RU2442263C1 - METHOD FOR SUPPLYING POWER FROM n-PHASE POWER SUPPLY (VARIANT 2) - Google Patents

Abstract

FIELD: electrical engineering. ^ SUBSTANCE: according to the method, both reactive power and the active power component of the balanced phase group are used to supply DC load. Upon that, initially, the reactive power component is extracted from n-phases of the power grid, and then the active power component is extracted from at least one of the grid's phases, the active power component consists of a balanced phase group, via balancing currents. Furthermore, the power from reactive and active currents is extracted by means of a fully controlled solid state PWM rectifier, with phases being individually controlled via corresponding modulating signal. This power is extracted in the form of equivalent power of unidirectional repeating width-modulated current pulse sequence. ^ EFFECT: increase of power usage efficiency by reducing its non-productive losses. ^ 1 dwg

Description

The method relates to energy and can be used to increase energy efficiency, while improving its quality indicators, in energy systems with stationary power flows.

The known method (1) of supplying a direct current load from a three-phase power supply system, adopted as an analogue, by means of an uncontrolled three-phase rectifier, in which, from each of its phases, the active energy is taken in almost equal quantities.

The known method (2) of supplying a DC load from a three-phase power supply system, adopted as a prototype, by means of a controlled three-phase rectifier, the implementation of which, from each of its phases, the active energy is extracted in predetermined, practically equal amounts. Moreover, if the loads of the power system are non-linear and asymmetric, the known analogue method and prototype method do not allow to eliminate or reduce the negative consequences caused by them associated with unproductive energy losses.

The problem solved by the invention is to increase the efficiency of electricity use by reducing its unproductive losses caused by reactive currents of the main and higher harmonics and the asymmetry of phase currents, while increasing its quality indicators.

This is achieved by the fact that according to the proposed method, both the active component of the power of the group of symmetrizable phases of the n-phase power supply system and the reactive power are used to power the DC load, and, first, the reactive power is extracted from the n-phases and used as a fraction of the power needed to power the said load, and then from at least one phase making up the group of symmetrized phases, the active power is extracted, so that the main current remaining in each phase of the said group is frequency, selected by an asymmetric nonlinear load, would have a modulus equal to either a predetermined or equal to the magnitude of the current module in the reference phase, while the reference phase is preselected from the n-supply phases of the asymmetric power supply system under the condition of the maximum value of the current module.

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

ES - three-phase power supply system

1, 2, 3 - phase current sensors, A, B and C, respectively

4, 5 - phase-correcting circuit

6, 7 - phase inverters

8, 9 - blocks for the formation of differential signals of symmetrized phases

10 - three-phase fully controllable PWM rectifier

11 - capacitive storage

12 - DC load

13 - asymmetric nonlinear load of the power supply system

14, 15, 16 - blocks of the formation of a logical signal

17, 18, 19 - voltage sensors

20, 21, 22 - blocks the formation of the reactive component of the modulating signal

23, 24 - mixers

25 - block job phase, external regulatory influences

The essence of the claimed method is disclosed by the example of a three-phase system. In the process of power take-off by an asymmetric non-linear load in phases “A, B and C” of the power system, currents of different modulus and phase flow, the spectrum of which is composed of 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 load returns back to the source in the form of the aforementioned reactive components of the current. The flow of reactive currents 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. 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 component of the load, are known to be opposite. The negative effect associated with reactive currents, as is known, consists in additional unproductive energy losses in the power system. In accordance with the claimed method, at its first stage, the task of improving the quality and efficiency of energy use is solved by reducing its unproductive losses due to the reactive components of the main and higher harmonics. Moreover, at those times when the load in the power system is reactive, it is proposed to extract the reactive current of the main and higher harmonics from the power stream, with the aim of further using its energy, together with the active harmonic energy of the main frequency, to power the DC load. The problem of extracting the aforementioned reactive components from the phases of 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 provided 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 pulses, the energy of which is equivalent to the reactive component of the currents of the main and higher harmonics extracted from the power system; and the duration of which varies according to the law of variation of its envelope, formed, for each of the phases, by means of a corresponding modulating signal.

