JPH01190293A - Controller for induction motor - Google Patents

Abstract

PURPOSE:To prevent an induction motor from being stopped due to load fluctuation, by feeding the V-F pattern of constant output voltage and output frequency to the induction motor regardless of the fluctuation of line voltage. CONSTITUTION:A control circuit section 7 together with a micro-computer 10 is composed of a DC/DC converter circuit 12 and a V/F converter circuit 13. By the DC/DC converter circuit 12, the DC voltage of an inverter 5 is DC/ DC-converted to generate the driving power source of the control circuit section 7, and by the V/F converter circuit 13, the frequency conversion of line voltage fed to an inverter section 4 is performed. By the micro-computer 10, regardless of the fluctuation of the DC line voltage and with the V-F pattern of constant output voltage and output frequency and with optimum voltage for primary current coming to a minimum, an induction motor 6 is driven.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for an induction motor used in a compressor or the like, and particularly to a control device incorporating an inverter device that performs variable frequency control.

[Conventional technology]

An example of a device for variable speed control of an induction motor is disclosed in the specification of Japanese Patent Application No. 61-43023.

FIG. 13 is a circuit configuration diagram showing a conventional example. In the figure, 1 is an AC power supply, 2 is a converter section that converts the AC input from the AC power supply 1 into DC, 3 is a smoothing capacitor, and 4 is a smoothing capacitor. The inverter device 5 is an inverter unit that converts the DC current into alternating current at an arbitrary frequency. 6 is an induction motor which is a load of the inverter device 5, and 7 is a control circuit section of the inverter device 5, which constitutes an overload region determining means. That is, this control circuit section 7 includes a voltage detection circuit 8 for the AC voltage applied to the inverter device 5 and a comparator 9 that compares the detected value with a reference value, and detects the overload region from the comparison result of the comparator 9. Determine. 10 is a microcomputer (hereinafter referred to as microcomputer) that outputs an arbitrary frequency command to the inverter unit 4; 11 is a data storage unit that stores V-F pattern data of the output voltage and output frequency of the inverter unit 5; .

FIG. 14 is a diagram showing data of the V-F pattern of the inverter device 5 that drives the induction motor 6. In the figure, curve A is data for a normal steady load region, and curve B is dedicated data for an overload region. The characteristics of this overload region are the voltage (V, +oZ) at the lowest output data.
is higher than the voltage (V, n, .) in the steady load region. The microcomputer 10 then drives the inverter section 4 based on the conditions of these data.

In the above configuration, when the inverter section 4 is operating in a steady load region, for example, if it is used for the induction motor 6 or the compressor of an air conditioner, when the outer peripheral temperature changes and the inverter section 4 shifts to the overload region, the induction The current of the motor 6 increases and the voltage applied to the inverter device 5 gradually decreases. At this time,
A detection signal corresponding to the voltage applied to the inverter device 5 is inputted to the comparator 9 through the pressure detection circuit 8 and compared with a reference voltage signal for comparison.Here, the applied voltage If the comparator 9 outputs an "H" (high level) signal when the signal decreases, the microcomputer 10 to which the comparator 9 inputs the "H" signal at this time is dedicated as shown by curve B in Figure 13. The inverter device 5 converts the signal with the V-F characteristic of
Output to. As a result, a voltage higher than that of the bait port is outputted to the induction motor 6, and the current flowing through the induction motor 6 decreases.

On the other hand, if the comparator 9 outputs a signal of "'L" (low level), it is determined that the load is in the steady load region, and a signal with the normal V-F characteristic shown by curve A in FIG. Output to the inverter device 5.

In this way, the control circuit section 7 determines the overload region, and when the overload region is entered, the induction motor 6 is driven with a V-F pattern different from the V-F pattern in the steady load region. Therefore, excessive current flowing through the induction motor 6 can be suppressed.

