Thyristor

Thyristor - a device for adjusting the transmit power of electric energy using triac power switch design. Used to change the engine rotational speed, power luminosity illumination devices and other purposes.

Overview

All modern technical solutions are formed at the beginning of the second half of the XX century. It is foolish to assume that time textbooks obsolete. We can not ignore gratitude Shubenko VA IJ Braslavsky and the rest of the team of authors, readers prepared for such a wonderful material.

Thyristors are so often used in the controllers that have long been supplanted transistors. This is due to high performance and power characteristics as controlled rectifiers. The main advantage is considered smooth settings. Although the early models and modern it is implemented fundamentally different ways. As a result, the drive has a number of positive qualities:

1. Increased efficiency;
2. performance;
3. Sharply contoured shape of the control signal;
4. cheapness;
5. Simplicity;
6. Small size.

Thyristor today there are everywhere. In washing machines smoothly change the speed of rotation of the shaft by the cutoff current, in kitchen machines largest arcing will adapt to stabilize the power consumption of revolutions. Earlier thyristor regulators used only for asynchronous motors, mostly paired with a squirrel cage. Today, new technical solutions much pushed the boundaries of this industry. Already in the 60 years of the scheme used in two ways:

• Setting voltage amplitude.
• Frequency conversion power supply.

The first method is considered to be universal and suitable for the vast majority of engines. The second shows the limitations at the present stage in household appliances is extremely rare, having won among the segment of industrial applications. The home equipment now used a different technique - the cutoff current (phase method). Part period key transmits an alternating voltage, closes at other times. This mode is characterized by minimum energy consumption at an acceptable performance.

Typical Use

In most cases, the application of the scheme thyristor controller remains the same, little changed over the years:

1. Software settings (PU) are laid in the form of code in memory of the arithmetic unit (AU) of the electronic unit. In the washing machine is the most expensive part. So that the replacement is often impractical.
2. Thyristor serves input device (RD), where a control signal is supplied.
3. The changed voltage affects the service actuator (SP) of the motor winding, collector and so forth. feedback line shows that the low volatility compensated directly without involvement of the CPU. It has already been said about the amount of sparks.
4. Mechanism (M) fulfills command. On the shaft stands centralized position sensor (CDP), in which the processor understands what is happening as a result of giving commands. algorithm is adjusted if necessary.

Before thyristor regulators used generators with direct management or mercury rectifiers, with easily changeable characteristics. However, these devices only work together with a commutator motor. Hence, simplicity, low cost, simplicity of induction appeared not claimed until the thyristor regulators.

Driving motor control phase

The figure shows a simple thyristor circuit for controlling movement of the shaft. Pass through the branches of the pulses of both polarities. If necessary, a thyristor may be locked. Depending on the set of control signals varies the phase sequence that enables the reversing shaft. The first scheme solves the problem, while the second defines the cutoff angle.

The undoubted advantage of this technical solution is considered to be the possibility of painless switching off the engine from the network in the braking period. This blocked energy back to the network. It becomes possible opposition mode. When the thyristors 1 and 7 on the one winding attached to all voltages. As a result, the constant component is formed palpable. the magnetic field produced by it is intense dynamic braking of the shaft due to flux. This scheme is called differently in the literature dvuhpulsnym power in a network with isolated neutral.

The intensity of the braking magnetic field is adjusted by introducing a phase and an additional resistor, not involved in the work, but only to stop. At the same time the thyristors 9 and 10 are completely closed, the current does not remain other way. This is to avoid overheating and the impact of a large reactive power peak in the chain. The control circuits not shown to simplify the illustration.

Thyristors are characterized by a finite switching time, it remains possible to create a situation where one key still works, but the second has already joined. Which will lead immediately to the interphase short circuit. As a result both the thyristor will be destroyed due to overheating, because the semiconductor p-n-junction irreversibly loses its properties in the latter case. Silicon devices preferably can withstand heat up to almost 150 degrees Celsius. Of course, the power switches are equipped with powerful radiators.

