SU862344A1 - Device for controlling frequency-controlled asynchronous motor - Google Patents

Description

one

The invention relates to electrical engineering, in particular to automated electric drives with thyristor frequency converters and can be used in multi-loop systems using integrating controllers, as well as in frequency-controlled electric drives in metallurgical and papermaking installations, in mechanisms of copying machines and machine tools with program management.

A device 1 is known that contains an intensity master, the output of which is connected to the input of a speed regulator (and a voltage regulator in variable frequency asynchronous electric drives), which, through a series of intermediate regulators (depending on the type of drive), acts on the thyristor converter of other type. Using a temp master, in systems with high-speed transducers, it is possible to reduce overshoot and, without the use of delayed communications, limit the dynamic loads of the transducer and engine in the processes of starting, braking and speed control. In addition, in frequency-controlled drives, the intensity control knob prevents the induction motors from overturning (switching to a hard frequency start).

However, using a presetter at a preset tempo reduces the drive speed, since even when the resistance moment and current are constant, the tempo must be set below the maximum allowable, since the moment constant is taken with a known approximation .JJ. In real systems, there is always a moment of movement, a change in the moments of mechanical and ventilation losses, not to mention random effects. Therefore, the tempo adjuster forms a rather complicated function of changing the frequency

15 in time.

Most often, the dependence of the moment on speed, slip frequency does not lend itself to rigorous approximation, and if it is possible to do this, it is necessary to have a moment margin, since all possible changes in moments in

20 real systems in the start-up process can not be taken into account. Switching the intensity setting device to the mode of automatic regulating the acceleration rate of the frequency-controlled electric drive as a function of current 2 eliminates the tilting of the induction motor, but leads to a further slowing down, because by reducing the rate, the amplitude control channel is reduced. The closest technical solution to the invention is a device for frequency control of an induction motor 3, comprising its frequency converter with a frequency control channel and a voltage control channel, an intensity setter, a speed sensor on the motor shaft, the output of which is connected to the first inputs of the first and second blocks the second input of the first comparison unit is connected to the intensity control unit, and the output is connected to the frequency control channel via the speed controller and through the second input the second unit of comparison with the voltage control channel and the source of the reference voltage. In this drive, the intensity master must also be adjusted taking into account possible changes in the load torque, i.e. set the pace below the maximum allowable, which, as mentioned, reduces speed. The purpose of the invention is to increase speed. The goal is achieved by the introduction of a tempo standard block and a third comparison block, while the input of the tempo standard block is connected to the output of the speed regulator, and the output is connected to the first input of the third comparison block, the first input of which is connected to the reference voltage source, and master of intensity. FIG. 1 shows the functional scheme of the variable frequency drive; in fig. Figure 2 shows the mechanical characteristics of feedback drives. The drive consists of intensity setting 1, speed regulator 2, frequency control channel 3, converter 4, motor 5 with speed sensor 6, tempo reference block 7, voltage regulator 8 in voltage control channel 9, first 10, second 11 and the third 12 units of comparison, the source 13 of the reference voltage. The device works as follows. With the help of the reference voltage 0, the rate of change of the reference voltage LJj. Is set, which is obviously greater than the maximum allowable. Then, when the voltage of the voltage jump of the setpoint AUs is applied to the input of the setpoint 1, the system, due to the presence of feedback loops and controllers, forcibly goes to a point with a reference error in speed corresponding to the moment Mjnt. (see Fig. 2). In this case, the block 7 of the tempo standard is opened, which in the simplest case can be a Zener diode with voltage, and negative feedback on the reproduction error of the speed Ug starts to work (see Fig. 1), reducing the rate of change of the signal to an acceptable level . If the reference signal during operation changes by a small amount, resulting in an error Ug, then a forced change in speed occurs without a tempo limit. When using such a device in frequency control systems, since the rate control loop and the flow control loop (see Fig. 1) are not directly connected to each other, the circuit and voltage regulator 8 are forced to increase and then stabilize and this does not directly affect the reduction in the rate and reduction of the force in the flow control loop. The flow control loop can also be built using an EMF sensor, a flux, or a voltage drop in the stator circuits. Since the acceleration time t p to the steady-state speed WUCA. is defined as CJytm A-a. motor torque can be expressed as M KnttUg., where Kok is the transmission coefficient of the direct link units (see Fig. 1), then. Since the intensity adjuster in the device stabilizes U at the level corresponding to the maximum allowable level. (see Fig. 2), this corresponds to the maximum permissible torque of the engine, and consequently, to the maximum permissible excess torque, with any law of variation of the moment of resistance Mc- and of the moment of inertia J. Therefore, in such a system, the intensity adjuster performs the functions of the minimum controller acceleration time. In frequency-controlled electric drives, the flow stabilization circuit results in the mechanical characteristics of the drive in the area of working moments to the characteristics of type 14, corresponding to direct-current drives without feedback (see Fig. 2). Then, the frequency (speed) control loop, together with the variable intensity setting unit, performs the same tasks as in DC drives, forms rigid mechanical characteristics of type 15 (see Fig. 2) and provides the maximum speed. Thus, maintaining the maximum excess m-oment ensures the maximum possible speed of the drive in the start and deceleration modes, and the absence of rate limitations at small AUj provides a high speed in the mode of adjusting the set speed.

The use of a tempo generator with a linear characteristic and the absence of the need to use only for the purpose of limiting the dynamic currents and moments of special feedback simplifies the circuit. The control device is equally suitable for DC and AC valve drives, and in the latter case, it simultaneously provides a soft, close to critical frequency start.

Claims (3)

1. Chilikin M. G., Klyuchev I. I., Sandler A. S. Theory of automated electric drive. M., “Energie, 1979, p. 507-522. 2. USSR author's certificate number 640412, cl. H 02 R 7/42, 1978. 3. Sandler A.S., Sarbatov R.S. Automatic frequency control of asynchronous motors. M., “Energie, 1974, p. 144, fig. 5-10 (prototype). V