RU2442262C1 - Method for increasing quality and efficiency of power usage (variant 8) - Google Patents

Abstract

FIELD: electrical engineering. ^ SUBSTANCE: according to the method, the quadrature component of the grid's power flow is reduced either by extracting the inductive component in the form of unidirectional repeating width-modulated current pulse sequence, or via generation of compensating current in the power grid through an additional controlled power source. In the first case the extracted inductive component after being transformed returns into the power grid in the form of basic frequency harmonic component. In the second case the compensating current is formed: by means of reactive energy of higher harmonic components which are formed by non-linear load; or by means of active energy of basic frequency harmonic component; or by means of energy which comprises reactive energy of higher harmonic components and a part of active energy of basic frequency harmonic component. ^ EFFECT: reduction of non-productive losses in the power flow of the grid. ^ 1 dwg

Description

The method relates to electrical engineering and can be used to increase the efficiency of electricity use, by reducing unproductive losses in the power flow of the power system.

A known method of reactive power compensation (1), adopted as an analogue, in which the inductive component of the current generated by the non-linear load is compensated by the capacitive current of capacitor banks (BC). The known method - the analogue has disadvantages, the main of which are the dependence of the reactive power generated by the BC from voltage and their sensitivity to distortions in the shape of the supply voltage. In this case, there is a short service life of the battery and their insufficient electrical strength.

The known method (2), adopted as a prototype, in which a part of the energy that causes its unproductive losses is extracted from the power flow, taken by an inactive load, and returned to the power system after conversion to the harmonic of the fundamental frequency. In the known method, compensation for reactive “power” is not provided, and thus, unproductive energy losses due to reactive currents occur.

The problem solved by the invention is to improve the quality and efficiency of energy use.

This is achieved by the fact that according to the proposed method, the reactive component in the power flow of a power system is reduced depending on its nature: either by extracting the inductive component of energy, 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 the inductive component of the current, either through generation into the power system, using an additional regulated source of power spine - of the compensating current, and in the first case, the extracted inductive component of the energy after conversion is returned to the power system in the form of harmonic energy of the fundamental frequency, and in the second, the compensating current is generated either due to the reactive energy of the group of higher harmonic components generated by the nonlinear load, or due to the active energy of the harmonic of the fundamental frequency, or due to the energy consisting of the reactive energy of the group of higher harmonic components and the fraction of the active energy of the harmonic of the fundamental frequency, and the reactive energy of the group of higher harmonic components, and the active harmonic energy of the fundamental frequency, or its fraction, are extracted from the power system in the form of the 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 of the extracted current.

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 - additional regulated power source

5 - harmonic filter of the fundamental frequency current

6 - block generating a logical signal

7 - the first block generating the modulating signal

8 - nonlinear load

9 - voltage sensor

10 - rectifier

11 - controlled scale amplifier

12 - control unit

13 - current sensor

14 - capacitive storage

15 - voltage sensor

16 - the first logical block

17 - the second block of the formation of the modulating signal

18 - phase-correcting link.

The essence of the method is as follows. As you know, the following facts take place in the power network when non-linear reactive loads are supplied from it: the shape of the current is distorted due to the appearance of higher harmonic components of the fundamental frequency in it; a reactive component of the instantaneous harmonic power of the fundamental frequency appears in the power system. The latter fact is due to the fact that part of the energy stored in the electric or magnetic field of the reactive load returns back to the source in the form of a reactive component of the current. The flow of reactive current in inductive loads is ensured by the action of EMF self-induction, in capacitive ones - by the voltage accumulated in the electric field of the capacitance. In this case, the signs of the supply voltage and EMF of self-induction, as well as the supply voltage and voltage on the capacitive element, are known to be opposite. High harmonic currents are also reactive. The negative effect associated with reactive currents, as is known, consists in additional unproductive energy losses in the power system.

In the claimed method, the task of improving the quality and efficiency of energy use is solved by reducing its unproductive losses. At the same time, it is proposed at those times when the load in the power system is reactive in nature to extract the inductive component of the harmonic current of the fundamental frequency and the reactive currents of higher harmonics, the proportion of which must be reduced, from the power flow selected by the active-reactive load, and return it to the power system after conversion in the form of active energy by means of a current of fundamental frequency. At the same time when the load of the power system changes its character to capacitive, it is proposed by means of an additional regulated power source, which is advisable to use a PWM inverter of transistor type, to generate a compensating current in the power system, the magnitude and phase of which is formed due to the energy of the main frequency current , so as to adjust the power factor of the power system to a predetermined value.

