Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
  • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
  • H02J3/1807—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators, e.g. thyristor-controlled series capacitors [TCSC]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
  • Y02E40/10—Flexible AC transmission systems [FACTS]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
  • Y02E40/30—Reactive power compensation

Definitions

• the invention relates to a system and a method for controlling a TCSC in an electric power transmission network, in particular via a Lyapunov approach.
• the active P and reactive Q powers provided by the source respectively have the following expressions:
• Fiber Capacitor is the most common. However, it does not allow adjustment of the degree of compensation. If such an adjustment is required, it is then possible to use a TCSC system.
• FACTS FACTS
• phase shift, voltage, impedance In this way, power transfers are better controlled and tensions are better maintained. which makes it possible to increase the margins of stability and to tend towards an exploitation of the lines of transport of energy by a maximum transfer of current to the limit of the heat resistance of these lines with high and very high tension.
• FACTS can be grouped into two families: parallel FACTS and FACTS series:
• - Parallel FACTS include the Mechanical Switched Capacitor (MSC), the Static Var Compensator (SVC) and the Static Synchronous Compensator (STATCOM).
• MSC Mechanical Switched Capacitor
• SVC Static Var Compensator
• STATCOM Static Synchronous Compensator
• the FACTS series include the FC ("Fixed Capacitor"), the TSSC ("Thyristor Switched Capacitor Series”), the TCSC ("Thyristor Controlled Capacitor Series”), and the SSSC ("Static Synchronous Series Compensator").
• FACTS series consists of a single capacitor (FC) placed in series on the transmission line. This capacitor compensates for a part of the inductance of the line. By noting Xc the impedance of this capacitor, and neglecting the resistance of the cables, the power transmitted by the compensated line is written:
• Figure 1 shows the evolution of the active power as a function of the transmission angle for three different values of the compensation rate: 0% (curve 10), 30% (curve 11), and 60%
• the higher the compensation rate the greater the transmittable power or the lower the transmission angle for the same power transported.
• the increase in transmissible power makes it possible, by increasing the stability margin (ie the available active power margin before the critical stability angle), to improve the overall stability of the network in the event of a transient defect on the transmission line.
• the combination of capacitors, of fixed and constant capacitance, with the inductance of the transmission line forms a resonant system with little damping. In particular cases, particularly in the case of a return to normal operation following a fault on the transmission line, this resonant system can oscillate through an exchange of energy with the resonant mechanical system consisting of the masses and turbine shafts generators.
• a TCSC consists of two parallel branches.
• the first comprises two thyristors T1 and T2 connected back-to-back in series with an inductance L.
• This branch is called TCR or "Thyristor Controlled Reactor" for thyristor controlled inductance which can be compared to a variable inductance.
• the second branch contains only one capacitor C.
• the variable inductance connected in parallel with this capacitor, makes it possible to vary the impedance of the TCSC by offsetting all or part of the reactive energy produced by the capacitor.
• the modification of the value of this impedance is done by adjusting the thyristor firing angle, ie the moment in a period when the thyristors start to drive.
• FIG. 3 shows the overall impedance of the TCSC as a function of the initiation angle.
• the resonance zone 15 is clearly visible.
• the TCSC has two main modes of operation: capacitive mode and inductive mode.
• the operating mode depends on the value of the boot angle.
• the start of the TCSC can only be done in capacitive mode.
• the TCSC is in capacitive mode, and the current is in advance of the voltage.
• the TCSC then functions as a capacitor and offsets a part of the inductance of the line.
• the voltage across the capacitor is increased (or boosted) by a surplus current from the inductance load which is added to the line current during the closing of one of the thyristors, for example Tl.
• a surplus current from the inductance load which is added to the line current during the closing of one of the thyristors, for example Tl.
• Kb X ⁇ csc / X c ⁇ called Boost factor, where X c ⁇ is the impedance of the capacitor alone.
• the initiation of the other thyristor, for example T2 makes it possible to reproduce the cycle for the opposite half cycle.
• the priming of the thyristors T1 and T2 thus causes a charge / discharge cycle of the inductance towards the capacitor C at each half-period.
• the complete cycle lasts a full period of line current.
• the two thyristors T1 and T2 are controlled in parallel, one being open the other being closed, this sequence varying with the alternation of the current.
• the initiation angle is lower than the resonance value, and the current is delayed on the voltage.
• the firing order of the thyristors is reversed.
• the voltage is strongly deformed by the presence of non-negligible harmonic.
• FIG. 5 thus illustrates an operation in inductive mode, the curve 25 illustrating the capacitive current, the curve 26 illustrating the line current, the curve 27 illustrating the capacitive voltage.
• TCSCs are mainly used in capacitive mode, but in special cases they must operate in inductive mode.
• the transition from one mode to another is done by a particular control of the thyristors. These transitions are only possible if the time constant of the LC circuit is less than the period of the network.
• the thyristors are connected in a single line connecting a generator generating in an infinite bus
• ⁇ ignition angle of the thyristors
• ⁇ conduction end angle
• 0 phase shift angle
• Qo resonance pulse
• ⁇ s pulsation of the network a ⁇ ⁇ 0 - ⁇ s
• V 1 * and V 2 * reference voltages
• V 1 CtV 2 error of continuation of the voltages.
