Electrical system for turbine/alternator on common shaft

• US 20020070716A1
• Filed: 04/23/2001
• Published: 06/13/2002
• Est. Priority Date: 12/03/1996
• Status: Active Grant

• Current Assignee: Capstone Turbine Corp.
• Original Assignee: Elliott Energy Systems, Inc.
• Inventors: Teets, J. Michael, Gupta, Suresh C., Teets, Jon W., Burnham, Douglas R.
• Granted Patent: US 6,605,928 B2
• Time in Patent Office: Days
• US Class Current: 322/59
• CPC Class Codes: F01D 15/10 Adaptations for driving, or combinations with, electric generators
• CPC Class Codes: F02C 7/26 Starting; Ignition
• CPC Class Codes: F02C 7/268 Starting drives for the rotor , acting directly on the rotor of the gas turbine to be started
• CPC Class Codes: F02C 7/275 Mechanical drives
• CPC Class Codes: F02N 11/04 the motors being associated with current generators
• CPC Class Codes: H02P 9/48 Arrangements for obtaining a constant output value at varying speed of the generator, e.g. on vehicle H02P9/04 - H02P9/46 take precedence
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft
• CPC Class Codes: Y10T 24/201 with screw threaded or notch engaging securing means
• CPC Class Codes: Y10T 24/202 Resiliently biased

Abstract

An electrical system for a turbine/alternator comprising a gas driven turbine and permanent magnet alternator rotating on a common shaft comprises 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 to the AC output circuit, electrical power having a frequency unrelated to the rotational speed of the alternator.

Claims

1. An electrical system for a turbine/alternator comprising a gas driven turbine and permanent magnet alternator on a common shaft comprising:

a) said alternator having a permanent magnet rotor and a stator winding;

b) a stator circuit connected to the stator winding;

c) an AC output circuit;

d) an inverter circuit connected to the AC output circuit;

e) a first contactor for connecting the inverter circuit to the stator circuit;

f) a DC bus connected to the inverter circuit;

g) a rectifier connected between the stator circuit and the DC bus;

h) a temporary power supply circuit connected to the DC bus;

i) a driver connected to cause switching of the inverter circuit;

j) a signal generator driven by signals derived from the rotation of the common shaft;

k) an open loop waveform generator;

l) a second contactor for connecting either the signal generator or the open loop waveform generator to the invertor; and

m) a control circuit for during a startup mode switching the first contactor to connect the inverter circuit to the stator circuit and switching the second contactor to connect the signal generator to the pulse driver and during a power out mode switching the first contactor to disconnect the inverter circuit from the stator circuit and switching the second contactor to connect the open loop waveform generator to the driver;

whereby 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 to the AC output circuit, AC electric power having a frequency unrelated to the rotational speed of the alternator.

2. The system according to claim 1, wherein the driver connected to cause switching of the inverter current is a pulse width modulated driver.

3. An electrical system according to claim 1, wherein the stator winding of the alternator is a three-phase winding and the inverter circuit and the AC output circuits are three-phase circuits.

4. An electrical system according to claim 1, wherein the battery powered supply circuit comprises a battery and a boost from 0 inverter circuit for outputting to the DC bus a voltage between 0 and that required to raise the alternator to safe ignition speeds.

5. An electrical system according to claim 1, wherein the battery powered supply circuit comprises a step-down circuit for recharging the battery during the output mode.

6. An electrical system according to claim 1, wherein the battery powered supply circuit comprises an inverter circuit sharing a common inductor for, during the startup mode, stepping up the voltage to the DC bus and during the battery charging mode, stepping down the DC bus voltage to charge the battery.

7. An electrical system according to claim 1, wherein the battery powered supply circuit comprises a constant frequency pulse width modulator for driving the boost circuit.

8. An electrical system according to claim 7, wherein the control circuit controls the duty cycle of the pulse width modulator to control the voltage to the DC bus.

9. An electrical system according to claim 7, wherein the battery powered circuit comprises a constant frequency pulse width modulator for driving the charger circuit and means to adjust the duty cycle of the pulse width modulator to control the charging voltage of the battery.

10. An electrical system according to claim 1, wherein the signal generator is driven by pickup signals from magnetic sensors excited by a magnet attached to the common shaft.

11. An electrical system according to claim 10, wherein the magnetic sensors are Hall effect sensors.

12. An electrical system according to claim 11, wherein the closed loop waveform circuit further comprises a Hall sensor encoder circuit.

13. An electrical system according to claim 1, wherein the oil pumps and fuel pumps and power supplies for electronics are supplied by DC power from the battery.

14. An electrical system according to claim 1, wherein the AC output circuit comprises a current sense transformer for providing current limit control.

15. An electrical system according to claim 1, wherein the AC output circuit comprises filter inductors and capacitors for each phase.

16. The electrical system according to claim 15, wherein a contactor controlled by the control circuit removes the filter capacitors from the AC output circuit during startup.

17. The electrical system according to claim 1, wherein the open loop waveform generator is used to initiate startup followed by closed loop control to raise the speed of the common shaft to a safe rotation speed for ignition.

18. The electrical system according to claim 1, wherein the waveform generation comprises counters, PROMs, digital-to-analog converters and amplifiers with amplitude control for each phase being individually controllable.