JPH10136689A - Inverter equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent that when an induction motor is operated by applying AC power higher than a base frequency, the operation is continued in the state that a load current higher than or equal to the continuous operation rating level flows. SOLUTION: When a load detecting value I of an induction motor 6 exceeds a load setting value Iref, and a frequency constant signal Fco is outputted from a frequency constant detecting circuit 15, in the state that an output frequency signal fout which an adjustable speed control circuit 13 gives to an inverter main circuit 5, exceeds a base frequency fbase, a frequency command selector 11 changes a frequency command value fc, so as to decrease the output frequency fout until the load detection value I becomes lower than or equal to the load setting value Iref. Thereby the induction motor 6 is operated at the maximum rotational speed, wherein the load torque balances with the continuously operating torque.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inverter device having an inverter main circuit for supplying AC power to an induction motor.

[0002]

FIG. 7 shows an example of a torque characteristic when a general-purpose three-phase induction motor (hereinafter, simply referred to as a motor) is driven by an inverter device. As can be understood from FIG. 7, the output frequency of the inverter device is equal to the base frequency (e.g.
0 Hz), both the short-time operating torque and the continuous operating torque of the motor decrease.

A conventional technique for accelerating such a motor to a region above the base frequency in a short time without stalling it is disclosed in, for example, JP-A-6-284787. This is because, when the output frequency of the inverter device exceeds the base frequency of the motor and the maximum torque of the motor exceeds the frequency at which the overcurrent stall prevention operation level is set in advance, the above-mentioned overcurrent stall The preventive operation level is configured to be gradually lowered, thereby aiming at minimizing the extension of the required acceleration time while effectively utilizing the torque of the electric motor.

The above-mentioned prior art is effective in preventing stall during acceleration of the motor. However, when the load torque of the motor is balanced with the stall prevention operation level, the motor cannot be accelerated further and its output frequency is constant. May drive. However, in such an operation state, the level of the load current flowing through the motor may exceed the continuous operation rated level in some cases. If the continuous operation is performed in this state, the life of the motor is reduced. Further, when the motor is provided with an overload relay or the inverter device is provided with a thermal relay or the like, there is a problem that the operation of the motor may be inadvertently stopped by operating these.

[0005] The present invention is to solve the above problems,
The purpose is to prevent the situation where the operation is continued with the load current of the continuous operation rated level or higher flowing when the AC motor is operated by supplying AC power at the base frequency or higher to the induction motor. An object of the present invention is to provide an inverter device having an effect.

[0006]

To achieve the above object, an inverter device according to a first aspect of the present invention comprises an inverter main circuit for supplying AC power to an induction motor, and a load detecting the output current of the inverter main circuit. Load detection means for outputting a detection value, acceleration / deceleration control means for outputting an output frequency signal for controlling the output frequency of the inverter main circuit, and an output current preset according to the output frequency of the inverter main circuit A load setting means for outputting a value as a load setting value, a load setting value excess detecting means for outputting a load setting value excess signal in a state where the load detection value exceeds the load setting value, and A base frequency excess detection means for outputting a base frequency excess signal in a state in which the frequency exceeds the frequency, and a fluctuation width of the output frequency signal is continuously within a predetermined range for a predetermined time. A constant frequency detection means for outputting a constant frequency signal when detecting that the load setting value excess signal, the base frequency excess signal and the frequency constant signal are both output. Protection means for reducing the output frequency signal output by the acceleration / deceleration control means until the output is stopped.

According to such a configuration, a state where AC power having a frequency exceeding the base frequency is applied to the induction motor (as shown in FIG. 7, the short-time operation torque and the continuous operation torque of the motor) The state in which the fluctuation range of the output frequency is within the predetermined range for a predetermined time, and the load current flowing through the induction motor (output current of the inverter main circuit) exceeds the load set value. Means that a signal exceeding the load set value, a signal exceeding the base frequency, and a constant frequency signal are output.

