Power point tracking

Abstract

A local power converter may include a controller to manipulate the operating point of a local power converter to cause the power point tracking feature of a central power converter to operate at a point determined by the controller. In some embodiments, the controller can manipulate the operating point of the local power converter by alternating between at least two modes. In some other embodiments, the controller can manipulate the operating point of the local power converter to provide a substantially constant slope. In some other embodiments, the controller can maintain a substantially constant impedance ratio. In some other embodiments, the controller enables perturbations from the power point tracking feature of the central power converter to reach the power source.

1 . A method of operating a local power converter comprising:
 operating a controller of a local power converter to periodically alternate operation of the local power converter between two or more operating modes, the local power converter receiving voltage from a voltage generating source and the local power converter outputting to a central power converter having a power point tracking feature;   wherein one of the operating modes is a constant power mode and one of the operating modes is a constant voltage ratio mode,
 the constant power mode outputs power to the central power converter within a predetermined range and conducts Maximum Power Point Tracking for the local power converter to identify a Maximum Power Point, 
 the constant voltage ratio mode including maintaining a constant ratio between input and output voltage of the local power converter, the ratio causing an MPPT algorithm in the central power converter to lock onto an operating point selected by the local power converter. 
   
     
     
         2 . The method of operating a local power converter of  claim 1  wherein the voltage generating source comprises one or more of a solar panel, a fuel cell, a wind turbine or a battery. 
     
     
         3 . The method of operating a local power converter of  claim 1  wherein a Maximum Power Point is identified before maintaining a constant ratio between input and output voltage for the constant voltage ratio mode and wherein the controller moves marginally off the Maximum Power Point and uses this marginal move to maintain the constant ratio between input and output voltage for the constant voltage ratio mode. 
     
     
         4 . The method of operating a local power converter of  claim 3  wherein marginal movement off of the Maximum Power Point provides an amount of slope that causes an MPPT function in the central power converter to lock onto an operating point selected by the local power converter rather than an operating point the central power converter would have selected. 
     
     
         5 . The method of operating a local power converter of  claim 1  wherein the local power converter continuously cycles between the constant power mode and the constant voltage ratio mode and wherein the relative amount of time spent in each mode may be adjusted. 
     
     
         6 . The method of operating a local power converter of  claim 1  wherein an operating point may be preselected and resident in the controller as well as be variable and configurable by an outside source. 
     
     
         7 . A method of operating a local power converter comprising:
 at a local power converter, receiving voltage from a voltage generating source, the local power converter outputting to a central power converter having power point tracking functionality, determining a ratio of local converter impedance to photovoltaic panel impedance;   using the determined ratio in a controller of the local converter as a control variable, and   sending the determined ratio to the central power converter to maintain a constant impedance ratio and sustain an operating point at the central power converter at a constant distance from a maximum power point.   
     
     
         8 . The method of operating a local power converter of  claim 7  wherein an impedance ratio of one indicates that the local power converter is operating at its maximum power point. 
     
     
         9 . The method of operating a local power converter of  claim 7  wherein operating the local converter with an impedance ratio of less than one causes the central power converter to slope down in operating voltage. 
     
     
         10 . The method of operating a local power converter of  claim 7  wherein operating the local power converter with an impedance ratio of greater than one causes the central power converter to slope up in operating voltage. 
     
     
         11 . The method of operating a local power converter of  claim 7  further comprising:
 repeatedly perturbing the voltage generating source using a frequency outside of the frequency band that can be monitored by the central power converter; and 
 monitoring the results of the perturbations by the local power converter independent of conventional perturbations generated by the central power converter. 
 
     
     
         12 . A method of operating a local power converter comprising:
 initializing a local power converter at a desired operational voltage ratio, the local power converter receiving voltage from a voltage generating source and the local power converter outputting to a central power converter having a power point tracking feature;   observing at the local power converter perturbations caused by the central power converter and determining an AC portion of the pertubations, and associated direction and slope amount, for the central converter.   
     
     
         13 . The method of operating a local power converter of  claim 12  further comprising:
 operating a control loop in the local power converter to move a DC level up or down to maintain a voltage ratio and wherein the central power converter raises or lowers its operating point using this voltage level maintained by the local central converter. 
 
     
     
         14 . The method of operating a local power converter of  claim 12  wherein when the voltage ratio is above the desired ratio value, a DC level is adjusted such that the central converter pertubations are centered at a power point above a Maximum Power Point voltage level. 
     
     
         15 . The method of operating a local power converter of  claim 14  wherein if the voltage ratio is observed to be within bounds of a desired level then the DC level of the local power converter is maintained such that inverter pertubations are centered at a power point below a Maximum Power Point voltage level. 
     
     
         16 . The method of operating a local power converter of  claim 15  wherein the Maximum Power Point (MPP) is associated with the central power converter and wherein the MPP always remains within a ripple range of pertubations of the central power converter.