Separately excited DC motor with boost and de-boost control

• US 6,031,965 A
• Filed: 09/29/1998
• Issued: 02/29/2000
• Est. Priority Date: 07/08/1997
• Status: Expired due to Term

• Current Assignee: Solaria Research Enterprises, Ltd.
• Original Assignee: Solaria Research Enterprises, Ltd.
• Inventors: Killian, Christopher M., Hammer, Joseph K., Lankin, Robert, Stang, David B., Harman, John R.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US09/162,268
• Time in Patent Office: 518 Days
• Field of Search: 318/244, 318/245, 318/432, 318/433, 388/801, 388/803, 388/806, 388/907.2, 388/907.5
• US Class Current: 388/801
• CPC Class Codes: H02P 7/2985 whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value

Abstract

A motor control system is provided comprising an electrically charged battery, an electrical motor, a battery voltage sensor, a motor speed sensor, an armature voltage sensor, an armature current sensor, and a microprocessor. The magnitude of the armature current applied to the motor is a function of a predetermined armature current setpoint signal and the magnitude of the field current applied to the motor is a function of a predetermined field current setpoint signal, a field current correction signal, and a field current de-boost signal. The microprocessor programmed to generate an armature current setpoint signal, a field current setpoint signal, and an armature voltage reference signal. Further, the microprocessor is programmed to (i) compare the armature voltage reference signal to the measured armature voltage signal and generate an armature voltage error signal based on the comparison; (ii) generate the field current correction signal as a function of the armature voltage error signal; (iii) generate an armature-to-field current check function, wherein the check function defines a set of armature current to field current ratio values as a function of armature current; (iv) calculate a ratio of the measured armature current signal to the field current setpoint signal to establish an operating ratio value, (v) compare the operating ratio value to a corresponding armature current to field current ratio value of the armature-to-field current check function, and (vi) establish the field current de-boost signal, wherein the magnitude of the field current de-boost signal is a function of the measured armature current signal and the comparison of the operating ratio value to the corresponding ratio value.

Claims

1. A motor control system comprising:

an electrically charged battery characterized by an operating battery voltage;

an electrical motor coupled to said battery, said electrical motor including

an armature assembly responsive to an armature current, wherein a magnitude of said armature current is a function of a predetermined armature current setpoint signal I_a.sbsb.--_SET and

a field assembly responsive to a field current, wherein a magnitude of said field current is a function of a predetermined field current setpoint signal I_f.sbsb.--_SET and a field current de-boost signal I_f.sbsb.--_DE-BOOST ;

a battery voltage sensor arranged to generate an operating battery voltage signal V_BAT from said operating battery voltage;

an armature voltage sensor arranged to generate a measured armature voltage signal V_a from an electrical potential of said armature assembly;

an armature current sensor arranged to generate a measured armature current signal I_a indicative of an amount of current flowing through said armature assembly;

a microprocessor programmed to

generate the armature current setpoint signal I_a.sbsb.--_SET and the field current setpoint signal I_f.sbsb.--_SET,

generate an armature-to-field current check function, wherein said check function defines a set of armature current to field current ratio values (I_a /I_f)_CHECK as a function of armature current,

calculate a ratio of said measured armature current signal I_a to said field current setpoint signal I_f.sbsb.--_SET to establish an operating ratio value I_a /I_f.sbsb.--_SET,

compare said operating ratio value I_a /I_f.sbsb.--_SET to a corresponding armature current to field current ratio value (I_a /I_f)_CHECK of said armature-to-field current check function, and

establish said field current de-boost signal I_f.sbsb.--_DE-BOOST, wherein the magnitude of said field current de-boost signal I_f.sbsb.--_DE-BOOST is a function of said measured armature current signal I_a and said comparison of said operating ratio value I_a /I_f.sbsb.--_SET to said corresponding ratio value (I_a /I_f)_CHECK.

2. A motor control system as claimed in claim 1 wherein said microprocessor is programmed to compare said operating ratio value I_a /I_f.sbsb.--_SET to said corresponding armature current to field current ratio value (I_a /I_f)_CHECK by determining whether said operating ratio value I_a /I_f.sbsb.--_SET is greater than said corresponding ratio value (I_a /I_f)_CHECK.

3. A motor control system as claimed in claim 1 wherein said microprocessor is programmed to establish the magnitude of said field current de-boost signal I_f.sbsb.--_DE-BOOST according to a selected one of two distinct de-boost equations, and wherein the identity of the selected equation depends upon the outcome of the comparison of said operating ratio value I_a /I_f.sbsb.--_SET to the corresponding armature current to field current ratio value (I_a /I_f)_CHECK.

4. A motor control system as claimed in claim 3 wherein said two distinct de-boost equations are as follows:

##EQU6## where I_f.sbsb.--_SET '"'"' represents a de-boosted field current setpoint signal, where I_f.sbsb.--_GAIN represents a preselected gain parameter, and wherein said microprocessor is further programmed to generate an armature current error signal I_a.sbsb.--_ERROR by comparing said armature current setpoint signal I_a.sbsb.--_SET and said measured armature current signal I_a.

