WO2014044293A1 - Procédé de commande d'un système de transmission de puissance et système de commande correspondant - Google Patents

Procédé de commande d'un système de transmission de puissance et système de commande correspondant Download PDF

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Publication number
WO2014044293A1
WO2014044293A1 PCT/EP2012/068339 EP2012068339W WO2014044293A1 WO 2014044293 A1 WO2014044293 A1 WO 2014044293A1 EP 2012068339 W EP2012068339 W EP 2012068339W WO 2014044293 A1 WO2014044293 A1 WO 2014044293A1
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WIPO (PCT)
Prior art keywords
inverting
converters
converter
inverting converters
link
Prior art date
Application number
PCT/EP2012/068339
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English (en)
Inventor
Paulo Fischer De Toledo
Original Assignee
Abb Technology Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Abb Technology Ltd filed Critical Abb Technology Ltd
Priority to PCT/EP2012/068339 priority Critical patent/WO2014044293A1/fr
Publication of WO2014044293A1 publication Critical patent/WO2014044293A1/fr

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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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/75—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
    • H02M7/757—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H02M7/7575—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only for high voltage direct transmission link
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • the present invention generally relates to power systems.
  • the 5 present invention relates to a method in a power transmission system, a
  • HVDC High Voltage Direct Current
  • Converters in HVDC power transmission systems convert between a relatively high alternating current (AC) voltage and such high level direct current (DC) voltages.
  • a HVDC power transmission system there can be included a first AC power line and a second AC power line interconnected via a DC link or line.
  • the first AC power line is connected to the DC link at a first end thereof, and the second AC power line is connected to the DC link at a second end thereof.
  • the DC link includes two inverting converters 101 a, 101 b connected in parallel and two rectifying converters 102a, 102b connected in
  • the inverting converter 101 b is connected to the line via the inverting converter 101 a.
  • the rectifying converter 102b is connected to the line via the rectifying converter 102a.
  • the rectifying converters 102a, 102b and the inverting converters 101 a, 101 b are connected to AC lines schematically indicated by reference numerals 103 and 104 via transformers 105a, 105b of the rectifying
  • the operation of the inverting converters 101 a, 101 b is often controlled by having one of the inverting converters 101 a, 101 b control the DC line voltage, i.e. the DC voltage over the DC link, and the other one of the inverting converters 101 a, 101 b control the current through it. Furthermore, the rectifying converters 102a, 102b are controlling the currents therethrough, i.e. each of the rectifying converters 102a, 102b is controlling the current through it.
  • a converter controlling the current therethrough may control the current by varying or adjusting the firing angle of the converter, or the firing angle of converter valves included in the converter, so as to meet the voltage on the DC side of the converter.
  • Control of the DC voltage can be achieved by varying or adjusting the extinction angle reference value for the converter, which extinction angle reference value for example is supplied from a controller or control unit of the power transmission system, accordingly controlling the DC voltage across the converter.
  • the tap position of a transformer of the converter may be varied or adjusted, thereby controlling the AC voltage across the converter.
  • firing angle of a converter it is generally meant the time or angle between the converter valve voltage becoming positive and the instant at which the converter valve is fired.
  • the voltage conversion ratio between the DC output and AC input, if acting as a rectifier, or between the AC output and DC input, if acting as an inverter is a function of the firing angle of the converter.
  • extinction angle of a converter it is generally meant the time or angle between when the current in a converter valve ceases and the subsequent positive zero crossing or transition of the anode voltage on that converter valve.
  • commutation margin angle of the converter it is generally meant the angle between the end of commutation and the subsequent converter valve voltage positive zero crossing or transition.
  • the inverting converters 101 a, 101 b may operate at different extinction angles.
  • one of the inverting converters 101 a, 101 b may operate at a higher extinction angle when controlling the DC current therethrough, which may result in a higher reactive power consumption of the inverting converter 101 a, 101 b and/or an increased stress on the converter valves of the inverting converter 101 a, 101 b.
  • an imbalance between the currents through the respective inverting converters 101 a, 101 b may occur, in particular following possible disturbances in the power transmission system.
  • the inverting converter 101 a, 101 b that is controlling the DC line voltage may be more prone to accept or take more current compared to the inverting converter 101 a, 101 b which controls the current through it and may therefore operate with a higher static characteristic than the inverting converter 101 a, 101 b that is controlling the DC line voltage.
  • a concern of the present invention is to provide a method in a power transmission system including a DC link in which at least two inverting converters are connected in parallel, which method facilitates or enables the current flow between the inverting converters to become more balanced as compared to using a control scheme for operation of the inverting converters such as described with reference to Fig. 1 .
  • a further concern of the present invention is to provide a method in a power transmission system including a DC link in which at least two inverting converters are connected in parallel, by which method occurrence of imbalance between the currents through the respective inverting converters may be reduced or even eliminated.
