Classifications

• • 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
  • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
  • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
  • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/483—Converters with outputs that each can have more than two voltages levels
  • H02M7/49—Combination of the output voltage waveforms of a plurality of converters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
  • B60L15/007—Physical arrangements or structures of drive train converters specially adapted for the propulsion motors of electric vehicles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
  • B60L15/02—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles characterised by the form of the current used in the control circuit
  • B60L15/06—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles characterised by the form of the current used in the control circuit using substantially sinusoidal ac
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L50/00—Electric propulsion with power supplied within the vehicle
  • B60L50/50—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells
  • B60L50/60—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells using power supplied by batteries
  • B60L50/64—Constructional details of batteries specially adapted for electric vehicles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
  • B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
  • B60L58/18—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries of two or more battery modules
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
  • B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
  • B60L58/18—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries of two or more battery modules
  • B60L58/21—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries of two or more battery modules having the same nominal voltage
• • 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
  • H02M1/00—Details of apparatus for conversion
  • H02M1/0095—Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
• • 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
  • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
  • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
  • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/483—Converters with outputs that each can have more than two voltages levels
  • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L2200/00—Type of vehicles
  • B60L2200/26—Rail vehicles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L2210/00—Converter types
  • B60L2210/40—DC to AC converters
  • B60L2210/42—Voltage source inverters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L2240/00—Control parameters of input or output; Target parameters
  • B60L2240/40—Drive Train control parameters
  • B60L2240/52—Drive Train control parameters related to converters
  • B60L2240/527—Voltage
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L2240/00—Control parameters of input or output; Target parameters
  • B60L2240/40—Drive Train control parameters
  • B60L2240/52—Drive Train control parameters related to converters
  • B60L2240/529—Current
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
  • B60L2240/00—Control parameters of input or output; Target parameters
  • B60L2240/80—Time limits
• • 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
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/64—Electric machine technologies in electromobility
• • 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
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/70—Energy storage systems for electromobility, e.g. batteries
• • 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
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/72—Electric energy management in electromobility

Definitions

• the present invention relates to a converter apparatus for converting direct voltage into alternating voltage and conversely, which comprises a first VSC-converter in cascade connection with at least one second VSC-converter, each VSC-converter of the apparatus comprising on one hand a direct voltage intermediate link, having a positive and a negative pole and one or more members for capacitive energy storage, and on the other current valves having controllable semiconductor devices, in which the apparatus comprises a unit adapted to control the semiconductor devices to generate voltages between the connection points of the respective VSC-converter mutually , separated in steps with a size of the direct voltage between the positive and the negative pole of the direct voltage intermediate link of the converter, and in which the unit is adapted to control said semiconductor devices and thereby the converter apparatus to generate a phase voltage constituted by the sum of said voltages generated in said first and said second VSC- converters, as well as a method for the control of such an apparatus.
• Such converter apparatuses may be used in all kinds of situations where direct voltage is to be converted into alternating voltage and conversely, in which examples of such uses are in stations of HVDC-plants (High Voltage Direct Current), in which direct voltage is normally converted into a three phase alternating voltage or conversely, or in so called back-to-back-stations where an alternating voltage is firstly converted into direct voltage and this is then converted into alternating voltage, as well as in SVC's (Static Var Compensator), where the direct voltage side consists of one or more capacitors hanging freely.
• HVDC-plants High Voltage Direct Current
• SVC's Static Var Compensator
• the invention is not restricted to any levels of the voltage of the alternating voltage side of the apparatus, the powers that the converter apparatus may transmit or the number of phases of the alternating voltage side of the apparatus, and it may ac- . cordingly very well be designed to generate a one-phase alternating voltage, for example for feeding of railway vehicles.
• the invention is particularly, but not exclusively, di- rected to intermediate and high voltages, i.e. where the peak voltage of the alternating voltage side of the apparatus is 10 kV or higher.
• the apparatus permits obtaining of comparatively many different levels on the alternating voltage side thereof, which in its turn means that comparatively fine curve shapes of the alternating voltage out from the apparatus may be obtained without any necessity to switch the controllable semiconductor devices included in the converters with - particularly high frequencies for that sake.
• it gets possible to obtain a certain quality of the alternating voltage out from the apparatus by a lower switching frequency of the controllable semiconductor devices at a pulse width modulation pattern for controlling these than if for example a two level converter would be used.