When the respective signals are output together as described above, the protection means operates only during a period until the output of the load set value excess signal is stopped, that is, a period until the detected load value becomes equal to or less than the load set value. Since the output frequency signal output by the acceleration / deceleration control means is reduced, the level of the load current flowing through the induction motor is suppressed to a level corresponding to the load set value or lower. By performing such suppression control, the induction motor can be operated at the maximum rotation speed in a state where the load torque is balanced with the continuous operation torque. Therefore, for the induction motor,
In a state where AC power having a frequency exceeding the base frequency is applied, it is possible to prevent a load current exceeding the continuous operation rated level from continuing to flow due to insufficient load torque of the induction motor. There is no danger that the life of the induction motor will be adversely affected.

In this case, as described in claim 2, when the output of the fixed frequency detection signal from the fixed frequency detection means continues for a predetermined time, the load average waiting time detection means outputs a load average waiting time signal. Load average means for outputting a load average value obtained by time-averaging the load detection value at the time of output of the constant frequency detection signal, wherein the load set value excess detection means, in a state where the load average value exceeds the load set value Outputting a load set value excess signal, wherein the protection unit stops outputting the load set value excess signal when the load set value excess signal, the base frequency excess signal, and the load average waiting time signal are output together. It is preferable that the output frequency signal output by the acceleration / deceleration control means is reduced until the operation is completed. With this configuration, the load averaging means can reduce a detection error due to a change in the output current.

The protection means may reduce the output frequency signal of the acceleration / deceleration control means to a predetermined value equal to or higher than the base frequency of the induction motor and lower than the output frequency signal. A configuration may be adopted. With such a configuration, substantially the same operation and effect as those of the second or third aspect can be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. In FIG. 1 showing the electrical configuration, each phase output terminal of a three-phase AC power supply 1 is connected to an input terminal of a full-wave rectifier circuit 2 composed of a diode bridge, respectively. Are connected to the DC buses 3a and 3b. DC bus 3
A smoothing capacitor 4 is connected between a and 3b.

The inverter main circuit 5 connected between the DC buses 3a and 3b is constituted by connecting three transistors in which a freewheel diode is connected in parallel between a collector and an emitter in a three-phase bridge connection. The output terminals 5u, 5v and 5w are connected to the respective phase input terminals of a three-phase induction motor (hereinafter simply referred to as a motor) 6, respectively.
Current detectors 7 u and 7 w are provided between the output terminals 5 u and 5 w of the inverter main circuit 5 and the electric motor 6. The current detectors 7u and 7w detect U- and W-phase currents flowing through the windings of the electric motor 6, and output detection signals Iu and Iw of current levels corresponding to the detected currents to the load detector 8. ing.

The load detector 8 outputs a signal Iv (=-(Iu + I) indicating the V-phase current of the electric motor 6 from the detection signals Iu and Iw.
w)), and these signals Iu, I
The peak value among the absolute values of w and Iv is peak-held with a predetermined decay time constant, so that the load detection value I
(Output as a voltage signal). The load detector 8 supplies the load detection value I to an inverting input terminal of a negative logic output comparator (load setting value excess detection means) 9. Note that all output signals described below are also output as voltage signals.
Further, the current detectors 7u and 7w and the load detection circuit 8 constitute a load detection means according to the present invention.

A load setting value (Iref) is given to a non-inverting input terminal of the comparator 9 from a load setting device (load setting means) 10. This load set value Iref
Is set to a constant value corresponding to the rated current value of the electric motor 6 in this embodiment. Thus, the load set value Ire
By setting f, the continuous operation torque T of the electric motor 6 in the region equal to or higher than the base frequency fbase is expressed by the following equation, as will become clearer later. T = K · (V / f) · Iref (1) where K: constant, V: output voltage, and f: rotation speed (frequency) of the motor 6.

The comparator 9 comprises switches S1 and S2
Switch S in the frequency command selector 11 composed of
When the load detection value I> the load setting value Iref, a load setting excess signal Lov (high level signal) is output to the second switching signal terminal C2.

Switch S in frequency command selector 11
The frequency setting signal fset set by the frequency setting device 12 is supplied to one fixed contact S1a.
The fixed contact S1b of the switch S1 is connected to the movable contact S2c of the switch S2. Fixed contact S2a of switch S2
Is supplied with an output frequency signal fout from an acceleration / deceleration control circuit (acceleration / deceleration control means) 13, and a fixed contact S2b is supplied with a base frequency signal fbase of the electric motor 6. . Then, the acceleration / deceleration control circuit 1
3, a signal output through the movable contact S1c of the switch S1 is given as a frequency command value fc.

