WO2010000315A1 - Modular converter system supporting harmonic suppression - Google Patents
Modular converter system supporting harmonic suppression Download PDFInfo
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- WO2010000315A1 WO2010000315A1 PCT/EP2008/058508 EP2008058508W WO2010000315A1 WO 2010000315 A1 WO2010000315 A1 WO 2010000315A1 EP 2008058508 W EP2008058508 W EP 2008058508W WO 2010000315 A1 WO2010000315 A1 WO 2010000315A1
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- power
- power converter
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- 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
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
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- Control Of Eletrric Generators (AREA)
Abstract
The present invention relates to an electronic power converter system comprising a plurality of power converter modules operatively connected to a DC intermediate circuit, the electronic converter system comprising first and second power converter modules being operable in the same plurality of modes of operation. The electronic converter system further comprises a third power converter module being operable in a plurality of modes of operation, wherein one of said modes of operation is concerned with suppression of system and/or grid harmonics. The first and second power converter modules are operable in identical modes of operation thereby forming a pair of interchangeable power converter modules.
Description
MODULAR CONVERTER SYSTEM SUPPORTING HARMONIC SUPPRESSION
FIELD OF THE INVENTION
The present invention relates to a modular converter system comprising a plurality of interchangeable power converter modules forming a reliable, scalable and redundant converter system. In particular, the present invention relates to a modular converter system comprising at least one converter module being capable of suppressing harmonics, such as grid harmonics, harmonics generated by a converter or other system harmonics. The present invention further relates to various devices applying such electronic converter system.
BACKGROUND OF THE INVENTION
Various types of modular converter systems have been suggested in the patent literature over the years.
One particular interesting arrangement has been suggested by Aloys Wobben in US2006/0103137 where a number of independent rectifier modules may be combined with an equal number of inverter modules thus forming a complete frequency converter for a wind turbine.
In US2006/0103137 a number of rectifier modules can be by-passed whereas other rectifier modules may remain active. Similarly, a certain number of inverter modules can be by-passed whereas other inverter modules may remain active. In this way the number of active rectifier and inverter modules can be chosen to match specific demands, such as an amount of power to be delivered.
However, it is a disadvantage of the arrangement suggested by Aloys Wobben that total flexibility is not provided. A rectifier module can only be operated as a rectifier. Thus, a rectifier module can not replace an inverter module and vice versa.
It is an object of the present invention to provide a scalable power converter system offering harmonic suppression and full flexibility in terms of replacing one power converter module with another power converter module within the power converter system.
SUMMARY OF THE INVENTION
The electronic converter system according to the present invention is directed towards a modular converter system that is well suited (but not limited to) large power systems. One field of application may be wind turbines, but many other systems could benefit from the solution suggested by the present invention.
In wind turbines the module weight is an issue in a service and production situation. Also the life time requirements for wind turbines are very high. This requires replacement of parts in due time to avoid downtime of a wind turbine. Service of wind turbines (especially offshore) is extreme costly and very time consuming so a better scheduling of service is desired. This implies that if a fault in an offshore facility occurs it is obviously a huge advantage if the wind turbine could maintain operating until the next scheduled service. As more and more wind turbines are placed in wind power plants and are perceived and operated as such new requirements have arisen for grid support. This means that the wind turbines must be able to deliver power at a very low power factor (PF). This normally requires a very overrated output of the converter system.
The above-mentioned object and other objects are complied with by providing, in a first aspect, an electronic converter system comprising a plurality of electronic converter modules operatively connected to a DC intermediate circuit, the electronic converter system comprising
- a first power converter module being operable in a plurality of modes of operation, and
- a second power converter module also being operable in the plurality of modes of operation,
wherein both the first and second electronic converter modules are operable in identical modes of operation thereby forming a pair of interchangeable electronic converter modules if so required.
