Transistorized tree-phase reactive-current supply

FIELD: electrical engineering.

SUBSTANCE: proposed device tat can be used to raise efficiency of electrical energy consumption due to relieving power supply mains of reactive currents has three-phase diode bridge connected to supply mains through three reactors; connected at dc output of this diode bridge through isolating diodes are three storage capacitors. Device also has bridge inverter built around six transistors connected through their outputs to ac input of diode bridge and three additional transistors connecting dc input of inverter to storage capacitors. Transistor control system functions to convert signals arriving from outputs of voltage sensors across load, load and supply mains current sensors, and to generate thyristor control signals so that source automatically generates correction currents equal to reactive currents consumed by load, and only resistive component of load currents is consumed from supply mains.

EFFECT: reduced mass and size of device, ability of generating sine-wave corrective currents.

1 cl, 2 dwg

The present invention relates to electrical engineering, the field devices that increase the efficiency of electricity consumption, in particular devices for the compensation of reactive currents by generating them on the place of consumption and thereby unloading them from the power mains.

It should be noted that in the literature often uses the term "source of reactive power", although in our opinion it is more correct to say "the source of reactive currents," as a parallel connection of the load and said source in this connection there is an effect of the resonance currents, in which the power source is not consumed reactive component of current, which is locked inside path load - source reactive currents", and if we proceed to the analysis of circuits in the loop "inductance - capacitance". (Polivanov K.M. Linear electric circuits with lumped. M: Energy, 1972.)

The most common sources of reactive currents are static capacitor Bank connected in parallel to the load and providing required for her reactive currents.

With the advent of the thyristors have been numerous attempts to create sources of reactive currents due to artificial commutation of the thyristors, which allows to obtain the load current, the leader phase voltage is e, and thus would be to compensate the reactive currents of other consumers. (New schemes of static reactive power compensator. Survey information. Ser. Electrical networks and systems, issue 2. - M.: Informania, 1991.)

One of such devices, which is an analog of the invention under examination proposed in the as of the USSR № 1737618, CL H 02 J 3/18. BI No. 20, 1992, the Device comprises a charging and discharge thyristor units that control the charge and discharge of the storage capacitor, so that when a current compensation desired shape.

The disadvantage of this device is its complexity, a large percentage of the higher even harmonics in single-phase networks and the impossibility of generating sinusoidal reactive currents in three-phase networks due to the use of only one storage capacitor.

The prototype of the present invention is a source of reactive power, as stated in the as of the USSR № 1610540, CL H 02 J 3/18. BI No. 44, 1990. This source is designed as a three phase monoblock device contains a thyristor bridge with shut-off diodes and switching capacitors, bridge freewheeling diodes, three commuting and three damping throttle and storage capacitor. The disadvantages of the proposed device is its complexity due to the large number of elements equal to the mouth of the established power (12 diodes and 6 thyristors), the necessity of using extra elements for artificial commutation (6 capacitors and three throttle) and, consequently, increased the weight and dimensions. But the main drawback, as well as similar (as the USSR № 1737618, CL H 02 J 3/18. BI No. 20, 1992), is the impossibility of the formation of sinusoidal currents compensation in three-phase networks, so as to service of each phase accumulation capacitor is only 120 electrical degrees (1/3 of the period) instead of 360, that is, the full period.

This drawback is devoid of the invention, the technical result is to provide the formation of a practically sinusoidal phase current compensation in three-phase networks, and a significant reduction of mass-dimensional parameters by reducing the number of elements in the schema and use as keys transistors.

