U.S. patent application number 10/074864 was filed with the patent office on 2002-08-29 for reverse voltage protection for motor drive.
This patent application is currently assigned to Woodward Governor Company. Invention is credited to Petruska, David C..
Application Number | 20020118497 10/074864 |
Document ID | / |
Family ID | 25164503 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020118497 |
Kind Code |
A1 |
Petruska, David C. |
August 29, 2002 |
Reverse voltage protection for motor drive
Abstract
A reverse voltage protector for a motor drive is presented. The
circuit is in series with an external electrical power source and
the motor drive or electrical motor. The reverse voltage protector
comprises a switch having a zener diode to protect the switch from
overvoltage and a resistor regulating electrical current flow in
the control terminal of the switch.
Inventors: |
Petruska, David C.; (Fort
Collins, CO) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
6815 WEAVER ROAD
ROCKFORD
IL
61114-8018
US
|
Assignee: |
Woodward Governor Company
1000 East Drake Road
Fort Collins
CO
80525
|
Family ID: |
25164503 |
Appl. No.: |
10/074864 |
Filed: |
February 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10074864 |
Feb 13, 2002 |
|
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09795045 |
Feb 26, 2001 |
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Current U.S.
Class: |
361/23 |
Current CPC
Class: |
H02P 7/04 20160201 |
Class at
Publication: |
361/23 |
International
Class: |
H02H 005/04 |
Claims
What is claimed is:
1. A reverse voltage protector interposed between an electrical
power source having a positive terminal and a negative terminal and
an electrical motor, the reverse voltage protector comprising an
n-channel switch having a gate terminal, a drain terminal, and a
source terminal, the gate terminal connected to the positive
terminal, the source terminal connected to the electrical motor,
the drain terminal connected to the negative terminal, the switch
remaining passively open and preventing flow of electrical power
when the positive terminal and negative terminal are connected to
the motor in reverse, the switch allowing flow of electrical power
when the positive terminal and negative terminal are correctly
connected to the motor.
2. The reverse voltage protector of claim 1 such that current flows
in the switch from the source terminal to the drain terminal when
the switch is on.
3. The reverse voltage protector of claim 1 further comprising: a
zener diode arranged in parallel with the gate terminal and the
source terminal; and a resistor connected to the gate terminal and
the positive terminal.
4. The reverse voltage protector of claim 1 wherein the switch is a
metal oxide semiconducter field effect transistor.
5. The reverse voltage protector of claim 1 further comprising a
diode in parallel with the switch.
6. A reverse voltage protector interposed between an electrical
power source having a positive terminal and a negative terminal and
an electrical motor, the reverse voltage protector comprising: a
p-channel switch having a gate terminal, a drain terminal, and a
source terminal, the gate terminal connected to the negative
terminal, the source terminal connected to the electrical motor,
the drain terminal connected to the positive terminal, the switch
remaining passively open and preventing flow of electrical power
when the positive terminal and negative terminal are connected to
the motor in reverse, the switch allowing flow of electrical power
when the positive terminal and negative terminal are correctly
connected to the motor;
7. The reverse voltage protector of claim 6 wherein the switch is a
metal oxide semiconducter field effect transistor.
8. The reverse voltage protector of claim further comprising: a
zener diode arranged in parallel with the gate terminal and the
source terminal; and a resistor connected to the gate terminal and
the positive terminal.
9. The reverse voltage protector of claim 8 wherein the gate
terminal has a maximum rated gate voltage and the zener diode is
sized so that a maximum voltage across the gate terminal and source
terminal is below the maximum rated gate voltage.
10. A reverse voltage protector interposed between an electrical
power source having a positive terminal and a negative terminal and
an electrical motor, the reverse voltage protector comprising: a
switch having a control terminal, an input terminal, an output
terminal, and a diode between the input terminal and the output
terminal, the output terminal connected to the electrical motor,
the control terminal connected to one of the positive terminal and
the negative terminal and the input terminal connected to an other
of the positive terminal and the negative terminal such that the
switch turns on when the positive terminal and the negative
terminal are correctly connected, the switch remaining passively
open when the positive terminal and the negative terminal are
connected to the motor in a reverse orientation.
11. The reverse voltage protector of claim 10 further comprising: a
zener diode arranged in parallel with the control terminal and the
output terminal; and a resistor connected to the control terminal
and the one of the positive terminal and the negative terminal.
