Interleaved sampling power calibration for power stealing in smart home devices

Abstract

Smart home devices may use a technique known as “power stealing” in order to steal power from an external environmental system. For example, thermostats may steal power from an HVAC system. Different algorithms and techniques may be used for efficiently stealing power from the HVAC system, each of which may provide different levels of power to the thermostat at different times. The smart home device may test an external system to determine which power stealing methods are compatible and calibrate various power stealing parameters. A calibration routine may sample at a plurality of discrete intervals while increasing a test load to determine a maximum current limit and an optimal power stealing method.

What is claimed is: 
     
         1 . A thermostat comprising:
 a power stealing circuit configured to steal power from a power wire connector for controlling a heating, ventilation, and air conditioning (HVAC) function of an HVAC system, wherein an output of the power stealing circuit provides power to operational systems of thermostat;   an adjustable test load coupled to the output of the power stealing circuit;   one or more processors configured to perform operations comprising:
 switching the output of the power stealing circuit from the operational systems of the thermostat to the adjustable test load; 
 causing the power stealing circuit to steal power from the HVAC system with different loads provided by the adjustable test load; 
 sampling a voltage provided by the power stealing system at the different loads provided by the adjustable test load; and 
 calibrating operation of the power stealing circuit based the voltage provided by the power stealing circuit at the different loads provided by the adjustable test load. 
   
     
     
         2 . The thermostat of  claim 1 , wherein the output of the power stealing circuit provides power to the operational systems of thermostat by providing power to a power management integrated circuit (PMIC), and the PMIC switches the operational systems of the thermostat to a rechargeable battery power when switching the output of the power stealing circuit to the adjustable test load. 
     
     
         3 . The thermostat of  claim 1 , wherein the adjustable test load is configured to simulate different load levels of the operational systems of the thermostat. 
     
     
         4 . The thermostat of  claim 1 , wherein the adjustable test load comprises a resistor in series with a field-effect transistor (FET) switch, and the one or more processors cause the adjustable test load to provide the different loads by changing a pulse-width modulation (PWM) of a signal driving the FET switch. 
     
     
         5 . The thermostat of  claim 1 , wherein calibrating the operation of the power stealing circuit comprises selecting a power-stealing method that is phase-aware of a zero-crossing of a current waveform through one or more switching elements for the HVAC function. 
     
     
         6 . The thermostat of  claim 1 , wherein calibrating the operation of the power stealing circuit comprises selecting a power-stealing method that is not based on a phase of a current waveform through one or more switching elements for the HVAC function. 
     
     
         7 . The thermostat of  claim 1 , wherein calibrating the operation of the power stealing circuit comprises selecting a power-stealing method that is active when the HVAC function is not active. 
     
     
         8 . The thermostat of  claim 1 , further comprising:
 a power wire connector for the HVAC function;   a return wire connector for the HVAC function; and   one or more switching elements configured to operate in:
 a first operating state in which the one or more switching elements create a connection between the power wire connector and the return wire connector to activate the HVAC function; and 
 a second operating state in which the one or more switching elements interrupt the connection between the power wire connector and the return wire connector; 
   wherein the one or more processors control the one or more switching elements based on a selected power stealing method.   
     
     
         9 . A method of calibrating power stealing for a thermostat, the method comprising:
 operating a power stealing circuit configured to steal power from a power wire connector for a function of a controlling a heating, ventilation, and air conditioning (HVAC) system, wherein an output of the power stealing circuit provides power to operational systems of thermostat;   switching the output of the power stealing circuit from the operational systems of the thermostat to an adjustable test load that is coupled to the output of the power stealing circuit;   causing the power stealing circuit to steal power from the HVAC system with different loads provided by the adjustable test load;   sampling a voltage provided by the power stealing system at the different loads provided by the adjustable test load; and   calibrating operation of the power stealing circuit based the voltage provided by the power stealing system at the different loads provided by the adjustable test load.   
     
     
         10 . The method of  claim 9 , wherein calibrating the operation of the power stealing circuit comprises setting maximum current limit for a power management integrated circuit. 
     
     
         11 . The method of  claim 9 , wherein calibrating the operation of the power stealing circuit comprises selecting a power wire connector for an HVAC function for power  5  stealing. 
     
     
         12 . The method of  claim 9 , wherein sampling the voltage provided by the power stealing system comprises sampling a plurality of discrete sampling intervals at each of the different loads provided by the adjustable test load. 
     
     
         13 . The method of  claim 12 , wherein each of the plurality of discrete sampling intervals are separated by a delay that is at least half the length of each of the plurality of discrete sampling intervals. 
     
     
         14 . The method of  claim 12 , wherein each of the plurality of discrete sampling intervals are between about 20 ms and about 50 ms. 
     
     
         15 . The method of  claim 12 , wherein each of the plurality of discrete sampling intervals are between about 30 ms and about 40 ms. 
     
     
         16 . The method of  claim 9 , wherein sampling the voltage provided by the power stealing system comprises sampling at between about 5 kHz and about 15 kHz. 
     
     
         17 . A method of calibrating power stealing for a smart home device, the method comprising:
 operating a power stealing circuit configured to steal power from an external system, wherein an output of the power stealing circuit provides power to operational systems of smart home device;   switching the output of the power stealing circuit from the operational systems of the smart home device to an adjustable test load that is coupled to the output of the power stealing circuit;   causing the power stealing circuit to steal power from the external system with different loads provided by the adjustable test load;   sampling a voltage provided by the power stealing system at the different loads provided by the adjustable test load; and   calibrating operation of the power stealing circuit based the voltage provided by the power stealing system at the different loads provided by the adjustable test load.   
     
     
         18 . The method of  claim 17 , further comprising detecting when the voltage provided by the power stealing system drops below a minimum threshold. 
     
     
         19 . The method of  claim 18 , further comprising calibrating the operation of the power stealing circuit after detecting when the voltage provided by the power stealing system drops below the minimum threshold without requiring subsequent sampling intervals or test load levels. 
     
     
         20 . The method of  claim 17 , wherein sampling the voltage provided by the power stealing system comprises sampling at least three discrete sampling intervals at each of the different loads provided by the adjustable test load.