Thus, it is an essential feature of the first aspect of the present invention that the power converter modules are interchangeable thereby providing a flexible, fully redundant and reliable electronic converter system. Obviously, fully redundancy requires at least three power converter modules. Even further, the electronic converter system according to the present invention is a scalable system in that the number of power converter modules may be adjusted to match for example the amount of power or current to be delivered. Thus, according to the present invention converter systems in the MW range may be provided as easily as converter systems in the kW range just by varying the number of power converter modules incorporated into the converter system.
It is another advantage of the first aspect of the present invention that the power converter modules are capable of covering the same functionalities of the converter system. In this way the power converter modules become interchangeable and may thus replace each other. Thus, in case a given converter module, for example an AC/DC converter module, breaks down another converter module in the system may immediately be appointed an AC/DC converter module in replacement of the previous AC/DC converter module which may be repaired or physically replaced by another converter module. In this way the first aspect of the present invention provides a fully redundant converter system.
The DC intermediate circuit may be implemented as a DC capacitor bank in a bus bar configuration, or as simple interconnection structure. Also overcurrent protective devices may be present in the DC intermediate circuit to limit fault propagation. The DC intermediate circuit may physically extend the boundary of the structure with the purpose of connecting more similar structures.
The electronic converter system according to the first aspect of the present invention may be used in connection with various applications. Thus, the
converter systems according to the first aspect of the present invention may be applied as part of frequency converters for individual wind turbines or frequency converters for wind power plants. Since the converter system according to the present invention may also be configured as a DC/DC converter, other applications may also be applicable.
In case of a frequency converter-like configuration, a first mode of operation may involve operating the first power converter module as a AC/DC converter. Similarly, a second mode of operation may involve operating the second power converter module as a DC/ AC converter.
In case of a DC/DC converter, both the first and the second power converter modules are operated as DC/DC converters.
The electronic converter system may further comprise one or more additional power converter modules also being operable in the plurality of modes of operation, the one or more additional power converter modules being operatively connected to the DC intermediate circuit.
In a preferred embodiment of the first aspect of the present invention, there are at least two power converter modules. Each of them comprises a four quadrant power converter thereby allowing power conversion from AC to DC in a first mode of operation, and power conversion from DC to AC in a second mode of operation.
Controllable switching means shall be provided in each of the power converter modules, said controllable switching means being adapted to control a power flow to and/or from each of the power converter modules. Thus, by operating the controllable switching means appropriately it may be controlled whether an individual converter module should provide power to the DC intermediate circuit or draw power from the DC intermediate circuit.
The electronic converter system may further comprise an input filter for filtering input power signals to the electronic converter system. In addition, the
electronic converter system may further comprise an output filter for filtering power signals leaving the electronic converter system.
Each of the power converter modules may comprise control means adapted to communicate with a higher level central control module of the converter system.
In a second aspect, the present invention relates to a power generating facility comprising means for generating AC power and an electronic converter system according to the first aspect of the present invention. In a third aspect, the present invention relates to a wind turbine comprising generator means for generating AC power, and an electronic converter system according to the first aspect of the present invention.
In a fourth aspect, the present invention relates to a wind power plant comprising a plurality of generator means for generating AC power, and an electronic converter system according to the first aspect of the present invention.
In terms of implementation, the electronic converter systems according to the second, third and fourth aspects of the present invention may be implemented and configured by following the design routes mentioned in connection with the first aspect of the present invention.
In a fifth aspect, the present invention relates to an electronic converter system comprising a plurality of power converter modules operatively connected to a DC intermediate circuit, the electronic converter system comprising
- a first power converter module being operable in a plurality of modes of operation,
- a second power converter module also being operable in the plurality of modes of operation, and
- a third power converter module being operable in a plurality of modes of operation,
wherein the first and second power converter modules are operable in identical modes of operation thereby forming a pair of interchangeable power converter modules, and wherein the third power converter module, in one of its modes of operation, is adapted to suppress system and/or grid harmonics.