12. The reverse voltage protector of claim 10 wherein current flows
through the switch in a reverse direction, the reverse direction
being from the output terminal to the input terminal, the diode has
a forward voltage drop, the switch has an on resistance, and the
switch is selected so that the on resistance does not exceed a
ratio of the forward voltage drop divided by a predetermined
current magnitude flowing through the switch.
13. The reverse voltage protector of claim 12 wherein the
predetermined current magnitude is a magnitude of a maximum
continuous current flowing through the switch.
14. The reverse voltage protector of claim 8 wherein the control
terminal has a maximum rated voltage and the zener diode is sized
so that a maximum voltage across the control terminal and output
terminal is below the maximum rated voltage.
15. The reverse voltage protector of claim 8 wherein the resistor
has an impedance and the impedance is selected so power dissipation
in the zener diode is limited to a predetermined value.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application is a continuation-in-part of
copending U.S. patent application Ser. No. 09/795,045, filed Feb.
26, 2001.
FIELD OF THE INVENTION
[0002] The present invention relates generally to motor drives for
electric motors, and more particularly relates to an apparatus for
reverse voltage protection of motor drives.
BACKGROUND OF THE INVENTION
[0003] A schematic drawing of a prior art motor drive 10 for an
electrical motor 12 (the ProAct Generation 1, which is a form of
Limit Angle Torque motor (LAT) commercially available from Woodward
Governor) is illustrated in FIG. 1. The motor drive 10 serves the
purposes of conditioning the electrical power received from an
external power source 14 and maintaining the proper electrical
power levels for driving the electrical motor 12. The motor drive
10 includes an input diode 16 for ensuring reverse voltage
protection, an electromagnetic (EMI) filter 17 for filtering out
high frequency interference, and a bus capacitor 18 for storing
electrical power and smoothing out any spikes or intermittent
declines in the electrical power and a switch network for
modulating electrical energy to the motor.
[0004] In the prior art circuit illustrated in FIG. 1, it should
first be noted that the motor drive 10 is not integrated with
electrical motor 12 but instead is intentionally mounted remotely
such that the motor drive 10 is subject to relatively low
temperatures of about a maximum of 85.degree. Celsius. The motor 12
is driven by an H-bridge configuration comprising four switches 20,
21, 22, 24. When the first and fourth switches 20, 23 are closed
(with switches 21, 22 open), the motor 12 is driven in a first
rotational direction. When the second and third switches 21, 22 are
closed (with switches 20, 23 open), the motor 12 is driven in a
second rotational direction.
[0005] When the external power source 14 for the motor drive 10 is
a DC voltage power bus, it is possible that the motor drive 10
could be hooked up backwards (i.e., reverse-biased) to the external
power source 14. Many components in the motor drive 10 will be
destroyed if they are hooked up backwards to a power source. Other
components of the motor drive 10 could behave unpredictably after
being reverse biased, which could result in an unsafe response from
the motor 12.
[0006] In prior art designs, the input diode 16 is used to prevent
destruction of the motor drive in the event that the battery is
installed the opposite way. The use of diode 16 introduces problems
in the motor drive 10. The input current of the motor drive 10
produces a forward voltage drop in the diode, resulting in power
being dissipated in the diode 16. For high input currents, the
dissipated power can be significant, requiring heat sinks or other
cooling means to keep the diode temperature below the diode's
maximum allowable junction temperature. The heat sink or other
cooling means increases package size and cost. Another problem the
diode 16 creates is when the motor 12 acts as a generator during
transient conditions, resulting in inductive flyback current
flowing into the motor drive 10. This forces the motor drive 10 to
be designed to handle the inductive flyback. One way the prior art
has dealt with this specific problem has been to incorporate a very
large internal bus capacitance to handle and temporarily store this
inductive flyback current load. The use of the very large internal
bus capacitance results in an increased size and cost of the motor
drive 10. Another method to deal with the inductive flyback is to
use an active snubber as described in U.S. patent application Ser.
No. 09/795,045, filed Feb. 26, 2001, to clamp the voltage across
the bus capacitor 18.
[0007] Industry improved the efficiency of the reverse voltage
protection by adding a switch in parallel with the input diode. In
the prior art circuit illustrated in FIG. 2a, a metal oxide
semiconductor field effect transistor (i.e., MOSFET) 30 is used.
