Naki Guler

Design and application of a novel single input — Multi output DC/DC converter

A novel single input-multi output DC/DC converter has been developed to feed the loads that have different voltage levels. For independent voltage control and high voltage gain, the converter has two layers as positive and negative. The presented design of converter structure has been analyzed theoretically and its state equations have been worked out. Theoretical analysis has been tested in MATLAB environment and verified with successful results. During simulation studies, voltage control of power layers was realized by adjusting the duty cycles of the switches with a PI controller. It has been observed from the simulations that the model presented operates successfully under the variable input voltage and different output voltage conditions and the output voltages are controlled as independent from each other. Once the model has been verified in simulation environment, a real prototype has been designed and then voltage control and efficiency tests have been performed experimentally on the prototype. Results show that the operating efficiency of the system is between 75–88% and the output voltages are also controlled independently similar to the simulation results. Thanks to the model developed, the overall structure of the system has been simplified and thus its applicability has been increased because fewer components were used in the design and also high voltage gain was provided.

Short-circuit fault analysis on microgrid

This paper presents, a fault simulation on a microgrid consisting of a wind turbine, a solar panel and fuel cell. The power produced by different sources is combined on the same DC bus and converted to AC form using a three phase inverter in order to transfer it to 3-phase AC load. The system takes some precautions against some undesired situations. In case of a fault, the failed section of microgrid has been seperated from the grid rapidly using breakers located at the output side of each energy sources and inverters.

Application of a boost based multi-input single-output DC/DC converter

Design and application of a multi-input single-output (MISO) dc/dc power converter is presented that provides the interoperability of separate energy sources having different power levels those are connected to the same dc bus through a double-layer boost converter. Thus, power control of the proposed MISO converter is realized on both the negative and the positive layers. As the first step, mathematical model and state equations of the converter are created and then verified in Matlab/Simulink. Control of the power flow and the output voltage is achieved by setting the duty cycles of switches located on each layer. A PI controller is added to the model to optimally perform the voltage and load sharing control. Furthermore, a real prototype of the proposed MISO converter is carried out to verify the simulation results. Experimental results show that the proposed MISO converter is a powerful solution for hybrid energy systems consisting ofdifferent kind ofenergy sources.

PI controlled solar energy supported static excitation system desing and simulation for synchronous generators

In this study, an automatic excitation control system design and simulation has been realized. Especially on the energy generation power plants, generator terminal voltage is increased by the step-up transformers and equalized for the parallel connection to the grid. Terminal voltage of the synchronous generators is adjusted according to the field current and the rotor speed, therefore these two variable has to be controlled at simultaneously. So in this study generator voltage and the speed are controlled at the same time. Mechanical control is realized by PI for the constant frequency. Thyristor Controlled rectifier is connected to the output of the transformer that is connected to the generator terminal voltage and controlled closed loop. On static excitation an external DC voltage source is required. In this work as external DC source solar energy has preferred. For the field flashing DC voltage has taken from solar panels. When generator has excited enough for the TCR, field flashing has stopped. Firing angle of the TCR is controlled by PI. Hence, generator terminal voltage is equalized reference voltage that is determined before. For block the over excitation failure a software has been realized. Excitation system will be operated between two determined frequencies that are lower and upper limits. Excitation and frequency system control has been realized with MATLAB/Simulink.

Design of a computer controlled speed control system for wound-rotor inducion machines

This study introduces a novel and powerful speed control system with computer interface for wound-rotor induction machines (WRIM). In order to improve the sensitivity and stability of the control process, a high-speed digital signal processor (DSP) is used as the main controller. A serial resistor is connected to rotor side of WRIM to control the output power of the machine. The power consumed on the serial resistor is continuously controlled by PWM signals generated from DSP. A zero-crossing detector is used for calculating the rotor frequency. Thus, the rotor speed is obtained without using a mechanical sensor like external encoders. Thanks to using this method, measurement accuracy is increased and the total cost is decreased as well. After calculating the mechanical speed using the measured rotor frequency, the rotor speed is fixed to the reference value by a PI controller. In addition to speed control system, a graphical user interface (GUI) is also designed to set the reference speed through a computer screen. On this GUI, users can also observe and monitor the some parameters in real time such as rotor frequency, rotor slip, actual rotor speed, actual effective value of the serial resistor, switching ratio of PWM signals.

FPGA based parallel connection system of separate voltage sources

In this study, parallel connection of separate voltage sources has been realized using cuk converters. For this aim, output voltages of converters are measured continuously and then fixed to a reference value. The PWM signals which are required to control the converters and to sense the current and voltage signals are generated by an FPGA. Since the FPGA has parallel processing feature, voltage and current data of the system are measured at the same time. Thus, the converters are connected in parallel punctually and load sharing between them are provided in order to eliminate some undesired cases like unbalanced loading. In the system realized, two identical cuk converters are used. As cuk converters can operate both in buck and boost modes, output voltages are fixed to the reference voltage successfully, even though input voltages are low or high. Experimental results show that the system achieved operates with a reasonable efficiency ranging from 81% to 88%.