JPH01103194A - Controller for voltage type inverter - Google Patents

Abstract

PURPOSE:To switch from a commercial power source to inverter operation smoothly, by bringing a voltage command and an output from a voltage regulating means to zero before switching is made. CONSTITUTION:Upon interruption of a commercial power source 15, a frequency command holding circuit 21 maintains the frequency command at the frequency of the commercial power source 15. A first slow reset circuit 36 brings the amplitude of a voltage command to zero simultaneously with interruption of the commercial power source 15, and recovers the voltage command slowly upon elapse of predetermined time after the time point when residual voltage drops below a predetermined level. A second slow reset circuit 37 brings the output from a voltage regulating circuit 6 to zero simultaneously with interruption of the commercial power source 15, and recovers the output from the voltage regulating means slowly when the residual voltage drops below the predetermined level. A frequency modifying circuit 23 detects current of an AC motor 10 and modifies the frequency command to a frequency corresponding to the speed of the AC motor 10.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a method for smoothly transferring an AC motor running on a commercial power source to a voltage source inverter that outputs variable voltage and variable frequency AC, without stopping the AC motor. The present invention relates to a control circuit for a voltage source inverter that can be switched.

(Prior art) A rectifier as a power supply side converter that converts alternating current supplied from a commercial power source into direct current, a smoothing capacitor that absorbs and removes ripples in the direct current output from the rectifier, and Conventionally, speed control was extremely difficult by constructing an inverter device with a voltage source inverter as a load-side converter that converts direct current to alternating current at the desired voltage and frequency, and connecting an induction motor to this inverter device. Such inverter devices are widely used because the induction motor can be easily operated at variable speeds.

By the way, the rectifier that makes up this inverter device,
Alternatively, if the voltage source inverter fails, the induction motor becomes inoperable. However, if the load connected to this induction motor is of a type that cannot be interrupted,
If the power source is switched to commercial power as soon as a failure is detected in the inverter device, the motor can continue to operate without interruption, although its speed cannot be controlled.

Once the abnormality in the inverter device has been eliminated, the induction motor returns its power from the commercial power supply to the inverter device, but in this case as well, the motor cannot be stopped, so the power is turned off while it is still running. Therefore, by connecting this inverter device in parallel to the commercial power source that is driving the induction motor, and then shutting off the commercial power source, the motor drive power source can be smoothly switched from the commercial power source to the inverter device.

However, in order to connect an inverter device in parallel to a commercial power source, it is first necessary to detect the synchronization state of both devices, that is, the matching of voltages, matching of frequencies, and matching of phases. The device has the disadvantage of being complex and expensive.

Therefore, when switching the power supply of an electric motor running on commercial power to an inverter device, first cut off the commercial power and allow this electric motor to rotate freely. A method has come to be adopted in which the inverter is connected to an inverter and the AC output from the inverter is used to continue operation.

(Problem to be Solved by the Invention) By the way, when a freely rotating induction motor is restarted by applying AC from an inverter device by cutting off the commercial power supply, the frequency of the AC output by the inverter device and If the frequency corresponding to the speed at the point when the induction motor resumes operation does not match, a problem will occur.In other words, if the output frequency of the inverter device is higher, a large transient current will flow to the motor. As a result, the overcurrent protection device will activate and stop the operation.Furthermore, if the output frequency of the inverter is lower, reverse power will flow in from the motor side and the voltage will rise abnormally, causing an overvoltage trip. As a result, the device will still stop.

That is, the motor reduces its speed during the free rotation period, so when the power is switched and it resumes operation,
It is important that the speed of this motor is accurately known. Therefore, a speed transmitter is combined to detect the motor speed, but this requires a non-standard motor and an expensive speed transmitter, which is inconvenient due to many factors that increase costs. It is. Therefore, there is a method of detecting the frequency of the voltage remaining in the armature of a freely rotating induction motor without using a speed transmitter, but this residual voltage frequency detection device is complicated and expensive. It has its drawbacks.

