Inverter, more specifically for photovoltaic plants

Abstract

On an inverter ( 1 ) for converting an electric direct voltage, in particular of a photovoltaic direct voltage source into an alternating voltage with a direct voltage input with two terminals (DC+, DC−) and one alternating voltage output with two terminals (AC 1, AC 2 ) and with one bridge circuit including semiconductor switching elements (S 1 -S 6 ), said bridge circuit comprising one first bridge branch (Z 1 ) including four switching elements (S 1 -S 4 ) and one second bridge branch (Z 2 ) including two additional switching elements (S 5, S 6 ) as well as a freewheeling circuit provided with additional diodes (D 7, D 8 ), the efficiency is further increased without high frequency interferences and capacitive leakage currents having the possibility to occur on the generator side. This is achieved in that a respective one of the freewheeling diodes (D 7, D 8 ) forms a freewheeling branch together with a respective one of the switching elements (S 2, S 3 ) located in the first bridge branch (Z 1 ), said freewheeling branch carrying a freewheeling current in a condition decoupled from the direct voltage.

We claim: 
     
       1. An inverter for converting an electric direct voltage, more specifically of a photovoltaic direct voltage source, into an alternating voltage with a, the inverter comprising: 
 direct voltage input with two terminals between which there is provided;  
 a bridge circuit arranged in parallel,;  
 grid chokes being provided at the alternating voltage outputs of said bridge circuit, for connecting the bridge circuit to alternating output terminals; and with an 
 alternating voltage output with two terminals, 
 characterized in that there is providedwherein  
 a first bridge branch with at least of the bridge circuit comprises four series connected first through fourth switching elements and a second bridge branch with at least one of the bridge circuit comprises a fifth and one a sixth switching element and that, between the alternating voltage terminal, which takes departure from said second bridge branch, and the, 
 a first connecting point between the second and the third switching elements in the first bridge branch is connected to a first alternating output terminal, 
 a second connecting point corresponding to between the fifth and sixth switching element provided elements in the second bridge branch and the respective is connected to a second alternating output terminal, 
 a third connecting points point between the first and the second or the third and the fourth switching element elements of the first bridge branch there is respectively connected one via a first diode in the direction opposite the forward direction so that a respective one of the central second or third switches of the first bridge branch and a respective one of the diodes carries a freewheeling current in a condition decoupled from the direct voltage to the second connecting point, wherein a cathode of the first diode is connected to the third connecting point, and 
 a fourth connecting point between the second and the third switching elements of the first bridge branch is connected via a second diode to the second connecting point, wherein an anode is connected to the fourth connecting point. 
 
     
     
       2. The inverter as set forth in  claim 1 , characterized in that all wherein the first through sixth switching elements and the first and second diodes are integrated in a semiconductor module. 
     
     
       3. The inverter as set forth in  claim 1 ,
 characterized by an implementation aswherein the inverter is a transformerless inverter. 
 
     
     
       4. The inverter as set forth in  claim 1 ,
 characterized by awherein the inverter comprises a multiple phase implementation. 
 
     
     
       5. A method of converting an electric direct voltage into an alternating voltage with an inverter as set forth in  claim 1 , characterized in that both triggering signals at mains frequency and such with a high clock frequency are available for the first through sixth switching elements of the bridge circuit, wherein the second switching element being is clocked at mains frequency and the first and sixth switching element being is clocked at a high clock rate during a half wave of the grid voltage, wherein the third switching element being is clocked at the mains frequency and the fourth and fifth switching elements is clocked at a the high clock rate during the other half wave of the grid voltage, and wherein the first, fourth, fifth and sixth switching elements being triggered so asymmetrically are switched such that the first or the fourth switching element of the first bridge branch is respectively triggered switched, whilst the fifth or the sixth switching element of the second bridge branch is clocked switched at the same clock rate and that, during at least one freewheeling phase, a freewheeling current flows through the second switching element and the first diode at the one half wave of the grid voltage or that a freewheeling current flows through the third switching element and the second diode at the other half wave of the grid voltage so that the alternating voltage circuit decouples from the direct voltage circuit during freewheeling. 
     
     
       6. The method of converting an electric direct voltage into an alternating voltage with an inverter as set forth in  claim 5 ,
 characterized in thatwherein the second and third switching elements of the first bridge branch are connected at mains frequency, in particular at 50 Hz or 60 Hz, whilst the two other first and fourth switching elements of the first bridge branch as well as the fifth and sixth switching element of the second bridge branch are clocked at high frequency, in particular in the kHz range. 
 
