Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2000-09-20
2002-03-19
Ip, Paul (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S721000, C318S700000, C318S701000
Reexamination Certificate
active
06359415
ABSTRACT:
TECHNICAL FIELD
This invention relates to a synchronous motor controller for driving a synchronous motor at variable speed by means of a power converter, and more particularly to a synchronous motor controller capable of controlling a synchronous motor even when the maximum output voltage of a power converter is made equal to the rated voltage of the synchronous motor.
BACKGROUND ART
FIG. 1
is a functional block diagram showing the configuration,of a conventional synchronous motor controller of this type disclosed in, for example, Jpn. Pat. Appln. KIKAI Publication No. 4-127893.
In
FIG. 1
, a synchronous motor controller comprises a speed computing unit
1
, a speed controller
2
, a three-phase dq converter
3
, a magnetic flux computing unit
4
, a dq axis current computing unit
5
, a dq axis current controller
6
, a dq three-phase converter
7
, and a field current computing unit
8
.
The speed computing unit
1
performs differential operations on the basis of the magnetic pole position sensed value &thgr;r of a synchronous motor (not shown) and outputs the result as the speed sensed value &ohgr;r of the synchronous motor.
The speed controller
2
performs proportional integral control on the basis of the deviation of the speed sensed value or outputted by the speed computing unit
1
from the speed reference value &ohgr;r* of the synchronous motor and determines and outputs the torque current reference value I
T
* of the synchronous motor according to the magnetic flux reference value &phgr;* of the synchronous motor.
The three-phase dq converter
3
determines the d-axis current sensed value Id of the current in the direction of magnetic pole of the synchronous motor and the q-axis current sensed value Iq of the current in the direction perpendicular to the magnetic pole on the basis of the three-phase armature current sensed values Iu, Iv, and Iw of the synchronous motor and the magnetic pole position sensed value &thgr;r, and outputs the resulting values.
The magnetic flux computing unit
4
calculates not only the dq axis gap fluxes &phgr;gd and &phgr;gq using the constant of the synchronous motor on the basis of the d-axis current Id and q-axis current Iq of the synchronous motor and the field current sensed value If but also the internal phase difference angle &dgr; on the basis of the dq axis gap magnetic fluxes &phgr;gd and &phgr;gq and outputs the results.
The dq axis current computing unit
5
calculates the dq axis current reference values Id* and Iq* using the internal phase difference value &dgr; on the basis of the torque current reference value I
T
* and outputs the results.
The dq axis current controller
6
performs proportional integral control of each of the d-axis and q-axis on the basis of the deviation of the dq axis current sensed values Id and Iq from the dq axis current reference values Id* and Iq*, respectively, and determines and outputs the dq axis voltage reference values Vd* and Vq*.
The dq three-phase converter
7
determines the three-phase voltage reference values Vu*, Vv*, and Vw* on the basis of the dq axis voltage reference values Vd* and Vq* and the magnetic pole position sensed value &thgr;r and outputs the results.
The armature power converter of the synchronous motor controls the armature voltage on the basis of the three-phase voltage reference values Vu*, Vv*, and Vw*.
The field current computing unit
8
determines the field current reference value If* according to the magnetic flux reference values &phgr;* and outputs the result.
The field power converter of the synchronous motor controls the field current on the basis of the field current reference value If*.
In a conventional synchronous motor controller as described above, the d-axis and q-axis of the armature current of the synchronous motor are controlled independently in the amount of direct current on the dq coordinates. To increase or decrease the dq axis current, it is necessary to increase or decrease the magnitude of the dq axis voltage, which means that the amplitude is increased or decreased on the three-phase coordinates. Consequently, when the armature current must be increased to increase the torque, while the synchronous motor is being operated at the rated voltage, it is necessary to make the output voltage of the power converter higher than the rated voltage.
As a result, it is necessary to make the maximum output voltage of the power converter higher than the rated voltage of the synchronous motor. This lowers the voltage use efficiency of the power converter.
In a state where the output voltage of the power converter has reached the maximum output voltage and been saturated, the response speed of current control can reduce or become unstable.
The object of the present invention is to provide a synchronous motor controller capable of controlling a synchronous motor stably, even when the maximum output voltage of the power converter is made equal to the rated voltage of the synchronous motor.
DISCLOSURE OF INVENTION
The foregoing object is accomplished by the following apparatuses.
In an embodiment of the invention, a synchronous motor controller for driving a synchronous motor at variable speed by means of a power converter, comprises speed control means for calculating the active current reference value the power converter is to output, on the basis of the deviation of the speed sensed value of the synchronous motor from the speed reference value of the synchronous motor; three-phase PQ conversion means for calculating the active current value and reactive current value the power converter is to output, on the basis of the three-phase current sensed value, or the armature current of the synchronous motor, and the voltage phase reference value of the voltage the power converter outputs; active current control means for calculating the voltage phase compensating value of the voltage the power converter outputs, on the basis of the deviation of the active current value calculated by the three-phase PQ conversion means from the active current reference value calculated by the speed control means; voltage phase computing means for calculating the voltage phase reference value of the voltage the power converter is to output, on the basis of the voltage phase compensating value calculated by the active power control means and the magnetic pole position sensed value of the synchronous motor; and polar-coordinate three-phase conversion means for calculating the three-phase voltage reference value of the voltage the power converter is to output, on the basis of the voltage phase reference value calculated by the voltage phase computing means and the voltage amplitude reference value of the voltage the power converter outputs.
With the synchronous motor controller according to this embodiment, the active current the power converter outputs is controlled by changing the phase of the voltage, while keeping constant the amplitude of the voltage outputted from the power converter. This enables the synchronous motor to be controlled stably, even when the maximum output voltage of the power converter is made equal to the rated voltage of the synchronous motor.
In another embodiment of the invention, the synchronous motor controller further comprises reactive current control means for calculating the field current compensating value of the synchronous motor on the basis of the deviation of the reactive current value calculated by the three-phase PQ conversion means from the reactive current reference value the power converter outputs; and field current computing means for calculating the field current reference value of the synchronous motor on the basis of the field current compensating value calculated by the reactive current control means and the magnetic flux reference value of the synchronous motor.
With the synchronous motor controller according to this embodiment, the reactive current the power converter outputs can be controlled to a given value. Reducing the reactive current particularly to zero enables the power factor to be kept at one.
In another embodiment o
Suzuki Kentaro
Uchino Hiroshi
Ip Paul
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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