• this means lower losses in the converter apparatus.
• the same switching frequency as for a two level converter used the curve shape of the alternating voltage may be made considerably better.
• Each phase 1 , 2, 3 has n one-phase converters 4, 5, 6 in cascade connection having each two branches 9, 10 of two current valves 1 1 -14 connected in series connected in parallel between two direct voltage poles 7, 8 belonging to the respective con- verter, said current valves comprising a controllable (of turn-off type) semiconductor device 15 and a rectifying member 16 connected in anti-parallel therewith, such as a rectifying diode, with a midpoint of one branch 10 of a converter connected with the midpoint of a branch 17 of a subsequent converter 5 in the cas- - cade connection.
• a controllable (of turn-off type) semiconductor device 15 and a rectifying member 16 connected in anti-parallel therewith, such as a rectifying diode, with a midpoint of one branch 10 of a converter connected with the midpoint of a branch 17 of a subsequent converter 5 in the cas- - cade connection.
• the cascade connection of the one-phase converters is at one end at a phase reactor 19 connected to the alternating voltage phase 1 , while the cascade connection is at the other end connected to a point 20 in a Y-connection in common with the other phases.
• the direct voltage poles of the re- spective VSC-converter receive voltage through a direct voltage source illustrated in the form of a capacitor 21 -23. "The direct voltage pole" in the claims is defining that there is some type of direct voltage source connected to or included in the converter, which is expressed by "one or more members for capacitive en- ergy storage".
• the different direct voltage sources 21 -23 deliver the same voltage to the respective VSC-converter, and it is in this way possible to obtain 2n+1 different levels of the voltage of the respec- " tive cascade connection on the alternating voltage side.
• different levels of the voltage may be obtained, namely - 3U, -2U, -U, 0, +U, +2U, and +3U, if U is the voltage level between said direct voltage poles of the respective VSC-converter.
• So many levels means a "fine" curve shape of the alternating voltage without using a high switching frequency of the controllable semiconductor devices 15.
• One controllable semiconductor device and a diode are for the rest shown for each current valve in the figure, but these are intended to be symbols for a possibly larger amount of such members connected in series and adapted to function as one single, i.e. the controllable semiconductor devices connected in series in such a current valve are intended to be controlled simultaneously for functioning as one single such device.
• the object of the present invention is to provide a converter ap- paratus of the type defined in the introduction, which is able to fulfil the desires just mentioned in a not negligible degree.
• the current valves of the first VSC-converter have a plurality of semiconductor devices connected in series.
• the first VSC-converter has a substantially higher direct voltage between the two poles thereof it is in many applications, especially when using the apparatus in stations in a transmission system, desired and also necessary that each current valve has a plurality of semiconductor devices connected in series, so that these are together able to hold the voltage to be held by the valve when it is blocked.
• the second VSC- converter or -converters have only one, or fewer, semiconductor devices connected in series in the current valves thereof than the first VSC-converter.
• VSC-converters may be designed in different ways with respect to the number of semicon- ductor devices, and possibly also with respect to the properties of each individual semiconductor device, so that the existing substantially different level of the direct voltage between the poles of the converters may be utilized to an optimum.
• the apparatus has a plurality of said second VSC-converters in cascade connection and all the VSC-converters of the cascade connection have mutually different voltages between the positive and negative pole thereof.
• the number of possible levels of the voltage out on the alternating voltage side of the converter apparatus for a certain number of VSC-converters of said cascade connection may in this way be increased remarkably with respect to such converters already known with the advantages mentioned above as a result.
• a stepwise change of the direct voltage level of the respective VSC-converter and possibilities to obtain many different levels of the total voltage out on the alternating voltage side of the converter apparatus by adding these in an appropriate way are hereby obtained.
• These levels extend from -7/4U 0 to +7/4U 0 in steps of %U 0 .
• the first VSC-converter is adapted to handle a substantially higher apparent power than said second VSC-converters.
• the first VSC-converter may be controlled in a different way than the second VSC-converter for obtaining an amount of different objects, which among others appear from the further preferred embodiments of the invention discussed below.
• the switching frequency of the first VSC-converter with high apparent power may for exam- pie be reduced for obtaining lower switching losses and thereby a higher efficiency of the converter, while the second VSC-converter with a substantially lower apparent power may be switched with a higher frequency for obtaining a desired curve shape of the alternating voltage on the alternating voltage side of the apparatus.