Scheme of the present invention is shown in figure 1. In this diagram:

1-6 - three-phase diode rectifier bridge through which the charge storage capacitors 10-12;

7, 8, 9 separating the diodes, not allowing positive conclusions capacitor to equalize the potentials in the process;

10, 11, 12 - storage capacitors;

13-18 six transistors forming the inverter voltage, I is DNAME voltages are voltage capacitor, and the output is the AC input diode bridge, 14, 16, 18 transistors, shunt diodes 2, 4, 6 anode groups rectifier bridge, and 13, 15, 17 transistors with their emitters connected to the anodes of the diodes 1, 3, 5 cathode groups rectifier bridge or, equivalently, to its AC input;

19, 20, 21 - additional transistors with their collectors connected to the positive findings of the storage capacitors, and their emitters connected to the collectors of transistors 13, 15, 17 of the inverter;

22 - three inductor through which the rectifier bridge and the inverter connected to the AC network in parallel with the load;

23 - sensors current consumption of the network;

24 - sensors load current;

25 - sensors load stress;

26 - load;

27 - specifies the source device reactive currents, which converts the signals from the sensors voltages and currents load signal 29 specify the current network and generates three signals 28: 28a, 28C, 28C job phase current i_tocompensation for the load to become reactive current i_to=i_p;

30 - node comparison of the reference signal with the output signal of the sensor currents network;

31 - regulator current consumption of the network;

32, 33, 34 - modulators pulse duration control transistors 13-21 source, which signal to output the and of the current controller and the signals 28a, 28C, 28C set the current shape of the setting device 27;

35, 36, 37 - shapers of the control pulses of the transistors;

38, 39, 40 - valve control pulses transistors;

41 - generator frequency switching transistors. The source of reactive currents according to the scheme 1 represents a system of automatic control of the compensation currents i_CA, i_kV, i_CCin all phases, which displace the reactive current i_RA, i_RV, i_pcconsumed by the load from the power source and thereby provide a discharge power source and power supply networks from a reactive currents.

In Fig. 2 shows time diagrams of a major change of coordinates in the scheme of figure 1, illustrating the operation of the major elements of a source of reactive power.

Line voltage U_ABU_BCU_CAshown in Fig. 2A and are determined by the expressions:

where θ=ω·t

Phase voltage U_AU_BU_Cand behind them on the cornersreactive current i_pa, i_RV, i_pcshown in figb and are determined by the expressions:

The consumption of reactive currents is a necessary condition for the normal functioning of the load, as in most of the as cases in its composition there is inductance, reflecting the need to create magnetic flux (induction motors, transformers, solenoids, and the like).

Therefore, the load current reactive component typically must be present:

If the reactive current is consumed from the network (from power source), then

If the source of reactive currents is a special plug-in parallel with the load in the immediate vicinity of the power source and the supply line are discharged from the reactive currents from the power source is consumed only active currents

In transmission line losses are reduced by the value of

where R_lequivalent resistance of the network power supply from the power source to the load;

I_p- the current value of the reactive current.

The essence of the reactive currents is that special source produces (generates) the currents compensation

which displace the reactive currents from the power source and power supply networks and closed through the load.

The source of reactive currents (RTI) scheme figure 1 accomplishes this as follows.

To ensure that the conditions (8) and (6) provided automatically power part of RTIs on the items 1-22, combined with a system of automatic control of the transistors 13-21, and hence the processes of charge and discharge capacitor 10, 11, 12. One of the key elements in the management system is the setting device 27, on which input signals from the current sensors load 24 and voltage 25. The transformation of these signals specify the device produces a signal 29 setting the value of the current consumed from the network (power supply), is proportional to the active component of the load current.

In addition, specifying the device generates three signals 28 job form phase current compensation 28a, 28C and 28C.

The signal 29 setting the value of the current network is fed to the comparison element 30, which also receives a feedback signal via the current network from the sensor 23. At the output node 30 comparison signal is allocated deflection currents of the network from the given value, which is supplied to the regulator currents 31. The signal from the controller output currents 31 is fed to the first inputs of three modulators 32, 33 and 34 duration (width) of the pulses of the control transistors 13-19 inverter. On the second inputs of the modulators signals 28a, 28C, 28C forms of compensation currents. The outputs of modulators 32, 33, 34 is connected to the first input shapers 35, 36, 37 of the control pulses of the transistors of the inverter. On the second inputs of formirovanie the th signal generator 41 of the switching frequency of the transistors. The outputs of the generators are connected to the inputs of distributors pulses 38, 39, 40, which define the required combination of pairs of transistors 13-16; 13-18; 15-14; 15-18; 17-16; 17-14, specify the duration of the open and closed States of the transistors 19, 20, 21 to provide the necessary phase compensation currents i_CA, i_kV, i_CC.

