Circuit apparatus for transformerless conversion of an electric direct voltage into an alternating voltage

Abstract

In a circuit apparatus for transformerless conversion of an electric direct voltage of a two-pole direct voltage source ( 1 ) connected to ground having a first voltage pole (+) and a second voltage pole (−) into an alternating voltage, hazardous capacitive leakage currents are avoided by connecting the direct voltage source ( 1 ) to ground and the DC-AC converter ( 400 ) is operated at a controlled intermediate circuit voltage, a DC-DC converter stage ( 300 ) being connected between the direct voltage source ( 1 ) and the DC-AC converter ( 400 ), said DC-DC converter stage providing at its output a +/− voltage that is symmetrical with respect to the grounding point, two series-connected capacitors ( 41, 42 ) having the same polarity and being connected to ground at their connecting point (V) and controlled are charged by two buck-boost choppers ( 100, 200 ) connected one behind the other.

I claim: 
     
       1. A circuit apparatus for transformerless conversion of an electric direct voltage of a two-pole direct voltage source ( 1 ) connected to ground having a first voltage pole (+) and a second voltage pole (−) into an alternating voltage for feeding into an alternating voltage network, a DC-AC converter ( 400 ) for feeding into said alternating voltage network being connected downstream of a DC-DC converter ( 300 ), and two first and second capacitors ( 41 ,  42 ) being present in an intermediate circuit between said the DC-DC converter ( 300 ) and said the DC-AC converter ( 400 ), said capacitors being connected in series and comprising a connection point (V) at ground potential so that a +/− voltage that is symmetrical with respect to ground potential ( 80 ) is available on the an output side of the DC-DC converter stage ( 300 ), characterized in that there is provided comprising:
 a first inverting buck-boost chopper ( 100 ) that is connected in parallel with the direct voltage source ( 1 ) downstream thereof and that is connected such that it charges the first capacitor ( 41 ); and 
 a second inverting buck-boost chopper ( 200 ) that is connected in parallel with said the first inverting buck-boost chopper ( 100 ) downstream thereof and is connected such that it the second inverting buck-boost chopper charges the second capacitor ( 42 ), 
 wherein the twofirst and second inverting buck-boost choppers ( 100 ,  200 ) formingform the DC-DC converter ( 300 ), wherein the first inverting buck-boost chopper ( 100 ) consisting of at least onecomprises a first switch ( 11 ), at least onea first diode ( 21 ) and at least one a first choke ( 31 ), and wherein said second inverting buck-boost chopper ( 200 ) consisting of at least one comprises a second switch ( 12 ), at least one a second diode ( 22 ) and at least one a second choke ( 32 ). 
 
     
     
       2. The circuit apparatus as set forth in  claim 1 , characterized in that each wherein the first and second inverting buck-boost chopper ( 100 ,  200 ) is choppers are configured such that there is to set a fixed DC operating point for the DC-AC converter ( 400 ), and that wherein the direct voltage source ( 1 ) is connected to ground at one of the voltage poles (−). 
     
     
       3. The circuit apparatus as set forth in claim  2  1, characterized in that wherein a controlled +/− DC voltage and/or a controlled constant +/− current is available at the one an input of the DC-AC converter. 
     
     
       4. The circuit apparatus as set forth in claim  3  2, characterized in that a wherein the DC operating point is at least 10% higher than a maximum momentary value of the a grid voltage of a connected grid ( 80 ). 
     
     
       5. The circuit apparatus as set forth in  claim 2 , characterized in that a DC operating point is at least 10% higher than a maximum momentary value of the grid voltage of a connected grid ( 80 ). 
     
     
       6. The circuit apparatus as set forth in  claim 1 , characterized in that wherein the DC-AC converter ( 400 ) is configured to be pulse-width controlled for controlling a sine-shaped current and for controlling an import variable for a grid ( 60 ). 
     
     
       7. The circuit apparatus as set forth in  claim 1 , characterized in that wherein the DC-AC converter ( 400 ) is configured to be single-phase or multiple-phase. 
     
     
       8. The circuit apparatus as set forth in  claim 1 , characterized by an implementation for a photovoltaic generator ( 1 ) as wherein the direct voltage source comprises a photovoltaic generator. 
     
     
       9. A method for diverting capacitive leakage currents away and for protecting persons against hazards and solar generators against damages using a circuit apparatus as set forth in  claim 1 . 
     
     
       10. The circuit apparatus as set forth in claim 1, wherein the first inverting buck-boost chopper consists of the first switch, the first diode and the first choke. 
     
     
       11. The circuit apparatus as set forth in claim 1, wherein the second inverting buck-boost chopper consists of at the second switch, the second diode and the second choke. 
     
