Piezo Vibration Harvester Active Rectifier Enable Circuit
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Solution Overview
Problem
Existing piezo energy harvesting systems waste significant power due to inefficient energy transfer from piezo vibration harvesters to DC-DC converters, with conventional systems able to collect less than a third of available energy and requiring additional switches or inductors to enhance efficiency.
Innovation Solution
A piezo energy harvesting system that includes an active rectifier and an enable circuit to detect direction reversals in the AC output current, enabling the DC-DC converter only during necessary discharge phases, thereby eliminating waste and optimizing energy transfer without additional switches or inductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional DC-DC converter is used with piezo harvester, then the converter can transfer energy to battery, but significant energy is wasted due to inefficient energy transfer and continuous operation
Solution Approach 1:
The DC-DC converter operates periodically rather than continuously, being enabled only during specific discharge phases when the piezo harvester voltage exceeds the battery voltage. This periodic operation eliminates energy waste during charging phases while maintaining effective energy transfer during discharge phases, directly resolving the contradiction between energy loss and harvesting efficiency.
Solution Approach 2:
The system uses voltage comparison feedback between the piezo harvester output and battery voltage to control the enable signal of the DC-DC converter. When the harvester voltage exceeds the battery voltage, the converter is enabled; otherwise, it is disabled. This feedback mechanism ensures energy is transferred only when beneficial, eliminating waste while maximizing productivity.
2Loss of energy
If DC-DC converter operates continuously to ensure energy transfer, then energy can be constantly supplied to battery, but energy is wasted during charging phases when harvester voltage is below threshold
Solution Approach 1:
The converter operates in periodic cycles, enabling during discharge phases when harvester voltage exceeds battery voltage and disabling during charging phases. This periodic operation eliminates energy waste while maintaining reliability through consistent energy transfer during active phases.
Solution Approach 2:
The system automatically enables or disables the DC-DC converter based on the voltage comparison between harvester and battery, without external control. This self-service mechanism ensures continuous energy supply during discharge phases while eliminating waste during charging phases, resolving both energy loss and reliability concerns.
3Productivity
If additional switches or inductors are added to enhance efficiency, then energy transfer efficiency can be improved, but device complexity increases
Solution Approach 1:
The patent extracts and utilizes the existing capacitance of the piezo harvester itself as the energy storage element, eliminating the need for additional inductors or switches. By leveraging the harvester's inherent capacitance and using a simple enable circuit controlled by voltage comparison, the system achieves high efficiency without increasing device complexity.
Solution Approach 2:
The piezo harvester's capacitance serves multiple functions: it stores energy during vibration and acts as the energy storage element for the DC-DC converter, eliminating the need for separate inductors or additional switching components. This multi-functionality improves energy transfer efficiency while maintaining simple device architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system significantly increases energy harvesting efficiency by up to four times, ensuring that all vibration energy is utilized and minimizing waste, with the DC-DC converter being enabled only during required discharge phases to match the input impedance of the piezo harvester.
Implementation Method 1
a piezo harvester (2) for generating an AC output voltage (VP(t)) and an AC output current (IPZ(t)) representing energy harvested from the vibration source
Implementation Method 2
an active rectifier (3) to produce a DC output voltage (Vhrv) and current (Ihrv)
Data Source
AI summary
A system (1-2) for efficiently transferring harvested vibration energy to a battery (6) includes a piezo harvester (2) generating an AC output voltage (VP(t)) and current (IPZ(t)) and an active rectifier (3) to produce a harvested DC voltage (Vhrv) and current (Ihrv) which charge a capacitance (C0). An enable circuit (17) causes a DC-DC converter (4) to be enabled, thereby discharging the capacitance into the converter, when a comparator (A0,A1) of the rectifier which controls switches (S1-S4) thereof detects a direction reversal of the AC output current (IPZ(t)). Another comparator (13) causes the enable circuit (17) to disable the converter (4) when the DC voltage exceeds a threshold (VREF), thereby causing the capacitance be recharged.