  • the power transmission system comprises a first AC power line and a second AC power line, and at least two inverting converters connected in parallel in a DC link between the first AC power line and the second AC power line.
  • the first AC power line is
  • the power transmission system comprises a controller for controlling operation of the DC link.
  • the method comprises receiving current reference value for the desired current through the respective inverting converters from the controller. For each of the inverting converters, a current through the inverting converter is measured, and a first difference value between the measured current and the current reference value is determined.
  • a second difference value between the first difference value determined for the inverting converter and the first difference value determined for the other inverting converter is determined.
  • a firing angle offset value is determined based on the second difference value determined for the inverting converter.
  • a firing angle of each inverting converter is adjusted or determined based on the firing angle offset values determined for the respective inverting converters.
  • adjustment or determination of the firing angle of each of the inverting converters may comprise summing a firing angle reference value for the inverting converter, e.g. received from the controller, and the firing angle offset values determined for the inverting converter, thereby obtaining an adjusted firing angle for the inverting converter.
  • the current through each of the inverting converters may be adjusted at least in part based on the adjustment of the firing angle of the respective inverting converters. By adjustment of the firing angle of a inverting converter, an adjustment of the current through the inverting converter may be achieved.
  • a control loop which for example may be a proportional type (P-type) of control loop or a proportional-integral type (Pl- type) of control loop as will be further described in the following
  • P-type proportional type
  • Pl- type proportional-integral type
  • the current flow between the inverting converters may become more balanced, or the difference between the currents through the inverting converters may become less, as compared to using a control scheme for operation of the inverting converters such as described in the foregoing with reference to Fig. 1 .
  • occurrence of imbalance between the currents through the respective inverting converters may be reduced or even eliminated.
  • the adjustment of the respective firing angles of the inverting converters according to the method in the control loop may be repeatedly carried out until a selected requirement is met and/or a selected criteria for the difference between the currents through the inverting converters is complied with.
  • the selected requirement may for example be expiry of a timer or reaching a certain number of successive executions of the method steps.
  • the selected criteria for the difference between the currents through the inverting converters may for example be the difference between the currents through the inverting converters falling below a predefined current difference threshold value.
  • the measurement of the currents in the respective inverting converters may be performed at the same time or substantially at the same time, e.g. within a few microseconds.
  • the firing angle offset values may be determined as a product of the respective second difference values determined for the inverting converters and a proportional gain value.
  • steps (ii)- (vi) may thereby be comprised in a control loop for repeatedly adjusting the respective firing angles of the inverting converters.
  • the control loop may for example be a P-type control loop.
  • control loop may for example be a Pl-type control loop, as further described in the following.
  • a plurality of successive second different values are generated for each inverting converter.
  • the adjustment of the firing angle of each of the inverting converters may comprise selecting one of the plurality of successive second different values such that there is at least one second different value the determination of which preceded the determination of the selected one of the successive second different values.
  • a firing angle offset value may be determined as a sum of a product of the selected one of the successive second different values and a proportional gain value, and a product based on an integral gain value and a sum of the selected one of the successive second different values and preceding one or ones of the successive second different values.
  • a firing angle of the inverting converter may be adjusted based on the firing angle offset value. Thereby, adjustment of the current through the inverting converter may be effected.
  • a firing angle offset value may be determined as a product of the selected one of the successive second different values and a proportional gain value.
  • a firing angle of the inverting converter may be determined based on the firing angle offset value. Thereby, adjustment of the current through the inverting converter may be effected.
  • the receiving of a current reference value for the desired current through the respective inverting converters from the controller may also be repeated at least once and be comprised in the control loop.
  • the power transmission system may comprise communication means for communication of signals between the at least two inverting converters.
  • the communication means may be wired and/or wireless.
  • the communication means may for example comprise a wireless communication link of a type as known in the art.
  • the determination, for each of the inverting converters, of a second difference value between the first difference value determined for the inverting converter and the first difference value determined for the other inverting converter, may be implemented in the respective inverting converters.
  • a current reference value for the desired current through the respective inverting converter from the controller may be received at each of the at least two inverting converters at least once.
  • Each of the at least two inverting converters may communicate the value of the measured current through the inverting converter, the current reference value and/or the first difference value determined for the respective inverting converter to at least one other of the at least two inverting converters at least once.
  • An extinction angle reference value for the desired extinction angle of the respective inverting converters may be received or retrieved, e.g. from the controller in the power transmission system.
  • the extinction angle of the respective inverting converters may be determined or measured. On a condition that there is a difference between the extinction angle of the respective inverting converters and the extinction angle reference value, the extinction angle of the respective inverting converters may be adjusted so as decrease the difference between the extinction angle of the respective inverting converters and the extinction angle reference value. Adjusting the extinction angle of the inverting converters may for example comprise adjusting the tap positions of transformers of the respective inverting converters.
