SU1571722A1 - Method of compensation of current distortions in multi-phase circuits with non-linear loads - Google Patents

Abstract

The invention relates to power engineering and electrical engineering, in particular, to the compensation of reactive loads in industrial and autonomous electric networks using static valve compensators. The purpose of the invention is to improve the accuracy of current distortion compensation and to expand the functionality of a non-sinusoidal supply voltage in multiphase circuits with non-linear elements. Current distortions are compensated for by dividing the load current I _n (T) into two components — active I _a (T) and reactive I _p (T) and then compensating the reactive component I _p (T) by connecting to the input terminals of each the phase of the power source of a single phase of a multiphase compensator, which is a source of a given current form. To extend the functionality and increase the accuracy of compensation in the presence of long intervals of the operating period, when the same I phase of the power source and the current distortion compensator work in the generator mode or the I phase of the compensator operates in the generator mode and the load phase I energy, it is proposed to connect the first phase of the compensator to the first phase of the power source, which has opposite polarity in this interval compared to the first phase of the load. 2 Il.

Description

The invention relates to power engineering and electrical engineering, in particular, to the compensation of reactive loads in industrial and autonomous electric networks using static valve compensators.

The purpose of the invention is to improve the accuracy of the compensation of current distortions and the expansion of functionality with non-sinusoidal supply voltage.

FIG. 1 shows a compensator circuit diagram; in fig. 2 - structural

control circuit of the device for the distortion of the current

The compensator contains a two-phase source with phases 1, 2, a two-phase load with phases 3, 4, transformers 5 and 6, current sensors 7 and 8, voltage sensors 9 and 10, transformers 11 and 12, key elements (valves) 13-20, current sensors 21-24, key elements (valves) 25-32, control system 33.

The control system 33 (FIG. 2) contains circuits 34 and 35 for controlling the transfer of the primary winding of the transfer

Xj

go yu

mators 11 and 12, respectively, multiplier 36, comparator 37, valve control pulse shaper 38, multiplier 39, comparator 40, valve control pulse shaper 41, multipliers 42 and 43, integrators 44 and 45, divider 46. memorization sampling circuit 47 counting, multiplier 48. adders 49-51. first order delay block 52, comparator 53 with hysteresis, driver control pulse generator 54, synchronization unit 55.

The power part connected between the two phases of the power source u (t) -1, eu (g) -2, in series with which the first 7 and second 8 current sensors are connected, and in parallel the first 9 and second 10 voltage sensors and two the load phases ZA 3, ZB 4, in series with which the fifth 23 and sixth 24 current sensors are connected, respectively, are galvanically developed through the first 5 and second 6 transformers and contain two groups of controllable gates; bridge circuit, in which one diagonal is included the primary winding of the third transformer 11, and the nodes of the second diagonal through rentil 25 and 26 are connected to the secondary winding of the first transformer 5 and through the valves 29, 30 are connected to the secondary winding of the second transformer 6, the secondary winding of the third transformer 11 in series with the third current sensor 21 is connected in parallel to phase A of load 3, in the second group, valves 17-20 are connected according to a bridge circuit, in one diagonal of which the primary winding of the fourth transformer 12 is included, and the nodes of the second diagonal through valves 27 and 28 along connected to the secondary winding Ye of the second transformer 6 and through valves 31 and 32 connected to the secondary winding of the first transformer 5, the secondary winding of the fourth transformer 12 in series with the fourth current sensor 22 is connected in parallel to the phase B of the load 4, the control terminals of the valves 13-20 , 25-32 are sub-center to the outputs of the control system 33, the inputs of which are connected to the outputs of sensors 7 and 8, current 21-24 and sensors 9 and 10 of voltage.

In the control system shown in FIG. 2, the inputs of switching circuits 34 and 35 of the primary windings of transformers are connected to the outputs of sensors 7 and 8, current 21-24 and sensors 9 and 10 of voltage, and the outputs of blocks 34, 35 to control inputs of valves 13-20, inputs The multipliers 36 and 39 are connected to the outputs of sensors 7, 8, 21 and 22, the outputs of multipliers 36 and 39, respectively, through the comparators 37 and

40 are connected to the inputs of the formers 38 and 41 of the control pulse of the valves, the outputs of which are connected to the control inputs of the valves 25-32, and in the switching control circuit 35

