U.S. patent application number 10/885103 was filed with the patent office on 2006-04-06 for motor controller.
This patent application is currently assigned to RT Patent Company, Inc.. Invention is credited to George Holling, Ned Warner.
Application Number | 20060071629 10/885103 |
Document ID | / |
Family ID | 34981312 |
Filed Date | 2006-04-06 |
United States Patent
Application |
20060071629 |
Kind Code |
A1 |
Holling; George ; et
al. |
April 6, 2006 |
Motor Controller
Abstract
Abstract of the Disclosure A system and method for controlling
an electric motor is disclosed. The method comprises determining
the operating load of the electric motor and then calculating the
voltage to be applied to the electric motor in response to the
operating load. The voltage to be applied operates the motor in an
efficient manner for the given load. The frequency of the voltage
to be applied to the electric motor is calculated in response to
the operating load such that the frequency of the voltage to be
applied operates the motor in an efficient manner. Power is applied
to the motor with the voltage and frequency calculated in order to
operate the motor in an efficient manner for the given load.
Inventors: |
Holling; George; (Riverton,
UT) ; Warner; Ned; (Provo, UT) |
Correspondence
Address: |
JONES DAY;ANDREWS & KURTH LLP
111 CONGRESS AVE
SUITE 1700
AUSTIN
TX
78701
US
|
Assignee: |
RT Patent Company, Inc.
1209 Orange Street
Wilmington
DE
19801
|
Family ID: |
34981312 |
Appl. No.: |
10/885103 |
Filed: |
July 7, 2004 |
Current U.S.
Class: |
318/807 |
Current CPC
Class: |
Y02P 80/116 20151101;
H02P 23/0004 20130101; Y02P 80/10 20151101 |
Class at
Publication: |
318/807 |
International
Class: |
H02P 5/28 20060101
H02P005/28 |
Claims
1. A controller for an electric motor with a rotational speed and
using electrical current, the controller comprising: a voltage
controller for generating a voltage control signal in response to
the speed and the current usage of the motor wherein the voltage
control signal represents an efficient operating mode of the motor;
a frequency controller for generating a frequency control signal in
response to the speed and current usage of the motor wherein the
frequency control signal represents an efficient operating mode of
the motor; and a multiplier for combining the frequency control
signal and the voltage control signal such that the combined signal
is applied to the voltage operating the motor.
2. The controller of claim 1 wherein the frequency controller is
configured to control the frequency of the motor in order to limit
saturation of the motor.
3. The controller of claim 1 wherein the voltage controller
comprises a voltage/frequency curve for the operating load of the
motor, the voltage/frequency curve being configured to determine
the operating voltage for the motor in order to maximize
efficiency.
4. The controller of claim 1 wherein the frequency controller
comprises a voltage/frequency curve for the operating load of the
motor, the voltage/frequency curve being configured to determine
the operating frequency for the motor in order to maximize
efficiency.
5. The controller of claim 1 wherein the motor has a speed sensor
operative to generate a speed sensing signal and the voltage
controller is configured to generate the voltage control signal in
response to the speed sensing signal.
6. The controller of claim 1 wherein the motor has a current sensor
operative to generate a current sensing signal and the voltage
controller is configured to generate the voltage control signal in
response to the current sensing signal.
7. The controller of claim 1 wherein the motor has a current sensor
operative to generate a current sensing signal and a speed sensor
operative to generate a speed sensing signal, and the voltage and
frequency controllers are configured to generate a respective
voltage control signal and frequency control signal in response to
the current sensing signal and the speed sensing signal.
8. The controller of claim 7 wherein the frequency controller and
the voltage controller are configured to operate an AC induction
motor.
9. A method of controlling an electric motor, the method comprising
the following steps: generating a voltage control signal in
response to a speed of the motor and a current usage of the motor
wherein the voltage control signal represents an efficient
operating mode of the motor; generating a frequency control signal
in response to the speed of the motor and the current usage of the
motor wherein the frequency control signal represents an efficient
operating mode of the motor; and combining the voltage control
signal and the frequency control signal and applying the combined
signal to the voltage operating the motor such that the motor
operates efficiently for the given load.
10. The method of claim 9 further comprising the step of
determining a speed of the motor with a speed sensor prior to
generating the voltage and frequency control signals.
11. The method of claim 10 further comprising the step of
determining the current usage of the motor with a current sensor
prior to generating the voltage and frequency control signals.
