Selective power point tracking

Abstract

A controller receives electrical power at an input from one or more energy capture device and outputs electrical power to one or more external loads. The controller adjusts, according to a first algorithm, an electrical property affecting an apparent load resistance applied across the input. The controller determines, while the first algorithm is running, whether a first amount of power received by the input is satisfactory. If it is, the controller continues using the first algorithm. If it is not, the controller switches to a algorithm. The first and second maximum algorithms may be optimized for different environmental conditions, such as different amounts of sunlight incident on the one or more energy capture devices.

What is claimed is: 
     
         1 . A controller characterized by an operating point and comprising:
 an input configured to receive electrical power from one or more energy capture devices;   an output configured to provide electrical power to an external load;   one or more processors;   memory; and   one or more programs, the one or more programs stored in the memory and configured to be executed by the one or more processors, the one or more programs including instructions for:
 adjusting, according to a first algorithm, an electrical property affecting an apparent load resistance applied across the input; 
 determining, while the first algorithm is running, whether a first amount of power received by the input is satisfactory;
 in accordance with a determination that the first amount of power is satisfactory, continuing to adjust the electrical property according to the first algorithm; and 
 in accordance with a determination that the first amount of power received is not satisfactory, performing a method comprising (i) switching to a second algorithm, and (ii) adjusting the electrical property according to the second algorithm, 
 
 wherein the first algorithm is different from the second algorithm. 
   
     
     
         2 . The controller of  claim 1 , wherein:
 the first algorithm corresponds to a first power production characteristic of the one or more energy capture devices;   the second algorithm corresponds to a second power production characteristic of the one or more energy capture devices; and   a determination that the first amount of power is unsatisfactory corresponds to a determination that the one or more energy capture devices are operating according to the second power production characteristic.   
     
     
         3 . The controller of  claim 2 , wherein the first power production characteristic corresponds to a condition of higher illuminance of the one or more energy capture devices as compared to the second power production characteristic. 
     
     
         4 . The controller of  claim 2 , wherein the first power production characteristic corresponds to direct sunlight conditions, and the second power production characteristic corresponds to at least partially indirect sunlight conditions. 
     
     
         5 . The controller of  claim 1 , the one or more programs further including instructions for performing a maximum power point seeking scan, including instructions for:
 adjusting the electrical property over a range of values;   while adjusting the electrical property over the range of values, identifying a maximum power point;   selecting one of the first algorithm or the second algorithm for use after the maximum power point seeking scan;   determining that a termination condition for the maximum power point seeking scan is satisfied; and   in accordance with a determination that the termination condition is satisfied:
 adjusting the electrical property according to the selected algorithm, using a value of the electrical property corresponding to the maximum power point as the operating point. 
   
     
     
         6 . The controller of  claim 5 , the instructions for performing the maximum power point seeking scan further including instructions for determining whether the power produced by the one or more energy capture devices over the range of values varies according to a slope indicative of a first environmental condition or a second environmental condition, wherein the second environmental condition is different from the first environmental condition. 
     
     
         7 . The controller of  claim 6 , the one or more programs further including instructions for:
 in accordance with a determination that the power produced by the one or more energy capture devices over the range of values varies according to a slope indicative of a first environmental condition, determining that the first amount of power is satisfactory; and   in accordance with a determination that the power produced by the one or more energy capture devices over the range of values varies according to a slope indicative of a second environmental condition, determining that the first amount of power is not satisfactory.   
     
     
         8 . The controller of  claim 6 , wherein the one or more programs further include instructions for:
 after switching to the second algorithm, determining whether a second amount of power received by the input is satisfactory;   in accordance with a determination that the second amount of power is satisfactory, continuing to adjust the electrical property according to the second algorithm;   in accordance with a determination that the second amount of power is unsatisfactory, performing a method comprising (i) switching to the first algorithm, and (ii) adjusting the electrical property according to the first algorithm.   
     