  • At least one of the inverting converters may be configured to control the DC voltage over the DC link.
  • a DC voltage reference value for the desired DC voltage over the respective inverting converters may be received or retrieved, e.g. from the controller in the power transmission system.
  • the DC voltage over the at least one of the inverting converters which is configured to control the DC voltage over the DC link may be determined, and on a condition that there is a difference between the DC voltage over the at least one of the inverting converters and the DC voltage reference value, the DC voltage over the at least one of the inverting converters may be adjusted so as decrease the difference between the DC voltage over the at least one of the inverting converters and the DC voltage reference value.
  • the determination and adjustment of the DC voltage over the at least one of the inverting converters may be conditional on that the difference between the extinction angle of the respective inverting converters and the extinction angle reference value is below a predefined extinction angle difference reference value.
  • the adjustment of the DC voltage over the at least one of the inverting converters may for example comprise adjusting the tap positions of a transformer of the at least one of the inverting converters.
  • a power transmission system comprising a first AC power line and a second AC power line, and a DC link between the first AC power line and the second AC power line.
  • the first AC power line is connected to the DC link at a first end thereof and the second AC power line is connected to the DC link at a second end thereof.
  • the power transmission system comprises at least two inverting converters connected in parallel in the DC link. Each of the at least two inverting converters is adapted to convert DC power to AC power. The output from the at least two inverting converters is outcoupled from the DC link at one of the first and second ends thereof.
  • the power transmission system comprises a controller for controlling operation of the DC link, and a converter control system.
  • the converter control system is adapted to receive current reference value for the desired current through the respective inverting converters from the controller, and for each of the inverting converters, measure a current through the inverting converter and determine a first difference value between the measured current and the current reference value.
  • the converter control system is adapted to, for each of the inverting converters, determine a second difference value between the first difference value determined for the inverting converter and the first difference value determined for the other inverting converter.
  • the converter control system is adapted to, for each of the inverting converters, determine a firing angle offset value based on the second difference value determined for the inverting converter, and adjust a firing angle of each inverting converter based on the firing angle offsets determined for the respective inverting converters.
  • a converter control system for a power transmission system.
  • the power transmission system comprises a first AC power line and a second AC power line, and a DC link between the first AC power line and the second AC power line.
  • the first AC power line is connected to the DC link at a first end thereof and the second AC power line is connected to the DC link at a second end thereof.
  • the power transmission system comprises at least two inverting converters connected in parallel in the DC link. Each of the at least two inverting converters is adapted to convert DC power to AC power.
  • the output from the at least two inverting converters is outcoupled from the DC link at one of the first and second ends thereof.
  • the power transmission system comprises a controller for controlling operation of the DC link.
  • the converter control system is adapted to receive current reference value for the desired current through the respective inverting converters from the controller, and for each of the inverting converters, measure a current through the inverting converter and determine a first difference value between the measured current and the current reference value.
  • the converter control system is adapted to, for each of the inverting converters, determine a second difference value between the first difference value determined for the inverting converter and the first difference value determined for the other inverting converter.
  • the converter control system is adapted to, for each of the inverting converters, determine a firing angle offset value based on the second difference value determined for the inverting converter, and adjust a firing angle of each inverting converter based on the firing angle offsets determined for the respective inverting converters.
  • a computer program product adapted to be executed in a converter control system in a power transmission system.
  • the computer program product comprises computer-readable means carrying computer program code.
  • the power transmission system comprises a first AC power line and a second AC power line, and a DC link between the first AC power line and the second AC power line.
  • the first AC power line is connected to the DC link at a first end thereof and the second AC power line is connected to the DC link at a second end thereof.
  • the power transmission system comprises at least two inverting converters connected in parallel in the DC link. Each of the at least two inverting converters is adapted to convert DC power to AC power.
  • the output from the at least two inverting converters is outcoupled from the DC link at one of the first and second ends thereof.
  • the power transmission system comprises a controller for controlling operation of the DC link.
  • the computer program code is configured to, when executed in the converter control system, cause the converter control system to:
  • Fig. 1 which has already been described in the foregoing, is a schematic view of a DC link in a power transmission system according to an example.
  • Fig. 2 is a schematic view of a part of a power transmission system in accordance with an embodiment of the present invention
  • Fig. 3 is a schematic view of a part of a power transmission system in accordance with an embodiment of the present invention.
  • Fig. 4 is a schematic flowchart of a method according to an
  • the DC link includes two inverting converters 101 a, 101 b connected in parallel and two rectifying converters 102a, 102b connected in parallel as illustrated in Fig. 2.
