Electric circuit for converting direct current into alternating current
Electric circuit for converting direct into alternating current specially designed for photovoltaic systems connected to the electrical grid without a transformer, and enabling the earthing of one of the input terminals ( 2 ) of the photovoltaic generator, thereby working with a wide range of input voltages and having a high efficiency.
1. Electric circuit for converting direct current into alternating current, being a single-phase inverter circuit that conditions and converts direct current into alternating current, which comprises:
two direct current connections ( 1 , 2 ) to which a source of direct current is connected;
a first temporary energy accumulator (C 1 ) connected between the direct current connections ( 1 , 2 );
a first branch connected between the direct current connections ( 1 , 2 ), and which comprises a first switching element (E 1 ), a first inductance (L 1 ) and a second switching element (E 2 );
a second branch comprising a third switching element (E 3 ), connected at the junction point of the second switching element (E 2 ) with the first inductance (L 1 );
a third branch comprising a fourth switching element (E 4 ), connected at the junction point of the second switching element (E 2 ) with a direct current connection ( 2 );
a second temporary energy accumulator (C 2 ) connected between the third and fourth switching elements (E 3 , E 4 );
a fourth branch comprising a fifth switching element (E 5 ) and a sixth switching element (E 6 ); with the fifth switching element (E 5 ) being connected to the junction point of the second temporary energy accumulator (C 2 ) with the third switching element (E 3 ), and with the sixth switching element (E 6 ) being connected to the junction point of the second temporary energy accumulator (C 2 ) with the fourth switching element (E 4 );
a fifth branch comprising a seventh switching element (E 7 ) that is connected between the junction point of the first switching element (E 1 ) with the first inductance and the junction point of the second temporary energy accumulator (C 2 ) with the fourth switching element (E 4 ) and the sixth switching element (E 6 );
two alternating current connections ( 3 and 4 ), to which an element selected from electrical grid and a load ready to work with alternating current, is connected;
a sixth branch comprising a second inductance (L 2 ) connected between the junction point of the fifth switching element (E 5 ) and the sixth switching element (E 6 ) and an alternating current connection ( 3 ).
2. Electric circuit according to claim 1 wherein:
the first switching element (E 1 ) is selected from MOSFET, IGBT and J-FET transistors;
the second, third, fourth, fifth and sixth switching elements (E 2 , E 3 , E 4 , E 5 and E 6 ) are selected from MOSFET, IGBT and J-FET transistors, connected in antiparallel with respective diodes; the seventh switching element (E 7 ) is diode-type.
3. Electric circuit according to claim 1 wherein an eighth switching element (E 8 ) connected in parallel with the third switching element (E 3 ) and the second switching element (E 2 ) is included.
4. Electric circuit according to claim 3 wherein:
the first and second switching elements (E 1 , E 2 ) are selected from MOSFET, IGBT and J-FET transistors;
the fourth, fifth, sixth and eighth switching element (E 4 , E 5 , E 6 and E 8 ) are selected from MOSFET, IGBT and J-FET transistors, connected in antiparallel with respective diodes, the third and seventh switching element (E 3 and E 7 ) are diode-type.
5. Electric circuit according to claim 1 wherein the first and second temporary energy accumulators (C 1 , C 2 ) are selected from capacitive, ultra capacitive elements, batteries and a combination thereof.
6. Electric circuit according to claim 1 comprising an electromagnetic compatibility filter at a location selected between the direct current connections ( 1 , 2 ), alternating current connections ( 3 , 4 ) and distributed in the circuit.
7. Electric circuit according to claim 2 wherein said circuit is connected to a control unit adapted to control the switching through a series of turn-on signals generated at its output and directed to the first, second, third, fourth, fifth and sixth switching elements (E 1 , E 2 , E 3 , E 4 , E 5 and E 6 ).
8. Electric circuit according to claim 4 wherein said circuit is connected to a control unit adapted to control the switching through a series of turn-on signals generated at its output and directed to the first, second, fourth, fifth, sixth and eighth switching elements (E 1 , E 2 , E 4 , E 5 , E 6 and E 8 ).
9. Electric circuit according to claim 7 or 8 wherein the turn-on signals on the switching elements are carried out by means of pulse width modulation.
10. Electric circuit according to claim 7 or 8 wherein the control unit contains at least one calculation module, comprising at least one programmable electronic device selected from a general purpose processor, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC) and a programmable card (FPGA).
11. Electric circuit according to claim 1 wherein the source of direct current is selected from a photovoltaic unit, an electro-chemical cell unit and a source of direct current.
12. Electric circuit according to claim 1 , wherein the alternating current connection ( 4 ) that is directly connected to the direct current connection ( 2 ) is the neutral terminal.