JPS6039396A - Drive device of induction motor - Google Patents

Abstract

PURPOSE:To enable to drive an induction motor of larger capacity than that of an inverter by connecting an impedance to the output terminal of the inverter. CONSTITUTION:A switching circuit 18 which is composed of thyristors is connected in parallel with a variable impedance circuit 12. Switching elements of the circuit 18 are all turned OFF at the starting time, and the impedance of the circuit 12 is increased to the maximum value. When an induction motor 14 is rotated, the rotating speed of the motor is detected by a rotary sensor 20, and a switching circuit 18 is controlled so that the impedance in response to the rotating speed is obtained by a controller 24.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction motor drive device, and more particularly to an induction motor drive device for fully driving an induction motor having a capacity larger than that of an inverter.

To perform constant torque load operation by connecting a general-purpose induction motor to the output end of a general-purpose inverter, the capacity of the inverter and the capacity of the induction motor are matched according to the load rating. Therefore, as shown in Figure 1, if the speed-torque characteristic of the load is line H, the speed-output characteristic of the load is gold line K, and the speed-torque characteristic of the induction motor is line ■, then at the rated rotation speed this induction motor The required characteristics of the load can be obtained using

However, below the rated rotational speed, the required load characteristics cannot be obtained due to problems with thermal characteristics. For example, at a rotation speed of 10% of the rated rotation speed, the output torque of the induction motor is limited to 50% of the required torque of the load. For this reason, for constant torque loads that require continuous operation below the rated rotation speed (approximately 10% to 80% of the rated rotation speed), the capacity of the induction motor should be approximately twice the load rating, or Outside! It is necessary to either forcefully cool the motor to improve its thermal characteristics or to increase the thermal strength of the motor coil. When increasing the capacity of the electric motor, the capacity of the inverter must be approximately twice the full load rating of the inverter in order to match the total capacity of the induction motor. In addition, when forced cooling is used, an external cooling device is required, and in places where machines are crowded, it becomes impossible to install all external cooling devices. Furthermore, it is very difficult to increase the thermal strength of the coil. In any of the above cases, the cost will be higher than the cost that can be selected based on the load. Note that when using an inverter that is smaller in capacity than the induction motor, the load impedance seen from the inverter becomes smaller and the current that flows through the inverter at startup becomes excessive, causing the inverter's protection device to activate and prevent startup.

The present invention has been made to solve the above problems, and when driving an induction motor with a capacity larger than the capacity of an inverter, the induction motor does not require a cooling device or an inverter to match the capacity of the entire induction motor. The drive system provides all-purpose equipment for all purposes.

In order to achieve all of the above objects, the present invention has a configuration in which an inverter is connected to an induction motor having a capacity larger than that of the inverter via a variable impedance circuit whose impedance is increased when the inverter is started and whose impedance is decreased after the inverter is started. It is something.

According to the above configuration of the present invention, when the inverter is started, the impedance of the variable impedance circuit is sharpened, so that the inverter can be started without passing an overcurrent, and then the impedance is made smaller as the speed increases at the set speed. Voltage drops within the variable impedance circuit can be prevented.

Therefore, according to the above configuration of the present invention, it is possible to drive an induction motor with a capacity larger than that of an inno-kuri simply by providing a variable impedance circuit, so it is inexpensive and does not require a large installation space, and it is possible to The effect is that it is possible to provide an entire induction motor drive device without an increase in energy.

Examples of the present invention will be described in detail below. FIG. 2 shows a first embodiment of the present invention. The three-phase power converter 10 that converts DC power into AC power is a variable impedance circuit 12? The three-phase induction motor 14 has a capacity larger than that of the inverter 10. A constant torque load 16 is connected to the output shaft of the three-phase induction motor 14.

Next, the operation of this embodiment will be explained. First, it is assumed that the three-phase induction motor 14 has the characteristics shown by line J in FIG. It is also assumed that the capacity of the inverter 10 is large enough to drive a three-phase induction motor having the characteristics of the lineman shown in FIG. In this case, the impedance of the three-phase induction motor 14 seen from the variable impedance circuit 12 is smaller than the impedance of an induction motor having wirework characteristics. Therefore, by using an operation device (not shown), the variable impedance circuit 1
Adjust the magnitude of the impedance in step 2. As a result, the starting current becomes smaller than the capacity of the inverter, and the induction motor 14 can be driven. -1: Also, as the induction motor 14 increases to the set speed, the voltage drop in the variable impedance circuit becomes a problem, so the impedance of the variable impedance circuit is adjusted to be small.

Next, a second embodiment of the present invention will be described with full reference to FIG.

In this embodiment, the thickness of the impedance of the variable impedance circuit is controlled by the rotational speed of the induction motor. In FIG. 3, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted.

The variable impedance circuit 12 is connected to a switching circuit 18 in which switching elements each composed of a thyristor or a transistor are all connected in parallel. The switching circuit 18 adjusts the impedance of the p variable impedance circuit by turning on and off the switching elements. In the example shown in the figure, the impedance is reduced by turning on the switching element at the top stage, and the impedance at the bottom stage is reduced by turning on the switching element at the top stage. By turning on the switching element 2, the impedance is increased. Although the figure shows a switching circuit for only one phase, the same switching circuit is also provided for the other phases.

A rotation sensor 20 is attached to the output shaft of the three-phase induction motor 14 to detect the rotation speed of the induction motor. This rotation sensor 20 is connected to a speed calculator 22 that calculates all the speeds of the induction motor based on the rotation speed. The Zuberi calculator 22 is an induction chamber! ? It is connected to a control circuit 24 that determines the impedance according to the rotational speed of the I1 machine and controls the switching circuit 18' (r on-on. It is input and used as an auxiliary value for impedance determination.

To explain the operation of this embodiment, at startup, all the switching elements of the switching circuit are turned off and the impedance of the gainable pedance circuit is set to the maximum value. When the flat motor is rotated, the rotational speed of the induction turtle motor is detected by the rotation sensor, and the switching circuit is controlled by the control circuit so that an impedance corresponding to the rotational speed is obtained.

According to this embodiment, an effect can be obtained in that the magnitude of the impedance of the variable impedance circuit can be automatically adjusted.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between rotational speed, torque, and output, Fig. 2 is a block diagram showing the first embodiment of the present invention, and Fig. 3 is a block diagram showing the entire relationship of the second embodiment of the invention. It is. 10...Inverter, 12...Variable inhibition circuit, 14...Induction motor, 16...Constant torque load. Agent: Tatsuyuki Unuma (and 1 other person)

Claims (1)

[Claims] (2) An inverter that converts DC power into AC power, a variable impedance circuit that is connected to the output end of the inverter and whose impedance is increased when the inverter is started and whose impedance is decreased after the inverter is started, and an output of the variable impedance circuit. An induction motor drive device including an induction motor connected to one end of the inverter and having a larger capacity than the inverter.