RU2300169C1 - Method and device for controlling slip-ring induction motor - Google Patents

Abstract

FIELD: electrical engineering; alternating-current drives for load-lifting and traveling cranes.

SUBSTANCE: proposed method and device for controlling slip-ring induction motor designed for use in load-lifting and traveling crane drives operating at reduced (creeping) speeds are characterized in that turn-on moment of thyristors or triacs is determined by comparing desired and reference voltages and thyristors or triacs are turned on at moments found in this way. Turn-on moment is determined for each thyristor of triac irrespective of other ones. Separate reference voltage is obtained from actual voltages across power circuit by summing them up. Introduced in rotor circuit of slip-ring induction motor are impedance units whose outputs are closed through thyristors or triacs in delta, transformers with secondary windings, thyristor or triac comparison and control units, feedback shaping unit, positive voltage separating units, sawtooth voltage generating units, adders, and setting unit.

EFFECT: ability of attaining parametric speed regulation effect at limited torque fluctuations.

2 cl, 3 dwg

Description

The invention relates to electrical engineering and can be used in AC electric drives based on an asynchronous motor with a phase rotor, mainly for crane hoisting and moving mechanisms requiring lower (creeping) speeds.

A known control method (SU 646800, 04/15/1980), in which the actual voltage of the rotor is converted into a reference voltage sawtooth with constant amplitudes and a duration equal to half the period of the voltage of the rotor. With phase control, the moment pulsations are minimal.

A device is known (SU 646800, 04/15/1980) containing an induction motor, a three-phase transformer, a sawtooth voltage shaper, an intensity adjuster, a comparison circuit, a pulse shaper control, a thyristor power circuit, a ballast resistor, a threshold device, a shunt device.

However, with this method, the effect of parametric stabilization of speed disappears and the technical design is very complex.

Closest to the invention and adopted as a prototype is a method of controlling an asynchronous motor with a phase rotor (patent RU 2202850, IPC 7 Н02Р 5/40, published on 04/20/2003. Bull. No. 11). The method is based on obtaining the effect of parametric stabilization of speed while limiting the pulsations of the moment.

However, with this method, the complex shape of the reference voltage does not provide a uniform change in the angle of control with increasing load, which leads to nonlinear mechanical characteristics when controlling the speed and limits the torque to values less than possible in a circuit with impedances turned on.

The basis of the invention is the technical problem, which consists in eliminating the pulse mode of speed control and increasing the rigidity of the mechanical characteristics due to the linearity of the sawtooth voltage ("saw"). Since the "saw" is linear, the linearity of the mechanical characteristics is ensured when controlling the speed. Increases the rigidity of the mechanical characteristics.

The specified technical problem is solved by the fact that in the method of controlling an asynchronous motor with a phase rotor, in which a reference voltage is set for the thyristor or triac of each circuit of the phase rotor circuit, then the reference voltage is generated and compared with the reference voltage, and when the reference voltage exceeds the reference, turn on the thyristor or a triac of each circuit of the phase rotor circuit, according to the invention, the reference voltage is formed by summing the feedback voltage and the sawtooth voltage generated when ozhitelnoy half-wave of the line voltage to the rotor rings.

To implement the method, a device for controlling an asynchronous motor with a phase rotor is proposed. The device contains impedances in each phase of the rotor, thyristors or triacs, closing impedance outputs in a triangle, transformers with secondary windings connected to the voltage on the rotor rings, comparing and controlling thyristors or triacs, the outputs of which are connected to thyristors or rotor triacs, characterized in that a feedback forming block, positive voltage highlighting blocks, sawtooth voltage generating blocks, adders and a task block are introduced into it, while one of the transfer windings the ormator of each phase of the rotor is connected to a feedback forming unit, the output of which is connected to the sawtooth voltage generating units and an adder in each phase of the rotor, the other secondary windings of the transformer are connected to positive voltage isolation units in each phase of the rotor, the outputs of which are connected to the sawtooth voltage generating units in each phase of the rotor connected to the adders, the outputs of which, together with the output of the task unit are connected to the comparison and control units of thyristors or simi tori in each phase of the rotor.