     
         9 . The controller of  claim 8 , wherein the one or more programs further include instructions for:
 in accordance with a determination that the power produced by the one or more energy capture devices over the range of values varies according to a slope indicative of the second environmental condition, determining that the second amount of power is satisfactory; and   in accordance with a determination that the power produced by the one or more energy capture devices over the range of values varies according to a slope indicative of the first environmental condition, determining that the second amount of power is not satisfactory.   
     
     
         10 . The controller of  claim 1 , wherein the instructions for adjusting the electrical property according to the first algorithm and/or the second algorithm include instructions for:
 while maintaining a power trend, wherein the power trend is a repeatedly updated value based at least in part on two power values of the one or more energy capture devices:   over a first series of steps, adjusting the electrical property in a first direction, wherein each respective step in the first series of steps corresponds to a respective value of the electrical property;   determining a first respective power value for each respective step of the first series of steps;   determining whether the power trend over the first series of steps satisfies a first condition;   in accordance with a determination that the power trend satisfies the first condition during the first series of steps:
 over a second series of steps, adjusting the electrical property in a second direction, different from the first direction; 
 determining a second respective power value for each respective step of the second series of steps; 
 determining whether the power trend over the second series of steps satisfies a second condition; and 
 subsequent to determining that the power trend satisfies the second condition:
 based on power values determined over the first and the second series of steps, identifying a maximum power point; and 
 using a value of the electrical property corresponding to the maximum power point as the operating point for the controller. 
 
   
     
     
         11 . The controller of  claim 10 , wherein the instructions for maintaining the power trend include instructions for determining a plurality of slope values, each slope value of the plurality of slope values being based on at least two respective power values. 
     
     
         12 . The controller of  claim 10 , wherein:
 the instructions for adjusting the electrical property in the first direction include instructions for decreasing a duty cycle of a transistor that controls a flow of current from the one or more energy capture devices to the external load; and   the instructions for adjusting the electrical property in the second direction include instructions for increasing the duty cycle of the transistor.   
     
     
         13 . The controller of  claim 10 , wherein the power trend satisfies the first condition when the power trend is negative for a predetermined number of steps. 
     
     
         14 . The controller of  claim 10 , wherein the power trend satisfies the first condition when a change in the power trend over a plurality of steps satisfies a third condition. 
     
     
         15 . The controller of  claim 14 , wherein the power trend satisfies the second condition when the power trend is substantially constant for a predetermined number of steps. 
     
     
         16 . The controller of  claim 15 , wherein the power trend satisfies the second condition when the power trend is indicative of a constant current condition of the energy capture device for a predetermined number of steps. 
     
     
         17 . The controller of  claim 16 , wherein the power trend satisfies the second condition when the power trend is substantially equal to 1. 
     
     
         18 . The controller of  claim 17 , wherein the second condition is different from the first condition. 
     
     
         19 . The controller of  claim 10 , wherein the instructions for adjusting the electrical property according to the first algorithm and/or the second further include instructions for:
 operating the controller at a first value of the electrical property;   observing a change in power produced by the one or more energy capture devices;   determining whether the power produced by the one or more energy capture devices has increased or decreased;   in accordance with a determination that the power produced by the one or more energy capture devices has increased:
 adjusting the electrical property in the first direction includes decreasing a duty cycle of a transistor that controls a flow of current from the one or more energy capture devices to the external load; and 
 adjusting the electrical property in the second direction includes increasing the duty cycle of the transistor; and 
   in accordance with a determination that the power produced by the one or more energy capture devices has decreased:
 adjusting the electrical property in the first direction includes increasing the duty cycle of the transistor; and 
 adjusting the electrical property in the second direction includes decreasing the duty cycle of the transistor. 
   
     
     
         20 . The controller of  claim 10 , wherein:
 when adjusting the electrical property according to the first algorithm, a minimum difference in the value of the electrical property between two adjacent steps is a first value; and   when adjusting the electrical property according to the second algorithm, the minimum difference in the value of the electrical property between two adjacent steps is a second value that is greater than the first value.   
     
