Open-Circuit Voltage Sensing for MPPT Energy Harvesters
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Solution Overview
Problem
Energy conversion efficiency is compromised when the load current or voltage requirements are mismatched with the output characteristics of energy sources like piezoelectric energy harvesting (PEH) devices, photovoltaic (PV) devices, or thermo-electric generators (TEG), leading to suboptimal power transfer.
Innovation Solution
A power conversion circuit is configured to measure the open-circuit voltage of the energy source and adjust operating parameters, such as frequency or impedance, to converge on a desired terminal voltage using a maximum power point tracking (MPPT) technique, ensuring efficient energy transfer by isolating the load and using capacitors to control settling times and sampling frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the load is directly connected to the energy source, then power transfer occurs continuously, but energy conversion efficiency deteriorates due to mismatched load current or voltage requirements
Solution Approach 1:
A power conversion circuit is introduced as an intermediary between the energy source and the load. This circuit includes switching elements and control logic that convert the source output to match load requirements, thereby resolving the mismatch problem while maintaining continuous power transfer capability
Solution Approach 2:
The power conversion circuit dynamically adjusts electrical parameters (voltage, current, impedance) based on the operating conditions of both the energy source and the load. By changing these parameters in real-time, the system optimizes energy conversion efficiency while ensuring adequate power delivery
2Measurement precision
If open-circuit voltage measurement is performed with direct load connection, then measurement can be taken without isolation, but measurement precision deteriorates due to load influence on the voltage reading
Solution Approach 1:
The system periodically switches between measurement mode and power transfer mode. During measurement intervals, the load is temporarily disconnected to obtain accurate open-circuit voltage readings, then reconnected for power transfer. This periodic switching enables precise measurements without permanent circuit complexity
Solution Approach 2:
The measurement circuit captures the open-circuit voltage before the load is connected or during predetermined measurement intervals. By performing the measurement action preliminarily (before load connection), the system obtains accurate source characteristics without the complicating influence of the load
3Productivity
If sampling frequency is increased for frequent MPPT tracking, then power transfer efficiency improves, but settling time requirements increase causing measurement delays
Solution Approach 1:
The measurement circuit is designed with dynamic response characteristics that can adapt to different sampling rates. The circuit includes components with optimized time constants that allow fast settling for high-frequency sampling while maintaining accuracy, enabling frequent MPPT tracking without excessive settling time delays
Data Source
AI summary
Apparatus and techniques described herein can include using an electronic circuit comprising a rectifier circuit, an open-circuit voltage (OCV) sampling circuit coupled to the output of the rectifier circuit, and a regulator circuit coupled to the output of the rectifier circuit. In an example, an isolation switch can be located between the regulator circuit and the rectifier circuit, the isolation switch configured to isolate the regulator circuit from the rectifier circuit for sampling of the open-circuit voltage by the open-circuit voltage sampling circuit. In another example, a buffer circuit can be used, such as placed in-line with a divider circuit between a divider circuit and an open-circuit voltage sampling capacitor. In this manner, the buffer circuit can provide a low output impedance, isolating the voltage sampling capacitor from the divider circuit.