Maker takes solar energy on-the-go
We’ve all experienced a power outage in our lifetimes. Wouldn’t it be nice if next time, instead of breaking out the candles and flashlights, you could simply flip on your personal solar-powered generator? Nathaniel VerLee, an electrical engineer and Maker, is developing a solar energy generator to do just that. His generator is an all-in-one application that will not only be able to provide temporary electricity during a power outage, but will also provide power to devices that are not connected to the grid like street lights and mesh networks, as well as provide power to remote areas such as cabins or sail boats.
Nathaniel is currently developing the PCB to go into a “grid in a box” type of application, where a battery, folding solar panel, LED lamps and power cables all fit into a single rugged case for use on camping trips or during power outages. He developed this project as a way to combine his interest in solar energy and desire to use maximum power point tracking (MPPT) in medium-power DC applications.
Nathaniel’s solar energy generator has a buck boost topology DC/DC converter that can step up or step down the output voltage from the input voltage. The generator is based on a Texas Instruments C2000™ Piccolo™ TMS320F28035 microcontroller (MCU), which enables MPPT so that the system can operate at peak efficiency, or the maximum power point. The maximum power point is sensed by TI’s OPA2317 operational amplifiers for current and voltage. The information is used as inputs to the MPPT algorithm which periodically changes the input to output voltage relationship of the DC-DC converter to determine the MPPT operating point. The system also integrates a TI LMR62014 boost regular IC for 12V rail, a TI TPS54360 buck regular IC for 5V rail, two TI TPS62260 buck regular ICs for 3.3V and 1.8V rail, and gate drivers for the converter. In the final single-PCB solution, a buck converter will be connected to a panel input and the battery, which will source power from the higher of the two voltages. The 5V rail will then supply power for a 12V rail (boost) for the FET gate drivers, and the 3.3V and 1.8V rails will supply power for the microcontroller, sensor circuits, OLED display and other circuits. In addition, a TI ULN2003 high-voltage high-current Darlington transistor array features high-voltage outputs with common-cathode clamp diodes for switching inductive loads. This is critical to protecting the battery from over discharge and short circuit.
Nathaniel chose to use TI’s C2000 Piccolo TMS320F28027 LaunchPad development kit in the prototyping stage of his project since it offers the necessary debugging and programming interface as well as 5V and 3.3V power supplies. He migrated to the C2000 F28035 MCU for development, as this MCU offers the higher pin count needed in his final project as well as many peripheral features ideal for digital power applications. “Configuring [the F28035 MCU] to drive the buck boost converter is not only easy, but powerful, allowing multiple converters to be driven in a phase relationship, and for fast shut down of the converter stage in the event of a dangerous transient event,” said Nathaniel. As a self-proclaimed analog and power engineer, Nathaniel also appreciated the simplicity and low cost of entry of using the Code Composer Studio™ integrated development environment with the XDS100 debugging tool to tackle this embedded project.
Nathaniel also commented on why he chose TI’s boost and buck regular ICs, which are abundant in his project. “I like that TI has a comprehensive portfolio of ICs for generating rail voltages,” he said. He also enjoys being able to use TI’s WEBENCH® design environments to quickly develop designs with less time and effort.
This solar energy generator is a side project that Nathaniel works on in addition to a full-time job, and his biggest obstacle has been finding time to stay on track and design his project on weekends. He says that although he may eventually decide to sell the hardware as a complete product, his main objective for now is using the project as “more of a learning and exploration platform that [he] hopes to eventually share with others in some sort of hobby or educational type capacity.” He also hopes to experiment with different features and test them in the hands of other engineers to see which features will be most useful in his generator.
Although this project has been quite an undertaking, Nathaniel says, “Living during a period of rapid growth in energy saving technologies is very exciting to me – I hope that as these technologies grow, they help save energy and work towards reducing our environmental footprint.”