Apparatus and method for electric hot water heater primary frequency control

Abstract

An energy storing apparatus is provided which comprises: a first region having a thermostat which includes: a temperature sensor; a controller coupled to the temperature sensor; and a power-converter coupled to the controller; and a second region thermally coupled to the first region. An apparatus is provided which comprises: an interface to be coupled to an electric grid; a temperature sensor; a controller coupled to the temperature sensor; and a power-converter coupled to the controller, wherein the power-converter is to couple via passive devices to a heating element, wherein the power-converter is to apply power to the heating element according to a temperature sensed by the temperature sensor and a frequency of the electric grid.

What is claimed is: 
     
         1 . An energy storing apparatus comprising:
 a first region having a thermostat which includes:
 a temperature sensor; 
 a controller coupled to the temperature sensor; and 
 a power-converter coupled to the controller; and 
   a second region thermally coupled to the first region.   
     
     
         2 . The energy storing apparatus of  claim 1 , wherein the power-converter is to control the amount of power applied to the first region. 
     
     
         3 . The energy storing apparatus of  claim 2 , wherein the power-converter is operable to apply power to the first region according to temperature sensed by the temperature sensor and a frequency of an electric grid. 
     
     
         4 . The energy storing apparatus of  claim 1  comprises:
 a first proportional loop to regulate a temperature sensed by the temperature sensor; and 
 a second proportional loop to adjust frequency of an electric grid. 
 
     
     
         5 . The energy storing apparatus of  claim 4 , wherein the first and second proportional loops are to operate in parallel. 
     
     
         6 . The energy storing apparatus of  claim 4 , wherein the second proportional loop is to emulate inertia of the electric grid. 
     
     
         7 . The energy storing apparatus of  claim 1 , wherein the first region has a set point which is set to a temperature lower than a temperature of the second region. 
     
     
         8 . A method for controlling frequency of an electric grid, the method comprising:
 determining whether an upper relay direction flag is positive or negative, and if negative, determining whether an upper tank temperature is less than   an upper tank lower temperature limit, and if positive, determining whether an upper tank temperature is greater   than an upper tank upper temperature limit; and   applying power to an upper heating element, setting the upper relay direction flag to positive, and applying zero power to a lower heating element in response to determining that the upper tank temperature is less than the upper tank lower temperature limit,   wherein the upper and lower heating elements are part of a water heater.   
     
     
         9 . The method of  claim 8  comprising: applying zero power to the upper heating element in response to determining that the upper tank temperature is greater than or equal to the upper tank lower temperature limit. 
     
     
         10 . The method of  claim 9  comprising:
 applying zero power to the upper heating element and setting the upper relay direction flag to negative in response to determining that the upper tank temperature is greater than the upper tank upper temperature limit; or 
 applying power to the upper heating element and applying no power to the lower heating element in response to determining that the upper tank temperature is less than or equal to the upper tank upper temperature limit. 
 
     
     
         11 . The method of  claim 10  comprising: determining whether a lower tank temperature is greater than a lower tank temperature limit. 
     
     
         12 . The method of  claim 11  comprising:
 applying zero power to the lower heating element in response to determining that the lower tank temperature is greater than the lower tank temperature limit; or 
 computing first and second parameters in response to determining that the lower tank temperature is less than or equal to the lower tank temperature limit, wherein the first parameter is a function of the lower tank temperature and a lower temperature set point, and wherein the second parameter is a function of the frequency of the electric grid and a frequency set point of the electric grid. 
 
     
     
         13 . The method of  claim 12  comprising:
 determining whether a sum of the first and second parameters is greater than a maximum lower heating element power rating; and 
 applying a maximum rated power to the lower heating element in response to determining that the sum of the first and second parameters is greater than the maximum lower heating element power rating. 
 
     
     
         14 . The method of  claim 13  comprising:
 determining whether a sum of the first and second parameters is less than zero; 
 applying zero rated power to the lower heating element in response to determining that the sum of the first and second parameters is less than zero; or 
 applying power to the lower heating element in response to determining that the sum of the first and second parameters is greater than or equal to zero, wherein the applied power is a function of the sum of the first and second parameters. 
 
     
     
         15 . An apparatus comprising:
 an interface to be coupled to an electric grid;   a temperature sensor;   a controller coupled to the temperature sensor; and   a power-converter coupled to the controller, wherein the power-converter is to couple via passive devices to a heating element, wherein the power-converter is to apply power to the heating element according to a temperature sensed by the temperature sensor and a frequency of the electric grid.   
     
     
         16 . The apparatus of  claim 15  comprises at least two diodes coupled to the interface. 
     
     
         17 . The apparatus of  claim 15 , wherein the power-converter includes at least two transistors coupled in series such than a common node of the least two transistors is coupled to at least one of the passive devices, and wherein the power-converter is to control an amount of power applied to the heating element. 
     
     
         18 . The apparatus of  claim 15  comprises:
 a first proportional loop to regulate a temperature sensed by the temperature sensor; and 
 a second proportional loop to adjust frequency of an electric grid. 
 
     
     
         19 . The apparatus of  claim 18 , wherein the first and second proportional loops are to operate in parallel. 
     
     
         20 . The apparatus of  claim 18 , wherein the second proportional loop is to emulate inertia of the electric grid.