The task of extracting the aforementioned reactive components is solved by the use of a fully controlled transistor PWM rectifier, built on IGBT modules. The flow of reactive currents in each of the arms of a fully controlled transistor rectifier is provided, in each half-cycle 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 under the influence of the self-induction EMF for a time during which the reactive components of the harmonic currents flow in the power system: the fundamental frequency and the higher components. Transistors are controlled by a modulating signal with predetermined characteristics. The use of IGBT transistors for rectification of current allows you to use their control properties relative to currents. In this case, selective rectification of only those current components that are set by the control signal is carried out. 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 is equivalent to the energy of the reactive component of the currents extracted from the power system: main and higher harmonics; and the duration of which varies according to the law of change of its envelope. Further, the extracted energy is accumulated in the capacitive storage and, after conversion by means of an additional adjustable power source, is returned to the power system in the form of active energy by means of a fundamental frequency current. In this case, the circuit in which the reactive energy of the current of the fundamental frequency and the higher harmonics generated by the load is closed is limited to the connection point of the device providing its extraction. Thus, the power system is unloaded from the inductive component of the current.

In the case described above, when the PWM inverter generates a compensation current for the capacitive component, the controlled transistor PWM rectifier only works with the active component of the current in the power system, like a normal bridge. In this case, the active energy component is extracted as usual, respectively, by each rectifier arm, during each half-cycle of the supply voltage. The compensation current generated by the PWM inverter and generated in the power system is controlled by a modulating signal generated by the load current,

The method is as follows. Nonlinear reactive load 8 selects from the power system together with the active reactive component of energy, which at the same time changes its character. Thus, in the power system, along with reactive currents of higher harmonics, either inductive or capacitive currents of the fundamental frequency are present at different instants of time. In this case, reactive currents cause unproductive power losses. By the proposed method, it is possible to reduce the reactive currents generated by the load with a different nature (inductive or capacitive). Consider the implementation of the proposed method during the phase of the generation of a load of inductive current and reactive currents of higher harmonics. By means of a current sensor 2 and a supply voltage sensor 15, signals proportional to them are generated. At the same time, from the output of the current sensor 2, a signal proportional to the current taken by the load 8 is simultaneously fed to one of the inputs: a harmonic filter of the current of the fundamental frequency 5, a logical signal generating unit 6, the first logical unit 16, and the first modulating signal generating unit 7 to the input phase-correcting link 18. From the output of the supply voltage sensor 15, a signal proportional to the supply voltage to the load is supplied to one of the inputs: a logical signal generating unit 6, a first logical unit 16, a second block f rmirovaniya modulating signal 18, a fully managed transistor PWM rectifier 3. In block 16, built including trigger principle analyzed nature of the load 8. In this case, from signals proportional to current and voltage, at the last zero crossing pulses generated sequence. If the voltage is ahead of the current, an enable signal is generated at the output of block 16, for example, a logical unit, in the opposite case, a logical ban. Thus, if the load 8 is inductive, from the output of block 16 the enable signal is supplied to the control inputs of the first modulating signal generating unit 7, controlled by a large-scale amplifier 11, and the inhibit signal is transmitted to the second modulating signal generating unit 17. In the logical signal generating unit 6 the signs of the signals arriving at its inputs from the outputs of the current sensor 2 and the sensor of the supply voltage 15 are compared, and a digital sequence of zeros and ones is formed at its output, and if the signs coincide with Ignals proportional to current and voltage, a logical unit is formed at the output of block 6, and in other cases a logical zero. Thus, the logical unit corresponds to that part of the period during which the load 8 selects active power from the power system. Next, the signal from the output of block 6 is fed to one of the signal inputs of the block for generating the modulating signal 7, the second input of which receives a signal proportional to the current taken by the load 8. Thus, at those moments during which the logical zero coming from the output of block 6 coincides at the input of block 7 with the positive half-wave of the current taken by load 8, modulating voltage pulses are generated at the output of block 7, which are proportional to the inductive component of the current taken by load 8, and in-phase with respect to . During the duration of the action of voltage pulses generated by block 7, 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 is extracted, which includes the reactive currents of the harmonics of the fundamental frequency and higher harmonics, selected by the active-inductive load 8, in a form that contributes to its accumulation. At the same time, at its output, a sequence of unipolar, periodically repeating pulse-width modulated current pulses is formed, which, through the capacitive storage 14, is supplied to an additional regulated power source 4, which uses a PWM inverter. In a capacitive storage device, a sequence of unipolar, periodically repeating pulse-width modulated current pulses, the energy of which is equivalent to the reactive current extracted from the power system, including the inductive component of the harmonic current of the fundamental frequency and the reactive components of the higher harmonics currents, selected by the active-inductive load, and their duration varies according to the law of change the envelope of said reactive component of the current is accumulated in the form of direct current energy. The voltage thus obtained is used to power an additional regulated power source 4, by which the stored energy is converted into harmonic energy of the fundamental frequency and returned to the power system. In this case, the control unit 4 is carried out by a signal generated by the supply voltage, specifying the phase (equal to zero in relation to the supply voltage) of the current returned to the power system. Obviously, the power spent on generating the fundamental frequency current must be greater than the total reactive power of the fundamental frequency harmonics and higher harmonics extracted from the power system, and, accordingly, accumulated in the capacitive storage 14 by the amount of losses that occur during energy conversion. In this regard, the magnitude of the signal controlling the PWM inverter must ensure this correspondence, otherwise the power flow in the circuit "PWM inverter - PWM rectifier - power supply system" will not be continuous. The magnitude of the signal, ensuring compliance with the mentioned powers, is formed as follows. By means of a voltage sensor 9, a signal is generated, predetermined by its minimum value, proportional to the total reactive power of the higher harmonics and the reactive power of the fundamental frequency harmonic extracted from the power system, fed to one of the inputs of the control unit 12, to the second input of which a signal formed by a circuit consisting of a current sensor 13 and a rectifier 10, by means of a harmonic signal of the fundamental frequency and proportional to the power returned to the power system using a controlled conversion power indicator 4. In this case, the control signals 12 are compared in magnitude, and their difference is converted into a signal proportional to it, which is fed to the control input of the controlled scale amplifier 11 and which controls the signal generated by the method described above from the voltage supplying the load at its signal input. Thus, the magnitude of the signal that controls the operation of the PWM inverter, and therefore, controls the amount of power returned to the power system, is formed depending on the power ratio: the total reactive power of the higher harmonics extracted from the power system and the harmonic reactive power of the fundamental frequency and the power returned to power system. In this case, the magnitude of the current generated in the power system increases until the voltage in the capacitive storage 14 reaches the minimum value. Thus, the decrease in voltage in the capacitive storage 14 to a minimum level reflects the fact that almost all of the reactive power extracted from the power system is converted into the fundamental harmonic energy.

