SU752726A1 - Double-motor electric drive - Google Patents

Description

The invention relates to electrical engineering and can be used to create an asynchronous electric drive for industrial mechanisms, such as mechanisms for lifting machines. A two-motor electric drive is known, which contains two asynchronous motors, the stator of one of the motors is connected to an AC network, and the stator of the second motor is connected to a DC network, which is realized by means of a rectifier connected to the AC network and connected to its output a resistor, the value of which is selected on the basis of ensuring the required amount of direct current in the stator circuit of the second motor. Such a circuit provides a rigid mechanical characteristic of the electric drive in the area of low speeds, which makes it possible to obtain stable engine operation at low speeds in the event of a change in load on the weight. The disadvantage of this electric drive is the increased losses in the motor windings when operating at low speeds. Indeed, a constant current flows through the stator windings of the second motor, the magnitude of which has to be chosen large enough to obtain the required braking moments, and the magnitude of this current with changes in the load on the shaft (including when the load is equal to zero) is maintained unchanged. The purpose of the invention is to reduce energy loss in an electric motor. The goal is achieved by the fact that in a two-motor electric drive containing two asynchronous motors with a phase-rotor, the stator box of the first of which is connected to an AC network, and the second terminal of the stator winding of the second is connected to one of the terminals of the resistor and rectifier input p; ; 1 connected to the network, alternating current, additionally introduced by the input to the rotor winding of the first motor rectifier, the output of which is shunted by the additionally introduced resistrom and connected alone m {CONCLUSION with the same output of the first rectifier, and the other with the second output of the main resistor.

FIG. 1 shows a diagram of the device; see 2 - mechanical characteristics of the drive.

In the device, the stator of the asynchronous motor 1 is connected to the AC mains, and the stator of the asynchronous motor 2 is connected to the output of rectifier 3 through series-connected resistor 4 and output of rectifier 5, in parallel with which resistor 6 is turned on. to a friend. The input of the rectifier 3 is connected to the AC network, and the input of the rectifier 5 is connected to the rotor of the engine 1. Resistors 7 are connected to the rotor of the engine 2.

FIG. 2 shows the following mechanical characteristics: the rh-static characteristic cxrfb for engine 1, corresponding to open rectifier 5 and closed rectifier 3, when the currents in the stator of engine 2 are zero; dynamic braking performance for engine 2 ,. a corresponding open rectifier 3 and a closed rectifier 5 when the currents in the rotor of the engine are zero; the characteristics of the ootccfe of the engine 1, resulting in its operation in the circuit shown in FIG. one; the characteristic of the engine, engine 2, is obtained when operating in the circuit shown in FIG. one; the resulting eclucfS characteristic of the twin-motor electric drive for the circuit shown in FIG. one.

The device works as follows. in a way.

The device can work in one of three modes.

In the first mode, rectifier 3 is closed, and rectifier 5 is open. In this case, the torque of engine 2 is zero, and engine 1 operates on the rheostatic characteristic oiff & .

In the second mode, rectifiers 3 and 5 are open, in the third mode, rectifier 3 is open, and rectifier 5 is closed. In this case, the torque of the engine 1 is zero, and the engine 2 operates on the dynamic braking characteristic of 1.9 V,

The operation of the circuit in one of the three indicated modes is determined by the voltage values and the Dots at the output of the rectifiers 3 and 5, respectively. At the same time, aUplB Engine 1 increases with an increase in engine slip, since the input of rectifier 3 is connected to a network with constant voltage, and the input of rectifier 5 is connected to the rotor of engine 1, the voltage of which increases with increasing slip. Therefore, the operation mode of the circuit shown in FIG. 1 is determined by how much

Genie motor 1, i.e. speed vgipa electric drive.