  • the inverting converter 101 b is connected to the line via the inverting converter 101 a.
  • the rectifying converter 102b is connected to the line via the rectifying converter 102a.
  • the power transmission system 100 depicted in Fig. 2 is according to an example embodiment of a power transmission system, including a DC link in which at least two inverting converters or inverters are connected in parallel, and that many variations of the particular arrangement of the other elements in the power transmission system relatively to each other can be contemplated.
  • the DC link may include at least three inverting converters connected in parallel.
  • the rectifying converters 102a, 102b and the inverting converters 101 a, 101 b may for example be thyristor-based.
  • the rectifying converters 102a, 102b and the inverting converters 101 a, 101 b are connected to first and second AC lines schematically indicated by reference numerals 103 and 104 via transformers 105a, 105b of the rectifying converters 102a, 102b and via transformers 106a, 106b of the inverting converters 101 a, 101 b, respectively.
  • the first AC power line 103 is connected to the DC link at a first end thereof
  • the second AC power line 104 is connected to the DC link at a second end thereof.
  • Each of the inverting converters 101 a, 101 b is adapted to convert DC power to AC power.
  • the respective outputs from the inverting converters 101 a, 101 b are outcoupled from the DC link at the second end thereof.
  • the power transmission system 100 comprises a controller 108 for controlling operation of the DC link.
  • the power transmission system 100 comprises converter control units 1 10a, 1 10b.
  • the converter control unit 1 10a is adapted to control operation of the inverting converter 101 a
  • the converter control unit 1 10b is adapted to control operation of the inverting converter 101 b.
  • One or both of the inverting converters 101 a, 101 b may be configured to control the DC line voltage, i.e. the DC voltage over the DC link.
  • This may be achieved for example by means of varying or adjusting the extinction angle reference value for the one or both inverting converters 101 a, 101 b, which extinction angle reference value for example is supplied from the controller 108, thereby controlling the DC voltage across the inverting converter 101 a, 101 b, or by means of varying the tap position of the respective transformers 106a, 106b of the inverting converters 101 a, 101 b.
  • the rectifying converters 102a, 102b may be configured to control the currents therethrough, i.e. each of the rectifying converters 102a, 102b is controlling the current through it.
  • Each of the converter control units 1 10a, 1 10b is adapted to receive a current reference value, or current order, for the desired current through the inverting converters 101 a and 101 b, respectively, e.g. from the controller 108 as illustrated in Fig. 2.
  • the converter control units 1 10a, 1 10b are coupled with the controller 108 so as to be able to transmit signals to and receive signals from the controller 108.
  • the converter control units 1 10a, 1 10b are coupled with the controller 108 so as to be able to receive signals from the controller 108, but not necessarily so as to be able to transmit signals to the controller 108.
  • the converter control units 1 10a, 1 10b are coupled with the inverting converters 101 a and 101 b, respectively, so as to be able to transmit signals to and receive signals from the inverting converters 101 a and 101 b, respectively.
  • the converter control units 1 10a, 1 10b are intercoupled so as to be able to transmit signals therebetween.
  • Transmission of signals between different elements in the power transmission system 100 as discussed in the foregoing and in the following may be effected by means of communication means which may be wired and/or wireless.
  • communication means which may be wired and/or wireless.
  • transmission of signals between the converter control units 1 10a, 1 10b may be effected by means of a wireless
  • Each of the converter control units 1 10a, 1 10b is adapted to cause the inverting converter 101 a and 101 b, respectively, to measure current / D c , i , bc,2 through the respective inverting converter 101 a, 101 b, and to determine a first difference value between the measured current and the current reference value.
  • the inverting converters 101 a, 101 b after having measured the current through the respective inverting converter 101 a, 101 b, transmits the respective measured current values to the converter control units 1 10a and 1 10b, respectively, at which the determination of the first difference value is performed.
  • each of the converter control units 1 10a is a single converter control unit 1 10a.
  • 1 10b may be adapted to cause a current sensor or sensors (not shown in Fig. 2), connected to the converter control units 1 10a, 1 10b, to measure currents /DC,I , /DC,2 through the respective inverting converters 101 a, 101 b.
  • the first difference values for the respective inverting converters 101 a, 101 b are exchanged between the converter control units 1 10a, 1 10b.
  • a second difference value between the first difference value determined for the inverting converter 101 a and the first difference value determined for the other inverting converter 101 b is determined.
  • the converter control unit 1 10a may be adapted to cause the inverting converter 101 a to perform the determination of the second difference value.
  • the converter control unit 1 10a is adapted to determine a firing angle offset value for the inverting converter 101 a, or for converter valves of the inverting converter 101 a, based on the second difference value determined for the inverting converter 101 a.
  • a second difference value between the first difference value determined for the inverting converter 101 b and the first difference value determined for the other inverting converter 101 a is determined.
