Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2002-03-19
2004-11-09
Duda, Rina (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S798000, C318S805000
Reexamination Certificate
active
06815924
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a control method of an AC motor by which a speed of the AC motor is varied by a variable speed control apparatus to output the AC voltage, and specially to a control method and an apparatus by which the AC motor can be smoothly started after the return from the power failure.
BACKGROUND TECHNOLOGY
Conventionally, to speed control the AC motor, a V/f constant control method by which a ratio of the output voltage V and an output frequency f is made constant, is well known. Further, recently, in order to more accurately control the AC motor, a vector control to respectively independently control the primary current to be supplied to the AC motor, in the exciting current (current to generate the magnetic flux) and the torque current (current to generate the torque) which directly relate to the torque, is brought into the practical use. However, in the conventional control system, during the continuous running, the stable control is conducted, however, in the case where the instantaneous power failure is generated in the running of the AC motor once, and restarting after the instantaneous power failure is conducted, when the residual voltage of the AC motor and the phase of the voltage command of the variable speed control apparatus are not matched, the speed of the AC motor is rapidly changed, or a slip of the AC motor is increased, thereby, the over current flows, resulting in a danger such as a trip. In order to prevent this, it is necessary that the residual voltage of the AC motor and the phase of the voltage command of the variable speed control apparatus are matched, and the re-running is conducted, however, the matching of the phase is very difficult. Therefore, because, after the residual voltage does not exist, the angular velocity of the AC motor and the output frequency of the variable speed control apparatus are calculated from the speed detector, or the residual voltage of the AC motor is detected by the voltage detector, and by being calculated from its frequency component, the phases of the residual voltage and the output voltage command signal are made to coincide with each other, and re-running is conducted, there is a problem that the restart after the instantaneous power failure takes a long period of time, or a smooth re-running is difficult.
As described above, in order to smoothly start the AC motor, there is a problem that it is necessary to wait that the residual voltage does not exist, or the detector such as the speed detector or voltage detector is necessary.
Accordingly, the object of the present invention is to provide the control method and control apparatus of the AC motor by which, by accurately measuring the phase and angular velocity of the residual voltage of the AC motor after the recovery of the instantaneous power failure, the re-running can be quickly and smoothly conducted.
DISCLOSURE OF THE INVENTION
The summary of a control method and control apparatus of the AC motor of the present invention to solve the above problem, exists in the following (1) to (23).
(1) A control method of an AC motor which is characterized in that: it has an electric power converter to output the electric power to the AC motor, and is provided with a current control section to control the output current of the electric power converter based on the difference signal of the current command signal and the output current detection signal of the electric power converter, and when the AC motor is in a free run condition, the current command signal is forcibly made zero so that the current of the AC motor is made zero, and current controlled, and on the base of the output voltage command signal which is calculated by using the current control section output at this time, the amplitude and phase and angular velocity of the residual voltage of the AC motor are obtained.
(2) A control method of an AC motor according to (1), wherein, when the phase and the angular velocity of the residual voltage of the AC motor are obtained based on the output voltage command signal, a signal holding means is provided, and the amplitude, and phase and angular velocity of the residual voltage are obtained from the addition value of the phase command signal just before the AC motor free runs, and the phase signal of the output voltage command signal.
According to this control method of the AC motor, in the case where the AC motor is in the free run condition, when it is controlled so that the current of the AC motor becomes zero, it is utilized as this result that the residual voltage of the AC motor appears in the voltage command signal, the amplitude and phase and angular velocity of the residual voltage of the AC motor which is in the free run condition, are obtained on the base of the phase and angular frequency of the this voltage command signal. Thereby, the smooth speed-return after the power failure recovery becomes easy.
Further, when the phase and angular velocity of the residual voltage are searched, a signal holding means is provided, and because the phase and angular velocity of the residual voltage are searched from the addition value of the phase command signal and the phase signal of the output voltage command signal just before the AC motor free-runs, there is no discontinuity of the phase command signal and a disadvantage such as the mechanical shock occurrence can be prevented.
(3) A control method of an AC motor which is characterized in that: in the control method by which an arbitrary electric power is outputted to the AC motor by the electric power converter, and the current supplied to the motor is detected by the current detection circuit, and it is controlled by the current control circuit so that the given current command and the current detection value detected by the current detection circuit coincide to each other, and the switching of the electric power converter is determined from the voltage command outputted from the current control circuit, the electric power converter is controlled by a start control circuit so that it is normally operated at the start time, and the speed of the AC motor in the free run condition is estimated by a speed estimation circuit.
(4) A control method of an AC motor according to (3), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command so that the current detection value is made zero, is calculated, and by the time change of the voltage command, the speed estimation circuit estimates the speed of the AC motor.
(5) A control method of an AC motor according to either one of (3) or (4), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when its voltage level is lower than the set voltage level, after the set-level DC current command is applied for a set time period from zero, the current command is forcibly made zero again, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and the speed estimation circuit estimates the speed of the AC motor.
(6) A control method of an AC motor according to any one of (3) to (5), wherein the start control circuit forcibly makes the current command zero, and by the current control circuit, the voltage command by which the current detection value is made zero, is calculated, and when its voltage level is lower than the set voltage level, after the set level DC current command is applied for a set time period from zero, the current command is forcibly made zero again, and by the current control circuit, even when the voltage command by which the current detection value is made zero, is calculated, when that voltage level is lower than the set voltage level, the speed estimation circuit estimates that the AC motor is stopped.
(7) A control method of an AC motor according to any one of (1) to (6), wherein the start control circuit forcibly makes the current comman
Iura Hideaki
Kawachi Tomohiro
Yamamoto Yo-ichi
Duda Rina
Kabushiki Kaisha Yaskawa Denki
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