RU2001486C1 - Method of compensation of interchange power and gear to implement it - Google Patents

Abstract

Usage: in devices providing improved quality of electricity in networks with powerful non-linear loads. SUMMARY OF THE INVENTION An exchange power compensation device comprises a power unit which includes switched resonant U-cells connected in parallel to a non-linear load and consisting of a reactor with control branches and capacitors connected by one terminal through the switching keys to the reactor and other terminals to the mains supply, and the control unit The microprocessor included in the control unit solves the optimization problem, the target function of which is the minimum exchange power, and The parameter used is the turn-on angle of the thyristors of the resonant circuit involved in the operation relative to the supply voltage signal. Thus, due to the switching of resonant U-chains with frequencies equal to their own resonant frequencies, higher harmonics are generated that enter the supply network and optimize the energy transfer mode by minimizing the amount of exchange power involved in the energy exchange between the power source and non-linear load 4 ill.

Description

The invention relates to electrical engineering and the electric power industry, in particular to methods and devices for improving the quality of electric power in networks with powerful non-linear loads.

Devices are known that are close in technical essence to the claimed using filter-compensating circuits (FCC). The FCC contains a set of circuits consisting of series-connected capacitors and reactors tuned to frequencies to be compensated and connected in parallel to load 1. In the presence of higher harmonics in the voltage of such circuits, the supply line currents are filtered.

A drawback of FCC is that it is fundamentally impossible with such devices to filter out harmonics that do not create voltage across the filter. In addition, the operability of the device is determined by the ratio of its own resistance and the resistances of the generator and the transmission line, which limits the functionality of devices of this type.

Known methods for compensating the exchange power 2, in which the instantaneous values of the current and load voltage are measured, the orthogonal component of the current is extracted - the instantaneous value, the mains voltage and the voltage on the power element (resonant circuit) are compared and depending on the sign of comparison the circuit is switched to the load. In this case, the orthogonal component of the current is approximated by the instantaneous values of the negative current of the power device.

The disadvantage of this method is that the method is tied to instantaneous values, which does not ensure the optimality of integral values (powers, effective values). In addition, the control device and the power unit are quite complex, which reduces their reliability.

The closest in technical essence to the proposed one is a power factor correction device for non-linear loads with a microprocessor control system, which contains a reactor switched in series with opposite parallel-thyristor switches and connected in parallel to a non-linear load, a constant capacitor connected through inductor in parallel to the terminals of the nonlinear load, a control unit whose inputs are connected to the outputs of the load current sensor and a voltage sensor of the supply network, and outputs with control electrodes of the thyristors switching the reactor. Job

the device is based on controlling the switching angles of counter-parallel thyristors, which are connected to the reactor power network and, depending on the magnitude of the turning angles of the thyristors, is provided

the required value of the power factor during the operation of the variable nonlinear load (2).

The disadvantage of this device is the fundamental inability to provide a high-quality form of the current consumed by the non-linear load from the supply network, especially when the network resistance tends to zero.

The problem solved by the invention is to improve the quality of compensation by minimizing the amount of exchange power generated by the nonlinear load and expanding the functionality of the elements of the power part of the device.

The problem is solved in that in the method of compensating the exchange power using a resonant circuit connected to the load through a thyristor

a switch based on measuring instantaneous values of current and voltage at a load, the resonant circuit is made of several resonant circuits, including a partitioned switched

capacitance and inductor with tap, calculate the exchange power satisfying the condition

j Ipto Uc (t) dt - O

according to the formula

Robm (x) - Rn (x) - Rnopt (x), where RnoptM Rn (1 - cos2 tutu;

Rn - average load power;

w is the angular frequency;

hi - current measurement time; and form a control signal that regulates the turn-on phase of the thyristor switch with a frequency synchronized with the frequency

network and equal to the resonant frequency of a given resonant circuit, the exchange power is again calculated, compared with its value at the previous control cycle, and when the exchange power decreases, the phase of switching on of the thyristor switch in the next cycle in the same direction, with an increase in the exchange power, in the opposite direction.