0 the primary winding of the transformer 12, the inputs of the multiplier 42 are connected to the outputs of the sensors 10 and 24, the inputs of the multiplier 43 - to the output of the sensor 10, the output of the multiplier 42 - to the input of the integrator 44, the output of which

5 is connected to the first input of the divider 46, the output of the multiplier 43 is connected to the input of the integrator 45, the output of which is connected to the second input of the divider 46, the output of the divider 46 is connected to the first input of the multiplier 48, the second input of which is connected to the output of the sensor 10, the output of the multiplier 48 is connected to the non-inverting input of the adder 49 cat j the inverting input connected to the output of the current sensor 8, and the output to the non-inverting input of the adder 50, the inverting input of which is connected to the output of the current sensor 22, the output su The mmator 50 is connected to a non-inverting input of the adder 51, the output of which through the first-order delay block 52 is a hysteresis comparator 53 connected to the input of the valve control generator 54 whose outputs

5 are connected to the control electrodes of four controllable valves 17-20, the output of the comparator 53 is also connected to the hysteresis with the inverting input of the adder 51, the outputs of the synchronization unit 55 are connected

0 with regulating inputs of integrators 44 and 45 and sampling memory 47 circuits

The method is carried out as follows.

5 In accordance with the method of compensating for current distortions in multiphase circuits, instantaneous values of the supply voltage and load current are measured, the current is divided by the load

0 active and reactive components at intervals of the period of operation when the same i e phase of the power source and compensator work in generator mode or phase 1 of the compensator is working

5 in the generator mode, and the i-phase of the load is in the energy consumption mode, the i-th phase of the compensator is connected to the i-th phase of the power source, which has opposite polarity of voltage in this interval compared to i and the phase forms the current

a compensator connected in parallel with the load equal to the opposite values of the reactive component of the load current.

Thus, the current consumed from the power source becomes equal to the active component of the load current, i.e. the form consumed from the current power source coincides with the voltage form on its terminals, and the accuracy of distortion compensation increases when the same I-e phases the power source operates in generator mode,

The separation of the load current iH (t) into components ia (t) and ip (t) for each phase is as follows

If the voltage of one phase of the power source is arbitrary periodic with a period T, the function Ur (t). then the load current iH (t) can be represented as the sum of the active and reactive components.

iH (t) la (t) + ip (t).

where la (t) P / U2flUr (t); P jSJ0 iH (t) Ur (t) dt active power consumed by the load;

1) e is the actual value of the voltage of the power source. For currents ia (t) and ip (t), the relations are:

T / ia (t) Ur (t) dt P;

T / o IpWUrMdt 0.

(one)

If parallel to the load we connect a compensator with a current IK (t) -ip (t), then the current ir (t) consumed from the power source will be equal to

ir (t) lH (t) + iK (t) ia (t). (2)

In this case, the compensator according to the expression (1) will not consume reactive power.

Let us consider the formation of algorithms for connecting the phases of a throttle compensator to the phases of the power source when generating the i-th phase of the current compensator ip.i (t) in accordance with the expression (1). When forming such algorithms, it is necessary to bring a real balance in power supply systems containing multiphase circuits with nonlinear elements, in particular, valve converters. To determine the balance of electricity, it is necessary to take into account the characteristics of such goals: a large number of valve switches during the period of operation, distortion of currents and voltages, the intensity of conversion of electromagnetic energy into other types, the disconnection of system elements from each other, the change in the nature of the load (cos load ) Definition

1 The controlled cross section of the system is the cross section of the system in which the

values of instantaneous currents and voltages

2Energy unchanged state (ENS) of the system - the state of the system, characterized by the interval of work

0 (ti-ti-i), for which the instantaneous energy fluxes through controlled sections are unchanged in direction.

We introduce the notation - Pans number ENS

5 systems; Пгг (pgn) - the number of phases of the power source - Ptsg (pnn) the number of phases of the load operating in the mode of generation (consumption) of electricity, / U, (L / g) - the energy generated (consumed) by the phases of the generators; L / ng (L / nn) - the energy generated (consumed) by the phases of the loads, fi, 12, hz. T4 are the functions of integer variables that establish the relationship between the sequence number of the phase of the power supply or load, the ENS of the system, and the summation indices j, k, I, m. The balance of electricity in the system for a variety of controlled sections

pensrr i

LNM

Ј ((2 Wrr.fl (i, j) + 2 I Wnr f2 (l.k) l V

- 1 x x I 1k 1

i 1 v j

PNN

35

2 WHH fa (i.e) + I 1

PHN

+ 2 I L / h

m 1

.m) i)) 0

(3)

40

The magnitude of Pnes, Pn-.i, nHrj, PnnL PHz.1, components of energy, type of function fi, f2, c3. f4 is determined based on the calculation of the energy regime in the system.