The acceleration / deceleration control circuit 13 outputs an output frequency signal fout in which an appropriate acceleration / deceleration time is added to the input frequency command value fc. The output terminal of the acceleration / deceleration control circuit 13 is connected to input terminals of a PWM control circuit 14 and a constant frequency detection circuit (constant frequency detection means) 15 in addition to the fixed contact S2a of the switch S2. It is also connected to the inverting input terminal of a comparator (base frequency excess detection means) 16 which is a logical output.

The PWM control circuit 14 supplies a PWM signal corresponding to the output frequency signal fout as a base signal to the base of each transistor of the inverter main circuit 5, and the inverter main circuit 5 receives the PWM signal based on the PWM signal. By performing the switching operation, AC power having a frequency corresponding to the output frequency signal fout is supplied to the motor 6.

The constant frequency detecting circuit 15 determines that the state in which the fluctuation range of the output frequency signal fout is within a predetermined range for a predetermined time T.
When only w is continuous, a constant frequency signal Fco (high-level signal) is generated to generate a D-type flip-flop (hereinafter, referred to as D-type flip-flop).
DFF) 17 to the latch enable terminal LE. The non-inverting input terminal of the comparator 16 is supplied with the base frequency signal fbase.
When out exceeds the base frequency signal fbase, an excess frequency detection signal Fov (high level signal) is generated and the DFF 17
Is output to the data input terminal D.

The output terminal Q of the DFF 17 is connected to the switching signal terminal C1 of the switch S1 of the frequency command selector 11. The DFF 17 outputs a signal corresponding to the level of the frequency excess detection signal Fov supplied to the data input terminal D from the output terminal Q in synchronization with the rise of the constant frequency signal Fco.

The movable contact S1c of the switch S1 constituting the frequency command selector 11 switches from the fixed contact S1a to the fixed contact S1b when the signal applied to the switching signal terminal C1 changes from low to high. ON). The movable contact S2c of the switch S2 is
When the signal supplied to the switching signal terminal C2 changes from a low level to a high level, the fixed contact S2a is switched to the fixed contact S2b (ON). The frequency command selector 11 and the DFF 17 correspond to the protection means according to the present invention.

Next, the operation of the first embodiment will be described with reference to FIG. FIG. 2 is a timing chart showing an example of an acceleration pattern when the inverter device having the above configuration accelerates the motor 6 from a stopped state to a speed equal to or higher than the speed corresponding to the base frequency fbase. In this case, the horizontal axis represents time t, and (a) represents the output frequency signal fout on the vertical axis.
In (b), the vertical axis represents the load detection value I. (C) and (d) show the base frequency excess signal Fov and the constant frequency detection signal Fco, respectively, and (e) and (f) show the ON / OFF states of the switches S1 and S2, respectively.

It is assumed that a frequency setting value fset = F1 equal to or higher than the base frequency fbase is set by the user in the frequency setting unit 12. This frequency set value fset is
This is a value that the user predicts and sets the output frequency fout of the inverter device when the motor 6 is continuously operated with the torque of the motor 6 balanced with the load torque. When the power is turned on in such a state, the acceleration of the electric motor 6 is started from time 0. The acceleration / deceleration control circuit 13 receives the frequency setting value F1 as the frequency command value fc,
A predetermined acceleration pattern (for example, when the load detection value I is 1
The output frequency signal fout is raised in accordance with a pattern which is substantially constant at about 30 to 140%).

Then, in response to the acceleration of the electric motor 6, the load detection value I exceeds the load set value Iref at a time T-1 at which a short time has elapsed, so that the comparator 9 outputs a load set value excess signal Lov (high level). ), The switch S2 of the frequency command selector 11 is turned on (see (f)), and the fixed contact S1b of the switch S1 is supplied with the base frequency signal fbase.

At time T0, when the output frequency signal fout reaches the base frequency fbase (see (a)), the comparator 16 outputs the base frequency excess signal Fov.
(High level signal) is output (see (c)).