The formation of currents compensation is carried out by changing the length of open intervals t_inand closed t_othe state of the corresponding pair of transistors during the switching frequency T_P=1/f_P

wherethe relative duration of the open state of the transistors.

When pulse-width modulation (PWM) ε is control.

Switching frequency f_Pis chosen much greater than the frequency of the network

f_P>>f_With; T_P<<T_With.

The values of the capacitances storage capacitors 10, 11, 12 are determined by the magnitude of the currents compensation; the values of the inductances of the inductors 22 are determined by the conditions for resonant character of the process of the charge storage capacitors.

All coordinates of the source in figure 1 i_KiU_cie_Lican be divided into "smooth" components of i_CU_c0ie_L0ifrom estudiosa with frequency f _withand variable components Δi_tothat ΔU_cthat Δe_Lvarying with frequency switching transistors.

The index i is used to display the fact that there are several identical elements and the corresponding coordinates in the scheme of figure 1.

Under the terms of the normal functioning of the inventive device smooth components of the increments of the cumulative stresses on the capacitors 10, 11, 12 ΔU_c01that ΔU_c02that ΔU_c03coincide in phase with the line voltage U_ABU_BCand U_CAsmooth components of i_C, phase current compensation reproduce the reactive current i_pa, i_RV, i_pcin accordance with expressions (3)and smooth components e_L0i, EMF on the throttles 22 coincide in phase with the phase voltages of the power sources in accordance with the expression (2).

Source for the circuit of Fig. 1 generates a linear compensation currents i_C1=I_CAW; i_C2=i_FAC; i_C3=i_KSAthat is converted in phase in accordance with the terms of

Source for the circuit of Fig. 1 operates as follows. After inclusion in the network is the initial charge of all three storage capacitors 10, 11, 12 through a diode bridge to a voltage approximately equal udoe the specific value of the amplitude of the line voltage 2U _m. For the duration of this process is the interval of not more than one half-cycle ( Fig. 2 is not shown). At the same time in the master device 27 is the formation of the signals 28 and 29 job currents form of compensation and value of the active current component, which should be consumed from the network. If the load does not consume reactive currents, the signal 29 specify the current network and the feedback signal from the output of the current sensor 23 will be the same, at the output of the comparison element 30 of the signal is not, the current regulator 31 will not generate the control signal modulators 32, 33, 34 and transistors don't come. If the reference signals of the current network and the feedback signal from the output of the current sensors 23 are different, the output of the comparison element 30 you receive the error signal, the current controller 31 and the modulators 32, 33, 34 and starts the formation of the compensation currents i_CA, i_kV, i_CCwhich displace the reactive currents from the power source and closed through the load. During this positive half-wave current of capacitor i_c1, i_c2, i_c3corresponds to their discharge, i.e. the voltage decrease from the maximum value to the minimum. These intervals transistors 13-18 work in pairs, as described previously and the transistors 19 and 21 are in the open state with the shift of 120°. Negative sex is olna current of each capacitor corresponds to his charge: these intervals the current in the capacitor goes through a diode bridge 1-6 and barrier diodes, transistors 19 and 21 are closed also closed the transistors 13, 15, 17, and to provide sinusoidal currents charge enough to use in PWM mode regulation only transistors of the groups 14, 16, 18.

