An Inductor-less Piezoelectric Energy Harvesting And Management System Based On Switched Capacitors

Wireless sensor networks（WSNs）are becoming more and more widespread in daily life.Their functions are becoming more and more complex.However,the nodes’volume and power consumption are required to be smaller and lower,respectively.The traditional battery power supply has many problems,such as large size,limited battery life and high maintenance costs,which impedes the promotion and development of WSNs.Environmental energy harvesting technology has the advantages of self-powering,small size,etc.,which can replace battery power supply and has broad application prospects in WSNs.Among the common environmental energy sources,piezoelectric energy has a higher power density.Therefore,it is favored by many researchers.There are three research interests on piezoelectric energy harvesting:improving rectification efficiency of the interface circuit,optimizing maximum power point tracking（MPPT）algorithm,and reducing volume of piezoelectric energy harvesting system.First,to improve the rectification efficiency of the interface circuit,it needs to be able to use the energy wasted on the parasitic capacitance of the piezoelectric transducer when rectifying.Therefore,how to flip the voltage across the parasitic capacitance is one of the keys to improving the efficiency.In addition,to maximize the extracted power from the source,MPPT algorithm must be optimized;finally,to reduce the volume of the entire circuit as much as possible,large-volume inductors should be avoided to use.For the key and difficult points of the above piezoelectric energy harvesting,this paper proposes an inductance-less piezoelectric energy harvesting and management system based on switched capacitors（SC）.For the interface circuit,in order to realize the parasitic capacitor voltage flipping,this paper proposes an algorithm to calculate the value of the parasitic capacitance flipping voltage,which is based on the working principle of parallel synchronized switch harvesting on capacitor（P-SSHC）technology.The algorithm can determine the optimal value and number of capacitors.Besides,this paper designs a two-stage synchronous rectifier with P-SSHC for high rectification efficiency.For MPPT algorithm,a new maximum power point algorithm is proposed,which is based on equivalent input impedance analysis of the SC-type DC/DC converter.The algorithm can sample the open-circuit voltage rapidly,greatly shortening the open circuit time when energy cannot be harvested.Moreover,it can work with P-SSHC without time difference before and after open-circuit sampling.Equivalently,the loss is reduced,thereby improving the harvesting efficiency.Finally,the proposed system only uses switched capacitor to complete the parasitic capacitor voltage flipping and maximum power tracking,avoiding large-volume inductor used in parallel synchronized switch harvesting on inductor（P-SSHI）technology and the traditional Buck/Boost converter,whcih greatly reducing the volume of the system.Based on SMIC 0.18μm CMOS process,this paper designs and simulates the proposed inductor-less piezoelectric energy harvesting and management system based on switched capacitors.What’s more,layout is also designed and its area is 1602×1079μm².The simulation results show that the flipping efficiency of the P-SSHC in this design is 0.75.It takes the MPPT circuit only 1.5 excited cycles to sample the open-circuit voltage without being affected by the charging capacitor’s value.When the input voltage(V_REC)of MPPT is3.4V,its peak voltage tracking efficiency is 98.89%;when the input voltage of MPPT is3.06V,its peak conversion efficiency is 82.03%,and the static power consumption of the control circuit is about 3.67μW.The input open-circuit voltage range of the energy harvesting system is 1V-1.8V,and the output is 1.8V.The system does not use inductors.