RU2442259C1 - METHOD FOR INCREASING QUALITY AND EFFICIENCY OF POWER USAGE IN n-PHASE POWER SUPPLY SYSTEM (VARIANT 1) - Google Patents

Abstract

FIELD: electrical engineering. ^ SUBSTANCE: according to the method, for every phase of the n-phase power supply system, the equivalent compensating current which includes currents from higher harmonic components equivalent to higher harmonic currents that must be reduced, is formed either by self-extracted quadrature component of power taken by non-linear load, or by both quadrature and a part of active components. Furthermore, the latter are extracted by means of a fully controlled length PWM rectifier, they come in the form of equivalent energy of a repeating width-modulated current pulse sequence. This energy is used after its transformation to DC energy to form the abovementioned equivalent compensating current. ^ EFFECT: reduction of higher harmonic component levels in the power feeding system and increased power usage efficiency. ^ 1 dwg

Description

The invention relates to energy and can be used to improve the quality and efficiency of energy use in n-phase power supply systems.

A device (1) is known that is used to improve the quality of electric energy, containing a thyristor source of reactive power, made in the form of a thyristor bridge, one diagonal of which includes two control windings of a controlled reactor, and a resistor in the other. The analogue method has disadvantages, the main of which are low profitability and a limited range of reactive power regulation.

A known method (2) to improve the quality of electricity, which consists in the fact that the first and the highest harmonic components are extracted from the "voltage of the electric network, rectify them, convert the rectified voltage into alternating voltage with a frequency equal to the frequency of the main harmonic of the network, and return the alternating voltage to the electric network ". The known method, adopted as a prototype, has a number of disadvantages, the main of which are as follows. In a known method to improve the quality of electricity, the authors propose compensation for 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. It is also known that 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 analogue method, will not occur. The limitations of the known method consists in: "lowering" the voltage levels of harmonics of strictly defined frequencies; the impossibility of compensation in a reactive power system. In addition, additional unproductive power losses during the implementation of the prototype method are due to the use of a power transformer.

The problem solved by the invention is to improve the quality and efficiency of energy use by: increasing the efficiency of the process of compensation of higher harmonic components (due to compensation of higher harmonic components in the spectrum of the current, selected by non-linear load); reduction of unproductive losses of electricity caused by reactive currents of the main and higher harmonics; use for the implementation of the process of compensation of the higher harmonic components of the current, the reactive energy of the harmonic of the fundamental frequency.

This is achieved by the fact that according to the proposed method, the equivalent compensating current, including the currents of the group of higher harmonic components, equivalent to the currents of higher harmonics, the proportion of which must be reduced, for each of the phases of the n-phases of the power supply system, is formed either due to the independently extracted reactive component of the power taken non-linear load, or due to the jointly extracted reactive and active component fractions. At the same time, the latter are extracted by means of an n-phase fully controlled PWM rectifier, in the form of an equivalent energy, of a sequence of unipolar, periodically repeating pulse-width modulated current pulses, which, after conversion to direct current energy, are used to form the said equivalent compensating current.