     
     
       7. The method of converting an electric direct voltage into an alternating voltage with an inverter as set forth in  claim 5 ,
 characterized in thatwherein the first switching element of the first bridge branch and the sixth switching element of the second bridge branch are clocked in synchronism during the one half wave of the grid voltage and that the switching element of the first bridge branch and the switching element of the second bridge branch are clocked in synchronism during the other half wave of the grid voltage. 
 
     
     
       8. The method as set forth in  claim 7 ,
 characterized in thatwherein the additional switching elements located in the first bridge branch are clocked at high frequency in synchronism with the two other fifth and sixth switching elements of the second bridge branch. 
 
     
     
       9. The method as set forth in  claim 7 ,
 characterized in thatwherein part of the switching elements, in particular the first, second, fourth and fifth switching elements, which are clocked at high frequency, are triggered with pulse-width modulation. 
 
     
     
       10. A method for converting an electric photovoltaic direct voltage into an alternating voltage with an inverter as set forth in  claim 1 . 
     
     
       11. A method for converting an electric photovoltaic direct voltage into an alternating voltage with a method as set forth in  claim 5 . 
     
     
       12. An inverter comprising:
 direct voltage input terminals;   alternating voltage output terminals; and   a bridge circuit connected to the direct voltage input terminals and the alternating voltage output terminals, wherein the bridge circuit is configured to transform a direct voltage into an alternating voltage, wherein the bridge circuit comprises six switching elements, wherein a first bridge branch comprises four switching elements in series, and wherein a second bridge branch comprises two switching elements in series.    
     
     
       13. The inverter as set forth in claim 12, further comprising a first inductor and a second inductor, wherein the first inductor is connected to the first bridge branch at a first connection point, and wherein the second inductor is connected to the second bridge branch at a second connection point.  
     
     
       14. The inverter as set forth in claim 13, wherein the second inductor is further connected to the first bridge branch at a third connection point via a first diode and a fourth connection point via a second diode.  
     
     
       15. The inverter as set forth in claim 14, wherein a cathode of the first diode is connected to the third connection point and an anode of the first diode is connected to the second connection point, and wherein an anode of the second diode is connected to the fourth connection point and a cathode of the second diode is connected to the second connection point.  
     
     
       16. The inverter as set forth in claim 13, wherein the first connection point is between two upper switching elements and two lower switching elements, and wherein the second connection point is between an upper switching element and a lower switching element.  
     
     
       17. The inverter as set forth in claim 13, wherein the second inductor is further connected to the first bridge branch between a first switching element and a second switching element, and between a third switching element and a fourth switching element.  
     
     
       18. An inverter comprising:
 direct voltage input terminals;   alternating voltage output terminals; and   a bridge circuit connected to the direct voltage input terminals and the alternating voltage output terminals, wherein the bridge circuit is configured to transform a direct voltage into an alternating voltage, wherein the bridge circuit comprises six switching elements, wherein a first bridge branch comprises four switching elements in series, wherein a second bridge branch comprises two switching elements in series, wherein the bridge circuit is configured such that   for a first period of time, a first switching element of the first bridge branch and a second switching element of the second bridge branch are closed while a second switching element of the first bridge branch and a first switching element of the second bridge branch are open, and   for a second period of time, the second switching element of the first bridge branch and the first switching element of the second bridge branch are closed while the first switching element of the first bridge branch and the second switching element of the second bridge branch are open.    
     
     
       19. The inverter as set forth in claim 18, wherein the bridge circuit is further configured such that, between the first period of time and the second period of time, the first and second switching elements of the first and second bridge branches are open and a first period of freewheeling occurs.  
     
     
       20. The inverter as set forth in claim 19, wherein the bridge circuit is further configured such that, after the second period of time, the first and second switching elements of the first and second bridge branches are open and a second period of freewheeling occurs.  
     
     
       21. The inverter as set forth in claim 18, wherein the first and second switching elements of the first and second bridge branches are configured to switch with the same frequency.  
     
     
       22. The inverter as set forth in claim 18, wherein the bridge circuit is further configured such that, between the first period of time and the second period of time, a first period of freewheeling occurs through a first diode and a first central switching element of the first bridge branch.  
     
     
       23. The inverter as set forth in claim 22, wherein the bridge circuit is further configured such that, after the second period of time, a second period of freewheeling occurs through a second diode and a second central switching element of the first bridge branch.  
     
     
       24. The inverter as set forth in claim 23, wherein the first and second switching elements of the first and second bridge branches are configured to switch with a first frequency, wherein the first and second central switching elements are configured to switch with a second frequency, and wherein the second frequency is higher than the first frequency.  
     