• the main objective is to propose a TCSC state model capable of representing its dynamic behavior over its entire operating range. Based on Kirchoff's laws and the description of how the TCSC works, the equations governing the dynamics of the system boil down to the following equation system:
• the generalized mean method performed here to obtain the phasor dynamic model is based on the fact that a sinusoid x (.) Can be represented on the interval tT, t] using a Fourier series. of shape :
• harmonic of rank k of the function x the sinusoidal function obtained with the Fourier coefficient of index k. This is the function X k e jkw ' ⁇ .
• the first harmonic is called fundamental.
• V lc The real (cosine) and imaginary (sinus) parts of the fundamental (or first phasors) of voltage and current are denoted V lc , V ls , l lc , l ls . So we have :
• ⁇ depends on the zero crossing of the current in the inductor, and can be determined by solving a transcendental equation. Consequently, ⁇ does not depend solely on V 1 , I 1 and I f . But some approximations allow to convert the previous system into a real state model. It suffices for it to be able to express 0 according to the quantities mentioned above. It was assumed that the signal was sufficiently well approximated by the signal obtained with the fundamental only. We can therefore express 0 as the difference between the fundamental of the line current and the fundamental of the current in the inductance, ie:
• Control laws of the TCSC The document referenced [1] at the end of the description defines a control device of a TCSC according to a control law such that the instants of the zero crossings of the voltage across the capacitor of the TSC are substantially equidistant even during times when the current flowing in the power line contains subsynchronous components in addition to its fundamental component.
• a second document of known art describes three nonlinear control laws for a TCSC system: a control law whose synthesis is performed by a Lyapunov-type approach, a control law of the type IDA ("Interconnection and Damping Assignment") and a control law obtained by a technique of the FLC ("Feedback Linearization Control”) type.
• This paper analyzes the stability of these three control laws, and uses simulations in the time domain to verify the performances obtained by these three control laws.
• This document thus describes a so-called Lyapunov type control law.
• the performances with this control law prove to be insufficient notably through the two following technical problems:
• the subject of the invention is a system and a method for controlling a TCSC in an electrical energy transport network making it possible to solve these two technical problems, by proposing new control laws that generate the starting times of the thyristors of the TCSC.
• the invention relates to a control system for a TCSC disposed on a high voltage line of an electric power transmission network, comprising:
• a voltage measurement module which makes it possible to extract the harmonics from the voltage at the terminals of the TCSC; a measurement mode of the current which makes it possible to extract the amplitude of the fundamental and possibly other harmonics of the current flowing in the line; high tension,
• a regulator according to a non-linear control law, which receives as input the outputs of the two voltage and current measuring modules, and a reference voltage corresponding to the fundamental of the voltage that is to be obtained at the terminals of the TCSC, and which delivers an equivalent effective admittance
• a control angle extraction module according to an extraction algorithm which receives this equivalent effective admittance and which delivers a control angle, characterized in that it further comprises:
• control module of the TCSC thyristors which receives this control angle and a reference of zero current delivered by a phase locked loop giving the position of the current, and in that the control law is such that:
• V 1 u 11 * - sign (u *) R 2 V 2 + u * V 1 ⁇ - V * - R 3 -
• the angle extraction algorithm comprises a table, a modeling or a search by dichotomy.
• the invention also relates to a method for controlling a TCSC disposed on a high voltage line of an electric power transmission network, which comprises the following steps:
• a measurement step of the current which makes it possible to extract the amplitude of the fundamental and possibly the other harmonics of the current of the high-voltage line; a step of regulation according to a nonlinear control law, from the measurement signals of voltage and current, and a reference voltage corresponding to the fundamental of the voltage that is to be obtained at the terminals of the TCSC, in order to obtain an equivalent effective admittance,
• a step of extracting the control angle according to an angle extraction algorithm from this equivalent effective admittance, to obtain a control angle characterized in that it furthermore comprises:
• Vi and V2 measured voltages
• V 1 * and V 2 * reference voltages
• V 1 and V 2 error of continuation of voltages
• R2, R3 and ⁇ parameters of adjustment
• sign Switching function of which examples are given in FIGS. 12 and 13.
• control law can be determined from a Lyapunov type approach.
• Figure 1 illustrates the active power versus the transmission angle for three different values of the compensation rate.
• Figure 2 illustrates the circuit diagram of the TCSC.
• Figure 3 illustrates the impedance of the TCSC as a function of the initiation angle.
• Figure 4 illustrates the operation of the TCSC in capacitive mode.
• Figure 5 illustrates the operation of the TCSC in inductive mode.
• Figure 6 illustrates the current and voltage curves of the TCSC in capacitive mode.
• Figure 7 illustrates the system of
• FIG. 8 illustrates the equivalent effective admittance of the TCSC as a function of the angle ⁇ , in a system of the known art.
• FIG. 9 illustrates the static error on the fundamental of voltage in operation close to resonance (58.7 degrees) in a system of the known art.
• Figure 10 illustrates an approximation of the sign function.