[Problem to be solved by the invention]

However, in the above-mentioned control device, when entering a certain overload region, the output turn of the inverter device is changed to suppress the current flowing to the induction motor, but there is a difference between the steady load region and the overload region. If a sudden load change occurs during a period of time, or if a load change that causes an excessive overload occurs, a current exceeding the overcurrent protection level will flow through the semiconductor elements used in the inverter, so the induction motor should not be used. There was a problem in that the induction motor had to be stopped and the induction motor could not continue to operate. Furthermore, there is a problem in that the primary current of the induction motor is not minimized, making it impossible to save energy.

This invention was made with a focus on these problems, and it is possible to continue operation without stopping the induction motor even if sudden or excessive load fluctuations occur.
The present invention also provides an induction motor control device that can save energy.

[Means to solve the problem]

The induction motor control device of the present invention has a converter section that converts input alternating current into direct current, and an inverter section that converts the direct current back into alternating current at a given frequency, and the induction motor is variable from the inverter section to the induction motor. In a control device having a built-in inverter device that provides a frequency output, there is provided a voltage discrimination means for discriminating the DC power supply voltage supplied to the inverter section, and an optimum drive voltage for discriminating the drive voltage at which the primary current of the induction motor is minimized for each frequency. Control for driving the induction motor at a constant output voltage and output frequency pattern regardless of fluctuations in the DC power supply voltage and at an optimal voltage that minimizes the primary current based on voltage discrimination means and the discrimination results. It is equipped with a section.

[Effect]

In the induction motor control device of the present invention, the voltage determining means determines the DC power supply voltage supplied to the inverter section, and even if the voltage varies, the control circuit section maintains a constant output voltage and output frequency pattern. An induction motor is driven. Further, the optimum voltage determining means determines whether the driving voltage minimizes the primary current of the induction motor for each frequency, and the induction motor is driven with that voltage.

〔Example〕

FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention, and the same reference numerals as in the conventional FIG. 13 indicate corresponding parts.

In the figure, 1 is an AC power supply, 2 is a converter unit that converts the AC input from the AC power supply 1 into DC, 3 is a smoothing capacitor, and 4 is an inverter unit that converts the smoothed DC back into AC of an arbitrary frequency. These elements constitute the inverter device 5. 6 is an induction motor to which a variable frequency output is given from the inverter unit 4; 7 is a control circuit unit that controls the inverter unit 5; 10 is a microcomputer that outputs an arbitrary frequency command to the inverter unit 4; 11 is the output of the inverter unit 5. 12.13 Data storage unit storing V-F pattern data of voltage and output frequency
constitute the control circuit section 7 together with the microcomputer 10, the C/DC converter circuit and the ? ``This is a V/F converter circuit that performs pressure-frequency conversion, and the DC/DC converter circuit 12 converts the DC voltage V1 of the inverter device 5 from DC to DC to generate the drive power for the control circuit section 7,
The /F converter circuit 13 performs frequency conversion of the power supply voltage supplied to the inverter section 4. 14 is a current transformer that detects the primary current of the induction motor 6.

The V/F converter circuit 13 constitutes a voltage discrimination circuit for the DC power supply voltage V1 supplied to the inverter section 4, and compares its output frequency value with an arbitrary set reference value to determine the fluctuation of the power supply voltage V. is determined. Also, microcontroller 10
, the V/F converter circuit 13, and the current transformer 14 constitute an optimum voltage determining means for determining the drive voltage at which the primary current of the induction motor 6 is minimum for each frequency. This optimum voltage determining means varies the output voltage to the induction motor 6 in an arbitrarily set range to determine the drive voltage at which the primary current is minimum. Based on these determination results, the microcomputer 10 determines the V-F of a constant output voltage and output frequency regardless of fluctuations in the DC power supply voltage.
This corresponds to a control unit that drives the induction motor 6 in a pattern and at an optimum voltage that minimizes the primary current.

