RU2382467C1 - Method for improvement of quality of electric energy of multiphase system in balancing of currents by specified phase - Google Patents

Abstract

FIELD: electricity. ^ SUBSTANCE: application: in the field of electric engineering. According to method, process of power coefficient control in main n-phase circuit and process of balancing of the latter is realised jointly and serially, in two stages. At the same time reactive power required for user at the first stage is compensated only in one phase that has been previously specified: either phase with load current closed to average one or least loaded phase selected as reference, at the same time power coefficient is brought up to required value. The latter is realised with the help of additional n-phase source of power, by means of generation into reference phase - current, with required module and phased angle. Lacking reactive power in remaining (n-1) phases is compensated with the help of mentioned additional n-phase source of power, balancing the latter relative to reference phase current. ^ EFFECT: improved efficiency and simplified realisation. ^ 1 dwg

Description

The method relates to electrical engineering and can be used to improve the quality of electricity in multiphase power supply systems with loads, the parameters of which vary over time, by expanding the range of reactive power regulation, stabilizing the power factor at the level of any predetermined value, carried out together with an increase in the balancing efficiency for by improving performance and simplifying implementation.

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 is included in the other diagonal. The analogue method has disadvantages, the main of which are low profitability and a limited range of reactive power regulation.

A known method of automatically balancing the voltage on a submersible induction motor, implemented in the device (2), by means of which the voltage at the terminals of the consumer is balanced by regulating the resistance of the power supply circuit of individual phases. This method is the closest in technical essence to the claimed and therefore adopted as a prototype. The known prototype method has the disadvantages of low efficiency and low speed. In addition, the prototype method does not provide for reactive power compensation.

The problem solved by the invention is to improve the quality of electric energy of the main n-phase system by expanding the range of reactive power regulation, stabilizing the power factor at the level of any predetermined value, carried out in conjunction with balancing, the efficiency of which is achieved by increasing speed, simplifying implementation and increasing efficiency .

The problem solved by the invention is to improve the quality of electrical energy of the main n-phase system by expanding the range of reactive power regulation, increasing efficiency and stabilizing the power factor at the level of any predetermined value, carried out in conjunction with balancing, the efficiency of which is achieved by increasing speed and simplifying implementation .

This is achieved by the fact that the proposed method is carried out sequentially, in two stages, and at the same time, in the first stage in the main n-phase system using an additional n-phase power source, the power factor is stabilized at the level of the required value by generating in a predetermined phase, selected previously and defined as a reference current, the module and the phase angle of which are preliminarily formed so that the geometric sum of the currents — the generated current and the load current of the reference phase — is equal to ull of the aforementioned load current, and the phase angle formed by the total current of the reference phase and its voltage would be equal to the specified one, and in the second stage, the asymmetric n-phase load is balanced with respect to the current in the reference phase equal to the total current of the latter, by generating into each symmetrized phase the main n-phase network with the help of the mentioned n-phase power source of currents in which the module and the phase angle are preliminarily formed so that in each of the phases being balanced the geometric sum of the corresponding of the generated current and the current, which is the load current of the corresponding phase, would be equal to the modulus of the total current of the reference phase obtained by geometrical addition in the reference phase of the current generated in it and the current of its load, and the angle formed by the total current of the reference phase and the current equal to the geometric sum currents in the phase following the reference order, with direct phase rotation, and also between the total currents of adjacent (n-1) symmetrized phases, would be equal to 360 / n el. degrees. The choice of the reference phase is carried out depending on the combination of the complex loads of the individual phases of the n-phase network. Either a phase with a load current close to the average or the least loaded phase is chosen as the reference one.

The essence of the method is determined by the following. As you know, for most AC consumers, their normal operation is associated with the consumption of reactive power. At the same time, the fact of reactive power consumption is associated with an increase in electric energy losses in power supply elements having reactance through which it is transited, as well as an increase in voltage losses at the consumer terminals. The fact that the fluctuation of reactive power necessary for the normal operation of the consumer can be concentrated in a special circuit, having completely or partially removed the power circuit of the power system, it has led to the creation of a number of methods for compensating reactive power.