• the relationship between the apparent power han- died by the respective second VSC-converter/the apparent power handled by the first VSC-converter is 0.10-1.0, in which said relationship is preferably 0.30-1.0 when the apparatus is designed for SVC-operation and 0.10-0.30 when the apparatus is designed for transmitting active power between the direct volt- age side and the alternating voltage side thereof.
• SVC-operation i.e.
• the relationship when transferring reactive power, it may be advantageous that the relationship is high, since the higher this relationship the more contribution will be given by the second VSC-converter to the total apparent power of the apparatus, and the lower switching frequency may be used for the first VSC- converter with high apparent power.
• the second VSC-converter when active power passes the converter apparatus the second VSC-converter may usually not be used for increasing the total apparent power of the plant, but it is then mainly used for compensating away different disturbing harmonics generated by the first VSC- converter, in which it is then advantageous to let the apparent power of the second VCS-converter be considerably lower.
• the apparatus has a first VSC-converter in the form of a three phase converter having three phase legs with controllable semiconductor devices between the two direct voltage poles thereof, one phase output of each phase leg is on the alternating voltage side thereof connected to a phase line, the apparatus has three said cascade connections with said first VSC-converter in com- mon for the cascade connections, a second VSC-converter of each cascade connection is at one end opposite to the alternating voltage side thereof connected to said phase output of a phase leg of the first VSC-converter each, and the second VSC- converters are formed by H-bridges with two branches of con- trollable semiconductor devices, a first one of which is connected to a phase leg of the first VSC-converter and a second one of which is connected to the alternating voltage side of the apparatus.
• each second VSC-converter is through the direct voltage side thereof connected to the phase leg of the first VSC-converter through a potential of the direct voltage intermediate link of the converter located substantially in the middle of the potential of the two direct voltage poles of this converter and connected to the alter- nating voltage side of the apparatus through a branch of controllable semiconductor devices, the total switching losses of the converter apparatus are certainly slightly increased, since the second VSC-converter may only provide two different levels, so that in the case of one second VSC-converter per cascade con- nection the number of different voltage levels will be four, but the advantage that the number of current valves of the converter apparatus to be controlled will be lower is instead obtained, so that costs for the components included therein may be saved.
• the apparatus has a first VSC-converter in the form of a three phase converter having three phase legs with controllable semiconductor devices between the two direct voltage poles thereof, one phase output of each phase leg is on the alternating voltage side thereof connected to a phase line, in which this is obtained through the fact that each phase leg is connected to a secondary winding of its own of a transformer, the second end of the secondary winding is connected to a phase leg of a second VSC-converter in the form of a three phase converter, and the transformer has three primary windings, each one connected to a said phase line each of the alternating voltage side of the apparatus.
• An advantage of this embodiment is that only two direct voltage intermediate links are required, one for the first VSC- converter and one for the second VSC-converter, in spite of the fact that we are here talking about three phases, which simplifies the control of the converter apparatus. Furthermore, the fact that the direct voltage intermediate link capacitors for both converters are in common for the three phases means that the size of the direct voltage intermediate link capacitors may be chosen comparatively small, which reduces the costs for the converter apparatus.
• the direct voltage side of the first VSC-converter is con- nected to a network for transmitting active power between the direct voltage side and the alternating voltage side of the apparatus, in which the direct voltage side of the first VSC-converter is preferably connected to a HVDC-transmission plant. It is in such a case particularly advantageous if a second three phase- VSC-converter is connected to the direct voltage side of the second VSC-converter with the midpoints of the phase legs thereof connected to a phase line each of an alternating voltage network for feeding power in towards and out from said second VSC-converter, respectively.
• the second VSC-converter which has a substantially lower voltage between the direct voltage poles thereof than the first VSC-converter may hereby handle active as well as reactive power, since said further second three phase-VSC-converter with the alternating voltage network connection thereof means that the capacitors of the direct voltage intermediate link of the second VSC-converter may be kept charged on a desired level and not be discharged or charged too much for transmitting active power through the second VSC- converter. Accordingly, for a given level of the direct voltage on the direct voltage network the voltage on the alternating voltage side of the apparatus may be regulated upwardly or downwardly by controlling feeding of power in towards and out from, respectively, the second VSC-converter through said alternating voltage network if desired.