At time T1, the output frequency signal fout
Reaches the frequency set value F1, the acceleration / deceleration control circuit 13 controls the output frequency signal fout to be maintained at that level, and the load detection value I starts to decrease from this point. When detecting that the fluctuation range of the output frequency signal fout is within a predetermined range centered on the frequency set value F1 for a time Tw, the constant frequency detection circuit 15 detects the constant frequency detection signal Fco at time T1 + Tw. (High level signal) is output (see (d)).

Then, the DFF 17 outputs a signal of a level (high) according to the base frequency excess signal Fov applied to the input terminal D from the output terminal Q in synchronization with the rise of the constant frequency detection signal Fco. (See (e)).
Here, the time Tw corresponds to the output frequency signal fout
= F1, the rotational speed f of the electric motor 6
Is also constant, and is set to a time sufficient for the load detection value I to fall from a falling state to a constant level (see (b)).

When the switch S1 of the frequency command selector 11 is turned on in response to the high level signal output from the DFF 17, the movable contact S1c is switched to the fixed contact S1b side, and the acceleration / deceleration control circuit 13 receives the frequency command value. The base frequency signal fbase is given as fc. Then, the acceleration / deceleration control circuit 1
3 lowers the output frequency signal fout, so that the constant frequency detection signal Fco is not output. However, the output of the DFF 17 remains at the high level, and the switch S1 maintains the ON state (see (e)).

As described above, when the output frequency signal fout is reduced, the slip of the motor 6 is reduced, and the load detection value I
Decrease. Then, at time T2, the load detection value I
Is lower than the load set value Iref, the load set value excess signal Lov
Is not output, the switch S2 of the frequency command selector 11 is turned off, the movable contact S2c is switched to the fixed contact S2a, and the output frequency signal fout is given to the fixed contact S1b of the switch S1. Therefore, the acceleration / deceleration control circuit 13
Calculates the output frequency signal fout (= F2) at that time as P
It continuously outputs to the WM control circuit 14.

Even if the output frequency signal fout is constant,
At this time, the slip of the electric motor 6 in which the continuous operation torque and the load torque cannot be balanced increases. And time T
At 2 + Ts, when the load detection value I exceeds the load set value Iref, the load set value excess signal Lov is output again, the switch S2 of the frequency command selector 11 is turned on again, and the fixed contact S1b of the switch S1 is connected to the base. A frequency signal fbase is provided. Then, the output frequency signal fout turns down again.

At time T3, the load detection value I becomes equal to or less than the load set value Iref, and the fixed contact S1b of the switch S1 is supplied with the output frequency signal fout. The acceleration / deceleration control circuit 13 outputs the current output frequency signal fout. fout (= F3)
To the PWM control circuit 14 continuously. At this time, since the continuous operation torque of the motor 6 is balanced with the load torque, the detected load value I does not exceed the load set value Iref, and the motor 6 is continuously operated at the output frequency F3.

If the load torque does not match the continuous operation torque even at the output frequency F3, the motor 6 is operated at a frequency lower than the frequency F3 by repeating the same process as described above. Thus, the electric motor 6
Is operated at the maximum rotation speed f in a state where the load torque is balanced with the continuous operation torque.

As described above, according to the present embodiment, when the output frequency signal fout supplied from the acceleration / deceleration control circuit 13 to the inverter main circuit 5 exceeds the base frequency fbase, the frequency command selector 11 sets the load. When the detection value I exceeds the load set value Iref and the fixed frequency detection signal Fco is output from the fixed frequency detection circuit 15, the output frequency signal fout is output until the load detection value I becomes equal to or less than the load set value Iref.
The frequency command value fc is switched so as to reduce the frequency.

Therefore, the motor 6 can be operated at the maximum rotational speed in a state where the load torque is balanced with the continuous operation torque, and the motor 6 is supplied with AC power having a frequency exceeding the base frequency fbase of the motor 6. In addition, since it is possible to prevent a load current exceeding the continuous operation rated level from flowing due to insufficient load torque, the life of the motor 6 is not adversely affected. Further, even when the inverter device includes an overload protection circuit, the overload protection circuit does not operate to stop the operation of the electric motor 6, so that the operation can be continuously performed. , Operation efficiency can be improved.