     
       25. An inverter comprising:
 direct voltage input terminals;   a first alternating voltage output terminal;   a second alternating voltage output terminal; and   a bridge circuit connected to the direct voltage input terminals and the first and second alternating voltage output terminals, wherein the bridge circuit is configured to transform a direct voltage into an alternating voltage, wherein the bridge circuit comprises:
 a first bridge branch having four switching elements in series, wherein the first bridge branch comprises first to third connection points, and wherein the first connection point is connected to the first alternating voltage output terminal; 
 a second bridge branch having two switching elements in series, wherein the second bridge branch comprises a fourth connection point, and wherein the fourth connection point is connected to the second alternating voltage output terminal; 
 a first diode connected to the second connection point and a fifth connection point; and 
 a second diode connected to the third connection point and the fifth connection point, and wherein the fourth connection point is connected to the fifth connection point.  
   
     
     
       26. The inverter as set forth in claim 25, further comprising a first inductor and a second inductor, wherein the first inductor is connected between the first connection point and the first alternating voltage output terminal, and wherein the second inductor is connected between the fourth connection point and the second alternating voltage output terminal.  
     
     
       27. The inverter as set forth in claim 25, wherein a cathode of the first diode is connected to the second connection point and an anode of the first diode is connected to the fifth connection point.  
     
     
       28. The inverter as set forth in claim 27, wherein a cathode of the second diode is connected to the fifth connection point and the anode of the second diode is connected to the third connection point.  
     
     
       29. The inverter as set forth in clam 25, wherein outer switching elements of the first bridge branch are configured to be clocked at a first frequency, and wherein the inner switching elements of the first bridge branch are configured to be clocked at a second frequency, the first frequency being different than the second frequency.  
     
     
       30. The inverter as set forth in claim 29, wherein the second frequency is higher than the first frequency.  
     
     
       31. The inverter as set forth in claim 30, wherein the second frequency is a mains frequency.  
     
     
       32. The inverter as set forth in claim 29, wherein the two switching elements of the second bridge branch are configured to be clocked at the first frequency.  
     
     
       33. An inverter comprising:
 direct voltage input terminals;   alternating voltage output terminals; and   a bridge circuit between the direct voltage input terminals and the alternating voltage output terminals, the bridge circuit comprising:
 a first bridge branch comprising four switching elements in series, wherein the four switching elements comprise a first switching element, a second switching element, a third switching element, and a fourth switching element; and 
 a second bridge branch comprising two switching elements in series, wherein the two switching elements comprise a fifth switching element and a sixth switching element, wherein the second and third switching elements are configured to switch at a first frequency and wherein the first switching element and the fourth to sixth switching elements are configured to switch at a second frequency, the second frequency being different than the first frequency.  
   
     
     
       34. The inverter as set forth in claim 33, wherein a first diode is connected between a first connection point of the first bridge branch and a first alternating voltage output terminal.  
     
     
       35. The inverter as set forth in claim 34, wherein a second diode is connected between a second connection point of the first bridge branch and the first alternating voltage output terminal.  
     
     
       36. The inverter as set forth in claim 35, further comprising a first inductor and a second inductor, wherein the first inductor is connected to the first bridge branch, and wherein the second inductor is connected to the second bridge branch.  
     
     
       37. The inverter as set forth in claim 33, wherein the first frequency is higher than the second frequency, and wherein the first frequency is a mains frequency.  
     
     
       38. An inverter comprising:
 direct voltage input terminals;   alternating voltage output terminals comprising a first alternating voltage terminal and a second alternating voltage terminal;   a bridge circuit between the direct voltage input terminals and the alternating voltage output terminals, the bridge circuit comprising:
 a first bridge branch comprising four switching elements in series, wherein the four switching elements comprise a first switching element, a second switching element, a third switching element, and a fourth switching element; and 
 a second bridge branch comprising two switching elements in series, wherein the two switching elements comprise a fifth switching element and a sixth switching element, 
 a first connection path connecting the first bridge branch to the first alternating voltage output terminal; and 
 a second connection path connecting the first bridge branch and the second bridge branch to the second alternating voltage output terminal.  
   
     
     
       39. The inverter as set forth in claim 38, wherein the second connection path comprises a first diode.  
     
     
       40. The inverter as set forth in claim 39, wherein a cathode of the first diode is connected to first bridge branch.  
     
     
       41. The inverter as set forth in claim 40, wherein the second connection path comprises a second diode.  
     
     
       42. The inverter as set forth in claim 41, wherein a anode of the second diode is connected to the second connection path.  
     
     
       43. The inverter as set forth in claim 38, wherein the first and fourth switching elements are configured to switch at a first frequency, wherein the second and third switching elements are configured to switch at a second frequency, and wherein the fifth and the sixths switching elements switch are configured to switch at a third frequency.  
     
     
       44. The inverter as set forth in claim 38, wherein the second frequency is higher than the first frequency and the third frequency.  
     
     
       45. The inverter as set forth in claim 44, wherein the first frequency and the third frequency are the same.