This non-provisional patent application claims priority under 35 U.S.C. § 119(a) from Patent Application No. 200610143217.3 filed in China on 31 Oct. 2006.
This invention relates an electronic start control device for controlling a permanent-magnet rotor of a synchronous motor, so that rotation only occurs in one direction, and also to a synchronous motor having said electronic start control device.
Electronic start control devices for synchronous motors are known. However, these are only concerned with starting the motor, which is problematic due to the rotor having to achieve synchronous speed with a mains frequency power supply in a very short period. One such device is suggested in EP0574823A.
The rotor of a standard or typical synchronous motor rotates in either of two directions. Consequently, the rotor can only drive a bidirectional device, such as a blade or impeller of, for example, a water drain pump for a washing machine or dishwasher. Typically, the bidirectional device will therefore not be as efficient as a unidirectional device.
Other common disadvantages of synchronous motors are that the rotor can be extremely difficult to turn under very low nominal mains voltages, for example +/−30%, and that demagnetisation of the rotor tends to occur under very high nominal mains voltages.
Reliability and cost-effectiveness are also highly important factors.
The present invention seeks to provide a solution to these problems.
According to a first aspect of the invention, there is provided an electronic start control device for unidirectionally rotating a permanent-magnet rotor of a synchronous motor, the device comprising: a static switch for series connection to a winding of a stator of the synchronous motor; and a position sensor for detecting a position of the rotor of the synchronous motor and for providing a corresponding output; characterised by the device including an AC to AC converter having an input from an alternating current-voltage source at a fixed frequency connected in series with the stator of the synchronous motor, and a single output derived from the voltage input; and an XNOR unit having a first input in communication with the output of the AC to AC converter, a second input in communication with an output of the position sensor, and an output in communication with the static switch, the static switch being controllable by a signal output from the XNOR unit so that the rotor of the synchronous motor only rotates in a single direction.
Preferably, the AC to AC converter is a phase shifter.
Preferably, the AC to AC converter has two voltage inputs (Va′; Vb′).
Preferably, a diode is connected to one of the voltage inputs (Vb′) of the phase-shifter.
Preferably, the static switch is a triac.
Preferably, the position sensor is a Hall-effect sensor.
Preferably, the AC to AC converter outputs a signal (νcon; νcon′) having a phase lag (λ) in a range of 90 degrees to 180 degrees.
Preferably, the fixed frequency is in the range of 50 to 60 Hz.
According to a second aspect of the invention, there is provided an electronic start control device for unidirectionally rotating a permanent-magnet rotor of a synchronous motor, the device comprising: a static switch for series connection to a winding of a stator of the synchronous motor; and a position sensor for detecting a position of the rotor of the synchronous motor and for providing a corresponding output; characterised by the device including a phase-shifter having two voltage inputs from an alternating current-voltage source at a fixed frequency connected in series with the stator of the synchronous motor, and a single output derived from the voltage input; and an XNOR unit having a first input in communication with the output of the phase-shifter, a second input in communication with an output of the position sensor, and an output in communication with the static switch, the static switch being controllable by a signal output from the XNOR unit so that the rotor of the synchronous motor only rotates in a single direction.
According to a third aspect of the invention, there is provided a synchronous motor having a permanent-magnet rotor and a stator connected in series with an alternating current-voltage source at fixed frequency, the motor including an electronic start control device in accordance with the first or second aspects of the invention by which the rotor is controlled to only rotate in one direction.
Preferably, the synchronous motor further includes a unidirectional blade drivable by the rotor.
The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:
a to 4c show a schematic view of the synchronous motor, similar to
a to 5c show the waveforms of the voltage, current and position signal, when the rotor is running under a heavy-load; the signal output from the phase shifter; and the waveforms of the voltage, current and position signal, when the rotor is running under a light-load, respectively;
Referring firstly to
In order to impart a starting torque to the rotor 14, asymmetric air gaps 18 are formed between adjacent surfaces of the stator 12 and the rotor 14, so that the polar axes R and S of the rotor 14 and the stator 12, respectively, will be angularly offset by an angle α during the stopped or stalled condition.
Referring to
A first embodiment of an electronic start control device 20 is shown in
The static switch 22 is connected in series with the alternating current-voltage source Vac and the windings 16 of the stator 12 of the motor 10.
The position sensor 24 is located on or within the stator 12, offset by an angular displacement α from the polar axis S of the stator 12. The polarity, and thus position of the rotor 14 is determined via the position sensor 24, both when the rotor 14 is stopped and during operation of the motor 10.