5. A motor control system as claimed in claim 4 wherein said microprocessor is programmed to select equation (3) when said operating ratio value I_a /I_f.sbsb.--_SET is greater than the corresponding armature current to field current ratio value (I_a /I_f)_CHECK.

6. A motor control system as claimed in claim 4 wherein said microprocessor is programmed to select equation (4) when said operating ratio value I_a /I_f.sbsb.--_SET is not greater than the corresponding armature current to field current ratio value (I_a /I_f)_CHECK.

7. A motor control system as claimed in claim 1 wherein said electrical motor is characterized by a set of commutation limits, and wherein said microprocessor is programmed to generate said armature-to-field current check function such that said check function simulates said commutation limits as a function of armature current.

8. A motor control system as claimed in claim 1 wherein said electrical motor is characterized by a set of commutation limits, and wherein said armature-to-field current check function is defined by the following equations:

space="preserve" listing-type="equation">(I.sub.a /I.sub.f).sub.CHECK =(I.sub.a /I.sub.f).sub.MAX +(I.sub.a /I.sub.f).sub.GAIN -(I.sub.a /I.sub.f).sub.SLOPE equation (

     1)

space="preserve" listing-type="equation">(I.sub.a /I.sub.f).sub.CHECK =(I.sub.a /I.sub.f).sub.MIN +(I.sub.a /I.sub.f).sub.GAIN equation (

     2)

where (I_a /I_f)_MAX represents a maximum armature current to field current ratio within said commutation limits, (I_a /I_f)_MIN represents a minimum armature current to field current ratio within said commutation limits, (I_a /I_f)_GAIN represents the following product

space="preserve" listing-type="equation">G.sub.DE.sbsb.--.sub.BOOST ×

(V.sub.REF -V.sub.BAT)

where G_DE-BOOST is a predetermined gain parameter, V_REF represents a reference battery voltage, and (I_a /I_f)_SLOPE represents the following product

space="preserve" listing-type="equation">I.sub.a ×

m.sub.DE.sbsb.-- BOOST

where m_DE-BOOST is a predetermined slope parameter.

9. A motor control system as claimed in claim 8 wherein said predetermined gain parameter G_DE-BOOST represents an allowable increase in armature to field current ratio per battery volts.

10. A motor control system as claimed in claim 8 wherein said predetermined slope parameter represents a maximum ratio of armature to field current per amp of armature current.

11. A motor control system as claimed in claim 8 wherein said microprocessor is programmed to generate said armature to field current check function such that said check function is defined by equation (1) when

12. A motor control system as claimed in claim 8 wherein said microprocessor is programmed to generate said armature to field current check function such that said check function is defined by equation (2) when

13. A motor control system as claimed in claim 1 wherein said microprocessor is further programmed to

generate a full-on indication signal when said measured armature voltage signal V_a is substantially equal to said operating battery voltage signal V_BAT,

generate an armature current error signal I_a.sbsb.--_ERROR by comparing said armature current setpoint signal I_a.sbsb.--_SET and said measured armature current signal I_a,

generate a low armature current indication signal when said armature current error signal I_a.sbsb.--_ERROR exceeds a predetermined value, and

enable said field current de-boost signal establishing step according to whether said full-on indication signal and said low armature current indication signal are generated.

14. A motor control system as claimed in claim 13 wherein said microprocessor is further programmed to generate said armature current error signal according to the following equation

15. A motor control system as claimed in claim 13 wherein said microprocessor is programmed to generate said full-on indication signal when

16. A motor control system as claimed in claim 13 wherein said microprocessor is programmed to generate said low armature current indication signal when

17. A motor control system as claimed in claim 1 wherein:

said field assembly is further responsive to a field current correction signal I_f.sbsb.--_CORRECTION ;

said motor control system further comprises a motor speed sensor arranged to generate an actual motor speed signal ω

representative of an actual speed of said electrical motor; and

said microprocessor is further programmed to

generate an armature voltage reference signal V_a.sbsb.--REF,

compare said armature voltage reference signal V_a.sbsb.--_REF to said measured armature voltage signal V_a and generate an armature voltage error signal V_a.sbsb.--_ERROR based on said comparison, and

generate said field current correction signal I_f.sbsb.--_CORRECTION as a function of said armature voltage error signal.

