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DEVICES AND METHODS OF ECONOMY AND PRESERVATION OF ELECTRICITY
INVENTION
Patent of the Russian Federation RU2088015

METHOD OF CONTROLLING THE STATIC TIRISTOR COMPENSATOR OF REACTIVE POWER

METHOD OF CONTROLLING THE STATIC TIRIST COMPENSATOR
REACTIVE CAPACITY

The name of the inventor: Kuzmenko VA; Tropin V.V.
The name of the patent holder: All-Russian Electrotechnical Institute named after VILenin
Address for correspondence:
Date of commencement of the patent: 1994.12.26

The invention relates to means for compensating or stabilizing the reactive power of three-phase alternating loads of industrial enterprises, for example, arc-furnace furnaces, using static thyristor expansion joints containing three independent linear reactors connected to a three-phase network by a triangle, each through a pair of interconnected thyristors with Corresponding to the system of pulse-phase control (SIFU). SUMMARY OF THE INVENTION: the phase position of the thyristor control pulse of the corresponding phase of the thyristor-reactor group triangle is determined not only by the reactive power currently required from this phase, but by the power of the phase of the triangle which is 60 eV ahead of this phase. Deg. This makes it possible to react with a high degree of accuracy, and therefore speed, to the change in the reactive power of the load in the linear wires of the supply network. It is possible to take into account the power of the advanced phase schematically by establishing between the independent calculators the current values ​​of the required reactive powers and the NRFD summers of the required power value of the "own" phase of the reactor triangle and the increment of the power of the advanced phase during the time from the moment of its activation until the moment of formation of the control pulses of its phase.

DESCRIPTION OF THE INVENTION

The invention relates to electrical engineering, specifically to means for compensating or stabilizing the reactive power of three-phase, abruptly charged loads of industrial enterprises, for example, arc-furnace furnaces, by means of statistical thyristor compensators containing three independent linear reactors connected to a three-phase network of a triangle, each through a pair of oppositely-connected Thyristors with an appropriate system of pulse-phase control (SIFU).

Control devices of such a compensator are known, containing three independent calculators of current reactive power values. These devices correspond to the known method of controlling the STC computation by a certain algorithm, converting the network voltages and linear load currents, the current values ​​of the reactive powers of the said linear reactors, and setting them into correspondence with the angles of thyristor control of the corresponding reactors [1]

There are also known CCP control devices containing between each calculator the current values ​​of the required reactive power of the reactors and the corresponding pulse-phase control system (NIFF), a correction device for the current value of the required reactive power, including an adder and two "sample-store" circuits storing the required Reactive power values ​​of the reactors calculated for the previous two discoveries of the thyristors of the reactor, which also determines the method of controlling the STC, which consists in predicting the required reactive power of the corresponding reactor by the sum of the current value of the required reactive power and two fixed values ​​of the same signal obtained in the previous two cycles (In the absolute time, two half-periods of the network line voltage applied to the thyristors) and taken with certain coefficients found as a result of the statistical processing of the process of changing the reactive power of the load [2]

The disadvantage of the known devices and methods of STK control is low speed, i.e., low dynamic accuracy of the formation of three output currents of the STC executive body, resulting from the summation of the corresponding phase currents of the thyristor-reactor "triangle". That is, each output current of the STC is formed from the currents of two adjacent phases of the thyristor-reactor "triangle" shifted in the initial phase relative to the linear reactive current vector of this phase (A, or B, or C) of the network, or thirty electric degrees ahead, Or thirty electric degrees with a lag. It follows that the reactor, whose current vector goes ahead of time, will form its fraction of the reactive line current of the network that is unchanged during the half-period of the phase voltage, before allowing the corresponding phase-to-neutral voltage of the network. A neighboring reactor, whose current vector is late, will form its fraction of the reactive linear current of the network that is unchanged during the half-phase of the phase voltage, more corresponding to the required value of the linear current at that moment. But since the reactive current of the previous phase of the "triangle" is unchanged (in the sense of the amplitude value), the output linear current of the STC will differ from the calculated one, which is the main reason for the low speed of the known methods and control devices. As for the proposal to predict the control signals of the SCC thyristors, i.e. Predictions of the "current requirements" of the reactive powers of linear reactors using statistical regression load models, one can only doubt this possibility in principle, since it is well known that sharply varying loads, such as arc steelmaking furnaces, have nonstationary characteristics and mathematical expectation , And dispersion, and the initial phase of the currents of the forward and reverse sequences, which change drastically during 1.2 periods of the mains voltage, and moreover depend on many different technological features: the time of the melting process, the raw materials, the dynamics of the electric drive of the furnace electrodes, and so on.