In addition, the goal is achieved by the fact that the composition of the compensation device for exchange power, comprising a power part connected in parallel to a non-linear load, a control unit consisting of a synchronization circuit, a pulse amplifier, a master oscillator, and connected, with its inputs to the load current sensors and voltage of the network, and the outputs to the control electrodes of the switching devices of the power unit, introduced switched resonant LC circuits connected in parallel to a non-linear load and consisting of reactors with regulating branches, capacitors connected by one terminal through the switching keys to the reactor, and other terminals to the mains. Moreover, the control unit contains analog-to-digital converters, the inputs of which are connected to the outputs of the load current and voltage sensors of the network, and the outputs are connected to the input ports of the microprocessor, the information outputs of which are connected to the data buses of the thyristor on-delay delays, the outputs of which are connected to the inputs of the pulse amplifiers control, and the outputs of the amplifiers are connected to the control electrodes of the switching devices, and the controlled timing oscillators and phase compars are introduced into the synchronization circuit oors, the outputs of which are connected to the control inputs of the master oscillators, the outputs of the control master oscillators are connected to the inputs of the frequency dividers and the clock inputs of the thyristor on-delay delays, the outputs of the frequency dividers are connected to the first inputs of the phase comparators, the second inputs of the phase comparators are connected to the output of the inverter, the input of which is connected to the output of the driver of the network clock, the input of the driver is connected to the output of the voltage sensor of the network.

In FIG. 1 shows a graph of the dependence of the exchange power on the unlock angle of the thyristors; in FIG. 2 - structural diagram of the proposed device; in FIG. 3 is a diagram for explaining the connection of capacitors and a reactor of one resonant circuit; in FIG. 4 is a block diagram of the control of an exchange power compensation device.

The optimization (compensation) process occurs in stages with a step At when the angle p of unlocking the thyristors of the resonance cells changes. In this case, the exchange power value changes, the losses in the generator and the line decrease, the efficiency and power factor increase, and the exchange power of the entire system decreases (Fig. 1). The control system maintains a mode in the vicinity of 0 rpm (Woop). Exchange compensation device

power (Fig. 2) contains resonant LC circuits 1-3, connected with thyristor switches 4 to the mains in parallel with a non-linear load 5, a constant capacitor 6, connected

through the inductor 7 also parallel to the non-linear load 5. current sensor 8, voltage sensor 9 connected to the inputs of the control unit 10, the outputs of the control unit 10 are connected to the control electrodes of the switching thyristors 4.

Each of the resonant LC circuits (Fig. 3) consists of a set of capacitors 11 of constant capacitance, one of the terminals of which is connected to the supply network, and the second terminals are connected via switching switches 12 to a reactor 13 having control branches.

The control unit (Fig. 4) consists of analog-to-digital converters (ADCs) 14, the inputs of which are connected to the sensors 8 and 9 of the load current and mains voltage. The ADC outputs are connected to the inputs of the input ports of the central processor 15. The information outputs of the central processor 15 are connected to the data bus of the thyristor turn-on delay drivers 16, the outputs of which are connected to the inputs of the pulse amplifiers 17, the outputs

which are connected to the control electrodes of the thyristor switches 4. Controlled master oscillators 18 of the synchronization circuit of the control unit of the control inputs are connected to the phase outputs

comparators 19, and the outputs to the control inputs of the formers 16 of the delay of the thyristors and frequency dividers 20, the outputs of the frequency dividers are connected to the first inputs of the phase comparators

19, and the second inputs of the phase comparators are connected to the output of the inverter 21, the input of which is connected to the output of the driver 22 of the network clock, and the input of which is connected to the output of the sensor 9

mains voltage.

The exchange power compensation device operates as follows.

When switching resonant circuits 1-3 thyristor keys 4 with frequencies,

equal to the natural resonant frequencies of consecutive 1 C-loops

s. (1)

Vli-ci

where U is the inductance of the 1st resonant circuit;

Ci is the capacitance of the 1st resonant circuit; undamped periodic oscillations of the current of the natural resonant frequency of the circuit appear in the oscillatory circuits. Moreover, the parameters of the resonant chains are selected so that their resonant frequencies are equal to the frequencies of the harmonic components contained in the load current to be compensated. The number of resonant circuits included in the exchange power compensation device is determined by the number of predominant harmonic components contained in the load current to be compensated and the requirements for compensation accuracy. The spectral composition of the load current is determined by a preliminary harmonic analysis.

