An FPGA Implementation of PWM for DC-DC SEPIC Converter for Wireless Sensor Network

A field programmable gate array (FPGA) is a complex integrated circuit having millions of logic gates inside and can be configured to design any multifunction electronic system. FPGAs are programmed using Hardware descriptive languages, i. Verilog HDL and VHDL. In this research work an FPGA chip has been used to control overall operation of a DC-DC SEPIC converter aimed for providing power to the wireless sensor network (WSN) nodes. Provision of continuous and smooth electric power to the WSN nodes is considered as the challenging task. In most cases the WSN nodes are placed at hard locations, where it is not an easy job to replace the batteries frequently. The ultimate solution is to provide the electrical energy to the WSN nodes from a battery, which is connected with the Photovoltaic (PV) array. But there are huge fluctuations in the output voltage of the PV array as a result of the variations in environmental parameters, i.e. ambient temperature, light intensity, humidity and dust. On the other hand the battery voltage also drops due to the continuous use. The previous studies shows, that in a common 12V PV array the output voltage varies between 2V and 20V, while most WSN nodes are operated by 3.3V battery, so this battery will also need 3.3VDC for the purpose of charging. Now the solution of this problem is to design an efficient DC-DC converter, which will convert the complete range of output voltage from the PV array to the 3.3VDC. In this study a SEPIC converter has been designed to fulfill the energy requirements of the WSN nodes. The proposed converter design is based on Pulse Width Modulation (PWM). The PWM method is very useful, because it charges the battery with minimum stress; as a result we get extended life of the battery. In conventional DC-DC converters analog components are used for controlling the PWM, but in this design the analog circuitry has been replaced by the field programmable gate array (FPGA). The reason of using the FPGA is to enhance the accuracy of the design and availability of cheap FPGA devices in the today's electronics market. For circuit design and simulation well-known software PSIM has been used, while for FPGA implementation the ModelSim simulator has been used. The designed DC to DC converter has been tested under different circumstances.