Abstract:
A wind power installation having external and/or internal redundancy derived by multiple, independent power generating systems arranged in parallel, but switchably interconnected to allow substantial continued operation in the event of a critical component failure.

Description:
RELATED APPLICATIONS 
     This application is a divisional application of application Ser. No. 10/344,481 (now U.S. Pat. No. 6,946,750), filed Jun. 10, 2003, which is the National Stage of International Application No. PCT/EP01/09239, filed on Aug. 10, 2001, both of which claim priority to German Patent Application No. 100 40 273.9, filed on Aug. 14, 2000, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention concerns a wind power installation with preferably at least rectifiers and two inverters. 
     Such a wind power installation is known from patent specification DE 196 20 906.4. A disadvantage with that wind power installation however is that, in the event of failure of the generator and/or the transformer, the wind power installation can no longer generate or deliver any electrical power. In the event of failure of a rectifier and/or an inverter it is still approximately half of the possible power yield that is lost at any event, so that rapid repair is required in order to limit at least the economic damage to the operator of the installation due to the energy yield which is lost. 
     That known wind power installation has two phase-displaced stator windings which are arranged jointly on the same stator. The windings however are electrically insulated from each other and have a phase angle of 30° relative to each other. In the event of failure of a stator winding therefore half of the possible output power is still available. 
     In order to eliminate the fault and to repair the wind power installation service personnel travel to the faulty wind power installation and deal with the fault, either by a repair to the faulty or damaged components or, if repair is not possible, by replacing the defective components by a replacement part. 
     It will be noted that rapid repair presupposes inter alia that the wind power installation is quick to reach and if necessary spare parts can be quickly brought to the installation. 
     If it can still be assumed that wind power installations which are set up on land can be quickly reached in that way, the situation is already markedly different in relation to off-shore installations, that is to say wind power installations which are set up off the coast and thus at sea. On the one hand a suitable transport means must be available, with which possibly even large-volume and/or heavy spare parts can be transported and handled, while on the other hand the weather and the state of the sea must allow the installation to be safely reached, even with the loaded spare parts. Even if it is possible to reach the installation however, it is in no way certain in that respect that the sea swell and the weather will permit immediate repair. 
     It will be seen therefore that, if the swell is high or if the weather is bad, such as for example if there is a storm, it is definitely not possible to reach or repair off-shore installations, for a relatively long period of time, and therefore the off-shore installations cannot generate or deliver power for a prolonged period of time. 
     A further disadvantage with the previously known wind power installation, as also all others, is that the concept on which that wind power installation is based means that the dimensions and the inherent weight of the individual components become greater, with an increasing generator output. 
     SUMMARY OF THE INVENTION 
     In order to limit the damage due to the failure of components of a wind power installation and to allow the use of standard components, in accordance with the invention there is proposed a wind power installation of the kind set forth in the opening part of this specification, having at least two stators each with at least one stator winding, and at least two transformers. Advantageous developments are described in the further claims. 
     Accordingly the wind power installation according to the invention has at least two stators, two rectifiers, two inverters and two transformers. They respectively form, starting from the stator, a specific and complete system for the production of electrical energy, for conversion into for example a sinusoidal ac voltage and for feeding into an ac voltage network. 
     A preferred embodiment of the invention has four stators which are arranged in the form of a circular ring and which are in the shape of circular ring segments and which each have at least one winding of their own. As a result, the dimensions and the inherent weight of each stator remain in a range in which transportation and handling of the stator can be implemented with the usual available aids. 
     In a preferred development of the wind power installation according to the invention each stator has two three-phase current windings which are electrically separated from each other and which are displaced relative to each other at a phase angle of 30°. By virtue of that measure a part of the exciter current for the rotor can be produced in the stator winding. 
     In a particularly preferred development of the invention a rectifier, an inverter and a transformer are associated with each stator. That arrangement affords four separate power production systems, apart from the common rotor. Accordingly each system produces a quarter of the possible total output power. It follows therefrom that, in the event of failure of a component, only one system fails, and therewith just a quarter of the instantaneous overall output power. Accordingly therefore three quarters of the output power are still available. 