Thus, due to the switching of resonant LC chains with frequencies equal to their own resonant frequencies, higher harmonics are generated that enter the supply network and optimize the energy transfer mode by minimizing the amount of exchange power involved in the energy exchange between the power source and non-linear load .

The capacitor 6 is used to compensate for the load current along the main harmonic component, the coil 7. having a small inductance, eliminates the possibility of resonant phenomena in parallel circuits of the power part of the device. The current and voltage sensors 8 and 9 are used to collect information about the values of the load current and the mains voltage supplied to the control unit 10.

Each of the resonant circuits (Fig. 3) includes an adjusting branch reactor 13 connected via keys 12 to the capacitors 11. This circuit is used to control the amplitude of the oscillations generated by the resonant chains. The parameters of the capacitors 11 and the reactor 13 are selected from the condition LIX xCi - const, which excludes the possibility of detuning the resonant circuit when switching the branches of the reactor. The effect of controlling the amplitude of the generated harmonics is achieved due to a change in the characteristic impedance of the resonant circuit

where C is the inductance of the working part of the resonant circuit;

Ci is the capacitance of the capacitor connected to the working part of the reactor. 5Required characteristic impedance of the resonance chain 1-3. therefore, the circuit of its internal switching is determined by preliminary harmonic analysis of the load current to be compensated, and remains unchanged in the process of oscillation generation by resonant chains.

The control unit 10 operates as follows.

15 Using the measured ADC 14, the instantaneous values of current and voltage by the central processor 15 determine the law of variation of the active power transmitted along the line

20 Pn (t) - Un (t) in (t) -mi mu. (3)

where n is the number of measured values;

Un (t) is the measured voltage value;

ln (t) is the measured current value; 25 mi - current scale factor;

mu is the voltage scale factor.

The law of variation of the optimal power transmitted along the line is 30 s in the form

PnonrW - Rn (1 - COS2 O) tn) (4)

where Rn is the load power; angular frequency: Chi - current measurement time. 35 Moreover

Pn - {/ Un (t) ln (t) dt. (5)

where in (t); Un (t) are instantaneous current values and 40 load voltages.

The expression describing the law of change in the exchange power is defined as the difference between expressions (3) and (4), i.e.

Pobom W Pn (t) - PnomW- (6)

45 the average exchange power per period is determined by the exchange energy

Q- f -W06-j (P + -G-P- O. (7)

where P is the average over the period of the value of the positive instantaneous power;

P is the average over the period the value of the negative instantaneous power;

t + is the sum of time integrals on which the instantaneous power is positive; 55 is the sum of the time intervals at which the instantaneous power is negative;

T is the period of the exchange power curve. Moreover

t% f

(8)

Further, the calculated value of the exchange power participating in the energy exchange between the source and the nonlinear load is stored in accordance with the algorithm. the microcomputer solves an optimization problem, the objective function of which is the minimum exchange power, and the variable parameter is the turn-on angle of the thyristors of the resonant circuit involved in the operation relative to the signal of the supply voltage of the network.

By analyzing the change in the magnitude of the calculated exchange power depending on the change in the turn-on angle of the thyristors of the working resonant circuit, the control system determines the location of the minimum, which is further refined until the desired accuracy of compensation for this harmonic component of the load current is reached. After determining the value of the thyristor turn-on angle corresponding to the minimum exchange power participating in the energy transfer, the resonant circuit is operated with the turn-on delay angle of the thyristor corresponding to the optimal mode, and the mode is optimized for the next harmonic component (the next resonant chain is included in the work) according to the above principle.

Having completed work with all available resonant chains, the microcomputer again turns to the first chain to clarify the optimality of the energy transfer mode. Further, the cycles of accessing the resonant circuits are repeated during the operation of the exchange power compensation device, which ensures constant monitoring of the optimization process.

Through the information outputs of the microprocessor 15, the thyristor on delay angle code is supplied to the data bus of the delay formers 16, which provide a reference to the thyristor on angle relative to the supply voltage signal and, upon completion of the count. With the aid of amplifiers 17 pulses, the formation of unlocking pulses occurs, which are supplied to the control electrodes of switching thyristors 4.