18. A motor control system comprising:

an electrically charged battery characterized by an operating battery voltage;

an electrical motor coupled to said battery, said electrical motor including

an armature assembly responsive to an armature current, wherein a magnitude of said armature current is a function of a predetermined armature current setpoint signal I_a.sbsb.--hd SET and

a field assembly responsive to a field current, wherein a magnitude of said field current is a function of a predetermined field current setpoint signal I_f.sbsb.--_SET, a field current correction signal I_f.sbsb.--_CORRECTION, and a field current de-boost signal I_f.sbsb.--_DE-BOOST ;

a battery voltage sensor arranged to generate an operating battery voltage signal V_BAT from said operating battery voltage;

a motor speed sensor arranged to generate an actual motor speed signal ω

representative of an actual speed of said electrical motor;

an armature voltage sensor arranged to generate a measured armature voltage signal V_a from an electrical potential of said armature assembly;

an armature current sensor arranged to generate a measured armature current signal I_a indicative of an amount of current flowing through said armature assembly;

a microprocessor programmed to

generate an armature current setpoint signal I_a.sbsb.--_SET, a field current setpoint signal I_f .sbsb.--_SET, and an armature voltage reference signal V_a.sbsb.--_REF,

compare said armature voltage reference signal V_a.sbsb.--_REF to said measured armature voltage signal V_a and generate an armature voltage error signal V_a.sbsb.--_ERROR based on said comparison,

generate said field current correction signal I_f.sbsb.--_CORRECTION as a function of said armature voltage error signal,

generate an armature-to-field current check function, wherein said check function defines a set of armature current to field current ratio values (I_a /I_f)_CHECK as a function of armature current,

calculate a ratio of said measured armature current signal I_a to said field current setpoint signal I_f.sbsb.--_SET to establish an operating ratio value I_a /I_f.sbsb.--_SET,

compare said operating ratio value I_a /I_f.sbsb.--_SET to a corresponding armature current to field current ratio value (I_a /I_f)_CHECK of said armature-to-field current check function, and

establish said field current de-boost signal I_f.sbsb.--_DE-BOOST, wherein the magnitude of said field current de-boost signal I_f.sbsb.--_DE-BOOST is a function of said measured armature current signal I_a and said comparison of said operating ratio value I_a /I_f.sbsb.--_SET to said corresponding ratio value (I_a /I_f)_CHECK.

19. A motor control system as claimed in claim 18 wherein said microprocessor is further programmed to generate said field current correction signal I_f.sbsb.--_CORRECTION such that it is inversely proportional to said actual motor speed signal ω

.

20. A motor control system as claimed in claim 18 wherein said microprocessor is further programmed to generate said field current correction signal I_fCORRECTION as a function of said armature voltage error signal V_a.sbsb.--_ERROR and said actual motor speed signal ω

.

21. A motor control system as claimed in claim 20 wherein said microprocessor is further programmed to generate said field current correction signal I_f.sbsb.--_CORRECTION according to the following equation:

space="preserve" listing-type="equation">I.sub.f.sbsb.--.sub.CORRECTION =V.sub.a.sbsb.--.sub.ERROR ×

C.sub.1 ×

(G.sub.v /ω

)

where V_a.sbsb.--ERROR is the armature voltage error signal, C₁ is a constant, G_v is a variable gain parameter, and ω

is the actual speed of the motor.

22. A motor control system as claimed in claim 21 wherein said electrical motor includes a characteristic air gap between poles of said field assembly and an armature core of said armature assembly, and wherein said constant C₁ includes a motor constant K, unit scaling corrections, and a coefficient for dI_f.sbsb.--_SET /dB where I_f.sbsb.--_SET is the field current setpoint and B represents the magnetic flux in said air gap of said electrical motor.

23. A motor control system as claimed in claim 18 wherein said armature assembly includes high and low voltage nodes, and wherein said armature voltage sensor is arranged to measure armature voltage at said low voltage node.

24. A motor control system as claimed in claim 18 wherein said microprocessor is further programmed to modify said measured armature voltage signal V_a by summing said measured armature voltage signal V_a and said operating battery voltage signal V_BAT prior to comparing said measured armature voltage signal V_a to said armature voltage reference signal V_a.sbsb.--_REF.

25. A motor control system as claimed in claim 18 wherein:

said motor control system further comprises a speed command generator arranged to generate a speed command signal S indicative of a desired speed of said electrical motor; and

said microprocessor is further programmed to generate said armature voltage reference signal V_a.sbsb.--_REF, said field current setpoint I_f.sbsb.--_SET, and said armature current setpoint I_a.sbsb.--_SET as a function of said speed command signal S and said actual motor speed signal ω

.

26. A motor control system as claimed in claim 25 wherein said microprocessor is programmed to generate said armature voltage reference signal V_a.sbsb.--_REF, said field current setpoint I_f.sbsb.--_SET, and said armature current setpoint I_a.sbsb.--_SET from a look-up table having at least one input value derived from said speed command signal S and said actual motor speed signal ω

.

27. A motor control system as claimed in claim 25 wherein said microprocessor is programmed to generate said armature voltage reference signal, said field current setpoint, and said armature current setpoint from a look-up table.

28. A motor control system as claimed in claim 25 wherein said microprocessor is programmed to generate said armature voltage reference signal V_a.sbsb.--_REF, said field current setpoint I_f.sbsb.--_SET, and said armature current setpoint I_a.sbsb.--SET from a dual-input look-up table, wherein a first input of said look-up table comprises a torque setpoint signal T_SET, and wherein a second input of said look-up table comprises said actual motor speed signal ω

.

29. A motor control system as claimed in claim 28 wherein said microprocessor is programmed to generate said torque setpoint signal T_SET as a function of said actual motor speed signal ω

and said speed command signal S.