If the load 8 is capacitive in nature, from the output of block 16 the inhibit signal is supplied to the control inputs of the first modulating signal generating unit 7, controlled by a large-scale amplifier 11, and the enable signal is sent to the second modulating signal generating unit 17. In this case, the operation of blocks 7 and 11. In block 17 of the analog signal supplied to its signal input, proportional to the current selected by the load 8 and adjusted in the phase-correcting link 18 to an angle that is initially determined by the condition is formed I generated by a controlled source of additional power 4 - inductive current - the latter is formed modulating control signal. Moreover, in case it is necessary to completely compensate for the capacitive component of the current, the aforementioned analog signal entering the block 17 is shifted by 180 el. degrees. Thus, in the power system generated by the described method, the compensation current of the capacitive component.

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, improving the quality and efficiency of electricity use, it is achieved that the reactive component of the power flow of the power system is reduced depending on its nature: either by extracting the inductive component of energy, in the form of an equivalent energy of a unipolar sequence periodically repeating pulse-width modulated current pulses, the duration of which vary according to the law of change the envelope of the inductive component of the current, or by generating a compensating current of the capacitive component in the power system using an additional adjustable power source.

INFORMATION SOURCES

1. Rekus G.G. Electrical equipment production: Ref. allowance [Text] / Rekus G.G. - M .: Higher. school., 2007, p.334.

2. RF patent No. 2237334, published: 2004.05.20.

Claims (1)

A method of improving the quality and efficiency of energy use, in which the unproductive power losses in the power system are reduced by utilizing a part of the energy, which, after conversion to a main frequency current, is returned to the power system, characterized in that the unproductive power losses in the power system are reduced by utilizing a part of the energy only if the load is of an active-inductive nature, while if the nature of the load changes on a capacitive, into the power system by means of an additional adjustable power source, a current compensating current is generated from the current supplying the load, the magnitude and phase of which is formed by the energy of the main frequency current, so as to adjust the power factor of the power system to the value that is initially set, and the main frequency current generated into the power system, is formed by means of the said additional regulated power source, which is controlled by means of a voltage generated, p emitting a load, a modulating signal, the value of which is preliminarily formed as the geometric difference of the signals proportional to the power components of the reactive component extracted from the power system and generated into the power system by the main frequency current, and the additional regulated power source is supplied by the energy of the reactive components of the main frequency currents and groups higher harmonics that are extracted from the power system in the form of an equivalent sequence energy unipolar periodically repeating pulse-width modulated current pulses, the duration of which varies according to the law of the envelope of the extracted total reactive current by means of a fully controlled transistor-type PWM rectifier, the extraction of which is controlled by a modulating signal, which, in turn, is preliminarily formed by comparing the signs of its two components - analog, proportional to the extracted inductive component of the current and the component, which in the case of equal The signs of the signs of the compared voltages: supplying the load and proportional to the mentioned analog component, are formed in the form of a logical signal, in this case, if the signs of the components of the modulating signal are opposite, by means of the latter, the said inductive current is extracted in each half-cycle of the supply voltage.