Proposed Superconducting Magnetic Energy Storage Controller Research Articles

Artificial electric field algorithm based superconducting magnetic energy storage system for damping inter area oscillations

This paper presents an artificial electric field algorithm (AEFA) based optimal control of superconducting magnetic energy storage (SMES) system for damping inter area oscillations. The artificial electric field algorithm is based upon Coulomb’s law of electrostatics and Newton’s law of motion. The proposed technique is used to optimize the SMES controller parameters for effective damping of inter area oscillations. Because of the potential for system damage and the subsequent constraints on power transmission along select lines, low frequency inter-area oscillations have been identified as a serious problem in utility systems. With the advancement in power electronics technologies, a new option for damping of power system oscillations has been created by integrating energy storage devices to it. The proposed scheme is tested on a two area interconnected power system which is suitably modelled and it’s modal analysis is done. The participation of each area towards the inter area mode is analyzed by using participation matrix and the suitable placement of SMES units is decided accordingly. MATLAB Simulations are carried out to prove the efficacy of proposed scheme. The simulation results show that proposed SMES controller along with the incorporation of SMES units to each generator bus effectively damps out the inter area oscillations.

Enhancement of DFIG LVRT Capability During Extreme Short-Wind Gust Events Using SMES Technology

Wind energy is one of the premier renewable energy sources that have gained popularity during the last decade. Among the currently available wind energy conversion systems (WECS), doubly fed induction generator-based technology has been widely employed due to its superior advantageous. The key features of the DFIG-based WECS include its ability to capture more wind energy and support the grid with large reactive power during short disturbance events. On the other hand, DFIG is very sensitive to grid faults which affect its fault ride through (FRT) capability. Furthermore, extreme wind gust even for short durations may lead to the violation of the low voltage ride through (LVRT) threshold limits set by worldwide transmission line operators. This situation cannot be mitigated by the turbine blades pitch controller since the response of the pitch mechanical control is much slower than the rapid dynamic change in the wind speed during short duration of wind gust events. While DFIG FRT capability has been discussed in several papers in the literature, not much attention was given to the mitigation of the effects of extreme wind gust of short duration on the DFIG performance. In this paper, the effect of various levels of wind gust on the performance of a DFIG-based wind energy conversion grid-connected system is investigated and mitigated using a new controller for superconducting magnetic energy storage (SMES) unit. A combination of hysteresis current and fuzzy logic controllers is employed to control the voltage source converter and the DC-DC chopper interfacing the SMES coil with the investigated system. Simulation results reveal the effectiveness of the proposed SMES controller that can be easily implemented within existing as well as new WECS installations.

Decentralized robust mixed [formula omitted] reactive power control of DFIG cluster using SMES

This paper proposes a method for developing a decentralized robust mixed H2/H∞ output feedback reactive power control using superconducting magnetic energy storage (SMES) which improves transient stability of the DFIG cluster. The decentralized mixed H2/H∞ output feedback optimal control design provides robustness via optimization of the worst-case quadratic performance of the underlying uncertain cluster system and guarantees that the obtained controller is a locally optimal or on the boundary of the H∞ norm constraint. The proposed controller takes into account the uncertainty of model parameters, which have a significant effect on the stability of the critical modes, which are identified from the critical parameter analysis. The proposed controller also tackles local uncertainties as well as interconnection effects of decentralized systems. The iterative optimization method to synthesize the controller and the steps involved in the controller design for the test system are presented. The performance of the proposed SMES controller is evaluated and the superiority of the designed control method over the conventional PI-based SMES controller is demonstrated.

SMES-Based Fuzzy Logic Approach for Enhancing the Reliability of Microgrids Equipped With PV Generators

The fluctuated nature represents the main obstacle for increasing the penetration level of photovoltaic (PV) generators in utility microgrids. The energy storage systems (ESSs) represent the main solutions to get over these fluctuations. Among various ESSs, the superconducting magnetic energy storage (SMES) systems have proven themselves as an effective solution. The SMES control systems in the literature result in a shortened lifetime, degraded thermal behavior, and high AC losses in the SMES. Thence, reliable operation of SMES systems and microgrids has been given wide concerns due to the large fluctuations in microgrids with high levels of PV penetrations. This paper presents a SMES-based fuzzy logic approach for improving the reliability of SMES and utility microgrids with high PV penetration levels. The proposed SMES controller employs the state of charge (SOC) of SMES as an input. This, in turn, can effectively extend the lifetime of SMES due to eliminating the overcharge and deep discharge operating states. Moreover, the proposed system controls smoothly the SMES current using the fuzzy rules' system. The superiority and effectiveness of the proposed SMES controller are verified using simulation-based case studies of utility grids with high PV penetration levels. The obtained results show the effective smoothing of fluctuated power and constant bus voltages in the studied microgrid under the proposed controller. In addition, the proposed SMES controller provides superior performance regarding the lifetime and reliability of the SMES systems and microgrid components.