Foamiroo tag-n 16 ..; To turn on the resonant LC-cahde by the cadence, they operate according to the clock cycle of pulses generated by their controlled master oscillators 18, the pulse frequency of the generator clock sequence being equal to the natural resonant frequency of the switched LC circuits 1-3. To synchronize the pulses of the master oscillators with the mains supply, the control unit provides frequency dividers 20, phase comparators 19, the clock generator 22 and the inverter 21. Frequency dividers 20 reduce the frequency of the master oscillators 18 to the frequency of the mains, phase comparators 19 compare phase sequences pulses coming from the frequency dividers 20 and inverted. using the inverter 21 network clocks coming from the output of the driver 22, the input of which is connected to the sensor 9 n April Network. The control actions from the outputs of the phase comparators 19 are supplied to the control inputs of the master oscillators 18, and changing their operating mode ensures synchronization of the generated clock pulses with the supply network.

B of the power part of the exchange power compensation device, high-quality inductive reactors and capacitors having high breakdown voltage are used. Power thyristors switching resonant circuits must be protected against overvoltage.

The control unit of the device can be made on the basis of a microprocessor

k580BM80A the logical part of the control unit is carried out using (the basic elements of TTL logic, for example, the k1b5 series, controlled master oscillators are performed using microelements of the type k531GG1, analog-to-digital converters are performed on microelements of the type kP572PV1.

(56) 1 Zhezhelenko I.V. Higher harmonics in the power supply system of enterprises. - M .: Ziergoatomizdat, 1986.p. (60.

2. USSR author's certificate N: 1494111, cl. H 02 J 9/06, 1987.

FORMULA AND E BROBETE N AND

METHOD FOR COMPENSATION OF EXCHANGE POWER AND DEVICE FOR ITS IMPLEMENTATION

1. A method of compensating the exchange power, which consists in connecting a resonant circuit to the load through a thyristor switch and measuring the instantaneous values of current and voltage across the load, characterized in that several resonance circuits are used as the resonant circuit, including a partitioned switching capacitance and a solder inductor, the exchange power is calculated by the formula

Robm-Rn-Ri-opt -

where Рм.олЧ t) -Рн (1 - с $ 2ш tu): РЙ - average load power; o is the angular frequency; Chi is the current measurement time, and a control signal is generated that regulates the turn-on phase of the thyristor switch with a frequency synchronized with the mains frequency and equal to the resonant frequency of this resonant circuit, the exchange power is calculated again, compared with its value at the previous control cycle and when the exchange power decreases, the turn-on phase of the thyristor switch changes in the next cycle in the same direction, and when the exchange power increases, the reverse phase.

2. A device for compensating the exchange power, containing a resonant circuit connected to the terminals for connection to the load through a thyristor switch, the control electrodes of which are connected to the inputs of the control unit, the inputs of which are connected to the load current and voltage sensors of the network, the control unit consists of a circuit synchronization, pulse amplifier and master oscillator, characterized in that the resonant circuit is made of several

fifty

5

0 5

0

resonant LC circuits connected in parallel to the terminals for connecting to the load and consisting of a reactor with control branches, capacitors connected by one terminal through the thyristor switch to the reactor, and other terminals to terminals for connecting to the mains, the control unit is equipped with analog-to-digital converters, thyristor on-delay delays, controlled by master oscillators, frequency dividers, phase comparators, an inverter and a network clock driver, moreover, the inputs of analog-to-digital converters are connected to the outputs of the load current and voltage sensors of the network, and the outputs are connected to the input ports of the introduced microprocessor, the information outputs of which are connected to the data buses of the thyristor on-delay delays, the outputs of which are connected to the inputs of the control pulse amplifiers, and the outputs of the amplifiers pulses - with control electrodes of thyristor switches, and in the synchronization circuit are introduced controlled oscillators and phase comparators, the inputs of which are connected to the control inputs of the master oscillators, the inputs of the control master oscillators are connected to the inputs of the frequency dividers and the clock inputs of the thyristor on-delay delays, the inputs of the frequency dividers are connected to the first inputs of the phase comparators, the second inputs of the phase comparators are connected to the output of the inverter, the input of which is connected to the output of the driver clock of the network, the input of the driver of the clock of the network is connected to the input of the voltage sensor of the network.

QoSn.

pin

8 l in

E

Wopt FL

9

I

and

€

& &

/.2

 

T

C2

 I AM

:

in KZ

1G.Z