The third power converter module may be regarded as a power quality module in that it improves the quality of the delivered electric power. Thus, the third power converter module will in the following description be denoted both as a power quality module and a third power converter module.
Thus, it is an essential feature of the fifth aspect of the present invention that the first and second power converter modules are interchangeable thereby providing a flexible, fully redundant and reliable electronic converter system. Even further, the electronic converter system according to the present invention is a scalable system in that the number of power converter modules may be adjusted to match for example the amount of power or current to be delivered. Thus, according to the present invention, converter systems in the MW range may be provided as easily as converter systems in the kW range just by varying the number of power converter modules incorporated into the converter system. Moreover, it is an essential feature of the fifth aspect of the present invention that the third power converter module, in one of its modes of operation, is adapted to suppress system and/or grid harmonics.
It is another advantage of the fifth aspect of the present invention that a number of the power converter modules are capable of covering the same functionalities of the converter system. In this way, a number of the power converter modules become interchangeable and may thus replace each other. Thus, in case a given converter module, for example an AC/DC converter module, breaks down, another converter module in the system may immediately be appointed an AC/DC converter module in replacement of the previous AC/DC converter module which may be repaired or physically replaced by another
converter module. In this way, the present invention provides a fully redundant converter system.
The DC intermediate circuit may be implemented as a DC capacitor bank in a bus bar configuration, or as simple interconnection structure. Also overcurrent protective devices may be present in the DC intermediate circuit to limit fault propagation. The DC intermediate circuit may physically extend the boundary of the structure with the purpose of connecting more similar structures.
The electronic converter system according to the fifth aspect of the present invention may be used in connection with various applications. Thus, the converter systems according to the present invention may be applied as part of frequency converters for individual wind turbines or frequency converters for wind power plants. Since the converter system according to the present invention may also be configured as a DC/DC converter, other applications may also be applicable.
The first, second and third power converter modules may, in a first mode of operation, be adapted to be operated as AC/DC converter modules. Similarly, the first, second and third power converter modules may, in a second mode of operation, be adapted to be operated as DC/AC converter modules.
The third power converter module may be adapted to suppress harmonics generated by a power converter module, such as to suppress harmonics being generated by the second power converter module when said second power converter module is being operated as a DC/AC converter module. In order to comply with this, the third power converter module may be operated as a DC/ AC converter module in parallel with the second power converter module.
Alternatively or in addition, the third power converter module may be adapted to suppress grid harmonics and/or other electrical system disturbances, such as higher order harmonics in the current supplied to the electrical grid. These current harmonics can originate from nonlinearities in the converter control
system, low switching frequency of first/second power converter modules or higher order harmonics in the grid voltage.
Moreover, in case the third power converter module is operated as a AC/DC converter, and inserted between a wind turbine generator and the DC intermediate circuit, the third power converter module may be adapted to suppress harmonics generated by said generator of the wind turbine.
Additional power converter module(s) being operable as AC/DC or DC/ AC converter modules may be provided. The additional power converter module(s) may be operatively connected to the DC intermediate circuit.
Controllable switching means shall be provided in each of the power converter modules, said controllable switching means being adapted to control a power flow to and/or from each of the power converter modules. The controllable switching means may comprise IGBTs or other suitable switching means. The controllable switching means of the third power converter module are modulated with a frequency being significantly higher than the switching frequency of other power converter modules. As an example the switching frequency of the third power converter module may be within the range 10-30 kHz whereas the switching frequency of the other power converter modules may be within the range 1-5 kHz. The third power converter module may deliver less power compared to the other power converter modules due to the higher switching frequency. Thus, the third power converter module may be operated in a derated power mode.
In one embodiment, the third power converter module may be designed to operate with the significantly higher switching frequency,
In another embodiment, the third power converter module may be a standard module like the first and second power modules. However, when operated with the significantly higher switching frequency, the power rating of the third power module is reduced.
