1. M OBILE P OWER S TATION A BSTRACT The Mobile Power Station (MPS) is a device that manages and stores solar energy in a lithium ion (Li-ion) battery pack while tracking the maximum power point (MPPT) of the connected solar array. The MPS utilizes a DC buck converter design to control the impedance of the Li-ion battery pack and external load, allowing maximum power transfer from source to load. Our client, PowerFilm Inc., expressed a need for the MPS in military and consumer markets. P ROBLEM S TATEMENT & S OLUTION Photovoltaic (PV) solar arrays can be used to power mobile devices; however, solar array output power is non-constant and most mobile device chargers require a constant voltage and current source. Team dec1013 purposed building a MPS that would supply a constant voltage and current to mobile devices, while tracking the maximum power point of a PV solar array. M AIN P ROJECT R EQUIREMENTS FR-01Solar panel input – 1.2A @ 5.4V (20W) Amorphous Silicon Panel FR-02100W minimum Lithium-Ion battery capacity FR-0315V DC input (with AC-DC Adapter) FR-0412V DC output FR-05Operation in temperature range of -20°C and 60°C FR-07Charge Balancing Circuitry to keep Li-Ion Batteries balanced FR-08 Achieve 80% or greater efficiency NFR-01 MPS should have a weight of less than 5 pounds NFR-02 MPS should be manufactured for a cost of under $500 per unit NFR-03 MPS should easily fit inside a military backpack MPPT & L I - ION C HARGING C ONCEPT Li-ion battery charging cycle includes thee phases: trickle, constant current, and constant voltage. The charging cycle must be strictly followed to prevent battery pack overcharge and fire. Measuring the output voltage and current of the buck converter, the MPS changes the duty cycle of the buck converter to follow the Li-ion charging cycle. When the MPS enters the constant current charging phase, it will also track the MPP, providing maximum power transfer until the battery pack voltage reaches 12.6V. The MPS will continue to hold the output voltage at 12.6V during the constant voltage phase until the battery pack is fully charged. P ROJECT D ESIGN The basis of the MPS is a buck converter, which controls the voltage to the battery pack, and thus the current flowing to pack. The buck convertor is controlled by varying the duty cycle of a PWM signal generated and controlled by the MSP430. Programmed in C code, the MSP430 follows a charging algorithm based on feedback voltages and currents. UART communication to a PC provides diagnostic information, and the charge controller balances the Li-ion battery pack. Li-ion Batteries (3 series cells x 8Ah) Buck Converter Microprocessor (MSP430) Solar Panel Source 5VDC (USB) 12VDC 120VAC Serial Communication (UART) to PC Voltage and Current Sense PWM Control Signal Charge Control (BQ20Z70) Feedback Voltage/Current Sense Possible Loads C ONCLUSION Our team designed and created the MPS, which effectively tracks the MPP of a connected solar array while charging and balancing a Li-ion battery pack. The MPS will provide an efficient, lightweight, and affordable source of energy for users in remote locations, with the adaptability of charging from a non-solar source. S CHEDULE & B UDGET Costs Per Unit (when ordered in units of 100) MPS components $ 21.25 Battery protection circuitry $ 9.55 Battery (3x 3.7V 8Ah Li-ion) $ 97.25 PCB $ 5.00 AC/DC input & output adapters $ 12.75 Total $ 145.80 T ESTING & F ABRICATION The MPS was rapidly developed and tested on a breadboard for functionality. Next, a PCB was designed, populated, and tested with great improvements in voltage and current sensing. The MPS was first tested with a constant power supply, then a solar array. Team: Brad Jensen (EE) Will Klema (EE) Nate Schares (EE) Advisor: Dr. Ayman Fayed Client: PowerFilm Inc. Project ID: dec1013 GUI A GUI was developed to display and plot critical data (via USB) from the MPS including voltage, current, and duty cycle.