• the converter having a low apparent power may then be used on one hand for reducing harmonics generated by the converter with a high apparent power and on the other for gen- erating a fundamental tone.
• the converter having a high apparent power may in this way use a pulse width modulation method with a very low switching frequency and with a fixed relationship between the alternating voltage and the direct voltage, while the converter having a low apparent power may be used for compensating harmonics, but also for reactive power compensation and/or for rapidly adjusting the total fundamental voltage of said converter apparatus on said alternating voltage side.
• each phase leg of the first VSC-converter is connected to one phase line of the alternating voltage side of the apparatus of its own, and the apparatus has at least two second VSC-converters with each a connection to a direct voltage pole each of the first VSC-converter and a second connection to a pole conductor of a direct voltage network.
• This way to connect the VSC-converters to each other is particularly suitable in the case of HVDC, where the first VSC-converter on the direct voltage side is connected to an alternating voltage transmission network through reactors and filters without any intermediate transformer.
• the apparatus has at least one dc/dc-converter having a high frequency transformer connected through one side thereof to said second VSC-converter and with the other side thereof to an arrangement for feeding power in towards and out from, respec- tiveiy, said second VSC-converter.
• This arrangement enables broadened possibilities of use of the second VSC-converter, both for contribution to reactive power compensation and transmission of active power in a similar way as for the embodiment discussed above with a further three phase-VSC-converter con- nected to an alternating voltage network.
• the unit is adapted to control the semiconductor devices of said VSC-converter according to a pulse width modulation pattern with a frequency being the lower the higher the direct voltage between the direct voltage poles of the VSC-converter in ques- tion.
• VSC-converters of the same apparatus are intended here and that in this those with a higher voltage between the direct voltage poles thereof are controlled with a lower frequency than those having a lower corresponding voltage.
• this may very well be controlled with a lower frequency than a converter with 20 kV between the poles of another apparatus.
• said unit is adapted to control the first VSC-converter with a determined fundamental frequency and the second VSC-converters with a frequency being substantially higher, preferably a multiple of the fundamental frequency. This keeps the total switching losses of the converter apparatus on a very low level.
• the unit is for obtaining said phase voltage adapted to keep the first VSC-converter in fixed switching positions during periods of time being as long as possible and during these periods of time control the semiconductor devices of the second VSC-converters to alternatively add different voltages to the voltage from the first - VSC-converter according to a pulse width modulation pattern. It is then particularly advantageous if the unit is adapted to control the VSC-converters according to a voltage set value for said phase voltage with the shape of a sine curve having a third tone component or a multiple of third tone components with respect to a fundamental tone of the sine curve added thereto for pro- longing said time the first VSC-converter may be present in a fixed position and does not have to be switched.
• Such an addi- tion of a third tone component, or an optional multiple of third tone components, does not influence the voltage between the phases, which accordingly will get a desired shape, which is known per se, but the number of switchings of the VSC-converter with high apparent power may be reduced further and the losses thereby be decreased.
• the increase of the efficiency means often in the practice that the apparent power of the converter apparatus may be raised thanks to a lower thermal load on the components included therein.
• said unit is adapted to control the second VSC-converters to add the voltage to the voltage from the first VSC-converter for compensating away low frequency voltage harmonics generated as a consequence of the fact that the first VSC-converter is adapted to be located in a fixed position during great parts of the period of time of the fundamental tone voltage on the alternating voltage side of the apparatus.
• the apparatus is designed for SVC-operation, i.e. for a reactive power compensation, and the unit is adapted to control the semiconductor devices of the other VSC-converters to generate voltage pulses having a fundamental tone being displaced with respect to the current through the converter by 90 electric degrees and to control the first VSC-converter with the same relationship between the voltage fundamental tone and the current through the converter for adding the contribution of the first and the second VSC-converters to a reactive power compensation.
• Advantages of utilizing the second VSC-converters in this way appear from the discussion above.
• the apparatus is designed for transmitting active power between the direct voltage side and the alternating voltage side thereof, and said unit is adapted to control the semiconductor devices of the second VSC-converters for compensating away harmonics generated as a consequence of the operation of the first VSC-converter without giving any contribution to the transmission of active power.
