JPH0634624B2 - Instantaneous power failure restart device for voltage-type inverter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for driving an induction motor, which is capable of automatic restart during a momentary power failure, and more particularly to a stable and reliable momentary power failure recovery with a simple configuration. The present invention relates to a device for restarting an instantaneous power failure of a voltage type inverter that can be started.

[Background of the Invention]

In recent years, an inverter device has been widely adopted for driving an induction motor (hereinafter, referred to as IM).

In such an IM drive inverter device,
If a power failure occurs and the IM rotation speed drops below a certain level and then the power is restored, an excessive current may flow and the equipment or IM may malfunction. When it occurred, the power was automatically turned on and off.

However, if power is turned on and off in this way, there is no problem in terms of equipment protection, but IM operation must be stopped and restarted each time a power failure occurs. In terms of aspects, it causes a great inconvenience.

Therefore, for example, in the case of a short power failure of a few seconds or less, a so-called momentary blackout, where the rotation speed of the IM does not decrease much even after a power failure, the inverter is automatically restarted to operate the IM almost continuously. The inverter device of the instantaneous blackout restart system adapted to obtain the above has become widely used, and an example thereof can be found in, for example, Japanese Patent Laid-Open No. 58-127592.

However, such a conventional method of restarting the instantaneous blackout of the inverter requires various means for detecting the rotation speed and the rotation phase of the IM at the time of power recovery, and thus the configuration is complicated and the cost tends to increase. I got it.

[Object of the Invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an instantaneous power failure restart device for a voltage-type inverter that does not require detection of the rotational phase of (1) and enables restart with a simple configuration to eliminate the risk of cost increase.

[Outline of Invention]

In order to achieve this object, the present invention provides a bypass circuit means on the direct current side of the inverse converter of the inverter to forcibly attenuate the residual magnetic flux of IM, and at this time, direct current flowing in the bypass circuit means. It is characterized in that the rotational speed of the IM is detected by the ripple component contained in the current and the inverter output frequency at the time of restart is determined.

Example of Invention

Hereinafter, a device for restarting an instantaneous power failure of a voltage type inverter according to the present invention will be described in more detail with reference to the illustrated embodiment.

FIG. 1 shows an embodiment of the present invention, 1 is a three-phase AC power supply, 2 is a forward converter, 3 is a smoothing capacitor, 4 and 5 are contacts of an electromagnetic contactor, 6 is a bypass resistor, and 7 is Inverter, 8 is I
M and 9 are speed setters, 10 is a linear acceleration / deceleration circuit (LA
D), 11 is a speed command selection relay switching contact, 12 is a frequency control circuit, 13 is a voltage control circuit, 14 is a PWM waveform synthesizing circuit, 15 is an AND circuit, 16 is a relay contact, 1
7 is a switching drive circuit, 18 is a voltage comparison circuit, 19
Is a rotation speed detection circuit, 20 is a direct current detector, 21 is an instantaneous power failure detection circuit, and 21 is a restart control circuit.

The forward converter 2, the smoothing capacitor 3, and the inverse converter 7 constitute a well-known voltage type inverter device, and based on a speed command N ^* given from the speed setter 9 via the LAD 10, the frequency control circuit 12 and the voltage control are performed. The frequency signal f and the voltage signal v generated by the circuit 13 are input to the PWM waveform synthesizing circuit 14 to obtain the PWM signal P, and the PWM signal P here is input to the switching drive circuit 17 to inversely convert the gate pulse GP obtained. By supplying the voltage to the device 7, the IM8 operates so that the three-phase AC power of the voltage V at the frequency F is supplied. Note that such a PWM type inverter device is also known.

Working voltage comparator circuit 18 a signal V _R had it occurred detected DC current detector 20 with a predetermined reference value E, which generates a signal only g when being summer lower than the signal V _R is the reference value E do. Follow go-between, g = a _(V R <E).

The rotation speed detection circuit 19 functions to detect the pulsating component of the signal V _R by the detector 20 and generate a rotation speed detection signal N _D representing the ripple frequency thereof.

The instantaneous blackout detection circuit 21 has a function of constantly monitoring the AC voltage supplied from the AC power supply 1 and detecting that the AC voltage has dropped to a predetermined value or less.

The control circuit 22 includes a microcomputer, performs control necessary for restarting the instantaneous blackout by a signal from the instantaneous blackout detection circuit 21, and outputs a signal g. Determining an operating state by captures and like N _D and the speed command N ^*, base and or disconnection signal B at a predetermined timing
B. It functions to generate the contact actuating signals RL1, RL2, the switching signal T, the reset signal R and the like.

