Active snubber circuit for electrical rotary actuator

Details Active snubber circuit for electrical rotary actuator Active snubber circuit for electrical rotary actuator

2001-02-26

2004-05-18

Jackson, Stephen W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Motor protective condition responsive circuits

C361S030000

Reexamination Certificate

active

06738239

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to motor drivers for electrical motors and more particular to apparatus and methods of dissipating regenerative inductive currents in motor drives.
BACKGROUND OF THE INVENTION
A schematic drawing of a prior art motor driver
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 driver
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 driver
10
includes a diode
16
for ensuring one 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.
In the prior art circuit illustrated in
FIG. 1
, it should first be noted that the motor driver
10
is not integrated with electrical motor
12
but instead is intentionally mounted remotely such that the motor driver
10
is subject to relatively low temperatures of about a maximum of 85° 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.
During normal steady state operation, the net flow of current is out of the motor driver
10
and into the motor
12
. However, when it is desired to switch the direction of flow quickly and therefore switch the motor direction, the electrical motor
12
momentarily acts as a generator and forces inductive “flyback” current into the motor driver
10
. If there were no line impedance
26
, EMI filter
17
or diode
16
, the inductive flyback current could be dissipated in the external power source
14
assuming that the power source
14
is capable of withstanding the amount of inductive energy produced by the motor
12
. However, in prior art designs, the diode
16
has not allowed the electrical flow to reverse and is necessary to prevent destruction of the motor driver in the event that the battery is installed the opposite way. The way the prior art has dealt with this specific problem has been to incorporate an aluminum electrolytic capacitor
18
with a large capacitance of 3000 &mgr;F to handle and temporarily store this inductive flyback current load. The aluminum electrolytic capacitor
18
has allowed for a very high capacitance to volume ratio along with a low cost to capacitance ratio.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide an electrical motor that may include integral electronics including the motor driver, which can operate at an elevated temperature of over 100° Celsius (typical approaching about 115° Celcius) at which temperature aluminum electrolytic capacitors are not reliable.
It is a further objective in regard to the previous objective to achieve the foregoing object without creating cost or size drawbacks.
In accordance with these and other objectives, the present invention is directed toward a novel motor driver with an active snubber circuit. The motor driver is interposed between an external electrical power source and an electrical motor. The electrical motor is driven in first and second states such that the electrical motor produces an inductive flyback current when it switches between states. The motor driver comprises a reverse voltage protector in series between the electrical power source and the electrical motor allowing flow of electrical power to the electrical motor; and a bus capacitor arranged in parallel circuit with the motor (or switch network of the motor driver) between electrical motor and the reverse voltage protector. The active snubber circuit is arranged in parallel circuit with the bus capacitor (or switch network) between the reverse voltage protector and the electrical motor. The active snubber circuit comprises a switch having a circuit that senses an increase in voltage on the bus when inductive flyback occurs. A resistor is in series with the switch. When the voltage of the bus increases, the resistor is switched into the circuit and diverts the inductive flyback current. The snubber circuit dissipates inductive flyback current through the resistor.


REFERENCES:
patent: 3890551 (1975-06-01), Plunkett
patent: 4496886 (1985-01-01), Gordon
patent: 4891764 (1990-01-01), McIntosh
patent: 4904918 (1990-02-01), Bailey et al.
patent: 5270597 (1993-12-01), Yubazaki et al.
patent: 5296790 (1994-03-01), Fincher
patent: 5304802 (1994-04-01), Kumagai
patent: 5552976 (1996-09-01), Munro et al.
patent: 5586000 (1996-12-01), Sakata et al.
patent: 5724218 (1998-03-01), Tihanyi
patent: 5757600 (1998-05-01), Kiraly
patent: 6016234 (2000-01-01), Blank
patent: 6078156 (2000-06-01), Spurr
Staff, Feb. 01, 2001, Electronic Component News, High-Temperature Aluminum Electrolytic Capacitor.

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