Inverter terminal voltage adjustment in power system

Abstract

A utility-scale energy storage and conversion system can operate two or more inverter groups such that their reactive power commands are proportional to their available reactive power range. The control system can therefore distribute the reactive power commands in proportion to the available Q range, thereby ensuring that all inverters in the utility-scale energy storage and conversion system 100 operate with the same Q “headroom”. In addition, the utility-scale energy storage and conversion system can use an on-load tap changer (LTC) to adjust a terminal voltage associated with a first group of inverters and a second group of inverters. The first group of inverters can be associated with a first rating and the second group of inverters can be associated with a second rating that is greater than the first rating.

The claimed invention is: 
     
         1 . A utility-scale energy storage and conversion system that adjusts a terminal voltage associated with a first group of inverters and a second group of inverters, wherein the first group of inverters is associated with a first rating, wherein the second group of inverters is associated with a second rating that is greater than the first rating, the utility-scale energy storage and conversion system comprising:
 a control circuit to:
 determine, using a representation of a first available reactive power value associated with the first group of inverters and a representation of a second available reactive power value associated with the second group of inverters, a representation of a total available reactive power; 
 generate, using the representation of the first available reactive power value and a representation of a total required reactive power value, a first control signal representing a first desired reactive power value proportional to the first available reactive power value; and 
 generate, using the representation of the second available reactive power value and the total required reactive power value, a second control signal representing a second desired reactive power value proportional to the second available reactive power value. 
   
     
     
         2 . The utility-scale energy storage and conversion system of  claim 1 , wherein the first group of inverters associated with the first rating is associated with a first plurality of batteries having the first rating, and wherein the second group of inverters associated with the second rating is associated with a second plurality of batteries having the second rating. 
     
     
         3 . The utility-scale energy storage and conversion system of  claim 1 , wherein the first group of inverters includes a first number of inverters, wherein the second group of inverters includes a second number of inverters different than the first number of inverters. 
     
     
         4 . The utility-scale energy storage and conversion system of  claim 1 , the control circuit to:
 determine, using a representation of a first available apparent power value and a representation of a first required active power value, the first available reactive power value, wherein the first available apparent power value and the first required active power value are associated with the first group of inverters; and   determine, using a representation of a second available apparent power value and a representation of a second required active power value, the second available reactive power value, wherein the second available apparent power value and the second required active power value are associated with the second group of inverters.   
     
     
         5 . The utility-scale energy storage and conversion system of  claim 1 , wherein the utility-scale energy storage and conversion system forms part of an electric network, and wherein the total required reactive power value represents an amount of desired reactive power at a point of interconnect between the electric network and another electric network. 
     
     
         6 . The utility-scale energy storage and conversion system of  claim 1 , wherein the first group of inverters are coupled with a first voltage bus, wherein the second group of inverters are coupled with a second voltage bus, wherein the first voltage bus and the second voltage bus are coupled with a third voltage bus through corresponding first step-up transformers, wherein the third voltage bus is coupled with a fourth voltage bus on an electric network through a second step-up transformer, wherein the fourth voltage bus of the electric network is coupled with a point of interconnect coupled with another electric network, wherein voltages of the first voltage bus and the second voltage bus are less than a voltage of the third voltage bus, and wherein the voltage of the third voltage bus is less than a voltage of the fourth voltage bus. 
     
     
         7 . A method of adjusting a terminal voltage associated with a first group of inverters and a second group of inverters, wherein the first group of inverters is associated with a first rating, wherein the second group of inverters is associated with a second rating that is greater than the first rating, the method comprising:
 determining, using a representation of a first available reactive power value associated with the first group of inverters and a representation of a second available reactive power value associated with the second group of inverters, a representation of a total available reactive power;   generating, using the representation of the first available reactive power value and a representation of a total required reactive power value, a first control signal representing a first desired reactive power value proportional to the first available reactive power value; and   generating, using the representation of the second available reactive power value and the total required reactive power value, a second control signal representing a second desired reactive power value proportional to the second available reactive power value.   
     
