RU2435276C1 - Method to extract reactive component of power - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: from a flow of a power system power, an inductive current component of one or more fixed frequencies is extracted by means of a bridge PWM rectifier of transistor type, as an equivalent energy of sequence of unipolar periodically repeating width-modulated pulses of current, duration of which changes according to the law of variation of envelope of inductive component of current extracted from the power system.

EFFECT: improved efficiency and expansion of functional capabilities.

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Description

The method relates to electrical engineering and can be used when extracting inductive components of energy from the power flow of a power system.

The known method (1) to improve the quality of electricity, adopted as an analogue, in the implementation of which from the power stream, selected by an inactive load, part of the energy that causes its unproductive losses is extracted. The known analogue method does not provide for the extraction of the inductive component from the power flow of the power system.

A known method of extracting, including reactive energy of harmonics, by means of resonance filters, each of which is tuned to the harmonic of a strictly defined frequency, described in (2). The known prototype method does not provide for the extraction of the reactive component of energy in a form that ensures its further use.

The problem solved by the invention is to increase the efficiency of the method of extracting the inductive component of the current of one or more fixed frequencies by expanding its functionality. At the same time, it is proposed to extract the inductive component of energy in a way that facilitates its further use.

This is achieved by the fact that according to the proposed method, the inductive component of the current of one or several fixed frequencies is extracted from the power supply of the power system by means of a bridge PWM rectifier of a transistor type in the form of an equivalent energy of a sequence of unipolar, periodically repeating pulse-width modulated current pulses, the duration of which varies according to the law of the envelope signal proportional to the current extracted from the power system.

The drawing shows a diagram explaining the essence of the claimed method. The following notation is introduced:

1 - power system

2 - load current sensor

3 - fully controlled transistor PWM rectifier

4 - block forming the spectrum of the group of inductive currents

5 - voltage sensor

6 - nonlinear load

7 - block generating a logical signal

8 - block generating a modulating signal

9 - capacitive storage

The essence of the method is as follows. As you know, in a power system when actively inductive loads are supplied from it for a quarter of a period, the sign of instantaneous power changes to the opposite. This is due to the fact that part of the energy stored in the magnetic field of the reactive load returns back to the source in the form of reactive current, which causes unproductive power losses. In this case, the flow of reactive current is ensured by self-induction EMF.

In the claimed method, the task of increasing the efficiency of the method of extracting the inductive component of the current of one or more fixed frequencies is solved by using the method of extraction of the aforementioned inductive component, which ensures its further use.

The inductive component extraction problem is solved by means of a fully controlled transistor PWM rectifier built on IGBT modules. The flow of the inductive component of the current through each of the arms of a fully controlled transistor rectifier is provided in each half-period of the supply voltage by the action of the self-induction EMF. In this case, the transistors of each of the arms of the controlled bridge open for a time during which the inductive component of the current flows in the power system. Transistors are controlled by a modulating signal with predetermined characteristics. The use of IGWT transistors for rectifying current allows their control properties to be used with respect to currents. In this case, selective rectification of only that current component is carried out, which is set by the control signal. At the output of the controlled transistor PWM rectifier, there is a sequence of unipolar periodically repeating pulse-width modulated pulses, the energy of which for the period of their repetition is equivalent to the energy extracted from the power system of the inductive component of the current, and the duration of which varies according to the law of variation of its envelope. The energy thus extracted is stored in the form of direct current energy. In this case, the circuit in which the reactive component of the energy generated by the load is closed is limited by the connection point of the device providing its extraction, and the power system is thus unloaded from the inductive component of the current.

