Hatem Diab

Simulation of Islanding Detection Scheme Based on Fast Angle Estimation Method for Grid Connected Photovoltaic Systems Using ADALINE Technique

This paper introduces a proposed passive islanding detection technique for grid connected photovoltaic (PV) systems. This method is based on fast estimation of voltage angle and it is compared with the conventional passive islanding detection method based on power factor angle estimation. The two methods are simulated using MATLAB/SIMULINK program. Furthermore, an evaluation of the proposed method under the system dynamics is made. The main advantages of the proposed voltage angle detection method based on ADALINE algorithm are its independency of the load power factor, its quick response as it detects islanding condition in less than 0.1 second and a stable performance under system dynamics.

A modified reduced frequency capacitor voltage balancing strategy with reduced number of sensors for modular multilevel converters

The balancing of sub-module capacitor voltages of modular multi-level converters (MMC) is considered to be an essential process for keeping the quality of the output power at considerable limits. This paper presents a new capacitor voltage estimation technique which feeds the capacitor voltage balancing control. This strategy not only eliminates the need for measuring the sub-module capacitor voltages but also it removes the communication channels needed to transmit the readings of these measurements. The proposed strategy is tested using PSCAD/EMTDC software package and simulation results showed a robust behavior during normal as well as abnormal operating conditions.

Detection and diagnosis of sub-module faults for modular multilevel converters

This paper presents a new fault detection technique for the diagnosis and localization of sub-module faults that are developed due to failures in switching devices inside Modular Multilevel Converters (MMC). Unlike other fault detection strategies that have been proposed in literature, the proposed fault detection technique does not need extra sensors or special power circuits as it depends on an ADAptive LINEar Neuron (ADALINE) capacitor voltage estimation algorithm. The proposed fault detection technique is validated by Hardware In the Loop (HIL) real time simulations through which different case studies are simulated to test the algorithm under different operating conditions.

Reliability enhancement of modular multilevel converter by applying fault tolerant control

Modular Multilevel Converters (MMC) are considered very suitable for the transmission of bulk power. Increasing the reliability of MMCs forms a real challenge since they are built from series connection of sub-modules. Applying the concept of fault tolerance to the MMC control system can significantly increase the reliability of the MMC as it will be available in normal as well as faulty conditions. This paper presents an analysis of the MMC reliability enhancement gained from applying different fault tolerant control techniques. The reliability is investigated through solving differential equations generated from Markov chains.

Real time simulation of a current flow controller for HVDC grid applications

Interconnecting several offshore wind farms using High Voltage dc (HVDC) connections and forming multi terminal HVDC grid are some of the targets set by industry leaders to be achieved in the near future. Researchers have introduced a few methods of power flow control based on either the control of AC/DC converter stations or the connection of new power electronic equipment to the grid. In this paper, the operation and control of an extended three-port IGBT based current flow control (CFC) device suitable for multi terminal HVDC systems is presented. Features and functionalities of the proposed controller including the balancing of cable currents, limiting the magnitude of cable current and current nulling are demonstrated. The proposed three-port CFC is real time simulated using OP4510 real time simulator. Real time simulation studies explore fast dynamic response and the results show that the CFC studied may have a significant role to play in the control a of power flows in multi terminal high voltage DC systems.

Enhanced Approach for Modelling and Simulation of Modular Multilevel Converter Based Multiterminal DC Grids

Multi-terminal direct current (MTDC) grids are gaining the interest of many researchers because of their unique features that improve the transmission network functionality and reliability. Unlike two level and three level voltage source converters (VSC), modular multi-level converters (MMC) are suitable for the application of MTDC grids because of their generous advantages such as the elimination of DC link capacitor, the improved quality of the output power and the lower footprint. However, simulation of MMC based MTDC grids is a real challenge because of the huge computational burden due to the high number of submodules. This paper proposed a modeling approach for a four terminal MTDC grid which is based on average MMC models with 401 voltage levels. The control system structure which controls the power through the MTDC grid and the MMCs at each terminal is presented. The whole system is tested and simulated using PSCAD/EMTDC under different operating conditions to verify the validity and evaluate the performance of the proposed modelling approach.

Reduced Switch Count Topology of Current Flow Control Apparatus for MTDC Grids

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.

An ADALINE based capacitor voltage estimation algorithm for modular multilevel converters

This paper presents a novel capacitor voltage estimation using the adaptive linear neuron (ADALINE) algorithm for monitoring of MMC sub-module voltages. The proposed estimation unit requires only three voltage sensors per phase for the arm reactors and the output phase voltages. Measurements of sub-module capacitor voltages and associated communication links with the central controller are not needed. The proposed strategy can be applied to MMC systems that contain a large number of sub-modules. The method uses PSCAD/EMTDC, with particular focus on dynamic performance during boost operation.

A current flow control apparatus for meshed multi-terminal DC grids

The absence of a reliable current flow control method is one of the main problems that need to be solved to allow the realization of multi terminal high-voltage direct current (HVDC) transmission. Industry leaders and researchers have introduced a few methods of power flow control based on either the control of converter station or the connection of new power electronic equipment to the grid. This paper presents the operation and control of an extended three-port IGBT based current flow control (CFC) device suitable for multi terminal HVDC systems. Features and functionalities of the proposed controller including the balancing of cable currents, limiting the magnitude of cable current and current nulling are demonstrated. The three-port CFC is simulated using PSCAD/EMTDC, network simulation software to evaluate its steady state and dynamic performance. Simulation studies explore the fast dynamic response and the results show that the CFC studied may have a significant role to play in the control a of power flows in multi terminal high voltage DC systems.