Power Factor Adjustment in Multi-Phase Power System

Abstract

A multi-phase power generation system for renewable energy, in which reactive elements (i.e., capacitors and/or inductors) can be selectively switched in and out in order to meet a particular power factor requirement, is provided. Each phase of the multi-phase power system receives generated powers from a set of inverters, and each phase has a set of switch reactive elements for making power factor adjustments to the power generated by the set of inverters. The power outputs of the set of inverters belonging to a particular phase are combined into a one combined ac power output, and the power factor adjustment for that particular phase is performed on the combined power output by the set of the switch reactive elements of that particular phase. In some embodiments, at least some of the inverters are micro-inverters that convert DC power from one or two solar panels to AC power.

What is claimed is: 
     
         1 . A system for multi-phase volt-ampere reactive (VAR) control in a multi-phase power generation system comprising:
 a plurality of sets of inverters for converting DC power generated by an array of solar panels into AC power;   a plurality of AC current combiners, each combiner combining power output from one set of inverters from the plurality of sets of inverters into a combined AC power output for one phase of the multi-phase power generation system;   a plurality of reactive power compensators, each reactive power compensator comprising a set of reactive elements, each reactive element switchable to be connected to the combined AC power output for performing power factor adjustment for one phase of the multi-phase power generation system; and   a plurality of VAR control modules, one for each phase of the multi-phase power generation system, each operable to perform a power factor adjustment operation on the combined AC power output for that phase based on a grid requirement and the combined AC power output of that phase.   
     
     
         2 . The system of  claim 1  further comprising a grid sensor coupled to an output of each VAR control module and configured to measure a voltage and a current being injected into the grid for that phase. 
     
     
         3 . The system of  claim 2  wherein a micro-controller is coupled to the grid sensor and performs a computation based on the measured voltage and current to determine which of the reactive elements in the set of reactive elements to switch in or to switch out. 
     
     
         4 . The system of  claim 3  wherein the micro-controller also determines a displacement power factor to determine which of the reactive elements in the set of reactive elements to switch in or to switch out. 
     
     
         5 . The system of  claim 1  further comprising a communications link that transmits a required necessary power factor adjustment value to a micro-controller. 
     
     
         6 . The system of  claim 5  wherein a micro-controller determines which of the reactive elements in the set of reactive elements to switch in or to switch out based on the necessary power factor adjustment value. 
     
     
         7 . The system of  claim 1  further comprising a communications link that commands each VAR control module to switch in or to switch out reactive elements in the set of reactive elements. 
     
     
         8 . The system of  claim 1 , wherein the set of reactive elements comprises a plurality of capacitors and a plurality of inductors. 
     
     
         9 . The system of  claim 1 , wherein each of the plurality of sets of inverters are micro-inverters for converting DC power from photovoltaic (PV) cells from one solar panel. 
     
     
         10 . A system for performing power factor correction in a multi-phase power generation system comprising:
 a plurality of micro-inverters, each micro-inverter receiving DC power at an input and generating AC power at an output;   an AC combiner for each phase of the multi-phase power generation system, each AC combiner receiving AC power from a set of the plurality of micro-inverters and generating a combined AC output for each phase of the multi-phase power generation system;   a volt-ampere reactive (VAR) control module for each phase of the multi-phase power generation system, each VAR control module having an input coupled to an output of an AC combiner and an output coupled to one phase of a multi-phase AC grid, the VAR control module operable to perform a power factor adjustment operation on the combined AC power output for each phase based on a an AC grid requirement and voltage and current measurements of the combined AC power output of that phase, wherein each VAR control module includes a plurality of reactive power compensators, each reactive power compensator comprising a set of reactive elements, each reactive element switchable to be connected to the combined AC power output for that phase for performing power factor adjustment for that phase.   
     
     
         11 . The system of  claim 10  wherein a grid sensor is coupled to the output of the VAR control module and configured to measure the voltage and current of the combined AC power output. 
     
     
         12 . The system of  claim 11  wherein a micro-controller is coupled to the grid sensor and performs a computation based on the measured voltage and current to determine which of the reactive elements in the set of reactive elements to switch in or to switch out. 
     
     
         13 . The system of  claim 12  wherein the micro-controller also determines a displacement power factor to determine which of the reactive elements in the set of reactive elements to switch in or to switch out. 
     
     
         14 . The system of  claim 10 , wherein the set of reactive elements comprises a plurality of capacitors and a plurality of inductors. 
     
     
         15 . The system of  claim 10 , wherein each of the plurality of micro-inverters receives the DC power from photovoltaic (PV) cells from one solar panel. 
     
     
         16 . A method of compensating reactive power in a multi-phase power generation system, the method comprising:
 generating AC power with a plurality of micro-inverters;   combining AC power outputs of a set of the plurality micro-inverters for one phase of the multi-phase system into one combined AC power output for that phase;
 receiving a current measurement and a voltage measurement for the combined AC power output for that phase; and 
 performing a power factor adjustment operation on the combined AC power output for that phase with a volt-ampere reactive (VAR) control module including a plurality of reactive power compensators, each reactive power compensator comprising a set of reactive elements, each reactive element switchable to be connected to the combined AC power output for that phase for performing power factor adjustment for that phase based on the current measurement, the voltage measurement and an AC grid requirement. 
   
     
     
         17 . The method of  claim 16  further comprising measuring a voltage and a current being injected into the AC grid for that phase with a grid sensor that is coupled to an output of the VAR control module. 
     
     
         18 . The method of  claim 17  wherein a micro-controller is coupled to the grid sensor and performs a computation based on the measured voltage and current to determine which of the reactive elements in the set of reactive elements to switch in or to switch out. 
     
     
         19 . The method of  claim 18  wherein the micro-controller also determines a displacement power factor to determine which of the reactive elements in the set of reactive elements to switch in or to switch out. 
     
     
         20 . The method of  claim 16  wherein the AC grid requirement specifies a power factor requirement from a 0 percent power level ratio to a 100 percent power level ratio.