     If a total output power of 6 MW is considered for a wind power installation, each system accordingly involves an output power of 1.5 MW. That output power makes it possible to use standard components which are already available and produced in large numbers nowadays, as rectifiers, inverters and transformers. As a result the probability of failure is markedly reduced due to the use of technically matured components which are produced in large numbers, and that in turn contributes to a permanently high level of yield from a wind power installation according to the invention. 
     In accordance with a preferred embodiment of the invention a rectifier, an inverter and a transformer are associated with each stator winding. A power production system is accordingly formed from a stator winding, a rectifier, an inverter and a transformer. That design configuration means that each of the systems is only involved with an eighth of the instantaneously available output power. Therefore, in the event of failure of a component and thus a system, only an eighth of the available power is no longer available, but seven eighths are still available. 
     In addition this concept in turn permits production of an even higher number of standard components and thus a reduction in cost. In addition transportation and handling means, procedures and methods are available for those components and have been tried out in many situations. 
     In a particularly preferred embodiment of the invention the rectifiers, the inverters and the transformers are designed to be over-dimensioned, preferably by about 20%, and provided between each two rectifiers, between each two inverters and between each two transformers are switch devices which in the event of failure of a component permit it to be by-passed. 
     Due to the over-dimensioning the remaining components can at least temporarily take over the function of the failed component without that causing an overloading to occur. If therefore, for example, a rectifier fails the switch devices between the failed rectifier and one or more adjacent operational rectifiers can be actuated. In that way the operational rectifiers are acted upon with a correspondingly higher output power and also rectify the ac voltage from the system with the failed rectifier. 
     In a particularly preferred feature control of the switch devices is effected having regard to the output power to be switched, so that only one switch device switches when the level of output power is low. If the output power to be switched is higher a plurality of switch devices are actuated in order thereby to distribute the loading to a plurality of components and to avoid overloading. 
     In a particularly preferred development of the invention switch devices are provided in the feed line and/or the out line of each component with the exception of the stators. By actuation of the corresponding switch devices it is possible to reliably avoid any reaction on the part of the component to be by-passed if that component is completely disconnected by the switch devices. 
     In an alternative embodiment of the invention the feed lines and out lines of the individual components are connected in parallel. That saves on switch devices, in the event of failure of a component all the other components are always automatically operated and the control system is simplified as it is only the failed component that has to be disconnected by switch devices in the feed lines and/or out lines. 
     The redundancy of the individual components is referred to as ‘external redundancy’ and identifies the possibility, in the event of failure of a component, of causing the function thereof to be taken over by a redundantly present, other component. In the event of failure of a rectifier therefore other rectifiers take over the function, in the event of failure of an inverter other inverters take over the function and in the event of failure of a transformer other transformers take over the function. 
     In comparison there is also internal redundancy. That denotes constructing a component with a plurality of modules which are present redundantly with each other and which relative to the exterior form a component such as for example an inverter. Therefore in the event of failure of one of a plurality of modules of an inverter that inverter can definitely still remain operational as the remaining modules of the inverter can still continue to implement the function involved. 
     Accordingly a stator with two windings also has internal redundancy as, in the event of failure of one winding, the second winding is still available for generating power so that the stator can still deliver half of the possible output power. 
     Accordingly the wind power installation according to the invention can deliver all of the instantaneously available output power even in the event of failure of individual components or modules, with the exception of a stator or a stator winding. 
     Further advantageous developments of the invention are described in the appending claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention is described in greater detail hereinafter by means of an example. In the drawings: 
         FIG. 1  shows a simplified view of a system according to the invention, 
         FIG. 2  shows a view, supplemented by switch devices, of the system illustrated in  FIG. 1 , 
         FIG. 3  shows an example of two stator windings displaced through 30°, with a rectifier connected on the output side thereof, 
         FIG. 4  shows an example of an inverter according to the invention, 
         FIG. 5  shows an example of redundantly provided transformers having switch devices, 
         FIG. 6  shows a second embodiment of the present invention, 
         FIG. 7  shows an example of redundantly provided transformers in the second embodiment of the present invention, and 
         FIG. 8  shows a known system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 8  shows a known electrical system of a wind power installation. That electrical system includes a generator which in this example is in the form of a ring generator. The ring generator has a rotor (not shown) and two stator windings  111 ,  112  which are electrically insulated from each other and which are phase-displaced through 30° relative to each other. 