From the balance equation (3) it follows that

Each of the power supply and load phase sets is divided into two subsets. The first such subsets are elements that operate in the mode

generation of electromagnetic energy, and to the second - in the mode of consumption. At the same time, the instantaneous and integral for the time to () quantities of energy generated and consumed by the elements

multiphase circuit are equal.

According to the proposed method, ENS systems in which the phases of the power source operate in the mode of consumption of electromagnetic energy, and the phases of loads - in the modes of consumption or generation of electromagnetic energy or phases of the power source work in the mode of consumption, and phases of loads - in the generation mode, should be excluded . During ENS, when the phases of the power source operate in the generation mode, and the phases of the loads - in the consumption mode, the form of the compensator current i "(t) should satisfy the conditions (1) and (2)

Formation of the required law of change of current 1k on the ENS intervals, when the considered phase of the power source is operating in the generation mode, and the load phase is in the consumption mode, or this phase of the power source and load is operating in the generation mode, and the load phase is in the consumption mode, or the phase of the power source and the load operate in the mode of consumption of electromagnetic energy, is carried out due to the pulse-width modulation of the signal fed to the corresponding throttle compensator from the phase of the same name and source of power. To eliminate other types of ENS, when the i-phase of the load operates in the mode of generation of electromagnetic energy, the required form of the compensator current is generated by connecting the next phase of the power source to this i-th phase of the compensator. The mode of this compensator phase is different compared to Phase 1 of the low load At the same time, the voltage of the next phase of the power source has a voltage that is opposite in sign to the i-th phase of the load

The outcome of the above, the algorithm of the device that implements this method is to perform the following steps:

measurement of the instantaneous values of the current and voltage of the power supply phases, as well as the current of the throttle compensator and the load;

determining the phase of the power source to be connected to the i-th phase of the throttle compensator;

generation of reference signals for the compensator gok;

tracking instantaneous values of the throttle compensator current.

Consider the operation of a circuit with nonlinear elements containing two phases - A and B.

The device shown in FIG. 1 and 2, which implements the proposed method for compensating currents in multiphase circuits with nonlinear elements, works as follows.

Using sensors 7, 8, 21-24 of the current and 9 and 10 of the voltage, galvanic isolation, coordination of the levels of the energy circuits and

the measuring part of the device, as well as the measurement of the instantaneous values of the phase voltage of the power source UA (T), L) B (t), the phase current of the power source d (g), isft), the throttle compensator current in (t), ii2 (t) phase current

load izA (t), IzB (t). The output voltage of these sensors, proportional to the measured values of currents and voltages, is fed to the input of control system 33, which produces control pulses at the valves 13-20, 25-32.

The first 5 and second 6 transformers introduced are galvanically isolated not only from power sources (windings SU1, a) A with a converter and load (windings 0) 2, from b), but also from a power source of throttle compensators built on the basis of transformers 11 and, 12 (windings siz, le).

The formation of control pulses on the valves will be considered using the example of phase B. To do this, we analyze the operation of blocks 35, 39-41,55

Depending on the values of currents and voltages taken from sensors 8, 10, 22 and

24, the power supply of the throttle compensator to the base of the transformer 12 is carried out either from the winding of the transformer 6 or the winding w of the transformer 5 In the period of operation in accordance with the expression (3) in

In general, we can distinguish four characteristic operating modes listed in the table, where the designations G are entered - generator mode, P - consumption mode. In operation mode 1, the throttle compensator based on transformer 12 is connected to the second transformer 6. Keys 27 and 28 are in closed state, and the keys 31, 32 - in the open. To compensate for current distortion, it is necessary to eliminate operating modes 2-4.

In accordance with the proposed method, in the presence of modes 1 and 3 on the period of operation of the circuit, the current u (t) is formed in accordance with expressions (1) and (2) due to the pulse-width modulation of the signal applied to the input of the throttle compensator (blocks 12, 17-20) from phase B of the power source. For these modes, a throttle compensator connected to phase B of the power source. If operating modes 2 and 4 are present, the throttle compensator based on transformer 12 is disconnected from transformer 6 and connected to transformer 5 of to phase

power supply (keys 27 and 28 - in the open state, keys 31 and 32 - in the closed state),.

