Asynchronous-valve cascade

The simplest scheme of the valve stage is a outline with an intermediate DC circuit and a gate converter. The asynchronous-valve cascade provides the types of protection and interlocks from. The applied control scheme for regulating the speed of movement.

Рубрика Коммуникации, связь, цифровые приборы и радиоэлектроника
Вид статья
Язык английский
Дата добавления 15.08.2017
Размер файла 219,1 K

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Asynchronous-valve cascade

Vashchenko M. A.

Studying the electrical drive, we can often hear the phrase an AC engine with an asynchronous-valve cascade. The AVC is easily included in the system of automatical the monitoring of the production process. This stage significantly increases interest in electrical drives, capable of engine speed monitoring. It is used in frame for high-power fans, pumps and compressors. One of the main advantages of this stage is the reduction of electricity intake. That is due to the fact that in large enterprises energy saving is one of the most grave criteria. Another big advantage is advance of the qualitative of products achieved by the energy recuperation slip of the AC engine.

 Fig. 1. Theelectricaloutline (a), theoutline forreplacing the rectified currentoutline (b), themechanicalcharacteristics (c)

The figure shows a diagram of the AVC that provides the engine operation. If we look at the specifications, we will see that the speed lower than the synchronous engine's speed is continuously adjustable down to the natural characteristics. If you look at the startup circuit, you will see an equivalent resistor.

In addition, the converter used at the valve phase is only rated for power proportion to this control range. At the same time, in group with frequency control, the converter participates in the creation of a magnetic flow, and when designing it, it is necessary to take into account the total power of the drive.

The simplest scheme of the valve stage is a outline with an intermediate DC circuit and a gate converter. In the AVC, the energy of sliding is first converted into immediate current energy, and then by the inverter UZ2 into the AC energy of a fixed frequency. The transformer T is designed to match the output voltage of the inverter with the mains voltage. To control the speed of the AVC, it is necessary to change the value of the inverter's electromotive force on the DC side by changing the opening angle of the thyristors (b).

In this electrical drive, with a simple regulating device, a wide speed range and torque monitoring is provided for the engine, and high energy values are achieved by transferring energy from the motor rotor outline to the capacity supply network.

The energy given by the cascade pollutes the network with higher harmonics, which adversely affect the work of a number of consumers. And, finally, the largest capital and estimated costs required for the equipment for driving the cooling fans according to the AVC scheme exclude its request in the coming years to the drives of the cooling fans.

Thus, in the proposed AVC, a wide speed range and torque monitoring is provided, with the motor's sliding energy from the rotor circuit being returned to the alternate current outline across an optocoupler bridge converter operating in an inverter mode, which provides energy saving. The proposed monitoring system is simple and reliable; mechanical characteristics are favorable for hoisting and transport mechanisms.

One of the biggest drawbacks of this stage is its low the force factor and the cost of the converter that increases the cost of the drive. In terms of amount and value of the equipment, there is a certain relationship. The greater the volume, the greater the cost of the equipment, so advantageous to use the asynchronous-valve cascade with little regulation of the engine speed.

The asynchronous-valve cascade provides the following types of protection and interlocks from:

- external and internal short outlines;

- inadmissible by magnitude and duration of the overload currents of the power outline elements and the powered motors (time-current protection);

- violation of the cooling system;

- increased and reduced supply voltage;

- exceeding the speed of the engine;

- an unacceptable reduction in the tension of own needs;

- malfunction of power supplies;

- blocking the activation when there are emergency and warning signals.

The applied control scheme for regulating the speed of movement is based on a change in the additional resistance in the rotor circuit, which causes large losses of the electric power consumed by heating the resistors and a low range of shaft speed regulation.

Mathematical models of open and closed systems of the AVC allow conduction of the research of dynamic processes and static characteristics of the electrical drive under various constructions of the power part and automatical monitoring systems. gate converter asynchronous valve cascade

A system for starting an asynchronously valve stage is designed to smoothly control the voltage at the output of a controlled rectifier connected to the windings of the motor rotor as a function of the electromotive force of the rotor winding, which expands the functionality of the asynchronously valve stage. Thus, using the AVC by different companies, we can achieve energy savings and get an manageable electrical drive.

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