The proposed method for reactive power compensation in the n-phase system is based on the principle that the reactive power needed by the consumer at the first stage is compensated only in one phase selected as the reference phase, bringing the power factor to the required value. The latter is carried out using an additional n-phase power source by generating current in the reference phase with the necessary module and phase angle. The missing reactive power in the remaining (n-1) phases is compensated by balancing the latter with respect to the current of the reference phase. In addition, in some cases, when, depending on the combination of the complex loads of the individual phases, one of the phases is selected as the reference phase, either a phase with a load current close to the average or the least loaded phase, the power taken from the n-phase balanced system is optimal.

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

1 - main n-phase power system

2 - unbalanced load

3, 4, 5 - phase current shape sensors

6 - the first phase-shifting unit

7 - second phase-shifting unit

8 - the first block generating differential signals

9 - additional power source

10 - logical block analysis of the reference phase

11 - reference phase sensor

12 - the third phase-shifting unit

13 - block forming a given phase angle

14 - the second block generating the differential signal

The proposed method is considered as an example of a three-phase system and is carried out as follows.

Preliminarily, depending on the situation (depending on the ratio of the load complexes), one of the phases is selected as the reference phase - either a phase with a load current close to the average, or the least loaded phase, and then symmetrization is carried out relative to the latter. At the first stage of the method implementation, depending on the statement of the problem of balancing by the logic analysis unit of the given phase 10, by comparing the currents of the individual phases, a reference phase is selected from them - either a phase with a load current close to the average or the least loaded phase. In this case, the group of information inputs of block 10 from the outputs of the phase current sensors of phases 3, 4 and 5 receives signals proportional to the shape of the current signals of the phases of the three-phase balanced system. At the output of block 10, control signals for prohibiting (allowing) the operation of individual modules are generated. The absence of prohibition signals at the individual outputs of block 10 is equivalent to the presence of resolution signals at the last. Prohibition (permission) signals are received, including, at the control inputs of the reference phase sensor 11, the information inputs of which receive signals proportional to the voltages of the supply phases. In block 11, reference current signals are generated from the supply phase voltages, which have a zero shift with respect to their voltages and simulate a purely active form of the load. Due to the fact that the prohibition (permission) signals coming from the output of block 10 block all phase signals except the reference signal in block 11, there is only one signal at the output of the latter — the generated reference signal of the reference phase. Suppose, it was previously determined that symmetrization will occur relative to the least loaded phase, i.e. phase with a minimum load current, and by means of block 10 it was determined that this is phase "A". Thus, the beginning of the first stage of the implementation of the proposed method for the considered example ends with the selection of the reference phase "A", in which the load current is minimal, and the formation of the corresponding current reference signal. Further, by means of the third phase-shifting unit 12 and the unit for generating the predetermined phase angle 13, the phase angle of the reference signal is set and thus the necessary power factor of the main three-phase system is formed. Then, by means of the second block of the difference signal 14, a difference signal is formed from the signal proportional to the current of the reference phase and the adjusted reference signal. At the same time, signals from the outputs of sensors 3, 4, and 5 are sent to the first group of information inputs of block 14, the generated and, if necessary, corrected standard current signals proportional to the voltage of the supply phases are supplied to the second group of information inputs of the last, and the control inputs of block 14 prohibition (permission) signals coming from the output of block 10. But in view of the fact that in block 14, like in block 11, the prohibition (permission) signals coming from the output of block 10 block the signals of all phases, except the reference, at the output of the block 14 persons there is only one signal — the difference signal, which is the result of comparing the signal proportional to the current of the reference phase and the reference signal adjusted if necessary. In the general case, the reference signal may not be corrected in phase, then a power factor of one will be achieved, which will correspond to the purely active load of the reference phase. In this case, at the output of block 14, there is a difference signal generated from the reference signal of the reference phase “A” and the signal from block 3 proportional to the current of phase “A”. From the output of block 14, the generated differential signal, which is a control signal, is fed to the control input corresponding to phase "A" of the control circuit of an additional power source 9, through which it is supplied to the reference phase "A". Thus, as a result of the sequence of actions performed in accordance with the first stage of the claimed method, an adjustable compensation of reactive power in the reference phase is carried out. In this way, a power factor is set for the entire main symmetrical three-phase system.

