Distributed substring architecture for maximum power point tracking of energy sources

Abstract

A photovoltaic array system includes multiple strings of series coupled photovoltaic modules to provide current at a voltage dependent on the number of modules in each string and their operating efficiency. Each string is coupled to a DC-to-DC converter to convert the current from each string for output to a DC bus. An inverter is coupled to DC bus to convert the current from the strings of series coupled photovoltaic modules to AC current at a grid-compatible voltage.

1 . (canceled) 
     
     
         2 . A photovoltaic combiner comprising a plurality of independent DC-DC converters, each converter accepting input from a string of photovoltaic modules, performing maximum power point tracking (MPPT) tracking, and providing its output to a common DC bus having DC rails, wherein the DC-to-DC converters are adapted to maintain bus stability by a concerted autonomous current response of the DC-to-DC converters, with the aggregate effect of controlling the DC bus voltage in cooperation with other units coupled to DC rails of the common DC bus. 
     
     
         3 . The photovoltaic combiner of  claim 2  wherein each DC-to-DC converter autonomously Berates it output linearly in response to a sensed voltage of the DC rails passes a pre-determined threshold. 
     
     
         4 . The photovoltaic combiner of  claim 2  wherein bus stability is maintained by controlling a duty cycle of a pulse width modulated signal to a DC-to-DC converter switch. 
     
     
         5 . The photovoltaic array system of  claim 2  wherein the DC-to-DC converters provide maximum powerpoint tracking. 
     
     
         6 . The photovoltaic array of  claim 5  wherein the maximum powerpoint tracking for each string is independent of other strings. 
     
     
         7 . The photovoltaic array system of  claim 2  wherein at least one string comprises between 4 and 10 modules. 
     
     
         8 . The photovoltaic array system of  claim 2  wherein the number of modules in a string is optimized to provide a voltage output suitable for efficient conversion to a regulated voltage. 
     
     
         9 . The photovoltaic array system of  claim 2  wherein at least one string includes a number of modules such that a voltage of the string provided to its corresponding dc to dc converter is approximately 240V. 
     
     
         10 . The photovoltaic array of  claim 9  wherein each dc to dc converter provides a set collection voltage of approximately 380 V to the DC bus. 
     
     
         11 . The photovoltaic array system of  claim 2  wherein the action of each DC-to-DC converter is independent of the other DC-to-DC converters. 
     
     
         12 . The photovoltaic array system of  claim 2  wherein the DC bus comprises two conductors, the two conductors operating at substantially equal and opposite voltage with respect to neutral. 
     
     
         13 . A photovoltaic array system comprising:
 a first string of series-coupled photovoltaic modules, said first string being coupled to a first DC-to-DC converter, wherein the first DC-to-DC converter converts a DC output of the first string, for output to a DC bus having DC rails;   a second string of series-coupled photovoltaic modules, said second string being coupled to a second DC-to-DC converter, wherein the second DC-to-DC converter converts a DC output of the second string for output to the DC bus in parallel to the output of the first converter; and   an inverter coupled to the DC bus, said inverter converting the DC outputs of the first and second DC-to-DC converters to an AC output, wherein the DC-to-DC converters maintain bus stability by a concerted autonomous current response of the DC-to-DC converters, each DC-to-DC converter autonomously derating its output linearly once a sensed voltage between the DC rails passes a pre-determined threshold, with the aggregate effect of controlling the DC bus voltage.   
     
     
         14 . The photovoltaic array system of  claim 13  wherein the DC-to-DC converters provide maximum powerpoint tracking. 
     
     
         15 . The photovoltaic array of  claim 14  wherein the maximum powerpoint tracking for each string is independent of other strings. 
     
     
         16 . The photovoltaic array system of  claim 13  wherein at least one string comprises between 4 and 10 modules. 
     
     
         17 . The photovoltaic array system of  claim 13  wherein the number of modules in a string is optimized to provide a voltage output suitable for efficient conversion to a regulated voltage. 
     
     
         18 . The photovoltaic array system of  claim 13  wherein at least one string includes a number of modules such that a voltage of the string provided to its corresponding dc to dc converter is approximately 240V. 
     
     
         19 . The photovoltaic array of  claim 18  wherein each dc to dc converter provides a set collection voltage of approximately 380 V to the DC bus. 
     
     
         19 . The photovoltaic array system of  claim 13  wherein the action of each DC-to-DC converter is independent of the other DC-to-DC converters. 
     
     
         20 . The photovoltaic array system of  claim 13  wherein the DC bus comprises two conductors, the two conductors operating at substantially equal and opposite voltage with respect to neutral. 
     
     
         21 . A method comprising:
 receiving DC current on DC rails from multiple sets of series coupled photovoltaic modules, the current being at a voltage dependent on the number of modules in each set;   independently converting the current from each set to a selected DC set collection voltage;   providing the current from each set at the set collection voltage to a set collection line;   receiving a voltage representative of sensed voltage of the DC rails; and   providing the currents from each set via the set collection line to an inverter to convert the currents to an AC current, wherein the current from each set at the set col lection voltage is autonomously modified by each set and the AC current from the inverter is autonomously modified to maintain bus stability, wherein each DC-to-DC converter autonomously derates its output once the sensed voltage passes a pre-determined threshold.