Electrical system for turbine/alternator on common shaft
An electrical system for a turbine/alternator comprising a gas driven turbine and a permanent magnet alternator rotating on a common shaft includes an inverter circuit connectable either to an AC output circuit or the stator winding of the alternator. A control circuit during a startup mode switches the inverter circuit to the stator winding of the alternator and during a power out mode switches the inverter circuit to the AC output circuit. Thus, during the startup mode, the alternator functions as a motor to raise the speed of the turbine to a safe ignition speed and in the power out mode the electrical system outputs the AC output circuit, electrical power having a frequency unrelated to the rotation speed of the alternator.
1. A method for controlling a turbine/alternator comprising a gas driven turbine and a permanent magnet alternator, the method comprising:
a startup process to provide startup electrical power to the turbine/alternator through an inverter section to controllably rotate the permanent magnet alternator to start the turbine/alternator; and
a power output process, after the turbine/alternator has reached speeds necessary to sustain operation of the turbine, to reconfigure the inverter section to extract output electrical power for providing user electrical power from the turbine/alternator,
wherein during the startup process, the inverter section provides the permanent magnet alternator with a controlled time variant AC power,
wherein during the power output process, a frequency of the output electrical power is independent of a rotor speed of the turbine.
2. The method according to claim 1 , wherein the inverter section comprises an inverter, an inverter power circuit to input/output power to/from the inverter, and an inverter control circuit to control the inverter.
3. The method according to claim 1 , wherein the inverter section comprises a single inverter.
4. The method according to claim 2 , wherein reconfiguring of the inverter section includes switching of the inverter power circuit and switching of control of the inverter.
5. The method according to claim 1 , wherein the time variant AC power has time variant frequencies and/or time variant frequency voltages.
6. The method according to claim 1 , wherein the time variant AC power is controlled in a closed loop manner.
7. The method according to claim 6 , wherein the closed loop manner control is based upon rotor position feedback.
8. The method according to claim 7 , wherein the rotor position is detected by a shaft position sensor.
9. The method according to claim 8 , wherein the shaft position sensor is a Hall effect sensor.
10. The method according to claim 1 , wherein a power boost is utilized during the startup process.
11. The method according to claim 10 , wherein the power boost is a boost chopper.
12. The method according to claim 11 , wherein the boost chopper is controlled by a controller to ramp the voltage supplied to the inverter section.
13. The method according to claim 2 , wherein a variable voltage DC power supply applies a time variant voltage to a power input circuit of the inverter during the startup process.
14. The method according to claim 13 , wherein once the permanent magnet alternator has reached its normal operating speed, the variable voltage DC power supply is deactivated.
15. The method according to claim 2 , wherein the AC output voltage of the permanent magnet alternator is rectified and the resulting DC output voltages are applied to a power input circuit of the inverter during the power output process.
16. The method according to claim 2 , wherein the reconfiguration permits the inverter to operate as a fixed frequency power output source independent of the rotor speed of the turbine.
17. The method according to claim 2 , wherein the inverter provides output power through an output filter during the power output process.
18. The method according to claim 17 , wherein the output filter comprises an inductor and a capacitor.
19. The method according to claim 17 , wherein the filtered output power is supplied to load through an output contactor controlled by a system controller and an output breaker.
20. The method according to claim 17 , wherein a system controller controls fuel flow, ignition, rotation speed, temperature, and/or pressure.
21. The method according to claim 1 , wherein the startup electrical power is supplied from a temporary power supply.
22. The method according to claim 2 , wherein at an initial stage of the startup process, a fixed low frequency signal is supplied to the inverter control circuit.
23. The method according to claim 1 , wherein the time variant AC power is a three-phase AC power.
24. The method according to claim 1 , wherein the time variant AC power is controlled in an open-loop manner.
25. The method according to claim 2 , wherein the output current is sensed and is fed back to enable current limit and power balancing of the inverter output.
26. The method according to claim 1 , wherein during the power output process, a phase of the power grid voltage is monitored.
27. The method according to claim 1 , wherein during the power output process, a voltage amplitude of the power grid voltage is monitored.