RU2574380C2 - Method for pulse-frequency regulation of alternating current drive with source of variable frequency and device for its implementation - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is referred to the area of electric engineering and may be used at designing of electric drives for machines and mechanisms with large inertia moment and impact load, and also in transportation vehicles. In the method and device for pulse-frequency regulation auxiliary winding of the motor is controlled from the control panel. The following equipment is connected to inputs of the panel: double-pulse generator, frequency divider of the voltage source, current transformer for operating winding phases. Two outputs of the panel are connected to control electrodes of four bidirectional thyristors joined into a bridge circuit and switching two phases of the auxiliary winding in the voltage source phases. The invention presents also electrodifferential drive with two identical squirrel-cage motors and their respective control.

EFFECT: decrease in dynamic load in drive transmission, development of the process similar in variable component of drive moment, regulation of the motor speed, optimal usage of flywheel kinetic energy with further acceleration forcing, elimination of cycle slip mode at failure of wheel adhesion to sliding surface.

3 cl, 2 dwg

Description

The invention relates to the field of electrical engineering and is intended for electric drives of mechanisms and machines with a large moment of inertia, shock load, as well as vehicles.

, где t₁ - время включения двигателя, t_ц - время цикла, температура обмоток достигла Θ=122,5° уже через 8 мин работы (1, стр.363).In the classical theory of electric drive, a pulse method for regulating a squirrel-cage induction motor is known [1]. In operating mode, the engine is periodically disconnected from the network. Constantly in the start-up mode, - free run-out - a certain average speed is determined in the drive, determined by the duration of the start-up (PV%). Such regulation is associated with rapid heating of the motor due to heat losses, which have a quadratic dependence on inrush currents. So, the AL 32-4 engine at an average speed of 600 rpm with a relative duration of inclusion $$\epsilon =\frac{t_{\mathrm{one}}}{t_c}=0.648$$

, where t ₁ is the engine start time, t _c is the cycle time, the temperature of the windings reached Θ = 122.5 ° after 8 minutes of operation (1, p. 363).

A device for pulse-key regulation of an asynchronous electric motor with a phase rotor, in particular in electric drives of tower cranes [2, 3]. The essence of regulation is to periodically open-close the circuit of the rotor windings with resistors at the junction point of the star of the latter with a triac switch with a threshold (key) element operating at a given level of rotor EMF in automatic mode. Such a device is applicable to a special case - a drive with an engine having a phase rotor, and uses the classical method of pulse control of the speed of an induction motor, transferring the shutdown from the stator windings to rotor windings - only by opening the latter.

In the proposed method for regulating an AC electric drive, the main one - the working winding is controlled only by the frequency of the voltage source (basic regulation), and all the work on changing the stator magnetic field - changing the mechanical characteristics of the motor - is performed by the 2nd additional winding, with the "threshold (key) element" is the current cutoff phase of the working winding from the current transformer. The fundamental difference of the proposed technical solution is that the method works in the entire frequency range of the voltage source (basic regulation) due to the dependence of the pulse frequency on the frequency of the source; creates the possibility of both strengthening and weakening the stator magnetic field, and transient electromagnetic processes associated with the operating mode of the main winding are absent.

Since the additional winding works in the motor mode, the active materials (copper, steel, magnetic wires) are fully used for the thermal state of the motor.

Theoretically, such regulation can be used in any AC drive.

The electric drive circuit shown in figure 1, operates as follows. At start-up, the magnetic starter P, with contacts P1, P2, P3, supplies the source voltage to the phases 1P, 2P, 3P of the working winding and phase 1D of the additional winding, and the control panel of the PU includes control electrodes of the triacs 1, 2, while the source frequency f is monitored through a frequency divider PM, the pulse-pair of the PP operates and the load current of the working winding through the CT current transformer is controlled.

The magnetic fields of both windings rotate in one direction, and the additional winding is turned on after the starting current reaches the working winding threshold of limitation - cutoff automatically.

The frequency of the power source sets the duration of the pulse-pause cycle of the pulse pair, i.e. pulse frequency.

After the inrush current drops, the pulse-pair is switched off and both windings operate in motor mode.

There are two more options for controlling the drive, depending on the required depth of magnetic field ripple - driving torque:

a) the additional winding is switched on by pulses of opposite polarity when its two phases are switched to the “counterclockwise” mode,

b) the additional winding is switched on by pulses, the polarity of which periodically changes as a function of the frequency of the voltage of the power source or according to a given program.

The circuit diagram of the device of the control panel PU is not the subject of the claimed technical proposal and therefore is not considered.

In shock-loaded mechanisms using a flywheel electric drive, during the operation, it is necessary to transfer the engine to soft mechanical characteristics, when the load is received, the engine “falls through” in speed and the flywheel gives off stored kinetic energy.

The proposed method and device solve this problem. When the current in the working winding increases above the “cut-off”, the pulse-pair is automatically turned on according to option a) and the programmed control panel of the control unit, turning off the triacs 1, 2, switches the pulse-pair to the second output connected to the electrodes of the triacs 3, 4 - 2D windings and 3D switches in phases B, C of the power source. After the work is completed, the PU program switches the triacs again, restoring the motor mode of the additional winding - the engine accelerates forcibly.

