JPS63274397A - Controlling circuit for magnetic flux controlling type inverter - Google Patents

Abstract

PURPOSE:To smoothly re-start operation after instantaneous stop, by resetting the output of a magnetic flux regulating means slowly at the point of time when the residual flux of a motor is reduced to come to a specified value or less on the instantaneous stop, and after that, by applying a magnetic flux command value and a frequency command value to. CONSTITUTION:When the residual flux of an induction motor 10 comes to a value approximating zero or lese on instantaneous stop and the output of signal H is generated from a logical circuit 34, then a PWM inverter 9 and the induction motor 10 are combined with each other. When a time is beyond the limit of the time set by a timer 35, than the output of a first slow reset circuit 36 starts increasing, and the amplitude of a magnetic flux command value starts increasing from zero. By a current transformer 22, current to the induction motor 10 is detected, and via a frequency changing circuit 23, to an acceleration or deceleration arithmetic circuit 2, the change of a frequency command value is commanded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a flux-controlled inverter that drives an AC motor at variable speed and can continue operating smoothly even if the power supply of the flux-controlled inverter is interrupted for a short time. Regarding control circuits.

[Conventional technology]

A rectifier as a power supply side converter that converts alternating current supplied from a commercial power source into direct current, a capacitor that absorbs and removes ripples in the direct current output from this rectifier, and a capacitor that converts the smoothed direct current to a desired voltage and frequency. By using an inverter device configured with an inverter as a load-side converter that converts AC into AC, it is possible to easily operate an induction motor at variable speed, which was extremely difficult to control in the past. Impark devices are widely used.

When an inverter device is supplied with AC power from a commercial power source, the commercial power source may experience a power outage due to line switching, lightning strikes, or other accidents.

When this power outage is for a long time, the motor is stopped and then restarted after the power is retransmitted, but even if the power outage is only for a short time, it is troublesome to stop the motor and then restart it. This will also reduce the operating rate of the equipment, so in the case of such a momentary power outage (hereinafter referred to as an instantaneous power outage), the motor is disconnected from the inverter and allowed to rotate freely as soon as the power outage occurs. It is convenient to leave the inverter control circuit in operation so that the motor can resume operation as soon as power transmission is resumed, reducing the need for equipment stoppages, and this method of operation is often used. It has started to be done. In order to operate the inverter control circuit even during a power outage, there are cases where a separate uninterruptible power supply is prepared, but it is necessary to use a so-called DC intermediate circuit that connects the DC side of the rectifier and the DC side of the inverter. The connected smoothing capacitor has a large capacitance, so if there is a short power outage, the electrical energy stored in it can be used as a power source to operate the control circuit. The uninterruptible power supply can be omitted and the cost required for this can be reduced.

[Problem that the invention seeks to solve]

By the way, when the momentary power outage is restored and the induction motor is restarted by the inverter, the frequency of the AC output by the inverter does not match the frequency corresponding to the speed of the induction motor at the time of restarting operation. , this will cause problems. In other words, if the output frequency of the inverter is higher, a large transient current will flow to the motor, causing the overcurrent protection device to operate and stop the motor. Also, if the inverter's output frequency is lower, reverse power will flow in from the motor side, causing the voltage to rise abnormally.
An overvoltage trip also causes the device to shut down.

That is, since the motor reduces its speed by free rotation during the instantaneous power outage, it is important that the speed of the motor is accurately known when the motor resumes operation after the instantaneous power outage is restored. Therefore, a speed transmitter is combined to detect the motor speed, but this requires a non-standard motor and an expensive speed transmitter, which increases the cost. This is inconvenient. Therefore, there is a method to detect the frequency of the voltage remaining in the armature of an induction motor that is freely rotating after a power outage without using a speed transmitter, but this residual voltage frequency detection device is complicated and expensive. It has some drawbacks.

SUMMARY OF THE INVENTION An object of the present invention is to smoothly resume operation without using expensive motor speed detection means when the power supply of an inverter that drives an AC motor at variable speed recovers from a momentary power failure.