FIG. 3 and FIG. 4 show a second embodiment of the present invention. Hereinafter, only different portions in the second embodiment will be described. FIG. 3 showing an electrical configuration
, An average load waiting time detecting circuit (hereinafter, referred to as a waiting time detecting circuit) 18 is provided between the constant frequency detecting circuit 15 and the DFF 17, and the waiting time detecting circuit (load average waiting time detecting means) is provided. 18, when the constant frequency detection signal Fco is output from the constant frequency detection circuit 15,
After measuring the waiting time Tw1 therefrom, the waiting time detection signal Iav is output to the latch enable terminal LE of the DFF17.

A switch S3 is connected between the load detector 8 and the comparator 16 by a fixed contact S3a and a movable contact S3c.
, And the fixed contact S3b is connected to an output terminal of a load averaging circuit (load averaging means) 19.
The load detection value I is supplied from the load detector 8 to the input terminal of the load averaging circuit 19, and the constant frequency detection signal Fco is supplied to the control input terminal of the load averaging circuit 19 from the constant frequency detection circuit 15. It has become.

When the rising edge of the constant frequency detection signal Fco is given as a trigger signal, the load averaging circuit 19 starts sampling and averaging of the load detection value I, and outputs a load average value I0. The movable contact S3c of the switch S3 is switched (ON) from the fixed contact S3a to the fixed contact S3b when the level of the switching signal output from the waiting time detecting circuit 18 changes from low to high. . Other configurations are the same as in the first embodiment.

Next, the operation of the second embodiment will be described with reference to FIG. It is the same as that of the first embodiment until the acceleration / deceleration control circuit 13 raises the output frequency signal fout to the frequency set value F1 and the constant frequency detection circuit 15 outputs the constant frequency detection signal Fco after the lapse of the time Tw. . The constant frequency detection signal Fco is also supplied to the waiting time detecting circuit 18, and the waiting time detecting circuit 18 turns on the switching signal given to the switch S3 only for the time Tw1, and the movable contact S
3c is switched from the fixed contact S3a to the fixed contact S3b. Then, the load average value I0 output from the load average circuit 19 is given to the comparator 9.

The waiting time detecting circuit 18 detects the time T
After elapse of w1, the wait time detection signal Iav is output to the latch enable terminal LE of the DFF 17 (see (d)).
That is, at time T1 + Tw + Tw1, a switching signal for the switch S1 of the frequency command selector 11 is output.

Thereafter, similarly to the first embodiment, even when the output frequency signal fout becomes constant at the frequency F3, the waiting time detecting circuit 18 turns ON the waiting time detecting signal Iav given to the switch S3 for the time Tw1. The average load value I0 is given to the comparator 9 at time T3 + Tw + Tw1,
A switching signal for the switch S1 is output from the DFF 17.

As described above, according to the second embodiment, when the constant frequency detection signal Fco is output, the load averaging circuit 19 calculates and outputs the average value I0 of the load detection value I, and outputs the result. 18 is a switch S for a time Tw1 from that time.
3 to output the load average value I0 to the comparator 9 to compare the load set value Iref with the load average value I0. Therefore, it is possible to reduce the load detection error due to the fluctuation of the output current. .

FIGS. 5 and 6 show a third embodiment of the present invention. Hereinafter, only different portions in the third embodiment will be described. FIG. 5 showing the electrical configuration
In the frequency command selector 11 in the first embodiment,
Is replaced by a frequency command selector 20 having only the switch S1. The fixed contact S1b of the switch S1 has
The output terminal of the frequency command calculator 21 is connected so that a frequency calculation value fco is given. The input terminal of the frequency command calculator 21 is supplied with the base frequency fbase and the acceleration / deceleration control circuit 13 with the output frequency signal fout.

An output terminal of an AND gate 22 is connected to a control input terminal of the frequency command calculator 21. Two input terminals of the AND gate 22 are connected to output terminals of the constant frequency detection circuit 15 and the comparator 9, respectively. Each is connected to a terminal. When a high-level signal is supplied to the control input terminal, the frequency command calculator 21 uses the rising edge as a trigger to trigger the output frequency signal fout and the base frequency fout.
The frequency calculation value fco is calculated from the base and is output as follows. fco = (fbase + fout) / 2 (2) That is, the frequency calculation value fco is the base frequency fba of the electric motor 6.
It is calculated as a predetermined value equal to or greater than se and less than the output frequency signal fout. The DFF 17, the frequency command selector 20, the frequency command calculator 21, and the AND gate 22 correspond to protection means.

