WO2010033101A1

WO2010033101A1 - Improved motor driver for damping movement of an oscillatory load, and method of damping movement of an oscillatory load

Info

Publication number: WO2010033101A1
Application number: PCT/US2008/010852
Authority: WO
Inventors: Michael J. Willers; Raymond Walsh
Original assignee: Moog Inc.
Priority date: 2008-09-18
Filing date: 2008-09-18
Publication date: 2010-03-25

Abstract

An improved motor driver (40) is adapted to controllably supply a variable voltage to each of the terminals (12A, 12B, 12C) of the three-phase electric motor (13) for selectively causing the motor to move a load (18). The improved driver includes a diode (34A, 34B, 34C) connected to each of the motor terminals, these three diodes being connected such that their cathodes are connected to one another; a damping resistor (R_damp) connected in series with the diodes; and a damping switch (Q_damp) connected in series with the damping resistor and connected to the DC bus return. The damping switch is controlled as a function of the voltage supplied to the motor. When no voltage is supplied to the motor and the load develops a back EMF at the motor terminals due to oscillatory movement of the load, the damping switch may be closed to permit current in the coils of the motor to pass through the damping resistor and damp movement of the load.

Description

IMPROVED MOTOR DRIVER FOR DAMPING MOVEMENT OF AN OSCILLATORY LOAD, AND METHOD OF DAMPING MOVEMENT OF AN OSCILLATORY LOAD

Technical Field

[0001] The present invention relates generally to electric motors and drivers therefor, and, more particularly, to an improved motor driver for damping movement of an oscillatory load in the absence of a voltage supplied to the motor.

Background Art

[0002] In some cases, a motor is used to controllably displace an airfoil surface, such as a flap, aileron, or the like. When the aircraft is in flight, displacement of the airfoil surface into an airstream requires that a voltage be supplied to the motor. It is sometimes desired to hold the load in a neutral position without an applied voltage to the motor. In this condition, and without additional intervention, the load may flutter or oscillate about this neutral point. Such oscillatory movement of the load may create a back electromotive force ("EMF") at the terminals of the motor through the movement of the motor via the connecting linkage. [0003] It would be highly desirable to damp such oscillatory movement of the load.

Disclosure of the Invention

[0004] With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, in one aspect, the present invention provides an improved motor driver (40) that is adapted to controllably supply a variable voltage to each of the terminals of a three-phase electric motor (13) for selectively causing the motor to move a load (18).

[0005] The improvement broadly comprises: a diode (34A, 34B, 34C) connected to each of the motor terminals (12A₁ 12B₁ 12C), the diodes being arranged with their cathodes connected together; a damping resistor (R_damp) connected in series with the diodes; and a damping switch (Qdamp) connected in series with the damping resistor and connected to a DC bus return. The damping switch is controlled as a function of the voltage supplied to the motor such that, when no voltage is supplied to the motor and the load develops a back EMF at the motor terminals due to move- ment of the load, the damping switch may be closed to permit the current in the coils of the motor to pass through the damping resistor to damp movement of the load. [0006] The damping switch may be a transistor, such as an insulated gate bipolar transistor, a MOSFET transistor, or the like.

[0007] The load may be an airfoil surface. However, the invention is not limited to this particular end use.

[0008] In another aspect, the invention provides an improved method of damping movement of a load (18) that is selectively controlled by a three-phase electric motor (13) controllably supplied with a variable voltage at its terminals (12A, 12B, 12C). This improved method broadly comprises the steps of: providing three diodes (34A, 34B, 34C); connecting each diode to respective ones of the motor terminals such that the cathodes of these three diodes are connected to one another; providing a damping resistor (R_damp); connecting the damping resistor in series with the diodes; providing a switch (Q_damp); connecting the switch between the damping resistor and a DC bus return; opening the switch when the variable voltage is supplied to the motor; closing the switch when the variable voltage is not supplied to the motor such that movement of the load may produce a back EMF at the motor terminals; and permitting the current in the motor coils attributable to the back EMF to pass through the damping resistor; thereby to damp movement of the load.