• said unit is adapted to only control semiconductor devices of two of the phase legs of the first VSC-converter at a time during parts of the period of the voltage fundamental tone of the converter and at the same time have the connection on the alternating voltage side of the third phase leg connected to one of the poles of the direct voltage intermediate link of the first VSC-converter and alternate between the three phase legs with respect to said connection to one of the poles at the transition between said pe- riod parts for applying a so called dead band-PWM on said VSC- converter, and the unit is adapted to at the same time control the VSC-converters according to a voltage set value for said phase voltage with the shape of a sine curve having a zero sequence component or zero sequence components, for example a third tone component or a multiple of third tone components, added thereto.
• the advantage of such a dead band-PWM is primarily that the switching frequency of the first VSC-converter, ' which preferably is adapted to handle a high apparent power, then may be reduced to 2/3, since the phases only have to switch during 2/3 of the period of the fundamental tone.
• the disadvantage is that zero sequence components of third tone character or multiples of third tones have to be added to a voltage set value of all the phases, which does not influence the phase- phase-voltage but well the voltage between the phase and ground.
• the invention also relates to a method for control of a converter apparatus as above, in which the semiconductor devices of said VSC-converter are controlled according to a pulse width modu- lation pattern having a frequency being the lower the higher the direct voltage between the direct voltage poles of the VSC-converter in question is.
• the invention also relates to a computer program product as well as a computer readable medium according to the corre- sponding appended claims. It is easy to understand that the method according to the invention defined in the appended set of method claims is well suited to be carried out through program instructions from a processor influenceable by a computer ' program provided the program steps in question.
• Fig 1 is a simplified circuit diagram of a converter apparatus according to a preferred embodiment of the invention.
• Fig 2 is a view corresponding to Fig 1 of a converter apparatus according to a second preferred embodiment of the invention
• Figs 3 and 4 illustrate a sinusoidal voltage set value and a voltage set value in the form of a sine curve having a third tone component added thereto for the voltage between the respective phase line and the first direct voltage intermediate link midpoint of the first VSC-converter in the converter apparatus according to Fig 2, which is utilized for pulse width modulation of the converter apparatus
• Fig 5 illustrates schematically what a pulse width modulation pattern starting from a voltage set value according to Fig 3 may look like for a converter apparatus according to Fig 2,
• Fig 6 is a view corresponding to Fig 2 of a converter apparatus according to a third preferred embodiment of the invention.
• Fig 7 a converter apparatus according to a fourth preferred embodiment of the invention, which constitutes a variation of the converter apparatus according to Fig 2,
• Fig 8 is a view corresponding to Fig 2 of a converter apparatus according to a fifth preferred embodiment of the invention.
• Fig 9 is a view corresponding to Fig 8 of a converter apparatus being a variation of the one shown in Fig 8,
• Fig 10 is a view corresponding to Fig 8 of a converter apparatus according to a further variation of the converter apparatus according to Fig 8,
• Fig 1 1 is a view corresponding to Fig 2 of a converter apparatus according to an eighth preferred embodiment of the invention
• Fig 12 is finally a view corresponding to Fig 2 of a converter apparatus according to a ninth preferred embodiment of the invention.
• a converter apparatus having a general construction being known per se and described above is illustrated in Fig 1 and has three cascade connections, one for each phase of the alternating voltage network, interconnected according to a Y-connection in the common point 20.
• each cascade connection has only three one phase converters.
• the converter 4 may then between the connections 24 and 25 thereof deliver the voltage -U 0 /4, 0 or +U 0 /4 depending upon the state of the current valves 1 1 -14.
• the corresponding fact is valid for the one-phase- converter 5, which may deliver 0, 1 /2U 0 or -1 /2U 0 between the connection 24 and the connection 26 to the one-phase- converters 6 following thereupon.
• the levels 0,U 0 and -U 0 are in their turn valid.
• semiconductor devices of turn-off type in the one-phase-converter 6 with the highest voltage between the two direct voltage poles thereof is preferably such ones that may handle high powers used, but they are preferably operated at low frequencies, in which high frequency components are used as semiconductor devices of turn-off type in the one-phase-con- verter 4 with the lowest voltage between the direct voltage poles thereof and the frequency for the control of the semiconductor devices of the one-phase converters is increased in the direction from the one-phase-converter 6 to the one-phase-converter 4 for obtaining a desired pulse width modulation pattern (PWM) on the connection 25 to the reactor 19 of the alternating voltage side.