[Means for solving problems]

In order to achieve the above object, the control circuit of the present invention includes:
A magnetic flux command means that outputs a magnetic flux command value with a frequency and amplitude corresponding to the frequency command value output by the frequency setting means, a magnetic flux detection means that detects the magnetic flux of the AC motor, and a deviation between these magnetic flux command values and magnetic flux detection values. and a magnetic flux adjustment means that outputs a control signal to make the voltage zero, outputs an alternating current of a desired voltage and frequency, and operates the alternating current motor at variable speed. , a magnetic flux control type inverter that allows the AC motor to rotate freely and resumes operation with the inverter if the residual magnetic flux detected by the magnetic flux detection means becomes a predetermined value or less when the power outage is restored after a short time; , frequency command holding means for maintaining the frequency command value at the value at that time upon detection of a power outage, and zeroing the amplitude of the magnetic flux command value at the same time as the power failure is detected;
a time limit means and a first slow recovery means for slowly recovering the magnetic flux command value after a certain period of time has passed after the power outage is restored and the residual magnetic flux becomes equal to or less than the predetermined value; and the magnetic flux adjusting means upon detecting the power outage. When the output of
a second gradual recovery means for slowly recovering the output of the flat means;
By the above-mentioned gradual return means! The apparatus includes frequency change command means for detecting the current of the AC motor when the amplitude of the R flux command value increases and changing the frequency command value to a frequency value corresponding to the speed of the AC motor.

[Effect]

In this invention, when the power supply of a magnetic flux control type inverter that drives an AC motor at variable speed is interrupted, the motor is allowed to rotate freely, but the frequency command value remains the value at that time, and the amplitude of the m flux command value is and the output of the magnetic flux adjustment means are set to 1, and when the power outage is restored after a short time, the output of the magnetic flux adjustment means is slowly restored when the residual magnetic flux of this motor decreases below a predetermined value, and the output of the magnetic flux control type inverter is and an AC motor, and after a certain period of time has elapsed from this point, the amplitude of the magnetic flux command value is slowly restored, and at that time, the current flowing to the motor is detected and the frequency change means is activated to change the frequency command value to the motor. By changing the value to match the speed, restarting operation after a momentary power outage can be smoothly performed.

〔Example〕

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

In FIG. 1, in order to operate the induction motor 10 at variable speed, a magnetic flux control type pulse width modulation inverter (hereinafter abbreviated as a PWM inverter) 9 composed of transistors is provided. 9
A rectifier that supplies power and a commercial power source to which this rectifier is connected are not shown.

A magnetic flux control type PWM inverter is, for example, disclosed in Japanese Patent Application Laid-open No. 1983
It is known from Japanese Patent No. 94585, and the basic parts of the control are as shown in FIG. It is composed of a circuit 5, a magnetic flux adjustment circuit 6, a carrier generation circuit 7, a modulation circuit 8, and a magnetic flux detection circuit 11.

That is, the output from the frequency setter 1 is converted by the acceleration/deceleration calculation circuit 2 into a frequency command value that changes at a predetermined rate of change. This frequency command value is input to a magnetic flux command means constituted by a sine wave generation circuit 3, a function generation circuit 4, and a multiplier circuit 5, and the sine wave generation circuit 3 has an amplitude proportional to the input signal. A sine wave signal of 1 is output, and the function generating circuit 4 generates the amplitude of the magnetic flux command value that has a predetermined functional relationship with respect to the input signal, so the multiplier circuit 5 multiplies the two. As a result, a magnetic flux command value corresponding to the frequency command value is obtained. On the other hand, since a magnetic flux detection value is obtained from the terminal voltage of the induction motor 10 via the magnetic flux detection circuit 11, the deviation between these magnetic flux command values and the magnetic flux detection value is calculated, and this calculation result is input to the magnetic flux adjustment circuit 6. Then, this magnetic flux adjustment circuit 6 outputs a voltage command signal for the PWM inverter 9 that should make the input deviation zero. This voltage command signal and the carrier signal output from the carrier generation circuit 7 are guided to the modulation circuit 8 and subjected to pulse width modulation, so that the PWM inverter 9
A pulse train signal is generated to sequentially turn on and off each transistor constituting the transistor. Therefore, this pulse train signal allows the PWM inverter 9 to output an alternating current with a desired voltage and frequency.

In the present invention, the basic circuit of the magnetic flux control type inverter described above includes a frequency command holding circuit 21, a current transformer 22, a frequency changing circuit 23, a power failure detection circuit 31, and a residual magnetic flux setting device 32.
, residual 6n bundle detection circuit 33, logic circuit 34, timer 35
, the first slow return circuit 3G, the second slow return circuit 37, and the multiplication circuit 38 constitute the embodiment circuit shown in FIG. Explain.