12. The method of claim 9 further comprising the step of applying
the voltage to an AC induction motor.
13. The method of claim 12 further comprising the step of applying
the voltage to a three-phase AC induction motor.
14. A system for controlling the speed of an electric motor, the
system comprising: a speed sensor for measuring the rotational
speed of the electric motor and generating a speed sensing signal;
a current sensor for measuring the current usage of the electric
motor and generating a current sensing signal; a voltage controller
for generating a voltage control signal in response to the speed
sensing signal and the current sensing signal wherein the voltage
control signal represents an efficient operating mode of the motor;
a frequency controller for generating a frequency control signal in
response to the speed sensing signal and the current sensing signal
wherein the frequency control signal represents an efficient
operating mode of the electric motor; and a multiplier for
combining the frequency control signal and the voltage control
signal such that the combined signal is applied to the voltage
operating the motor.
15. The system of claim 14 wherein the voltage controller comprises
a voltage/frequency curve for the operating loads of the motor, the
voltage/frequency curve being configured to determine the operating
voltage for the motor in order to maximize efficiency.
16. The system of claim 14 wherein the frequency controller
comprises a voltage/frequency curve for the operating loads of the
motor, the voltage/frequency curve being configured to determine
the operating frequency for the motor in order to maximize
efficiency.
17. The system of claim 14 wherein the motor is an AC induction
motor.
18. The system of claim 19 wherein the motor is a three-phase AC
induction motor.
19. A method for controlling an electric motor, the method
comprising the following steps: determining the operating load of
the electric motor; calculating the voltage to be applied to the
electric motor in response to the operating load wherein the
voltage operates the motor at an efficient mode; calculating the
frequency of the voltage to be applied to the electric motor in
response to the operating load wherein the frequency of the voltage
to be applied operates the voltage in an efficient mode; and
applying the voltage at the frequency calculated in order to
operate the motor in an efficient mode.
20. The method of claim 19 further comprising the step of
determining the operating load of the electric motor by determining
the speed of the electric motor and the current usage of the
electric motor.
21. The method of claim 20 wherein the step of calculating the
voltage applied to the electric motor comprises determining the
voltage with a voltage/frequency curve for the operating load.
22. The method of claim 20 wherein the step of calculating the
frequency of the voltage applied to the electric motor comprises
determining the frequency with a voltage/frequency curve for the
operating load.
23. The controller of claim 8 wherein the AC induction motor is a
three-phase induction motor.
Description
Detailed Description of the Invention
FIELD OF THE INVENTION
[0001] The present invention generally relates to controllers for
electric motors and more specifically to a controller which can
vary the voltage and frequency of the power applied to the motor in
order to obtain maximum efficiency at any load.
BACKGROUND OF THE INVENTION
[0002] Controllers for electric motors provide electrical energy to
the motor for proper operation. Typically, the controller applies a
voltage to the motor at a prescribed frequency. The voltage and the
frequency are chosen to optimize the speed and torque output of the
motor.
[0003] It has been shown that with an AC induction motor, the
torque output of the motor can be improved if an over-voltage
condition is applied. During this condition, the motor is operated
in a partial saturation condition due to the magnetization current
at low loads. However, the efficiency of the motor is decreased at
lower speeds when operated in the over-voltage condition.
[0004] Referring to Figure 1, a graph showing the efficiency of an
AC induction motor operating in various conditions is shown. In
Figure 1, line 10 illustrates the efficiency of a standard AC
induction motor operating in an over-voltage condition. As can be
seen, the efficiency of the motor is low (i.e., approx. 50-75%) at
low load conditions and the efficiency increases as the load
increases. An AC induction motor operating normally is shown as
line 12 and as can be seen, the efficiency of the motor is greatest
at low load conditions and decreases as the load on the motor
increases.
[0005] Currently, motor controllers can use vector controls for
operating the motor at maximum efficiency. Vector controls are
complex mathematical formulas which model the operation of the
motor and use real-time monitoring of the motor. Specifically, the
vector controls are a closed-loop feedback system that control the
phase relationships between the input voltages. In order for the
vector control to be effective, very sensitive measurements of the
operating parameters of the motor are needed. In this respect,
vector controls require very sensitive and expensive sensors to
measure the operation of the motor.
[0006] Accordingly, there is a need for a motor controller to
operate an electric motor in an efficient manner at different load
conditions without the use of sensitive or complex control
techniques.