Sag and Flicker Reduction Using Hysteresis-Fuzzy Control-Based SMES Unit

The issue of power quality is one of the prominent factors in determining the reliability of power systems. It is inevitable to consider power quality issues and include appropriate mitigation techniques in the design of any future power system project construction. Voltage sag and flicker are the two most common short disturbance types of power quality issues that frequently occur in power systems. A widely accepted mitigation strategy to enhance the power quality of disturbed networks is by connecting a flexible ac transmission system. In this paper, a superconducting magnetic energy storage (SMES) unit along with hysteresis-fuzzy controller to suppress the severe impacts of voltage sag and flicker events on the power quality of a power system is proposed, implemented, and tested. The proposed SMES configuration with hysteresis current control and fuzzy logic controller is effective, simple, and easy to implement. Simulation results show the ability of the proposed SMES controller in compensating sag and/or flicker distortions.

Load Frequency Control of an Interconnected Reheat Thermal system using Type-2 fuzzy system including SMES units

The transient behavior of many large scale systems is heavily influenced by perturbations and in particular, usually, due to changes in operating points. Load Frequency Control (LFC) in power systems is very important in order to supply reliable electric power with good quality. The goal of LFC is to maintain zero steady state errors for frequency deviations in each control area. Several control strategies, such as classical control, optimal control, suboptimal control, adaptive control, variable structure control etc. have been employed in the past to explore an optimum controller for LFC. In practice LFC systems use simple Proportional Integral (PI) controllers, Proportional Integral Derivative (PID) controllers etc. This paper presents a method based on Type-2 Fuzzy System (T2FS) for Load frequency control (LFC) of power systems including Superconducting magnetic energy storage (SMES) units of a two-area interconnected reheat thermal system. This paper proposes a Type-2 (T2) fuzzy approach for load frequency control of two-area interconnected reheat thermal power system with the consideration of Generation Rate Constraint (GRC), Boiler Dynamics (BD) and SMES. The salient advantage of this controller is its high insensitivity to large load changes and plant parameter variations even in the presence of non-linearities. The proposed method is tested on a two-area power system to illustrate its robust performance with various area load changes. The performance of the Type-2 (T2) fuzzy controller is compared with optimal PID (Khamsum’s optimal PID) controller and Fuzzy PI Controller (Type-1 Fuzzy) controller in the presence of GRC, BD and SMES. Simulation results confirm the high robustness of the proposed SMES controller with small power capacity against various disturbances and system uncertainties in comparison with SMES in the previous research.

Improving dynamic performance of wind energy conversion systems using fuzzy-based hysteresis current-controlled superconducting magnetic energy storage

Application of distributed wind energy conversion systems (WECS) in modern power systems and smart grids has significantly increased during the last decade. In particular, wind turbines equipped with doubly fed induction generator (DFIG) have dominated the market since 2004 as they represented about 55% of the worldwide total wind capacity during this year. This study investigates the application of superconducting magnetic energy storage (SMES) units to improve the dynamic performance of DFIG-based WECS during small and large disturbances in the grid side. A new control approach for the SMES unit using hysteresis current regulator and fuzzy logic is introduced. Detailed simulation results show that the proposed SMES controller is very effective in improving the dynamic performance of the WECS and is able to maintain its parameters within the safety margins of various grid codes during disturbance events considered in this study.

Simultaneous Optimization of SMES Coil Size and Control Parameters for Robust Power System Stabilization

As the coil size is the heart of superconducting magnetic energy storage (SMES), the simultaneous optimization of coil size and control parameters of SMES for robust power system stabilization is proposed. The structure of active and reactive power controllers of SMES is the practical first-order lead/lag compensator. To handle system uncertainties such as various generating and loading conditions, unpredictable network structures etc., the multiplicative uncertainty model is embedded in the system modeling. As a result, the optimization problem of SMES coil size and controller parameters based on the enhancement of system damping and robust stability margin against system uncertainties can be formulated. Solving the problem by a particle swarm optimization, both optimal coil size and controller parameters are obtained simultaneously and automatically. Simulation study in the West Japan six-area interconnected power system with two SMES units confirms the superior robustness and damping performance of the proposed SMES controller with an optimal coil size under various situations in comparison with the conventional SMES controller.