, где m - порядковый номер фазы, следующей за опорной при прямой последовательности чередования фаз, n - количество фаз в системе. В данном случае одной из цепочек отдельного модуля упомянутый сигнал сдвигается соответственно на 120, другой - на 240 эл. градусов, в зависимости от порядкового номера фазы, следующей за опорной, при прямом чередовании фаз, для симметрирования которых он будет использован. С выхода блока 6 сигналы, пропорциональные току опорной, наименее нагруженной фазы, и сдвинутые на 120 и 240 эл. градусов соответственно, поступают на первую группу информационных входов блока формирования разностных сигналов 8, на вторую группу информационных входов которого поступают сигналы, пропорциональные форме токов нагрузок симметрируемых фаз, сформированные в датчиках формы тока фаз 3, 4 и 5 и проинвертируемые на 180 эл. градусов вторым фазосдвигающим блоком 7. Блок 8 также, в общем случае, состоит из n×2 суммирующих цепочек. При этом постоянно в работе задействованы только две из них, относящиеся к соответствующим фазам. Так, для данного случая сдвинутый на 120 эл.градусов сигнал фазы «А» может взаимодействовать (суммироваться) только с сигналом фазы «В», проинвертированным на 180 эл. градусов, сдвинутый на 240 эл. градусов сигнал фазы «А» может суммироваться только с сигналом фазы «С», проинвертированным на 180 эл. градусов, и т.д., согласно логике работы схемы и принципу заявляемого способа. При этом выбор пар цепочек блока 8 или, что-то же самое, модуля, в который они входят, осуществляется управляющими сигналами, поступающими от блока 10, в зависимости от выбранной опорной фазы.Further, in accordance with the second stage of the implementation of the claimed method, the three-phase system is balanced with respect to the reference, minimally loaded phase “A”, in which the power factor of the main three-phase system is set, i.e. the total current in the reference phase has a predetermined phase shift relative to its voltage. As has already been shown, in accordance with the first stage of the implementation of the claimed method, control signals for prohibiting (allowing) the operation of blocks and modules, which determine the functional choice of a predefined reference phase, are generated at the output of block 10. In addition, these same control signals determine the phase in which controlled compensation of reactive power is carried out by means of an additional source 9, and thus the power factor of the entire system is set. For the case of the considered example, the minimum loaded phase “A” is selected as the reference phase. Further, it should be noted that in accordance with the second stage of the implementation of the claimed method, by means of the same control signals of prohibition (permission) generated by block 10, a logical linking of the symmetrization function in the three-phase system to a predetermined reference phase is provided. At the same time, from the output of block 10, the control signals of the prohibition (permission) are received, including the group of control inputs of the individual modules of the logic block for generating differential signals 8. The blocks 6, 7 involved in the formation of the signal at the output of block 8 consist of modules related to which a certain phase. So, for example, modules 6.1 and 7.1 belong to phase “A”, modules 6.2 and 7.2 to phase “B”, modules 6.3 and 7.3 to phase “C”. In block 7, the signals proportional to the currents of the phases "A", "B" and "C" are shifted by an angle equal to 180 el. degrees (inverted), in relation to the signals at the outputs of blocks 3, 4 and 5. Block 6, in the general case, consists of n × 2 phase-shifting chains - 2 for each phase (2 phase-shifting chains are included in each module). Only two of them are constantly involved in the work, i.e. only one specific module. A pair of such chains or the module into which they enter is activated depending on which of the phases is chosen as the reference. With each pair of phase-shifting chains, a signal proportional to the current signal of the reference phase is generally shifted by an angle, respectively

, where m is the sequence number of the phase following the reference one in the direct sequence of phase rotation, n is the number of phases in the system. In this case, one of the chains of a separate module, the signal is shifted by 120, respectively, the other - by 240 el. degrees, depending on the sequence number of the phase following the reference, with a direct alternation of phases for which it will be used to balance. From the output of block 6, signals proportional to the current of the reference, least loaded phase, and shifted by 120 and 240 e. degrees, respectively, are fed to the first group of information inputs of the differential signal generating unit 8, to the second group of information inputs of which signals are proportional to the shape of the load currents of the phases being balanced, formed in phase current sensors of phases 3, 4 and 5 and inverted by 180 e. degrees by the second phase-shifting block 7. Block 8 also, in the general case, consists of n × 2 summing chains. At the same time, only two of them related to the corresponding phases are constantly involved in the work. So, for this case, the phase “A” signal shifted by 120 electrical degrees can interact (add up) only with the phase “B” signal, inverted by 180 electronic degrees. degrees shifted by 240 e. degrees the signal of phase "A" can only be summed with the signal of phase "C", inverted by 180 el. degrees, etc., according to the logic of the circuit and the principle of the proposed method. In this case, the choice of pairs of chains of block 8 or, equivalently, the module into which they enter is carried out by control signals coming from block 10, depending on the selected reference phase.

