Modeling and Design of Series Voltage Compensator for Reduction of DC-Link Capacitance in Grid-Tie Solar Inverter

A grid-tie solar inverter with a series voltage compensator for reducing the high-voltage dc-link capacitance is presented. The compensator obtains energy from the dc link to sustain the voltage on its dc side and generates an ac voltage to counteract the voltage ripple on the dc link. As the compensator processes small ripple voltage on the dc link and reactive power, it can be implemented with low-voltage devices, and thus, its volt-amp rating is small. As the required energy storage of the dc link, formed by a reduced value of the dc-link capacitor and the compensator, is reduced, the architecture allows replacing popularly used electrolytic capacitors with alternatives of longer lifetime, such as power film capacitors, or extending the system lifetime even if there is a significant reduction in the capacitance of electrolytic capacitors due to aging. Detailed mathematical analysis on the static and dynamic behaviors of the overall system, and the control method will be presented. A simplified design procedure for the compensator will be given. A 2-kW, 220-V, 50-Hz prototype has been built and evaluated. The theoretical predictions are compared favorably with experimental results. Finally, the implementation cost with electrolytic-capacitor and compensator for the dc link will be compared.