A power outage in the commercial power supply supplying power to the impark device including the PWM inverter 9 is detected by the power outage detection circuit 31, and this power outage signal is sent to the logic circuit B34.
is applied to the PWM inverter 9 through P
Since the gates of the transistors constituting the WM inverter 9 are cut off, the induction motor 10 is in a free rotation state from this point on, but at the same time, the frequency command holding circuit 2
1, a command to maintain the frequency command value at that time is given to the acceleration/deceleration calculation circuit 2.

The power outage signal output from the logic circuit 34 is input to the first FA recovery circuit 36 via the timer 35 and its output is made zero, so the acceleration/deceleration calculation circuit 2 outputs the frequency command value at the time of the power outage. Despite this, the amplitude of the magnetic flux command value is zero. Furthermore, the power outage signal output from the logic circuit 34 is also given to the second recovery circuit 37 to make its output zero, so even if there is an offset in the output of the magnetic flux adjustment circuit 6, the power outage signal is transmitted through the multiplication circuit 38. The output voltage command value is zero.

The residual magnetic flux detection circuit 33 compares the magnetic flux detection value outputted from the magnetic flux detection circuit 11 and the value set by the residual magnetic flux setting device 32 to determine that the residual magnetic flux of the induction motor 10 during free rotation is a predetermined value. It is determined whether or not the following is true. In addition, the logic circuit 34 inputs the signal output from the residual magnetic flux detection circuit 33 and the signal output from the power outage detection circuit 31, and outputs a logical signal as a power outage signal at the same time as a power outage occurs, so that the power outage is restored. Logic 11 is activated when the residual magnetic flux becomes equal to or less than the setting value of the residual magnetic flux setting device 32.
A circuit is configured to output a signal.゛When the commercial power supply is restored after a short period of time and the magnetic flux remaining in the freely rotating induction motor IO is attenuated and becomes less than the above-mentioned set value, the output of the logic circuit 34 changes from the logic signal. Since the signal is switched to a logic H signal, the induction motor a 10 is coupled to the PWM inverter again. However, due to this logic H signal, the output of the second slow return circuit 37 is released from the atmosphere, and the output is changed to a predetermined value. rate of increase. Furthermore, since the logic 1 signal is also given to the first slow return circuit 36 via the timer 35, after the time set by the timer 35 has elapsed, the output of the first slow return circuit 36 also changes from zero to a predetermined value. rate increases. .

That is, when the power outage is restored and the residual magnetic flux of the induction motor 10 becomes below a set value close to zero, and the logic circuit 34 outputs a logic H signal, the PWM inverter 9 and the induction motor 10 are coupled again. However, PWM inverter 9
The output of the induction motor 10 is zero, and the induction motor 10 is still rotating freely while gradually reducing its speed. When the set time limit of the timer 35 has elapsed, the 111th return circuit 36
Since the output of the magnetic flux command value starts to rise, the frequency of the magnetic flux command value remains the same as before, but its amplitude starts to increase from zero.

In other words, the PWM inverter 9 outputs an alternating current with a low voltage and a higher frequency than that corresponding to the speed of the induction motor 1O, so that this induction motor 1! Although current flows to the PWM inverter 10, there is no risk of excessive current because the output voltage of the PWM inverter 9 is sufficiently low.

The current transformer 22 detects this current and instructs the acceleration/deceleration calculation circuit 2 to change the frequency command value (actually lower the frequency command value tS) via the frequency change circuit 23. This changes the frequency command value. Then, the PWM inverter 9 outputs an alternating current with a frequency that matches the speed of the induction motor at that time, and the voltage also rises to a value related to this frequency, so that the normal operating state can be restored. Complete.

FIG. 2 is an operation waveform diagram showing the operation of each part in the embodiment circuit shown in FIG. Figure 2 (c) shows the operation of the base cutoff of the magnetic flux! l! Figure 2 (d) shows the situation of the zero limiter of the node circuit, Figure 2 (d) shows the change in the amplitude of the magnetic flux command value, Figure 2 (e) shows the change in the frequency f of the PWM inverter 90 and the speed N of the induction motor lO. FIG. 2(F) shows the change in the detected magnetic flux value, and FIG. 2(G) shows the change in the current of the induction motor 10.