• PWM pulse width modulation pattern
• IGBT's Insulated Gate Bipolar Transistor
• GTO's Gate Turn-Off thyristor
• the unit 27 for controlling the respective one-phase-converter, i.e. the power semiconductor devices 15 thereof, is designed to achieve this.
• a converter apparatus is shown in Fig 2, in which the first VSC- converter 6 here is present in the form of a three-phase-converter with three phase legs 28-30 with controllable semiconductor devices between the two direct voltage poles thereof (see furthest to the right in the Figure).
• a phase output of each phase leg is on the alternating voltage side thereof connected to a phase line 1 -3.
• This is achieved through a second VSC-converter 5, 5', 5" for each phase line, in which the second VSC- converter is formed by a H-bridge having two branches 31 , 32 of controllable semiconductor devices, one of which is connected to a phase leg of the first VSC-converter and the second of which to the alternating voltage side of the apparatus.
• the voltage between the direct voltage poles 7, 8 of the first VSC-converter is U
• the voltage of the direct voltage intermediate link 33 of the second VSC-converters is k x U, in which k is substantially lower than 1 , preferably 0.05-0.5.
• the VSC-converters connected in series 5, 5', 5" are controlled according to a pulse width modulation pattern, in which they generate an alternating voltage between the input and the output thereof.
• the voltage between the input and the output may assume three discrete levels, namely k x U, 0 or -k x U.
• the first VSC-converter has in this embodiment three connection points 35-37 on the alternating voltage side thereof, while the second VSC-converter has two connection points 38, 39 for each phase.
• the second VSC-converter connected in series in each phase may be controlled for generating a fundamental voltage being 90 - electrical degrees phase shifted with respect to the fundamental tone of the phase current, exactly as for the first VSC-converter.
• the converter with low apparent power may in this way be controlled to give a contribution to the total reactive power of the converter apparatus.
• the second VSC-converter connected in series in each phase may be controlled to compensate away low frequency voltage harmonics generated as a consequence of the fact that the first VSC-converter does not switch during great parts of the period of the fundamental volt- age.
• the harmonics in question are primarily the fifth and seventh harmonics, the eleventh and thirteenth harmonics, but also higher harmonics or tones.
• the factor k may be chosen freely, preferably within the interval 0.15-0.5. If k for example is chosen to be 1 /3 the six voltage levels will be uniformly distributed, which may be particularly advantageous. The higher number chosen the greater contribution is given by the second VSC-converters connected in series to the total apparent power of the converter apparatus, and the lower switching frequency may be used for the first VSC-converter with a high apparent power.
• a sine curve 40 as a voltage set value for the phase voltage of the converter apparatus according to Fig 2 intended to form the basis for the pulse width modulation of the VSC-converters included therein is illustrated in Fig 3.
• the voltage levels U and -U which may be obtained between the midpoint 34 and the connection point 35-37 of the respective phase leg on the alternating voltage side are shown, as well as the possible additions that may be made through controlling the second VSC- converters around the respective level, so that 41 corresponds to (1 /2+k)U, 42 to (1 /2-k)U , 43 to (-1 /2+k)U and 44 to (-1 /2-k)U.
• the second VSC-converter having low apparent power connected in series in each phase switches.
• the phase output 35-37 thereof may during this period of time be connected to the positive pole 7.
• the phase output for the first VSC-converter is in corresponding way connected to the negative pole and the pulse width modulation switching is car- ried out for the second VSC-converter with low apparent power connected in series in the phase. Only during the rest of the time, see the arrow 45, it is necessary to switch the first VSC- converter with high apparent power.
• the switching frequency of the second VSC-converter is typically in the region of 1-3 kHz.
• a third tone component which is here about 20 % of the fundamental tone, has been added to the voltage set value in all phases.
• Such an addition of a third tone component or an optional multiple of third tone components does not influence the voltage between the phases.
• the voltage set value of the phase-phase-voltage is still sinusoidal.
• This pulse width modulation method may advantageously be combined with the use of a second VSC-converter with low apparent power connected in series in each phase.
• the second VSC-converters connected in series in each phase may then not in the same way be used for increasing the total apparent power of the plant.
• These convert- ers may namely not contribute to the active power of the converter apparatus, since this would result in either a charging or a discharging of the direct voltage capacitor of the respective VSC-converter.
• the second VSC-converters connected in series may in this case be controlled for compensating away voltage components of for example the fifth and seventh harmonic, the eleventh and thirteenth harmonic and higher harmonics generated by the converter with low apparent power according to the above.
