Ibrahim Sefa

Fault Detection and Protection of Induction Motors Using Sensors

Protection of an induction motor (IM) against possible problems, such as overvoltage, overcurrent, overload, overtemperature, and undervoltage, occurring in the course of its operation is very important, because it is used intensively in industry as an actuator. IMs can be protected using some components, such as timers, contactors, voltage, and current relays. This method is known as the classical method that is very basic and involves mechanical dynamic parts. Computer and programmable integrated circuit (PIC) based protection methods have eliminated most of the mechanical components. However, the computer-based protection method requires an analog-to-digital conversion (ADC) card, and the PIC-based protection method does not visualize the electrical parameters measured. In this study, for IMs, a new protection method based on a programmable logic controller (PLC) has been introduced. In this method, all contactors, timers, relays, and the conversion card are eliminated. Moreover, the voltages, the currents, the speed, and the temperature values of the motor, and the problems occurred in the system, are monitored and warning messages are shown on the computer screen. Experimental results show that the PLC-based protection method developed costs less, provides higher accuracy as well as safe and visual environment compared with the classical, the computer, and the PIC-based protection systems.

Sliding-Mode Control for Single-Phase Grid-Connected

This paper presents a sliding-mode control (SMC) strategy for single-phase grid-connected LCL-filtered voltage source inverters (VSIs) with double-band hysteresis scheme. The proposed SMC is simpler than the existing SMC methods devised for grid-connected VSIs since its sliding-surface function requires the sensing of capacitor voltage and grid current only. In addition, a double-band hysteresis scheme which ensures the switching of a transistor in the VSI during a half cycle while it remains either on or off in the other half cycle of the fundamental period is used to mitigate the switching frequency. Furthermore, the analytical expressions for the instantaneous and average switching frequencies are derived. The theoretical considerations and analytical results are verified through computer simulations and experimental results obtained from a 3.3-kW system. Simulation and experimental results show that the proposed SMC strategy exhibits an excellent performance in achieving the required control objectives such as fast dynamic response, robustness, sinusoidal grid current with low total harmonic distortion, and simplicity in a practical implementation.

\mbox{LCL}

In this study, an extended Lyapunov-function-based control strategy that assures global asymptotic stability is proposed for single-phase UPS inverters. The Lyapunov function is formed from the energy stored in the inductor and capacitor due to the fact that the system states converge to the equilibrium point if the total energy is continuously dissipated. It is shown analytically that the classical Lyapunov-function-based control leads to a globally asymptotically stable system at the expense of steady-state errors in the output voltage, which exist due to the lack of outer voltage loop in the control input. Therefore, an extended Lyapunov-function-based control strategy is proposed, which eliminates the steady-state error without destroying the global stability of the closed-loop system. The steady state and dynamic performance of the proposed control strategy has been tested by simulations and experiments under resistive and diode bridge rectifier loads. The results obtained from a 1-kW inverter demonstrate that the developed control strategy not only offers global stability, but also leads to good quality sinusoidal voltage with a reasonably low THD, almost zero steady-state error in the output voltage, and fast dynamic response under linear and nonlinear loads.

-Filtered VSI With Double-Band Hysteresis Scheme

This paper presents a new control strategy based on Lyapunov-function and proportional-resonant (PR) controller for single-phase grid-connected LCL-filtered voltage-source inverters (VSIs). While Lyapunov-function-based control guarantees the global stability of the system, the PR controller is employed to process the grid current error and determine the inverter current reference. However, it is shown that the conventional Lyapunov-function-based control (CLFBC) together with the PR control cannot damp the inherent resonance of the LCL filter. Therefore, this control approach is modified by adding a capacitor voltage loop so as to achieve the desired resonance damping. In addition, a transfer function from the reference grid current to actual grid current is formulated in terms of the LCL-filter parameters and their possible variations in the proposed control strategy. An important consequence of using the PR controller is that the need for performing first and second derivative operations in the generation of inverter current reference is eliminated. Also, a zero steady-state error in the grid current is guaranteed in the case of variations in the LCL-filter parameters. The computer simulations and experimental results obtained from a 3.3-kW system show that the proposed control strategy exhibits a good performance in achieving the required control objectives such as fast dynamic response, zero steady-state error, global stability, and sinusoidal grid current with low total harmonic distortion (THD).