Stabilization of microgrid with intermittent renewable energy sources by SMES with optimal coil size

It is well known that the superconducting coil is the vital part of a superconducting magnetic energy storage (SMES) unit. This paper deals with the power controller design of a SMES unit with an optimal coil size for stabilization of an isolated microgrid. The study microgrid consists of renewable energy sources with intermittent power outputs i.e., wind and photovoltaic. Since power generations from such renewable sources are unpredictable and variable, these result in power fluctuations in a microgrid. To stabilize power fluctuations, a SMES unit with a fast control of active and reactive power can be applied. The structure of a power controller is the practical proportional-integral (PI). Based on the minimization of the variance of power fluctuations from renewable sources as well as the initial stored energy of SMES, the optimal PI parameters and coil size are automatically and simultaneously tuned by a particle swarm optimization. Simulation studies show that the proposed SMES controller with an optimal coil size is able to effectively alleviate power fluctuations under various power patterns from intermittent renewable sources.

Robust Frequency Control of Wind-Diesel Hybrid Power System Using Superconducting Magnetic Energy Storage

In an isolated wind-diesel hybrid power system, the variable power consumptions as well as the intermittent wind power may cause a large fluctuation of system frequency. If the system frequency can not be controlled and kept in the acceptable range, the system may lose stability. To reduce system frequency fluctuation, a superconducting magnetic energy storage (SMES) which is able to supply and absorb active power quickly, can be applied. In addition, variation of system parameters, unpredictable power demands and fluctuating wind power etc., cause various uncertainties in the system. A SMES controller which is designed without considering such uncertainties may lose control effect. To enhance the robustness of SMES controller, this paper focuses on a new robust control design of SMES for frequency control in a wind-diesel system. The coprime factorization is used to represent the unstructured uncertainties in a system modeling. The structure of a SMES controller is the practical first-order lead-lag compensator. To tune the controller parameters, the optimization problem is formulated based on loop shaping technique. The genetic algorithm is applied to solve the problem and achieve the control parameters. Simulation results confirm the high robustness of the proposed SMES controller with small power capacity against various disturbances and system uncertainties in comparison with SMES in the previous research.

Transient Stability Enhancement of Wind Generator by PWM Voltage Source Converter and Chopper Controlled SMES Unit

In order to investigate the impacts of the integration of wind farms into utility networks, transient stability should be analyzed before connecting wind turbine generator system (WTGS) to the power system. This paper proposes a robust controller for Superconducting Magnetic Energy Storage (SMES) unit to enhance the transient stability of a grid connected fixed speed wind generator system. In the proposed controller, both SMES active and reactive powers are controlled to decrease the fluctuations of output power and terminal voltage of the wind generator during transient condition. The power conversion system (PCS) of SMES unit used in this paper is composed of a sinusoidal Pulse Width Modulated Voltage Source Converter (PWM-VSC) and a two-quadrant DC-DC chopper using Insulated Gate turn-off Bipolar Transistors (IGBT). Stability during symmetrical and unsymmetrical faults in the network system is analyzed.  The effects of the faults on the generator dynamics are also discussed clearly. Simulation results demonstrate that the proposed SMES controller is very effective for stabilizing wind generator as well as the entire power system. Keywords:  Fixed speed wind generator system; Transient analysis; System faults; PWM-VSC; DC-DC chopper and SMES unit.© 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v1i2.2281

Application of simultaneous active and reactive power modulation of SMES unit under unequal α-mode for power system stabilization

A simple and novel control strategy for damping electromechanical oscillations through control of power converter firing angles /spl alpha//sub 1/ and /spl alpha//sub 2/ of a superconducting magnetic energy storage (SMES) unit is proposed. Both active and reactive power modulations are used under unequal /spl alpha/-mode of operation. The choice of unequal mode is discussed in detail. The gains of the proposed SMES controller are determined once offline depending on the power system and the rating of the SMES unit. Simulation results show that the SMES unit can effectively suppress power system oscillations by utilizing its active and reactive power modulation capabilities. The control algorithm is simple and its realization will require very little hardware.