Switched Capacitor Energy Buffer Architecture
- Photovoltaic (PV) system
- PV energy extraction
- Solar cells
Researchers
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systems approach to photovoltaic energy extraction
United States of America | Granted | 9,407,164
Figures
A sub-module string is formed by connecting a group of solar cells in series (for example, six solar cells). Three sub-module strings are used to provide a solar panel. Even when partial shading causes imbalance between the sub-module strings. The asymmetries would be attributed entirely to the external operating conditions due to the small variations among maximum-power current of each cell which is well-approximated
The invention uses two separate controllers to achieve maximum power point tracking and energy balance. The input current sink serves as the MPPT tracking control by demanding a current from the PV array that maximizes the product of the demanded current and the PV array voltage. The input power from the PV array can then be monitored by measuring the PV array input voltage. An energy balance control loop can then be designed to use this informat
Technology
The invented solar panel is a series of connected solar cells coupled in a layout that substantially reduces the amount of mismatch caused by an imbalance in solar irradiance between the sub-module strings. Within the system lies a switched-capacitor DC-DC converter with a plurality of conversion levels. A conversion level is selected to provide the maximum power current of the solar cell in order for the converter to increase overall array tracking efficiency. Also included is a grid-tie inverter for coupling a PV array to a power grid. The inverter ensures the system operates stably by relying on feedforward rather than feedback processes.
Problem Addressed
Asymmetric PV strings can result from temperature variation, dirt, panel aging, or panel orientation. These asymmetries negatively impact tracking efficiency. To maximize energy extraction, distributed power conversion is employed to enable per-panel or sub-panel maximum-power-point-tracking (MPPT). There are three common architectures deployed in residential and commercial PV installations for delivering power to the grid: string inverters, micro-inverters, and DC-DC series power supplies working with a string inverter. Each of these systems has limitations. For example, they are typically constructed with magnetic components which are possibly obtained on a per-panel basis and increase manufacturing costs. High frequency switching complicates electromagnetic interface created by distributed converters.
Advantages
- Increased efficiency in overall array tracking
- Achieves high energy utilization and highly effective energy density
- Reduced manufacturing cost
Publications
Minjie Chen, et al. Stacked Switched Capacitor Energy Buffer Architecture. IEEE. 2012 Feb 5-9. doi: 10.1109/APEC.2012.6166004
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