Such a drive can operate in a simplified version from a 50 Hz network without a frequency converter and switch the polarity of the pulses using relays with position sensors - end switches according to the circuit shown in Fig.2.

Figure 2 shows the device of a differential electric drive of a vehicle with motor wheels, in which 2-winding asynchronous motors with squirrel-cage rotors are used, designed for inclusion in the "star" scheme.

The start of the electric drive is carried out similarly to the circuit in figure 1. The triac 1, 2, 5, 6 turn on through normally closed relay circuits Р1К, Р2К. In case of malfunctions (short circuit) of the triacs of the overcurrent relay PM1, PM2 disconnect the circuit. When turning the machine, the position sensors KB1 or KB2 are activated and the pulse-frequency control of the speed of one of the engines starts in the “on-off” mode, when the magnetic field is weakened according to options a) or b). The controlled motor is braked, and the second motor accelerates due to the properties of the circuit that combines their working windings. An automatic control of the magnetic field of one of them is superimposed on the self-regulation circuit of the engines as a function of load moments. When windings are commensurate in parameters, the circuit allows you to make a maneuver - a turn in place due to the “reverse” command for one of the engines. This is very important in cramped quarry conditions, especially for highlands.

In figure 1 is indicated:

U is the voltage source of the variable frequency of the 3-phase voltage;

A, B, C - phase voltage source;

P1, P2, P3 - power contacts of the magnetic starter P;

f is the frequency of the source;

TT - current transformer;

PP - pulse pair;

DC - frequency divider;

PU - control panel;

F1 F1 - the magnetic flux of the motor windings;

1P, 2P, 3P - phase working windings;

1D, 2D, 3D - phase additional windings;

1, 2, 3, 4 - triac keys;

RM - overcurrent relay;

SK - stop button;

P - magnetic starter coil;

PC - start button;

On - starter contact block.

Figure 2 is indicated in addition to Figure 1:

4P, 5P, 6P - phase working windings of the second motor;

1D1, 2D1, 3D1 - phase additional windings of the first motor;

1D2, 2D2, 3D2 - phase additional windings of the second motor;

PU1, PU2 - control panel of the first and second engines;

5, 6, 7, 8 - triac keys of the second engine;

P1k, P2k - normally closed relay contacts;

P1ko, P2ko - normally open relay contacts;

KB1, KB2 - position sensors;

PM1, PM2 - maximum current relay;

a - common contact control circuit;

P1, P2 - relay coils.

Information sources

1. V.P. Andreev, Yu.A. Sabinin. Moscow, Gosenergoizdat, 1956 Fundamentals of electric drive. Pulse Speed Control of Squirrel Cage Induction Motors, p. 361.

2. Patent RU 2101843 C1.10.01.1998.

3. RF patent No. 229296 09/24/2002.

Claims (3)

1. The method of pulse-frequency regulation of an AC electric drive with a voltage source of variable frequency, which consists in the fact that it forms the magnitude of the magnetic flux of a 3-phase stator by algebraically summing the field of a constantly working one - the working winding and the field of the second - additional winding, which is switched on by pulses, different the fact that the switching frequency of the 2nd winding is determined by the frequency of the voltage of the source, when the time fraction of the pulse in the pulse-pause cycle is fixed, and the duration of the cycle itself is It is inversely proportional to the variable frequency of the voltage, and the polarity of the pulse, which determines the direction of rotation of the magnetic field of the 2nd winding, and permission to turn it on is obtained from the control panel, including taking into account the threshold for limiting current peaks in the working winding. 2. A device for pulse-frequency regulation of an AC electric drive with a voltage source of variable frequency, containing, in addition to the named source: an squirrel-cage induction motor, having two 3-phase windings assembled according to the "star" scheme and connected by normally open contacts of the magnetic starter in three phases working winding and one phase of the second - additional winding with 3 phases of the voltage source, two pairs of triac keys, combined into a bridge circuit, one diagonal of which is connected on with clamps of 2 other phases of the 2nd winding, and the other diagonal through the overcurrent relay connected to the unoccupied 2nd winding phases of the source, a pulse pair with electronic timers, characterized in that an additional control panel is inserted into it, forming the frequency, duration and polarity of the pulses to the inputs of which are connected: the current transformer of the phase of the working winding, the output of the pulse pair, the output of the voltage divider frequency of the source, and two outputs of the remote control are connected: one with the clamps of the control electrodes of the 1st pair of triac keys, giving a coordinated rotation of the magnetic fields of both windings, and the other with similar clamps of the 2nd pair, which provides the mode of opposition of the 2nd winding, reconnecting its two phases in the phases of the voltage source. 3. The device according to claim 2, characterized in that a second identical motor with an identical mechanism is connected to a voltage source of variable frequency, and their shafts do not have a rigid connection, and the working stator windings of the motors are combined into a common triangle, forming an electric differential system, the number of identical control panels is doubled, and two relays are introduced, in the coil circuit of which position sensors are included, and the normally open and normally closed contacts of one relay are connected to one panel, similar contacts are different go relay - to the second console.

Images