RU2442260C1 - Method for increasing quality and efficiency of power usage (variant 7) - Google Patents

Abstract

FIELD: electrical engineering. ^ SUBSTANCE: according to the method, energy of quadrature current components is extracted from the power flow tapped by active inductance via a fully controlled solid-state PWM rectifier load. These current components belong to base frequency currents and higher harmonic components generated by non-linear load. The energy is extracted in the form of the equivalent energy of a repeated width-modulated current pulse sequence. The duration of these pulses is measured according to the change law of the idle current envelope curve, and, after the transformation via a controlled power source, the energy is returned into the power grid in the form of active energy via the basic frequency current. The suggested abovementioned power source is a PWM rectifier. ^ EFFECT: increase of the power usage quality and efficiency through the reduction of non-productive losses in the grid's power flow. ^ 1 dwg

Description

The method relates to electrical engineering and can be used to improve the quality and efficiency of energy use.

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 analogue method has disadvantages, the main of which are the dependence of the reactive power generated by the BC, on the voltage and their sensitivity to distortion of 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 a known method, the authors propose the disposal of the higher harmonic voltage components. However, it is known that the percentage of harmonics in the supply voltage does not repeat the percentage of harmonics in the current flowing in the power system, which is formed under the influence of a nonlinear load. Moreover, it is the current taken by the nonlinear load that determines the harmonic composition and percentage of harmonics in the power supply network. Thus, a significant decrease in the amplitudes of higher harmonics in the phases of the power system, when implementing the known prototype method, will not occur. In addition, the prototype method does not provide compensation for reactive "power", and, thus, there are unproductive energy losses due to reactive currents.

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, from the power flux selected by the nonlinear active-inductive load, its reactive component, determined by the inductive component of the fundamental frequency harmonic, and the total reactive energy of higher harmonics, the proportion of which must be reduced, are extracted in the form of equivalent energy of a unipolar sequence, periodically repeating pulse-width modulated current pulses, the duration of which varies according to the law of variation of the envelope extracted by the reactive which leaves a current, and, after its conversion, is returned to the power system in the form of active energy by means of a current of fundamental frequency.

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 controllable transistor PWM rectifier;

4 - controlled power converter;

5 - harmonic filter of the current of the fundamental frequency;

6 - block generating a logical signal;

7 - block generating a modulating signal;

8 - nonlinear load;

9 - voltage sensor;

10 - rectifier;

11 - controlled scale amplifier;

12 - control unit;

13 - current sensor;

14 - capacitive storage;

15 - sensor voltage supply.

The essence of the method is as follows. As you know, the following facts take place in the power network when it is powered by non-linear active-inductive loads: 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 related to the fact that part of the energy stored in the magnetic field of the reactive load returns back to the source as a reactive component of the current. The flow of reactive current is provided by self-induction EMF. In this case, the signs of the supply voltage and EMF of self-induction, as is known, are 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 to extract the inductive component of the harmonic current of the fundamental frequency and the reactive currents of higher harmonics, the fraction of which must be reduced, and, after conversion, return to the power system in the form of active energy by means of the current of the fundamental frequency from the power flow selected by the active-inductive load. 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. At the same time, the transistors of each of the arms of the controlled bridge open under the influence of the self-induction EMF, for the 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 power source, which is proposed to use a PWM inverter, 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.

The method is as follows. Nonlinear active-inductive load 8 selects the active inductive component of energy from the power system together and generates higher harmonic components. In this case, the power system is loaded with reactive currents of harmonics of the fundamental frequency and higher harmonics, causing unproductive power losses. By means of a current sensor 2 and a supply voltage sensor 15, signals proportional to them are generated. At the same time, at the output of the current sensor 2, the signal proportional to the non-sinusoidal current sampled by the load 8 lags the voltage at its terminals by an angle determining the power factor in the power system relative to the fundamental frequency harmonic. In the block for generating the logical signal 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 generated at its output, and if the signs of the signals are proportional to the current and voltage, the output of block 6 a logical unit is formed, 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. Further, the signal from the output of block 6 is fed to one of the 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 a 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 it. During the duration of the 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 fed to the input of a controlled power converter 4, which uses a PWM inverter. In a capacitive storage device, a sequence of unipolar periodically repeating pulse-width modulated current pulses, whose energy 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 the envelope said reactive component of the current, is accumulated in the form of direct current energy. The voltage thus obtained is used to power a controlled power converter 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, the gain of which is selected based on the mentioned power loss, and which controls the signal, formed by the method described above, from the voltage supplying the load to 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 in proportion to the ratio of powers: the total reactive power of the higher harmonics and the reactive power of the harmonic of the fundamental frequency extracted from the power system and the power returned to the 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 harmonic energy of the fundamental frequency.

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 improving the quality and efficiency of electricity use, the inductive component of the main frequency current and the reactive energy of higher harmonics are extracted and disposed of from the power system, the proportion of which must be reduced in the power flow selected by the nonlinear active-inductive load.

INFORMATION SOURCES

1. Rekus G.G. Electrical equipment of production: Reference, 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 a part of the energy that causes its unproductive losses is extracted from the power flow taken by an inactive non-linear load, and after conversion to the fundamental frequency harmonic is generated into the power system, characterized in that the main frequency current generated in the power system is formed as active due to the energy of the reactive components of the currents of the fundamental frequency and the group of higher harmonics generated by the nonlinear energy extracted from the power system load, in the form of 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 total reactive current extracted from the power system, through a fully controlled transistor-type PWM rectifier controlled by a modulating signal, which is preliminarily generated by the result comparing the signs of two components - an analogue, proportional to the extracted reactive component of the current, and which, in the case of equal signs of the compared voltages: supplying the load and proportional to the mentioned analogue component, is formed in the form of a logical signal, in this case, if the signs of the components are opposite, the said modulating signal is generated and by means of it the said voltage is extracted into each half-period of the supplying load reactive current, while the active current of the main frequency generated in the power system is generated by an additional controlled source power, the power of which is provided by the extracted reactive component of energy, and which is controlled by a modulating signal generated from a voltage supplying the aforementioned non-linear load, the value of which is pre-formed in proportion to the geometric difference of the signals proportional to the power components: the reactive component extracted from the power system and generated in power system of the active component of the current of the main frequency.