[0009] Accordingly, the general object of the invention is to provide an improvement in a motor driver that is adapted to controllably supply a variable voltage to each of the terminals of a three-phase electric motor for selectively causing the motor to move a load.

[0010] Another object is to allow movement of the load to be damped regardless of the state of the voltage being supplied to the DC bus via the rectifier. [0011] These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings and the appended claims.

Brief Description of the Drawings

[0012] Fig. 1 is a schematic circuit diagram of a prior art driver that was adapted to supply a variable voltage to each of the terminals of a three-phase motor for selectively causing the motor to move a load, such an airfoil surface. [0013] Fig. 2 is a greatly enlarged fragmentary portion of the schematic circuit shown in Fig. 1 , and illustrates the various diodes in the inverter functioning as a six- diode rectifier to damp movement of the load when voltage is not supplied to the motor.

[0014] Fig. 3 is a schematic circuit showing another prior art motor driver, this form having a high-side inrush-limiting switch.

[0015] Fig. 4 is a schematic circuit of an improved motor driver, this view is showing the addition of the diodes connected to the motor terminals, the damping resistor, and the damping switch.

[0016] Fig. 5 is a schematic view of the circuit shown in Fig. 4, this view illustrating three closed switches proximate the power supply, showing Q_damp as a closed switch, showing the opto-electrical transistor as an open switch, and schematically illustrating the inverter circuit as being six open switches with anti-parallel rectifier diodes.

[0017] Fig. 6 is another simplified schematic of the structure shown in Fig. 5, this view is showing the voltage supply switches as being open, showing Qdamp as being closed, showing the opto-electrical switch as being open, and again schematically illustrating the inverter circuit as being six open switches with anti-parallel rectifier diodes.

[0018] Fig. 7 is still another schematic circuit showing the various power supply switches as being closed, showing Q_damp as being open, showing the opto-electrical coupler switch as being closed, and schematically illustrating the inverter circuit as being six transistors that can be turned on or off.

Description of the Preferred Embodiments

[0019] At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof (e.g., "horizontally", "rightwardly", "upwardly", etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer - A - to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

[0020] Referring now to the drawings, and, more particularly, to Fig. 1 thereof, a prior art motor driver is generally indicated at 10. Driver 10 is supplied with 115-volt three-phase AC voltage on lines 11A, 11 B, 11C, and is arranged to provide a variable voltage on lines 12A, 12B, 12C to the terminals of a motor 13. Motor 13 is schematically shown as having an externally-threaded rotatable output shaft 14. A nut 15 is matingly engaged with shaft 14, and is arranged to translate motion via connecting rod 16 to a load, such as an airfoil surface 18. This particular load is illustrative only, and the invention possesses general utility beyond this particular end use. Rod 16 is shown as being pivotally connected at 20 to the leftward or rear portion of the airfoil surface. Hence, the motor may be selectively operated so as to rotate screw 14 in the appropriate direction to move the leftward or rear end of the load either upwardly or downwardly, as desired, to cause the airfoil surface to pivot about axis 19.

[0021] The input voltage is supplied via lines 11 A, 11 B, 11C to a rectifier 21. The rectifier has a DC bus outlet, indicated on line 22, and a grounded DC bus return, indicated on line 23. Line 23 is indicated as being grounded at 25. Two capacitors C₁, C₂ are provided between the DC power supply bus 22 and the DC bus return 23. Four series-connected resistors, R-i, R₂, R₃, R4, are connected to a Zener diode 24. The node between diode 24 and resistor R₄ is connected to the base of a damping transistor switch, Q_dam_p- This transistor switch may be an insulated gate bipolar transistor, a MOSFET transistor, or the like. The collector of Qdamp is connected to bus 22 via a damping resistor R damp. The emitter of Qdamp is connected to the DC bus return. A six-switch inverter circuit, generally indicated at 26, is connected between the DC bus supply and the DC bus return, and is arranged to supply a variable voltage to the motor terminals 12A, 12B, 12C.

