This application claims the priority benefit of French patent application Ser. No. 07/52553, filed on Jan. 5, 2007, entitled “Control of an Asynchronous Motor,” which is hereby incorporated by reference to the maximum extent allowable by law.
1. Field of the Invention
The present invention generally relates to asynchronous motors and, more specifically, to the control of the speed and the direction of rotation of a motor powered by an A.C. voltage.
2. Discussion of the Related Art
Generally, asynchronous motor devices require a relay-type bipolar switch to reverse the motor rotation direction. This increases the system power consumption since, for one of the two rotation directions, a current must permanently supply the relay coil.
Further, electromagnetic relays generate noise and electromagnetic disturbances, are often expensive and adversely affect the integration of the control devices.
At least one embodiment of the present invention aims at overcoming all or part of the disadvantages of multispeed control systems reversing the direction of an asynchronous motor.
At least one embodiment of the present invention more specifically aims at avoiding the use of a relay control to reverse the rotation direction of the motor.
To achieve all or part of these and other objects, as well as others, the present invention provides a device for controlling the speed and the direction of rotation of an asynchronous motor, having:
a first circuit of two individually-controllable bidirectional switches having first conduction terminals connected to a common terminal of application of a D.C. voltage and having second conduction terminals capable of being respectively connected to first ends of windings of the motor stator;
a second circuit of at least two individually-controllable bidirectional switches in parallel, having first respective conduction terminals connected to the common terminal.
According to an embodiment of the present invention, one of the bidirectional switches of the second circuit has its second conduction terminal directly connected to a terminal of application of an A.C. voltage, the other bidirectional switches of the second circuit having their second respective conduction terminals connected, by an impedance, to this terminal of application of the A.C. voltage.
According to an embodiment of the present invention, the bidirectional switches of the second circuit have their second respective conduction terminals connected, by an impedance, to a second terminal of application of the A.C. voltage.
According to an embodiment of the present invention, the number of bidirectional switches of the second circuit is equal to the number of rotation speeds desired for the motor minus one, an impedance directly connecting the common terminal to the terminal of application of the A.C. voltage.
According to an embodiment of the present invention, the number of bidirectional switches of the second circuit is equal to the number of rotation speeds desired for the motor.
According to an embodiment of the present invention, second respective ends of the windings of the motor are capable of being connected together to another terminal of application of the A.C. voltage, a capacitive element connecting their first respective ends.
According to an embodiment of the present invention, each impedance comprises at least one capacitive element in parallel with a resistive element.
According to an embodiment of the present invention, said bidirectional switches are triacs having their cathodes directly connected to the common terminal.
According to an embodiment of the present invention, respective control terminals of the bidirectional switches are capable of being connected to output terminals of a control circuit providing two-state signals.
The present invention also provides a device having an asynchronous motor capable of being powered by an A.C. voltage and a device for controlling the direction and the speed of rotation, in which first respective ends of windings of the motor stator are connected to the first respective conduction terminals of the switches of the first circuit.
The foregoing and other objects, features, and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.
The same elements have been referred to with the same reference numerals in the different drawings. For clarity, only those elements useful to the understanding of the present invention have been shown in the drawings and will be described hereafter. In particular, the applications of an asynchronous motor controlled by a device according to the present invention have not been detailed, such applications being compatible with the control of any multipolar asynchronous motor.
Two ends 11 and 12 of a first winding of the stator are respectively connected to a terminal 21 of application of voltage Vac and to a first terminal 31 of a speed selection circuit 3 (SPEED) having its other terminal connected to the other terminal 22 of application of voltage Vac. Two ends 13 and 14 of a second winding of the stator are connected to a circuit 4 (DIR) for reversing the rotation direction, which is supplied between terminal 21 and terminal 31. Speed selection circuit 3 receives several reference values (as many as there are possible speeds) from a control unit 5 (for example, a microcontroller MCU) powered by a low D.C. voltage Vcc. Unit 5 also generally controls the system for reversing the rotation direction (link in dotted lines 55). For voltage reference reasons which will be better understood from the following discussion in relation with
The speed selection control is performed by selecting that of triacs T1, T2 or T3 which is controlled by microcontroller 5. To enable flowing of a gate current and control the triacs, voltage Vcc is applied on the cathodes thereof to provide a positive voltage reference, and optional resistors R35i ensure a gate-cathode potential difference desensitizing the gate control.
An element for clipping the voltage across speed selection circuit 3 (for example, a varistor R38) may connect terminals 31 and 22.
On the side of circuit 4 for reversing the motor rotation direction, the other stator winding 16 has its ends 13 and 14 respectively connected across a bipolar switch having a first terminal 41 connected to terminal 21 and having a second terminal 42 connected to terminal 31. In a first position, the switch connects terminal 41 to end 13 of the winding and terminal 42 to end 14 of winding 16. In a second position, end 14 is connected to terminal 21 while end 13 is connected to terminal 31 to reverse the current in the winding, and thus the motor rotation direction. A resistor R43 in series with a capacitor C43 between terminals 13 and 14 limit the overvoltages on switchings. The switch is of relay type and is controlled by a coil 44 having its two ends, for example, powered from microcontroller 5.