Those persons skilled in the art recognize that the MOSFET 30 has
an inherent body diode 31 (see FIG. 2b) that can be used in place
of the input diode 16 of FIG. 1. The driver power supply 32
generates a voltage at the MOSFET gate sufficiently higher than the
input voltage that results in a voltage across the gate to source
that turns the MOSFET 30 on. In operation, the circuit of FIG. 2
works as follows. Initially, there is no voltage potential across
the gate to source of the MOSFET 30 because the driver power supply
32 is off, resulting in the MOSFET 30 being off. When a properly
polarized input voltage is applied to the input of the motor drive
10, the body diode 31 conducts current that charges up the
capacitor 18 and the driver power supply 32. The driver power
supply 32 starts to operate and outputs a voltage to the gate of
the MOSFET 30 that is approximately 9 to 15 volts higher than the
input voltage. This turns the MOSFET 30 on and input current flows
through the MOSFET channel rather than the body diode. Once on, the
MOSFET 30 conducts current in both directions, allowing motor
inductive flybacks to be absorbed by the external power source 14.
If a reverse input voltage is applied, the body diode 31 blocks
current flow and the MOSFET 30 will remain off because there is no
gate to source voltage. The disadvantage of FIG. 2 is that the
driver power supply 32 is needed to provide the gate to source
voltage. The driver power supply 32 typically requires a boost
switching power supply or a charge pump power supply circuit. These
circuits add cost, size, weight, and complexity to the motor drive
design.
BRIEF SUMMARY OF THE INVENTION
[0008] In light of the above, it is an objective of the present
invention to provide a motor drive for an electrical motor that
increases the efficiency of the reverse voltage protection.
[0009] In that regard, it is also an object of the present
invention to achieve the foregoing object without creating cost or
size drawbacks.
[0010] In accordance with these and other objectives, the present
invention is directed toward a motor drive with a passively biased
reverse voltage protection circuit. The reverse voltage protection
circuit comprises a switch in parallel with a diode in one of the
input lines to the motor drive. When a properly polarized input
voltage is applied to the input of the motor drive, the switch
turns on, allowing input power to flow to the motor drive. If a
reverse input voltage (i.e., improperly polarized voltage) is
applied, the switch remains off and the diode blocks current
flow.
[0011] Other objectives and advantages of the invention will become
more apparent from the following detailed description when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings incorporated in and forming a part
of the specification illustrate several aspects of the present
invention, and together with the description serve to explain the
principles of the invention. In the drawings:
[0013] FIG. 1 is a schematic illustration of a prior art reverse
voltage protection circuit for a motor drive.
[0014] FIG. 2 is a schematic illustration of a prior art reverse
voltage protection circuit for a motor drive.
[0015] FIG. 3 is a schematic illustration of a reverse voltage
protection circuit for a motor drive according to a first
embodiment of the present invention.
[0016] FIG. 4 is a schematic illustration of a reverse voltage
protection circuit for a motor drive according to a second
embodiment of the present invention.
[0017] While the invention will be described in connection with
certain preferred embodiments, there is no intent to limit it to
those embodiments. On the contrary, the intent is to cover all
alternatives, modifications and equivalents as included within the
spirit and scope of the invention as defined by the appended
claims.
DETAILED DESCRIPTION OF THE INVENTION
[0018] For purposes of illustration, a first embodiment of the
present invention has been illustrated in FIG. 3 as a electrical
motor unit 40 comprising an electrical motor 42 and motor drive 44.
The unit 40 can be electrically connected to an external or
integrated power source 50 (shown herein as a battery for engine
applications although non-battery sources are commonly used in
turbine applications) for receipt of electrical power to drive the
motor 42. Electrical motors of this type typically operate with a
power source 50 that is between 8 and 32 volts and between 70 and
400 watts. The unit 40 is typically sold and mounted as a single
component without the need to mount the electronics assembly
(including motor drive 44) separate or remote from the electrical
motor 42. Further structural details and advantages of the unit 40
are described in U.S. patent applications Ser. Nos. 09/793151,
09/793225, 09/793356, and 09/795,045, all filed on Feb. 26, 2001,
and owned by the present assignee, the entire disclosures of which
are hereby incorporated by reference.
[0019] The motor drive 44 is interposed on the bus 60 running from
the electrical power source 50 to the electrical motor 42. The
motor drive 44 an electromagnetic (EMI) filter 62 for filtering out
high frequency interference on the bus 58, a bus capacitor 46 for
smoothing out voltage spikes and natural inconsistencies in the
electrical power flow to the motor 42, and a switch network
(comprised of switches 52-58) for modulating electrical energy to
the motor.