Note that the contacts 4 and 16 are normally closed contacts (NC), and thus open when the signals RL1 and RL2 become "1", while the contact 5 is a normally open contact (NO) and therefore the signal RL1 is "1". Close only when On the other hand, the switching contact 11 is in the state shown in the figure while the signal T is "0", but when the signal T becomes "1", it is switched to the contact opposite to that shown in the figure. Also, LA
The input of D10 is set to zero while the reset signal R is applied, regardless of the setting state of the speed setter 9.

Next, the operation of this embodiment will be described with reference to the time chart of FIG.

Now, as shown in FIG. 2 (a), a power failure occurs at a certain time t _0, the input AC voltage V _in and Natsuta zero.

Then, the control circuit 22 starts measuring the time from the time t _0, and does not start any operation when the voltage V _in is restored by restoring the power for a predetermined time, for example, 15 mS. This is because, in the case of an extremely short instantaneous power failure, power is restored before the rotational speed of the IM8 is almost decreased, and the operation can be continued as it is.

When the power does not recover even after the time point t ₁ when 15 mS has elapsed from the time point t ₀ , the control circuit 22 at this time point t ₁ outputs the signals RL1, B as shown in FIGS. 2 (b) and (g).
Start up B, R, T and RL2.

As a result, the contact 4 is opened to disconnect the DC side of the inverse converter 7 from the forward converter side, and the contact 5 is closed to insert the resistor 6 in parallel. Further, since the signal BB is input to the drive circuit 17, the switching element in the inverse converter 7 is turned off by being turned on or off.

On the other hand, the IM8 continues to rotate due to inertia, and the residual magnetism remains in the iron, so an induced voltage appears on the primary side of the IM8. As a result, the freewheel diode in the inverse converter 7 rectifies the voltage. The generated direct current is bypassed by the resistor 6 and flows, and this current is detected by the detector 20 as the signal V _R shown in FIG. 2 (c).

The signal V _R representing the current due to the residual magnetic flux of the IM 8 detected in this way is compared with the predetermined voltage E by the voltage comparison circuit 18 on the one hand, and is input to the rotation speed detection circuit 19 on the other hand, and the ripple component in it is The frequency is detected and comes out as a signal N _D representing the rotational speed of IM8.

In this way, the switching element of the inverse converter 7 is turned off, and the resistor 6 is bypassed to the direct current side. As a result, the energy due to the residual magnetism of the IM 8 becomes a Jewil heat by the resistor 6 and is rapidly attenuated. signal V _R and the second view (c)
Decremented on or was quickly as shown in the drops to the voltage E in a relatively short time after the time t _3.

On the other hand, power is restored at time t ₂ during which the input voltage V _in is assumed to have Modotsu a predetermined value as shown in FIG. 2 (a).

Therefore, the control circuit 22 is the signal V _R is responsive to the signal g shown in FIG. 2 (d) which is generated from the comparator circuit 18 at equal Natsuta time t ₃ to a voltage E, the signal at this time t ₃ RL1, B
B and R are lowered, the contacts 4 and 5 are returned to the illustrated state, and the base circuit and disconnection by the drive circuit 17 are stopped.

As a result, inverse transformer 7 at time t ₃ starts switching-operation, but would like to supply the three-phase power to IM8, in this case, as is clear from FIG. 2 (g), still signal T Since the contact has been kept rising and the contact 11 has been switched upward, the signal N from the rotation speed detection circuit 19 is kept.
_D is input to the frequency control circuit 12 and the voltage control circuit 13, whereby the output frequency F of the inverse converter 7 and the voltage V
It becomes to correspond exactly to the actual rotational speed at this time t ₃ of IM8 and.

That is, at this time t ₃ , as shown in FIG. 2 (d),
Since the signal g rises, the AND circuit 15 opens, and as a result, the frequency signal f based on the speed signal N _D from the rotational speed detection circuit 19 and the PWM signal P based on the voltage signal v are input to the switching drive circuit 17. , Therefore,
The inverse converter 7 starts to output the frequency according to the speed signal N _D. Therefore, the IM8 is driven at the rotation speed N _D at this time t ₃ as it is, and this is detected by the rotation speed detection circuit 19 to become the speed signal N _{D.
After 3} , the actual rotation speed of IM8 is controlled so as to maintain this rotation speed N _D.

Then, at this time, the residual magnetism of the IM 8 is sufficiently attenuated by the bypass circuit of the resistor 6, so that the IM
The power supply to 8 is turned on in a sufficiently stable state.