[0022] The voltage supplied in lines 11 A, 11 B, 11C is also provided via lines 27A, 27B, 27C to a node 28. Each of lines 27A, 27B₁ 27C contains a diode. A voltage sensing and low-power comparator is arranged to sample the voltage at node 28. [0023] A control card 30 is connected via a damp disable switch to an LED 31 , which is arranged in a branch circuit connected between a +5V voltage source and the +5V voltage source return. This LED is arranged to selectively emit light, which is transmitted to the base of an opto-sensitive transistor 32. [0024] The prior art circuitry shown in Figs. 1 and 2 has two modes of operation. In the absence of a voltage applied to lines 11A, 11B, 11C, and in the presence of a back EMF at the motor terminals 12A₁ 12B, 12C due to flutter or vibrations of the load, the six-switch inverter acts as a simple six-diode rectifier. Voltage generated at motor terminals 12A, 12B, 12C is rectified to produce a DC bus voltage between nodes 22 and 23. This voltage turns on Q_damp via the aforementioned series- connected resistors, R₁, R2, R3 and R4. Thus, current in the motor coils attributable to the back EMF may pass through Rdamp to damp oscillatory movement of the load. [0025] Still another mode of operation of the prior art circuitry shown in Fig. 1 is as follows. When input voltage is applied to lines 11 A, 11 B, 11 C, the low-power comparator detects the presence of such applied input voltage. The output of the low- power comparator connects the base of transistor Q_damp to the DC bus return, thereby causing Q_damp to open. As a result, the damping function is disabled. [0026] The control card 30 may also selectively disable the damping function by closing the damp disable switch. This provides a back-up control of Q_damp in the event of a failure of the low-power comparator. In this way, there are two independent methods of opening Q_damp to prevent inadvertent dissipation of energy in Rdamp when the input voltage is applied to lines 11 A, 11 B, 11 C.

[0027] The prior art circuit shown in Fig. 1 has an inherent drawback for safety- critical applications, such as control of a flight surface. The aforementioned modes of operation are dependent on the application of the input voltage to lines 11 A, 11 B, 11C such that in the event of an input voltage being applied, a malfunction of the control card can possibly result in the system operating in a non-damped and non- driven mode, thereby allowing the flight surface to flutter without being damped. As a result, the system could potentially become unstable.

[0028] When the voltage is supplied in lines 11 A, 11 B, 11 C, the six-switch inverter acts as a simple six-diode rectifier, as schematically indicated in Fig. 2. Thus, a rectified voltage is supplied to the DC bus via the six-diode rectifier when the motor is moved by the flight surface.

[0029] Fig. 3 is a schematic view of another form of a prior art device. This device has a number of parts and components common to the device shown in Fig. 1. Hence, the same reference numerals have been again used in Fig. 3 to refer to like structure, previously described. The salient difference between the embodiments of Fig. 3 and Fig. 1 , is that the voltage sense and low-power comparator has been eliminated in Fig. 3. Rather, the control card provides a drive-enabled signal to a high drive and isolation block 33, which in turn controls a high-side transistor switch 34 in bus 22. This high-side transistor switch allows the input voltage to be disconnected effectively from the DC bus, thereby isolating the damping circuit and avoiding excessive power dissipation in Rdamp when Qdamp is closed and the AC input voltage is applied through closed switches 36A, 36B₁ 36C. A disadvantage of this prior art circuit is that the high-side transistor switch introduces increased complexity and increased power dissipation during normal operation of the motor drive. [0030] Fig. 4 is a schematic view of an improved motor driver, generally indicated at 40. The improved motor driver includes many elements common to those earlier forms previously described. Hence, the same reference numerals have again been used to refer to like structure previously described. The salient difference is that three-diodes 34A, 34B, 34C are connected to motor terminals 12A, 12B, 12C so that these three-diodes are arranged with their cathodes connected. Noteworthy is the fact that this common cathode connection (V_damp) is not connected to the DC bus. The cathodes of these diodes are connected via a line 35 (labeled V_damp) to the damping resistor R_damp. Thus, when a variable voltage is not applied to the motor terminals 12A, 12B₁ 12C, and the load flutters or oscillates to produce a back EMF at motor terminals 12A, 12B, 12C, current in the motor coils will pass via line 35 through R_damp when switch Q_dam_P is closed. Switch Q_damp is open when voltage is supplied to the motor terminals.