In this regard, the current cut-off mode is used in the current schemes, it looks much more attractive, a significant part of the period the key is resting. If we take into consideration the computer switching power supplies, cooling has been a small fan. Without it, Core Dimensions thyristor switch would have to be increased. In modern circuits commonly used pulse width modulation, one of the methods of implementing it becomes cut-off current.

To thyristors are not open simultaneously relies control signals supplied from the delay. speed adjustment circuit provided on the performed interleaving mode power and dynamic braking. For collector engines is unnecessary. Is much more effective to change the angle of the cut-off for adjusting the power supplied. This saves power consumption at the same time, increasing the efficiency of the installation.

Continuous mode is provided with engine power generation control pulses coordinated with the transition through zero voltage. One of the possible schemes for the implementation of that concept is represented in the figure. Its embodiment is shown to control the counter thyristors included to prevent simultaneous opening keys.

Phase control thyristors

Regulation of the rotational speed by means of the thyristors with the introduction of the feedback circuit detects a number of advantages. Prior to the introduction of such technical solution of this problem solved chokes work in saturation mode, differing number of disadvantages:

• Elevated lower threshold.
• Large losses.
• Slow performance.

The control circuit recalls shown above to provide dynamic braking. The only difference is the absence of a resistor. However, the above already does hint that the presented solution is suitable for creating the desired cut-off angle, which is similar in meaning. Based on empirical data, defines the requirements for the control pulse:

1. Abrupt front.
2. The width of not less than 60 degrees.
3. Initial moment of inclusion in the 20 degrees out of phase.

In circuits with neutral gluhozazemlonnoy possible to consider each phase individually, as if running a conventional motor of the washing machine in a network of 220 V. In circuits with isolated neutral for proper commutation necessary to take into account the phase angle of each power line and including thyristors pairs. With the change of time delay with respect to the passage of voltage through zero transmit power varies. At an angle of phase shift of 135 degrees on the shaft passes a minimum mode corresponding to idling (no load). This upper limit for the phase adjustment system by means of thyristors.

On a similar principle apply modern management system: a vacuum cleaner, washing machine, food processor, etc. Minimum cutoff angle for asynchronous motors considered 20 degrees. According obvious reasons, the phase shift control circuit should not depend on the input voltage oscillation is realized through a vertical principle. Examples of structures in the figure.

Capacitor C1 serves to generate a sawtooth voltage. Starting pulses synchronized with the power supply potential transition point through zero. Tooth length is 160 degrees (almost half the period), which is required, since the upper regulation threshold is 135. Measurement of the current state of the system is made in a bridge circuit. At the right moment it offers a key forming a pulse trigger blocking oscillator.

Transformer Tr1 is powered by a three-phase line network. When winding minus the diode D1 turns on, and the power goes past the condenser. The ramp pulse falls. The charge occurs when locked diode D1. The moment of opening and, as a consequence, the shape of the tooth, pulling Uy regulated voltage to the desired value. This deals with the control scheme that assesses both shaft speed. Blocking oscillator generates a pulse of predetermined length to the desired time, the thyristor control circuit implementing speed control.

optimal performance

The control systems for industrial use rate is not marked difficulties with the acceleration, which can be easily implemented using the relay system and multi-dimmers. When braking starts, the time required to calculate the start of the supply of control signals to reduce the negative effects.

Said problem is solved by a special unit dealing with the assessment of the current state of the system. Empirically calculated braking scheme, the control device is laid ready algorithm. By means of sensors is determined by a mismatch between the current state and the start of braking. Among these there are values ​​- angular path of the shaft up to the stop, and others.

Speed ​​feedback is non-linear and, as a rule, can not be calculated, the data on this relationship are entered in the memory of the calculator. As a result, according to the existing load and dynamic system parameters produces a stop command at the right point in time. Factors taken into account:

1. No overheating windings stop pulse current.
2. Minimizing the impact of reactive power in the network.
3. Extension of the plant.
4. Lack of conditions for creating accidents and mechanical overload.

During the development of thyristor control system takes into account the fact of immunity induction motor to the influencing factors at low revs. In this case, a minimum mismatch in speed between the rotor and stator fields, providing the appearance of eddy currents and, consequently, the presence of flux. This is a significant limitation of asynchronous motors, due to which their use in everyday life is reduced to a minimum.