Photovoltaic System, Direct Current Hybrid Switching Device, Use and Method for Switching a Photovoltaic String On and Off

Abstract

The present disclosure relates to a DC generator that has at least one string, wherein the at least one string is formed by modules which are series-connected by a string line so as to generate a string voltage; and a switching device which is connected in series in the string line, in order to switch on and off the at least one string using the switching device. The switching device comprises a hybrid switch including a relay and a semiconductor switching device connected in parallel to the relay, wherein the semiconductor switching device includes at least one semiconductor switch. The switching device comprises a current sensor which is adapted to measure a negative current flow.

1 . A DC generator, comprising:
 at least one string, wherein the at least one string is formed by modules which are series-connected by a string line so as to generate a string voltage; and   a switching device which is connected in series in the string line, in order to switch on and off the at least one string using the switching device;   wherein the switching device comprises a hybrid switch including a relay and a semiconductor switching device connected in parallel to the relay, wherein the semiconductor switching device includes at least one semiconductor switch; and   wherein the switching device comprises a current sensor which is adapted to measure a negative current flow.   
     
     
         2 . The DC generator of  claim 1 ,
 wherein the hybrid switch defines a closed state and an open state, and in the closed state transfers current from the at least one string to a current collector, and in the open state interrupts the transfer of the current from the at least one string; and   comprising a control device which is configured to open the hybrid switch in a user-controlled manner in response to a user input.   
     
     
         3 . The DC generator of  claim 2 ,
 wherein the hybrid switch is adapted to interrupt the current flow in both directions when in the open state.   
     
     
         4 . The DC generator of  claim 1 ,
 wherein the hybrid switch comprises a parallel circuit of the relay and two back-to-back connected semiconductor switches.   
     
     
         5 . The DC generator of  claim 1 , wherein the switching device is configured,
 when switching on the associated string, to first close the semiconductor switching device, and then, only after a time delay, to close the relay; and   when switching off the associated string, to first open the relay and then, only after a time delay, to open the semiconductor switching device.   
     
     
         6 . The DC generator of  claim 5 ,
 wherein the time delay upon switching on and switching off is less than or equal to 2000 ms, at least if the string carries a string current corresponding to the rated current.   
     
     
         7 . The DC generator of  claim 1 ,
 wherein the switching device comprises a control device and a sensor device connected to the control device for measuring at least one electrical parameter on the associated string, wherein the control device is configured to electrically connect the associated string to a current collector in response to the at least one electrical parameter measured by the sensor device, when release has been accorded by the user.   
     
     
         8 . The DC generator of  claim 7 , wherein said sensor device comprises:
 an input voltage sensor measuring a string side input voltage on the switching device; and   an output voltage sensor measuring a current collector side output voltage on the switching device; and   wherein the control device is configured to electrically connect the associated string to a current collector in response to at least one of the measured string side input voltage or the measured current collector side output voltage, when release has been accorded by the user.   
     
     
         9 . The DC generator of  claim 1 ,
 wherein the switching device is adapted for a DC switching voltage of greater than or equal to 300 V and for a DC lead-through current of greater than or equal to 5 A; and   wherein the hybrid switch produces a power dissipation of less than or equal to 10 W, calculated on the basis of the rated current of the at least one string, when the semiconductor switching device and the relay are closed; and   wherein the semiconductor switching device is adapted for a DC switching voltage of greater than or equal to 300 V.   
     
     
         10 . The DC generator of  claim 9 ,
 wherein the relay is adapted for at least one of the DC lead-through current of greater than or equal to 5 A, or a DC switching current of less than or equal to 8 A; and   wherein the relay has a maximum AC switching voltage of less than or equal to 800 V.   
     
     
         11 . The DC generator of  claim 1 , wherein the at least one semiconductor switch is one or more field effect transistors. 
     
     
         12 . The DC generator of  claim 11 , wherein the one or more field effect transistors are adapted
 for a drain-source voltage (VD's) of greater than or equal to 300 V; and   for a drain current (ID) of greater than or equal to 5 A.   
     
     
         13 . The DC generator of  claim 11 ,
 wherein the one or more field effect transistors have a drain-source on-resistance of greater than or equal to 100 mOhms; and   wherein the one or more field effect transistors produce a power dissipation, calculated on the basis of the rated current of the at least one string, of greater than or equal to 2 W, when the field effect transistors are closed and the relay is open.   
     
     
         14 . The DC generator of  claim 1 , wherein the semiconductor switch is a MOSFET. 
     
     
         15 . The DC generator of  claim 1 , wherein the hybrid switch includes a parallel circuit of the relay and two back-to-back connected field effect transistors. 
     
     
         16 . The DC generator of  claim 1 , wherein the hybrid switch includes a parallel circuit of the relay and two back-to-back connected MOSFETs. 
     
     
         17 . The DC generator of  claim 1 ,
 wherein the current sensor is adapted to measure a negative current flow and a positive current flow, or   wherein the switching device comprises a further current sensor which is adapted to measure a positive current flow.   
     
     
         18 . An electronically controlled DC hybrid switching device configured for a DC generator, for switching off at least one string of the DC generator from a current collector,
 wherein the DC hybrid switching device comprises:
 a hybrid switch including a relay and a semiconductor switching device connected in parallel to the relay; and 
 a current sensor, wherein the current sensor is adapted to measure a negative current flow. 
   
     
     
         19 . A method for switching off and back on individual strings of a DC generator, wherein at least one string of the DC generator comprises a hybrid switching device with a control device and a current sensor which is connected to the control device, wherein the current sensor is adapted to measure a negative current flow, comprising the steps of:
 user-controlled triggering of the switching device of the associated string by a trigger signal in order to individually disconnect the associated string from the current collector;   user-controlled triggering of the switching device of the associated string by a trigger signal in order to individually reconnect the associated string to the current collector.