Figure 2 shows the DC/DC converter circuit 12 and V/F.
3 is a circuit diagram showing details of a converter circuit 13. FIG. D.C.
/DC converter circuit, 15 is a switching transformer, 16 is a switching transistor, 17.18 is a resistor and a capacitor that define the operating frequency of the circuit, 19
is a Zener diode, 20.21 is a resistor and capacitor connected in parallel, and 22 is a switching transistor 16.
A reverse bias circuit is formed by a diode that accelerates the OFF time of the switch. 23 is a rectifying diode, 2
4 is a smoothing capacitor, and the smoothed direct current is inputted to the input circuit 7a of the control circuit section 7 as a driving power source as described above.

In addition, in the V/F converter circuit, 25 is a diode, 2
6 is a capacitor, 27 is a Zener diode, 28 is a resistor, 29 is a transistor, and 30 is a capacitor, which generate the power supply voltage for the circuit. 31 is a conversion timer IC that converts the signal of the primary voltage (2) of the above 'tg and iJ'i voltage generators into a frequency signal, and this IC31 is a CR charging/discharging circuit consisting of resistors 32, 33 and capacitor 34. The time for outputting the frequency signal is defined by Also, resistors 32, 33, capacitor 34
The timer IC 31 constitutes an astable oscillation circuit. This V/F converter circuit 13 has a D
The above voltage signal is input from the secondary winding of the switching transformer 15 in the C/DC converter circuit.

FIG. 3 shows the power supply voltage V supplied to the inverter section 4.
, and the voltage generated in the secondary winding of the switching transformer 15 of the DC/DC converter circuit 12.

FIG. 4 shows the microcomputer 10 from the V/F converter circuit 13.
FIG. 3 is a diagram showing the relationship between the frequency F outputted to the primary voltage V2 and the primary voltage V2.

5I2I is a diagram showing a V-F pattern of the output voltage and output frequency given to the induction motor 6 from the inverter unit 4 described above.

FIG. 6 is a diagram showing the relationship between the voltage output from the inverter section 4 to the induction motor 6 and the primary current of the induction motor 6.

Next, the operation will be explained with reference to the above-mentioned FIGS. 3 to 6.

When the inverter device 5 is operating under a steady load, for example, when the voltage of the AC power source 1 decreases, the voltage v1 supplied to the inverter section 4 also decreases, and the current flowing to the induction motor 6 increases rapidly. At this time, the voltage of the secondary winding of the switching transformer 15 of the DC/DC converter circuit 12 to which the voltage v1 is input has a linear function characteristic in which the feedback value is the value of the voltage V1, as is well known. Therefore, V/
There is a characteristic shown in FIG. 3 between the voltage v2 for the F converter circuit and the voltage vl.

The frequency characteristics obtained from the CR charging/discharging circuit of the V/F converter circuit 13 are as shown in FIG. If VH2 is the voltage when V decreases, then VH2<Vll, V22<V2
1, and a frequency signal of F12[+1□] is output to the microcomputer 1o. In microcomputer 10, the frequency is F+2
When a signal of [+1°] is input, the above reference value Fz[H
z].

At this time, since F,□<F,, the microcomputer 1o changes the V-F pattern of the output voltage and output frequency given to the induction motor 6 from the inverter section 4 to the characteristics A to D shown in FIG. , the induction motor 6 is driven at a voltage ΔV higher than the same frequency F. At this time, the voltage V output to the induction motor 6 can be expressed by the following equation, and no matter what value the frequency output from the V/F converter circuit 13 changes, that is, the voltage V output to the inverter section 4 supplied voltage v1
Even if the value fluctuates, it is possible to always supply the induction motor 6 with a V-F pattern output having a constant output voltage and output frequency.

After controlling the induction motor 6 at variable speed using the V-F pattern with a constant output voltage and output frequency, for example, in the case of an air conditioner, if the room temperature, which is the load, and the frequency are stabilized, each There are characteristics as shown in FIG. 6 between the output voltage for each frequency and the primary current of the induction motor 6, and there is an optimum operating point where the primary current is minimum. Therefore, as described above, the microcomputer 10 increases or decreases the voltage currently being output to the induction motor 6 in an arbitrarily set range of ΔV, and the current transformer 1 detects the primary current of the induction motor 6.
4, the minimum voltage value, that is, the minimum primary current value is determined, and the induction motor 6 is driven at the optimum voltage. FIG. 7 shows a flowchart of the above-mentioned operation.