The closest to the proposed technical essence is the control device STK, which contains three independent calculators of the current values ​​of the required reactive powers of three independent linear reactors connected to a three-phase network by a triangle, each through a pair of counter-parallelly connected thyristors with a corresponding pulse-phase control system, which structurally Determines the method of controlling the STC independent calculation by a certain algorithm, converting the network voltages and linear load currents, the current values ​​of the required reactive powers of each reactor and their subsequent conversion by means of the NRFU to the control angles of the corresponding thyristors [3]

However, this device and the method of controlling the STK have the above mentioned drawbacks, which consist in discretizing the response of the thyristor-reactor circuit, which leads to a difference in the amplitude of the reactive linear output current of the STC from the calculated value in the dynamic mode due to premature fixation of the reactive current amplitude of the reactor for the entire half- Phase, the voltage vector of which precedes the initial voltage vector of the adjacent phase of the network. (For example, the voltage vector AB is ahead of the 30-volt phase vector voltage vector A).

The object of the present invention is to improve the performance of the STC.

METHOD OF CONTROLLING THE STATIC TIRISTOR COMPENSATOR OF REACTIVE POWER

This goal is achieved by the fact that the phase position of the thyristor control pulses of the phases, determined by the required value of the reactive power of the corresponding phase at the given time, is corrected depending on the reactive power of the phase ahead of this phase by 60 EL. Deg. Which allows to react more accurately and, consequently, speed response to the change in the reactive power of the load in the linear wires of the supply network. For this, to each current value of the required reactive power of the reactor, the increment of the corresponding sign of the current calculated power value of the reactor of that phase, the initial angle of the voltage vector, is advancing by 60 el. Deg. The initial angle of the phase voltage vector of said reactor, said increment being defined as the difference between the current calculated value of the required reactor power and its value fixed at the time of the last opening of the thyristor of the corresponding reactor.

To explain the essence of the proposed method for controlling a static thyristor compensator in FIG. 1 shows the scheme of the control device implementing it; In Fig. 2 and Fig. 3 time diagrams of the phase and output linear current of the STC, explaining the operation principle of the device and the control method.

The control device STK consists of three independent calculators 1, 2, 3 of the current values ​​of the required design capacities of the linear reactors 4, 5, 6, connected to the supply network by a triangle, each through a pair of counter-parallelly connected thyristors 7, 8, 9, , 11, 12, made according to any known scheme, to the inputs that connect the outputs of the respective adders 13, 14, 15, to the inverting inputs of which the outputs of the respective fixation blocks 16, 17, 18 are connected, each of which serves as a sampling and storage circuit in The current of the half-period of the line voltage of that value of the calculated reactive power of the reactor of the corresponding phase that was fixed at the time of the last opening of the thyristor in the circuit of the corresponding linear reactor. Locking units can be made in the form of a device for sampling and storing analog signals, for example, according to the book by Vanin VK. Pavlova G.M. Relay protection on elements of computer technology. L. Energoizdat, 1991, p. 56. The strobe signals for the latching units 16, 17, 18 are supplied respectively from the pulse inputs of the NDF 12, 10, 11. The signals from the outputs of the corresponding calculators 1, 2, 3 are fed to the first inverted input of the adder 13, 14, 15, and to the second inverted Input of adders 13, 14, 15, the signals from the outputs of the calculators 3, 1, 2, respectively, are generated, which ensures that each of the adders 13, 14, 15 is output at the output of the computed value of the reactive power of the reactors, respectively 7, 8, 9, An additional signal-increment of the calculated reactive power value of the reactor of that phase, the initial angle of the voltage vector of which in the system of Cartesian coordinates of the three-phase network is 60 eV ahead. Degrees the initial angle of the phase vector voltage of the reactor of the same name to the calculator. The input signals of the calculators 1, 2, 3 are the output signals of the voltage transformers of the network 19 and the current 20. The current of the alternating load 21 and the normally connected battery of the capacitors 22 (or the power filters of the STK) is measured.