The essence of the method is as follows. It is obvious that when feeding a nonlinear active-reactive load, from the n-phase energy supply system, in each of its phases, active-reactive currents flow, the spectrum of which is the main and higher harmonics. In this case, the sign of the instantaneous power of their reactive components during the quarter of their period changes to the opposite. This fact is due to the fact that part of the energy stored in the electric or magnetic field of the reactive component of the load returns back to the source in the form of the aforementioned reactive currents, the flow of which in inductive loads is provided by the action of self-induction EMF, in capacitive ones - by the voltage accumulated in the electric field of the capacitance . The signs of the supply voltage and EMF of self-induction, as well as the supply voltage and voltage on the capacitive component of the load, are opposite. In this case, the negative effect associated with reactive currents, as is known, consists in additional unproductive energy losses. In accordance with the claimed method, the task of improving the quality and efficiency of energy use is solved, on the one hand, by reducing its unproductive losses due to the reactive component of the harmonic current of the fundamental frequency, and on the other hand, by adjustable compensation of higher harmonics. It is also suggested that at those times when the load in the power system is reactive in nature, extract the reactive current of the fundamental frequency from the power stream in order to further use its energy, either independently or together with the active harmonic energy of the fundamental frequency, to form an equivalent compensating current , including the currents of the group of higher harmonic components, equivalent to the currents of higher harmonics, the proportion of which must be reduced. The mentioned compensating current is generated and generated into the power system through an additional power source, which is proposed to use a PWM inverter controlled by a modulating signal generated for each of the phases separately, by signals proportional to the geometric sum of the currents of the compensated higher harmonic components. If in the power system the total power of the group of compensated harmonics is greater than the power of the reactive component of the harmonic of the main frequency current, the latter is extracted from the power system together with a fraction of its active component, and both components, after conversion to direct current energy, are used to power the mentioned additional power source .

The problem of phase-by-phase extraction of the aforementioned reactive and a fraction of the active components of the main frequency current from the power system is solved by using a fully controlled n-phase transistor PWM rectifier built on IGBT modules. The flow of reactive currents in each of its arms, in each half-cycle of the supply voltage, is ensured by the action of the self-induction EMF, or by the voltage on the capacitive component of the load. 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 specified by a modulating control signal with specified characteristics is carried out. At the same time, at the output of the controlled transistor PWM rectifier, there is a sequence of unipolar periodically repeating pulse-width modulated current pulses, the energy of which is equivalent, respectively: either extracted from the power system, independently, the reactive component of the current energy of the fundamental frequency harmonic, or, when the reactive and the active components - the energy of the latter.

The claimed method is described by the example of a three-phase system. The drawing shows a diagram explaining its essence. The following notation is introduced.