An Extended Lyapunov-Function-Based Control Strategy for Single-Phase UPS Inverters

In this study, an interleaved boost converter cascaded with a battery charger buck converter is designed and implemented. The converter also has maximum power point tracking capability and the battery charge operation is designed for purpose of long life requirements of batteries. Proposed interleaved boost converter operates in conventional converter mode and in interleaved boost converter mode with different switching frequencies according to programmed power level to achieve maximum efficiency. A hybrid maximum power point tracking method is also introduced to provide obtainable maximum power from photovoltaic systems. If the batteries are not fully charged and the photovoltaic power more than the load power, charger starts to operate and charges the batteries. Batteries can be used as a backup power source when photovoltaic system power is incapable of supplying the load. Proposed system is controlled with a low cost PIC18F452 microcontroller. Simulation and experimental results show that the proposed interleaved converter structure has higher efficiency than other topologies and the proposed maximum power point tracking method provides fast and dynamic response.

Lyapunov-Function and Proportional-Resonant-Based Control Strategy for Single-Phase Grid-Connected VSI With LCL Filter

In this study, design and implementation of an interleaved boost converter have been proposed. Proposed converter doubles the switching frequency effect by means of phase shifting to overcome the limitations of power semiconductors. In addition, small size of core in building the converter has been used to reduce the cost. Interleaved converter operates in a single converter mode at low power levels and in interleaved converter mode at high power levels to obtain the maximum efficiency in all operation area. A hybrid maximum power point tracking method is also introduced to get the obtainable maximum power from photovoltaic systems. A flyback converter is designed to supply the power required by control system, so a self supporting converter structure is achieved. Proposed converter is controlled with a low cost PIC18F452 microcontroller. Simulation and experimental results show that the proposed converter structure has higher efficiency than other topologies and the proposed maximum power point tracking method provides fast and dynamic response.

Multifunctional interleaved boost converter for PV systems

Interest of renewable energy sources increases with the increasing world power demand and decreasing of fossil energy sources. Many of the new energy sources like the PV, the fuel cell or the wind, produces direct voltage so it is needed a suitable direct current to alternating current inverter to connect them to an alternating current load or the utility line. In this case utility interactive inverters became more important. In this study, a dSPACE based current controlled utility interactive inverter has been designed and implemented. PI current controller was used for the production of switching pattern and the output of the inverter was filtered by an LCL type filter. A graphical user interface has been designed to monitor the analog and the digital variables. Results of both MATLAB/Simulink simulation and experimental studies show that inverter output current is in phase with line voltage and current harmonics in the limits of international standards (<5%).

Experimental study of interleaved MPPT converter for PV systems

This paper describes the design and implementation of a data acquisition card for the hybrid energy system. Parameters of the solar and the wind sources such as the current, the voltage, the direction of wind, the operation conditions and the position of the solar system can be changed and illustrated on an LCD and displayed on a PC using the card developed. The hybrid system including a PIC 18F452 and a 18F2550 microcontroller has been tested on a 2.5 kW solar panel and a 2.5 kW wind turbine. It has been observed that this hybrid system works successfully and gives good performance such as low cost and easy programming.

dSPACE based control of voltage source utility interactive inverter

This paper presents a novel photovoltaic (PV) based three-phase three-level grid-interactive inverter. The proposed system consist of a DC/DC converter, and a three-phase three-level inverter. In order to ensure maximum power point tracking, incremental conductance (IC) technique is used. In addition, to meet international standards for all operating modes, three-phase three-level inverter has been designed and controlled by PI plus grid voltage feed-forward control technique. The proposed system can also operate in various modes to meet smart grids requirements: (1) active power mode in a day time, (2) active and reactive power mode in a day time, (3) reactive power mode at night. To support grid voltage regulation during the day, Mode 1 and Mode 2 are used. These three operation modes bring some benefits such as efficient operation, and reactive power support capability. The proposed system is designed and simulated in Matlab&Simulink software. The simulation results show that the proposed system has an excellent performance under different operating modes.

Low-cost and high sensitive microcontroller based data acquisition system for renewable energy sources

In this study, a single stage, three-phase, three-level neutral point clamped inverter is designed for grid connected renewable energy systems. The proposed voltage source inverter is operated in current controlled mode and a PI current controller is used for the production of switching pattern. Also the proposed inverter is operated in parallel with public grid by using phase locked loop method. Maximum power point tracking process which is aimed to obtain maximum energy from the supply is performed via the proposed inverter without using any additional DC-DC converter. Maximum power point tracking algorithm generates the current reference for the current controller. Results of experimental studies show that inverter output current is in phase with line and unity power factor operation is obtained. Also inverter output current total harmonic distortion is measured as 3.95%. This value is in the limits of international standards (5%).