Dithering Digital Ripple Correlation Control for Windowed Sensing for Photovoltaic Maximum Power Point Tracking
Christopher Barth with adviser R. C. N. Pilawa-Podgurski
A new maximum power point (MPP) tracking algorithm for use in switching power converters for photovoltaic (PV) applications is developed. To maximize energy harvested from PV panels, it is necessary to operate them at a particular value of current and voltage, the panel (MPP). This point changes with solar conditions, temperature, and panel age, necessitating continuous tracking. Digital dithering ripple correlation control (DDRCC) uses pulse width modulation (PWM) dithering to increase the control resolution of the solar power converter hardware, and then performs MPP tracking using the ripple created by dithering.
We demonstrated that DDRCC can be scaled to standard PV panel power levels using a windowed measurement approach, as shown in Fig. 18. Initially the voltage signal from the current sense resistor used for current measurement is very small and challenging to measure accurately using a low-cost microcontroller analog-to-digital converter (ADC). By amplifying the signal and shifting it into the ADC range, a high-resolution measurement can be obtained. This technique is beneficial in PV applications, where for MPP tracking dc measurement accuracy is less important than ac accuracy. An approximate measurement of the dc magnitude can be obtained from the known shift in the ADC measurement window.
This work was supported in part by the Illinois Center for a Smarter Electric Grid, through Illinois Department of Commerce and Economic Opportunity (DCEO) under grant 12-197001.