In FIG. 2, when a power outage occurs at time to, the inverter base is cut off, the output of the magnetic flux adjustment circuit 6 is zero, the amplitude of the magnetic flux command value is also zero, the motor current is also zero, and the motor speed N is Free rotation reduces its speed. 1. When the power outage is restored at time t, and the residual magnetic flux becomes less than the set value at time t, both the inverter base cutoff and the zero limiter of the magnetic flux adjustment circuit are released.

At time t, after the time limit set by the timer 35 has elapsed from this time t□, the amplitude of the magnetic flux command value starts to increase from zero, so that current flows to the motor and adapts the inverter frequency r to the motor speed N. to complete the inverter retraction.

From the time L4 when this retraction is completed, the induction motor lO
The acceleration is completed when the desired speed is reached at time L.

〔Effect of the invention〕

According to this invention, when the power supply of the magnetic flux control type inverter that drives the AC motor at variable speed is interrupted for a short time, the electric motor is allowed to rotate freely at the same time as the power outage occurs, but the frequency of the magnetic flux command value of the inverter changes immediately before the power outage. While keeping the value of , only the amplitude is set to zero, and the output of the magnetic flux adjustment means is also set to zero. If the residual magnetic flux is below a predetermined value when the power is restored, the motor is reconnected and the output of the magnetic flux adjustment means is set to zero. To cancel the zero value, further raise the amplitude amount of the magnetic flux command value from zero, and lower the frequency of the alternating current output by the magnetic flux control inverter with the motor current at that time to a value that matches the motor speed at that time. By connecting this electric motor, the electric motor can be restarted after a momentary power outage. By eliminating the need for detection means, we can reduce the cost of the device and contribute to miniaturization.
Smooth operation can be resumed without generating abnormal current or voltage when restarting operation.

[Brief explanation of drawings]

FIG. 1 is a control block diagram showing an embodiment of the present invention,
FIG. 2 is an operational waveform diagram showing the operation of each part in the embodiment circuit shown in FIG. 1. 1... Frequency setter, 2... Acceleration/deceleration calculation circuit, 3
...Sine wave generation circuit, 4...Function generation circuit, 5...
- Multiplier circuit, 6... Magnetic flux adjustment circuit, 7... Carrier generation circuit, 8... Modulation circuit, 9... PWM inverter, 10... Induction motor, 11... Magnetic flux detection circuit,
21... Frequency command holding circuit, 22... Current transformer, 2
3... Frequency change circuit, 31... Power outage detection circuit, 3
2...Residual magnetic flux setting device, 33...Residual magnetic flux detection circuit, 34...Logic circuit, 35...Timer, 36...
First slow return circuit, 37... Second slow return circuit, 38...
・Multiplication circuit.

Claims (1)

[Claims] 1) magnetic flux command means that outputs a magnetic flux command value of frequency and amplitude corresponding to the frequency command value output by the frequency setting means;
It is equipped with a magnetic flux detection means for detecting the magnetic flux of an AC motor, and a magnetic flux adjustment means for outputting a control signal to zero the deviation between the magnetic flux command value and the magnetic flux detection value, and outputs an alternating current of a desired voltage and frequency. , if a power outage of the magnetic flux control type inverter that operates the AC motor at variable speed is detected, the AC motor is allowed to rotate freely, and when the power outage is restored after a short time, the residual magnetic flux detected by the magnetic flux detection means is In the magnetic flux control type inverter, which restarts operation of the inverter when the value falls below a predetermined value, the frequency command holding means maintains the frequency command value at the current value at the same time as a power outage is detected; a time-limiting means for reducing the amplitude of the magnetic flux command value to zero and slowly recovering the magnetic flux command value after a certain period of time has elapsed after the power outage is restored and the residual magnetic flux becomes equal to or less than the predetermined value; and a first gradual return means; , a second gradual return means that sets the output of the magnetic flux adjusting means to zero at the same time as a power outage is detected, and slowly recovers the output of the magnetic flux adjusting means when the power outage is restored and the residual magnetic flux becomes equal to or less than the predetermined value; ,
Frequency change command means detects the current of the AC motor when the amplitude of the magnetic flux command value increases by the first gradual return means, and changes the frequency command value to a frequency value corresponding to the speed of the AC motor. A control circuit for a magnetic flux control type inverter, characterized by comprising: