Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2000-09-01
2002-05-28
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S721000, C318S723000
Reexamination Certificate
active
06396229
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to synchronous motor control methods and more particularly, to a method of estimating a rotor position of a synchronous motor having saliency and method and system of controlling the synchronous motor with no position sensor (without resort to a position sensor).
To drive a synchronous motor having a magnetic field generated by a permanent magnet, a synchronized operation method for driving the synchronous motor in open loop without detecting the rotation position as in the case of inverter control in induction motors and a brush-less DC motor operation method for operating the synchronous motor in closed loop by using any kind of rotation position detecting means have been employed.
In the case of the latter brush-less DC operation, any kind of rotor position sensor is provided and the number of wiring lines between an inverter and the motor increases as compared to inverter drive of an induction motor. As a result, maintainability and reliability are degraded to restrict the application range and especially, the motor cannot be used in special ambience such as a compressor. To cope with this disadvantage, a position-sensorless technique for estimating a rotation position without using a sensor has been proposed.
The method for use in the conventional position-sensorless technique is classified into two main methods of which one utilizes saliency that makes the winding inductance differ with rotation positions and the other utilizes a voltage of speed electromotive force induced in the motor winding. In the latter, no speed electromotive force is generated during stopping and low-speed operation and hence position estimation is difficult to achieve but during medium/high-speed operation, the latter method can advantageously be applicable to both the salient type and the non-salient type.
As the position-sensorless technique based on the speed electromotive force, there is available a technique described in, for example, The Institute of Electrical Engineers of Japan, Technical Report No. 719, page 17 (prior art 1). In this technique, speed electromotive force in a synchronous motor of non-salient type is determined from a voltage/current-measured value of the motor pursuant to a voltage/current equation and a rotor position as viewed from the stator is estimated.
There is also available a technique disclosed in JP-A-8-308286 (prior art 2). In this technique, in relation to a d-q real rotary coordinate system having d axis representing positions in the direction of magnetic flux of the permanent magnet rotor and q axis 90° leading the d axis in the rotary direction, a dc-qc rotary coordinate system having dc axis representing virtual rotary positions from the control viewpoint and qc axis 90° leading the dc axis in the rotary direction is defined from the control viewpoint. Estimation of a real rotary position takes advantage of the fact that when a difference between d axis current estimated on the basis of a motor model derived from a voltage/current equation on the d-q rotary coordinates and dc axis current on the control axis is calculated, this difference is proportional to an axis shift &Dgr;&thgr; of virtual rotary position.
Further, one may refer to a technique disclosed in The Institute of Electrical Engineers of Japan, National Conference lecture papers, 1999, pp4-480, paper No. 1026 (prior art 3). According to this technique, in a circuit equation of a synchronous motor having saliency on the stator coordinates (&agr;,&bgr; axis), a term specific to the salient-pole machine that depends on both the current and the position is decomposed into a component in a current vector direction and a component in an induced voltage (speed electromotive force) direction, and a term representing a voltage induced by permanent magnet flux and a term representing a voltage induced by reluctance flux are merged to define an expanded induced voltage. Subsequently, an expression for estimating vector components of the expanded induced voltage is derived pursuant to the known minimum dimension observer method and a rotor position of the motor is determined from an estimated expanded induced voltage. The derived estimation expression for the expanded induced voltage uses winding resistance r, inductances Ld and Lq as motor constants and performs an operation by using values of voltage and current on the stator coordinates and an estimated speed of the motor. In addition, to avoid the necessity of a current differential value for the operation, an intermediate variable constructed of the sum of components related to the expanded induced voltage and the current is introduced so that the expression may be reduced so as to estimate the intermediate variable without using the current differential value.
The prior art 1 cannot be applied to the salient-pole machine. This is because in the salient-pole machine, the winding inductance changes with the rotation position and therefore, unless the rotor position is known, the inductance cannot be determined and the magnitude of a voltage drop due to the inductance cannot be determined.
In the prior art 2, a current value on the dc-qc control rotary coordinate system representing the virtual rotary axis is estimated by using the motor model on the d-q rotary coordinates. Accordingly, when the virtual rotary axis shifts from the real rotary position, the position cannot be estimated correctly. Besides, an approximation of sin &Dgr;&thgr;≈&Dgr;&thgr; is carried out when deriving an operation expression of axis shift &Dgr;&thgr;. Consequently, when an actual axis shift is large, the axis shift &Dgr;&thgr; cannot be operated correctly. Therefore, the prior art 2 has a disadvantage that it is unsuited for applications in which the motor load changes abruptly or an abrupt accelerating/decelerating operation takes place.
The prior art 3 is based on the stator coordinates (&agr;&bgr; axis) as described above and hence, the expanded induced voltage about to be estimated is of an AC (alternating current) quantity. Consequently, during high-speed operation of the motor, the expanded induced voltage changes at a higher rate than the speed of estimation pursuant to the estimation expression based on the minimum dimension observer, giving rise to a problem that the rotor position cannot be estimated correctly.
In addition, the estimation expression not using a differential of observed current is employed. The differential of the observed current on the stator coordinates is mainly related to a voltage drop due to inductance, demonstrating that the technique of prior art 3 determines the position without using a voltage drop component due to inductance. Therefore, the estimation expression based on the minimum dimension observer is said to estimate the expanded induced voltage and the voltage drop component due to inductance indistinctively. The voltage drop component increases in proportion to current and accordingly, when a relatively large current flows, the voltage drop component becomes larger than the expanded induced voltage, thus raising a problem that the accuracy of position estimation based on the observer is degraded.
Further, with a recent trend toward miniaturization of motors, the inductance value is very liable to change owing the flux saturation during current increase. When estimating the position, the techniques of prior arts 2 and 3 require two parameters Ld and Lq of inductance in the motor winding. Accordingly, the rotor position must be estimated correctly without being affected by changes in the two inductance parameters Ld and Lq and because of the necessity of correcting the two parameters, the construction becomes complicated.
SUMMARY OF THE INVENTION
The present invention contemplates elimination of the above conventional problems and it is an object of the invention to provide a rotor position estimating method which can correctly estimate the rotor position of a synchronous motor having saliency from the phase of an induced voltage and method and apparatus of controlling t
Endou Tsunehiro
Fujii Hiroshi
Miura Haruo
Sakamoto Kiyoshi
Takahashi Naohiko
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Ro Bentsu
LandOfFree
Method of estimating a rotor position of synchronous motor,... 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 of estimating a rotor position of synchronous motor,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of estimating a rotor position of synchronous motor,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2867209