APEC: Tesla Roadster, solar-panel dangers kickstart power fest

Palm Springs, Calif.—The 25th Applied Power Electronics Conference (APEC) kicked off here this week with a dynamic plenary session that discussed the past and future of power, exposed the latest improvements to the Tesla Sports Roadster, uncovered the hidden dangers and inefficiencies of solar panels and showed how close-coupled cooling can achieve a 31 percent improvement in cooling efficiency for data centers.

The plenary session and the conference kicked off with a "History and Future of Power Electronics," preamble by Dr. John Kassakian. Kassakian reviewed the conference's origins and 25-year history before describing the rise in importance of today's power-design engineer as they pursue advances in energy harvesting, implement the smart grid and focus on power management and conservation.

Kassakian laid the path for the plenary's next speaker, J.B. Straubel, Tesla's chief technology officer. Straubel captivated the crowd with detailed explanations of the power system of the company's now famous Roadster and how continual improvements in power electronics had greatly improved power density and motor torque making the electric power train possible—and the fully electric vehicle (EV) a reality.

Now capable to reach distances of up to 244 miles one battery charge, the latest power train now features an improved inverter that can deliver higher motor current, an improved motor that can handle more current and torque, and the use of IGBTs to convert and regulate power from the battery.

According to Straubel, the use of IGBTs improved the power train's efficiency and power handling capability while also boosting the output current from 640 to 850 A rms—a 33 percent improvement.

The dangers of solar
While solar panels have the altruistic advantages that come with energy harvesting and relatively few environmental trade-offs, SolarBridge Technologies' Chief Executive Officer Rob Van Dell warned of the unforeseen dangers that come with its installation on rooftops.

Due to the high DC voltage these panels require there lies an inherent fire risk if an "arc fault" occurs. An example was given of fire fighters shutting down a building's but forgetting to shut off the power generated by the panels. Crews have learned that the electrical supply lines for a group of panels can arc and cause fires and they are now trained to take precautions to ensure that the panels are de-energized.

However, solar panels have other, more-insidious disadvantages when implemented in series. In such instances, a low output from any one of the panels in the series can impact the entire system and result in a voltage drop. Consequently, every panel in the series must be matched within 3 percent output to operate effectively.

Van Dell's solutions to this problem included the concept of an AC array implementation , which places the power microinverter immediately on the back of each individual panel and then incorporating filtering techniques such as passive DC bus configurations and electrolytic capacitors.