The phase-shifter 26 has an input Va taken directly from the alternating current-voltage source Vac. A single output signal νcon outputted from an output Vc of the phase-shifter 26 is thus based on the voltage of the alternating current-voltage source Vac. The phase-shifter 26 imparts a phase lag λ on the output signal νcon which is between 90 degrees and 180 degrees, depending on the load on the rotor 14.
The output Vc of the phase-shifter 26 and an output P of the position sensor 24 are connected to respective inputs G1 and G2 of the XNOR unit 28, and the output Go of the XNOR unit 28 is connected to the static switch 22. The static switch 22 is thus controlled via a signal Gcon outputted from the XNOR unit 28.
The electronic start control device 20 thus regulates the starting direction of the rotor 14, so that the rotor 14 only rotates in one single direction.
Referring to
Since the output νcon of the phase-shifter 26 corresponds to a negative average voltage, the stator 12 assumes the same polarity as the pole of the rotor 14 detected by the position sensor 24. In the configuration shown in
Similarly, if the position sensor 24 determines that the North pole of the rotor 14 is facing it in a stalled condition (
Since the output signal νcon of the phase-shifter 26 corresponds to a positive average voltage, the stator 12 again assumes the same polarity as the pole of the rotor 14 detected by the position sensor 24. In the configuration shown in
Referring to
Now, referring to
Consequently, providing the static switch 22 is triggered prior to the zero-crossing of the current I, the rotor 14 will continue to rotate. As such, similarly to the starting phase described above, the XNOR unit 28 continuously controls the static switch 22 in accordance with the logic of the output signals νcon and Pcon of the phase-shifter 26 and the position sensor 24, respectively. This can be appreciated when comparing
With reference to
The phase-shifter 126 now has two voltage inputs Va′ and Vb′, one taken directly from the alternating current-voltage source Vac′, and the other taken via a diode 130 connected in series with the phase-shifter 126 and the alternating current-voltage source Vac′. A single output signal νcon′ outputted from an output Vc′ of the phase-shifter 126 is thus based on the voltage of the alternating current-voltage source Vac′, and a half-wave of the alternating current-voltage source Vac′. The phase-shifter 126 imparts a phase lag on the output signal νcon′ which is between 90 degrees and 180 degrees, depending on the load on the rotor of the motor 110.
Although a phase-shifter is suggested, any suitable AC to AC converter can be utilised. For example, an attenuator and/or a filter can be used. A combination of devices can also be utilised.
Although only a two pole permanent-magnet rotor 14 has been described above, the electronic start control device can be used with a synchronous motor having a greater number of poles.
The static switch, although preferably a triac, can be in the form of a SCR, transistor, or any other suitable device.
Although the position sensor has been suggested as being a Hall-effect sensor, any other suitable device can be utilised, for example, a photoemitter/photodetector device, or any inductive-type coupler or coil.
The XNOR unit is a logic-functional unit, and can be realized by a circuit in the form of transistor, opamp, or any programmable device. The XNOR unit can also be a physical chip or a logic gate.
The synchronous motor is typically operated at mains frequency. However, other fixed frequencies are conceivable.
It is thus possible to provide a low cost and robust electronic start control device for unidirectionally rotating a permanent-magnet rotor. Consequently, a device to which the combined synchronous motor and electronic start control device is applied can utilise unidirectional elements drivable by the motor, instead of bidirectional elements. For example, a unidirectional blade or impeller can be used in a water pump incorporating such a combined motor and electronic device, resulting in improved efficiencies.
Furthermore, by the use of the electronic start control device, acoustic noise resulting from the previously bidirectional operation of the rotor and any element driven by the rotor is reduced or eliminated.
A smooth start of the rotor at a low mains voltage condition is also possible, while a starting current is limited during high mains voltage conditions, thus protecting the magnetisation of the rotor.
The electronic start control device utilises currentless detection to determine the position of the rotor of the motor, and thus the direction in which the rotor is to be moved.
The embodiments described above are given by way of example only, and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention, as defined by the appended claims. For example, in the first embodiment, the diode can be provided internally within the AC to AC converter or phase-shifter; and in the second embodiment, the diode can be dispensed with, or again provided internally within the AC to AC converter or phase-shifter.
Number | Date | Country | Kind |
---|---|---|---|
200610143217.3 | Oct 2006 | CN | national |