     
       12. An apparatus comprising:
 a first inverting buck-boost chopper connected in parallel with a direct voltage source, the first inverting buck-boost chopper comprising a first switch, a first diode and a first choke;   a second inverting buck-boost chopper connected in a cascade arrangement with the first inverting buck-boost chopper, the second inverting buck-boost chopper comprising a second switch, a second diode and a second choke;   a first capacitor, wherein the first inverting buck-boost chopper is connected in parallel with the first capacitor; and   a second capacitor, wherein the second inverting buck-boost chopper is connected in parallel with the second capacitor, and wherein the first capacitor is connected in series with the second capacitor.   
     
     
       13. The apparatus as set forth in claim 12, further comprising an DC-AC converter connected in parallel to the first and second capacitors. 
     
     
       14. The apparatus as set forth in claim 12, wherein the first inverting buck-boost chopper consists of the first switch, the first diode and the first choke, and wherein the second inverting buck-boost chopper consists of at the second switch, the second diode and the second choke. 
     
     
       15. The apparatus as set forth in claim 12, wherein a voltage pole of the direct voltage source is connected to ground. 
     
     
       16. An apparatus comprising:
 a first inverting buck-boost chopper configured to invert a first DC voltage received from a first input terminal and a second input terminal to a first inverted DC voltage;   a second inverting buck-boost chopper configured to invert a second DC voltage to a second inverted DC voltage, the second DC voltage being the same as the first inverted DC voltage;   a first capacitor configured to be charged by the first inverting buck-boost chopper; and   a second capacitor configured to be charged by the second inverting buck-boost chopper, wherein a positive pole of the first capacitor and a negative pole of the second capacitor are connected to a connection point, and wherein the connection point is connected to ground.   
     
     
       17. The apparatus as set forth in claim 16, wherein the connection point is connected to the second input terminal. 
     
     
       18. The apparatus as set forth in claim 16, further comprising an DC-AC inverter configured to invert the first inverted DC voltage and the second inverted DC voltage to an AC voltage. 
     
     
       19. The apparatus as set forth in claim 18, wherein the DC-AC inverter is a multiple phase DC-AC inverter. 
     
     
       20. The apparatus as set forth in claim 16, wherein the first DC voltage is provided by a photovoltaic generator. 
     
     
       21. The apparatus as set forth in claim 16, wherein the first inverting buck-boost chopper comprises a first switch, a first diode and a first choke, and wherein the second inverting buck-boost chopper comprises a second switch, a second diode and a second choke. 
     
     
       22. An apparatus comprising:
 a first input terminal;   a first node, a second node, a third node, and a fourth node;   a first inductor, the first inductor being connected to the first node and the second node;   a first switch, the first switch being connected to the first input terminal and to the first node;   a first diode, a first cathode terminal of the first diode being connected to the first node and a first anode terminal of the first diode being connected to the third node;   a second input terminal, the second input terminal being connected to the second node;   a first output terminal, the first output terminal being connected to the third node;   a second output terminal, the second output terminal being connected to the second node;   a second inductor, the second inductor being connected the second node and the fourth node;   a second switch, the second switch being connected to the third node and the fourth node; and   a second diode, a second anode terminal of the second diode being connected to the fourth node and a second cathode terminal of the second diode being connected to a third output terminal.   
     
     
       23. The apparatus as set forth in claim 22, further comprising
 a first capacitor, the first capacitor being connected to the first output terminal and the second output terminal, and   a second capacitor, the second capacitor being connected to the second output terminal and the third output terminal.   
     
     
       24. The apparatus as set forth in claim 22, further comprising
 a fifth node;   a third switch, the third switch being connected to the first output terminal and the fifth node; and   a fourth switch, the fourth switch being connected to the third output terminal and the fifth node.   
     
     
       25. The apparatus as set forth in claim 22, wherein the second input terminal and the second output terminal are set to ground. 
     
     
       26. An apparatus comprising:
 a first inverting buck-boost chopper configured to invert a first DC voltage received from a first input terminal and a second input terminal to a first inverted DC voltage;   a second inverting buck-boost chopper configured to invert a second DC voltage to a second inverted DC voltage, the second DC voltage being the same as the first inverted DC voltage;   a first capacitor configured to be charged by the first inverting buck-boost chopper;   a second capacitor configured to be charged by the second inverting buck-boost chopper; and   a DC-AC inverter configured to invert the first inverted DC voltage and the second inverted DC voltage to an AC voltage.   
     
     
       27. The apparatus as set forth in claim 26, wherein the DC-AC inverter is a multiple phase DC-AC inverter.