SUMMARY OF THE INVENTION
[0007] A controller is disclosed for operating an electric motor
having a rotational speed and using electrical current. The
controller has a voltage controller for generating a voltage
control signal in response to the speed and current usage of the
motor wherein the voltage control signal represents an efficient
operating mode of the motor. Furthermore, the controller has a
frequency controller for generating a frequency control signal in
response to the speed and current usage of the motor wherein the
frequency control signal represents an efficient operating mode of
the motor. The controller further includes a multiplier for
combining the frequency control signal and the voltage control
signal. The combined signal from the multiplier is applied to the
voltage operating the motor such that the motor operates in an
efficient manner for the given load.
[0008] A method for controlling an electric motor includes
generating a voltage control signal in response to the speed
(rotational frequency) of the motor and the current usage of the
electric motor wherein the voltage control signal represents an
efficient operating mode of the motor. Furthermore, a frequency
control signal is generated in response to the speed of the motor
and the current usage of the motor wherein the frequency control
signal represents an efficient operating mode of the motor. The
frequency and voltage control signals are combined and applied to
the voltage operating the motor so that the motor operates
efficiently for a given load.
[0009] A system for controlling an electric motor includes a speed
sensor for measuring the rotational speed (rotational frequency) of
the electric motor and generating a speed sensing signal in
response thereto. The system further includes a current sensor for
generating a current sensing signal in response to the current
usage of the motor. A voltage controller of the system generates a
voltage control signal in response to the speed sensing signal and
the current sensing signal. The voltage control signal represents
an efficient operating mode of the motor. Similarly, a frequency
controller of the system generates a frequency control signal in
response to the speed sensing signal and the current sensing
signal. The frequency control signal also represents an efficient
operating mode of the motor. The system further includes a
multiplier for combining the frequency control signal and the
voltage control signal. The combined signal is then applied to the
voltage operating the motor.
[0010] A method for controlling an electric motor comprises
determining an operating load of the electric motor. The voltage to
be applied to the electric motor is then calculated in response to
the load. The calculated voltage operates the motor in an efficient
mode. Similarly, the frequency of the voltage that operates the
electric motor is calculated in response to the operating load of
the electric motor. The frequency of the voltage is calculated such
that the motor operates in an efficient mode. The calculated
voltage is applied to the motor at the calculated frequency in
order to operate the motor in an efficient manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These, as well as other features of the present invention,
will become more apparent upon reference to the drawings
wherein:
[0012] FIG. 1 is a graph showing the efficiency of an electric
motor versus the operating load of the motor;
[0013] FIG. 2 is a block level diagram of a motor controller;
and
[0014] FIG. 3 is a flowchart illustrating the method of controlling
an electric motor with the motor controller illustrated in FIG.
2.
DETAILED DESCRIPTION
[0015] Referring now to the drawings wherein the showings are for
purposes of illustrating preferred embodiments, and not for
purposes of limiting the same, Figure 1 is a block level diagram of
a motor controller 16 used to control the operation of a 3-phase AC
induction motor 18. The motor 18 may be a conventional AC induction
type motor, or a motor operative with an increased gap as described
by Assignees co-pending patent applications Serial No.: 10/821,797
(Attorney Docket No. 146962-900002) and Serial No.: 10/894,688 ,
(Attorney Docket No. 146962-999006), the contents of which are
incorporated herein by reference.
[0016] The load of the motor is determined with a speed sense 20
and a current sense 22. Specifically, the speed sense 20 measures
the rotational speed (.omega.) of the motor 18 through either a
sensor or sensorless detection mechanism, as is commonly known. The
speed sense 20 generates a speed sensing signal that is related to
the rotational speed (.omega.). Similarly, the current sense 22
measures the electrical current (I) that the motor 18 is using. For
a three phase motor, the current sense 22 measures the RMS phase
currents for each phase. The current sense 22 generates a current
sensing signal that represents the total current (I) that the motor
is using. In this regard, the current (I) and rotational speed
(.omega.) indicate the load being placed on the motor 18.
[0017] The controller 16 uses the current (I) and the speed
(.omega.) to determine the frequency and the amount of the voltage
to be applied to the motor 18 such that the motor 18 operates in an
efficient manner. The controller 16 has a power supply 24 to
generate a regulated voltage that is applied to the motor 18. For
the example shown in Figure 2, the AC induction motor 18 is a
three-phase motor. Accordingly, the power supply 24 regulates
3-phase input power that is applied to the motor 18.