• the factor k is advantageously chosen to be low, for example 5-15%, since it is normally sufficient to add a small voltage component in series with the voltage from the big, first VSC-converter for generating and compensating away the harmonics mentioned above.
• the first VSC- converter as well as the smaller second VSC-converter connected in series in each phase are working with pulse width modulation.
• the higher number of available levels means that for a given requirement that the converter shall not generate more than a given amount of harmonics out on the connecting networks 1 -3 the switching frequency of the first VSC-converter 6 with high apparent power may be reduced.
• a converter apparatus differing from the one according to Fig 2 only by the fact that the second VSC-converters are with the di- rect voltage side thereof connected to a phase leg of the first
• VSC-converter through a potential of the direct voltage interme- diate link, which here has two capacitors, of the converter located substantially in the middle of the potential of the two direct voltage poles of this converter instead of being formed by H-bridges, and which is connected to the alternating voltage side of the apparatus to a branch of controllable semiconductor devices.
• the increased number of levels obtained in this way may be utilized for switching the current valves of the converters with a lower frequency for obtaining a given curve shape and in this way reduce the switching losses or switching the valves with an unchanged frequency and obtain an improved curve shape with less harmonic content.
• FIG 8 An apparatus according to a further variation of the invention is shown in Fig 8, which is very suitable when the converter apparatus is connected to a connecting network 1 -3 through a trans- former 47.
• the first VSC-converter is here on the alternating voltage side thereof with each phase leg connected to a secon- dary winding 48-50 of its own of the transformer, and the second end of the secondary winding is connected to a phase leg of a second VSC-converter in the form of a three phase converter.
• the transformer has further three primary windings 51 -53, which are each connected to a said phase line 1 -3 each of the alternating voltage side of the apparatus.
• the transformer Y-connected on the secondary side is phasewisely provided with an extra lead-through in the neutral point 54 of the transformer, through which the second VSC-converter with low apparent power has been connected.
• this embodiment may be varied freely with the other embodiments according to the invention if more levels are desired.
• An advantage of this embodiment is that it only includes two direct volt- age intermediate links, which simplifies the control of the converter apparatus, and that the direct voltage intermediate link capacitors for both VSC-converters are in common for all the three phases, which makes it possible to select the size of the direct voltage intermediate link capacitors comparatively small, . which reduces the costs for the converter.
• the phase voltage is here present across the secondary winding of the transformer.
• FIG 9 A variation of the embodiment according to Fig 8 is illustrated in Fig 9, which differs from the one according to Fig 8 by the fact that the first VSC-converter 6 with high apparent power on the direct voltage side thereof is connected to a transmission system for HVDC or alternatively directly to an identical station for a back-to-back-transmission, which is indicated through the cables 55, 56. Since the voltage between the direct voltage poles of the first VSC-converter now is assumed to be high also reactors 57 and filters 58 have been placed between this converter with high output voltage and the transformer 47 so as to avoid that the transformer is exerted to high voltage derivatives with respect to ground.
• FIG. 10 A further modification of the embodiment according to Fig 8 is shown in Fig 10 and this differs from the embodiment according to Fig 9 by the fact that on the direct voltage side of the second VSC-converter 5 a further three phase-VSC-converter 76 is con- nected with the midpoints and the phase legs thereof connected to a phase line each of an alternating voltage network 60 for feeding power in towards and out from, respectively, said second VSC-converter 5 with lower apparent power.
• the converter 5 with low apparent power may in this way be used on one hand for reducing harmonics generated by the converter 6 with high apparent power and on the other for generating fundamental tone.
• the converter 6 with high apparent power may in this way use a pulse width modulation pattern with very low switching frequency and with a fixed relationship between alternating volt- age and direct voltage, while the converter 5 with low apparent power is used both for harmonic compensation and for reactive power compensation and/or rapid adjustment of the total fundamental voltage of the converter apparatus on the alternating voltage side.
• a converter apparatus is illustrated in Fig 1 1 , in this apparatus each phase leg of the first VSC-converter 6 is connected to a phase line 1 -3 of its own on the alternating voltage side of the apparatus and two second VSC-converters 5, 5' are connected to on one hand a direct voltage pole of the first VSC-converter each and on the other to a pole conductor of a direct voltage network.
• This embodiment of the invention is particularly suited in the case of HVDC, where the first VSC-converter on the alternating voltage side is connected to an alternating voltage transmission network 1 -3 through reactors 58 and filters 59 without any intermediate transformer.
• the second VSC- converters with low apparent power are preferably controlled synchronously with a pulse width modulation pattern, so that both either add or subtract the voltage kU with respect to the respective pole voltage in relation to ground. They may also be connected so that the pole voltage of the converter 6 with high apparent power gets identical to the voltage across the respective direct voltage capacitor with respect to ground.
• the current flowing through both VSC-converters 5, 5' with low apparent power is mainly a direct current.
• the voltage generated thereby is a pure alternating voltage without any direct voltage component. Since they are switching synchronously they will generate a zero sequence voltage being present in all phases on the alternating voltage side.
• the first VSC-converter 6 has here three connection points on the alternating voltage side thereof and two 72, 73 on the direct voltage side thereof, while the respective second VSC-converter 5 has two connection points 74, 75.
• the phase voltage for one phase is between 34 and 1 .
• the converter apparatus is well suited for use of so called dead band-PWM.
• dead band-PWM During a given part of the period of the voltage fundamental tone only two of the three phases of the first VSC-converter 6 with high apparent power are in this way switched with their PWM pattern, while the third phase is connected to one of the direct voltage poles, 7, 8. It is for example possible to let one phase be connected to one direct voltage pole during 60 electrical degrees of the period of the fundamental voltage, whereupon the pole is switched during 120 electrical degrees, and the pole is then during 60 electrical degrees connected to the opposite pole, whereupon the pole is again switched during the remaining 120 electrical degrees.
• dead band-PWM is as mentioned above primarily that the switching frequency of the VSC-converter with high ap- parent power may be reduced to 2/3, since the phase only have to switch during 2/3 of the period of the fundamental voltage.
• the disadvantage is on the other that zero sequence components having third tone character or multiples of third tones have to be added to the voltage set values of all the phases, which however does not influence the phase-phase-voltage but the voltage between phase and ground.
• a typical value of the factor k may in this case be about 15-20%. Also higher values of the factor k may be used. This may for ex- ample be valuable if the VSC-converter with high apparent power is directly connected, i.e. without any transformer, to an alternating voltage transmission network being impedance grounded. For example on a one-phase ground fault a zero sequence component then appears on the alternating voltage side, inter alia of fundamental tone character.
• the VSC-converters with low apparent power may in such a case, provided that the factor k is selected sufficiently large, compensate this zero sequence component away and the converter apparatus may transmit power independently of any occurrence of one-phase faults in connecting networks.
• FIG 12 an apparatus according to a further preferred embodiment of the invention is illustrated in Fig 12, and in this the second VSC-converters may also contribute to the transmission of active power by the fact that their direct voltage side may exchange energy with a further alternating voltage network 61 through a dc/dc-converter 62.
• This embodiment has a dc/dc- converter 62 with a high frequency transformer 63 connected with one side thereof to a second VSC-converter 5 with its other side to an arrangement (61 ) for feeding power in towards and out from, respectively, said VSC-converter.
• the apparatus has a common dc/dc-converter for all the phase lines 1 -3 with a said transformer with three secondary windings 64-66 connected to a converter part 67-69 of its own connected to the respective second VSC-converter and a primary winding 70 connected to one single converter part 71 connected to said ar rangement.
• the additional network 61 may hereby feed power into or drain power from the second VSC-converters 5 with low apparent power, so that these may function in a similar way as the second VSC-converter 5 of the embodiment according to Fig 10.
• the embodiment lastly described may be modified by arranging a separate transformer/phase. However, it is advantageous to use a multiple winding transformer according to Fig 12, since the number of primary windings may then be reduced.
• Additional voltage is in this disclosure to be interpreted as also covering addition of negative voltages, i.e. a subtraction of a posi- tive voltage.
• the converter apparatuses described are preferably designed to handle phase voltages between 5 kV and 500 kV, even if other voltage levels are conceivable.

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• 2001
  • 2001-02-07 SE SE0100372A patent/SE521243C2/sv not_active IP Right Cessation
• 2002
  • 2002-01-16 WO PCT/SE2002/000066 patent/WO2002063758A1/en not_active Application Discontinuation
  • 2002-01-16 EP EP02715918A patent/EP1364450A1/en not_active Withdrawn

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