The logic of interaction of the above blocks is as follows. When you set the reference phase "A" at the output of block 10, a combination of signals is formed, indicating the prohibition of modules 8.2 and 8.3. Thus, the only 8.1 module remains in operation, at the output of which there are two signals, one of which is the sum shifted by 120 el. degrees of the signal of the reference phase "A", and inverted by 180 e. degrees of the “B” phase signal, and the second - the sum shifted by 240 e. degrees of the signal of the reference phase "A", and inverted by 180 e. degrees of a signal of phase "C". Thus, at the output of block 8, signals are proportional to the vector difference of the signal of the reference, minimally loaded phase “A” and the load signals of the symmetrized phases “B” and “C”. These two pairs of vector current differences are the generated signals used to balance the phases, the geometric sum of which and the load currents of each of the corresponding phases gives currents proportional to the current of the reference phase, and the phase angle formed by the said geometric sum of currents and the total current of the reference phase, and also between the total currents of the neighboring symmetrized phases, is 120 e. degrees. Thus, we obtain a completely symmetric system of generated current signals proportional to the currents of the symmetrical three-phase system, relative to the minimally loaded phase "A" with a given power factor. From the output of block 8, the generated control signals are supplied to the control inputs corresponding to the symmetrized phases "B" and "C" of the control circuits of the additional power source 9, through which they are fed into the symmetrized phases. As the source 9 can be used, for example, a system with double energy conversion, including a PWM rectifier, a PWM inverter and containing an intermediate DC link. From the output of block 8, the generated control signals are supplied to the control inputs corresponding to the symmetrized phases "B" and "C" of the control circuits of the additional power source 9, through which they are fed into the symmetrized phases. If, as a result of the analysis of the ratio of the load complexes, it was established that the balancing will occur relative to the phase whose current is close to the average with respect to the currents of other phases, then it is determined as the reference one, the logic of the implementation of the balancing method remains the same as in case with minimally loaded phase.

Thus, as a result of a phased sequence of actions performed in accordance with the claimed method, reactive power compensation is carried out by means of an additional power source in the main n-phase network, carried out at the level of any preset value, together with balancing the system, relative to the phase previously selected in as a reference, either a minimally loaded phase or a phase with a load current close to the average. At the same time, improving the quality of electric energy of the main n-phase system using the claimed method is achieved by expanding the range of reactive power regulation, stabilizing the power factor at the level of any predetermined value, carried out together with increasing the efficiency of balancing the multiphase system by increasing speed, simplifying implementation and increasing profitability.

INFORMATION SOURCES

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

2. A.S. USSR No. 562038, Bull. No. 22, 07/14/1977, Cl. H2O 3/26, 1977.

Claims (1)

A method of improving the quality of electrical energy of the main n-phase network, by compensating for the reactive power consumed by the n-phase load of the latter, characterized in that the process of regulating the power factor in the main n-phase network and the process of balancing the latter are carried out jointly and sequentially, in two stages, at the same time, at the first stage, in the main n-phase network, either a phase with a load current close to the average or the least loaded phase is pre-set, the selected phase is determined as the reference phase, I highlight in it, a signal proportional to the current of its load compares the latter with a reference signal, which, in turn, is formed from a signal proportional to the supply voltage of the reference phase, a difference signal is obtained, the latter is adjusted so that the phase shift between it and the reference signal was equal to a predetermined one, and a current proportional to the adjusted difference signal is generated through an additional n-phase power source into the reference phase, so that the current in the reference phases equal to the geometrical sum of the generated current and the load current of the reference phase would be equal to the modulus of the load current of the latter, and the phase angle formed by the current of the obtained geometric sum of currents in the reference phase and its voltage would be equal to the specified, in the second stage, using the mentioned additional n -phase power source generates currents in each of the remaining (n-1) phases, pre-forming each of them so that in each of the symmetric (n-1) phases of the main n-phase network, the geometric sum of the currents generated the phase being balanced and the current of its load - would be equal in absolute value to the current equal to the geometric sum of the currents in the reference phase, and the angle formed by the total current of the last and the current of the phase being symmetrical, next to the reference one during direct phase rotation, and also between the total currents of neighboring ( n-1) of symmetrizable phases would be equal to

email degrees.