A feature of the method is the formation of a sawtooth voltage to control each thyristor or triac, which provides a maximum opening angle of thyristors or triac up to 180 °, and the feedback voltage that raises this "saw" in the process of increasing the load on the motor shaft, leads to a sharp and linear change in the angle opening of thyristors or triacs, significantly increasing the rigidity of the mechanical characteristics, and at high loads it completely opens thyristors or triacs, providing access to performance with impedances shorted to a star. In the analogue, for the complete opening of thyristors or triacs, a significant drop in speed is necessary and therefore the drive never reaches the natural throttle characteristic, and the characteristic itself has significant non-linearity, especially at high loads.

The invention is illustrated by drawings, where

figure 1 presents a diagram of an electric drive that implements the method and control device of an induction motor with a phase rotor,

figure 2 is a diagram illustrating the operation of the driver voltage reference, at different static moments, made according to the scheme of figure 1, where U _ab is the sinusoidal voltage at the output of the transformer winding, U _BVPN is the voltage at the output of the positive voltage isolation unit, U _OS - voltage at the output of the feedback block, U _SAWS - voltage at the output of the sawtooth voltage shaper unit, U _OP - summation of voltage U _SAWS and U _OS and comparison with the reference voltage U _З , I _У - current of the control electrode of the thyristor or triac;

figure 3 - mechanical characteristics, while characteristic 1 corresponds to a circuit with impedances shorted to a star, characteristic 2 corresponds to a reduced speed in the motor mode, characteristic 3 corresponds to a reduced speed in the anti-inclusion braking mode.

A device that implements the method includes an asynchronous motor 1 with a phase rotor, impedances 2 in the form of inductors with massive cores and thyristors or triacs 3 in the rotor circuit, a feedback forming unit (BFOS) 4, positive half-wave extraction units (BWFP) 5, transformer windings 6, connected to the voltage on the rotor rings, sawtooth voltage generating units (BPF) 7, adders 8, thyristor or triac (BSUT) comparison and control units 9, reference unit (BZ) 10. The outputs of blocks 9 are connected to the control terminal and cathode of the corresponding thyristor or triac 3.

The implementation of the method is illustrated when considering the operation of the claimed device.

Explanations of the operation of the circuit for the formation of control pulses are given in the diagrams of figure 2.

The operation principle of controlling thyristors or triacs is sufficient to explain on the example of controlling one of the thyristors or triac. Figure 2 shows the control diagrams of a thyristor or triac connected between phases A and B of the rotor of the electric motor at different static moments.

To the voltage on the rings of the rotor of the electric motor 1 are connected step-down transformers TV _ab , TV _bc , TV _ca (figure 1). Each transformer has at least two connected windings, which are conditionally named as the first and second windings. The first secondary windings of the transformers are connected to the BFOS block 4, which is a rectifier with a filter at the output. The output voltage U _{OS of} block 4 BFOS is used as voltage feedback on the rotor rings. The second secondary windings of the transformers 6 are connected to the blocks 5 of the BVPN of their phase. Block BVPN is a comparator. Its output voltage U _{VHF of a} rectangular shape appears only with a positive voltage polarity at its input. In this case (figure 2), voltage U _{ab of the} second secondary winding of transformer 6 TV _ab is supplied to its input. The sawtooth voltage U _SAWS for each phase is formed by its own unit 7 BFP, which is an integrator, the input of which is supplied feedback voltage U _OS . Integration is possible only if there is voltage at the output of the unit 6 of the BVPN of its phase, i.e. ultimately, during the entire positive half-wave of the voltage at the controlled thyristor or triac 3. The adder 8 generates at its output a reference voltage U _OP . It consists of the feedback voltage U _OS and the voltage U _{SAWS of} its phase. Block 9 BSUT compare the reference voltage of the speed coming from the block of the task 10 BZ. The intersection point of the reference voltage with the reference voltage determines the angle α of the delay delay of the thyristor or triac. When the reference voltage exceeds the voltage U _OP , a control current I _U flows through the control electrode - cathode of the controlled thyristor or triac. Almost the “top” of the voltage U _OP operates at idle speed of the electric motor and the angle α is close to 180 °. With an increase in the static moment M _CT (load) on the motor shaft, its speed decreases, which leads to an increase in voltage on the rotor rings, and therefore to an increase in U _OS . Figure 2 shows the U _OP and the opening angles of the thyristor or triac with different values of M _CT on the shaft. The solid line represents the dependence of U _OD at M _CT1 , and the dashed line at M _CT2 > M _CT1 . It is seen that with increasing load, and consequently, with a decrease in the speed of the electric motor, both U _OS and the rate of rise of the “saw” increase. This leads to a significant change (decrease) in the opening angle of the thyristor or triac α and, consequently, to an increase in the electromagnetic moment of the electric motor supporting the speed of the electric motor within the specified value. With a further increase in load, the U _OS becomes larger than the reference voltage. This leads to the complete opening of thyristors or triacs, which is equivalent to shorting the impedance star short.