The principle of operation of the control device STK is enough to consider the example of the formation of one output linear current of the STC, for example, phase A of the network. Consider for this purpose Fig. 2. Let the signals i y1 , i y2 , i y3 corresponding to the required reactive power value of the reactors AB, BC, CA come from the outputs of the calculators 1, 2, 3. (This actually means the process of resetting the reactive power of the load). At the first moment, when the latching blocks are reset, the input of the 2nd phase thyristor of the phase CA will receive the signal i *y2 = i y2 + I y1 where I y1 increment of the current value of the required power of the reactor AB, defined as the difference between the current output of the phase calculator AB and the same signal, but fixed at the time of the last opening of the thyristor 1 of phase AB, the initial angle of the voltage vector of which by 60 el. Deg. Is ahead of the initial angle of the voltage vector of the AC phase synchronizing the operation of the thyristor 2. The signal i *y2 is compared with a pulse signal having an envelope of the time function f ), Linearizing the static characteristic of the thyristor-reactor circuit in the 1st (fundamental) harmonic. At the moment of coincidence i *y2 and f ( ) A control pulse is given to the thyristor pair 2.5 with the required control angle AC ( CA thyristor control angle 5). As a result, in the AC phase reactor, a current unit in the form of a sinusoidal vertex with a cutoff angle of 2 ( ) glad. Impulse control AC is also used for gating the latching unit 18, at the output of which the value of the signal i y2 At the time of the last opening of the thyristor 2. The thyristor of phase 3 BC comes into operation next, the signal i *y3 = i y3 + I y2 , where I y2 = i y2 -i y2 This thyristor will open earlier than it would be in the prototype device, as can be clearly seen from the current diagram i BC, the solid line represents the current diagram of the prototype device, and the bar code of the proposed device.

In Fig. 3 shows the calculated phase currents AB and BC and the output linear current of the STK i B , provided that the outputs of the calculators of the required reactive powers of the AB and BC phase reactors vary in harmonic order



Where = 2 F f 20 Hz is the partial frequency of the change in the envelope of the reactive power of the load. The solid lines are the curves relating to the prototype device, the dashed line to the proposed device. It is seen that, as the control signal i yB increases and when it decreases, the output linear current of the STK i B of the proposed device in sinusoidal form by almost 30 e. Deg. (In absolute time approximately 1.5 ms) is ahead of the analogous response of the prototype device. For the frequency of 20 Hz, the lead will be 12 e. Deg. Or 0.2 rad. What would mean an increase in the suppression factor of the 20 Hz reactive load power fluctuation by 20% For the frequency of the 10 Hz reactive power envelope (purely used for comparison of different STCs by the voltage flicker suppression ratio) this coefficient will be 10% higher for the proposed device as compared to the prototype . This is a tangible result, since it is usually required of the STK to transmit only 20.40% of the reactive power of the alternating load, varying with a frequency of 10 Hz, to the network.

Thus, the positive effect of the proposed method of controlling the STC, consisting in increasing the speed of implementation of its devices, is achieved due to new design (circuit) features of the latter - the introduction of three blocks of fixing the calculated required value of the reactive power of the respective reactors at each clock cycle of thyristors, The use of three-input adders included between each NIFU and the corresponding calculators of the required current reactive power values ​​of the reactors, such that at the output of each adder a control signal of the NIR of a given phase of the SFC is equal to the sum of the current signal output of the corresponding calculator, the output current signal of the phase power calculator of that phase STK, the initial voltage angle of which is 60 eV ahead. Deg. The initial voltage angle of the given phase of the STC and the negative value of the same signal fixed at the output of the fixation unit at the time of the last opening of the thyristor of the same phase of the STC.

CLAIM

A method for controlling a static thyristor reactive power compensator comprising three linear reactors, each of which is connected to the respective phases of the supply network via a pair of counter-connected thyristors with a pulse-phase control system, by measuring the line voltages and linear load currents, calculating the required Reactive powers of the reactors and their subsequent conversion to the control angles of the respective thyristors, characterized in that, at the moment of switching on the thyristor of the next phase, the corresponding value of the required reactive power of this phase is memorized, and at the time of generating the thyristor control signal of the next phase to the calculated required value of its reactive power, Between the stored and current value of the reactive power of the previous phase and the obtained value of the reactive power is converted into the control angles of the corresponding thyristors.

print version
Published on February 15, 2007