Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2000-04-05
2001-12-04
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S723000, C318S724000, C318S254100, C318S132000, C318S434000
Reexamination Certificate
active
06326760
ABSTRACT:
The present invention concerns a method for controlling a synchronous motor with a permanent magnet, without a direct sensor, including at least a phase, a coil and a rotor.
The invention also concerns a device for controlling a synchronous motor with a permanent magnet, without a direct sensor, including at least a phase, this device being powered by an electric power source.
Synchronous motors with permanent magnets, such as stepping motors, hybrid motors or direct current motors with no commutators, are currently well known and used to replace direct current motors with a commutator, the latter having a relatively short lifetime because of friction generated on the commutator by the carbon brushes.
In these motors with permanent magnets, an electronic phase switching circuit is necessary to replace the commutator function. Since this type of motor is synchronous, the rotor speed is the same as that of the rotating stator field. By removing the commutator and replacing it with an electronic circuit, the control logic has to know the position of the rotor to be able to perform the switching at the right time. This is usually achieved with Hall effect probes or an optical sensor called a direct sensor.
The presence of this type of sensor involves certain drawbacks. First of all, their cost has a non negligible effect on the cost of the motor. Moreover, the mounting thereof means that a certain volume has to be provided not just for the sensors themselves, but also for the electric connecting wires to pass. They therefore complicate assembly and increase the time thereof. Finally, the reliability of the system is thereby lessened.
The present invention proposes overcoming these drawbacks by removing the direct sensors and using the data given by the motor to perform phase switching. Each motor having a monophase or polyphase winding around the stator creates an induced voltage due to the movement of the rotor magnets. The passages through zero of this induced voltage of the nonpowered phase allow the rotor position to be known precisely and thus the motor to be speed and/or torque controlled.
This feature was used in particular in two inventions disclosed in the European Patent published under No. EP-B-0 449 687 and the European Patent Application published under No. EP-A-0 735 662.
European Patent No. EP-B-0 449 687 discloses a method for controlling a direct current motor with no commutator. More particularly, this method is only applicable to a three-phase bipolar motor. In this method, the power supply of the motor coils is controlled by an inverter, the conduction and extinction of the power supply being controlled by fixed frequency pulse width modulation. The rotor position is determined by detecting the passage through zero of the electromotive force induced in the non-powered motor coil. In order to remove the effect of disturbances which generate false passages through zero of the induced electromotive force, the signal picked up across the terminals of the non-powered coil is sampled in a synchronised manner with the inverter modulation frequency.
A method of this type has several drawbacks. First of all, it applies only to three-phase motors which are also bipolar. It cannot be transferred to other motor types, which limits its possible field of application. Moreover, the use of a fixed frequency as sampling frequency does not provide optimum yield. Finally, a delay is created between the detection of a passage through zero and the switching of the power supply. This delay is fixed, which generates noise.
The European Patent Application published under No. EP-A-0 735 662 describes a circuit and method for powering a direct current polyphase motor with no commutator. The main object of the invention described in this document is to reduce the disturbances generated by the pulse width modulation. As in the preceding case, a fixed switching delay is used, which generates noise.
Furthermore, a method of this type can only apply to bipolar polyphase motors and again uses pulse width modulation.
The present invention proposes overcoming these drawbacks and providing a method and a device for controlling a synchronous motor with a permanent magnet used in motor or generator mode, this motor being able to be monophase, polyphase, unipolar or bipolar, and able to be controlled with or without pulse width modulation.
This object is achieved by a method as defined in the preamble and characterised in that it includes the steps of:
controlling the powering of each motor phase,
simultaneously measuring the voltage of each motor phase,
determining a variable frequency from the rotor rotational speed and the motor load,
sampling at said variable frequency the output signals from the voltage measurement of each phase, and
controlling the powering of the phases as a function of the sampled signals.
The motor coil can be powered in a unidirectional or bidirectional manner.
Preferably, the rotor position and speed are determined from the voltage of each motor phase.
According to one embodiment, the rotor rotational speed is determined by introducing the voltage of at least one motor phase into a comparator and measuring the time interval which separates two sign changes in the signals from the comparator.
In an advantageous manner, the motor rotor rotational speed is determined by calculating the sum of the squares of the voltages of each phase and by extracting the square root of this sum.
Preferably, the motor power supply is switched as a function of the number of motor phases, the phase power supply type, the motor type and the operation mode thereof.
According to a preferred embodiment, as a function of the motor rotor position, a single switching type is authorised.
When the time separating two successive powering control actions of each motor phase exceeds a predefined threshold value, the variable frequency used for sampling the output signals from the voltage measurement of each phase is preferably fixed at a predetermined value greater than the maximum rotational frequency of the motor rotor.
According to a preferred embodiment, the real rotational speed of the motor rotor is determined repeatedly, this real rotational speed is compared to a predefined threshold speed, the powering of each motor phase is controlled by momentarily cutting off the powering of each phase when the real speed is less than the threshold speed, and, when the real rotational speed is greater than the threshold speed, the powering of each motor phase is controlled by measuring the voltage induced by the rotor movement over a non-powered phase.
The object of the invention is also achieved by a device implementing the above method characterised in that it includes a power bridge powering the motor coil, a unit for controlling the powering of the coil, a circuit measuring the voltage of each motor phase and means for sampling, at a variable frequency, signals from the measuring circuit.
The device according to the invention advantageously includes a control unit arranged to control the switching of the powering of each of the motor phases, this control unit including at least one control programme depending on the motor type, the number of phases, the type of powering of the phases and the motor operating mode.
The device preferably includes a phase comparator, arranged to measure the sign of the voltage of each phase.
According to a preferred embodiment, the voltage of each phase is introduced into the control unit in the form of analogue signals.
REFERENCES:
patent: 3885206 (1975-05-01), Hort
patent: 4409534 (1983-10-01), Bose
patent: 5245256 (1993-09-01), Cassat et al.
patent: 5345156 (1994-09-01), Moreira
patent: 5440219 (1995-08-01), Wilkerson
patent: 5569994 (1996-10-01), Taylor et al.
patent: 5877607 (1999-03-01), Masaki et al.
patent: 5955860 (1999-09-01), Taga et al.
patent: 735 662 (1996-10-01), None
patent: WO 901 0 973 (1990-09-01), None
Cardoletti Laurent
Perriard Yves
Baker & Botts L.L.P.
Leykin Rita
Nappi Robert E.
Sarl, Micro-Beam
LandOfFree
Method and device for controlling a synchronous motor with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for controlling a synchronous motor with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for controlling a synchronous motor with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593828