Dynamic Impedance Matching Circuit Suitable For Piezoelectric Energy Harvesting

Wireless Sensor Networks（WSNs）technology has been closely related to people’s life,providing people with a safe,reliable,comfortable and convenient lifestyle.So far,the vast majority of WSNs nodes still provide battery power,but battery power has its limitations,such as limited battery energy storage and short service life,which is only suitable for short-term power supply and use scenarios where the battery is easy to be replaced.With the development of WSNs,wireless sensor nodes will be comprehensively covered,battery replacement will become a huge challenge,and large quantities of waste batteries will also cause environmental and land pollution.In order to comply with the strategy of sustainable development,the energy collected from the environment is converted into electricity to power the wireless sensor network.Vibration is ubiquitous in nature and is not limited by natural conditions like solar energy,thermal energy and wind energy.Therefore,the study of vibration energy acquisition is becoming a hot topic.At present,the common vibration energy recovery technology is electromagnetic,electrostatic,piezoelectric.Among them,the piezoelectric type has simple structure,high power density,easy integration,and the wireless sensor node requirements.Therefore,it has become the main research direction.In this paper,an adaptive control method for adjusting the load impedance of piezoelectric transducer is proposed to improve the efficiency of vibration energy acquisition.The power transmission curve of the piezoelectric energy transducer is studied and analyzed.It is concluded that when the output Voltage of the piezoelectric energy collector rectified by the rectifying Circuit is controlled at half of the Open Circuit Voltage(V_OC/2),its output power is close to the maximum output power.Therefore,this paper proposes an adaptive hysteresis window control method,and designs an adaptive hysteresis window control circuit composed of capacitor and switch to control the change of the equivalent load impedance,so that the rectified output voltage can be controlled near V_OC/2 to maintain a high output power.The maximum power point tracking（MPPT）has a maximum tracking efficiency of 98.7%.In addition,the energy storage circuit structure proposed in this paper can ensure the continuous work of the load when the external vibration energy is low or there is no energy input for a short time.In order to adapt to the current development trend of low power consumption and integration,the power supply system also requires the development of miniaturization and integration to reduce power consumption,reduce volume and improve efficiency.A new type of high efficiency self-powered piezoelectric energy capture COMS integrated circuit is proposed,which combines the advantages of self-powered zero-current active rectifier and MPPT circuit to realize the high efficiency self-powered impedance matching circuit.Simulation results show that the proposed MPPT circuit has high tracking efficiency,up to 98.24%,and is less affected by load.