DC-DC Half Bricks Provide Reliable Power for Blue Sky Solar Racing

July 12, 2012
By
Blue Sky Solar Racing Team - University of Toronto

Blue Sky Solar Racing Team - University of Toronto

Last year we put up a post about how Cambridge University Eco Racing (CUER) has been using MegaMod chassis-mounted DC -DC converters in their solar-powered racing car. We just recently spoke to Blue Sky Solar Racing at University of Toronto about the Vicor products they’re using in their cars.

The University of Toronto’s Blue Sky Solar Racing group have been building cars for international competition since 1997. One of the main race events is the World Solar Challenge race, held every two years in Australia and development is now under way for 2013. But significant changes in the rules introduced by the organisers have created new challenges for the group. The vehicles must have four wheels instead of three as previously, while their maximum length has been reduced from 5 to 4.5 metres. The driver’s sitting position must also be more upright. These changes are all intended to stimulate further innovation and improve the practicality of solar car designs, paving the way towards production cars. However, as all the contestants have come to realise, implementing these changes means significant electrical, mechanical, aerodynamic and solar array modifications.

Blue Sky is using Vicor half brick DC-DC modules, which proved to be reliable power conversion components within their 2011 vehicle. The car’s electrical system comprises the solar array, battery pack, motor, and control, telemetry and communications electronics. Power is distributed between these components by a 120 Vdc high current power bus, while the electronics subsystem it supplies requires 12 Vdc. Accordingly, a VI-JT1-CZ-F3 DC – DC  module performs the voltage conversion, handling up to 25 W of power. The ‘junior’ sized half brick module is soldered directly onto the main electronics controller board, complete with an integral heat sink. The module’s ability to operate without a fan improves reliability and reduces power demand- a particularly important advantage, given the project and its objectives.

A second Vicor converter is used to solve a specific ‘bootstrap’ situation. For safety reasons, it must be possible to isolate the vehicle’s electronics, solar array and battery using a pushbutton and on/off relay. The converter feeds battery power directly to the relay, as this logically cannot be energised from any system that it switches. Finally, a third converter is used to power devices known as Peak Power Trackers (PPTs). Each solar array has a unique V/I characteristic that varies with changing sunlight conditions and ambient temperature. The PPTs continuously monitor these varying output voltage and current levels and determine the operating point that will deliver the maximum possible power to the batteries. The three Vicor converters together handle up to 50 W.

As well as these control functions, the electronics subsystem manages the car’s telemetry and communications. Status data from the battery and array, and other parameters such as speed and torque are collected through on board CAN buses, and streamed through a radio communications link to receiving equipment on board lead and chase vehicles. The information gathered is used for immediate race strategies, forecasting available power and comparing it with predicted requirements for hills and other upcoming race conditions. The information is also used as feedback for possible longer-term design improvements.

Reliability was a key consideration in choosing the Vicor DC-DC converters. “Because of their trouble-free performance within Azure, we trusted the converters and were happy to solder them directly on to the PCB for the communications system.” commented Zhe Gong, Electrical Team Lead on the project. “Additionally, we viewed our ability to use the devices without active cooling as an important benefit to the car.”

The project is progressing well, with the telemetry system nearly finished and already working on the bench. The plan is to race the car in the Australian World Solar Challenge 2013, and again in the American Solar Challenge 2014.

Blue Sky Solar Racing at University of Toronto

Blue Sky Solar Racing at University of Toronto

Blue Sky Solar Racing at University of Toronto

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