Input filter means for filtering input power signals to the electronic converter system may be provided. Moreover, a first low-pass filter for filtering power signals leaving at least part of the electronic converter system may be provided. By at least part is meant any power converter module(s) except the third power converter module.
A second filter for filtering power signals leaving the third power converter module may be provided. Due to the higher switching frequency of the third power converter module the second filter, in case it is a low-pass filter, may have a higher cut-off frequency than the first low-pass filter. The cut-off frequency of the first low-pass should match the switching frequency of the power converter modules other than the third power converter module. Thus, the cut-off frequency of the first low-pass filter may be around 2 kHz, for a switching frequency of 2.5 kHz. Possibly, the second filter is a low-pass filter with very high cut-off frequency so that a wide range of harmonics can be compensated.
Each of the power converter modules may comprise control means adapted to communicate with a central control means of the system.
In a sixth aspect, the present invention relates to a power generating facility comprising means for generating AC-power, said means for generating AC- power being operationally connected to an electronic converter system according to the first aspect of the present invention.
In a seventh aspect, the present invention relates to a wind turbine comprising a generator for generating AC-power, said generator being operationally connected to an electronic converter system according to the first aspect of the present invention. The wind turbine according to the seventh aspect may form part of a wind power plant comprising a plurality of such wind turbines.
In an eighth aspect, the present invention relates to a method for operating an electronic converter system comprising a plurality of power converter modules
operationally connected to a DC intermediate circuit, the method comprising the steps of
- providing a first power converter module being operable in a plurality of modes of operation and operating said first power converter module as an AC/DC converter,
- providing a second power converter module also being operable in the plurality of modes of operation and operating said second power converter module as an DC/ AC converter, and
- providing a third power converter module being operable in a plurality of modes of operation and operating said third power converter module in a manner so that it suppresses system and/or grid harmonics,
wherein the provided first and second power converter modules are operable in identical modes of operation thereby forming a pair of interchangeable power converter modules.
The third power converter module may be operated in a manner so that it suppresses harmonics generated by the second power converter module, grid harmonics and/or other system disturbances. Alternatively, the third power converter may be operated in a manner so that it suppresses harmonics generated by a wind turbine generator. The latter scenario typically implies that the third power converter module is operated as an AC/DC converter.
Further power converter modules being operatively connected to the DC intermediate circuit and being operated as AC/DC or DC/ AC converter modules may be provided.
A low-pass filter for low-pass filtering power signals leaving the second power converter module may be provided. Moreover, a filter for filtering power signals leaving the third power converter module may be provided, said filter having, in case it is a low-pass filter, a higher cut-off frequency than the first low-pass
filter. Said filter may, alternatively, be a band-pass filter for band-pass filtering power signals leaving the third power converter module. The band-pass filter may have a centre frequency in the range 1-8 kHz.
Each of the power converter modules may comprise control means adapted to communicate with a central control means of the system.
The power converter modules of the eighth aspect of the present invention may generally be implemented by following the same design route as set forth in connection with the seventh aspect of the present invention.
BRIEF DESCRIPTION OF THE INVENTION
The present invention will now be described in further details with reference to the accompanying figures, wherein
Fig. 1 shows a full scale modular power converter system according to the present invention, and
Fig. 2 shows a three-phase power module with IGBT's.
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in details herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
In its most general aspect the present invention relates to a modular power converter system where a plurality of interchangeable power converter modules, such as AC/DC converters, DC/ AC converters, DC/DC converters, or a combination thereof are connected to a common DC intermediate circuit, such as
a DC capacitor bank, and wherein at least one power converter module is operable in a manner which allows suppression of system and/or grid harmonics. Interchangeable means that a number of the power converter modules can replace each other in terms of functionality. Thus, if a given converter module is operated as for example an AC/DC converter and this converter breaks down another converter can immediately be appointed AC/DC converter in order to take over from the broken down converter. In this way, the converter system according to the present invention provides a fully redundant and very reliable converter system.