1 - n-phase power system

2 - nonlinear load

3 - n-phase fully controllable transistor PWM rectifier

4 - capacitive storage

5 - n-phase auxiliary power source

6, 7, 8 - phase current sensors

9, 10, 11 - voltage sensors

12, 13, 14 - blocks the formation of a logical signal

15, 16, 17 - blocks the formation of the modulating signal

18 - voltage sensor

19 - n-phase mixer unit

20 - n-phase capacitive storage unit

21, 22, 23 - harmonic filters of the fundamental frequency current

24 - n-phase block forming the active component of the control signal

25 - n-phase unit for setting groups of compensated harmonics

26 - n-phase phase inverter unit

27 - n-phase rectifier unit

The method is as follows. Due to the fact that for any n-phase power supply system, the claimed method is implemented in a similar way, it will be further considered with respect to a three-phase system. The method is as follows. From the outputs of the sensors 6, 7, 8, signals proportional to the non-sinusoidal currents selected by the non-linear load 2 from the phases “A, B and C” are received, including the input of the n-phase block for setting the groups of compensated harmonics 25, by which for each of the phases, in advance, a spectrum of harmonics is set, the proportion of which must be reduced, by reducing their levels, by the method of adjustable compensation. In this case, block 25 can be a group of filters (according to the number of phases) by which a spectrum of compensated harmonics is extracted from the signal selected by load 2 from each of the phases. Further, the signals thus formed are fed to the corresponding inputs of the n-phase block (according to the number of phases) of the phase inverters 26, by which they are inverted by 180 el. degrees, and then, from its outputs, they go to the control inputs of the n-phase (by the number of phases) additional power source 5, corresponding to the phases "A, B and C", through which equivalent compensating currents are generated in each of them, including group currents higher harmonic components equivalent to the currents of higher harmonics, the proportion of which must be reduced, and which are in antiphase with respect to them. Thus generated, controlling the corresponding phases of the power source 5, the modulating control signals are proportional to the geometric sum of the currents of the compensated higher harmonic components, the spectrum of which is set initially, for each of the corresponding phases of the power system, as described above, by means of block 25. For each of the phases of the power system, the equivalent compensating currents are formed either due to the energy of the reactive component of the harmonic extracted from the energy system independently he primary frequency, or by co-recoverable reactive and active components of its capacity. At the same time, the aforementioned components of the main-frequency current power are extracted from each phase of the power system 1 by means of a fully controlled transistor PWM rectifier 3, and after conversion to direct current energy by means of a capacitive storage 4, they are used to power an n-phase additional power source 5. The composition of the energy used for its power supply, is determined by means of a sensor 18, depending on the ratio of powers: reactive component of the harmonic power of the fundamental frequency and the power needed to compensate for the harmonic components, by measuring the latter, taken from the capacitive storage 4, - voltage. In this case, initially its value is dependent on the power extracted from the power system, so that if the extracted reactive component of the power is sufficient to form equivalent compensating currents, then at the output of the capacitive storage 4 there is a voltage that blocks the presence of the active component of the harmonic of the fundamental current in the modulating the control signal of the PWM rectifier 3, and in this case, only the reactive component of the power is extracted from the power system 1 harmonics of the fundamental frequencies at which energy is used to power the n-phase (for the considered case - phase), an additional power source 5, and therefore for generating compensating currents equivalent. Let us consider in more detail the case of the formation of the equivalent current for compensating the spectrum of higher harmonics, by means of an additional power source 5, only due to the energy of the reactive component of the harmonic of the current of the fundamental frequency, which characterizes its extracted power as sufficient for the formation of equivalent compensating currents. From the outputs of current sensors 6, 7 and 8, signals proportional to non-sinusoidal currents, phase-selected by a non-linear load, are received, including the inputs of blocks 21, 22, 23, which are, for each of them, primary frequency current filters, the output of which signals proportional to the harmonics currents of the fundamental frequency, are fed to the inputs of blocks 12, 13 and 14 (the number of which corresponds to the number of phases) of the formation of a logical signal, which, together with blocks 15, 16, and 17, of the formation of the modulating signal, participate in the formation of the latter . It is obvious that the number of blocks 6-8, 21-23, 12-14, 15-17 corresponds to the number of phases in the power system. In this case, by means of the said blocks, the reactive component of the modulating signal of the phases “A, B and C” is formed as follows. By means of blocks: current sensors 6-8, blocks 21-23, and sensors of supply voltage 9-11 (according to the number of phases of the power system), they generate signals proportional to the currents of the main part and the supply voltage. Moreover, in the signals present at the output of blocks 21-23, there is no common mode with respect to "their" supply voltages. Due to the fact that the process of generating the reactive component of the modulating signal is similar for all phases of the power system, we consider it using the example of phase “A”. In the block for generating a logical signal 12, the signs of the signals arriving at its inputs are compared: from the output of block 21 and the supply voltage sensor 9; and at its output a digital sequence of zeros and ones is formed, and if the signs of the signals are proportional to the current and voltage, a logical unit is formed at the output of block 12, and in other cases a logical zero. Thus, a logical unit corresponds to that part of the period during which load 2 selects active power from the power system. Further, the signal from the output of block 12 is fed to one of the inputs of the block 15 for generating the modulating signal, the second input of which receives a signal proportional to the current taken by load 2 from the corresponding phase, in this case, from phase “A”. Thus, at those moments during which the logical zero coming from the output of block 12 coincides at the input of block 15 with the positive half-wave of the current taken by load 2, modulating voltage pulses proportional to the reactive component of the current taken by load 2 are formed at the output of block 15 , and in-phase with respect to it. Next, the modulating control signals of the PWM rectifier, which are proportional to the reactive component of the harmonic current of the fundamental frequency, generated for each phase in the described manner, are fed to the first group of signal inputs of the n-phase block of the mixers 19, and then to the corresponding control inputs of the fully controlled transistor PWM rectifier 3. In this case, the second group of signal inputs of the mixer block 19, corresponding to the active component of the harmonic of the current of the fundamental frequency, is blocked by a signal from the output of the unit Single 18. The blocking signal is generated as a result matching the voltage level at the capacitive storage device 4, a predetermined value, which indicates the adequacy of the amount of power the reactive component of the fundamental frequency harmonics, per phase extracted from the power system 1, for forming equivalent per phase compensating currents. In this case, the signal from the output of block 18 blocks the n-phase (for the considered case, three-phase) block for the formation of the active component of the control signal 24, and there are no signals at its outputs. During the duration of the action of voltage pulses generated by block 15, at the control inputs of a fully controlled transistor PWM rectifier 3, the latter is powered by: either the self-induction EMF or the voltage on the capacitive component of the load, depending on its nature. Thus, by means of a controlled transistor PWM rectifier 3, the reactive component of the current selected by the active-reactive load 2 is extracted in a form that contributes to its accumulation. Further, in accordance with the claimed method, extracted in the described manner, the energy of the reactive current of the fundamental frequency is accumulated in the form of direct current energy in the capacitive storage 4 and then used to power the n-phase (according to the number of phases of the power system) additional power source 5, which is used A PWM inverter, by which, as described above, an equivalent compensating current is generated and generated in the power system, including currents of a group of higher harmonic components equivalent to OCAM harmonics, whose share should be reduced. The formation of the compensating current, as already shown above, is carried out for all phases of the power system in the same way by individually forming, for each of them, a modulating signal that controls the corresponding phase of the mentioned n-phase PWM inverter.