     
         8 . The method of  claim 7 , wherein the first group of inverters associated with the first rating is associated with a first plurality of batteries having the first rating, and wherein the second group of inverters associated with the second rating is associated with a second plurality of batteries having the second rating. 
     
     
         9 . The method of  claim 7 , wherein the first group of inverters includes a first number of inverters, wherein the second group of inverters includes a second number of inverters different than the first number of inverters. 
     
     
         10 . The method of  claim 7 , further comprising:
 determining, using a representation of a first available apparent power value and a representation of a first required active power value, the first available reactive power value, wherein the first available apparent power value and the first required active power value are associated with the first group of inverters; and   determining, using a representation of a second available apparent power value and a representation of a second required active power value, the second available reactive power value, wherein the second available apparent power value and the second required active power value are associated with the second group of inverters.   
     
     
         11 . The method of  claim 7 , wherein the total required reactive power value represents an amount of desired reactive power at a point of interconnect between an electric network and another electric network. 
     
     
         12 . The method of  claim 7 , wherein the first group of inverters are coupled with a first voltage bus, wherein the second group of inverters are coupled with a second voltage bus, wherein the first voltage bus and the second voltage bus are coupled with a third voltage bus through corresponding first step-up transformers, wherein the third voltage bus is coupled with a fourth voltage bus of an electric network through a second step-up transformer, wherein the fourth voltage bus of the electric network is coupled with a point of interconnect coupled with another electric network, wherein voltages of the first voltage bus and the second voltage bus are less than a voltage of the third voltage bus, and wherein the voltage of the third voltage bus is less than a voltage of the fourth voltage bus. 
     
     
         13 . A utility-scale energy storage and conversion system to use an on-load tap changer (LTC) to adjust a terminal voltage associated with a first group of inverters and a second group of inverters, wherein the first group of inverters is associated with a first rating, wherein the second group of inverters is associated with a second rating that is greater than the first rating, the utility-scale energy storage and conversion system comprising:
 a control circuit to:
 determine, using a representation of a measured current and a representation of a measured voltage at a transformer winding of a transformer, the terminal voltage associated with the first group of inverters and the second group of inverters; 
 determine, using a representation of a total required reactive power value, a target terminal voltage associated with the first group of inverters and the second group of inverters; and 
 generate, using a difference between the terminal voltage and the target terminal voltage, a tap setting on the LTC so that the terminal voltage associated with the first group of inverters and the second group of inverters adjusts accordingly. 
   
     
     
         14 . The utility-scale energy storage and conversion system of  claim 13 , wherein the utility-scale energy storage and conversion system forms part of an electric network, wherein the first group of inverters are coupled with a first voltage bus, wherein the second group of inverters are coupled with a second voltage bus, wherein the first voltage bus and the second voltage bus are coupled with a third voltage bus through corresponding first step-up transformers, wherein the third voltage bus is coupled with a fourth voltage bus through a second step-up transformer, wherein the fourth voltage bus of the electric network is coupled with a point of interconnect coupled with another electric network, wherein voltages of the first voltage bus and the second voltage bus are less than a voltage of the third voltage bus, wherein the voltage of the third voltage bus is less than a voltage of the fourth voltage bus, wherein the transformer is the second step-up transformer, and wherein the representation of the measured current and the representation of the measured voltage are measured at a low-side of the second step-up transformer. 
     
     
         15 . The utility-scale energy storage and conversion system of  claim 13 , wherein the control circuit to determine, using the representation of the total required reactive power value, the target terminal voltage associated with the first group of inverters and the second group of inverters is further configured to:
 determine the target terminal voltage using a transfer function that relates the total required reactive power value and the target terminal voltage.   
     
     
         16 . The utility-scale energy storage and conversion system of  claim 15 , wherein at least a portion of the transfer function includes a linear relationship between the total required reactive power value and the target terminal voltage. 
     
     
         17 . The utility-scale energy storage and conversion system of  claim 15 , wherein the control circuit configured to determine the target terminal voltage using the transfer function that relates the total required reactive power value and the target terminal voltage is configured to:
 determine the target terminal voltage using a stored data set.   
     
     
         18 . The utility-scale energy storage and conversion system of  claim 17 , wherein the stored data set is a lookup table.