In this way, the V-F pattern of the output voltage and output frequency supplied to the induction motor 6 is set to a pattern with constant characteristics even if the power supply voltage supplied to the inverter unit 4 fluctuates, so that Due to sudden load changes between the steady load region and the overload region, or in the region above the predetermined overload region, the load current exceeds the current protection level of the semiconductor used in the inverter section 4, and as a result, the inverter device 5 will not stop and the induction motor 6 will not be able to continue operating and will not stop.

In addition, since the voltage output to the induction motor 6 is set so that the primary current is the minimum when the frequency is stable, the inverter device 5
It is possible to achieve the original purpose of energy saving in air conditioners and the like that have a built-in device.

FIG. 8 is a circuit diagram showing a second embodiment of the invention. In this embodiment, the control circuit section 7 is provided with a comparison circuit 35 for comparing the output signal (frequency signal) of the V/F converter circuit 13 with an arbitrarily set reference value. C/D C conharc circuit 12. V/F converter circuit 13. and details of the comparison circuit 35 are shown. The same reference numerals as in FIG. 2 indicate the same parts, 36 is a photocoupler for electrically insulating the V/F converter circuit 13 and comparison circuit 35, and 37 is a photodiode in the photocoupler 36. Resistor to limit current, 38 &
1 comparator, 39.40 is a resistor that defines a reference voltage value for comparison and judgment, 41.42 is a fixed resistor, 43 is a capacitor for integrating the frequency signal output from the V/F converter circuit 13, 44 is a diode for preventing leakage to other than the resistor 42 when the capacitor 43 is discharged.

Further, FIG. 10 is a waveform diagram showing the frequency signal output from the V/F converter circuit 13, and FIG.
FIG.

The operation of the circuit shown in FIG.
The output of the pattern is supplied, and the induction motor 6 is driven at the optimum voltage that minimizes the primary current when the frequency is stable.

Here, in order to correspond to the development of an inexpensive air conditioner using the microcomputer 10, for example, the power supply voltage v1 of the control circuit section 7 is
After startup, the V/F converter circuit 13 is sent to the microcomputer 10.
If the output frequency is not input, the above (a)
Formula V=KX■・×−′! -! - In [■], the value of F8 is set to F, , [+1·]. This makes it possible to perform control equivalent to that of conventional inverter devices, and
Converter circuit 13. The cost of the current transformer 14 can be reduced.

As is well known, the oscillation characteristics of the DC/DC converter circuit 12 exhibit stable characteristics above any input terminal 71, but when the voltage drops below V, the voltage of the control circuit 7 suddenly changes. This decreases the protection function of the inverter device 5, and there is a risk that the semiconductor elements used in the inverter device may be destroyed. At this time, if the circuit is protected until the voltage V1 drops to vmin [V], and if VI2 [V] is the protection level, then the frequency signal from the V/F converter circuit 13 is used to protect the circuit as shown in FIG. A voltage 3 is generated between the collector and emitter of the phototransistor in the phytocoupler 36. When this voltage signal of voltage V3 is input to the comparator 38 via the diode 44, the voltage V3 is changed by the resistor 42 and capacitor 43 as shown in FIG.
4 integral waveforms are obtained. The voltage V4 of this integral waveform is
Since the value changes depending on the charging time of the capacitor 43,
By setting the value of the resistor 39.40 so that the voltage ■1□ at the frequency F +2 [Hz] reaches the reference voltage value v5, a protective operation signal is obtained from the comparator 38 when the voltage drops.

