Mehmet Tümay

A Novel Reference Signal Generation Method for Power-Quality Improvement of Unified Power-Quality Conditioner

This paper proposes a novel reference signal generation method for the unified power quality conditioner (UPQC) adopted to compensate current and voltage-quality problems of sensitive loads. The UPQC consists of a shunt and series converter having a common dc link. The shunt converter eliminates current harmonics originating from the nonlinear load side and the series converter mitigates voltage sag/swell originating from the supply side. The developed controllers for shunt and series converters are based on an enhanced phase-locked loop and nonlinear adaptive filter. The dc link control strategy is based on the fuzzy-logic controller. A fast sag/swell detection method is also presented. The efficacy of the proposed system is tested through simulation studies using the Power System Computer Aided Design/Electromagnetic Transients dc analysis program. The proposed UPQC achieves superior capability of mitigating the effects of voltage sag/swell and suppressing the load current harmonics under distorted supply conditions.

Hierarchical neuro-fuzzy current control for a shunt active power filter

This paper presents the design of a hierarchical neuro-fuzzy current control scheme for a shunt active power filter compared with a single fuzzy controller scheme. A single fuzzy controller scheme is presented first and an ANFIS based neuro-fuzzy controller is connected hierarchically to the first one to improve the performance. Simulation results show that harmonic compensation is achieved with both schemes, however switching performance is superior for hierarchical scheme. The method of switching controller development in this paper is new and can be applied to other power electronic converter applications for improved performance.

A robust control of dynamic voltage restorer using fuzzy logic

In this paper, a new control method for Dynamic Voltage Restorer (DVR) is described by combining fuzzy logic (FL) with a carrier modulated PWM inverter. The proposed control scheme is simple to design and has excellent voltage compensation capabilities. The proposed method for voltage sag/swell detection has the ability of detecting different kinds of power disturbances faster than conventional detection methods. Effectiveness of the proposed detection method is shown by the comparison with the conventional methods in the literature. Simulation results under unbalanced supply voltage are presented to evaluate the performance of the designed DVR.

Dynamic control of unified power flow controller under unbalanced network conditions

Abstract The effective and reliable use of existing transmission lines are critically important because high-voltage transmission networks met enormous power demands are very expensive investments in terms of their costs. Flexible Alternating Current Transmission Systems (FACTS) are quite efficient to control the power flow of the transmission lines and increase the current capacity of system. Unified Power Flow Controller (UPFC) is the more efficient among FACTS equipments which have the potential to increase the power flow and stability of the transmission line. This paper develops new control approaches for both series and shunt inverters of UPFC. The proposed controller algorithms of shunt and series inverters are based on fuzzy logic controller and rotating orthogonal-coordinate method, respectively. Dynamic control of power flow using proposed UPFC is analyzed as mathematically. Power System Computer-Aided Design (PSCAD) is used to simulate the system and test UPFC in the simulation environment. The test results are presented to show the increased stability of the system and improved dynamic response of UPFC during faults occurred in the transmission line.

Simulation Study of Fuzzy Based Unified Power Flow Controller on Power Flow Controlling

Unified power flow controller (UPFC) is the most widely used FACTS device to control the power flow and to optimize the system stability in the transmission line. The controller used in the control mechanism has an important effect on the performance of UPFC. According to this, the performance of UPFC for several case studies was observed by using different control mechanisms based on Proportional-Integral (PI) and fuzzy controllers in this study. Fuzzy Logic Controller (FLC) was developed by using Takagi-Sugeno inference system and used in UPFC. The case studies are applied to prove the capability of UPFC on power flow and the effectiveness of controllers on the performance of UPFC at the different operating conditions. PSCAD/EMTDC program is used to model UPFC and to verify the performance of UPFC with different controllers in the transmission line.

Simulation modelling and analysis of modular cascaded multilevel converter based shunt hybrid active power filter for large scale photovoltaic system interconnection

Abstract Modular multilevel inverters are promising candidates for next generation of efficient, robust and reliable inverters in large scale photovoltaic system. A modular cascaded multilevel inverter based shunt hybrid active power filter (SHAPF) for three phase grid-connected large scale PV systems is represented in this paper. The main contribution of this paper is to model and control of grid interfaced large scale photovoltaic system with embedded hybrid active power filter functions. In proposed system, the features of hybrid active power filter have been amalgamated in the control circuit of the voltage controlled voltage source inverter interfacing the photovoltaic system to the grid. As a result, the same inverter part of SHAPF is utilized to inject power generated from photovoltaic source to the grid and also to act as hybrid active power filter to compensate harmonics and reactive power demand. With using compensation ability, the grid currents are sinusoidal and in phase with grid voltages. The whole system is modeled in PSCAD/EMTDC. The simulation results are demonstrated to verify the operation and the control system of the proposed system.

A New Control Approach for Shunt Hybrid Active Power Filter to Compensate Harmonics and Dynamic Reactive Power with Grid Interconnection

The grid interconnection of renewable energy source is a popular issue in the electric utilities. Different types of converter topology in grid interconnection have been improved by researchers to improve power quality and efficiency of the electrical system. The main contribution of this paper is that shunt hybrid active power filter (SHAPF) with a DC-DC converter at dc link is to provide interconnection between renewable source and grid with linear dynamic loads. The other contribution of this paper is to present a novel control strategy for reactive power compensation and harmonics elimination in industrial networks using a hybrid active power filter as a combination of a three phase, two level voltage source converter connected in parallel with single tuned LC passive filter. In proposed control method, reactive power compensation is achieved successfully with perceptible amount. Besides, the performance results of harmonic compensation are satisfactory. Theoretical analyses and simulation results are obtained from an actual industrial network model in PSCAD. The simulation results are presented for proposed system in order to demonstrate that the harmonic compensation performance meets the IEEE-519 standard.

Dynamic model of a current transformer

The performance of current transformers and its errors during short-circuit conditions are very important with regard to protective devices in power networks. Core saturation of protective current transformers due to the d.c. component of fault current and the qualitative effect of core hysteresis resulting in residual flux are both well-known phenomena which can produce distorted output currents. A numerical technique for the mathematical representation of the flux density/field strength relationship, including the effects of hysteresis for a current transformer magnetic material, is presented, based on the use of exponential series. The simulation results are compared with experimental results obtained from a sample current transformer.

Implementation of a Non-Linear Adaptive Filter Based Sag Detection Method for Dynamic Voltage Restorers under Unbalanced Fault Conditions

The most common power quality problems in distribution systems are related to unbalanced voltage sags. Voltage sags must be detected quickly and corrected in a minimum amount of time. One of the most widely used methods for sag detection is based on the d-q transformation. This method has the disadvantage of missing the detection of unbalanced faults, because this method uses a voltage sag level signal obtained from the average of 3 phases for sag detection. In this paper, an adaptive filter sag detection method is proposed for Dynamic Voltage Restorers (DVR) under unbalanced fault conditions. The proposed DVR controller is able to detect balanced, unbalanced and single phase voltage sags. A novel reference voltage generation method is also presented. To validate the proposed control methods, a 3-phase DSP controlling a DVR prototype with a power rating of 1.5-kVA has been developed. Finally, experimental results are presented to verify the performance of the proposed control methods.

Analysis and comparison of passive damping methods for shunt active power filter with output LCL filter

Recently, LCL filter which is commonly preferred in grid connected inverters has found its common usage in shunt active power filters. LCL filter can suppress the switching harmonic ripples effectively. However, it has resonance problem which results unstable system. The resonance problem can be solved with damping the resonance using passive damping methods. The design of LCL filter with using PD is a challenging issue because APF generates currents in a wide harmonic spectrum range to compensate harmonics. The aim of this paper is to present the design procedure of LCL filters with different passive damping methods for SAPF and analyze them in terms of damping performances and power losses. The performance and analysis of LCL filters designed for SAPF is performed with simulation model developed in MATLAB/Simulink.