WIDE SPEED RANGE ELECTRIC POWER GENERATION SYSTEM USING HIGH REACTANCE PERMANENT MAGNET MACHINE

• US 20080290843A1
• Filed: 05/21/2007
• Published: 11/27/2008
• Est. Priority Date: 05/21/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: ALKHATIB, ADDY FOUAD, DRUZSBA, ANDREW R., GANEV, EVGENI
• Granted Patent: US 7,595,612 B2
• Time in Patent Office: Days
• US Class Current: 322/28
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 7/04 by static converters
• CPC Class Codes: H02P 2101/30 for aircraft
• CPC Class Codes: H02P 9/008 wherein the generator is controlled by the requirements of the prime mover
• CPC Class Codes: H02P 9/04 Control effected upon non-electric prime mover and dependent upon electric output value of the generator
• CPC Class Codes: H02P 9/10 Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load

Abstract

A device and method for controlling the output of a wide speed range high reactance permanent magnet machine based PGS is provided. The windings of a permanent magnet machine are coupled to a three-phase diode bridge. A transistor is used for temporarily short-circuiting said diode bridge. A capacitor smoothes the voltage at a voltage detection point. A control unit generates a signal that switches the transistor in response to a voltage detected at the voltage detection point. The control unit signal modifies the duty cycle of the switching of the transistor in response to variations in the speed of the power generator to maintain a desired voltage at the voltage detection point.

Claims

1. A device for controlling a variable speed electrical power generation system comprising:

a permanent magnet machine generating an output voltage across a pair of output terminals, said permanent magnet machine having a plurality of stator windings;

a diode bridge connected across said plurality of stator windings;

a transistor for at least temporarily short-circuiting said diode bridge;

a capacitor smoothing said output voltage detected across said pair of output terminals; and

a control unit for generating a signal that switches said transistor in response to a voltage detected across said output terminals, said control unit signal modifying the duty cycle of said switching of said transistor in response to variations in the speed of said power generator to maintain a desired voltage across said output terminals.

2. The device of claim 1 wherein during the time said transistor short-circuits said diode bridge, electrical energy is stored in said stator windings and after said transistor is switched from a short-circuiting mode to a non-short-circuiting mode, said energy is released to said capacitor, thereby boosting the voltage across said output terminals.

3. The device of claim 2 wherein said variable speed electrical power generator includes a rotor that rotates within a first rotational speed range and said boosting of said voltage occurs when said rotational speed is within said first range.

4. The device of claim 3 wherein, within said first rotational speed range said duty cycle decreases as said speed increases to maintain said desired voltage.

5. The device of claim 4 wherein said rotor also rotates within a second rotational speed range, which is higher than said first speed range and wherein said duty cycle is relatively constant throughout most of said second speed range to maintain said desired voltage.

6. The device of claim 1 wherein said electrical power generator is a high reactance permanent magnet machine.

7. The device of claim 6 wherein said permanent magnet machine is constructed such that the short-circuit current of said permanent magnet machine is approximately equal to the operating current of said permanent magnet machine.

8. The device of claim 7 wherein said permanent magnet machine is constructed such that the operating current I_RATED, the phase generated voltage E_EMF and the machine impedance Z_S result in a short-circuit current I_SC=E_EMF/Z_S, and a relative reactance X_PU=I_RATED/I_SC that is in the range of 0.8 to 1.0.

9. The device of claim 6 wherein said stator is a tooth stator.

10. The device of claim 6 wherein said stator is a toothless stator.

11. The device of claim 6 wherein said permanent magnet machine includes a two-pole rotor.

15. The variable speed permanent magnet machine of claim 1 wherein said variable speed permanent magnet machine is constructed such that said operating current I_RATED, said phase generated voltage E_EMF and said machine impedance Z_S result in a short-circuit current I_SC=E_EMF/Z_S, and a relative reactance X_PU=I_RATED/I_SC that is in a range of 0.8 to 1.0.

16. The variable speed permanent magnet machine of claim 15 wherein said voltage control circuit further comprises:

a diode bridge connected to said electrical windings;

a transistor for at least temporarily short-circuiting said diode bridge; and

a pulse width modulation control unit for generating a pulse width modulated signal that switches said transistor in response to variations in a voltage detected at said voltage detection point resulting from variations in the speed of said variable speed permanent magnet machine to maintain a desired voltage at said voltage detection point.

17. The variable speed permanent magnet machine of claim 16 further comprising a diode element coupled between said diode bridge and said voltage detection point.

12. A variable speed permanent magnet machine connected to a load comprising:

a permanent magnet rotor;

a stator assembly mounted adjacent said rotor and including a plurality of electrical windings disposed in a plurality of slots between a plurality of stator teeth and having a stator winding resistance R_S, said electrical windings being electrically connected to a permanent magnet machine output adapted to deliver generated output voltage from said permanent magnet machine;

a voltage control circuit providing a boost in said output voltage in a first rotational speed range, said voltage control circuit also providing limiting of output current to a pre-selected value in a second rotational speed range;

wherein, in use, movement of said rotor induces a first alternating voltage and current in said electrical windings of a first polarity, said first alternating voltage and current inducing a second alternating voltage and current of a second polarity in said electrical windings; and

said voltage control circuit limiting of output current being provided by said second alternating voltage and current of a second polarity.

13. The variable speed permanent magnet machine of claim 12 wherein:

each of said plurality of slots has a shape and construction and an associated windings with inductance which is sufficiently high relative to said induced alternating current such that, in use, a magnetic flux flows through said slot and around said electrical windings in response to said first alternating voltage and current of a first polarity in said electrical windings, thereby inducing said second alternating voltage and current in said electrical windings of a second polarity, which is opposite to said first polarity.

14. The variable speed permanent magnet machine of claim 12, said load having a load resistance R_L, a load reactance X_C, and a load admittance X_C, said permanent magnet machine having a phase-generated voltage E_EMF, an operating current I_RATED and a synchronous impedance Z_S, wherein:

said permanent magnet machine is configured such that a short-circuit current I_SC=E_EMF/Z_S of said permanent magnet machine is approximately equal to said operating current I_RATED of said permanent magnet machine.

18. A method for controlling a wide speed range high reactance permanent magnet machine in a plurality of speed ranges comprising:

determining an output voltage across output terminals of a circuit including a wide speed range high reactance permanent magnet machine having stator windings, a diode bridge connected across said stator windings, a solid state switch connected across said diode bridge and a PWM controller circuit connected to the solid state switch;

if said wide speed range high reactance permanent magnet machine is in a low speed range, and said detected output voltage is lower than a desired output voltage, increasing the duty cycle of said PWM controller to increase the detected output voltage; and

if said wide speed range high reactance permanent magnet machine is in said low speed range, and said detected output voltage is higher than said desired voltage, decreasing the duty cycle of said PWM controller to decrease said detected output voltage.

19. The method of claim 18 further comprising:

if said wide speed range high reactance permanent magnet machine is in a high speed range, and said detected output voltage is lower than a desired output voltage, decreasing the duty cycle of said PWM controller to increase the detected output voltage; and

if said wide speed range high reactance permanent magnet machine is in a high speed range, and said detected output voltage is higher than said desired voltage, increasing the duty cycle of said PWM controller to decrease the detected output voltage.

20. The method of claim 19 further comprising:

during the on-time of said duty cycle, using said solid state switch to short said diode bridge and cause energy to be stored in said windings; and

during the off-time of said duty cycle, releasing said energy stored in said windings.