Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—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
  • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
  • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
  • H02J3/1864—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein the stepless control of reactive power is obtained by at least one reactive element connected in series with a semiconductor switch
• • 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]

Definitions

• the invention relates to a circuit for stabilizing an ac power line.
• One or several of these circuits are connected in parallel to the line.
• the circuit is activated if one or s more line parameters, especially the line voltage, have left or will predictably leave preset tolerance ranges. This is for example the case when loads with inrush currents are connected to the line, while clearing short circuits in the iine by circuit breakers or fuses, or during malfunctioning of power transmission devices. Weak lines are especially endangered.
• These kind of lines are for example lines involving long interconnections, or converter-fed lines, where in case of overload the converter disconnects automatically from the line.
• the circuit according to the present invention consists of an oscillatory circuit and a link element. Current half-cycles are generated in the oscillatory circuit by a dc- precharged capacitance, an oscillatory inductance and a switching element.
• the circuit according to the invention has the advantage of a similar behaviour as a rotating var-compensator Stabilizing initial current and decay can be set over a wide range
• the circuit can also be used for damping of harmonics and oscillations in the line
• the circuit is of simple and robust design, there are no standby losses and while activated the circuit produces small harmonics It can be used for lines in the range of some few kVA up to some thousand MVA It profits from the steady development of capacitors towards more capacitance per volume
• Fig 1 shows the basic stabilizing circuit of the invention
• Fig 2 shows an embodiment of the switching elements of the circuit
• Fig 3 shows the principal electrical operation of the circuit
• Fig 4 shows an embodiment of the circuit comprising galvanic coupling to the capacitance
• Fig 5 shows an embodiment of the circuit comprising inductive coupling to the oscillatory inductance
• Fig 6 shows the connection to the line using a bridge connection in the link element
• Fig 7 shows the connection to a three-phase line using a bridge connection
• Fig 8 shows three circuits connected in delta to a three-phase line
• Fig 9 shows an embodiment of the capacitance by using polarized capacitors
• Fig 10 shows the use of elements of a pwm-converter for the circuit according to the invention
• Fig 1 shows the basic circuit of the invention
• the circuit consists of an oscillatory circuit 1 and a coupling of the line Pi, P 2 to the oscillatory circuit by means of the link element 2
• the oscillatory circuit 1 consists of the capacitance 3, the oscillatory inductance 4 and the switching element 5
• the switching element consists of two parallel switching branches 5a, 5b, each being capable of conducting in one direction and which are connected with opposite polarization
• the capacitance is held in precharged state in standby by a not shown charging device All the elements of the oscillatory circuit are connected such that they form a closed current loop
• the oscillatory circuit 1 In activated state the oscillatory circuit 1 generates current half-cycles
• the switching branches 5a, 5b of the switching element 5 are triggered such that positive and negative current half-cycles are generated in synchronism to the line
• galvanic or inductive coupling of the line to the oscillatory circuit 1 stabilizing current is fed to the line via the link element 2
• FIG. 2 A simple embodiment of the switching element 5 is shown in Fig 2 This consists of two thy ⁇ stors 50a, 50b connected in anti-parallel
• the switch of the link element 2 can also consist of two anti-parallel thynstors 20a, 20b
• a link inductance 6 can be inserted in the link to the line
• the principal electrical operation is shown in Fig 3
• the capacitance 1 is kept at a charging voltage V 0 This corresponds at least to the crest value of the rated line voltage
• Activating of the circuit is started by closing one of the switching branches, for example 5a, at the time ti, whereby the capacitance 3 starts a half-cycle swing with the oscillatory inductance 4 and the not shown line inductance
• This half-cycle swing produces a half-cycle current I in the capacitance
• the ratio of the inductances and the development of the disturbed line then determine the stabilizing current Is into the line