The generation of control pulses on the keys 25-32 is performed by the pulse shaper based on the information received from blocks 36, 37, 39 and 40, as described above.

Using the example of block 35, we will consider the formation of a given form of the current of the compensator in accordance with the information taken from the sensors 8, 22 and 24 of the current and voltage 10.

The signal from the output of the multiplier 43, proportional to Ur (t), is fed to the input of the integrator 45 and is integrated over a period T. The signal from the output of the integrator 45, proportional to the square of the effective value of the voltage Ud, is fed to the second input of the divider 46, the first input of which is supplied the signal from the output of the integrator 44, proportional to the magnitude of the active power P, consumed by the load 4 (we assume that the active power consumed by the key and reactive elements is small compared to the value of P and the magnitude of this power can be ebrech). The input to the integrator 44 is a signal from the output of the multiplier 42. proportional to the instantaneous power P (t) Ur (t) iH (t), which is also integrated over a period T.

A signal from the output of divider 46, proportional to P / U d, is fed to sampling circuit 47, the output of which remains constant during the next period of the frequency spectrum. The signal from this block is fed to the input of multiplier 48, to the other input of which a signal proportional to Ur (t) is fed. The output of the multiplier 48 generates a signal proportional to the active component of the load current ia (t) PUr (t) / U d, which is fed to the non-inverting input of the adder 49. The inverting input of block 49 receives a signal proportional to the instantaneous Current value ir (t), which allows at the output of the adder 9 to form the reference (reference) current value of the compensator iK (t) ii (t) on, which is monitored using a lying system based on blocks 50-53. For this purpose, an instantaneous value of the throttle compensator current based on transformer 12 is fed to the input of block 50. The output signal of the adder 50 is proportional to the value of AiL (t) ii (t) on - iL (t) T. sinks to the non-inverting input of the dummy 51, the inverting input of the coordinator receives a signal from the output of the comparator 53 with hysteresis. At the output, a signal is generated, which controls the valve control pulse generator 54. In order to implement a closed current control system of the transformer 12, the output signal from the adder 51 is fed to the input of the first order delay unit 52, whose transfer function (K / (1 + Ts)) and from it to the 10 input of the comparator 53 with hysteresis, due to the relay characteristic of which and feedback to the inverting input of the adder 51, the current of the comparator 15 ii (t) T is continuously monitored by the reference value iL (t) on.

Synchronization unit 55 produces sync pulses whose period is equal to the period of the power source. These sync pulses control the operation of integrators.

0 and sampling schemes with memorization of samples. The control signals from block 54 control the operation of valves 17-20, the inclusion of which by a bridge circuit makes it possible to form an instantaneous current function of a resettlement compensator compensator based on the transformer 12.

Thus, the summation of currents in the common node in accordance with expression (2) allows, at the output of phase B of the power supply, to obtain a current ir (t) proportional to the voltage Ur (t.

The development of devices based on the proposed method of compensating for distortions in multiphase circuits with nonlinear elements will reduce the exchange processes of the system elements, eliminate energy losses in the line, reduce the installed powers of electrical equipment.

0

Claims (1)

The invention method for compensating for current distortion in multiphase circuits with non-linear loads, including a power source 5 AC connected to it through a converter load and a compensator, according to which the instantaneous values of the generator voltage, the instantaneous values of the load current and 0 compensator, integrate the signal over a period of time equal to the generator voltage period, memorize the integral values for the integration time, form the instantaneous reference values of the compensator current, and depending on the resulting deviation change the instantaneous values of the compensator current, in order to improve the accuracy of current distortion compensation and expanding the functional possibilities at a non-sinusoidal supply voltage, multiply the instantaneous value of the power supply voltage for each phase and the instantaneous value of the throttle compensator current, the obtained value is compared with a zero value, on the time interval the time interval of negative values of the obtained value the phase of the throttle compensator is disconnected from the phase of the same name power supply and connect to the next phase of the source power, the formation of the reference instantaneous values of the current throttle compensator kst (1) of each phase are carried out according to ikon (t) / (t) U (t) dt, - U (t) -i ,, (t) J (t) dt ten where ln (t) is the instantaneous value of the phase load current; Ur (t) is the instantaneous value of the generator phase voltage, T is the period of the generator voltage. one 8 (13- Yu