The Solar Cells and the Battery Charger System Using the Fast and Precise Analog Maximum Power Point Tracking Circuits

We propose a simple, fast and precise power calculation circuit for photovoltaic (PV) power systems. The power is calculated according to the principle that the integration of the PV output current over the time interval proportional to the PV output voltage becomes the power. This power calculation circuit is realized using simple analog circuits; neither a microprocessor nor a DSP is necessary to perform the function of Maximum Power Point Tracker (MPPT). As the calculated result at the output of the power calculation circuit becomes the analog voltage, a power comparison between the previous result and the current result is easily done using analog comparators where the previous result is sampled-and-held. Using the comparison result, the duty ratio of the boost converter is controlled to find the maximum power point in the PV output voltage range by adopting the hill-climbing perturb and observe (P&O) method. The prototype of the PV power system was circuit-designed and laid out using a 0.18-mu m CMOS IC process. The SPICE circuit simulation results indicated that the PV power calculation achieved within +/-2% error for the PV output power from 50 mW to 300 mW, and +/-5% for the PV output power from 10 mW to 350 mW. The operation of the whole power system was verified in a transient simulation by applying the current step from the current source of the equivalent PV-cell circuit. The result shows convergence to the maximum power point when the PV output currents are 100 mA, 300 mA and 500 mA with a 50-O load resistor at the output of the boost DC-DC converter.