On the other hand, the LAD 10 is reset at time t ₁ by the rise of the signal R shown in FIG. 2 (b), and its input signal is made zero, so that the speed command N ^* which is its output is shown in FIG. 2 (f).
As shown in, Yuki decreases from time t _1, then the input voltage at time t ₃ is returned to the set value given from the speed setter 9, slide into increased from time t _3. Then, at time t ₄ , the magnitude of the speed command N ^* by the LAD 10 is the signal N _D from the rotation speed detection circuit 19.
It is assumed that the size is equal to V _n .

Then, the control circuit 22 outputs this signal N _D and the command N ^*.
At the time point t _{4 when} they become equal to each other, the signals RL2 and T are lowered, the contact 16 is returned to the closed state, and the switching contact 11 is restored to the illustrated state.

As a result, after time t _4, everything returns to the original state and LAD
Due to the function of 10, the rotation speed increase control at a predetermined speed increase rate up to the set speed given by the speed setting device 9 is smoothly performed, the instantaneous power failure restart is completed, and the IM 8 returns to the normal operation state. .

By the way, in the above description, from the instant t ₀
The case where the power is restored at time t ₂ until the time t ₃ at which the residual magnetic flux of No. 8 is sufficiently attenuated has been described, but this embodiment also applies to the case where power is restored after time t _3. Being able to get a stable restart is out of the question.

In addition, in such an inverter device, when the power failure time exceeds a predetermined time, the instantaneous power failure protection function operates,
Generally, the power supply is tripped. Therefore, also in the embodiment of the present invention, if the power is not restored even after a lapse of a predetermined time or more after the time t ₃ , the power is restarted. It is desirable to configure so that the operation is stopped without performing the operation.

〔The invention's effect〕

As described above, according to the present invention, the residual magnetic flux of the IM at the time of the instantaneous power failure is sufficiently attenuated and the restart is performed by the power recovery. Therefore, only the control according to the rotational speed of the IM is performed. Thus, it is possible to provide a sufficiently stable restart, and to easily provide a low-cost instantaneous power failure restart device with a simple configuration except for the drawbacks of the conventional technology.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an instantaneous blackout restart device for a voltage type inverter according to the present invention, and FIG. 2 is a time chart for explaining the operation. 1 ... AC power supply, 2 ... Forward converter, 3 ... Smoothing capacitor, 4,5 ... Electromagnetic contactor contact, 6 ... Bypass resistor, 7 ... Inverse converter, 8 ... Induction motor ( IM), 9 ...
… Speed setter, 10 …… Linear acceleration circuit (LAD), 11
...... Switching contact, 12 ...... Frequency control circuit, 13 ...... Voltage control circuit, 14 ...... PWM waveform synthesis circuit, 15 ...... AN
D circuit, 16 ... Relay contact, 17 ... Switching drive circuit, 18 ... Voltage comparison circuit, 19 ... Rotation speed detection circuit, 20 ... DC current detector, 21 ... Instantaneous power failure detection circuit, 22 ... ... control circuit.

Claims (1)

[Claims] 1. A forward conversion unit, an inverse conversion unit, a smoothing capacitor connected between the forward conversion unit and the inverse conversion unit, and an induction motor driven by the output of the inverse conversion unit. In a voltage-type inverter device of a method of variable speed control of an induction motor according to a predetermined speed command, a DC side bypass means for forcibly attenuating the residual magnetic flux of the induction motor at the time of momentary power failure, and the inverse conversion unit. A first opening / closing means connected between the DC side and the smoothing capacitor, a second opening / closing means connected between the DC bypass means and the DC side of the inverse converter, and operated by the occurrence of an instantaneous power failure. And a control means for starting the first opening / closing means after stopping the frequency control operation of the inverse conversion unit by the speed command at the time of occurrence of the instantaneous blackout by the control means. Movement to close the opening and closing means of 2 And the operation of monitoring the current flowing through the DC bypass means is started, and when the current flowing through the DC bypass means decreases to a predetermined value after power recovery, the operation of closing the first opening / closing means and the second operation. The opening and closing means and the operation of controlling the output frequency of the inverse converter by detecting the rotation speed of the induction motor from the current flowing on the DC side of the inverse converter, and thereafter, the speed command A momentary blackout restart device for a voltage type inverter, characterized in that, when the rotational speed of the induction motor is reached, control is performed to return to the frequency control operation of the inverse conversion unit by the speed command.