Enhanced system and method for string balancing

Abstract

A photovoltaic system, including: a plurality of photovoltaic panels having outputs connected in series as a string to provide a string output; a converter coupled to the string to receive the string output as an input and generate a direct current output from the input; a series connection of the string output and the direct current output; and a bus powered at least in part by the series connection of the string output and the direct current output.

What is claimed is: 
     
         1 . A photovoltaic system, comprising:
 a plurality of strings, each string comprising a plurality of photovoltaic panels that provide a string output for the string;   respective converters coupled to corresponding string outputs, each respective converter configured to up-convert a string output voltage at the string output to a target voltage at a converter output of the converter;   a bus coupled to each of the converter outputs, a bus voltage of the bus being set to the target voltage; and   a first string among the plurality of strings, wherein the first string is coupled to the converter of the first string via a first path and wherein the first string is coupled to the bus via a second path.   
     
     
         2 . The photovoltaic system of  claim 1 , wherein the target voltage is the voltage at the string output of the string having the largest string output voltage among the plurality of string outputs. 
     
     
         3 . The photovoltaic system of  claim 1 , wherein the bus is powered by the plurality of strings in parallel. 
     
     
         4 . The photovoltaic of  claim 1 , wherein each converter comprises a bypass switch configured to connect the string output to the bus when the string output is equal to the target voltage. 
     
     
         5 . The photovoltaic system of  claim 1 , wherein each converter is part of a respective logical management unit (LMU), wherein each LMU is configured to measure the string output voltage and compare the string output voltage to the bus voltage to determine the target voltage. 
     
     
         6 . The photovoltaic system of  claim 1 , wherein each converter is part of a respective logical management unit (LMU), wherein each LMU a communication unit to receive data indicating the target voltage. 
     
     
         7 . The photovoltaic system of  claim 6 , wherein each communication unit is wireless. 
     
     
         8 . A method of balancing string outputs, the method comprising:
 coupling a converter to a string output of a first string, the first string comprising a plurality of photovoltaic panels that provide the string output to the converter;   obtaining a target voltage;   up-converting, by the converter, a string output voltage at the string output to the target voltage at a converter output of the converter;   coupling the converter output to a bus, the bus being coupled to a string output of a second string, wherein the target voltage is the based on the voltage of the string output of the second string;   coupling the first string to the converter via a first path; and   coupling the first string to the bus via a second path.   
     
     
         9 . The method of  claim 8 , wherein the string output voltage of the second string is greater than a string output voltage of the first string. 
     
     
         10 . The method of  claim 8 , wherein the bus is powered by the first string and second string in parallel. 
     
     
         11 . The method of  claim 8 , further comprising connecting the string output of the first string to the bus when the string output voltage of the first string is equal to the target voltage. 
     
     
         12 . The method of  claim 8 , further comprising measuring the string output voltage of the first string and comparing the string output voltage of the first string to a bus voltage of the bus to determine the target voltage. 
     
     
         13 . The method of  claim 8 , wherein the converter is part of a respective logical management unit (LMU), wherein each LMU a communication unit to receive data indicating the target voltage. 
     
     
         14 . A method of balancing string outputs, the method comprising:
 coupling a converter to a string output of a first string, the first string comprising a plurality of photovoltaic panels that provide the string output to the converter;   obtaining a target voltage;   generating, by the converter, a current to match a string output voltage at the string output to the target voltage at a converter output of the converter;   coupling the converter output to a bus, the bus being coupled to a string output of a second string, wherein the target voltage is the based on the voltage of the string output of the second string;   coupling the first string to the converter via a first path; and   coupling the first string to the bus via a second path.   
     
     
         15 . The method of  claim 14 , wherein the string output voltage of the second string is greater than a string output voltage of the first string. 
     
     
         16 . The method of  claim 14 , wherein the bus is powered by the first string and second string in parallel. 
     
     
         17 . The method of  claim 14 , further comprising connecting the string output of the first string to the bus when the string output voltage of the first string is equal to the target voltage. 
     
     
         18 . The method of  claim 14 , further comprising measuring the string output voltage of the first string and comparing the string output voltage of the first string to a bus voltage of the bus to determine the target voltage. 
     
     
         19 . The method of  claim 14 , wherein the converter is part of a respective logical management unit (LMU), wherein each LMU a communication unit is configured to receive data indicating the target voltage. 
     
     
         20 . The method of  claim 19 , further comprising wirelessly receiving the data indicating the target voltage.