It is a characteristic of the power converter modules of the present invention that they may all be operated in a plurality of modes. Preferably, the power converter modules of the present invention are four quadrant semiconductor- based power converter modules since this type of power converter modules offer a high degree of flexibility. The active semiconductor components may be, but is not limited to, thyristors, IGCTs, GTOs, BJTs, mosFETs or IGBTs arranged in for example traditional three phase rectifier, converter or inverter bridge configurations. A traditional three-phase DC/AC converter bridge configuration applying six IGBTs is shown in Fig. 2. The DC intermediate circuit is represented by UDC whereas the AC three-phases are denoted A, B and C.
It should be noted that the present invention is not limited to three-phase systems. Thus, the present invention is in general applicable to all single or multiphase systems.
It is an advantage of the power converter system according to the present invention that the system is scalable simply by varying the number of power converter modules constituting the converter system. Thus, if power in the MW range is to be delivered, a relatively large number of power modules could be required. On the contrary, if power in the kW range is to be delivered, a significantly smaller number of power modules could be required. Obviously, the number of power converter modules in a given situation depends on the power handling capabilities of the chosen modules. Thus, the larger the modules the fewer modules are required.
Fig. 1 shows a wind turbine or wind turbine plant implemented version power converter system according to the present invention. However, it should be noted that the present invention is by no means limited to wind turbine or wind power plant applications.
Beside the power converter system itself, Fig. 1 depicts a drive train and a generator of a wind turbine. Moreover, a grid transformer and an associated power supply grid is depicted. Typically, the wind turbine generator, the grid transformer and the associated power supply grid are operated as three-phase AC elements. The drive train of the wind turbine involves the shaft to which the rotor blades are attached, the shaft to which the rotor of the generator is attached, and optionally a gear box inserted between the two shafts.
Fig. 1 shows power converter modules capable of converting between AC and DC using appropriate semiconductors components, such as thyristors, IGCTs, GTOs, BJTs, mosFETs or IGBTs. The power converter modules are all connected to a DC intermediate circuit and appropriate filters are provided at the output of the power converter system. Optionally an appropriate filter or filters may be provided at the input of the power converter system.
As depicted in Fig. 1, the DC-interfaces of the λλn" power converter modules are all connected to the DC intermediate circuit - in Fig. 1 denoted DC link infrastructure. A high level control module provides control signals to each of the "n" power converter modules. The high level controller gives each "n" power converter module a command defining its operating state. Each of the "n" power converter modules is equipped with a local controller. The software of the controller of the power quality module shall include the same functions for power conversion from the generator to power grid as the other power converter modules. Moreover, functions relating to harmonic current detection, harmonic current compensation and reactive power compensation shall be included. Control schemes for controlling active power filters and STATCOMs are very mature, but they may optionally be used in the power quality module.
As previous stated, each of the "n" power converter modules are preferably a four quadrant semiconductor-based power converter module. A number of controllable switches, in Fig. 1 denoted transfer switches, allow power to be provided to and/or from each of the "n" power converter modules. In Fig. 1 the upper transfer switch for each power converter module is adapted to provide AC power to the module when said module is operated as an AC/DC converter, whereas the lower transfer switch for each converter module is adapted to lead AC power away from the power converter module when said converter module is operated as an DC/ AC converter. Depending on the desired mode of operation, AC/DC or DC/ AC, the controllable transfer switches may be activated/deactivated accordingly.
As previously stated the converter system is a fully redundant system where the mode of operation of each of the "n" power converter modules can be varied in order to fulfil specific demands. Thus, a specific power converter module being operated as an AC/DC converter may be appointed to be operated as a DC/AC converter if demands so require. Also, if a converter module suddenly fails or breaks down the redundancy of the system ensures that another converter module immediately takes over the functionality of the faulty converter module thereby ensuring a reliable power delivery. The converter module taking over could be a spare converter module or it could be a converter module being operated in another mode of operation. Thus, if a converter module operating in AC/DC mode breaks down it could be replaced by a module operating in either AC/DC or DC/AC mode, or even a spare converter module. This selection depends on the required power and the available modules.
