Energy Harvesting DC-to-DC Converter MPPT via Cycle Count
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Solution Overview
Problem
Existing energy harvesting DC-to-DC converter circuits face inefficiencies in Maximum Power Point Tracking (MPPT) due to regular sampling of harvester output voltage, which reduces overall efficiency, and are costly for small wearables and wireless sensors, especially when using Perturb and Observe methods or fixed-frequency Discontinuous Conduction Mode boost converters.
Innovation Solution
An energy harvesting DC-to-DC converter circuit that determines a reference voltage based on the number of cycles per time period, allowing efficient tracking of maximum output power by switching between charging, discharging, and waiting states, optimizing efficiency by varying the reference voltage to maximize cycles and minimize losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If regular sampling of harvester output voltage is performed for MPPT, then maximum power point tracking is achieved, but overall efficiency is reduced due to zero output power during sampling periods
Solution Approach 1:
The system uses the existing switching cycles of the DC-to-DC converter to generate MPPT information without requiring separate sampling operations. The cycle counter naturally accumulates data during normal operation, allowing the controller to determine reference voltage based on existing operational patterns rather than interrupting operation for measurements
Solution Approach 2:
The DC-to-DC converter operates continuously without interruption for sampling. The cycle counter accumulates switching cycle information during normal power conversion operations, ensuring that the useful action of energy conversion continues uninterrupted while MPPT data is gathered as a byproduct
2Measurement precision
If Perturb and Observe method is used for MPPT, then maximum power point tracking is achieved, but additional cost and energy overhead is significant for small wearables and wireless sensors
Solution Approach 1:
The existing cycle counter, already necessary for DC-to-DC converter operation, is repurposed to provide MPPT information. No additional sensors or measurement circuits are needed - the converter's own switching behavior provides the data needed for maximum power point tracking
Solution Approach 2:
The cycle counter serves dual purposes: it controls the DC-to-DC converter operation and simultaneously provides MPPT data. This multi-functionality eliminates the need for separate measurement systems that would add cost and complexity to small wearable devices
3Productivity
If fixed-frequency Discontinuous Conduction Mode boost converter is used, then MPPT can be implemented, but optimal efficiency is limited to a narrow range of peak-inductor-currents
Solution Approach 1:
The system dynamically adjusts the reference voltage based on cycle count information, allowing the DC-to-DC converter to adapt its operating frequency and peak inductor current to match optimal efficiency points. This dynamic adjustment moves the system away from fixed-frequency operation toward variable-frequency operation that maintains optimal efficiency across varying load conditions
Solution Approach 2:
The reference voltage parameter is changed based on cycle count data, which indirectly adjusts the peak inductor current and operating frequency. This parameter adjustment allows the system to operate at optimal efficiency points across a wider range of conditions rather than being constrained to a narrow current range
Data Source
AI summary
An energy harvesting direct current to direct current ‘DC-to-DC’ converter circuit is presented. It is comprised of an energy storage element, an input configured to receive an input voltage, an output; switching means configured to perform cycles. Each cycle is marked when the input voltage reaches a reference voltage, switching the circuit such that the energy storage element enters into an energy charging state in which the energy storage element stores energy provided by the input voltage. Control means is configured to determine the reference voltage based on the number of cycles per time period performed by the circuit.