Per Panel Photovoltaic Energy Extraction with Multilevel Output DC-DC Switched Capacitor Converters

Technology

The DC-DC module integrated converters (MICs) typically operate with local autonomous MPPT control. In the system proposed here, the responsibility of MPPT is shared among the DC-DC modules and the central inverter. As a result, the required complexity of the DC-DC MICs is simplified. Significantly, the system can be implemented with switched capacitor multilevel DC-DC converters and a central ripple-port converter. Per panel magnets and electrolytic capacitors are eliminated. The simulated prototype of this configuration achieved the following efficiencies: tracking efficiency 95.43%, conversion efficiency 97.56%, and total efficiency of 93.10%.  

Problem Addressed

Total installed cost and total cost of ownership are two key metrics limiting grid penetration of solar power. Both the installed cost and the cost of ownership are affected by the power converter’s lifetime, system complexity, and tracking efficiency. Tracking efficiency is normally addressed with a maximum power point tracking (MPPT) algorithm embedded in the control of the converter or inverter. However, in the control of the converter or inverter the MPPT function’s effectiveness is reduced by the power ripple at the panel terminals. This is often overcome by an electrolytic capacitor, but these capacitors have a relatively short lifetime. The proposed technology is a  “ripple port” inverter, which still directly interfaces the PV cell, but directs the 120 Hz ripple power to a transformer couple ripple port and away from the cell. Significantly, the system can be implemented with switched capacitor multilevel DC-DC converters and a central ripple-port inverter.  

Advantages

• Improves energy extraction
• Reduces system complexity
• Reduces cost