An adaptive MPPT technology for RF energy harvesting systems

The ratio of maximum power tracking voltage to open-circuit voltage is not 50%, due to the nonlinearity of RF rectifier, and it varies with input power, so the traditional fractional open-circuit voltage (FOCV) method is no longer applicable. In order to maintain maximum power transmission efficiency for RF rectifier, an adaptive maximum power tracking technique for RF energy harvester was developed, which combined the FOCV method and the perturbation observation method (P&O). Based on PWM+PFM hybrid modulation, the technology adaptively adjusted the tracking voltage perturbator of the RF rectifier on the basis of half of the open-circuit voltage, meanwhile observing the charging time of the output capacitor of the DC-DC converter. When the charging time reached the shortest, the output power of the RF rectifier also reached the maximum, and the tracking voltage was the maximum power tracking voltage. The AMPPT technique can solve the problems of imprecision of the FOCV method and swaying around the MPPT tracking point of the P&O method. The circuit was designed in 180 nm CMOS process. The simulation shows that the peak tracking efficiency of MPPT is 99%, the peak conversion efficiency of DC-DC converter is 86.46%, and the system conversion efficiency peak is 58.57% (@P_AV=-8 dBm).