JP2011036057A - Control device for ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein, when an AC motor in a free-run state is started up, a conventional zero-current control or speed estimation method by DC current application cannot be used, when the motor is in a high-frequency free-run state and a mechanical shock occurs when a large current flows during speed estimation. <P>SOLUTION: During speed estimation, a voltage command is regulated by a voltage regulation circuit, and an output frequency is regulated by a frequency regulation circuit, based on a primary current and thereby the speed can be estimated, while suppressing current. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an AC motor that starts smoothly by estimating the speed of the AC motor in a free-running state when starting the AC motor.

In the inverter apparatus for driving an AC motor in which measures against power failure and power recovery described in Japanese Patent Application Laid-Open No. 61-196794 are provided, an inverter apparatus capable of restarting an AC motor that has become free-run due to an instantaneous power failure has been proposed. ing.
When the AC input is interrupted or momentarily interrupted, the power failure / recovery detection circuit detects this and stops the output of the control unit, the AC motor becomes free running, and the rotational speed gradually decreases due to the inertial force of the load. At this time, since the voltage gradient circuit makes the input of the second A / D converter of FIG. 3 zero, the output voltage command signal becomes zero.
On the other hand, the first A / D converter maintains the state before the power failure and generates an output frequency command signal. When the AC input is restored, the voltage ramp circuit gradually increases the input of the second A / D converter and gradually increases (cushion starts) the output voltage command signal, so that the output voltage of the inverter gradually increases. . At this time, the output voltage command signal is increased until the input current of the AC motor exceeds the overcurrent limit value (overload point), and the current droop circuit increases the output voltage command signal by the detection signal of the current detection circuit at the overload point. And the switch grounds the input of the acceleration / deceleration circuit to gradually reduce the output frequency signal generated by the first A / D converter, and the input current of the AC motor becomes constant at the overload point ( Control is performed while reducing the output frequency of the inverter so that constant current control is performed in an overcurrent state.
When the rotational speed of the AC motor matches the output frequency of the inverter, the overcurrent of the input current of the AC motor is eliminated (below the overload point), and even if the output voltage command signal is increased, the overcurrent state does not occur. At this time, the operation returns to the normal operation, and the AC motor is accelerated based on a predetermined acceleration / deceleration inclination signal to return to a normal state.

JP-A 61-196794

In the inverter apparatus for driving an AC motor in which measures are taken at the time of power failure and power recovery described in the above-mentioned JP-A 61-196794, the output voltage command signal is increased until the overcurrent limit value is exceeded. A large current flows through the AC motor, causing a shock that suddenly accelerates the reduced speed, or the AC motor accelerates rapidly while the increase in voltage is temporarily stopped to reduce the frequency. If the output voltage signal is returned to normal when the rotation speed is determined to be the frequency coincidence point, the current may suddenly increase and an overcurrent abnormality may occur, or a mechanical shock may occur. This is because, by temporarily holding the output voltage signal at a low value, it is determined that the rotation speed and the frequency do not coincide with each other.
The present invention has been made in view of such problems, and the AC motor is smoothly operated so as to suppress the current flowing through the AC motor in the free-run state and to make the rotational speed and frequency coincide with each other so that no mechanical shock is generated. An object of the present invention is to provide a control device for an AC motor that can be restarted.

In order to solve the above problem, the present invention is configured as follows.
The invention according to claim 1 is a power converter that outputs arbitrary power to an AC motor, a current detection circuit that detects a current supplied to the AC motor, and a current that converts the detected current into a primary current. V / f conversion circuit for calculating a voltage command based on a conversion circuit and a frequency command, a phase calculation circuit for calculating a phase from the frequency command, and a signal for switching the power converter from the voltage command and the phase command In a control apparatus for an AC motor comprising a PWM arithmetic circuit for generating a voltage, a voltage adjustment circuit that determines increase, hold, and decrease of a voltage command based on the primary current, a frequency adjustment circuit that adjusts a frequency based on the primary current, and the V A voltage command comparison circuit that detects that the voltage command output from the / f conversion circuit and the voltage command output from the voltage adjustment circuit match. It is characterized by restarting the alternating-current motor run state.

  According to the first aspect of the present invention, it is possible to limit the inverter output current when restarting the AC motor during free running and reduce mechanical shock.

The block diagram which shows the structure of embodiment of the control apparatus of the alternating current motor in this invention Improvement result diagram of the present invention Example of the device of the invention of the conventional example Operation explanatory diagram of the inventive device of the conventional example

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an embodiment of a control device for an AC motor according to the present invention.
The motor control device in this embodiment includes a power converter 1, an AC motor 2, a current detector 3, a current conversion circuit 4, a frequency adjustment circuit 5, a voltage adjustment circuit 6, a V / f conversion circuit 7, and a voltage command comparison circuit. 8, a phase calculation circuit 9 and a PWM calculation circuit 10 are provided. The power converter 1 converts a DC voltage obtained by converting a three-phase AC by a power element into an AC having an arbitrary frequency and voltage by a PWM control method, and supplies the AC voltage to the AC motor 2.
The current detector 3 detects a current supplied to the AC motor 2.
The current conversion circuit 4 converts iu and iw detected by the current detector 3 into a primary current ifb.
The frequency adjustment circuit 5 adjusts based on the primary current ifb so that the frequency corresponding to the speed of the AC motor 2 matches the frequency output from the power converter 1.
The voltage adjustment circuit 6 adjusts the voltage command Vref so that the current value detected by the current conversion circuit 4 does not exceed the first predetermined value.
The V / f conversion circuit 7 calculates a primary voltage command based on the output frequency.
The voltage command comparison circuit 8 is an output of the voltage adjustment circuit 6. The voltage command and the primary voltage command which is the output of the V / f conversion circuit 7 are compared, and information on whether or not they match is output to the frequency adjustment circuit 5.
The phase calculation circuit 9 calculates the phase based on the output frequency, and outputs it to the PWM calculation circuit 10.
The PWM calculation circuit 10 performs PWM calculation based on the voltage command selected by SW2 and the phase output from the phase calculation circuit 9, and drives the power converter 1.

Next, the method for estimating the speed of the AC motor of the present invention will be described.
When estimating the speed of the AC motor, the switches SW1 and SW2 are switched from the A side to the B side, the highest frequency is set in the frequency adjustment circuit 5, and 0 is set in the voltage adjustment circuit 6.
The voltage adjustment circuit 6 gradually increases the voltage command at an increasing rate that increases from 0 to the maximum voltage in the second predetermined time. The primary current ifb is monitored, and when the primary current ifb exceeds the first predetermined value, the voltage is reduced by a third predetermined value from the voltage command.
When the primary current is higher than the fourth predetermined value, the frequency adjustment circuit 5 decreases the frequency by the fifth predetermined value while holding the voltage command. When the primary current ifb becomes smaller than the sixth predetermined value, the frequency is held and the voltage command is increased again at an increasing rate based on the second predetermined time. When the voltage command output from the V / f conversion circuit 7 and the voltage command output from the voltage adjustment circuit 6 match, the voltage command comparison circuit 8 outputs a match signal, and the speed estimation is completed. The switches SW1 and SW2 are switched from the B side to the A side, and the operation is shifted to the operation based on the frequency command fref1.

  FIG. 2 is an example to which the present invention is applied, and is an example in which the AC motor of a single motor is restarted in the present invention from a stopped state and in a free run state at 30 Hz.

DESCRIPTION OF SYMBOLS 1 Power converter 2 AC motor 3 Current detector 4 Current coordinate conversion circuit 5 Frequency adjustment circuit 6 Voltage adjustment circuit 7 V / f conversion circuit 8 Voltage command comparison circuit 9 Phase calculation circuit 10 PWM calculation circuits SW1, SW2: Switch

Claims (1)

A power converter that outputs arbitrary power to an AC motor, a current detection circuit that detects a current supplied to the AC motor, a current conversion circuit that converts the detected current into a primary current, and a voltage based on a frequency command A V / f conversion circuit that calculates a command, a phase calculation circuit that calculates a phase from a frequency command, and a PWM calculation circuit that generates a signal for switching the power converter from the voltage command and the phase command. In an AC motor control device,
A voltage adjustment circuit for determining an increase in voltage command and a decrease in hold based on the primary current;
A frequency adjustment circuit for adjusting a frequency based on the primary current;
Restarting the AC motor in a free-run state by having a voltage command comparison circuit that detects that the voltage command output from the V / f conversion circuit and the voltage command output from the voltage adjustment circuit match. A control device for an AC electric motor that is characterized.

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