[0018] The controller 16 has a voltage controller 26 that produces
a voltage control signal in response to the speed (.omega.) and
current (I) of the motor. Specifically, the speed sensing signal
from the speed sense 20 and the current sensing signal from the
current sense 22 are input into the voltage controller 26. As
previously discussed, the load on the motor 18 can be determined
from the current usage and speed of the motor 18. The voltage
controller 26 determines the amount of voltage that should be
applied to the motor 18 based on the current sensing signal and the
speed sensing signal to achieve the maximum efficiency of the motor
18.
[0019] Similarly, the controller 16 has a frequency controller 28
for regulating the frequency of the applied voltage. The speed
sensing signal from the speed sense 20 and the current sensing
signal from the current sense 22 are input into the frequency
controller 26. The frequency controller 28 determines the frequency
of the voltage to be applied to the motor 18 based on the current
sensing signal and the speed sensing signal to achieve the maximum
efficiency of the motor 18.
[0020] The frequency controller 28 and the voltage controller 26
determine the frequency and amount of voltage to be applied based
upon the load and efficiency of the motor 18. Specifically, each of
the controllers 26, 28 has a voltage/frequency curve for each
operating speed of the motor 18. The voltage/frequency curve may be
expressed as a mathematical formula or as a table containing
values. The voltage/frequency curve is determined through either
experimental testing of the motor 18 to determine the amount of
voltage and frequency to be applied to obtain the maximum
efficiency, or by simulating the motor 18 to obtain the curves.
[0021] The voltage/frequency curves (e.g., voltage as a function of
rotational speed) maximize the efficiency of the motor by over
exciting the motor at higher loads. In this respect, the maximum
efficiency of the motor is obtained at any load and the motor will
operate at maximum efficiency over it full range of torque at any
speed. The frequency of the voltage applied to the motor is
controlled to allow the motor to operate at a speed that limits the
internal saturation of the motor`s steel and thus maximize the
motor`s operating frequency. Also, the motor`s efficiency is
improved by reducing the operating voltage of the motor when it is
operated at a constant speed below the motor`s rated torque. The
voltage/frequency curves take into account the motor`s operating
characteristics in order to determine the amount of voltage and the
frequency that the voltage should be applied in order to operate
the motor 18 efficiently. A control input 30 allows an operator to
vary the curves and operate the motor at a desired setting.
[0022] The voltage control signal from the voltage controller 26
and the frequency control signal from the frequency controller 28
are inputted into a signal multiplier 32 which combines the signals
together. The multiplier 32 applies the controls signals to the
power from the power supply 24 in order to control the frequency
and voltage of the power supplied to the motor 18. Specifically,
the multiplier 32 regulates the power from the power supply 24 in
response to the voltage control signal and the frequency control
signal. In this regard, the power applied to the electric motor 18
will operate the motor efficiently for the given load. Referring to
Figure 1, line 14 illustrates the efficiency of a motor using the
controller 16. The motor operates between about 85%-95% efficiency
using the controller 16 for all operating loads.
[0023] Referring to Figure 3, a flowchart showing the operation of
the controller 16 is shown. In steps 40 and 42, the load on the
motor 18 is determined. Specifically, in step 40, the speed of the
motor 18 is determined, while in step 42, the current that the
motor 18 is using is determined. In step 44, the voltage that
should be applied to the motor is calculated by the voltage
controller 26. In step 46, the frequency of the voltage that is
applied to the motor 18 is calculated by the frequency controller
28. The calculated voltage and frequency are applied to the motor
18 in step 48.
[0024] It will be recognized by those of ordinary skill in the art
that the controller 16 can be embodied as either discrete
electronic components or as instructions performed on a
multi-purpose computer. In this regard, it is possible that the
method as illustrated in Figure 3 can be embodied as programming
instructions stored on a computer-readable medium (i.e., disk
drive, memory, etc) that are implemented on a processor or
processor containing system. Similarly, the voltage controller 26,
frequency controller 28 and the multiplier 32 may be implemented as
instructions or programming modules of a computer program.
[0025] It will be appreciated by those of ordinary skill in the art
that the concepts and techniques described here can be embodied in
various specific forms without departing from the essential
characteristics thereof. The presently disclosed embodiments are
considered in all respects to be illustrative and not restrictive.
The scope of the invention is indicated by the appended claims,
rather than the foregoing description, and all changes that come
within the meaning and range of equivalents thereof are intended to
be embraced.
* * * * *