• Figure 11 illustrates an "optimized" approximation of the sign function.
• FIG. 12 illustrates the disappearance of the static error on the fundamental voltage, thanks to the method of the invention.
• Figures 13 to 15 illustrate the comparative results obtained with the control law defined in the referenced document [2] and with the control law of the invention.
• FIG. 7 The control system of a TCSC in an electric power transmission network according to the invention is illustrated in FIG. 7.
• This TCSC which is arranged on a high-voltage line 40, comprises a capacitor C, an inductor L, and a set of two thyristors T1 and T2.
• This control system 39 comprises:
• a voltage measurement module 41 which makes it possible to extract the harmonics from the voltage at the terminals of the TCSC
• a regulator 43 according to a determined nonlinear control law, which receives as input the outputs of the two voltage and current measuring modules 41 and 42, and a reference voltage V ref corresponding to the fundamental (harmonic 1 at 50 Hz) the voltage that one wants to obtain at the terminals of the TCSC, and which delivers an equivalent effective admittance,
• a module 44 for extracting the control angle according to an angle extraction algorithm (for example a table, a modeling or a search by dichotomy) which receives this equivalent effective admittance and which delivers a control angle,
• an angle extraction algorithm for example a table, a modeling or a search by dichotomy
• a module 45 for controlling the thyristors T1 and T2 of the TCSC which receives this control angle and a reference of zero current delivered by a phase-locked loop 46 giving the position of the current.
• the control method of a TCSC disposed on a high-voltage line of an electrical energy transmission network thus comprises the following steps:
• a voltage measurement step which makes it possible to extract the harmonics from the voltage at the terminals of the TCSC; a current measurement step which makes it possible to extract the amplitude of the fundamental and possibly other harmonics of the current flowing in the line; high tension,
• a regulation step according to a non-linear control law, from the voltage and current measurement signals, and from a reference voltage corresponding to the fundamental of the voltage that is to be obtained at the terminals of the TCSC, for obtaining an equivalent effective admittance; a step of extracting the control angle according to an angle extraction algorithm from this equivalent effective admittance to obtain a control angle,
• I and V denote the fundamental Fourier coefficients (or 1-phasors) of i and v, respectively the current in the inductance and the voltage across the TCSC.
• J denotes the matrix used instead of the complex j to express the phasors as vectors comprising the real and imaginary parts of the corresponding complex phasors.
• Leff ( ⁇ ) denotes the effective inductance of the TCR branch, depending on the conduction angle ⁇ .
• FIG. 8 shows the effective admittance ⁇ s C e ff ( ⁇ ). • The sign of this admittance varies according to the mode of operation of the TCSC: positive in capacitive, negative in inductive.
• the angle ⁇ can be found by means of the preceding equation giving C eff ( ⁇ ) (for example by dichotomy). It can also be extracted from a previously filled table. Knowing ⁇ we deduce the initiation angle ⁇ (measured with respect to the zero crossing of the line current) by calculating:
• the goal of control is to find a
• control signal (effective admittance) is restricted to a given interval for each operating regime:
• a Lyapunov function of this type is commonly used in the field of 1 electrotechnical. It can be regarded as a form of mechanical energy, sum of a kinetic energy (first term) and a potential energy (integral term).
• This static error can be explained in several ways: inaccuracy of measurement, simplifications of the model and absence of harmonic, bad adjustment of gain etc ....
• the object of the invention is therefore in particular to modify this law so as to eliminate this static error.
• a first possibility is to use an approximation of the type: x sign (x) - x + ⁇ with ⁇ rather low and determined as a function of the system time constant, as illustrated in FIG. 10, the curve 50 illustrating the sign function and the curve 51 illustrating the approximate sign function.
• ⁇ is chosen large, so as to "flatten" the approximate sign function 51 in the neighborhood of 0.
• Such an approach amounts to introducing a variable gain.
• the gain tends to zero when the error tends to zero (ie the controlled output tends to the reference), which avoids overloading the actuator when the output is close to the reference.
• M -sign (u *) R 2 V 2 + u * V 1 -S-V * -R 3 ⁇ y, y + ⁇ or:
• FIGS 13 to 15 illustrate comparative results obtained with the control law of the prior art as defined in the referenced document [2] and with the first control law of the invention.
• FIG. 13 thus illustrates a harmonic-free operation successively obtained in capacitive (from 0 to 0.9 seconds) and inductive (from 0.9 to 2 seconds) mode with:
• control law of the invention makes it possible to reduce the static error by referred to the referenced document [2]. In addition it allows a gain in speed.
• FIG. 14 illustrates an operation with a line current comprising harmonics, as illustrated in FIG. 15.
• the control law of the invention is less sensitive to disturbances (harmonics) than the document referenced [2]. In addition, it is more robust.
• This second control law is to take into account the harmonics in order to improve the robustness or dynamics of the control laws by taking into account the contribution of the harmonics as a measured disturbance.
• CV 1 MV 2 + (M - I) L ⁇

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• 2007
  • 2007-04-24 FR FR0754660A patent/FR2915635B1/fr not_active Expired - Fee Related
• 2008
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