In the event that the extracted reactive component of the power is not enough to form equivalent compensating currents, the voltage in the capacitive storage 4, controlled by the voltage sensor 18, becomes lower than a predetermined value. Thus, in the event that the voltage in the capacitive storage 4 becomes lower than a predetermined value, a voltage is generated on one of the control inputs of the block 24 by means of a voltage sensor 18, allowing its operation in principle. Block 24 can be formed from a group of amplifiers (one per phase) with the possibility of controlling their amplification factors for one group of control inputs and with the possibility of blocking them with another group of control inputs. At the same time, on another group of control inputs of block 24, there are voltages coming from the output of the n-phase (by the number of phases of the power system) block of capacitive storage 20, and formed by the n-phase (by the number of phases of the power system) block of rectifiers 27, proportional to the powers of the groups of compensated higher harmonics remaining in each phase of the power system, after their compensation, by means of equivalent compensating currents generated due to the energy of the reactive component of the main frequency currents. The power of the remaining higher harmonics remaining in each phase is obviously equal to the difference: the total power of the group of compensated higher harmonics and the power of the reactive component of the harmonic of the fundamental current (or the power of equivalent compensation currents generated by the said reactive components). Moreover, due to the fact that the control unit 24 of the voltage generated for each of the phases, through the n-phase unit for setting groups of compensated harmonics 25, which isolates from the current phase-selected by load 2, the spectrum of compensated harmonics, and, therefore, determines in each of of phases, their residual level, is proportional to the mentioned difference, then the generated amplification factors for signals proportional to the active currents of harmonics of the fundamental frequency of the corresponding phases, arriving at the information inputs of block 24, from the outputs blocks 21, 22 and 23, are also proportional to the difference in the total power of the group of compensated higher harmonics and the power of the reactive component of the harmonic of the fundamental current, for the corresponding supply phase. Thus, if at the output of block 18 there is a signal enabling the operation of block 24 to be supplied to one of the groups of inputs controlling its operation, and signals to the other group of its controlling inputs will be proportional to the difference between the total power of the group of compensated higher harmonics and the power of the reactive component of the harmonic main frequency current, for the corresponding supply phase, at the output of block 24, there are harmonic current signals of the main frequency, the proportion of which are equal to the mentioned power difference. The signals thus formed in block 24 are fed to a mixer 19, where they are mixed with signals of the corresponding phase proportional to the reactive component of the harmonic current of the fundamental frequency. Thus, by means of block 19, the envelope of the modulating control signal of the n-phase fully controlled transistor PWM rectifier 3 is formed, by means of which the reactive and active components of the harmonic current of the fundamental frequency are extracted from each phase of the power system, due to the energy of which equivalent compensating currents are formed, including group currents higher harmonic components equivalent to the currents of higher harmonics, the proportion of which must be reduced, and which are in antiphase with respect to them, A case when extracted from the grid, independently, a reactive power current component of the fundamental frequency harmonics are not sufficient for the formation of said compensating currents.

