing a direct connection, when closed, between said generator and said electrical network; and
a four-quadrant converter providing a second connection between said generator and said electrical network, said four-quadrant converter having a rated output which is no more than one-half of the rated output of said generator, said four-quadrant converter including:
an intermediate circuit, including a capacitor;
a first power converter, having three alternating voltage terminals each of which is connected to a respective one of said terminals of said generator and also having at least one direct current terminal connected to said intermediate circuit; and
a second power converter, having three alternating voltage terminals each of which is connected to said electrical network and also having at least one direct current terminal connected to said intermediate circuit.
2. The power converter circuit according to claim 1 , wherein each of said first and second power converters includes three half-bridge circuits, each of said half-bridge circuits having one upper power switch and one lower power switch.
3. The power converter circuit according to claim 2 , wherein each of said power switches includes at least one power transistor, and at least one power diode connected in antiparallel to each of said power transistors.
4. The power converter circuit according to claim 1 , wherein said switches each comprise two power semiconductor switches connected in antiparallel.
5. The power converter circuit according to claim 4 , wherein said power semiconductor switches are thyristors.
6. A triggering method for a power converter circuit for connecting a three-phase generator to an electrical network, said generator having a terminal for each of said three phases, said power converter circuit comprising:
three switches connected between said generator and said electrical network, each of said three switches being connected to one of said phases of said generator, and providing a direct connection, when closed, between said generator and said electrical network; and
a four-quadrant converter providing a second connection between said generator and said electrical network, said four-quadrant converter having a rated output which is no more than one-half of the rated output of said generator, said four-quadrant converter including:
an intermediate circuit, having a capacitor, for storing energy,
a first power converter, having three alternating voltage terminals each of which is connected to a respective one of said terminals of said generator and also having at least one direct current terminal connected to said intermediate circuit, and
a second power converter, having three alternating voltage terminals each of which is connected to said electrical network and also having at least one direct current terminal connected to said intermediate circuit;
wherein said power converter circuit is capable of providing reactive power compensation in the event of a short circuit in said electrical network, during which short circuit the remaining network voltage is equal to or greater than 10% of the rated voltage,
said method comprising the steps of:
during a first period of time after the short circuit, in which said switches are open because of said network short circuit, said second power converter outputs reactive power from the energy stored in said intermediate circuit into said electrical network via said alternating voltage terminals of said second power converter;
during a second period of time, with said switches continuing to be open, said second power converter feeds reactive power back into said electrical network; and
during a third period of time, with said switches being open, said four-quadrant converter controls the gentle restarting of said generator and thereby keeps the network load with minimal reactive power or prevents it, until said generator again furnishes energy to said electrical network either continuing to be connected to said electrical network via said four-quadrant converter or being connected directly to said electrical network through the closure of said switches.
7. The triggering method according to claim 6 , wherein within said first period of time, said power switches of said power converters are loaded beyond their rated loading, provided that this is possible without destruction of said power switches.