     The stator windings  111 ,  112  are each connected to the input of a respective rectifier  14  specific thereto. The output of each rectifier  14  is connected to an input of a respective inverter  16 . The outputs of the inverters  16  are connected in parallel to a transformer  18 . 
     Just the failure of the transformer  18  inevitably results in economic total failure of the wind power installation as it is not possible for any further energy to be delivered. As a result the operator suffers from considerable loss, depending on the respective duration of the failure. 
     The failure of a stator winding  111 ,  112 , a rectifier  14  and/or an inverter  16  also in any case results in a loss of half the possible energy yield and thus also results in considerable economic damage. 
       FIG. 1  shows a simplified example of a wind power installation according to the invention. Most components are redundantly present in this wind power installation. Such redundancy concerns parts of the generator, namely stators  121 ,  122 ,  123 ,  124 , rectifiers  141 ,  142 ,  143 ,  144 , inverters  161 ,  162 ,  163 ,  164  and transformers  181 ,  182 ,  183 ,  184 . 
     That redundancy which arises out of a parallel arrangement of the redundant components is external redundancy. In addition with some components there is also internal redundancy which arises out of the internal structure of the component being made up of a plurality of similar modules connected in parallel. That internal redundancy is to be found for example in the case of the inverters which are described in greater detail with reference to  FIG. 4 . 
     For the purposes of the description hereinafter, in a similar manner to the foregoing way of considering matters, each element  121 ,  122 ,  123 ,  124  which is in the form of a segment of a circular ring and which has at least one winding in which a voltage is induced by the rotating rotor R is referred to as a stator even if there are four elements  121 ,  122 ,  123 ,  124  which are in the form of a segment of a circular ring and they are arranged in such a way that together they approximately form the shape of a one-piece stator of a ring generator, as in the case of the present embodiment. 
     The stators  121 ,  122 ,  123 ,  124  which are arranged in the form of a circular ring and which are in the shape of segments of a circular ring together approximately form a circular ring in which the rotor R of the generator is centrally rotated by the wind power installation rotor hub (not shown) with the rotor blades fixed thereto. As the individual stators  121 ,  122 ,  123 ,  124  are separated from each other not only mechanically but also electrically, voltages are correspondingly induced in the windings on the stators  121 ,  122 ,  123 ,  124 . 
     Those voltages are ac voltages which are passed through conductors  201 ,  202 ,  203 ,  204  to rectifiers  141 ,  142 ;  143 ,  144 . Those conductors  201 ,  202 ,  203 ,  204  can be for example aluminum bars with a cross-sectional area of 4,000 mm 2 . In that respect a separate rectifier is associated with each stator  121 ,  122 ,  123 ,  124 . It follows therefrom that, even if a rectifier fails, only a quarter of the possible energy yield is no longer available. Accordingly three quarters of the possible output power is still available. 
     Connected on the output side of each rectifier  141 ,  142 ,  143 ,  144  is an inverter  161 ,  162 ,  163 ,  164  and also connected thereto by a conductor  205 ,  206 ,  207 ,  208 . Those conductors  205 ,  206 ,  207 ,  208  can also be aluminum bars of a cross-sectional area of 4,000 mm 2 . 
     Connected on the output side of each inverter  161 ,  162 ,  163 ,  164  there is again a transformer  181 ,  182 ,  183 ,  184  by way of which the ac voltage generated by the inverters  161 ,  162 ,  163 ,  164  is stepped up to for example 20 kV and fed for example into a medium-voltage network. 
     In that way, starting from the stator windings in which the voltage is induced by the generator rotor, there are mutually independent systems  101 ,  102 ,  103 ,  104  with rectifiers  141 ,  142 ,  143 ,  144 , inverters  161 ,  162 ,  163 ,  164  and transformers  181 ,  182 ,  183 ,  184  so that a failure of a component prevents at most the provision of a quarter of the possible output power. 
       FIG. 2  is expanded in comparison with  FIG. 1  by switch devices  130 ,  131 ,  132 ,  133 ,  134 ,  135 ,  136 ,  146 ,  147 ,  148 ,  149 ,  150 ,  151 ,  152 ,  153 ,  154 ,  155 ,  156 ,  166 ,  167 ,  168 ,  169 ,  170 ,  171 ,  172 ,  173 ,  174 ,  175 ,  176 ,  186 ,  187 ,  188 ,  189 . These are referred to hereinafter in their totality by reference numerals  130 – 136 ,  146 – 156 ,  166 – 176  and  186 – 189 . In order to retain clarity of the Figure, the references for the conductors between the stators  121 ,  122 ,  123 ,  124 , the rectifiers  141 ,  142 ,  143 ,  144  and the inverters  161 ,  162 ,  163 ,  164  and the markings of the systems  101 ,  102 ,  103 ,  104  have been omitted here. 
     In normal operation the switch devices  130 ,  131 ,  132 ,  150 ,  151 ,  152 ,  170 ,  171 ,  172  between the feed lines of the individual components are open and the switch devices  133 ,  134 ,  135 ,  136 ,  146 ,  147 ,  148 ,  149 ,  153 ,  154 ,  155 ,  156 ,  166 ,  167 ,  168 ,  169 ,  173 ,  174 ,  175 ,  176 ,  186 ,  187 ,  188 ,  189  in the feed lines and outlines in series with the respective components are closed in normal operation so that each system  101 ,  102 ,  103 ,  104  ( FIG. 1 ) operates separately from the others. 
     The switch devices  130 – 136 ,  146 – 156 ,  166 – 176 ,  186 – 189  are now controllable in such a way that they make connections between individual components of at least two systems  101 ,  102 ,  103 ,  104 . Those connections are made in such a way that the feed lines of two similar components are always connected parallel by each switch device  130 ,  131 ,  132 ,  150 ,  151 ,  152 ,  170 ,  171 ,  172 . 
     For example the feed lines of the rectifiers  141  and  142  are connected in parallel by actuation of the switch device  130 , the inputs of the inverters  161  and  162  by actuation of the switch device  150  and the inputs of the inverters  162  and  163  by actuation of the switch device  151 . It will be appreciated that combinations in that respect are also possible. 
     In order to avoid a reaction of failed or faulty components on those which are still operational, provided in the feed lines and out lines of the individual components are switch devices  133 ,  146 ;  134 ,  147 ;  135 ,  148 ;  136 ,  149 ;  153 ,  166 ;  154 ,  167 ;  155 ,  168 ;  156 ,  169 ;  173 ,  186 ;  174 ,  187 ;  175 ,  188 ;  176 ,  189  which preferably disconnect the respective component, with all lines. 
     In the case of a fault in a component therefore that component is by-passed by suitable actuation of the switch devices  130 – 136 ,  146 – 156 ,  166 – 176  and  186 – 189  so that, in spite of the fault, the wind power installation still delivers the major part of the power generated or even all the power generated. 
     In order to prevent overloading of the intact components which have remained, and thus to prevent premature failure thereof, those components are preferably over-dimensioned by about 20% so that even when those remaining components are loaded with the output power of a failed component, that does not cause any overloading. 
     The switch devices  130 – 136 ,  146 – 156 ,  166 – 176  and  186 – 189  are in this case so arranged and are controlled in such a manner that admittedly it is possible to by-pass a component such as for example a rectifier  141 ,  142 ,  143 ,  144  or an inverter  161 ,  162 ,  163 ,  164 , but it is not possible to skip over a function implemented by such components. 
     In the event of a failure for example of the inverter  162  the normally open switch devices  150 ,  151 ,  152  can be closed in order to connect the rest of the inverters  161 ,  163 ,  164  to the feed line of the inverter  162 . At the same time the normally closed switch devices  154 ,  167  are actuated and thereby opened in order to disconnect the failed inverter  162 . 
     Finally the normally opened switch devices  170 ,  171 ,  172  can be actuated and thus closed so that the three inverters  161 ,  163 ,  164  again act on all four transformers  181 ,  182 ,  183 ,  184 . 
     In that way the failed inverter  162  is by-passed and, in spite of the failure of the inverter  162 , the wind power installation can deliver all the available power produced. 
       FIG. 3  shows a particularly preferred embodiment of the stator windings and the rectifier connected downstream thereof, using the example of the system  101 . The stator windings  1211  and  1212  with the downstream-connected rectifier  141  are described here. This arrangement which is described by way of example is identical to that of the other redundant systems  102 ,  103 ,  104 . 
     The stator  121  which is not shown in  FIG. 3  carries two stator windings  1211 ,  1212  which are displaced through 30° relative to each other. Both stator windings  1211 ,  1212  are in the form of three-phase current windings and thus each has three phase windings  1213 ,  1214 ,  1215  and  1216 ,  1217 ,  1218 . That total of six phase windings  1213 ,  1214 ,  1215 ,  1216 ,  1217 ,  1218  are connected to a six-phase rectifier  141 . 
     The phase angle between the individual phases  1213 ,  1214 ,  1215  and  1216 ,  1217 ,  1218  of a winding is 120°. If a rotor (not shown) is assumed to be rotating in the clockwise direction, then the phases of the voltages induced in the winding  1211  trail the phases of the voltages induced in the winding  1212 , by 30°. As the phases of a winding are displaced relative to each other through 120°, for example the voltage in the phase  1214  in the winding  1211  trails the voltage in the phase  1217  in the winding  1212  by 30°, but leads the phase  1218  in the winding  1212  by 90°. In that way a part of the exciter power required for the phase  1218  can be produced in the phase  1214 . 
     As both three-phase current windings  1211 ,  1212  are arranged on a stator  121 , an internal redundancy is already embodied here so that, upon failure of a winding  1211 ,  1212 , the other winding  1212 ,  1211  can always still produce output power which is then passed to the rectifier  141 . 
     A preferred embodiment of an inverter  161 ,  162 ,  163 ,  164  according to the invention is shown in  FIG. 4 . The provision of a plurality of inverters  161 ,  162 ,  163 ,  164  provides for external redundancy. 
     Taking the example of the inverter  161  whose structure is the same as the structure of the other inverters  162 ,  163 ,  164 ,  FIG. 4  shows that it is made of three modules  1611 ,  1612 ,  1613  which embody internal resistance. The structure of the individual modules  1611 ,  1612 ,  1613  is the same with each other; in the present case they have IGBTs as switching elements which by suitable actuation produce the ac voltage from the applied dc voltage +Ud and −Ud. In addition the structure and the mode of operation of such modules are known from the state of the art and therefore a detailed description of the mode of operation will not be included here. 
     Each module  1611 ,  1612 ,  1613  produces a three-phase ac voltage from the applied dc voltage and can be connected by way of switches  1614 ,  1615 ,  1616  to the outputs L 1 , L 2 , L 3  of the inverter  161 . 
     The number of modules in an inverter  161 ,  162 ,  163 ,  164  however is not limited to three. It is equally possible to select a different number of modules  1611 ,  1612 ,  1613  and preferably a larger number in order to also embody a desired internal redundancy, besides the external redundancy. 
     The number of modules again makes it possible to implement over-dimensioning in order in this case also to obviate overloading and thus premature failure in the event of a fault in another inverter  161 ,  162 ,  163 ,  164 . 
       FIG. 5  shows a redundant arrangement of transformers  181 ,  182 ,  183 ,  184  which are preferably in the form of three-phase current transformers and which at the primary side are acted upon for example in each case with 3×400 V from the inverters  161 ,  162 ,  163 ,  164  and which on the secondary side deliver for example to a medium-voltage network an ac voltage which is transformed to for example 3×20 kV. 
     Those transformers  181 ,  182 ,  183 ,  184  are preferably also over-dimensioned in order to be able to operate reliably even after being subjected to the application of additional output power from a faulty or failed transformer  181 ,  182 ,  183 ,  184 . 
       FIG. 5  once again shows the switch devices  170 ,  171 ,  172 ,  173 ,  174 ,  175 ,  176 ,  186 ,  187 ,  188 ,  189  which permit by-passing of a failed transformer  181 ,  182 ,  183 ,  184 . In that case switch devices  173 ,  186 ;  174 ,  187 ;  175 ,  188 ;  176 ,  189  permit the primary and secondary windings of the failed transformers  181 ,  182 ,  183 ,  184  to be switched off in order in that way to avoid an impedance shift due to the parallel connection of the primary windings and/or the secondary windings of the transformers  181 ,  182 ,  183 ,  184  upon closure of the switch devices  170 ,  171 ,  172 . 
     For that purpose the switch devices  173 ,  174 ,  175 ,  176  arranged at the primary side and the switch devices  186 ,  187 ,  188 ,  189  arranged at the secondary side are so designed that they galvanically separate all terminals of the corresponding transformer winding. In that respect control is preferably effected in such a way that both switch devices  173 ,  186 ;  174 ,  187 ;  175 ,  188 ;  176 ,  189  at a transformer  181 ,  182 ,  183 ,  184 , that is to say for example the primary-side switch device  174  and the secondary-side switch device  187  at the transformer  182 , are always simultaneously actuated in order reliably to disconnect the transformer  182 . 
       FIG. 6  shows a second embodiment of the present invention. This embodiment corresponds in large parts thereof to the embodiment shown in  FIG. 2  and differs therefrom by virtue of the saving on the switch devices  130 ,  131 ,  132 ,  150 ,  151 ,  152 ,  170 ,  171 ,  172  in  FIG. 2  between each two components, so that the similar components of the individual systems  101 ,  102 ,  103 ,  104  in  FIG. 1  are connected in parallel and accordingly in normal operation are all acted upon by approximately a quarter of the output power produced. 
     In a manner corresponding to the arrangement in the first embodiment the switch devices  133 ,  134 ,  135 ,  136 ,  146 ,  147 ,  148 ,  149 ,  153 ,  154 ,  155 ,  156 ,  166 ,  167 ,  168 ,  169 ,  173 ,  174 ,  175 ,  176 ,  186 ,  187 ,  188 ,  189  are closed in normal operation so that all systems  101 ,  102 ,  103 ,  104  are operating. 
     If now a fault occurs at a component that component is disconnected by opening of the switch devices  133 ,  146 ;  134 ,  147 ;  135 ,  148 ;  136 ,  149 ;  153 ,  166 ;  154 ,  167 ;  155 ,  168 ;  156 ,  169 ;  173 ,  186 ;  174 ,  187 ;  175 ,  188 ;  176 ,  189  arranged in the feed line and the out line of the component in question, and the other components in the other systems  101 ,  102 ,  103 ,  104  ( FIG. 1 ) are automatically acted upon with a higher level of output power. 
     This can also be clearly seen once again from  FIG. 7  in which the transformers  181 ,  182 ,  183 ,  184  are connected in parallel by the normally closed switch devices  173 ,  174 ,  175 ,  176 ,  186 ,  187 ,  188 ,  189 . If now a transformer  181 ,  182 ,  183 ,  184  is found to be defective or faulty the associated switch devices  173 ,  186 ;  174 ,  187 ;  175 ,  188 ;  176 ,  189  are actuated (opened) and the transformer in question is disconnected while the other transformers  181 ,  182 ,  183 ,  184  are respectively acted upon with a higher level of output power and the wind power installation still delivers all the energy produced. 
     Preferably the rectifiers  141 ,  142 ,  143 ,  144  shown by way of example in  FIG. 1  are disposed in the machine housing, that is to say in the pod of the wind power installation. The inverters  161 ,  162 ,  163 ,  164  are preferably disposed in the base region of the pylon of a wind power installation and the inverters and the rectifiers are connected together by way of direct current bus bars  205 ,  206 ,  207 ,  208 . The transformer for feeding the electrical output power produced into the network, in the case of an off-shore wind power installation, can also be disposed in the lowermost base region of a pylon of the wind power installation, that is to say below the water line.