JPS5828830B2 - Induction motor speed control device - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a speed control device for an induction motor, and more particularly to a speed control device for an induction motor that uses a frequency conversion means to perform primary frequency control. be.

[Prior art]

Conventionally, it has been common to perform primary frequency control using frequency conversion means to control the speed of an induction motor.

Figure 1 is a circuit configuration diagram showing an example of a speed control device equipped with a conventional frequency conversion means for controlling an induction motor. 1 is a forward converter that converts alternating current sent from a commercial power source into direct current. , 2 is a DC reactor for smoothing the DC output current of the forward converter 1, 3 is an inverse converter that converts the DC sent from the forward converter 1 into three-phase AC, and 4 is driven by the inverse converter 3. 5 is a speed generator that outputs a DC signal (hereinafter referred to as a speed feedback signal or speed signal) proportional to the rotation speed of the induction motor 4; 6 is an induction motor 40;
a speed command circuit that outputs a signal that commands the number of rotations (hereinafter referred to as a speed command signal); 7 a speed deviation amplifier that amplifies a speed deviation signal obtained by comparing the speed command signal and the speed feedback signal; 8; 9 is a current detector that outputs a DC signal (hereinafter referred to as a current feedback signal) proportional to the AC input current of the forward converter 1, and 9 is a current obtained by matching the output signal of the speed deviation amplifier 7 with the current feedback signal. a current deviation amplifier for amplifying the deviation signal; 10 is an automatic pulse phase shifter for controlling the firing phase of the sirisk of the forward converter 1 according to the output signal of the current deviation amplifier 9; 11 is a slip of the induction motor 4; DC signal (hereinafter referred to as DC signal) for setting the frequency to a certain value
12 is a frequency command amplifier that amplifies the frequency command signal obtained by adding the speed signal and the slip frequency setting signal; 13 is a frequency command amplifier that outputs the frequency command signal; A voltage-frequency converter that outputs a signal with a proportional frequency; 14 is a voltage-frequency converter;
Each inverter gate amplifier receives the output signal of the frequency converter 13 at its input and outputs a gate signal for igniting the sirisk of the inverter 3.

The operation of the conventional induction motor speed control device having the above-mentioned configuration will be described below.

The speed command circuit 6, speed deviation amplification device 7, current detector 8, current deviation amplification device 9, automatic pulse phase shifter 10, etc. are configured to detect the magnitude of the output signal of the speed deviation amplification device 7, that is, the speed deviation signal. A control circuit for controlling the magnitude of the current of the induction motor 4 according to the current level is configured, and a slip frequency setting circuit 11. The frequency command amplifier 12, the voltage-frequency converter 13, and the inverse converter gate amplifier 14 constitute a control circuit for controlling the operating frequency of the induction motor 4.

In addition, in controlling the operating frequency, the operation is performed so that the relationship of operating frequency=rotation frequency+slip frequency is established.

That is, the output signal (speed signal) of the speed generator 5 is a signal proportional to the rotation frequency, and the output signal (slip frequency setting signal) of the slip frequency setting circuit 11 is a signal proportional to the slip frequency. Since the frequency of the output signal of the voltage-frequency converter 13 is determined in proportion to the magnitude of the sum signal, the operating frequency of the induction motor 4 is controlled so as to satisfy the above relationship.

By the way, in the conventional induction motor speed control device as described above, the slip frequency (
Since the frequency is controlled so that the slippage remains constant, the terminal voltage (excitation voltage) of the motor becomes excessive during overload, which may cause saturation of the iron core, resulting in inconveniences such as unsatisfactory operation. At the same time, the motor current becomes almost zero during no-load operation.
The main magnetic flux also disappears, and the next time a load is applied, it takes time to generate the main magnetic flux, and it takes a long time to generate sufficient torque.

That is, it has drawbacks such as slow torque response.

Furthermore, there was a problem that the unstable phenomenon during no-load operation caused by the above cannot be ignored.

[Purpose of the invention]

The present invention was developed in view of the drawbacks of the conventional induction motor speed control device as described above, and it eliminates the need to increase the motor voltage excessively during overload operation and prevent unstable phenomena during no-load operation. , and fast torque response during load fluctuations.
The present invention provides a speed control device for an induction motor that enables extremely stable operation.