  • the converter control unit 1 10b may be adapted to cause the inverting converter 101 b to perform the determination of the second difference value.
  • the converter control unit 1 10b is adapted to determine a firing angle offset value for the inverting converter 101 b, or for converter valves of the inverting converter 101 b, based on the second difference value determined for the inverting converter 101 b.
  • the converter control units 1 10a, 1 10b are adapted to adjust or determine a firing angle of the inverting converters 101 a, 101 b, respectively, based on the firing angle offset values determined for the respective inverting converters 101 a, 101 b.
  • the measurement of the current through the respective inverting converters 101 a, 101 b, determination of the first difference values for the respective inverting converters 101 a, 101 b, determination of the second difference values for the respective inverting converters 101 a, 101 b, determination of firing angle offset values based on the respective second difference values, and possibly the receipt of current reference values for the desired current through the respective inverting converters 101 a, 101 b, may be performed repeatedly and hence be part of a control loop, e.g. effected by the controller 108 and/or the converter control units 1 10a, 1 10b.
  • the converter control units 1 10a, 1 10b may be adapted to measure or determine the DC voltage L/DC,I , ⁇ DC,2 over the inverting converter 101 a and 101 b, respectively.
  • a control loop which for example may be a proportional type (P-type) of control loop or a proportional-integral type (Pl-type) of control loop
  • P-type proportional type
  • Pl-type proportional-integral type
  • the current flow between the inverting converters 101 a, 101 b may become more balanced, or the difference between the currents through the inverting converters 101 a, 101 b may become less, as compared to using a control scheme for operation of the inverting converters 101 a, 101 b such as described with reference to Fig. 1 .
  • occurrence of imbalance between the currents through the respective inverting converters 101 a, 101 b may be reduced or even eliminated.
  • 101 b defined as a difference between the current order and momentaneous current through the respective inverting converter 101 a, 101 b, is monitored over a period.
  • a difference between the determined current error for the inverting converter and the current error determined for the other inverting converter is formed.
  • This latter difference for each inverting converter can be multiplied by a proportional gain so as to obtain a contribution to a firing angle of the respective inverting converter or a firing angle of converter valves of the respective inverting converter.
  • the proportional gain may be time dependent or predefined or constant.
  • the contribution to the firing angle of the respective inverting converter or the firing angle of converter valves of the respective inverting converter can then be added to a firing angle of the respective inverting converter or a firing angle of converter valves of the respective inverting converter established by or obtained from some other control system, e.g. the controller 108, e.g. a Current Control Amplifier included in a Converter Firing Control functionality.
  • some other control system e.g. the controller 108, e.g. a Current Control Amplifier included in a Converter Firing Control functionality.
  • the converter control units 1 10a, 1 10b may be adapted to determine the firing angle offset values as a product of the respective second difference values determined for the respective inverting converters 101 a, 101 b and a proportional gain value, and possibly some other factor and/or constant.
  • the proportional gain value may be time- dependent or predefined or constant.
  • a transfer function of the control loop may for example be defined by the following equation, for each inverting converter:
  • (1 /[1 +sT]) represents a relatively small filter time constant, which may reduce the level of possible ripple in case introduced in the control system, /response, own is the current response, i.e. the measured current, for the inverting converter, or Own' inverting converter,
  • own is the current order, e.g. a current reference value, for the inverting converter
  • K p is a proportional gain
  • the control loop can use current order and current response from both inverter converters as input variables.
  • the current order and current response for the respective inverting converters are exchanged between between the inverting converters, and/or between the converter control units. Transmission of signals between different elements in the power transmission system may be associated with some latency in the time from sending of a signal from the source to the destination of the signal recieiving the signal.
  • latency may be between 4-10 ms or less. Latency may introduce restrictions on gain used in the control loop. Simulations have shown that it may be desired or required to reduce gain when taking into account effects of the latency in the control loop. To this end, a parametric analysis of the gain, including the effect of latency, may be performed.
  • a P-type control loop the transfer function of which is defined by the equation above, there might be a risk that a residual imbalance between the inverting converters occur.
  • a risk may be reduced or even eliminated by introducing a integral term in the above equation, i.e. by using a Pl-type of control loop instead of a P-type control loop.
  • Such an integral term may be introduced for only one of the inverting converters, or for both inverting converters.
  • such an integral term is introduced for the inverting converter or converters configured to control the DC voltage over the DC link, but possibly not for an inverting converter not configured to control the DC voltage over the DC link.
  • a Pl-type of control loop for adjustment of the firing angle is employed for two inverting converters
  • a P-type of control loop for adjustment of the firing angle is employed for one inverting converter.
  • the inverting converter static UDC-IDC characteristic includes two basic segments: a vertical line representing the condition of the inverting converter controlling the DC current and a horizontal line representing the operation of the inverting converter with constant commutation margin.