     
         21 . The controller of  claim 10 , wherein the instructions for adjusting the electrical property in the first direction over the first series of steps include instructions for:
 initially adjusting the electrical property of each subsequent step by a first amount;   if the power trend fails to satisfy the first condition after a predetermined number of steps, beginning to adjust the electrical property of each subsequent step by a second amount, wherein the second amount is greater than the first amount; and   subsequently, if the power trend fails to satisfy the first condition after a second particular number of steps, beginning to adjust the electrical property of each subsequent step by a third amount, wherein the third amount is greater than the second amount.   
     
     
         22 . The controller of  claim 21 , wherein the instructions for adjusting the electrical property in the first direction over the first series of steps further include instructions for:
 subsequent to beginning to adjust the electrical property of each subsequent step by the third amount, if the power trend fails to satisfy the first condition after a third particular number of steps, performing a maximum power point seeking scan, including, over a fourth series of steps:
 adjusting the electrical property in the first direction; 
 identifying a maximum power point over the fourth series of steps; 
 selecting one of the first maximum power point tracking algorithm or the second maximum power point tracking algorithm for use after the maximum power point seeking scan; 
 determining whether the power trend over the fourth series of steps satisfies the first condition; and 
 in accordance with a determination that the power trend satisfies the first condition:
 adjusting the electrical property according to the selected maximum power point seeking algorithm, using a value of the electrical property corresponding to the maximum power point as an initial operating point. 
 
   
     
     
         23 . The controller of  claim 22 , wherein each respective power value corresponds to an electrical power provided by the one or more energy capture devices during a step. 
     
     
         24 . The controller of  claim 22 , wherein each respective power value is determined by measuring only a current value corresponding to a flow of current from the one or more energy capture devices. 
     
     
         25 . The controller of  claim 1 , wherein the electrical property corresponds to a duty cycle of a transistor that controls a flow of current from the one or more energy capture devices to the external load. 
     
     
         26 . The controller of  claim 1 , wherein the output includes a universal serial bus port. 
     
     
         27 . The controller of  claim 1 , wherein the one or more energy capture devices is a solar panel. 
     
     
         28 . A method for tracking a maximum power point of one or more energy capture devices, comprising:
 at a controller with one or more processors and memory storing one or more programs for execution by the one or more processors, the controller characterized by an operating point:
 adjusting, according to a first algorithm, an electrical property affecting an apparent load resistance applied across the input; 
 determining, while the first algorithm is running, whether a first amount of power received by the input is satisfactory;
 in accordance with a determination that the first amount of power is satisfactory, continuing to adjust the electrical property according to the first algorithm; and 
 in accordance with a determination that the first algorithm is unsatisfactory, performing a method comprising (i) switching to a second algorithm during the epoch, and (ii) adjusting the electrical property according to the second algorithm, 
 
 wherein the first algorithm is different from the second algorithm. 
   
     
     
         29 . An electronic device, comprising:
 one or more processors;   memory; and   one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including instructions for:   adjusting, according to a first algorithm, an electrical property affecting an apparent load resistance applied across the input;   determining, while the first algorithm is running, whether a first amount of power received by the input is satisfactory;
 in accordance with a determination that the first amount of power is satisfactory, continuing to adjust the electrical property according to the algorithm; and 
 in accordance with a determination that the first amount of power is unsatisfactory, performing a method comprising (i) switching to a second algorithm, and (ii) adjusting the electrical property according to the second algorithm, 
   wherein the first algorithm is different from the second algorithm.   
     
     
         30 . A non-transitory computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by an electronic device, cause the device to:
 adjust, according to a first algorithm, an electrical property affecting an apparent load resistance applied across the input;   determine, while the first algorithm is running, whether a first amount of power received by the input is satisfactory;
 in accordance with a determination that the first amount of power is satisfactory, continuing to adjust the electrical property according to the first algorithm; and 
 in accordance with a determination that the first amount of power is unsatisfactory, performing a method comprising (i) switching to a second algorithm, and (ii) adjusting the electrical property according to the second algorithm, 
 wherein the first algorithm is different from the second algorithm.