Therefore, an object of the present invention is to smoothly switch an AC motor driven by a commercial power supply to a voltage type inverter capable of variable speed drive without using an expensive motor speed detection means. The objective is to provide a control circuit that allows the

[Means for solving the problems] In order to achieve the above object, the control circuit of the present invention has the following features:
A voltage command means that outputs a voltage command value with a frequency and amplitude corresponding to the frequency command value output by the frequency setting means, a voltage detection means that detects the voltage of the AC motor, and a deviation between these voltage command values and the voltage detection value. a voltage regulator that outputs a control signal that makes the voltage zero, and a voltage-type inverter that outputs alternating current at a desired voltage and frequency, and a commercial power source; A device that cuts off the commercial power supply, allows the motor to freely rotate, and resumes operation with the alternating current output from the voltage source inverter when the residual voltage of the alternating current motor detected by the voltage detection means becomes a predetermined value or less. a frequency command holding means for maintaining the frequency command value at the frequency value of the commercial power supply at the same time as the commercial power supply is cut off; A time limit means and a first gradual return means for slowly recovering the voltage command value after a predetermined period of time has elapsed since the voltage has fallen below the specified value; a second voltage regulator that gently restores the output of the voltage regulating means when the voltage becomes less than the same predetermined value as above
and a frequency change that detects the current of the AC motor and changes the frequency command value to a frequency value corresponding to the speed of the AC motor when the amplitude of the voltage command value increases by the 11th Y & return means. and command means.

[Effect]

In this invention, when switching the power source of an AC motor running on a commercial power source to a voltage-type inverter that outputs variable voltage/variable frequency AC, the commercial power source is first cut off and the motor is brought into a free rotation state. However, at this time, the frequency command value of the voltage source inverter remains the same as the frequency of the commercial power supply, the amplitude of the voltage command value and the output of the voltage adjustment means are set to zero, and the residual voltage of this motor is set to a predetermined value. At the point when the voltage has decreased to below, the output of the voltage regulating means is restored, and the voltage source inverter and the AC motor are connected, and after a certain period of time has elapsed from this point, the amplitude of the voltage command value is slowly restored, and at that time, By detecting the current flowing through the motor and acting on the frequency changing means, the frequency command value is changed to a value that matches the motor speed at that time, and this is done when the power source is switched from a commercial power source to a voltage source inverter. The purpose is to smoothly resume operation of the AC motor.

〔Example〕

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

In FIG. 1, a voltage-type pulse width modulation inverter (hereinafter abbreviated as a PWM inverter) 9 composed of transistors is provided in order to operate the induction motor IO at variable speed. The illustration of a rectifier that supplies DC power to and a commercial power source to which this rectifier is connected is omitted.

The basic parts of the control of the voltage source inverter are the frequency setter 11 acceleration/deceleration calculation circuit 2, sine wave generation circuit 3, function generation circuit 4, multiplication circuit 5, of the embodiment circuit shown in FIG.
It is composed of a voltage adjustment circuit 6, a carrier generation circuit 7, a modulation circuit 8, and a voltage 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 voltage command means constituted by a sine wave generating circuit 3, a function generating circuit 4, and a multiplier circuit 5, and the sine wave generating circuit 3 generates an amplitude proportional to the input signal. The function generating circuit 4 outputs a sine wave signal in which 1 is 1, and the function generating circuit 4 generates the amplitude of the voltage command value that has a predetermined functional relationship with respect to the input signal, so the multiplier circuit 5 multiplies both. As a result, a voltage command value corresponding to the frequency command value can be obtained. On the other hand, since a voltage detection value is obtained from the terminal voltage of the induction motor 10 via the voltage detection circuit 11, the deviation between these voltage command values and the voltage detection (direct) is calculated, and this calculation result is input to the voltage adjustment circuit 6. Then, the voltage 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. By performing pulse width modulation using the PWM inverter 9, a pulse train signal is created to sequentially turn on and off each transistor constituting the PWM inverter 9.Thus, with this pulse train signal, the PWM inverter 9 outputs
It is possible to output alternating current with desired voltage and frequency.

In the present invention, the basic circuit of the voltage source inverter described above includes a frequency command holding circuit 21, a current transformer 22, a frequency change circuit 23, a power failure detection circuit 31, a residual voltage setting device 32, a residual voltage detection circuit 33, and a logic circuit. 34, timer 35, first
By adding the No. 11 recovery circuit 36, the second slow recovery circuit 37, and the multiplication circuit 38, the embodiment circuit shown in FIG. .

If the contact 16A of the power supply switching circuit 16 is closed and the contact 16B is opened, the induction motor 10 is connected to the commercial power supply 15, so the induction motor 10 operates at a speed corresponding to the frequency of the commercial power supply 15. ing.

