Analysis of series parallel resonant converter and digital controlled design implementation

Due to the development of technology, increased use of electronic device and increasing the power consumption required by the spread of these devices cause to increase the importance of power converters. These power converters have small sizes and higher efficiencies day after day with the changes made by power electronics. As the resources of world are limited and the energy consumed increases day by day, the effects of energy loss and inefficiency in power converters are increasing. Therefore, studies on this subject are continuing in order to obtain converters with lower size and higher efficiency. Various structures have emerged about power electronics with the development of semiconductor technology. Because of efficiency and different requirements, power conversion devices used in modular construction are used in power distribution systems of telecommunication devices in data processing centers. In these modular systems, different type converters are applied according to requirements. Power converters can be grouped in three main categories when considering the working conditions. These titles are; linear, switching mode and resonant power converters. Each converter type has its own places of use because it has different advantages and disadvantages. Firstly, linear regulators are simple converters that emit low noise because they do not switch, regulate the output voltage at a good level and have a fast response time. These converters are used in low power, low voltage integrated circuit power supplies. In structures with high power and high input voltage, linear converters do not be used because of inefficiency. Secondly, switching mode power converters have been applied to switch in high frequencies and to use power converters capable of working with smaller size and higher efficiency by using low value inductance and capacitor structures. Switching mode power converters are quite advantageous in terms of efficiency because transmission losses are very low compared to linear converters. However, transmission losses are small relative to linear converters, this loss becomes an important factor affecting high power requirements. Another important factor limiting the efficiency of these converters is increased switching loss in high frequencies. When the semiconductor elements are switching at high frequency, the power is consumed on the element because the voltage and current is not zero instantaneously. In areas where higher powers are required, resonant converters have been developed with switching mode power converter efficiencies being inadequate and high electromagnetic interference being seen. Higher efficiencies have been achieved with resonant converters at high power applications. For this reason, resonant converters are frequently used in industrial and consumer electronics. Resonant power converters achieve higher efficiencies than switching mode power converters because they can make zero voltage switching and zero current switching. In this thesis study, LLC resonant converter analysis was performed by mentioning resonant power converters. Resonant power converters according to the type of resonance tank; there are three different categories as serial resonant converter, parallel resonant converter and series-parallel resonant converter. The series resonant converters and the parallel resonant converters are two-component resonant tanks and have a single resonance frequency. Serial parallel resonant converters have two resonant frequencies with three elements. These converters are divided into LCC resonant converter with two capacitances and an inductance, LLC resonant converter with one capacity and two inductances. Due to its structural features, the characteristics of the gain of each converter and the behaviors at the variable conditions are different. After mentioning resonant converters, LLC converters were analyzed. The effect of circuit parameters on gain is investigated by making fundamental harmonic approach and the methods of determining converter parameters are mentioned. The gain equation of the circuit was obtained by quality factor, inductance ratio and frequency ratio. Variations in the gain graphs are plotted to monitor the gain effect of changes in quality factor and inductance ratios. The decrease in the ratio of the total inductance to the resonance inductance in the resonance tank increases the gain but the increase in the ratio, decreases the gain. The reduction of this ratio reduces the total impedance as it reduces the magnetization inductance and the circulation current flowing from the tank is increasing. This leads to increased power loss and reduced efficiency. For this reason, optimum inductance ratio should be selected when designing a LLC. During continuous operation, the voltage and current graphs on the resonance elements can be obtained from the operating states of the LLC converters during a switching period. Considering the whole frequency range, the converter can work in 6 different situations. State equations for each circumstances were obtained to achieve these graphs. By using these equations state trajectory analysis were performed and the variation of the voltage and current graphs on the circuit elements according to frequency was investigated. After the analysis, a LLC power converter is designed by using these analysis results. The design of the LLC power converter for the determined operating values was tested on the circuit simulation program. Instead of the inductance in the resonance tank, the leakage inductance of the transformer used in the circuit is used and the circuit is implemented in accordance with the determined parameters. In the implemented circuit, a C2000 Launchpad microcontroller which belongs to Texas Instruments was used as a controller and it was programmed in C code to control digitally. The PI algorithm is also used to keep the output voltage constant and achieve the steady state error zero. Optocoupler is used to get feedback from the output voltage. The IR2110 integrated circuit is located between MOSFETs and microcontroller to drive the MOSFETs. The buck converter structure is added using the FSL306LR analog IC to provide IC supply voltages. The PCB was obtained through the circuit drawing program and the components were assembled. A programmable DC power supply and digital load are used to test the circuit. Different input voltages were tested under different load conditions and compared with the gain characteristics generated in the analysis section within the operating conditions. In this section, the current in the resonance tank is given the different operating frequencies. In addition graphs of load transient states have been obtained. Finally, it was observed that the LLC power converter was operating at zero voltage switching and the efficiency graph was obtained.