As depicted in Fig. 1 a so-called power quality module is depicted. The power quality module is electrically coupled to the DC intermediate circuit.
The overall functionality shall include the following modes of operation:
1. The power quality module shall serve as either a grid-side power converter or a generator-side power converter like other normal power modules in order to transfer real power from the generator to the power
supply grid when the power capacity of the other modules is insufficient. However, it should be noted that normal power modules have higher priority to transfer real power from the generator to the grid compared to the power quality module except in the case where a normal power module is not functioning properly.
2. When the wind speed is low and the power from the wind turbine generator is low, the power quality module shall connect to an output filter (denoted 2nd output filter in Fig. 1) and serve as an active power filter and STATCOM for harmonic current and reactive power compensation.
3. During grid faults, the power quality module could possibly supply reactive power for grid voltage support.
The power quality module is adapted to be operated with a significantly higher switching frequency than the remaining power converter modules. This allows that the power quality module may be operated in a manner which allows that grid and/or system harmonics can be effectively suppressed. The power quality module is typically a four quadrant semiconductor-based converter. This implies that the power quality module can be operated as an AC/DC or a DC/ AC converter. In case the power quality converter is operated as an AC/DC converter, the operation of the power quality converter can be optimized to suppress harmonics generated by the wind turbine generator. In case the power quality converter is operated as a DC/AC converter, the operation of the power quality converter can be optimized to suppress grid harmonics or other system disturbances, such as higher order harmonics in the current supplied to the electrical grid. These current harmonics can originate from nonlinearities in the converter control system or higher order harmonics in the grid voltage.
In order to effectively suppress grid and/or system harmonics, the power quality module is operated with a switching frequency within the range 10-30 kHz. In contrast to this, the other power converter modules of the system are typically operated with a switching frequency within the range 1-5 kHz.
At the output port of the converter system, appropriate output filters are arranged. As depicted in Fig. 1, the output filters is connected to a grid transformer, said grid transformer being adapted to match the output voltage level of the converter system with the voltage of an associated power grid. The output filters are both connected to the AC sides of the converter system.
Depending on the operating mode (AC/DC or DC/AC) of the converter modules and the load on the AC side of the converter system, different types of filter may be required.
The output filter denoted 2nd output filter in Fig. 1 is connectable to the power quality filter. This filter may be implemented in various ways, such as a low-pass filter or a band-pass filter. If this filter is implemented as a low-pass filter its cut-off frequency will be higher than the cut-off frequency of the low-pass filter connected to the other power converter modules. If the design of the low-pass output filter can be compromised or only low-order harmonic current needs to be compensated, it is possible to share the same output filter.
Alternatively, the output filters may each comprise a high-pass and a low-pass filter part. The high-pass filter part may comprise EMC-filters and/or dv/dt filters whereas the low-pass filter part may comprise switch harmonic filters. The power converter modules can be cooled by various means. In one embodiment, liquid cooling can be used. The cooling liquid for all power converter modules can circulate in a shared cooling system or in a system that is divided into two or more liquid systems.
Alternatively, each of the individual power converter modules may have their own cooling system including a pump for circulating a cooling liquid for each converter module. In this way, the redundancy of the system also includes the cooling arrangement. This is in contrast to conventional converter systems which purely rely on a shared cooling system having only a single or just a few common cooling pumps. Each converter module may include a complete cooling system, where part of the cooling system is placed in an suitable environment for dissipating the heat (i.e. outdoor)
In Fig. 1, additional modules such as means for obtaining advanced grid operations (AGOs), dump resistors, means for static VAr compensation, batteries or other energy storage means for power backup may be connected to the DC intermediate circuit. These functionalities may be performed by converter modules. For example, a converter modules being operated as a DC/ AC converter module can be appointed to fill out an AGO functionality.
As previously stated, the functionality of a faulty converter module may be taken over by another converter module. This means that the converter system may be kept running even though one or more converter modules are closed down for service, repair or replacement. The switching between converter modules is done on the fly, i.e. without interruption, in order to avoid short shut-down periods.
The generator of the wind turbine may be of various types, including a full scale solution as depicted in Fig. 1 or a doubly fed generator arrangement. The only difference between the doubly fed configuration and the full scale solution of Fig. 1 is a third transformer winding of the grid transformer and its connection to the wind turbine generator.
The flexibility of the power converter system shown in Fig. 1 is evident. In most typical cases, a plurality of converter modules are connected to the input side of the converter system, and thus operated as AC/DC rectifiers. Similarly, a plurality of converter modules are connected to the output of the converter system, and thus operated as DC/ AC inverters. The power quality module can be operated as an AC/DC rectifier or a DC/AC inverter depending of the harmonics to be suppresses. In case the power quality module is operated as a traditional DC/ AC inverter, the centre transfer switch is closed and the power quality filter feeds the upper output filter along with other DC/AC inverters. In case the power quality filter is operated to suppress harmonics, the lower transfer switch is closed and the power quality filter feeds the lower output filter, i.e. the 2nd output filter.
Depending on the load situation, the following adjustments to the converter system configuration may typically occur:
1. If more output current is desired an extra converter module is connected to the output side
2. If there is a fault in an input converter module an extra converter module is switched to the input side
3. If there is a fault in an output converter module an extra converter module is switched to the output side
4. If there is an overload on a converter module an extra converter module is provided - for example an input converter module may temporary be switched over to the output side
5. If there is a need for fast demagnetizing of the generator, more converter modules may be switched over to the input side
6. If a converter module approaches its expected end of life time a redundant module may take over its functionality, and the converter may request Converter Module replacement at the next service (alternatively accept reduced performance until next service).
7. If there is a need for a lower PF on the output of the system, modules could be transferred from the generator side to the output, maximizing the capability of the system as a whole.
8. If there is an overload of the output side, modules could be transferred from the input to the output to help provide the current needed to activate available overcurrent protective devices.
9. If an equal lifetime for the converter modules is decidable, the converter system may be configured to ensure that the converter modules experience an essentially equal load profile over their life.
10. When an AGO functionality is needed, converter modules can be transferred from either the input side (AC/DC) or the output side (DC/ AC) of the converter system to an AGO dump resistor.
11. A full rated AGO functionality could be established if the output converter modules (DC/AC) are transferred to AGO functionalities in case of a power grid failure. This ensures that the full load on the mechanical system of a wind turbine may be maintained. When the power grid failure is no longer present, the converter modules being operated to provide AGO functionalities are transferred to output converter modules (DC/ AC). To ensure a smooth transfer, the converter modules are transferred one at a time thereby enabling a fast reconnect of the wind turbine to the power grid. Pitch systems and the rest of the mechanical system of the wind turbine remain unaffected by the power grid dropout.
Claims
1. An electronic converter system comprising a plurality of power converter modules operatively connected to a DC intermediate circuit, the electronic converter system comprising
- a first power converter module being operable in a plurality of modes of operation,
- a second power converter module also being operable in the plurality of modes of operation, and
- a third power converter module being operable in a plurality of modes of operation,
wherein the first and second power converter modules are operable in identical modes of operation thereby forming a pair of interchangeable power converter modules, and wherein the third power converter module, in one of its modes of operation, is adapted to suppress system and/or grid harmonics.
2. An electronic converter system according to claim 1, wherein the first, second and third power converter modules, in a first mode of operation, are adapted to be operated as AC/DC converter modules.
3. An electronic converter system according to claim 1 or 2, wherein the first, second and third power converter modules, in a second mode of operation, are adapted to be operated as DC/AC converter modules.
4. An electronic converter system according to any of claims 1-3, wherein the third power converter module is adapted to suppress harmonics generated by a power converter.
5. An electronic converter system according to any of claims 1-4, wherein the third power converter is adapted to suppress grid harmonics and/or other electrical system disturbances.
6. An electronic converter system according to any of claims 1-3, wherein the third power converter is adapted to suppress harmonics generated by a generator in a wind turbine.
7. An electronic converter system according to any of the preceding claims, wherein the third power converter module is adapted to be operated with a switching frequency being higher than switching frequencies of the first and/or second power converter modules.
8. An electronic converter system according to claim 7, wherein the third power converter module is adapted to be operated in a de-rated power mode when operated with the high switching frequency.
9. An electronic converter system according to any of the preceding claims, further comprising one or more additional power converter modules being operable as AC/DC or DC/AC converter modules, the one or more additional power converter modules being operatively connected to the DC intermediate circuit.
10. An electronic converter system according to any of the preceding claims, wherein controllable switching means is provided in each of the power converter modules, said controllable switching means being adapted to control a power flow to and/or from each of the power converter modules.
11. An electronic converter system according to any of the preceding claims, further comprising a first low-pass filter for filtering power signals leaving the first or second power converter module.
12. An electronic converter system according to claim 11, further comprising a second filter, such as a low-pass filter or a band-pass filter, for filtering power signals leaving the third power converter module.
13. An electronic converter system according to any of the preceding claims, wherein each of the power converter modules comprises control means.
14. An electronic converter system according to claim 13, further comprising a central control module adapted to communicate with control means of each power converter module.
15. A power generating facility comprising means for generating AC-power, said means for generating AC-power being operationally connected to an electronic converter system according to any of the preceding claims.
16. A wind turbine comprising a generator for generating AC-power, said generator being operationally connected to an electronic converter system according to any of claims 1-14.
17. A wind power plant comprising a plurality of wind turbines according to claim 16.
18. A method for operating an electronic converter system comprising a plurality of power converter modules operationally connected to a DC intermediate circuit, the method comprising the steps of
- providing a first power converter module being operable in a plurality of modes of operation and operating said first power converter module as an AC/DC converter,
- providing a second power converter module also being operable in the plurality of modes of operation and operating said second power converter module as an DC/AC converter, and - providing a third power converter module being operable in a plurality of modes of operation and operating said third power converter module in a manner so that it suppresses system and/or grid harmonics,
wherein the provided first and second power converter modules are operable in identical modes of operation thereby forming a pair of interchangeable power converter modules.
19. A method according to claim 18, wherein the third power converter is operated in a manner so that it suppresses harmonics generated by the second power converter module.
20. A method according to claim 18 or 19, wherein the third power converter is operated in a manner so that it suppresses grid harmonics and/or other system disturbances.
21. A method according to claim 18, wherein the third power converter is operated in a manner so that it suppresses harmonics generated by a wind turbine generator.
22. A method according to any of claims 18-21, wherein further power converter modules being operated as AC/DC or DC/AC converter modules are provided, the further power converter modules being operatively connected to the DC intermediate circuit.
23. A method according to any of claims 18-22, further comprising the step of low-pass filtering power signals from the second power converter module.
24. A method according to any of claims 18-23, further comprising the step of low-pass filtering or band-pass filtering power signals from the third power converter module.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/EP2008/058508 WO2010000315A1 (en) | 2008-07-02 | 2008-07-02 | Modular converter system supporting harmonic suppression |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/EP2008/058508 WO2010000315A1 (en) | 2008-07-02 | 2008-07-02 | Modular converter system supporting harmonic suppression |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2010000315A1 true WO2010000315A1 (en) | 2010-01-07 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/EP2008/058508 WO2010000315A1 (en) | 2008-07-02 | 2008-07-02 | Modular converter system supporting harmonic suppression |
Country Status (1)
| Country | Link |
|---|---|
| WO (1) | WO2010000315A1 (en) |
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