When a power switching command is issued here, the contact 16 of the power switching circuit 16 is activated according to a control sequence (not shown).
Since the circuit is opened, the driving power of the induction motor 10 is cut off and the induction motor 10 becomes in a free rotation state, so that the speed of the induction motor 10 is gradually reduced according to the flywheel effect possessed by the motor 10. Further, following the opening of this contact 16A, the contact 16B is closed, and the PWM inverter 9
However, at this time, since the base of the transistor constituting the PWM inverter 9 is cut off, the induction motor 10 continues to rotate freely.

The above-mentioned power supply switching command is also input to the switching signal detection circuit 31 at the same time, and the switching signal outputted from the switching signal detection circuit 31 via the logic circuit 34 is sent to the PWM inverter 9.
As mentioned above, the main circuit output is turned off by cutting off the base, and at the same time, the acceleration/deceleration calculation circuit 2
, a command to maintain the frequency command value at that time, that is, the same value as the frequency of the commercial power supply 15 is given.

Furthermore, the switching signal No. 13 outputted from the logic circuit 34 is inputted to the first gradual return circuit 36 via the timer 35 and makes its output zero, so that the acceleration/deceleration calculation circuit 2 outputs the commercial power
Although the frequency command value having the same value as the frequency of No. 5 is output, the amplitude amount of the voltage command value becomes zero. Further, the switching signal output from the logic circuit 34 is transmitted to the second gradual return circuit 3.
7 to make its output zero, even if there is an offset in the output of the voltage adjustment circuit 6, the voltage command value outputted via the multiplier circuit 38 is zero.

The residual voltage detection circuit 33 compares the voltage detection value outputted from the voltage detection circuit 11 and the value set by the residual voltage setting device 32 to determine that the residual voltage of the induction motor 10 during free rotation is a predetermined value. It is determined whether or not the following is true. The logic circuit 34 receives the signal output from the residual voltage detection circuit 33 and the signal output from the switching signal detection circuit 31, outputs a logic signal as a switching signal at the same time as the switching command is issued, and switches the power supply. The circuit is configured to output a logic H signal when the switching operation by the circuit 16 is completed and the residual voltage becomes equal to or less than the setting value of the residual voltage setter 32.

When the power supply switching circuit 16 completes the power supply switching, if the voltage remaining in the freely rotating induction motor 10 attenuates to below the above-mentioned set value, the output of the logic circuit 34 changes from a logic high signal to a logic high. Since the signal is switched to the signal, the base cutoff of the transistor is released, and the induction motor 10 is thereby switched to P.
Although coupled to the WM inverter 9, the logic H signal causes the output of the second slow recovery circuit 37 to be released from zero, causing the output to rise at a predetermined rate of change. Also, the 113th! Since the logic H signal is also given to the recovery circuit 36, after the time set by the timer 35 has elapsed,
The output of the 111th recovery circuit 36 also increases from zero at a predetermined rate of change.

In other words, when the residual voltage of the induction motor 10 during free rotation becomes equal to or less than a set value close to zero, and a logic H signal is output from the logic circuit 34, the base cutoff of the PWM inverter 9 is released and the induction motor 10 is turned off. is coupled, but the output of the PWM inverter 9 at this time is zero, and the induction motor 10 is still freely rotating while gradually decreasing its speed. When the set time limit of the timer 35 has elapsed, the output of the first!1 return circuit 36 starts to rise, so the frequency of the voltage command value remains the same as before, but its amplitude starts to increase from zero. That is, PWM inverter 9
Since the AC outputs a low voltage and a higher frequency than the speed of the induction motor 8110, current flows to the induction motor 10, but the PWM inverter 9
Since the output voltage is sufficiently low, there is no risk of excessive current.

The current transformer 22 detects this current and instructs the acceleration/deceleration calculation circuit 2 to change the frequency command value (actually, reduce the frequency command value) via the frequency change circuit 23. As a result, the frequency command value changes, and the PWM inverter 9 outputs an alternating current with a frequency that matches the speed of the induction motor 10 at that time, and the voltage also rises to a value related to this frequency, so it is normal. Recovery to operating state is completed.

FIG. 2 is an operation waveform diagram showing the operation of each part in the embodiment circuit shown in FIG. 1, in which FIG. Figure 2 (C) shows the operation of the base cutoff of the inverter 9, Figure 2 (C) shows the situation of the zero mister in the voltage regulation circuit, Figure 2 (D) shows the change in the amplitude of the voltage command value, and Figure 2 (E) shows the operation of the base cutoff of the inverter 9. is the change in the frequency f of the PWM inverter 9 and the speed N of the induction motor 10, and FIG.
Figure (g) shows the changes in the current of the induction motor lO.

