Intern Zhan Su and PhD Student Matthew Qi with Advisor A. Banerjee

Illinois’s Electrical and Computer Engineering Building has sixty 400W solar panels dedicated solely for research. This project, funded by the Grainger CEME, aims to create an efficient, reliable, and safe hardware framework to extract power from these solar panels and feed it to the building grid (Figure 1). Each solar panel is connected to an isolated dc-to-dc converter that steps up the voltage from 72V (nominal) to 400V (constant). The 400V dc bus takes all the harvested power and delivers it to the grid using two 10KVA inverters. The dc-dc converter comprises two components—a boost converter cascaded with an LLC converter. The boost converter controls the power flow using algorithms such as maximum power-point tracking, while the LLC converter ensures isolation between the solar panel and the 400V dc bus. The experimental prototype achieves a peak efficiency of 95%. The grid-tied inverter uses three-level T-type topology, which has lower switching loss and harmonic distortion than a two-level inverter, thus reducing the output filter’s size and making the inverter more compact.
Currently, the 60 dc-to-dc converter modules are in production to populate our enclosure (Figure 2), which is designed and built to house the modules with a fan cooling array. Once integrated, the converters must constantly provide fault data while operating simultaneously to deliver power and shut down on command while operating. They must incorporate power sequencing and turn on control algorithms to prevent inrush current. All converters are digitally controlled and connected to a CANbus communication network. Each device’s voltage, temperature, and current are monitored, and each module is controlled remotely through a user terminal. The initial production test batch (Figure 3) has been assembled and is integrated into the enclosure to simulate the final operating conditions. Using the CANbus data, testing and programming are being performed on the steady-state, fault and transient conditions to ensure stable nominal operation and safe turn-on and turn-off conditions.

Figure 1. Power architecture diagram

Figure 2. Dc-dc converter enclosure with top row populated

Figure 3. One “shelf” of five dc-dc converters.