If the slip of the motor 1 is sufficiently large, then the circuit operates in the first mode and the current in the resistor 6 flows only from the rectifier 5. Indeed, in this case the inequality is satisfied

Ud Ud3 (1)

In this case, the rectifier 3 is closed. Assume, that when the speed of the shaft of the electric drive is zero, the circuit shown in FIG. 1, works in the first mode. Then the state of engine 1 is characterized by a dot in the rheostatic characteristic affft. When the speed of the electric drive shaft increases, the slip of the motor 1 decreases, which determines the decrease in voltage, and at a certain angular velocity J of the shaft, the magnitude з reaches UdljrT.e. there is equality

Ud5-Udl3- (2)

It follows that when the angular velocity of the shaft changes from zero to b, the state of the engine 1 is determined by the section & b characteristics about 6, where the point cf corresponds to the speed of the engine 2, the moment of which is zero, can be determined by the segment ge on the ordinate axis where r and 3 correspond to the zero velocity and the velocity uj4. With an increase in the angular velocity of the shaft above uj, the circuit operates in the second of the indicated modes. In fact, since the increase in the angular velocity of the shaft is higher and, 1 slip of the engine 1 decreases, the inequality Uds-UdIli, (3) is opposite to inequality (1) between the MHVJois and Uoi3 strains. This opens rectifier 3, and since rectifiers 5 and 3 turn out to be open, Oois currents from rectifier 5 and Os31 from rectifier 3, respectively, flow through resistor 6

..

(four)

dl5

(", R, 6

(five)

G13-R TW7

where Y, 3 HRg are the resistances of the stator windings of the motor 2 through which the current SbSchg of resistance of resistors 4 and 6 flows, respectively.

Claims (1)

From expressions (4) and (5), it follows that with an increase in the angular velocity of the shaft above 1x (| (i.e. when the slip decreases DQ) of the drive 1), the Doig current decreases, and the current 3 (313 increases, as in decreasing the slip decreases the voltage;; .READING a certain speed ShtoctT) H5Step to zero, rectifier 5 closes and the torque of engine 1 also becomes equal to zero. In the speed range, the mechanical characteristic of engine 1 is represented by cGS line, where the point is on the ordinate axis, corresponding to the speed o) / 1, and the mechanical characteristic engine 2 is represented by the line ES5 f where the d-point on the dynamic braking characteristic i.qe of engine 2 corresponds to the speed uJ. When the angular velocity of the shaft, more than; The circuit operates in the third mode. Indeed, at an angular velocity w ,, shaft, the value of Dd (5 is zero. At the same time, the numerator in the expression (4) tayuha is zero. Since as the angular velocity of the shaft increases in UJ1, the voltage Uols drops, then the current according to the formula (4) should to become negative, which is impossible due to the one-sided conduction of the rectifier 5, therefore the rectifier 5 is closed.In these conditions, the torque of the engine 1. up to the synchronous speed (point a in Fig. 2) is zero, and the mechanical characteristic of this engine can be represented by a segment of Ms on the axis of the hordes In this case, the engine 2 operates in the mode of dynamic braking (characteristic de Fig. 2, where the point e corresponds to greater than TDJ, the angular velocity of the engine 2). The resulting torque on the electric drive shaft is determined by the algebraic sum of the torques of engines 1 and 2 Section cTug the resulting mechanical characteristic of the electric drive (where the point and corresponds to the load moment equal to zero) has a high rigidity, which determines the stable operation of the electrical drive in the region of its low speeds when the load torque changes in wide limits. The device allows you to adjust the speed of the electric drive shaft, which is carried out by changing the resistance values of 6.4 and 7, as well as using an additional transformer connected between the AC network and the rectifier input 3. The rectifier 3 can be made not only in the form of a three-phase, but also in the form of a single-phase rectifier, as well as with control ekvlmi valves. The use of the invention allows to significantly reduce energy losses in electric motors, which makes it possible to reduce the dimensions of electric motors and, accordingly, the centrifugal mass of the entire electric drive, which also leads to a decrease in energy losses, or for the same losses to get more motor and braking moments of electric motors compared to with a proper device. The invention is a twin-motor AC drive containing two asynchronous motors with a phase-rotor, the stator winding of the first of which is connected to an AC network, and two terminals of the second stator winding are separately connected to one of the terminals of the resistor and the rectifier, the input connected to the AC network, characterized in that, in order to reduce the energy losses in the electric motors, a coupler is connected to the rotor winding of the first electric motor, the output of which is connected to the rotor winding of the first electric motor. It is shunted by an additionally inserted resistor and connected by one output to the same output of the first rectifier, and the other to the second output of the main resistor. Sources of information taken into account during the examination 1. M. Chilikin, M. Sokolova, V. Terekhov. and Shinskiy A.V. Basics of automated electric drive. Energie, 1974, p. 132.