Next, the operation of the third embodiment will be described with reference to FIG. The process is the same as that of the first embodiment until the output frequency signal fout is raised to the frequency set value F1 and the constant frequency detection circuit 15 outputs the constant frequency detection signal Fco after the lapse of the time Tw. At that time, the signals (Fco, Lov) applied to both input terminals of the AND gate 22
Are at a high level, the control input terminal of the frequency command calculator 21 is at a high level, and the frequency command calculator 21 calculates the following equation. fco = (fbase + F1) / 2 = F2 (3)

At this time, a switch signal is also given to the frequency command selector 20, so that the switch S1 is turned on.
As a result, the movable contact S1c is switched to the side S1b, and the acceleration / deceleration control circuit 13 sets the frequency operation value fco = F
2 is given. By switching the frequency command value fc from F1 to F2, the output frequency signal fout decreases from the time T1 + Tw. As a result, the load detection value I also decreases, and falls below the load set value Iref before the time T2 is reached.

At time T2, the output frequency signal fout
Reaches the frequency command value F2, and is controlled by the output frequency signal fout = F2 to be constant until the time Tw elapses from that time. During this time, the load detection value I rises and the load set value I
exceeds ref. After the lapse of the time Tw, the constant frequency detection signal Fco is output, so that the frequency command calculator 21 performs the following calculation. fco = (fbase + F2) / 2 = F3 (4)

At this time, a switching signal is also supplied to the frequency command selector 20 in the same manner as the previous time, but the switch S1 remains ON and the acceleration / deceleration control circuit 13 receives the frequency calculation value fco = F3. Given. Frequency command value f
Since c is switched from F2 to F3, time T2 +
The output frequency signal fout and the load detection value I are lower than Tw, and before reaching time T3, the load detection value I falls below the load set value Iref.

At time T3, the output frequency signal fout
Reaches the frequency command value F3, and is controlled by the output frequency signal fout = F3 to be constant until the time Tw elapses from that time, during which the load detection value I increases. In this case, the frequency command value F3 is set to a level at which the load detection value I does not exceed the load set value Iref even when the motor 6 is continuously operated, so that the load detection value I becomes constant in that state.

Therefore, the excess frequency detection signal Fov output from the comparator 9 becomes low level at time T3 +
Even if the constant frequency detection signal Fco is output at Tw,
The calculation of the new frequency calculation value fco by the frequency command calculator 21 is not performed. In this manner, the motor 6 is continuously operated at the frequency F3 at a level at which the load detection value I does not exceed the load set value Iref.

If the motor 6 is continuously operated with the frequency command value F3 and the load detection value I exceeds the load set value Iref, the calculation of a new frequency calculation value fco by the frequency command calculator 21 is performed as follows. It is performed like an expression. fco = (fbase + F3) / 2 = F4 (5)

As described above, according to the third embodiment, the frequency command calculator 21 outputs the constant frequency detection signal Fco when the load detection value I exceeds the load set value Iref.
The frequency calculation value fco is calculated by fco = (fbase + fout) / 2 and given to the acceleration / deceleration control circuit 13 as a predetermined value equal to or higher than the base frequency fbase and lower than the output frequency signal fout, and the load set value excess signal Lov is output. Since the above calculation is repeated until the load is no longer present, the motor 6 can be continuously operated at the frequency F3 at a level at which the load detection value I does not exceed the load set value Iref. can get.

The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications or extensions are possible. The configurations of the first to third embodiments are all hardware, but may be realized by software of a microcomputer. In the first to third embodiments, the load setting means is stored in advance so that the load set value Iref changes according to the output frequency signal fout, or determined and output by calculating according to the output frequency signal fout. May be configured.

In the third embodiment, the frequency calculation value fco is given as the frequency command value fc. Alternatively, the frequency command value fc may be reduced to the base frequency fbase, or the base frequency fbase may be set to the lower limit. A method of subtracting the frequency command value fc by a constant frequency may be used. In the third embodiment, similarly to the second embodiment, the waiting time detecting circuit 18, the load averaging circuit 19, and the switch S3
May be provided.