  • UDC-IDC ⁇ -cos a - (c/ X N-c/ r N)- (UjiON / /DCN DC, where: is the no-load direct voltage
  • L/diON is the no-load direct voltage at nominal converter transformer tap position and nominal AC voltage
  • a is the extinction angle for the inverting converter or converter valves of the inverting converter
  • c/ ⁇ is the relative inductive voltage drop at rated direct current and at rated no-load direct voltage
  • c/rN is the resistive voltage drop at rated operation
  • /DCN is the rated current
  • /DC is the direct current
  • a rectifying converter can be described with a UDC-IDC characteristic similar to that above for an inverting converter.
  • the operation of the inverting converter with constant commutation margin may in reality not be represented by a horizontal line but by a line having a negative slope, with the converter transformer reactance influencing the slope, assuming the inverting converter is connected to a 'stiff' AC system or line, otherwise the network impedance also influences the slope.
  • Such negative slope characteristics may decrease stability in the operation of the inverting converter.
  • the static characteristic of the inverting converter may be changed by introducing a positive slope, which can be achieved by adding an appropriate contribution or offset to the inverting converter firing angle proportional to (/response - /order), similarly to what has been described in the foregoing with respect to the transfer function.
  • the current balance control described in the foregoing can alternatively be interpreted as introducing an additional a-segment with positive slope in the inverting converter static characteristic.
  • This additional a-segment is affected not only by the current error from the Own' inverting converter but also from the inverting converter arranged in parallel with the Own' inverting converter.
  • This positive slope segment may have a stabilization effect in balancing of current flows between the inverting converters.
  • FIG. 3 there is shown a schematic view of a part of a power transmission system 100, to be specific a part of a DC link or line in a power transmission system 100, according to an embodiment of the present invention.
  • the embodiment depicted in Fig. 3 is similar to the embodiment depicted in Fig. 2, with an exception in that the power transmission system 100 in Fig. 3 comprises converter transformer tap changer control units 1 12a, 1 12b, as illustrated in Fig. 3.
  • the converter transformer tap changer control units 1 12a, 1 12b are configured to control a tap changer mechanism in the transformers 106a, 106b of the inverting converters 101 a, 101 b, respectively.
  • the tap changer mechanism can change the position of the transformer tap or tapping connection, which is a connection point along a transformer winding that allows a certain number of turns to be selected, thereby enabling voltage regulation of the outputs of the respective transformers 106a, 106b.
  • the tap changer mechanism may for example comprise on-load tap changers that can be used for changing the position of the tapping connection of energized transformer windings.
  • the converter transformer tap changer control units 1 12a, 1 12b are configured to control the tap changer mechanisms in the transformers 106a, 106b of the inverting converters 101 a, 101 b, respectively, in order to regulate the extinction angle of one or both inverting converters 101 a, 101 b so as to keep the extinction angle or angles within a selected angle interval, e.g. ⁇ 1 °, about an extinction angle reference value that for example may be received from the controller 108. By allowing a variation of the extinction angle within the selected angle interval, no or less 'hunting' of the tap changer mechanism may occur.
  • the regulation of the extinction angle of one or both inverting converters 101 a, 101 b may be performed over a time period so as to maintain the extinction angle or angles within the selected angle interval during that time period.
  • the tap changer mechanisms in the transformers 106a, 106b of the inverting converters 101 a, 101 b, respectively, may be manually controlled by an operator.
  • the extinction angle of the respective inverting converters 101 a, 101 b may be determined or measured at the inverting converters 101 a, 101 b, respectively. On a condition that there is a difference between the extinction angle of the respective inverting converters 101 a, 101 b and the extinction angle reference value, the extinction angles of the respective inverting converters 101 a, 101 b may be adjusted so as decrease the difference between the extinction angles of the respective inverting converters 101 a, 101 b and the extinction angle reference value.
  • the adjustment is achieved by means of the converter transformer tap changer control units 1 12a, 1 12b controlling the tap changer mechanisms in the transformers 106a, 106b of the inverting converters 101 a, 101 b, respectively, so as to adjust the tap positions of the transformers 106, 106b of the respective inverting converters 101 a, 101 b.
  • a no-load control function which for example may be implemented in the converter transformer tap changer control units 1 12a, 1 12b, may control the tap changer mechanism of the inverting converter transformers 106a, 106b when the inverting converters 101 a, 1 10b are in a blocked state so as to establish the no-load DC voltage level corresponding to the steady state requirement at a minimum current level.
  • no immediate stepping would be required by the tap changer mechanism.