[Summary of the invention]

The present invention provides a signal proportional to the rotational speed of an induction motor (hereinafter referred to as
A signal obtained by comparing a first signal having a certain functional relationship (proportional or close to it) with respect to the speed signal) and a second signal obtained by detecting the terminal voltage of the induction motor. obtaining a third signal having a 1:1 relationship and controlling the operating frequency of the induction motor so as to be proportional to a fourth signal obtained by adding the speed signal and the third signal; Therefore, extremely stable operation control of the electric motor is possible.

[Embodiments of the invention]

FIG. 2 shows a circuit configuration diagram of a speed control device for an induction motor according to an embodiment of the present invention, and 15 is an input current of the motor 4 at no load (for setting the magnitude of the excitation electric current). An excitation current setting circuit 16 outputs a signal (hereinafter referred to as an excitation current setting signal), an output signal of the speed deviation amplifier 7, a current feedback signal which is an output signal of the current detector 8, and an excitation current setting circuit 15. A current deviation amplifier that amplifies a current deviation signal obtained by matching three output signals, 1
7 is a DC signal (
A voltage detector that outputs a voltage feedback signal (hereinafter referred to as a voltage feedback signal), 18
19 is a voltage command generation circuit that outputs a voltage command signal for commanding the magnitude of the terminal voltage of the motor 4, which has a certain functional relationship with the speed signal that is the output signal of the speed generator 5; 19 is the voltage command signal; A voltage deviation amplifier 20 amplifies the voltage deviation signal obtained by matching the voltage feedback signal with the voltage deviation amplifier 20, which adds the speed signal which is the output signal of the speed engine 5 and the output signal of the voltage deviation amplifier 19. Each of the figures shows a frequency command amplifier that amplifies the obtained frequency command signal.

In the circuit configuration as described above, operations during overload operation and no-load operation will be described below.

Now, we will discuss the case where the load becomes even heavier from the state where the rated operation is being performed.

As the load increases, the speed deviation signal increases, and accordingly, the output current of the forward converter 1 and the input current of the motor 4 further increase from their rated values.

By the way, the excitation voltage E of the induction motor 4 is expressed by the following formula, where: 2 γ2' Secondary resistance converted to the secondary side: Secondary leakage reactance S converted to the primary side: Slip ■2': 1 Secondary current converted to the next side In conventional control devices, the slip frequency (slip S)
is controlled so that it remains constant regardless of the size of the load, so the excitation voltage E is proportional to the secondary current (approximately incoming current) In this case, the excitation voltage (approximately terminal voltage) becomes excessive, and saturation of the iron core may occur, making it impossible to operate satisfactorily.

However, in a configuration like the present embodiment described above, the slip frequency varies depending on the voltage deviation signal obtained by matching the voltage command signal, which is a substantially constant signal regardless of the load size, and the voltage feedback signal. is controlled, the excitation voltage will not become excessive even during overload.

This is because the terminal voltage of the motor 4 increases as the load increases, but at the same time the voltage deviation signal also increases, and the output signal of the voltage deviation amplifier 19 becomes the signal that controls the slip frequency. This is because the slip frequency (slip S) increases and acts to suppress an increase in terminal voltage.

Note that the amount of increase in the terminal voltage can be made sufficiently small by selecting a large gain for the voltage deviation amplifier 19.

Next, the operation during no-load operation will be described.

At this time, the magnitude of the speed deviation signal and the output signal of the speed deviation amplification device 7 becomes zero, but the excitation current setting signal sent from the excitation current setting circuit 15 and the current feedback signal are compared to correct the current deviation. Since the current is input to the amplifier 16, the output current of the forward converter 1 and the input current of the motor 4 maintain constant values corresponding to the excitation current.

On the other hand, at this time, the output signal of the voltage deviation amplifier 19 is set so that the slip S does not become negative due to the action of the negative voltage limiter, so the slip frequency becomes zero, and the input current flows while maintaining a constant value. Therefore, the electric motor 4 operates without load while maintaining a constant voltage (rated voltage).

Therefore, even if a load is applied to the electric motor during no-load operation, the voltage is already maintained and established, so it is possible to immediately draw out sufficient torque. Therefore, the torque response is extremely fast, and the torque response is It is possible to perform stable operation without instability caused by slow speed.