In accordance with the claimed method, reactive power is part of the power used to power a DC load. The load receives another part of the power in the form of active power from the balanced phases of the power system. It is assumed that after the implementation of the first stage of the claimed method, the power system is almost symmetrical with respect to the phase angles, and in its phases "A, B and C" only active currents with different modules flow. Next, the n-phase power system is balanced with respect to the phase current modules. In this case, the phase is selected in which the current with the largest module flows to the asymmetric load. In this case, it is assumed that this phase is most overloaded with current, and it is defined as a “reference” phase. In this case, by taking into the load a direct current of power from at least one of the other two underloaded phases, which are not the reference phase, they are equalized by the magnitude of their current modules. Thus, in the power system, balancing is carried out with respect to the modules of the phase currents. In this case, the phases from which active power is taken into the direct current load are defined as symmetrizable phases. The selection of power from the phases being balanced is carried out by means of the aforementioned fully controllable PWM rectifier transistor type in the form of an equivalent energy sequence of unipolar, periodically repeating pulse-width modulated current pulses, the duration of which varies according to the law of the magnitude of the extracted balancing current. In this case, the transistors are controlled by modulating signals, the envelopes of which are formed in proportion to the envelopes of the balancing currents. Thus, the modulating control signal of the reference phase is formed in proportion to the reactive current flowing in it, and the modulating control signals for power take-off from each of the symmetrized phases of the n-phase power supply system are formed from two components: the reactive current and the balancing current. In this case, by means of a fully controlled transistor PWM rectifier, the balancing current is selectively rectified in predetermined quantities determined by the control signal.

The method is as follows. From the outputs of the current sensors 1, 2, 3, signals proportional to the currents taken from the phases "A, B and C", an asymmetric non-linear load 13, are fed to the inputs of the blocks 14, 15 and 16 of the formation of the logical signal, which together with the blocks 20, 21 and 22 of the formation of the reactive component of the modulating signal are involved in the formation of the latter. 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 pairs of blocks: current sensors 1, 2 and 3 and sensors of the supply voltage 17, 18, 19 - signals proportional to them are formed. Moreover, in the signals present at the output of current sensors 1, 2, and 3, which determine the power factors in the phases of the power system and are proportional to the harmonic currents of the fundamental frequency and higher harmonics generated by load 13, 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 will consider it using the example of phase "A". In the block for generating a logical signal 14, the signs of the signals arriving at its inputs from the outputs of the current sensor 1 and the supply voltage sensor 17 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 the block 14 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 13 selects active power from the power system. Further, the signal from the output of block 14 is fed to one of the inputs of the block 20 of forming the reactive component of the modulating signal, the second input of which receives a signal proportional to the current taken by the load 13. Thus, at those moments during which a logical zero coming from the output of block 14, coincides at the input of block 20 with the positive half-wave of the current drawn by the load 13, modulating voltage pulses proportional to the reactive component of the current taken by the load 13 and in-phase are generated at the output of the block 20 in relation to her. During the duration of the voltage pulses generated by the block 20, at the control inputs of a fully controlled transistor PWM rectifier 10, 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 10, the reactive component of the current selected by the active-reactive load 13 is extracted in a form that facilitates its accumulation. As already mentioned, in accordance with the claimed method, reactive power is part of the power used to power a DC load. The load receives another part of the power in the form of active power from the balanced phases of the power system. The selection process from the active power system is as follows. Suppose that of the phases of the power system, phase “A” is selected as the reference, i.e. the current with the highest module value flows in it. It is assumed that after the implementation of the first stage of the claimed method, the power system is almost symmetrical with respect to phase angles. Thus, a signal proportional to the current of the reference phase generated by the current sensor 1, phase corrected by 120 el. degrees, by means of a phase corrector 4, it is fed to one of the inputs of the differential signal generating unit of the balanced phases 8, the second input of which receives a signal proportional to the current of phase “B”, formed by a current sensor 2 and phase-inverted by phase inverter 6. By means of a phase-correcting circuit 5, the signal formed in block 4, is additionally shifted by an angle equal to 120 el. degrees. In this case, a signal proportional to the current of the reference phase and corrected by 240 el. degrees, the second input of which receives a signal proportional to the current of phase "C", formed by a current sensor 3 and inverted in phase by a phase inverter 7. Thus, at the output of blocks 8 and 9 there are signals proportional to the arithmetic difference of the signal of the reference phase "A" and the symmetrized phase "B" and the arithmetic difference of the signal of the reference phase "A" and the symmetrized phase "C". These signals are the active components of the modulating control signals for extracting the active component of power from the corresponding symmetrized phases B and C. Next, the reactive and active components of the modulating control signals of the corresponding phases are summed in mixers 23, 24. In this case, the modulating control signal of the reference phase “A” is generated in proportion to the reactive the current flowing in it, and the modulating control signals for power take-off from each of the balanced phases “B and C” are formed proportionally of two components: reactive current and the balancing current. Thus, by means of a three-phase transistor PWM rectifier 10, controlled by modulating signals generated in the described manner, the reactive currents of the main and higher harmonics are selectively rectified, and in specified quantities determined by the control signal, the balancing current from the symmetrized phases. In this case, at each of its outputs, sequences of unipolar, periodically repeating latitudinally modulated current pulses are formed, the energy of which, for the period of their repetition, is equivalent to the energy extracted from the corresponding phase of the power system: for the reference phase, the reactive component of the main and higher harmonics currents, for symmetrized phases - the reactive component of the currents of the main and higher harmonics and the corresponding balancing current. Moreover, the duration of the latter changes according to the law of the envelope of the generated corresponding modulating signal. It should be noted that by means of a unit for setting phase, external regulatory actions 25, shown in the diagram explaining the claimed method, in the form of reference signals, additional limiting effects on the values of the generated modulating control signals of the corresponding phases of the PWM rectifier are generated for each phase of the power system if the asymmetry of currents in the power system is significant, and the DC load power is small compared to it. Moreover, in accordance with the claimed method, the degree of symmetrization is set additionally, by affecting the magnitude of the control modulating signal (its reduction), in order to stabilize it at a given level. Block 25 can be built on the principle of a device for generating predetermined reference voltages, by comparing with which the magnitude of the modulating signals is set (in this case, when the phase “A” is selected as the reference, generated respectively for phases C and B by blocks 23, 24). At the same time, the control of the values of the said modulating signals is carried out by additional control inputs organized in the said blocks. Thus, the current remaining in each of the phases being balanced has a modulus value equal to either a predetermined value by means of block 25 or equal to the magnitude of the current module in the reference phase. Block 25 may be absent if it is initially planned that the current remaining in each of the phases to be balanced should have a modulus equal to the magnitude of the current module in the reference phase. Further, both extracted energy components, one of which is the reactive current energy of the harmonics of the fundamental frequency and higher harmonics currents, and the other is the active energy of the symmetrizing currents of the symmetrized phases, after accumulation in the capacitive storage 11 are used to power the DC load 12.

