Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2001-08-30
2003-03-11
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S700000, C318S722000, C318S800000, C318S801000, C318S802000, C318S803000, C318S799000, C318S254100, C318S434000, C363S015000, C363S034000, C363S035000, C363S036000, C363S037000, C363S038000, C363S039000
Reexamination Certificate
active
06531843
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a driving system of an AC motor, and more particularly to a system which can realize a high-performance motor control without using a sensor which detects an electrical angle position of an AC motor.
As methods for controlling a synchronous motor without detecting an electrical angle position, methods which are described in Japanese Patent Laid-Open No. 245981/1995 (referred to as “literature 1” hereinafter), Japanese Patent Laid-Open No. 177788/1995 (referred to as “literature 2”hereinafter), “Method for estimating positions of magnetic poles of a PM motor which focuses on a magnetically non-linear electric current distortion”, Japan Electric Society, Industrial Application Section, Nationwide Convention, No.191, 1999 (referred to as “literature 3” hereinafter) and the like have been known. Methods described in all these literatures relate to the method for estimating magnetic poles in the inside of a synchronous motor.
The technique described in the literature 1 performs the estimation of positions of magnetic poles by making use of the electrically salient characteristics of a permanent magnet type synchronous motor (PM motor). In this technique, an alternating magnetic field is generated on an estimated magnetic pole axis (dc axis) of the PM motor, an AC current (or an AC voltage) having a component in an axis which intersects the estimated magnetic pole axis (qc axis) is detected, and the positions of magnetic poles in the inside of the motor are calculated by estimation based on the detected AC current. When there is an error between the actual magnetic pole axis and the estimated magnetic flux axis, the feature that the interference term of the inductance is present between the dc axis and the qc axis is used. However, to extract the AC current (voltage) component, the Fourier series (the Fourier expansion) or a band pass filter is used.
The technique described in the literature 2 performs the estimation calculation of the positions of the magnetic poles using the electrically salient characteristics and the magnetic saturation characteristics of the PM motor. The estimation algorithm is divided in two steps consisting of a step 1 and a step 2, wherein the estimation of the positions of the magnetic poles is performed using the electrically salient characteristics of the PM motor in the step 1 and the change of inductance due to the magnetic saturation is measured and the polarities of the magnetic poles are discriminated in the step 2.
The technique described in the literature 3 calculates the positions of the magnetic poles by estimation using the magnetic saturation characteristics of the PM motor. In this technique, a sinusoidal voltage having high frequency is applied to the PM motor and the current waveform generated according to such an application of voltage is subjected to a frequency analysis thus calculating the polarities of the magnetic poles and the positions of the magnetic poles by estimation based on the phase of the secondary higher harmonic components.
The technique described in the above-mentioned literature 1 uses the principle that the inductance of the PM motor is changed in accordance with the function of 2&thgr; for the phase &thgr; of the electrical angle. When the estimation of the positions of the magnetic poles is performed based on this principle, there may be a case that an error of 180° is present with respect to the result of the estimation. If this state is maintained as it is, there is a possibility that the PM motor becomes uncontrollable at the time of starting the PM motor. Accordingly, it becomes necessary to provide means which discriminates the polarity of the magnetic pole axis (d axis) separately.
Further, the technique described in the literature 2, in the step 1, as in the case of the literature 1, performs the estimation of the positions of the magnetic poles by using the change of inductance to the electrical angle as in the case of the literature 1 in the step 1. In the step 2, a voltage step is generated on the PM motor and the polarity discrimination of the magnetic poles is performed based on a current response time at this point of time. The step 2 makes use of a phenomenon that the magnetic saturation is generated or decreased in response to the relationship between the magnetic flux generated by the permanent magnet and the magnetic flux component generated by the voltage step and eventually the inductance (electrical time constant) is changed. With the use of this technique, the discrimination of the polarities of the magnetic poles is possible and hence, it is possible to surely start the PM motor. However, this technique has a drawback that the estimation algorithm is divided in two stages (step 1, step 2) and hence, it takes some time to start the PM motor. Accordingly, it is difficult to apply such a technique to an application where a rapid acceleration is to be performed from a point of time that a power supply is turned on and the control algorithm also becomes complicated.
The technique described in the literature 3 estimates the polarities of the magnetic poles and the positions of the magnetic poles by applying the high frequency (approximately 500 Hz) to the PM motor and by extracting the distorted current components which are generated due to such an application of high frequency. Since the technique uses the phenomenon that the distortion of the waveform is derived from the magnetic saturation, the estimation of the positions of the magnetic poles can be performed without performing the discrimination of the polarities of the magnetic poles. However, it is necessary to accurately extract the high-frequency distortion components and hence, the fine sampling of the electric-current waveforms becomes necessary. Further, the technique requires the complicate processing such as the Fourier series or the Fourier expansion. To increase the accuracy of the Fourier series or the Fourier expansion, the detection of current for a reasonably long time is necessary and it takes some time to start the PS motor.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned drawbacks of the prior art and it is an object of the present invention to provide a driving system of an AC motor which is applicable to an electrically non-salient motor and can perform the determination of polarities and the detection of the position of magnetic poles with a simple algorithm.
The gist of the present invention which is provided for achieving the above-mentioned object lies in that, in the inside of a controller which controls a motor, the discrimination of polarities of magnetic poles and the detection of the positions of magnetic poles are performed or the detection of the positions of the magnetic poles are performed including the discrimination of magnetic poles and a vector control is performed.
The discrimination of the polarities is performed such that a minute voltage change is given to a dc axis which is an estimation axis of a magnetic flux in the inside of the motor, with respect to ripple components contained in observed values of a current which flows in the motor, current flow times at a positive side and a negative side of the ripple components are measured, and the polarities of magnetic poles in the inside of the motor are discriminated based on these values. Alternatively, the current change rates at the positive side and the negative side of the ripple components are measured and the polarities of magnetic poles are discriminated based on these values.
Here, the detection of the positions of the magnetic poles is performed such that in parallel with the above-mentioned discrimination of polarities of the magnetic poles, the electric current which flows in the motor is observed in a qc axis which is perpendicular to the dc axis and the estimation of the positions of the polarities in the inside of the motor is performed using the change-rate components of the observed current.
Another detection of the positions of the magne
Ando Tatsuo
Endo Tsunehiro
Fujii Hiroshi
Iwaji Yoshitaka
Antonelli Terry Stout & Kraus LLP
Nappi Robert E.
Smith Tyrone
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