Two windings 15 and 16 of the stator, phase-shifted, enable controlling the motor in one direction or another, and a speed variation is obtained by means of bidirectional switches, for example, triacs.
According to this embodiment of the present invention, first respective ends 12 and 14 of windings 15 and 16 of the stator of motor 1 are each connected to the anode of a triac T′4 or T′5 of a circuit 7 for selecting the motor rotation direction. The respective gates of triacs T′4 and T′5 are, for example, connected to output terminals O4 and O5 of a microcontroller 5 (MCU), or another control circuit capable of providing adapted voltage signals, by resistors R74 and R75. Ends 12 and 14 are further connected to each other by a capacitive phase-shift element C17.
The respective cathodes of triacs T′4 and T′5 are connected to a common reference terminal 6 of the control device. Terminal 6 receives a D.C. voltage Vcc (typically, the most positive potential of a D.C. voltage Vcc, preferably, the same as that supplying unit 5) and is directly connected to the cathodes of triacs T1, T2, and T3 of a speed selection circuit 3′. The number of triacs used for the speed control has been arbitrarily set to 3. This number may be modified according to the number of different desired speeds. The respective anodes of triacs T1, T2, and T3 are connected to a terminal 22 of application of an A.C. voltage Vac by cells 331, 332, and 333, respectively, modifying the impedance in series with the windings. Each cell 33i (with i ranging between 1 and 3 in this example) is, for example, formed of a parallel association of a cell reset (discharge) resistor R33i, with a series association of a capacitive element C33i and an inrush current limiting resistor R′33i. The respective gates of triacs T1, T2, and T3 are connected to output terminals O1, O2, and O3 of microcontroller 5 by voltage-to-current conversion resistors R361, R362, and R363.
Second respective ends 11 and 13 of the two windings 15 and 16 of the motor stator are connected together to another terminal 21 of application of A.C. voltage Vac.
According to which triac T′4 or T′5 is turned on by microcontroller 5, the motor supply current runs through one or the other of windings 15 or 16 of the stator, which conditions the motor rotation speed.
As for the speed variation, the control uses an operating principle of circuit 3 of
Resistors (R34i,
Resistors (R35i,
Similarly, an element (R38,
As a specific example of embodiment, a control device such as illustrated in
R361, R362, R363, R74, and R75=130 ohms;
R33i=100 kohms;
R′33i=47 ohms;
C332=5 microfarads;
C333=6 microfarads;
C331=R331=R′331=0 (no cell 331); and
C17=4.5 microfarads.
The variations of
A common reference point 6 is provided between a first circuit 7 (DIR) with bidirectional switches for selecting the motor rotation direction and a second circuit 3′ (SPEED) with bidirectional switches for controlling the motor rotation speed. Accordingly, circuits 7 and 3′ are serially connected. Circuit 7 is controlled by two low-voltage signals (connection 56) originating from a control unit 5 (MCU) while circuit 3′ is controlled by n signals originating from unit 5 according to the number of possible speeds. Point 6 is connected to a D.C. voltage Vcc.
The bidirectional switches of the direction selection circuit and of the speed selection circuit are thus in series, their cathodes being interconnected.
An advantage of the present invention is that the control unit outputs may be uniform. Further, the integration of the device is eased due to the common cathode structure.
Another advantage of the present invention is that it avoids the power consumption of the coil of a relay. Further, the absence of an electromagnetic control relay decreases interferences and the electromagnetic noise.
Among the possible applications of the control circuit of the present invention, fan motors, washing-machine or drier motors, air conditioning fan motors, vacuum pump or vacuum cleaner motors should be noted.
Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In particular, although the present invention has been more specifically described in relation with an example using triacs, its transposition to an implementation based on any bidirectional switch architecture is within the abilities of those skilled in the art based on the functional indications given hereabove. For example, for each switch, an assembly of two thyristors head-to-tail in parallel may be used, one of the two being associated with a control element (optocoupler, pulse transformer, etc.) enabling control by a single signal. A triac however remains preferable. Bidirectional power switches having their control terminal referenced to a power electrode located on the surface opposite to that supporting the control electrode, for example, switches known under trade name ACS, may also be used.
Further, the values to be given to the different components depend on the motor features, on the desired rotation speeds, etc. and are here again adaptable according to the applications.
Moreover, although the present invention more specifically applies to a speed selection between discrete values, it is possible to provide a variable element (for example, a resistor or a variable capacitor) in at least one of cells 33i to obtain a continuous variation at least across a speed range settable, for example, by the user.
Finally, the generation of the control signals of the different bidirectional switches, for example, by a microcontroller, uses tools within the abilities of those skilled in the art.
Having thus described at least one illustrative embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.
Number | Date | Country | Kind |
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0752532 | Jan 2007 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR08/50010 | 1/4/2008 | WO | 00 | 9/28/2010 |