Thus, as a result of the sequence of actions carried out in accordance with the claimed method, increasing the efficiency of energy use in power systems with stationary power flows is achieved by reducing its unproductive losses caused by reactive currents and asymmetry of phase currents. Moreover, this goal is achieved by the fact that both reactive power and the active component of the power of the group of symmetrized phases are used to supply DC loads from an asymmetric n-phase system.

INFORMATION SOURCES

1. Zabrodin Yu.S. Industrial Electronics: Textbook for universities. [Text] - M.: Higher. school., 1982, p.334.

2. Zabrodin Yu.S. Industrial Electronics: Textbook for universities. [Text] - M.: Higher. school., 1982, p. 340.

Claims (1)

A method of supplying a direct current load from an n-phase asymmetric power supply system, characterized in that, as the power required to supply a direct current load, both the active component of the power flow in the group of symmetrical phases of the n-phase power supply system and reactive power are used, which is initially extracted from n phases, and then from at least one phase constituting a group of symmetrized phases by means of balancing currents, the active component of the power taken by n- is extracted a non-linear asymmetric load so that the main frequency current remaining in each phase of the said group has a modulus equal to either a predetermined value or equal to the magnitude of the current module in the reference phase, while the reference phase is selected from n supply phases of the power supply system according to the condition the maximum value of the current module of the fundamental frequency, and the power of reactive and active currents is extracted by means of a fully controlled PWM rectifier of a transistor type, phase-controlled by the corresponding modes by lasing signals in the form of equivalent power of a sequence of unipolar periodically repeating latitudinally modulated current pulses, the duration of which for each phase is separately generated, including by means of the envelope of the said modulating signals, each of which is generated for the symmetrized phase by a current proportional to the vector sum of the reactive current and balancing current, which, in turn, is formed proportional to the current equal to either the arithmetic difference of the current of the reference phase and the active component of the current of the corresponding symmetrized phase, or a current equal to the mentioned arithmetic difference, limited to a given value, while the modulating signal for the reference phase is formed as a result of comparing the signs of the two components - an analogue proportional to the current taken from each of the phases by a non-linear asymmetric load, and component, which in case of equality of signs of the compared voltage supplying the corresponding phase of the load, and voltage proportional to the mentioned analog ulation, formed into a logic signal, wherein if the generated baseband signal components have opposite signs, the latter is recovered by means of reactive power in each half cycle of the voltage supplying the proper phase load.