DESIGN AND IMPLEMENTATION OF BUCK CONVERTER FOR SOLAR CHARGE CONTROLLER

• Main Author: Dharma, Surya
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/82158
• Institution: Institut Teknologi Bandung

Solar is one of the renewable energy sources. There is a device that is able to convert solar energy into electrical energy called a solar panel. Solar panel functions well only when the solar panel is exposed to the sunlight. To use the electrical energy generated by solar panel at night, it is necessary to store the electrical energy generated in an energy storage device such as a battery. The simplest system consists of a solar panel directly connected to a battery. This system configuration results in low power transfer efficiency. In addition, this configuration will shorten the battery life due to the uncontrolled battery charging process. To solve this, a device to control the battery charging process is installed between the solar panel and the battery. The device is called a solar charge controller (SCC). Usually Pulse Width Modulation SCC (PWM-SCC) is used for a small scale system. As the name suggests, this type of SCC utilize PWM signals to control the battery charging process. However, the power transfer efficiency after installing PWM-SCC does not increase, because the PWM-SCC does not have features to maximize the power generated by solar panel. A SCC with a feature to control the battery charging process as well as a feature to maximize the power generated by solar panel is called Maximum Power Point Tracking SCC (MPPT-SCC). The power generated by solar panel is called power point, hence why it is called MPPT. The proposed MPPT-SCC design consists of four main parts, namely power conversion, charge controller, controller of the power conversion-charge controller circuit, and interface. The parts of the SCC designed and implemented in this final project are the power conversion, a part of the necessary firmware for the controller of the power-conversion-charge controller circuit, and voltage regulators. The power conversion subsystem consists of a DC-DC converter, input voltage sensing circuit, and input current sensing circuit. The DC-DC converter topology used is buck converter since the battery voltage is 12 V. Because efficiency is the main target, the topology used is synchronous. This synchronous buck converter topology requires two complementary PWM signals to control two switches alternately. The input voltage sensing circuit consists of a resistor divider network and an anti-aliasing filter, while the input current sensing circuit consists of a current resistor, a differential amplifier, and an anti-aliasing filter. The firmware implemented consists of PWM signals generation using MCPWM peripheral and sampling using ADC peripheral. Voltage regulators are implemented with the LM2596 step-down module as the voltage source for controllers, sensors, and switching circuits. The design of the DC-DC converter and sensing circuits starts from calculating the minimum component values required based on the specification. Because the components are assembled by the assembly services, the components selected must be able to be assembled, since only certain components can be assembled. PWM signal generation utilizes peripherals with fixed connections between the submodules, so it does not require a hardware design. The MPPT iv algorithm is implemented as the firmware on the ESP32, so it does not require a hardware design as well. Because the components are already assembled by the assembly services, the implementation of the buck converter and the sensing circuits only consist of soldering the header pins, connecting certain header pins, and testing the circuits. Generation of two complementary PWM signals utilize timing events generated by the PWM timer, while sampling utilizes functions from the ESP-IDF API. The implementation of the incremental conductance algorithm apparently causes the power point to oscillate at initial power point. To solve this, the algorithm is modified so that the modified algorithm favors the increment of the duty cycle. The designed and implemented buck converter has a maximum efficiency of 97,1% at 140 W input power. The testing was carried only up to an input voltage of 30 V and input current of 6,26 A due to the equipment limitations. The modified incremental onductance algorithm manages to track the maximum power point with a standard deviation of 1,0919 W.