Figure 3 presents the mechanical characteristics of the considered electric drive. Characteristic 1 corresponds to the case of fully open thyristors or triacs, i.e. with a closed star of thyristors or triacs short. Characteristic 2 corresponds to the operation of the electric drive at a reduced speed in the motor mode, and characteristic 3 corresponds to the operation of the motor in the anti-inclusion braking mode. As a result of the stabilizing action of the control method under consideration, the mechanical characteristic is more rigid than characteristic 1. At large values of the static moment, the thyristor or triac is fully open, and the characteristic coincides with characteristic 1. Due to the linearity of the saw, the mechanical characteristics are linear. In an analog, the reference stresses are formed from pieces of sinusoids and therefore the linearity of the mechanical characteristics cannot take place. In addition, the angle α decreases for the analog with an increase in the amplitude of the reference sinusoid, but cannot become equal to zero and cannot reach the maximum possible value of the electromagnetic moment, limited by characteristic 1, cannot.

The circuit of figure 1 was successfully tested in the laboratory on a 3.5 kW electric motor and on cranes of different lifting capacities of industrial enterprises.

A feature of the invention lies in the fact that the reference voltage generated in the prototype from pieces of sinusoids is replaced by a reference sawtooth voltage, consisting of feedback voltage (rectified voltage from the rotor rings) and linearly increasing voltage ("saw"), the rise rate of which is formed by voltage feedback during positive rotor voltage.

The implementation of the proposed method will allow you to create simple, affordable unskilled service electric drives, mainly crane mechanisms, with creeping speeds at low ripple moment.

Claims (2)

1. The method of controlling an asynchronous motor with a phase rotor, in which a reference voltage is set for the thyristor or triac of each phase circuit of the phase rotor, then the reference voltage is generated and compared with the reference voltage, and when the reference voltage exceeds the reference, turn on the thyristor or triac of each phase circuit loop rotor, characterized in that the reference voltage is formed by summing the feedback voltage and the sawtooth voltage generated with a positive half-wave of the linear voltage at ltsah rotor. 2. A control device for an asynchronous motor with a phase rotor, which includes impedances in each phase of the rotor, thyristors or triacs, which connect impedance outputs to a triangle, transformers with secondary windings connected to the voltage on the rotor rings, thyristor or triac comparison and control units, the outputs of which connected to thyristors or triacs of the rotor, characterized in that a feedback forming unit, positive voltage isolation units, sawtooth forming units are introduced into it voltages, adders and a reference unit, while one of the transformer windings of each phase of the rotor is connected to a feedback forming unit, the output of which is connected to sawtooth voltage generating units and an adder in each phase of the rotor, the other secondary transformer windings are connected to the positive voltage isolation blocks in each the rotor phase, the outputs of which are connected to the sawtooth voltage generating units in each phase of the rotor, connected to the adders, the outputs of which together with the output of the task unit connected to the comparison and control units of thyristors or triacs in each phase of the rotor.

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