Thus, as a result of the sequence of actions carried out in accordance with the claimed method, increasing the efficiency of energy use is achieved by increasing the efficiency of the process of compensation of higher harmonic components (due to compensation of higher harmonic components in the spectrum of the current, selected by non-linear load); reduction of unproductive losses of electricity caused by reactive currents of the main and higher harmonics; using for the implementation of the process of compensation of the higher harmonic components of the current, the reactive energy of the harmonic of the fundamental frequency. Moreover, this goal is achieved by the fact that according to the proposed method, the equivalent compensating current, including the currents of the group of higher harmonic components equivalent to the currents of the higher harmonics, the proportion of which must be reduced, for each of the phases of the n-phases of the power supply system, is formed either due to being extracted independently reactive component of power taken by non-linear load, or due to the jointly extracted reactive and the share of active components. At the same time, the latter are extracted by means of an n-phase fully controlled PWM rectifier, in the form of an equivalent energy, of a sequence of unipolar, periodically repeating pulse-width modulated current pulses, which, after conversion to direct current energy, are used to form the said equivalent compensating current.

INFORMATION SOURCES

1. A.S. USSR No. 1823072, Bull. No. 23, 06/23/1993, Cl. H02J 3/18, 3/26, 1993.

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

Claims (1)

A method of improving the quality and efficiency of energy use in an n-phase power supply system, in which the proportion of a number of higher harmonic components in the power flow of a power system is reduced by means of their adjustable compensation, characterized in that the equivalent compensating current, including currents of a group of higher harmonic components, equivalent to higher currents harmonics, the proportion of which must be reduced in the power flow sampled by an n-phase nonlinear load, is generated in each of the n phases power system by means of an additional n-phase power source, the power of which is provided either by extracting from each phase of the power system its own energy of the reactive component of the fundamental frequency harmonic if it is equal for the corresponding phase of the mentioned total current power of the group of higher harmonics, or if the latter is greater the reactive component of the harmonic current power of the fundamental frequency - due to its combined reactive power and the active component power, extracted of each of the n phases, while in the fraction corresponding to the difference in the total power of the group of compensated higher harmonics and the reactive power of the harmonic current of the fundamental frequency, the extraction of the reactive and active components from each phase is carried out by an n-phase fully controlled PWM rectifier in the form of an equivalent the energy of a sequence of unipolar, periodically repeating pulse-width modulated current pulses, which, after conversion to direct current energy, is used to form the aforementioned a vivalent compensating current, in the spectrum of which the higher harmonic components are in antiphase with respect to the equivalent currents of higher harmonics in the spectrum of the current taken by a nonlinear load, generated and generated in each phase by the mentioned n-phase additional power source, controlled by a signal generated for each of the phases separately, by means of the geometric sum of the currents of the compensated higher harmonic components, while in the aforementioned sequence of unipolar, periodically repeated pulse-width modulated current pulses generated by an n-phase fully controllable PWM rectifier, their duration is formed according to the law of the envelope of the corresponding control modulating signal proportional to the current extracted from the power system and generated accordingly: for the independently extracted reactive component of the main frequency current by means of a signal proportional to it, for the extracted reactive and active components by means of a signal proportional to the geometric nical amount of said reactive current component of the fundamental frequency, and its proportion of the active component.