  • a limitation function which for example may be implemented in the converter transformer tap changer control units 1 12a, 1 12b, may monitor, e.g. repeatedly measure, the voltage in the inverting converters 101 a, 101 b, and override the tap changer mechanisms in the transformers 106a, 106b of the inverting converters 101 a, 101 b, respectively, in case a no-load DC voltage level is detected that exceeds a predefined threshold value.
  • the threshold value may for example be received from the controller 108.
  • limitation function may regulate or step down the voltage and/or inhibit or reduce the tap changer mechanism operability or functionality in case a no- load DC voltage level is detected that exceeds the predefined threshold value.
  • the limitation function may protect the valves of the inverting converters 101 a, 101 b from excessive voltage stress.
  • At least one of the inverting converters 101 a, 101 b may be configured to control the DC voltage over the DC link.
  • the inverting converter 101 a may be configured to control the DC voltage over the DC link, whereas the inverting converter 101 b is not controlling DC voltage over the DC link.
  • the DC voltage control may for example be implemented in the converter transformer tap changer control unit 1 12a. The DC voltage over the the inverting converter 101 a is determined or measured at the inverting converter 101 a.
  • the DC voltage over the inverting converter 101 a may be adjusted so as decrease the difference between the DC voltage over the inverting converter 101 a and the DC voltage reference value.
  • the adjustment of the DC voltage over the inverting converter 101 a may for example be effected by means of adjusting the tap positions of the transformer 106a of the inverting converter 101 a, possibly controlled by the converter transformer tap changer control unit 1 12a.
  • the above- mentioned DC voltage control may be conditional on that the difference between the extinction angle of the respective inverting converters 101 a, 101 b and the extinction angle reference value is below a predefined extinction angle difference reference value.
  • the above-mentioned DC voltage control may only be carried out if a selected criteria for the extinction angles of the inverting converters 101 a, 101 b is fulfilled. For example, only if it is established that the inverting converters 101 a, 101 b are operating at extinction angles sufficiently close to the extinction angle reference value, control of the DC voltage of the DC link by one or both of the inverting converters 101 a, 101 b may be initiated or activated.
  • the regulation or control of the extinction angle may be performed for both of the inverting converters 101 a, 101 b while the above-mentioned DC voltage control is performed only for the inverting converter 101 a which is configured to control the DC voltage over the DC link.
  • the converter transformer tap changer control unit 1 12a is configured to control the tap changer mechanism in the transformer 106a of the inverting converter 101 a in order to regulate the DC voltage over the inverting converter 101 a so as to keep the DC voltage over the inverting converter 101 a within a selected DC voltage interval about the DC voltage reference value .
  • the regulation of the DC voltage over the inverting converter 101 a may be performed over a time period so as to maintain the DC voltage over the inverting converter 101 a within the selected DC voltage interval during that time period.
  • the rectifying converters 102a, 102b are controlling the currents therethrough, i.e. each of the rectifying converters 102a, 102b is controlling the current through it.
  • the firing angles of the rectifying converters 102a, 102b, or the converter valves of the rectifiying converters 102a, 102b can be controlled so as to keep the firing angles of the rectifying converters 102a, 102b close to a firing angle reference value, e.g. within a selected angle interval, e.g. ⁇ 1 °, about the firing angle reference value.
  • the firing angle reference value for the rectifying converters 102a, 102b may for example be received from the controller 108.
  • a schematic flowchart of a method 400 is carried out in a power transmission system comprising a first AC power line and a second AC power line, and at least two inverting converters connected in parallel in a DC link between the first AC power line and the second AC power line.
  • the first AC power line is connected to the DC link at a first end thereof and the second AC power line is connected to the DC link at a second end thereof.
  • Each of the at least two inverting converters is adapted to convert DC power to AC power.
  • the output from the at least two inverting converters is outcoupled from the DC link at one of the first and second ends thereof.
  • the power transmission system may comprise a controller for controlling operation of the DC link.
  • the method 400 comprises receiving or retrieving a current reference value for the desired current through the respective inverting converters, 401 , e.g. from the controller.
  • a current through the inverting converter is measured and a first difference value between the measured current and the current reference value is determined, 402.
  • a second difference value between the first difference value determined for the inverting converter and the first difference value determined for the other inverting converter is determined, 403.
  • a firing angle offset value is determined based on the second difference value determined for the inverting converter, 404.
  • a firing angle of each inverting converter is adjusted based on the firing angle offset values determined for the respective inverting converters, 405.
  • step 406 there is determined whether a selected requirement is met or a selected criteria for the difference between the currents through the inverting converters is complied with.
  • the selected requirement may for example be expiry of a timer or reaching a certain number of successive executions of the method steps.
  • the selected criteria for the difference between the currents through the inverting converters may for example be the difference between the currents through the inverting converters falling below a predefined current difference threshold value.