[0020] In the embodiment shown, the electrical motor 42 is
operatively arranged in an H-bridge circuit comprising four
switches 52-58 as an exemplary form of a switch network. When the
first and fourth switches 52, 58 are closed (with switches 54, 56
open) in a first state, the motor 42 is driven in a first
rotational direction. When the second and third switches 54, 56 are
closed (with switches 52, 58 open) in a second, the motor 42 is
driven in a second rotational direction. A third "free wheel" state
is also provided in which switches 54 and 58 are closed. Torque is
proportional to current. The current is modulated by the ratio of
switch states (e.g. switching between first and third states to
effect a selected torque in a first angular direction and switching
between second and third states to effect a selected torque in a
second angular direction).
[0021] The reverse voltage protection of the present invention
utilizes a switch 70 having an integral body diode arranged in
series with the battery 50 and the motor 42 (or the switch
network). In the embodiment shown, the switch 70 is an n-channel
MOSFET. When the proper polarity of input voltage is applied to the
motor drive 44, the integral body diode of the switch 70 conducts
current, allowing a positive potential to develop across the gate
72 (i.e., control terminal) relative to the source 74 (i.e., output
terminal). When the potential difference between the gate 72 and
source 74 reaches approximately 10 volts, the switch 70 turns on.
All current will flow (in the reverse mode of operation) through
the drain 73 (i.e., input terminal) and source 74 provided that the
voltage across the switch 70 does not exceed the forward voltage
drop of the integral body diode (typically 0.6 volts for silicon
devices). This is ensured if the peak drain current multiplied by
the on resistance of the switch 70 is less than the integral body
diode forward voltage drop. The impedance of the switch 70 is lower
than the prior art diode, which reduces power dissipation in the
motor drive 44. The zener diode 76 is used to protect the gate 72
from voltages higher than the switch's maximum gate voltage. The
resistor 78 is used to limit the current flow and power dissipation
in the zener diode. In the event the terminals of the battery 50
are reversed due to improper installation, the negative voltage on
the gate 72 will not allow the switch 70 to activate and therefore
the switch 70 remains open preventing a completed circuit and the
integral body diode will block current flow.
[0022] Turning now to FIG. 4, an alternate embodiment of the
present invention is shown. In this embodiment, the switch is
located on the positive input terminal of the motor drive 44. The
switch 88 is a p-channel device such as a p-channel MOSFET or IGBT.
The operation of the reverse voltage protection is similar to the
n-channel switch of FIG. 3. When the proper polarity of input
voltage is applied to the motor drive 44, the integral body diode
of the switch 88 conducts current, allowing a negative potential to
develop across the gate 90 relative to the source 92. When the
potential difference between the gate 90 and source 92 reaches a
magnitude of approximately 10 volts, the switch 88 turns on and
current flows through the drain 91 and the source 92 in the reverse
mode. The zener diode 76 is used to protect the gate 90 from
voltages higher than the switch's maximum gate voltage. The
resistor 78 is used to limit the current flow and power dissipation
in the zener diode. In the event the terminals of the battery 50
are reversed due to improper installation, the positive voltage on
the gate 90 will not allow the switch 88 to activate and therefore
the switch 88 remains open preventing a completed circuit and the
integral body diode will block current flow.
[0023] In certain applications, the power source may also be unable
to absorb the energy because of its internal make up, or it may be
unable to absorb the energy effectively because of the attenuation
of the EMI filter 62 and/or parasitic line impedance. In those
instances, the active snubber circuit 80 comprising switch 82,
resistor 84, and voltage sensor/drive 86 protects the motor driver
from over voltage conditions if the power lines were opened while
significant current was following in the motor. Further details on
the snubber circuit 80 are in U.S. patent application Ser. No.
09/795,045, filed Feb. 26, 2001, hereby incorporated in its
entirety by reference.
[0024] The foregoing description of various embodiments of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise embodiments disclosed. Numerous
modifications or variations are possible in light of the above
teachings. For example, those skilled in the art will recognize
that a three phase motor and motor drive configuration (e.g., a
pole-pair for each motor phase) can be used. The embodiments
discussed were chosen and described to provide the best
illustration of the principles of the invention and its practical
application to thereby enable one of ordinary skill in the art to
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. All
such modifications and variations are within the scope of the
invention as determined by the appended claims when interpreted in
accordance with the breadth to which they are fairly, legally, and
equitably entitled.
* * * * *