[0031] Figs. 5-7 are simplified schematics that are used to illustrate the operation of the improved circuit during various operational modes.

[0032] Fig. 5 shows the situation when the input voltage is supplied via lines 11 A, 11 B, 11 C. To this end, these three lines are shown as having switches 36A, 36B, 36C. In Fig. 5, these switches are shown as being closed, indicating that power is supplied to rectifier 21. Q_damp is schematically indicated as being a closed switch. This arrangement also represents transistor switch 32 as being open. In this case, because of either control card being in an inactive state or malfunctioning, should the load oscillate or flutter and produce a back EMF at motor terminals 12A, 12B, 12C, the current in the motor coils may pass via the diodes 34A, 34B, 34C through damping resistor R_damp and closed switch Q_damp. and may return via the DC bus return line and the lower anti-parallel rectifier diodes of the inverter 26.

[0033] Fig. 6 is another simplified schematic. However, switches 36A, 36B₁ 36C are shown as being open, this schematically indicating that voltage is not supplied to rectifier 21. Q_damp is shown as being closed in Fig. 6, and switch 32 is shown as be- ing open. Thus, should the load oscillate or flutter and produce a back EMF at motor terminals 12A, 12B, 12C, the current in the motor coils may pass via the diodes 34A, 34B, 34C through damping resistor R_damp and closed switch Q_dam_P, and may return via the DC bus return line and the lower anti-parallel rectifier diodes of the inverter 26.

[0034] Fig. 7 shown another operational mode in which voltage is supplied to rectifier 21 through closed switches 36A₁ 36B, 36C. Switch Q_dam_p is shown as being open, and switch 32 is shown as being closed. Thus, when voltage is supplied to the motor, Qdamp is normally open to prevent the load from being damped. [0035] As demonstrated in Figs. 5-7, the invention shown in Fig. 4 overcomes the drawback associated with the prior art circuit of Fig. 1 without introducing additional losses per the prior art of Fig. 3.

Modifications

[0036] The present invention expressly contemplates that many changes and modifications may be made. As noted above, Qdamp may be an insulated gated bipolar transistor, a MOSFET transistor, or the like. Other types of switches might be used as well. Various aspects of the invention are considered to be within the ambit of a person skilled in the art, and may be readily changed or modified as desired. [0037] Therefore, while the presently preferred form of the present invention has been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.

Claims

ClaimsWhat is claimed is:

1. In a motor driver adapted to controllably supply a rectified voltage to each of the terminals of a three-phase electric motor for selectively causing said motor to move a load, the improvement which comprises: a diode connected to each of the motor terminals, said diodes having their cathodes connected to one another; a damping resistor connected in series with said diodes; and a damping switch connected in series with said damping resistor and connected to a DC bus return, said damping switch being controlled as a function of the voltage supplied to said motor; whereby when no voltage is supplied to said motor and said load develops a back EMF at said motor terminals due to movement of said load, said damping switch may be closed to permit the current in the coils of said motor to damp movement of said load.

2. The improvement as set forth in claim 1 wherein said damping switch is a transistor.

3. The improvement as set forth in claim 2 wherein said transistor is an insulated gated bipolar transistor.

4. The improvement as set forth in claim 2 wherein said transistor is a MOSFET transistor.

5. The improvement as set forth in claim 1 wherein said load is an airfoil surface.

6. The method of damping movement of a load selectively controlled by a three- phase electric motor controllably supplied with a rectified voltage at its terminals, comprising the steps of: providing three diodes; connecting each diode to respective ones of said motor terminals such that the cathodes of said diodes are connected to one another; providing a damping resistor; connecting said damping resistor in series with said diodes; providing a switch; connecting said switch between said damping resistor and a DC bus return; opening said switch when said variable voltage is supplied to said motor; closing said switch when said variable voltage is not supplied to said motor such that movement of said load may produce a back EMF at said motor terminals; and permitting the current in the coils of said motor that is attributable to said back EMF to pass through said damping resistor; thereby to damp movement of said load.