In Fig. 2, at the same time as the issuance of the switching command to switch the power supply at time t, the closed contact 16^ of the power supply switching circuit 16 opens, and the output of the voltage regulation circuit 6 becomes zero and the voltage command value becomes zero. The amplitude amount becomes zero, the motor current also becomes zero, and the motor speed N decreases due to free rotation. At time tl, contact 16B closes and the power supply switching operation is completed, and furthermore, when the residual voltage becomes less than the set value at time tl, both the inverter's base cutoff and the voltage regulator circuit's zero limit are released. From time t3 to the time after the time limit set by the timer 35 has elapsed, the amplitude of the voltage 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. The induction motor 10 starts accelerating at the time t4 when this retraction is completed, and reaches the desired speed at time ts, completing the acceleration.

〔Effect of the invention〕

According to this invention, when switching the power source of an AC motor driven by a commercial power source to a voltage-type inverter that outputs alternating current of variable voltage and variable frequency, the commercial power source is first cut off and the AC motor is allowed to rotate freely. The frequency of the voltage command value of the inverter remains the same as the frequency of the commercial power supply, and only the amplitude is set to zero.
The output of the voltage adjustment means is also set to zero, and if the residual voltage of the motor is below a predetermined value when the power source is switched to the voltage type inverter, the motor is coupled to this voltage type inverter and the voltage is adjusted. The zero output of the means is canceled, and the amplitude of the voltage command value is gradually increased from zero, and the frequency of the alternating current output by the voltage source inverter at that time is set to a value that matches the motor speed at that time. By lowering the speed and pulling in this motor, the motor operation can be resumed after the power is switched. By eliminating the need for a voltage frequency detection means, it is possible to reduce the cost of the device and contribute to miniaturization, and at the same time, it is possible to restart operation smoothly without generating abnormal current or voltage when restarting operation.

[Brief explanation of the drawing]

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. l... Frequency setter, 2... Acceleration/deceleration calculation circuit, 3
...Sine wave generation circuit, 4...Function generation circuit, 5...
・Multiplication circuit, 6...Voltage adjustment circuit, 7...Kinaka rear generation circuit, 8...Modulation circuit, 9...PWM inverter, 10...Induction motor, 11...Voltage detection circuit ,
15... Commercial power supply, 16... Power supply switching circuit 1.16
A, 16B... Contact, 21... Frequency command holding circuit, 22... Current transformer, 23... Frequency changing circuit, 3
DESCRIPTION OF SYMBOLS 1... Switching signal detection circuit, 32... Residual voltage setting device, 33... Residual voltage detection circuit, 34... Logic circuit,
35...Timer, 3G-...1st EI return circuit, 37
River No. 211 return circuit, 38-...multiplication circuit. ￥ 2 Diagram

Claims (1)

[Claims] 1) Voltage command means for outputting a voltage command value of frequency and amplitude corresponding to the frequency command value output by the frequency setting means;
A voltage type that outputs alternating current at a desired voltage and frequency by a voltage detecting means that detects the voltage of an AC motor and a voltage adjusting means that outputs a control signal that makes the deviation between the voltage command value and the detected voltage value zero. The AC motor is equipped with an inverter and a commercial power source, and when the AC motor is operating on the commercial power source, the commercial power source is cut off by a power switching command to allow the motor to rotate freely, and the residual voltage of the AC motor detected by the voltage detection means is In a device that restarts operation by alternating current output from the voltage source inverter when the voltage falls below a predetermined value, frequency command holding means maintains the frequency command value at the frequency value of the commercial power source at the same time as the commercial power source is cut off. a time-limiting means for reducing the amplitude of the voltage command value to zero at the same time as the commercial power supply is cut off, and gradually recovering the voltage command value after a certain period of time has elapsed since the residual voltage became equal to or less than a predetermined value; and a second gradual return means that sets the output of the voltage regulating means to zero at the same time as the commercial power supply is cut off, and slowly recovers the output of the voltage regulating means when the residual voltage becomes equal to or less than the same predetermined value. and frequency change command means for detecting the current of the AC motor and changing the frequency command value to a frequency value corresponding to the speed of the AC motor when the amplitude of the voltage command value increases by the first gradual return means. A control circuit for a voltage source inverter, comprising: