JPH07245974A - Inverter - Google Patents

Abstract

PURPOSE:To stop an a.c. motor in a short time by producing d.c. braking stop command output when current shifts from a stable state to an unstable state in d.c. braking, and exerting braking force with reliability until the a.c. motor is about to stop. CONSTITUTION:Direct current braking command output is produced by a PWM generator 29, and braking force is exerted on an induction motor 24. Though the current I largely fluctuates in the early stage of braking, it stabilizes in the middle stage. At this point a rate-ofchange detector 38 detects that the fluctuation in the current I has fallen below a specified value. The value of current I is stored in a stable value storing means 39 as the stable current I0. When brought into an unstable state in the last stage the current I become smaller than I0. Therefore, a comparator 40 produces d.c. braking stop command S0 output through a d.c. braking command changing means 33B. This stops the d.c. braking command output from the PWM generator 29, and thus stops the induction motor 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for performing variable speed control of an AC motor, and more particularly to an inverter device having improved control characteristics during DC braking of the AC motor.

[0002]

2. Description of the Related Art In order to stop the rotation of an AC motor such as an induction motor, it has been practiced to excite the AC motor with a DC current to obtain a braking torque. Recently, it has been required to apply this DC braking to stopping the AC motor from a high frequency range or stopping from an arbitrary frequency. FIG. 9 shows a conventional configuration of an inverter device having a function of performing this type of DC braking. As shown in the figure, when the operation / stop switching means 1 is in the operation mode, the target frequency Fc set by the frequency setting means 2 is supplied to the acceleration / deceleration means 3 as the frequency command fc, and the acceleration / deceleration means 3 changes the frequency. It is converted into the reference f and output.

The frequency reference f is supplied to the PWM signal generator 4, converted into a voltage reference v by the V / f setting means 5, and given to the PWM signal generator 4. Then, the PWM signal generator 4 creates a PWM signal from both the references f and v, and supplies this PWM signal to the inverter circuit 7 through the drive circuit 6. This allows
The inverter circuit 7 is switching-controlled, and the AC electric motor 8 rotates at the frequency reference f. In addition, 9 is a three-phase AC power supply,
10 is a converter.

On the other hand, when the operation / stop switching means 1 is switched to the stop mode, the DC braking command switching means 11 is turned on. Along with this, the frequency command “0H
z ”is supplied, and the acceleration / deceleration means 3 sequentially lowers the current frequency fo from the current frequency fo. In this state, when the frequency detecting means 12 detects “frequency reference f ≦ FdB”, the frequency detecting means 12 outputs the DC braking start command Sa,
The voltage reference switching means 13 is switched to "VdB", the frequency reference switching means 14 is switched to "0 Hz", the DC braking command S is output from the PWM signal generator 4, and the AC motor 8 is used.
Braking force acts on. At the same time, the timer means 15 starts counting up, and when it detects that the predetermined time T has elapsed, it outputs the DC braking stop command So and releases the DC braking. FIG. 10 shows a current waveform flowing in one phase of the AC motor 8 during DC braking, where Ta is the output start time of the DC braking command S, Tb is the output stop time of the DC braking command S, and Tc is the AC motor 8. Is the stop time.

[0005]

However, in the above-mentioned conventional configuration, since the DC braking command S is output for the fixed time T with the DC braking start command Sa as the signal, the DC braking command S is stopped depending on the load state of the AC motor 8. In some cases, it may not be possible to apply the braking force to the last minute. Therefore, as shown in FIG. 10, after the output of the DC braking command S is stopped (at time T
b) The AC motor 8 may be in the free-run state, and it may take time before the AC motor 8 stops. Therefore, the user has to set an appropriate output time T of the DC braking command S, and there is a problem in that the usability of the device is poor. In addition, in some cases, a mechanical auxiliary brake is required, which causes a problem of increasing the cost of the device.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an AC electric motor without causing deterioration in usability and cost increase by surely applying a braking force to a position just before the AC electric motor stops. It is to provide an inverter device that can be stopped in a short time.

[0007]

According to the present invention, in an inverter device configured to apply a DC braking force to an AC electric motor driven by an inverter circuit, a current detection for detecting a current flowing through the AC electric motor. Means and
Start command output means for outputting a DC braking start command, and stop command output means for outputting a DC braking stop command based on a detected value of the current detecting means changing from a stable state to an unstable state during DC braking. It is characterized in that it is provided (Claim 1).

In this case, output timing changing means for changing the output timing of the DC braking stop command by the stop command output means may be provided (claim 2), or the current flowing through the AC motor may be changed from a stable state to an unstable state. When the limit time is not reached, a forced stop command output means for outputting a DC braking stop command instead of the stop command output means is provided (Claim 3), or a current detection means is provided on the input side of the inverter circuit. Alternatively (claim 4).

[0009]

According to the means described in claim 1, when the start command output means outputs the DC braking start command, the braking force acts on the AC electric motor. FIG. 3 shows experimentally the current waveform flowing in one phase of the AC motor during DC braking. As is clear from the figure, the current value fluctuates greatly at the beginning of DC braking, and stabilizes in the middle period. Immediately after the stop (late stage), it becomes unstable again. Therefore, claim 1
Like the described means, if the current detection means detects that the current value flowing in the AC motor changes from a stable state to an unstable state, and outputs a DC braking stop command from the stop command output means at this timing, the AC The braking force can be surely applied until the electric motor is about to stop. As a result, the output time of the DC braking command is automatically set, and the usability of the device is improved. In addition, the mechanical auxiliary brake can be eliminated, so that the cost can be reduced.

In this case, the time during which the AC motor is in an unstable state varies slightly depending on the usage conditions of the AC motor. Therefore, if the output timing of the DC braking stop command is changed by the output timing changing means so as to correspond to the length of the non-stabilizing time as in the means described in claim 2, the AC motor can be more surely stopped just before the stop. A braking force can be applied.

Further, it is considered that the change of the current value from the stable state to the unstable state cannot be detected due to the abnormality of the current detecting means or other circuit abnormality. In this respect, if a forced stop command output means for outputting a DC braking stop command is provided instead of the stop command output means as in the means according to claim 3, the current value changes from a stable state to an unstable state. The DC braking can be ended even if the above is not detected. When detecting the current flowing through the AC motor, the current detecting means may be provided on the input side of the inverter circuit as in the means according to the fourth aspect.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A first embodiment of the present invention will be described below with reference to FIGS.
It will be described based on. First, in FIG. 1, a converter circuit 22 is connected to the three-phase AC power supply 21. The converter circuit 22 includes a rectifier circuit 22a and a rectifier circuit 22.
a of the smoothing capacitor 22d connected to the DC power supply lines 22b and 22c.
2b and 22c are connected to the inverter circuit 23.
The inverter circuit 23 has a well-known configuration in which switching elements such as IGBTs are bridge-connected, and each output terminal of three phases is connected to each input terminal of an induction motor 24 as an AC motor.

The main control circuit 25 is composed mainly of a microcomputer, and its software configuration controls a series of rotation control to be described later. Then, the operation command and the stop command from the main control circuit 25 are given to the operation / stop switching means 26, and the operation / stop switching means 26 switches the operation mode and the stop mode based on the operation command and the stop instruction. . The frequency setting means 27 is for setting the target frequency Fc, and when the operation / stop switching means 26 is in the operation mode, the frequency setting means 27.
The target frequency Fc set by is given to the acceleration / deceleration means 28 as a frequency command fc. When the operation / stop switching means 26 is in the stop mode, the "frequency command fc = 0 Hz" is given to the acceleration / deceleration means 28.

The acceleration / deceleration means 28 adjusts the present frequency fo based on the target frequency fc to create the frequency reference f, and the created frequency reference f is the PWM signal generator 29 and V / f setting. Is supplied to the means 30. This V /
The f setting means 30 uses the given frequency reference f and a predetermined V.
The voltage reference v is created based on the / f value and
The voltage reference v created by the V / f setting means 30 is PW.
It is supplied to the M signal generator 29. Then, the PWM signal generator 29 obtains a sinusoidal PWM signal based on the frequency reference f and the voltage reference v, and outputs this PWM signal to the inverter circuit 23 via the drive circuit 31. As a result, the inverter circuit 23 is switching-controlled.

The frequency detecting means 32 is for detecting that the frequency reference f adjusted by the acceleration / deceleration means 28 is less than or equal to a predetermined value "FdB".
When ≦ FdB ”is detected, the DC braking start command Sa is output. That is, the frequency detection means 32 functions as a start command output means. The DC braking command switching means 33A is driven in conjunction with the run / stop switching means 26.
The stop switching means 26 is turned on when the stop mode is set, and the DC braking start command Sa is given by the frequency detecting means 32.
The voltage reference switching means 34 and the frequency reference switching means 35.
Supply to.

The voltage reference switching means 34 switches the voltage reference applied to the PWM signal generator 29 between the value v created by the V / f setting means 30 and a predetermined value "VdB". Further, the frequency reference switching means 35 switches the frequency reference given to the PWM signal generator 29 between the value f created by the acceleration / deceleration means 28 and a predetermined value "0 Hz". Then, these both switching means 34 and 3
5 is normally in a state of supplying the voltage reference v by the V / f setting means 30 and the frequency reference f by the acceleration / deceleration means 28 to the pulse signal generator 29, but the DC braking start command Sa
When it receives, it switches to a state where the predetermined values "Vdb" and "0 Hz" are given. As a result, the PWM signal generator 29
A DC braking command S is output from the DC motor, and DC braking is applied to the induction motor 24.

The DC braking ending means 36 is the induction motor 24.
Is detected, and the DC braking stop command So is output based on the detection result. The configuration of the DC braking termination means 36 will be described below with reference to FIG. The current detector 37 is composed of a current detector 37a and a converter 37b. The current detector 37a is provided on the output side of the inverter bridge of the inverter circuit 23,
The current value of one phase of the induction motor 24 is measured. Conversion means 3
Reference numeral 7b is for converting the current value measured by the current detector 37a into a voltage value and then sequentially storing it as digital data.

The rate-of-change detecting means 38 reads the current value I, which is the data of the converting means 37b, in chronological order and compares them. Based on the comparison result being less than a predetermined value, the current value I becomes stable. It is to detect that. For example, the current value "I1" at time "t1" and the current value "I2" at time "t2" are compared, and the absolute value "ΔI" of the difference between them is "ΔI≤Ik (predetermined value)". Based on the above, it is detected that the current value I is stable. Further, the stable value storage means 39 is for storing the stable current value Io detected by the change rate detection means 38.

The comparator 40 has a current value I obtained by the conversion means 37b and a stable current value Io stored in the stable value storage means 39.
Is compared with the current value I <stable current value Io to detect that the current value I has changed from the stable state to the unstable state, and the DC braking stop command So is output. is there. That is, the comparator 40 functions as a stop command output means. The DC braking command switching means 33B is driven in conjunction with the operation / stop switching means 26 (see FIG. 1), and is turned on when the operation / stop switching means 26 enters the stop mode, and the comparator 40 The output DC braking stop command So is supplied to the PWM signal generator 29. The DC braking termination means 36 is configured as described above.

Next, the operation of the above configuration will be described. First, as shown in FIG. 1, when the operation / stop switching means 26 is in the operation mode, the target frequency Fc set by the frequency setting means 27 is the acceleration / deceleration means 2 as the frequency command fc.
It is supplied to the output terminal 8 and converted into the frequency reference f by the acceleration / deceleration means 28 and then output. The frequency reference f is supplied to the PWM signal generator 29, converted into the voltage reference v by the V / f setting means 30, and provided to the PWM signal generator 29. Then, the PWM signal generator 29 creates a PWM signal from the frequency reference f and the voltage reference v,
This PWM signal is supplied to the inverter circuit 23 through the drive circuit 31. As a result, the inverter circuit 23
Is controlled so that the induction motor 24 rotates at the frequency reference f.

When the operation / stop switching means 26 is switched to the stop mode, the DC braking command switching means 33A and 33B are turned on. At the same time, the frequency command “0 Hz” is supplied to the acceleration / deceleration means 28, and the acceleration / deceleration means 28
The frequency reference f is gradually decreased from the current one to “0 Hz”. In this state, when the frequency detecting means 32 detects “frequency reference f ≦ FdB”, the frequency detecting means 32 outputs the DC braking start command Sa and the voltage reference switching means 3
4 switches to "VdB", the frequency reference switching means 35 switches to "0 Hz", the DC braking command S is output from the PWM generator 29 via the drive circuit 31, and the braking force acts on the induction motor 24. .

FIG. 3 is an experimental result showing the relationship between the current value (vertical axis) flowing in one phase of the induction motor 24 and the elapsed time (horizontal axis). When the DC braking command S is output at time T1. ,
In the initial stage, the current value largely fluctuates. Therefore, in FIG. 2, the comparison result ΔI (absolute value) of the current value I by the change rate detection means 38 becomes “ΔI> Ik (predetermined value)”, and the change rate detection means 38 repeats the comparison operation. Then, as shown in FIG. 3, when the current value stabilizes at time T2 in the middle of the period, "comparison result ΔI ≤ Ik (predetermined value)" is satisfied, so that the change rate detecting means 38 reads the read current value I. Is stored in the stable value storage means 39 as the stable current value Io.

Then, the comparator 40 uses the stable value storage means 39.
The stable current value Io is read from and the current value I read from the conversion means 37b is compared with the stable current value Io. In this case, since the current value I and the stable current value Io are substantially equal until the time T3 in FIG. 3, the comparison operation is repeated. Then, when the current value I becomes unstable at the end of the period, at time T3, "current value I <stable current value Io".
Therefore, from the comparator 40 to the DC braking command switching means 33
The DC braking stop command So is output through B. As a result, the output of the DC braking command S from the PWM generator 29 is stopped, and the induction motor 24 is stopped at time T4 in FIG.

According to this embodiment, when the DC braking is applied to the induction motor 24, the current value I flowing through the induction motor 24 is increased.
Experimentally found that the induction motor 24 becomes unstable just before the induction motor 24 stops, and the decrease timing of the current value I (time T
Since the output of the DC braking command S is stopped in synchronization with 3), the braking force can be surely applied until the induction motor 24 is about to stop. As a result, the output time of the DC braking command S is automatically set, and the usability of the device is improved. In addition, the mechanical auxiliary brake can be eliminated or made as simple as possible, so that the cost can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIGS.
It will be described based on. The same members as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted, and only different members will be described below. First, in FIG. 4, the DC braking end means 36 is provided with a timer 41. The timer 41 delays the output timing of the DC braking stop command So from the comparator 40 by ΔT, and functions as an output timing changing unit. Then, as shown in FIG.
When "current value I <stable current value Io" is detected at, the timer 41 is activated and at time (T3 + ΔT = T4),
The DC braking stop command So is output and the induction motor 24 is stopped.

In this embodiment, the time from the decrease of the current value I (time T3) to the stop of the induction motor 24 (time T4) (that is, the time during which the induction motor 24 is in an unstable state).
The output timing of the DC braking stop command So is delayed by ΔT by the timer 41, so that the induction motor 24 is controlled more reliably until it is about to stop. Power can be applied. The delay time ΔT by the timer 41 may be set appropriately according to the usage conditions of the induction motor 24.

Next, a third embodiment of the present invention will be described with reference to FIGS. 6 and 7.
It will be described based on. The same members as those in the second embodiment are designated by the same reference numerals and the description thereof will be omitted, and only different members will be described below.

First, referring to FIG. 6, the DC braking ending means 3
6, a limit timer 42 and an OR circuit 43 are provided. The limit timer 42 starts time-up by turning on the DC braking command switching means 33A,
The time-up is ended by the output of the DC braking stop command So from the comparator 40. When there is no time-up end command (output of the DC braking stop command So), the DC braking is performed after the limit time Tm has elapsed from the start of the time-up. The stop command S'o is transmitted. That is, the limit timer 42
Functions as a forced stop command output means. OR circuit 43
Is a PWM signal generator that preferentially outputs one of the DC braking stop command So output from the timer 41 and the DC braking stop command S'o output from the limit timer 42 (for example, the DC braking stop command So). It is output to 29.

As described above, the present invention provides the induction motor 2
This is done by paying attention to the fact that the current value I becomes instable immediately before the stop of No. 4, but the instability of the current value I is not detected due to the abnormality of the current detecting means 37 or other circuit abnormality. Can be considered. In this regard, in this embodiment, as shown in FIG. 7, even if the decrease of the current value I is not detected at time T3, the limit timer 42 detects that the limit time Tm has elapsed, and the DC braking is stopped at time T5. Command S'o
Is transmitted, it is possible to end the DC braking.
Moreover, the output of the DC braking stop command So from the comparison circuit 40 and the DC braking stop command S from the limit timer 42 are output.
When the output of ‘o’ is performed simultaneously, one signal (for example, the DC braking stop command So) is preferentially supplied to the pulse generator 29 by the OR circuit 43.
DC braking can be ended.

In the third embodiment, the limit timer 4 is activated when the DC braking command switching means 33A is turned on.
Although the number 2 starts the time-up, for example, the limit timer 42 may start the time-up in response to the output of the DC braking start command Sa from the current detection means 32.

In each of the first to third embodiments, the current detector 37 is provided on the output side of the inverter circuit 23.
Although a is provided, as shown in FIG. 8 showing the fourth embodiment of the present invention, by providing the current detector 37a on the DC power supply line 22c, even if the current detector 37a is positioned on the input side of the inverter bridge of the inverter circuit 23, The same effect as that of each of the above-described embodiments is obtained.

In each of the first to third embodiments, the DC braking stop command So is output when the current value I drops from the stable current value Io. The DC braking stop command So may be output when I rises again after falling from the stable current value Io. The point is that the value detected by the current detecting means 37 changes from the stable state to the unstable state. DC braking stop command S
Output o.

[0033]

As is apparent from the above description, the inverter device of the present invention has the following excellent effects. According to the means described in claim 1, since the braking force can be surely applied until the AC motor is about to stop,
Output time of DC braking command will be set automatically,
The usability of the device is improved. In addition, the mechanical auxiliary brake can be eliminated or made as simple as possible, so that the cost can be reduced.

According to the second aspect of the present invention, the output timing of the DC braking stop command can be changed according to the length of the non-stabilizing time, so that the braking force can be more reliably applied until the AC motor is about to stop. Can be operated. Claim 3
According to the described means, even if the unstable state of the AC motor is not detected, the forced stop command output means outputs the DC braking stop command, so that the DC braking can be ended.
According to the means described in claim 4, even if the current detecting means is located on the input side of the inverter circuit, the current flowing through the AC motor can be detected.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a current termination unit.

FIG. 3 is a waveform diagram of current flowing through the induction motor.

FIG. 4 is a view corresponding to FIG. 2 showing a second embodiment of the present invention.

FIG. 5 is a view corresponding to FIG.

FIG. 6 is a view corresponding to FIG. 2 showing a third embodiment of the present invention.

FIG. 7 is a view corresponding to FIG.

FIG. 8 is a view corresponding to FIG. 1 showing a fourth embodiment of the present invention.

FIG. 9 is a view corresponding to FIG. 1 showing a conventional example.

FIG. 10 is a view corresponding to FIG.

[Explanation of symbols]

23 is an inverter circuit, 24 is an induction motor (AC motor), 32 is frequency detection means (start command output means), 3
7 is a current detection means, 40 is a comparator (stop command output means), 41 is a timer (output timing changing means), 4
Reference numeral 2 denotes a limit timer (forced stop command output means).

Claims (4)

[Claims] 1. An AC motor driven by an inverter circuit, configured to apply a DC braking force to the AC motor, wherein a current detection means for detecting a current flowing through the AC motor and a DC braking start command are output. An inverter device comprising: a start command output unit that outputs a stop command output unit that outputs a DC braking stop command based on a detected value of the current detection unit changing from a stable state to an unstable state during DC braking. 2. The inverter device according to claim 1, further comprising output timing changing means for changing the output timing of the DC braking stop command by the stop command output means. 3. A forced stop command output means for outputting a DC braking stop command in place of the stop command output means when a limit time is reached when a change in the current flowing through the AC motor from a stable state to an unstable state is not detected. The inverter device according to claim 1, wherein the inverter device is provided. 4. The inverter device according to claim 1, wherein the current detecting means is provided on the input side of the inverter circuit.