Device for feeding electrical energy from an energy source

1. A device ( 1 ) for feeding electrical energy from an energy source with variable source voltage into an electric power supply network ( 15 ), said device ( 1 ) including a transformer ( 112 ) for galvanic isolation, a resonant inverter ( 11 ) with semi-conductor switches (a-d; A, B), one or several resonant capacitors ( 17 ; 18 , 19 ; 20 , 21 ) and one rectifier ( 113 ),

characterized in that the device ( 1 ) does not comprise a boost chopper or a buck chopper, and that the resonant inverter ( 11 ) is operated in a full resonant mode if an operating voltage is in a maximum power operation point (MPP) that exists in normal operation, whereby in the maximum power point (MPP) the current from the transformer ( 112 ) is a current made from sinusoidal half-waves, and the resonant inverter ( 11 ) is operated in a hard-switching mode if the voltages exceed the maximum operation point (MPP), so that the current from the transformer ( 112 ) comprises sine-wave portions, whereby the hard-switching mode only occurs in a start-up phase.

2. The device as set forth in claim 1 ,

characterized in that, in the operation point (MPP), the semi-conductor switches (a-d; A, B) of the resonant inverter ( 111 ) are operated with a duty cycle that is more than half a period of a resonance frequency of an oscillating circuit comprising one resonant capacitor or several resonant capacitors and of a transformer leakage inductance, at pulse widths ranging between 30 and 50% of a period of a pulse frequency, so that a voltage at an intermediate circuit capacitor ( 12 ) will not fall below a minimum value needed for feeding the network ( 15 ), even if a voltage at the maximum power point (MPP) of the energy source adopts a minimum voltage value imposed by the device, and that, if the voltages of the energy source are higher than the maximum power point voltage, said semi-conductor switches are operated at pulse widths of between zero and 50% so that the voltage at the intermediate circuit capacitor ( 12 ) will not exceed a maximum value given by an electric strength of the semi-conductor switches (a-d, A, B) of a regen-capable inverter ( 13 ), even if the voltage of the energy source is higher than the (MPP) voltage.

3. The device as set forth in claim 1 ,

characterized in that semi-conductor switches of the same electric strength as semi-conductor switches (a-d; A, B) are used in the resonant inverter ( 11 ) and in the regen-capable inverter ( 13 ).

4. The device as set forth in claim 1 ,

characterized by an implementation such that, in the hard-switching operation above the operation point (MPP), a transformer current of the transformer ( 112 ) consists of sine-wave portions.

5. The device as set forth in claim 1 ,

characterized in that the transformer ( 112 ) is a high-frequency transformer ( 112 ) and is operated at a frequency that is higher than a frequency of the energy supply network ( 15 ).

6. The device as set forth in claim 1 ,

characterized in that a high-frequency inverter ( 111 ), which is part of the resonant inverter ( 11 ) and comprises the semi-conductor switches (a-d; A, B), which are performed as MOS transistors, IGBT's, or GTO's, is mounted upstream of the transformer ( 112 ).

7. The device as set forth in claim 2 ,

characterized in that the regen-capable inverter ( 13 ) is a one-phase or a three-phase inverter.

8. The device as set forth in claim 1 ,

characterized in that the resonant inverter ( 11 ) comprises a full bridge.

9. The device as set forth in claim 1 ,

characterized in that the resonant inverter ( 11 ) comprises a half-bridge.

10. The device as set forth in claim 9 ,

characterized in that the resonant inverter ( 11 ) is performed as a centre tap connection circuit.

11. The device as set forth in claim 1 ,

characterized in that the rectifier ( 113 ) is devised as a half-bridge.

12. The device as set forth in claim 1 ,

characterized in that the one or several resonant capacitors ( 17 ; 16 , 19 ; 20 , 21 ) are connected in series or in parallel with a resonant circuit with respect to a primary winding of the transformer ( 112 ).

13. A device for feeding electrical energy as set forth in claim 1 ,

characterized in that a resonant capacitor ( 20 , 21 ) is connected in series or in parallel with a secondary winding of the transformer ( 112 ).

14. The device as set forth in claim 1 ,

characterized in that the the one or several resonant capacitors ( 18 , 19 ) of a half-bridge located on the primary side of the transformer ( 112 ) are utilized as resonant capacitors.

15. The device as set forth in claim 1 ,

characterized in that the one or several resonant capacitors ( 20 , 21 ) of a secondary side half-bridge are utilized as resonant capacitors.

16. The device as set forth in claim 1 ,

characterized in that a high-frequency inverter ( 111 ), the transformer ( 112 ) and the rectifier ( 113 ) form a resonant converter that is a DC/DC converter, a natural frequency formed by the one or more resonant capacitors ( 17 ; 18 , 19 ; 20 , 21 ) of a leakage inductance of the transformer ( 112 ) being higher than a switching frequency of the resonant inverter ( 11 ) in order to minimize switching losses in the semi-conductor switches (a-d; A, B) of the resonant inverter ( 11 ) as compared to a hard-switching mode of operation.

17. A device for feeding electrical energy as set forth in claim 1 ,

characterized in that a leakage inductance of the transformer ( 112 ) is complemented by one or several additional inductances in order to achieve a desired resonance frequency.

18. The device as set forth in claim 1 ,

characterized in that, on a primary side, several resonant inverters ( 11 ) are mounted in parallel at the energy source and, on a secondary side, are connected to a common intermediate circuit capacitor ( 12 ) discrete resonant inverters ( 11 ) being clocked at different times.

19. The device as set forth in claim 1 ,

characterized in that the resonant inverter ( 11 ) is connected to a regen-capable inverter ( 13 ).

20. A system with a device as set forth in claim 1 and with the energy source,

characterized in that the energy source is solar generator ( 10 ), a fuel cell, a battery, a wind power plant with a permanent-magnet generator, a combustion engine with a permanent-magnet generator or a water power plant with a permanent-magnet generator (PM-generator).

21. Use of a device as set forth in claim 1 , in a public energy supply network supplying a plurality of consumers or an island network with one or several consumers.

22. A method of operating a device as set forth in claim 1 , the energy source of which is a photovoltaic solar generator with at least one maximum power point (MPP) of a solar generator characteristic line, the resonant inverter ( 11 ) being operated in the full resonant mode in the MPP and in the hard-switching mode when the voltage exceeds the MPP.

23. The device as set forth in claim 1 ,

characterized in that high-performance semi-conductors capable of being switched off are mounted in parallel with the diodes D 5 through D 8 of the resonant rectifier ( 113 ) so that a circuit may be operated in both directions if the energy source is an energy accumulating device.