Power Conditioning Unit MPPT via AC Capacitor Ripple
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Solution Overview
Problem
Existing power conditioning units for converting DC power from sources like photovoltaic panels to AC for grid connection face challenges in efficiently tracking the maximum power point without measuring DC voltage or current, often introducing ripple that affects energy harvesting.
Innovation Solution
A power conditioning unit with an energy storage capacitor and a power injection control block that controls a DC-to-AC converter to track the maximum power point by sensing the sinusoidal voltage component on the capacitor, adjusting the AC current amplitude based on this component, and regulating the switching speed to maximize energy transfer without direct DC voltage or current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MPPT methods measure DC voltage and current to track maximum power point, then MPPT accuracy is improved, but device complexity and reliability are worsened due to additional sensors and measurement circuits
Solution Approach 1:
The patent extracts the MPPT control function from the traditional voltage/current measurement approach and relocates it to the AC side by measuring only the AC capacitor voltage. This eliminates the need for DC voltage and current sensors, reducing device complexity while maintaining MPPT functionality through the relationship between AC capacitor voltage ripple and DC power source output power.
Solution Approach 2:
The AC capacitor voltage measurement serves multiple functions: it provides the basis for MPPT control by indicating DC power source output power levels, enables sinusoidal current control, and replaces dedicated DC measurement circuits. This multi-functionality reduces the overall number of components and simplifies the system architecture.
2Productivity
If front-end MPPT control is implemented with direct DC measurement, then MPPT performance is improved, but reliability is worsened due to electrolytic capacitors prone to failure at high temperatures
Solution Approach 1:
The patent replaces unreliable electrolytic capacitors with long-lived non-electrolytic capacitors (film, polyester, or polypropylene). Although non-electrolytic capacitors have different electrical characteristics, they provide significantly improved reliability and longevity, especially in high-temperature environments behind solar PV panels, while maintaining adequate energy storage functionality for MPPT operation.
Solution Approach 2:
The patent changes the capacitor type parameter from electrolytic to non-electrolytic, fundamentally altering the reliability and temperature resistance characteristics of the system. This parameter change enables operation in high-temperature environments without the failure modes associated with electrolytic capacitors, directly improving system reliability while preserving MPPT functionality through alternative control methodology.
3Device complexity
If AC current amplitude is controlled based on sinusoidal voltage component, then MPPT tracking is improved without DC measurement, but power transfer precision is worsened
Solution Approach 1:
The patent implements feedback control by continuously monitoring the AC capacitor voltage and using its sinusoidal component to adjust the AC current amplitude. The controller compares the measured AC capacitor voltage with reference values and dynamically adjusts the inverter output to maximize power transfer. This feedback mechanism compensates for the indirect measurement approach and maintains accurate power transfer despite the simplified sensing methodology.
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
This approach enables efficient maximum power point tracking, maximizing energy harvesting from DC sources like photovoltaic panels by controlling the AC power delivery to the grid, reducing the need for front-end MPPT and avoiding electrolytic capacitors, thus enhancing reliability and longevity.
Implementation Method 1
an energy storage capacitor for storing energy from said dc power source for delivering to said ac mains power supply output
Implementation Method 2
a dc-to-ac converter coupled to said output for converting energy stored in said energy storage capacitor to ac power for said ac mains power supply output
Data Source
AI summary
We describe a power conditioning unit with maximum power point tracking (MPPT) for a dc power source, in particular a photovoltaic panel. A power injection control block has a sense input coupled to an energy storage capacitor on a dc link and controls a dc-to-ac converter to control the injected mains power. The power injection control block tracks the maximum power point by measuring a signal on the dc link which depends on the power drawn from the dc power source, and thus there is no need to measure the dc voltage and current from the dc source. In embodiments the signal is a ripple voltage level and the power injection control block controls an amplitude of an ac current output such that an amount of power transferred to the grid mains is dependent on an amplitude of a sinusoidal voltage component on the energy storage capacitor.