• the oscillatory inductance is in the range of 25 100% of the sum of link inductance and line inductance
• the chosen switching branch 5a opens automatically or by being actively switched off By dimensioning of capacitance and inductances and taking into account the line
• Vo dc charging-voltage of capacitance It is essential that the circuit consisting of capacitance 3, oscillatory inductance 4, link inductance 6 and line inductance must not be tuned to line frequency.
• the anti-parallel switching branch, for example 5b is closed, whereby the inverse polarized half-cycie is produced, and so on.
• the decay of the generated stabilizing current is determined by the losses of the circuit and the supply of real power into the line.
• the activated oscillatory circuit is switched such that the capacitance voltage is approximately in-phase with the line voltage.
• the triggering pulses for the switching branches 5a, 5b can be produced by an auxiliary circuit, generating an ideal line-voltage image. Such an image is realised in known circuits by use of phase-locked loop devices.
• Fig. 4 shows the embodiment of the circuit with galvanic coupling of the line to the capacitance 3.
• Fig. 5 shows an inductive coupling of the line to the oscillatory circuit. This is done by coupling to the oscillatory inductance 4 which is used as part of a transformer or autotransformer.
• the charging voltage of the capacitance 3 has to be adapted to the turns ratio.
• the capacitance 3 is precharged with a fixed polarity a period of up to 360° can elapse from starting of disturbance until first switching of the circuit.
• the maximum delay can be reduced to 180°.
• the branches of the bridge consist of the above mentioned
• RECTIFIED SHEET (RULE 91) switching branches, represented here by thyristor pairs 20a, 20b. During an activation of the circuit two diagonally arranged branches of the bridge stay closed.
• Fig. 7 shows the embodiment of the link element 2 as three-phase bridge for the connection to a three-phase line Pi, P 2 , P 3 . Thereby one circuit can selectively stabilize one of the three phases.
• the width of the generated current half-cycles can be self-adapted during operation by means of tappings in the inductances, thereby achieving half-cycles as wide as possible.
• the activating of the circuit can be triggered by the decay of the grid voltage beyond a preset value, preferentially combined with a minimum timing threshold. It is also possible to start triggering if the value of the difference between line voltage and ideal line-voltage image exceeds a preset value, preferentially combined with a minimum timing threshold.
• the circuit can be activated before an expected line disturbance.
• the circuit losses are then automatically supplied from the line.
• the circuit can be used in steady-state operation as harmonics filter and voltage-dip filter or, by slightly phase-shifting the triggering pulses to the line voltage, as low harmonics static var-compensator.
• the circuit is disconnected from line by one or several of the following processes: -voltage of capacitance 3 decays beyond preset value -voltage of capacitance 3 increases -line voltage increases
• the switching elements 2, 5 are preferentially equipped with elements of the type silicon carbide (SiC). Selected components of the circuit may be kept in a superconducting state.
• Fig. 9 shows the use of polarized capacitors as elements of the capacitance 3.
• the capacitance is composed of series-connected polarized capacitors 3a, 3b which are arranged in same amount in each polarity and which are protected in each polarity by at least one parallel diode 30a, 30b.
• Fig. 10 shows the use of elements of a pwm-converter for the stabilizing circuit.
• a part of the dc link capacitance is used as capacitance 3 of the circuit.
• a decoupling element 8 contains a thyristor or similar device 8a, a diode 8b and a resistor 8c.
• the stabilizing current is produced by inductive coupling to the oscillatory inductance 4 and feeding via the switching link element 2 to the line connections of the converter Pi, P 2 .
• the resistor 8c serves for voltage equilibration of the dc-link capacitors before reclosing the thyristor 8a.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Rectifiers (AREA)
• Control Of Electrical Variables (AREA)

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• 1998
  • 1998-08-20 AU AU96050/98A patent/AU9605098A/en not_active Abandoned
  • 1998-08-20 DE DE0934618T patent/DE934618T1/de active Pending
  • 1998-08-20 EP EP98946391A patent/EP0934618A1/de not_active Withdrawn
  • 1998-08-20 WO PCT/EP1998/005298 patent/WO1999010960A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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