The discharge process storage tanks 10, 11, 12 in a stationary mode begin with the points in time corresponding to the maximum values of the positive half-wave line voltage: the voltage at the positive terminals of the capacitors 10, 11, 12 also reached their maximum values (about 2U_m), and the currents i_cichange its sign to the opposite. On FIGU, g and D. for example, shows time diagrams of the voltage U_C2at the storage capacitor 11 (C2), the current i_C2and their constituents ΔU_c01that ΔU_c, i_c02that Δi_cThe EMF of the inductor 22 in phase C. the formation of the phase current i_kVand i_CCis carried out by the system control by PWM control, i.e. the change in the value εpairs of transistors 15-18; 14-15; 17-16; 17-14 with open transistor 20 during discharge of the capacitor 11, and the charge process when the closed state of the transistor 20 through the bridge diode 1-6 and barrier diode 7 by PWM control transistors 14, 16, 18, so that in the interval (half-period) of the charge of the capacitor current i_C2was sinusoidal.

In Fig. 2D shows di the gram e _LC(θ) EMF in the inductor 22 in phase C. the Role of the choke 22 in the scheme of figure 1 is to provide a high voltage at the storage capacitor during the initial charge and then the processes of charge in the stationary modes of the formation of currents and compensation, as well as to limit surge currents during switching transistors.

As is known solutions based on the three-phase bridge circuits (Review information Ser. Electrical networks and systems, vol. 2. - M.: Informania, 1991.), including type counterparts ( as the USSR № 1737618, CL H 02 J 3/18. BI No. 20, 1992) and the prototype (as the USSR № 1610540, CL H 02 J 3/18. BI No. 44, 1990), are physically unable to generate compensation currents sinusoidal, it is necessary to evaluate the effectiveness of the invention by comparison with the three-phase source of reactive currents in three-phase compensators (Labuntsov, VA, Zhang Daijun. Single-phase semiconductor compensators passive components of the instantaneous power// Elektrichestvo. 1993. No. 12. p.20-32)to be included either in a star or triangle parallel to the load. The RTI can be called a group, and build according to the invention, Fig. 1 - cased.

The proposed scheme figure 1 three-phase compensator can reduce the number of required elements of the transistor - diode 12 when the group postroeniya 9 monoblock. But this is not the main advantage of one-piece construction. The main advantage is to increase the reliability of the exchange processes between the network capacitances and inductances in the formation of currents compensation due to lack of time intervals, when the supply voltage is reduced to zero, which adversely affects the charging of storage tanks. Another advantage is the simplification of the management system by reducing hardware costs, and increased opportunities due to the presence of multiphase source for the formation of the auxiliary signals in the control system. So in three-phase networks monoblock construction transistor sources of reactive currents should be preferred.

Thus, the technical result of the invention is the reduction of mass-dimensional indicators of the source of reactive currents in comparison with the known solutions and the ability to generate compensation currents sinusoidal, as well as improving the reliability of monoblock design compared to the group.

Three-phase transistor, the source of reactive currents, the power of which consists of a three-phase diode bridge connected to the network through three inductor, inverter on six transistors, three of which shunter the individual diodes anode bridge group so that that their emitters are connected to the anode output of the bridge, three transistor connected by its emitter to the anodes of diodes cathode groups, and their collectors connected to the emitters of three additional transistors that connect the storage capacitors to the inverter at intervals of discharge, the system control transistors consists of sensors, current and voltage load current sensing network includes specifying a device which produces a reference signal currents consumed from the network, and the reference signals form of compensation currents, the input of which is connected to the voltage sensors and the current load, the node comparing the reference signal with the output signal from the current sensor network, the current regulator the network, which controls the deflection currents of the network from the given value, the output signal of the current regulator and the reference signals of the currents form of compensation from the setting device are fed to the inputs of the modulators pulse duration control transistors, which are produced by the pulse shapers and sent to the transistors distributors, characterized in that the DC output of the diode bridge includes three storage capacitor, negative findings are connected to the anode output of the bridge, and the positive terminals are connected with the cathodes of the separation diode and collectors three additional t is ansistors, moreover, the anodes of the separation diode connected to the cathode output of the diode bridge, and the emitter of the additional transistor is connected to the collectors of the three transistors of the inverter, which form the positive clamp of its DC input.