The method is as follows. Active-inductive load 6 selects from the power system together the active inductive component of energy. In this case, the latter loads the power system with reactive current. By means of a current sensor 2 and a supply voltage sensor 6, signals proportional to them are generated. In this case, if the inductive load 6 is non-linear, a signal is generated at the output of the current sensor 2, which is proportional to the inductive current generated by it, the main harmonic of which forms the angle of its delay relative to the supply voltage. The spectrum forming unit of the group of inductive currents 4, which can be used as a set of filters, forms a group of inductive currents of harmonics to be extracted from the power system. Moreover, the indicated group may include, in addition to the inductive component of the fundamental harmonic, reactive components of higher harmonics that must be extracted from the power system. In the event that the load is linear, there are no higher harmonics in its current, and, thus, the mentioned group will contain only the inductive component of the current of the fundamental frequency. In this case, block 4 may be absent. In the block of formation of the logical signal 7, the signs arriving at its inputs are compared from the outputs of the block 4 and the sensor of the supply voltage 5, signals, and a digital sequence of zeros and ones is generated at its output, and if the signs of the signals are proportional to the current and voltage, the output of block 7 is formed by a logical unit, and in other cases, a logical zero. Thus, the logical unit corresponds to that part of the period during which the load 6 selects active power from the power system. Next, the signal from the output of block 7 is fed to one of the inputs of the block for generating the modulating signal 8, the second input of which receives a signal proportional to the current taken by the load 6. Thus, at those moments during which a logical zero coming from the output of block 7, coincides at the input of block 8 with the positive half-wave selected by the load 6 of the current, modulating voltage pulses are generated at the output of block 8, which are proportional to the inductive component of the current selected by load 6, and in-phase with respect to it. During the duration of the voltage pulses generated by block 8, at the control inputs of a fully controlled transistor PWM rectifier 3, the latter is powered by self-induction EMF. Thus, by means of a controlled transistor PWM rectifier 3, the inductive component of the current selected by the active-inductive load 6 is extracted in a form that contributes to its accumulation. At the same time, at its output, sequences of unipolar, periodically repeating pulse-width modulated current pulses are formed, the energy of which, for the period of their repetition, is equivalent to the inductive component of the current extracted from the power system, and their duration varies according to the law of the envelope of the mentioned inductive component, which, by means of the capacitive storage 9 accumulates in the form of direct current energy.

On the implementation of the claimed method, the following should be noted.

The use in the claimed method of a fully controlled PWM rectifier transistor type, operating in key mode at frequencies higher than the frequency of the modulated control signal, is optimal. In this case, a fully controllable transistor PWM rectifier allows you to arbitrarily, depending on the task, to form the envelope of the rectified current consumed from the supply network. The interference from the operation of a fully controlled transistor PWM rectifier can be filtered out using standard solutions with minimal energy and material costs.

The following fact should also be noted. One of the advantages of extracting a current of a given frequency through a fully controlled transistor PWM rectifier is the simplicity of its adjustment when the current power factor in the power system changes. To do this, just change the modulating control signal.

Thus, as a result of the sequence of actions reproduced in accordance with the claimed method of increasing the efficiency of energy use from the power system, the inductive component of the current taken by the active-inductive load is extracted in a form that ensures its further use.

Information sources

1. RF patent №2320067, publ. 2007.01.20.

2. Zhezhelenko I.V. Higher harmonics in power supply systems of industrial enterprises [Text] / I.V.Zhezhelenko. - M .: Energoatomizdat, 1984, p. 109.

Claims (1)

A method of extracting harmonics energy of one or several fixed frequencies from a power flow of a power system, characterized in that the inductive component of the energy of a harmonic group including at least one harmonic of a fixed frequency is extracted from the power flow of the power system in the form of an equivalent energy of a sequence of unipolar, periodically repeating pulse-width modulated current pulses , the duration of which varies according to the law of variation of the envelope of the inductive component of the current of the said group, by m of a fully controlled PWM rectifier of a transistor type, while the energy extraction process of the said group is controlled by a modulating signal, which is preliminarily formed as a result of comparing the signs of two components: an analog one, proportional to the current taken by the active-inductive load, and a component which, if signs of the compared: voltage supplying the load, and voltage proportional to the mentioned analog component, - form in the form of a logical I drove, wherein if the signs are opposite to the components, and the modulation signal is formed by extraction of the latter is carried inductive component of the current in each half-cycle of the supply voltage load.