As described above, with the configuration of the present invention, it is possible to reduce the torque when the motor voltage is excessive during overload operation or when the load fluctuates due to conventional motor control, especially when a load is applied from a no-load operation state. It is possible to obtain a speed control device for an induction motor that eliminates problems such as slow response and unstable phenomena caused by slow torque response, and enables extremely stable operation.

Furthermore, what is shown in FIG. 3 is a circuit configuration diagram of a speed control device for an induction motor according to another embodiment of the present invention, and the difference from the above embodiment is the output signal of the speed generator 5. Instead of generating the voltage command signal based on the speed signal, the voltage command signal is generated based on the frequency command signal which is the output signal of the frequency command amplifier 20.

It is well known that good operation can be achieved if the motor voltage maintains a certain relationship (more or less proportional relationship) with the operating frequency, and this example also has the same effect as the above example. It is clear that the following can be obtained.

FIG. 4 shows still another embodiment of the present invention, in which 22 indicates a speed command signal for commanding the rotation speed of the induction motor 4 and a magnetic flux command signal for commanding the amount of main magnetic flux of the motor 4. 23 is a magnetic flux detector composed of a Hall element and the like that outputs a DC signal (hereinafter referred to as a magnetic flux feedback signal) proportional to the amount of main magnetic flux of the electric motor 4; 24 is a magnetic flux detector that outputs the magnetic flux command signal and the magnetic flux feedback signal; A magnetic flux deviation amplification device 25 amplifies the magnetic flux deviation signal obtained by matching the magnetic flux feedback signals, and is obtained by adding the speed signal, which is the output signal of the speed generator 5, and the output signal of the magnetic flux deviation amplification device 24. Each of the figures shows a frequency command amplifier that amplifies the frequency command signal.

This embodiment differs from the embodiment shown in FIG. 2 in that the circuit is configured so that the slip frequency is controlled in relation to the amount of main magnetic flux of the electric motor 4, and the amount of main magnetic flux and the operating frequency are Considering that the sum of the multiplication factors is approximately equal to the magnitude of the terminal voltage, by controlling the main magnetic flux to be constant in this way, the terminal voltage becomes proportional to the primary frequency, and in this example, the second It is clear that the same effect as the embodiment shown in the figure can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, when the motor voltage is excessive during overload operation or when the load fluctuates due to conventional motor control,
Induction motors that eliminate problems such as slow torque response when a load is applied from a no-load operating state, as well as unstable phenomena caused by slow torque response, and enable extremely stable operation. A control method and device can be obtained.

Note that the present invention can achieve similar effects even when a cycloconverter is used as the frequency conversion device.

Further, the present invention can be applied to a device that digitally controls the same operations as those in the above-mentioned embodiments, and the same effects can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an example of a conventional induction motor speed control device, FIG. 2 is a circuit configuration diagram of an induction motor speed control device according to an embodiment of the present invention, and FIG. 3 is a circuit configuration diagram showing an example of a conventional induction motor speed control device. FIG. 4 is a circuit diagram showing still another embodiment of the present invention. 1... Forward converter, 2... DC reactor, 3... Inverse converter, 4... Induction motor, 5... Speed Generator, 6... Speed command circuit, 7... Speed deviation amplifier, 8...
・Current detector, 9, 16...Current deviation amplifier,
10... Automatic pulse phase shifter, 11...
Frequency setting circuit, 12, 20, 25... Frequency command amplifier, 13... Voltage-frequency converter, 1
4... Inverse converter gate amplifier, 15...
・Exciting current setting circuit, 17...Voltage detector, 1
8, 21... Voltage command creation circuit, 19...
...Voltage deviation amplifier, 22... Operation command circuit,
23... Magnetic flux detector, 24... Magnetic flux deviation amplifier.

Claims (1)

[Claims] 1. In an induction motor speed control device that controls a frequency converter based on a frequency command signal obtained as the sum of a rotational frequency and a slip frequency to control a primary frequency, a change in magnetic flux due to a change in the load of the induction motor is suppressed. 1. A speed control device for an induction motor, characterized in that the slip frequency command signal is modified so that the slip frequency command signal is adjusted as follows.