一种适用于射频能量收集系统的自适应MPPT技术

An adaptive MPPT technology for RF energy harvesting systems

在射频能量收集系统中,射频整流器的非线性使其最大功率追踪电压(取得最大输出功率时的输出电压)与开路电压的比例并非为50%,且该比例随输入功率变化,因而传统的开路电压法(FOCV)不再适用。为保证射频整流器进行最大功率传输,将开路电压法和干扰观测法(P&O)相结合,发展了一种适用于射频能量收集系统的自适应最大功率追踪技术。该技术基于PWM+PFM的混合调制方式,在二分之一开路电压的基础上自适应地调整射频整流器的追踪电压微扰量,同时观测DC-DC转换器输出电容的充电时间。当充电时间达到最短时,射频整流器的输出功率达到最大,此时的追踪电压为最大功率追踪电压。自适应最大功率追踪技术可解决开路电压法追踪不精确以及干扰观测法在最大功率追踪点附近左右摇摆等问题。采用180 nm CMOS工艺进行设计及验证,结果表明,MPPT追踪效率峰值为99%,DC-DC转换器的转换效率峰值为86.46%,系统转换效率峰值为58.57%(@输入功率P AV=-8 dBm)。

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of RF rectifier,and it varies with input power,so the traditional fractional open-circuit voltage(FOCV)method is no longer applicable.In order to maintain maximum power transmission efficiency for RF rectifier,an adaptive maximum power tracking technique for RF energy harvester was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).