Switching device and method, in particular for photovoltaic generators
The subject matter of the invention is an inverter ( 3 ), more specifically for use in a photovoltaic plant ( 1 ) with a direct voltage input (connection terminals 4; 5 ) for connection to a generator ( 2 ) and an alternating voltage output (connection terminals 7; 8 ) for feeding into an energy supply network ( 6 ) as well as with a DC-AC converter ( 12 ) with semiconductor switch elements ( 15 ) and an intermediate circuit ( 11 ), at least one short-circuit switch element ( 18 ) being connected in parallel to the generator ( 2 ), so that the voltage will not exceed a maximum voltage value neither at the connection terminals ( 4; 5 ) of the generator ( 2 ) nor between the connection terminals ( 9; 10 ) of the inverter. This is achieved in that the inverter ( 3 ) comprises, in the intermediate circuit ( 12 ), a buffer capacitor ( 14 ) that is connected to the generator ( 2 ) through a protection diode ( 17 ) so that said buffer capacitor ( 14 ) will not be discharged upon actuation of the short-circuit switch element ( 18 ), the generator ( 2 ) working according to a clock rate in the short-circuit mode of operation.
1. A method of operating an inverter connected to a photovoltaic generator through a boost converter with a short-circuit switch element, the method comprising:
monitoring a voltage associated with an intermediate circuit within the inverter;
switching the generator into a short-circuit mode by closing and maintaining closed, subject to a current-limit mode condition, the short-circuit switch element when the monitored voltage exceeds a threshold voltage; and
switching the generator out of the short-circuit mode by opening the short-circuit switch element after the monitored voltage has dropped below the threshold voltage,
wherein switching the generator into the short-circuit mode subject to the current-limit mode condition comprises monitoring a current in the short-circuit switch element and opening the switch if the current exceeds a predetermined limit, and subsequently closing the short-circuit switch element again.
2. An inverter, comprising:
a DC input terminal configured to couple to a source of DC energy;
an intermediate circuit configured to provide a temporary storage of DC energy provided by a DC voltage at the DC input terminal;
a voltage limiting circuit coupled to the DC input terminal, and configured to generate and maintain a short-circuit condition, subject to a current-limit mode condition, at the DC input terminal when a monitored voltage associated with a DC voltage within the intermediate circuit exceeds a predetermined threshold; and
a DC/AC converter configured to convert a DC voltage provided at the DC input terminal into an AC voltage, and provide the AC voltage to an output terminal,
wherein the voltage limiting circuit is further configured to monitor a current therein when the short-circuit condition is generated, and temporarily suspend the short-circuit condition if the current exceeds a predetermined value.