RU2359393C1 - Method of controlling ac voltage - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: present invention relates to electrical engineering and can be used in ac voltage regulators, including those operating with a lamp as the load. In the method of regulating ac voltage, before the first connection of the transformer, connection is delayed by one period of the supply voltage, in the second half of which the state of the load is analysed, and, depending on the result, magnetic flux Φ_ren is created in the transformer in the second half by applying voltage across the transformer by opening a semiconductor switch, located on the input side of the transformer, with angle of opening γ, which depends on the state of the load. Without a load, the angle of opening of the semiconductor switch is minimum γ=0°, and with a nominal load γ=180°. In that case the semiconductor switch is not opened.

EFFECT: improvement of quality parametres of the circuit when the output transformer of the regulator is connected to an under-loaded circuit.

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Description

The invention relates to the field of electrical engineering and can be used in AC voltage regulators, including those operating on a lamp load.

A device for regulating and converting voltage, containing a transformer, in the circuit of one of the windings of which a semiconductor regulating element is included, and a control system for this element, wherein the regulating element is made in the form of a single-phase bridge rectifier, the thyristor is included in the diagonal of the direct current, and to the AC terminals - RC chain, (patent RU No. 2117376, H02M 5/12, 07/31/1996).

The disadvantage of this invention is that it cannot be used to regulate the voltage at the lamp load, since the law of regulation must take into account not only electrical, but also physiological processes.

A known method of regulating AC voltage, which consists in connecting and disconnecting the load for an entire number of periods of the supply voltage, the intervals of the disconnected state of the load being set constant and equal to the period of the supply voltage in the entire control range, and the interval of the connected state of the load is the number of periods of the supply voltage in each period pulse regulation over the entire regulation range, and the number of periods of the connected load state in proportion to the voltage level at the load, (copyright certificate SU No. 1001429, НОР 13/16, 06/15/1981).

There is a method of controlling AC voltage with a pulse-width regulator, namely, that the load is turned on and off for an integer number of periods of the mains voltage, and when controlling from 0 to 50% of the output maximum voltage, the load is switched on for one period of the supply voltage, and the intervals of the off state of the load change so that they are equal in the number of periods of the supply voltage in each period of the pulse regulation, when controlling from 50 to 100% of the output maximum voltage, turn off load for one period of the supply voltage, and the intervals included load status change so as to be equal to the number of periods of the supply voltage in every period pulse regulation, (Inventor's Certificate SU №1167690, N02M 3/00, 02.04.1983).

The disadvantage of the last two analogues is the high discreteness of the regulatory characteristic.

The closest in technical essence and the achieved result to the claimed invention is a method for controlling an alternating voltage, which consists in the fact that when working on a lamp load, both the number of periods of the supply voltage connected to the load and the duration of the regulation period vary from the period of the supply frequency voltage up to a period of critical frequency, which for operation on an incandescent lamp is 50 Hz, (copyright certificate SU No. 1809516, Н02М 5/257, 03/27/1989).

The disadvantage of the prototype is the presence of emissions of magnetizing currents in the output transformer of the regulator (if the lamp load is connected to the AC network through a transformer, and the regulating element is on the primary side of this transformer) during its first turn on when there is no load (or on an underloaded circuit), which 50-100 times can exceed the amplitude of the steady-state idling current of the transformer and more than 2 times the rated current.

The objective of the invention is to improve the quality parameters of the circuit when you first turn on the output transformer of the regulator on an underloaded circuit, which is achieved by reducing the emissions of magnetization currents.

This problem is solved by the method of regulating the alternating voltage, which consists in the fact that when operating on a lamp load, both the number of periods of the supply voltage connected to the load and the duration of the regulation period vary from the period of the frequency of the supply voltage to the period of the critical frequency, which for operation on the incandescent lamp is 50 Hz, in which, unlike the prototype, before turning on the transformer for the first time, they turn on the delay for one period of the supply voltage, in the first half They analyze the load state, and, depending on the result, create a magnetic flux Ф _оst in the second half of the transformer by turning on the transformer for voltage by opening the semiconductor switch located on the primary side of the transformer with an opening angle γ depending on the load state, moreover, without load, the opening angle of the semiconductor key is minimum γ = 0 °, and at rated load, the opening angle is maximum γ = 180 °, and the semiconductor key is not opened.