[0054]

Since the present invention is as described above,
The following effects are obtained. According to the inverter device of the first aspect, when the output frequency signal of the acceleration / deceleration control means is higher than the base frequency, the protection means detects that the load detection value exceeds the load set value and the frequency is fixed by the constant frequency detection means. When a constant signal is output, the output frequency signal is reduced until the load detection value becomes equal to or less than the load set value, so that the induction motor can be operated at the maximum rotation speed at which the load torque is balanced with the continuous operation torque. In addition, the life of the induction motor can be extended.

According to the inverter device of the second aspect,
Since the load set value excess detecting means outputs the load set value excess signal in a state where the load average value exceeds the load set value, it is possible to reduce a detection error due to a change in output current.

According to the inverter device of the third aspect,
The protection means reduces the output frequency signal of the acceleration / deceleration control means to a predetermined value which is equal to or higher than the base frequency of the induction motor and lower than the output frequency.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of an electric configuration showing a first embodiment of the present invention.

FIG. 2 is a timing chart.

FIG. 3 is a view corresponding to FIG. 1, showing a second embodiment of the present invention.

FIG. 4 is a diagram corresponding to FIG. 2;

FIG. 5 is a view corresponding to FIG. 1, showing a third embodiment of the present invention.

FIG. 6 is a diagram corresponding to FIG. 2;

FIG. 7 is a diagram showing characteristics of a short-time operation torque and a continuous operation torque with respect to an output frequency of an induction motor.

[Explanation of symbols]

5 is an inverter main circuit, 6 is an induction motor, 7u and 7w
Is a current detector (load detecting means), 8 is a load detector (load detecting means), 9 is a comparator (load setting value excess detecting means), 10 is a load setting device (load setting means), and 11 is a frequency command selector. (Protection means), 13 is an acceleration / deceleration control circuit (acceleration / deceleration control means), 15 is a constant frequency detection circuit (constant frequency detection means), 16 is a comparator (base frequency excess detection means), and 17 is a D flip-flop (protection means) ), 1
8 is a load average waiting time detecting circuit (load average waiting time detecting means), 19 is a load averaging circuit (load averaging means), 20 is a frequency command selector (protecting means), 21 is a frequency command computing unit (protecting means), Reference numeral 22 denotes an AND gate (protection means).

Claims (3)

[Claims] 1. An inverter main circuit for supplying AC power to an induction motor, load detection means for detecting an output current of the inverter main circuit and outputting the detected current as a load detection value, and controlling an output frequency of the inverter main circuit. Acceleration / deceleration control means for outputting an output frequency signal for the load circuit, load setting means for outputting an output current value preset according to the output frequency of the inverter main circuit as a load setting value, and wherein the load detection value is the load. Load set value excess detection means for outputting a load set value excess signal in a state exceeding a set value, and a base frequency excess detection means for outputting a base frequency excess signal in a state where the output frequency signal exceeds the base frequency. Constant frequency detecting means for outputting a constant frequency signal when detecting that the fluctuation range of the output frequency signal is within a predetermined range for a predetermined time continuously. An output frequency signal output by the acceleration / deceleration control means until the output of the load set value excess signal is stopped when the load set value excess signal, the base frequency excess signal, and the fixed frequency signal are output together. An inverter device comprising: a lowering protection unit. 2. A load average waiting time detecting means for outputting a load average waiting time signal when a constant frequency detecting signal from the constant frequency detecting means continues for a predetermined time; and a load detecting means for outputting the constant frequency detecting signal when the constant frequency detecting signal is outputted. Load average means for outputting a load average value obtained by time-averaging the values, wherein the load set value excess detection means outputs a load set value excess signal in a state where the load average value exceeds a load set value, The protection means outputs the acceleration / deceleration control means until the output of the load setting value excess signal is stopped when the load setting value excess signal, the base frequency excess signal, and the load average waiting time signal are all output. 2. The inverter device according to claim 1, wherein the output frequency signal is reduced. 3. The protection device according to claim 1, wherein the protection device reduces an output frequency signal of the acceleration / deceleration control device to a predetermined value equal to or higher than a base frequency of the induction motor and lower than the output frequency signal. Inverter device.