That is, when the output frequency signal of the V/F converter circuit 13 is not input to the control circuit section 7 after the power supply rises, the inverter section 4 is driven by assuming that the output frequency is an arbitrary value. Furthermore, if the output frequency of the V/F converter circuit 13 is smaller than an arbitrarily set reference value when driving the inverter section, the inverter device 5 is stopped.

In this way, control is switched between the conventional inverter device and the inverter device of the above embodiment depending on the presence or absence of the output frequency from the V/F converter circuit 13 after the power supply of the control circuit section 7 of the inverter device 5 is turned on. Therefore, it is easy to develop inexpensive inverter devices and highly reliable inverter devices. Furthermore, V of the power supply voltage determining means
Since the frequency data from the /F converter circuit 13 is used to detect when the frequency drops, that is, when the power supply voltage drops, it is possible to reliably protect the circuit of the inverter control section and protect the semiconductors in the inverter device. Destruction of the element can be prevented.

Further, FIG. 12 shows a third embodiment of the present invention, and in this embodiment, the above-mentioned optimum voltage determining means or the means for determining the minimum point of the current flowing into the inverter section 4 is used. There is. That is, the induction f and the minimum point of the motor's primary current are detected by detecting the current flowing into the inverter section 4 using the current transformer 14, and even with this configuration, it is different from the above embodiments. It has a similar effect.

〔Effect of the invention〕

As explained above, according to the present invention, a means for determining the power supply voltage supplied to the inverter section is provided, and a V-F pattern of a constant output voltage and output frequency is provided to the induction motor even when the power supply voltage fluctuates. Since the induction motor is supplied with the same amount of power, it is possible to prevent the induction motor from stopping due to load fluctuations, and there is an effect that the induction motor can be continuously operated. Additionally, during variable speed control, when the frequency is stabilized, an optimal voltage determination means is provided to determine the drive voltage that minimizes the primary current of the induction motor, and the induction motor is driven at that optimal voltage, resulting in energy savings. This has the effect of being able to achieve this goal.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention, and FIG.
The figure shows the DC70C converter circuit in Figure 1 and the V/
A circuit diagram showing details of the F converter circuit, Fig. 3 is a diagram showing the relationship between the power supply voltage supplied to the inverter section and the voltage of the secondary winding of the switching transformer in the DC70C converter circuit, and Fig. 4 is a diagram showing the switching A diagram showing the relationship between the voltage of the secondary winding of the transformer and the frequency output from the V/F converter circuit, Fig. 5 is a diagram showing the V-F pattern of the output voltage and output frequency of the inverter section, and Fig. 6 7 is a flowchart showing the operation of the circuit of FIG. 2, and FIG. 8 is a circuit showing a second embodiment of the present invention. 9 is a circuit diagram showing details of the DC70C converter circuit, V/F converter circuit, and comparison circuit in FIG. 8, and FIG. 10 is a frequency signal output from the V/F converter circuit in FIG. 9. 11 is a characteristic diagram of the comparison circuit shown in FIG. 10, FIG. 12 is a circuit configuration diagram showing a third embodiment of the present invention, and FIG. 13 is a circuit configuration diagram of a conventional induction motor control device. , FIG. 14 is a diagram showing a V-F pattern of the output voltage and output frequency of the inverter device in FIG. 13. 1... AC power supply 2... Converter section 4... Inverter section 5... Inverter device 6... Induction motor 7... ... Control circuit stage 15 ... Switching transformer 35 ...
・Comparison circuit Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] An inverter comprising a converter section that converts input alternating current into direct current, and an inverter section that converts the direct current back into alternating current of an arbitrary frequency, and provides a variable frequency output from the inverter section to an induction motor. A control device for an induction motor having a built-in device includes a voltage determining means for determining a DC power supply voltage supplied to the inverter section, and an optimum voltage determining means for determining a driving voltage at which the primary current of the induction motor is minimum for each frequency. and a control unit that drives the induction motor at a constant output voltage and output frequency pattern regardless of fluctuations in the DC power supply voltage and at an optimal voltage that minimizes the primary current, based on the determination results. A control device for an induction motor, characterized by comprising: