Abstract:
A feed converter system for small wind energy systems has a rectifier device and an inverter device disposed in a housing, and a common control device is provided for regulating the system components under different load cases, particularly when the wind energy system starts up, or when it is being operated at an optimal operating point.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Applicants claim priority under 35 U.S.C. 119 of German Application No. DE 10 2007 002 986.3 filed Jan. 19, 2007 and German Application No. DE 10 2007 039 726.9 filed Aug. 22, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a feed converter system for small wind energy systems. 
     2. The Prior Art 
     Inverter devices are known from the photovoltaic sector, with which the direct voltage obtained from photo cells can be converted into alternating voltage of a suitable number of volts for the operation of household appliances, for example, or for feed into the power network. Such devices from the photovoltaic sector are usually also used in connection with small wind energy systems, since devices specifically developed for small wind energy systems are often not economically efficient. However, since the wind energy systems are generally equipped with alternating current generators, a rectifier has to be additionally disposed between generator and inverter, in contrast to photovoltaic systems, in order to convert the alternating current having variable frequency, generated by the generator, into an alternating current having a constant frequency of 50 Hz or 60 Hz, which is suitable for being fed into the power network. However, such a combination of devices is complicated during installation, and is not easily manageable, because of the need for different devices. In addition, there is the fact that the small wind energy systems require additional load resistors for start-up or as over-voltage protection, so that at least one additional device is added, further increasing the aforementioned disadvantages. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a feed converter system for small wind energy systems that can be produced and installed in economically efficient manner, and allows the most economically efficient operation of the wind energy system. 
     This object is accomplished by a feed converter system comprising a rectifier device and an inverter device disposed in a housing, and a common control device for regulating the system components under different load cases, particularly when the wind energy system starts up, or when it is being operated at an optimal operating point. Because of the accommodation of rectifier and inverter in a single housing, a single device is obtained, which can be installed in particularly simple manner, and makes available the required functions for feed of the current obtained in the wind energy system into the power network. The common control device ensures that the feed converter system adapts to all the significant operating states of the wind energy system, and guarantees optimized start-up of the wind energy system, in particular, and setting of an optimal operating point during normal operation. 
     In an embodiment of the invention, the control device is configured to regulate the system components as a function of the measurement variables of voltage and/or current, as well as their frequency, and/or the speed of rotation of a synchronous generator of the wind energy system. Taking the aforementioned parameters into consideration allows the best possible adaptation to all the operating states. 
     If a load resistor that serves for start-up of the wind energy system and/or for over-voltage protection is integrated into the housing of the feed converter system, the compactness and simple manageability of the system is further improved. Optionally, the load resistor can be broken up into an internal load resistor having a low power, for over-voltage protection, and an external load resistor having a greater power. Optimally, the external load resistor can be air-cooled or water-cooled. 
     In an embodiment of the invention, a fan is integrated into the housing of the feed converter system, which only circulates the air within the housing, whereby the device cooling takes place by means of external natural air convection. This measure allows a sealed housing without ventilation openings, thereby resulting in a better type of protection of the feed converter system according to IP65. 
     In an embodiment of the invention, the control device is connected with consumers by way of an interface, and comprises consumption management that regulates the flow of energy from the wind energy system to the consumers and/or into the power network, or from the power network to the consumers, as a function of the operating state of the wind energy system. The consumption management is preferably integrated into the control device in the form of a computer program. In the case of low or no wind, it allows purchase of power from the power network to feed the consumers. As soon as the wind energy system supplies sufficient power, the consumers are then switched over for operation on the house power network. If less power is available than the consumers need, the power additionally required is purchased from the public power network. If more power from wind energy is available than the consumers need, the excess energy is fed into the power network. 
     In a further development of the measure last described, it is provided that the interface between control device and consumers comprises radio transmission of the control and regulation signals. In this embodiment, it is possible to do without laying signal lines. The electronics for radio transmission are, of course, also integrated into the same housing as the other components of the feed converter system. Preferably, the radio standard Zigbee 805.3 is used. 
     In an embodiment of the invention, a measurement point is provided in the transition region between a house network and the power network of a utility company, which point is connected with the control device by way of a data channel and transmits data concerning the power flow at the transfer point over this channel. Using the data of this measurement point, the electricity consumers in the house, which can be added and regulated, can be regulated in such a manner that the maximal electric power is used up in the house itself, and not fed into the power network. 
     In a particularly cost-advantageous and advantageous embodiment, the load resistor can be added as an additional consumer, to prevent the feed of excess energy into the power network, and the heat that occurs at the load resistor can be used for heating hot water or for heating. In this manner, the load resistor that otherwise serves for start-up of the wind energy system or as over-voltage protection, which is present in any case, is additionally utilized, without the need for the installation of a separate consumer. Of course, this utilization is only practical if the excess energy can be used in the house in a useful manner, instead of being fed into the power network. Here, heating hot water or heating the house by means of the heat that occurs at the load resistor is a useful effect. 
     In a further development of the invention, a heat pump can be added as an additional consumer, to avoid the feed of excess energy into the power network, and the heat pump can be used for heating or cooling. In contrast to the use of the load resistor as an additional consumer, the heat pump is more complicated in terms of design, but yields a greater benefit than the load resistor, because more heat is available for heating, and cooling is also possible. 
     The aforementioned embodiment can be further improved if the heat pump is disposed directly on the direct current intermediate circuit of the feed converter, by way of an inverter, and can be regulated by means of the control device. In this way, the losses that otherwise occur during the further conversion of the electrical energy can be saved. 
     As a further improvement of the invention, it is proposed that the control device is programmed in such a manner that it allows a deviation from the optimal operating point for a short time, during rapid increases of the speed of rotation or of the output of the synchronous generator, and then slowly returns to the optimal operating point. If the speed of rotation or the output of the synchronous generator increases relatively rapidly, this is generally attributable to wind gusts. However, since wind gusts generally last only a short time, it might not be advisable to add additional consumers in order to absorb the additional energy flow. If the control device now permits a higher speed of rotation, for a short time, than at the optimal operating point, the additional energy contained in the wind gusts is temporarily stored as rotation energy of the rotor of the wind energy system. Afterwards, this additional energy is slowly used up, in that the control device slowly regulates the speed of rotation down, until the optimal operating point has been reached again. This inventive measure allows continuous, uniform utilization of the electric energy for consumers that are classified as having a higher value, for some reason, but whose power consumption is limited in an upward direction. The measure according to the invention therefore allows preferring the “higher-value consumers” over the other consumers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawing. It is to be understood, however, that the drawing is designed as an illustration only and not as a definition of the limits of the invention. 
         FIG. 1  shows a block schematic with a feed converter system according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in detail to the drawing, housing  1  of a feed converter system according to the invention is shown by means of a dotted line. A rectifier  2  and an inverter  3  are integrated into the housing  1 , and are connected with one another by way of a direct current intermediate circuit  26 . Furthermore, a load resistor  4  is disposed in the housing  1 , and electrically connected with the other system components. A control device  5 , which is also disposed in the housing, serves for control. Finally, housing  1  also comprises a fan  6 , with which the air in the interior of housing  1  is circulated. This guarantees that the heat is removed from electric system components  2 ,  3 ,  4 ,  5  and transported to the inside wall of housing  1 . The ambient air flows around housing  1  on the outside, and thereby cools it. 
     Inverter  3  of the feed converter system is connected with electricity consumers  9  of a residence, on the one hand, and with power network  10 , on the other hand, by way of electricity lines  7 ,  8 . An electricity meter  11  is disposed in the immediate vicinity of the connection to power network  10 . Furthermore, additional consumers  12 ,  13  can optionally be added at electricity lines  7 ,  8 . For this purpose, each consumer  12 ,  13  has a switch  14 ,  15  assigned to it. Switches  14 ,  15  are connected with a consumption management of control device  5  by way of a radio interface indicated with broken line  16 . 
     During normal operation of the wind energy system, the alternating current generated by a synchronous generator of the wind energy system, which has a variable frequency, depending on the speed of rotation of the rotor of the wind energy system, flows to the rectifier  2  by way of the feed line  17 . There, the alternating current having a variable frequency is rectified. Load resistor  4  serves as protection against over-voltage, and is also needed when the wind energy system starts up from a standstill. The direct current obtained in this manner is converted to an alternating current having a constant frequency of 50 H, in inverter  3 , and regulated to a voltage of 230 V. Electric power  18  (P wind ) that comes from the wind energy system and is converted in feed converter system gets to electricity consumers  9  of the residence by way of electricity lines  7 ,  8 . 
     If a minimal electric power  18  from wind energy to be parameterized is available, the optional consumers  20  are released for operation. Depending on the programming of the consumption management in control device  5 , the latter adds any desired number of additional consumers  12 ,  13  by means of switches  14 ,  15 . If the wind energy is not completely used up by optional consumers  12 ,  13  and non-switchable household consumers  9 , the excess energy is fed into power network  10 . 
     If the wind energy system cannot make as much electric power  18  available as needed, the consumption management turns the optional consumers off. In this connection, control device  5  takes into consideration operating variables such as speed of rotation, frequency, voltage, and current of the generator of the wind system. 
     Furthermore, a measurement point  23  is disposed in the region of a transfer point  25  between the local house network and power network  10  of the utility company. Measurement point  23  is connected with control device  5  by way of a data channel  24 . Data channel  24  can be configured as a cable, but also without a cable, particularly as a radio connection. By means of measurement point  23 , control device  5  constantly receives current data about the power P purchase  purchased from power network  10  and the power P feed  fed into power network  10 , so that the power flows can be regulated by means of program-controlled reactions of control device  5 . 
     Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 
     REFERENCE SYMBOL LIST 
     
         
           1  housing 
           2  rectifier 
           3  inverter 
           4  load resistor 
           5  control device 
           6  fan 
           7  electricity line 
           8  electricity line 
           9  electricity consumer 
           10  power network 
           11  electricity meter 
           12  consumer 
           13  consumer 
           14  switch 
           15  switch 
           16  broken line/radio interface 
           17  feed line from the generator of the wind energy system 
           18  electric power from wind energy system Pwind 
           19  electric power for residence Phouse 
           20  electric power for optional consumer(s) Poptional 
           21  electric power from the power network Ppurchase 
           22  electric power into the power network Pfeed 
           23  measurement point 
           24  data channel 
           25  transfer point 
           26  direct current intermediate circuit