  • the method 400 returns to step 402, or alternatively to step 401 as indicated by the dashed line. In case the selected requirement is met and/or the selected criteria for the difference between the currents through the inverting converters is complied with, the method 400 ends.
  • the power transmission system comprises a DC link and and at least two inverting converters connected in parallel in the DC link.
  • Current reference value or values for the desired current through the respective inverting converters are received or retrieved, e.g. from a controller in the power transmission system.
  • a current through the inverting converter is measured and a first difference value between the measured current and the current reference value is determined.
  • a second difference value between the first difference value determined for the inverting converter and the first difference value determined for the other inverting converter is determined.
  • a firing angle offset value is determined based on the second difference value determined for the inverting converter.
  • a firing angle of each inverting converter is adjusted based on the firing angle offset values determined for the respective inverting converters.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

La présente invention porte sur un procédé de commande d'un système de transmission de puissance (100). Le système de transmission de puissance (100) comprend une liaison à courant continu (CC) et au moins deux convertisseurs inverseurs (101a, 101b) connectés en parallèle dans la liaison CC. Une ou des valeurs de référence de courant pour le courant souhaité à travers les convertisseurs inverseurs respectifs sont reçues ou extraites, par exemple depuis un contrôleur (108) dans le système de transmission de puissance. Pour chacun des convertisseurs inverseurs, un courant (IDC1, IDC2) à travers le convertisseur inverseur est mesuré et une première valeur de différence entre le courant mesuré et la valeur de référence de courant est déterminée. Pour chacun des convertisseurs inverseurs, une seconde valeur de différence entre la première valeur de différence déterminée pour le convertisseur inverseur et la première valeur de différence déterminée pour l'autre convertisseur inverseur est déterminée. Pour chacun des convertisseurs inverseurs, une valeur de décalage d'angle de tir est déterminée sur la base de la seconde valeur de différence déterminée pour le convertisseur inverseur. Un angle de tir de chaque convertisseur inverseur est ajusté sur la base des valeurs de décalage d'angle de tir déterminées pour les convertisseurs inverseurs respectifs. Par ajustement de l'angle de tir d'un convertisseur inverseur, un ajustement du courant à travers le convertisseur inverseur peut être atteint.
PCT/EP2012/068339 2012-09-18 2012-09-18 Procédé de commande d'un système de transmission de puissance et système de commande correspondant WO2014044293A1 (fr)

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PCT/EP2012/068339 WO2014044293A1 (fr) 2012-09-18 2012-09-18 Procédé de commande d'un système de transmission de puissance et système de commande correspondant

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Application Number Priority Date Filing Date Title
PCT/EP2012/068339 WO2014044293A1 (fr) 2012-09-18 2012-09-18 Procédé de commande d'un système de transmission de puissance et système de commande correspondant

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104242331A (zh) * 2014-08-14 2014-12-24 国家电网公司 一种适用于机电暂态仿真的特高压直流控制系统
WO2019068311A1 (fr) 2017-10-03 2019-04-11 Abb Schweiz Ag Coordination de commandes de stabilisation de courant par une commande de commutateur à prises de réglage

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5627734A (en) * 1993-03-16 1997-05-06 Siemens Aktiengesellschaft Method and control arrangement for DC transmission, and a control device
WO2008036009A1 (fr) * 2006-09-18 2008-03-27 Abb Technology Ltd. Convertisseur ccht
WO2008110211A1 (fr) * 2007-03-15 2008-09-18 Abb Technology Ag Procédé et agencement permettant d'inverser le débit de puissance d'un système de transmission de puissance en courant continu

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5627734A (en) * 1993-03-16 1997-05-06 Siemens Aktiengesellschaft Method and control arrangement for DC transmission, and a control device
WO2008036009A1 (fr) * 2006-09-18 2008-03-27 Abb Technology Ltd. Convertisseur ccht
WO2008110211A1 (fr) * 2007-03-15 2008-09-18 Abb Technology Ag Procédé et agencement permettant d'inverser le débit de puissance d'un système de transmission de puissance en courant continu

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104242331A (zh) * 2014-08-14 2014-12-24 国家电网公司 一种适用于机电暂态仿真的特高压直流控制系统
CN104242331B (zh) * 2014-08-14 2016-08-31 国家电网公司 一种适用于机电暂态仿真的特高压直流控制系统
WO2019068311A1 (fr) 2017-10-03 2019-04-11 Abb Schweiz Ag Coordination de commandes de stabilisation de courant par une commande de commutateur à prises de réglage
GB2581079A (en) * 2017-10-03 2020-08-05 Abb Power Grids Switzerland Ag Coordinating current stabilizing control with tap changer control
GB2581079B (en) * 2017-10-03 2022-05-04 Abb Power Grids Switzerland Ag Coordinating current stabilizing control with tap changer control

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