To explain the process of the occurrence of magnetization currents, we consider transients in a real transformer. From the equivalent circuit:

In this case, instead of the variable i ₁ it is advisable to introduce the variable Ф, then:

. Поэтому при интегрировании можно приближенно принять L₁₁ постоянным.The integration of this equation is very difficult because L ₁₁ ≠ const and is determined by the complex nonlinear coupling i ₁ = f (Φ) expressed by the magnetic characteristic of the transformer. However, the first term on the right side of the equation is small, because r _{1 is} small, compared with the second term of this equation, just as the voltage drop r ₁ i _{1 is} small compared to the EMF -

. Therefore, when integrating, you can approximately take L ₁₁ constant.

Under these conditions, the solution of the equation can be represented in the form of two terms:

where Ф ′ is the instantaneous value of the flow for steady state and Ф ′ ′ is the instantaneous value of the free flow.

A particular solution to the equation is flow

,

,

Where

;

;

The flow Ф ′ ′ is determined by solving the equation

and is equal

where C is the integration constant determined by the initial conditions. At the moment of switching on, the core may have some flux ± Fost of residual magnetization. Therefore, taking in the future φ = π / 2, for the moment t = 0 we obtain

where from

and therefore

In this way,

The invention is illustrated by the figures:

figure 1 shows a graph of the dependence of f = f (ωt);

figure 2 shows a graph of the voltage on the primary side of the transformer versus time U ₁ = f (ωt) at the opening angle of the thyristor γ = 0 °. The least favorable case is when ψ = 0 or 180 ° (the voltage at the moment of switching on passes through 0). Consider the case ψ = 0. Moreover, if Φ _ost at the moment t = 0 is directed counter to the flow Φ, then

The form of the curve Φ = f (ωt) for this case is shown in Fig. 1.

The maximum value of Ф is reached approximately half a period after switching on, i.e. at ωt≈π. Wherein

Since usually r ₁ << ωL ₁₁ . therefore

Thus, Ф _{max is} more than two times higher than the normal value of the working flow, and, therefore, the core is very saturated. This, in turn, leads to the appearance of very large magnetizing currents.

If we create a flow Φost directed counter to the free flow, then as a result, when the transformer is turned on in the most difficult idle mode, we have:

That is, the maximum current will exceed the rated current by less than 2 times, which depends on the ratio of F _m and F _ost . And the value of F _ost , in turn, depends on the magnitude of the bias voltage, which will turn on the transformer.

Thus, the amplitude of the magnetization currents will be reduced, which will thereby lead to an improvement in the process of turning on the output transformer of the regulator under partial load.

Since the regulator on the primary side of the transformer already has semiconductor switches (thyristors), switching on the bias voltage can be done by opening one of the thyristors, and the opening angle of this thyristor can be changed from 0 to 180 ° depending on the state of the load. If there is no load, then the opening angle of the thyristor is minimal (γ = 0 °), if the load is nominal, then the opening angle is maximum (γ = 180 °), that is, the thyristor does not open (figure 2).

So, the claimed invention allows to improve the quality parameters of the circuit when you first turn on the output transformer of the regulator on an underloaded circuit by reducing the emissions of magnetization currents.

Claims (1)

The method of regulating AC voltage, which consists in the fact that when operating on a lamp load, both the number of periods of the supply voltage connected to the load and the duration of the regulation period vary from the period of the frequency of the supply voltage to the period of the critical frequency, which for operation with an incandescent lamp is 50 Hz, characterized in that before the first turn on of the transformer, a turn-on delay is performed for one period of the supply voltage, in the first half of which a state analysis is performed load, and, depending on the result, in the second half of the transformer create a magnetic flux Ф _ost by turning on the transformer for voltage by opening the semiconductor switch located on the primary side of the transformer, with an opening angle γ depending on the state of the load, and without load, the angle the opening of the semiconductor key is minimum γ = 0 °, and at rated load the opening angle is maximum γ = 180 °, and the semiconductor key is not opened.

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