JPS6149914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable speed control device for a squirrel cage induction motor using slip frequency control, and particularly to a control device having a constant output control range suitable for an AC dynamo.

The horsepower and torque generated by a prime mover are measured by an electric dynamometer, and eddy current type and DC dynamo type dynamometers are known. The eddy current type has the drawback that constant torque characteristics cannot be obtained and a large amount of cooling water is required to dissipate the absorbed power, and the DC dynamo type has brushes and a commutator, making it difficult to increase speed. It also has drawbacks such as requiring time and effort for maintenance.

Compared to these dynamometers, there is an AC dynamo type that uses an induction motor and has superior characteristics, ease of use, and economy.

It is known that variable speed control is performed by primary voltage control, primary frequency control, etc. using a static power converter to control an induction motor. By the way, the prime movers to be tested, such as engines and gas turbines, have a variety of output horsepower, and are variable speed from low to high speeds, but they are constant outputs, with low torque at high speeds and high torque at low speeds. have characteristics.
Therefore, if the dynamo that exchanges power with the prime mover under test is a control device that enables constant output control regardless of its motoring or regenerative operation, the capacity of the power converter and electric motor can be effectively utilized. It turns out.

The present invention has been made in view of the above, and an object of the present invention is to provide a variable speed control device that can control a squirrel cage induction motor capable of high-speed rotation with a highly accurate constant output control range. do.

FIG. 1 shows a control device block diagram showing one embodiment of the present invention. The squirrel cage induction motor 2 connected to the prime mover 1 under test includes a current-controlled forward converter 3,
Variable speed control is performed by slip frequency control using a DC reactor 4 and a frequency-controlled inverter 5.

The rotational speed f _n of the electric motor 2 is determined by a pulse transmitter 6 and an F/V converter 7 that converts the pulse frequency into voltage.
It is then converted into a voltage signal and compared with the slip command f _s of the slip frequency setter 8 and with the speed command f _ns of the speed setter 9. The deviation between the speed command f _ns and the rotational speed f _o is made into an armature current command and a slip frequency command of the electric motor 2 through the speed control regulator 10 . An absolute value converter 11 takes out the absolute value of the armature current command, and a variable lower limit limiter 12 sets the lower limit value of the current command. The lower limit value control in the variable lower limit limiter 12 is performed using a function generator that generates a function that is constant up to the base speed f _{op of} the electric motor 2 and decreases exponentially in a range exceeding the base speed, with respect to the rotation speed f o. 13. As shown in Fig. 2, the characteristics of this function generator 13 are set to the no-load current characteristics of the motor, and the excitation current is corrected based on the relationship between the primary current and the slip frequency _s , and the field flux is kept constant at the rated value. control.

The output of the variable downward oscillation limiter 12 is made into a current command for a control section having the current input of the forward converter 3 (ie, the armature current of the motor 2) as a minor loop. The AC input current is detected by the current transformer 14 and the rectifier 15, and this detected value is compared with the current command and the amplifier 1
6. The integrator 17 and the phase controller 18 control the conduction angle of the main circuit thyristor of the forward converter 3 to control the current of the motor 2.

On the other hand, the slip frequency command of the speed control regulator 10 is multiplied by the output of the function generator 19 in a multiplier 20. The function generator 19 has a torque for obtaining a constant output with respect to the rotational speed f _n , that is, a function characteristic that is the inverse of the rated slip frequency characteristic shown in FIG. Obtain the command f _s . The addition of the slip command f _s and the rotational speed f _o and the frequency signal passed through the amplifier 22 are converted into a frequency signal by the V/F converter 22,
The frequency is divided by the frequency divider 23, distributed by the ring counter 24, and commutated by the gate circuit 25 for the main circuit thyristor of the inverter 5, so that the output frequency of the inverter 5 is controlled to ( _o + _s ).

Therefore, according to this embodiment, in slip frequency control that performs variable speed control of the motor by controlling the armature current of the motor and the slip frequency, constant output control can be performed above the reference rotation speed, and it can be applied to a dynamo. The capacity of the inverter and motor can be used effectively.
Furthermore, since the excitation current is corrected, highly accurate speed and output control is possible in a speed range close to the synchronous speed.

In addition, in the embodiment, to control the torque of the electric motor, the setting device 9 is used as a torque setting device, and the output of a load cell (broken line block 26) set in the prime mover 1 or the electric motor 2 is used to match this set value. It becomes possible.

Similarly, manual setting of torque can be achieved by using the regulator 10 as a constant gain amplifier and manually setting the input using the setting device 9 in the torque control described above. In this case, there is no torque feedback.

As clarified above, the variable speed control device for a squirrel cage induction motor according to the present invention enables control with a constant output control range, as well as torque control and manual torque setting by switching some circuits. High-precision control is possible, and it is especially effective as a dynamo that effectively utilizes the converter and electric motor.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a variable speed control device for a squirrel cage induction motor according to the present invention, and FIG.
3 are characteristic diagrams for explaining the operation of FIG. 1. 1... Prime mover under test, 2... Squirrel cage induction motor, 3... Forward converter, 5... Inverse converter, 9... Speed setter, 10... Speed regulator, 11... Absolute value converter , 12...Variable lower limiter, 13, 19
...Function generator, 20...Multiplier.

Claims (1)

[Scope of Claims] 1. A control device for variable speed control of a squirrel cage induction motor by slip frequency control using a current source inverter, which outputs a function signal of the no-load current characteristic of the motor in response to changes in the rotational speed of the motor. First thing to do
a function generator, a variable lower limiter circuit that limits the lower limit value of the inverter's current command using the output of the first function generator, and a function signal of the rated slip frequency characteristic of the motor with respect to changes in the rotational speed of the motor. A second function generator that outputs is a variable speed control device for a squirrel cage induction motor, which is characterized by obtaining constant output characteristics. 2. The speed regulator uses the torque output of the electric machine as a feedback signal, and the setting device that matches this signal is a torque setting device for the electric motor, and the setting device can be switched to control the torque of the electric motor. Variable speed control device as described in . 3. The variable speed control device according to claim 1, wherein the speed regulator is a constant gain amplifier, the set value of the input setter is inputted, and the setter is capable of switching to manual motor torque setting.