Sitthidet Vachirasricirikul

Robust LFC in a Smart Grid With Wind Power Penetration by Coordinated V2G Control and Frequency Controller

In the smart grid, the large scale wind power penetration tends to expand vastly. Nevertheless, due to the intermittent power generation from wind, this may cause a problem of large frequency fluctuation when the load-frequency control (LFC) capacity is not enough to compensate the unbalance of generation and load demand. Also, in the future transport sector, the plug-in hybrid electric vehicle (PHEV) is widely expected for driving in the customer side. Generally, the power of PHEV is charged by plugging into the home outlets as the dispersed battery energy storages. Therefore, the vehicle-to-grid (V2G) power control can be applied to compensate for the inadequate LFC capacity. This paper focuses on the new coordinated V2G control and conventional frequency controller for robust LFC in the smart grid with large wind farms. The battery state-of-charge (SOC) is controlled by the optimized SOC deviation control. The structure of frequency controller is a proportional integral (PI) with a single input. To enhance the robust performance and robust stability against the system uncertainties, the PI controller parameters and the SOC deviation are optimized simultaneously by the particle swarm optimization based on the fixed structure mixed H2/H∞ control. Simulation results show the superior robustness and control effect of the proposed coordinated controllers over the compared controllers.

Coordinated Control of Optimized SFCL and SMES for Improvement of Power System Transient Stability

It is well known that the Superconducting Magnetic Energy Storage (SMES) is effective to damp the power swing after the occurrence of faults. Nevertheless, if the SMES is also applied for transient stability improvement, a large power capacity of SMES is required. Additionally, the SMES is not able to absorb enough energy during faults since the bus voltage where the SMES is installed, drops considerably. To enhance the SMES control effect and transient stability, this paper proposes the coordinated control of the optimized resistive type superconducting fault current limiter (SFCL) and SMES. When the fault occurs, the SFCL rapidly suppresses the transient power swing by limiting the fault current. Subsequently, the SMES damps out the remaining power swing. The optimization problem of SFCL resistance and power controller parameters of SMES with optimal coil size is formulated based on an augmentation of transient stability margin and damping performance. Solving the problem by the particle swarm optimization, the optimal parameters of SFCL and SMES can be automatically obtained. Simulation study confirms the superior stabilizing effect of the coordinated SFCL and SMES over the individual device. The SFCL not only solves the voltage drop problem at the SMES bus, but also assists the SMES to stabilize the system. Besides, the MW and MJ capacities of the SMES operated with SFCL are significantly reduced.

Optimized SFCL and SMES Units for Multimachine Transient Stabilization Based on Kinetic Energy Control

Power system transient instability due to short circuits may result in loss of synchronism. To improve stability, resistive type superconducting fault current limiter (SFCL) and superconducting magnetic energy storage (SMES) can be effectively used. This paper proposes a new optimization of multiple SFCL and SMES units for transient stabilization in a multimachine power system based on kinetic energy control. Two applications of the proposed optimization are studied in the West Japan six-area interconnected power system. First, the SFCL is applied to solve the inevitable problems of SMES used for transient stability enhancement, i.e., required large power and energy capacities, and fail-operational performance due to the large voltage drop at the SMES bus. When the fault occurs, the SFCL swiftly reduces the increase in the kinetic energy of all generators by limiting the fault current. Subsequently, the SMES handles the remaining unbalanced kinetic energy. The optimization problem of the resistive value of the SFCL is formulated, considering energy dissipation in combination with the power controller parameters of SMES with optimal coil size. A simulation study shows the superior effect of the combined SFCL and SMES over either device separately. With SFCL, the low voltage ride-through capability of SMES can be enhanced. The MW and MJ capacities of the SMES are also significantly reduced. Second, a new optimization of multiple SFCL units considering optimal locations, optimal number, optimal resistive values, and energy dissipation during quenching state is presented. The optimization problem is formulated by maximizing the decreasing rate of energy function during fault in combination with minimizing the energy dissipation of the SFCL during quenching state. A simulation study confirms the superior effect of optimal SFCL units over nonoptimal SFCL units.

Design of optimal fuzzy logic-PID controller using bee colony optimization for frequency control in an isolated wind-diesel system

Generally, the inevitable problems in the fuzzy logic-PID (FLPID) control design are the trial and error of the setting of scale factors, membership functions and control rules. To solve these problems, this paper proposes the optimal FLPID controller design using bee colony optimization (BCO) for the load frequency control in the microgrid system. The considered microgrid is the hybrid wind-diesel isolated system. The BCO is applied to automatically optimize the FLPID controllers of governor in the diesel side and blade pitch control in the wind side. Simulation studies show the superior robustness of the optimal FLPID against system parameters variation in comparison with the optimal PID controller and the non-optimal FLPID controller.

Design of Optimal SMES Controller Considering SOC and Robustness for Microgrid Stabilization

The microgrid with wind and photovoltaic (PV) power sources unavoidably encounters the power fluctuation problem. To solve this problem, the superconducting magnetic energy storage (SMES) can be used. Nevertheless, large power fluctuation from wind and PV sources, and severe system faults may cause the overcharge or deep-discharge state of SMES. These abnormal states highly degrade the dynamic performance of the SMES. To handle these situations, this paper concentrates on the new SMES power controller design considering state-of-charge (SOC), robustness, and optimal inductance of the superconducting coil for microgrid stabilization. The active and reactive power controllers of SMES are represented by the proportional-integral (PI) control. The SOC deviation control and the mixed H2/H∞ control are proposed to optimize the SMES coil inductance and PI parameters. Simulation study is performed to signify the control effect of the proposed SMES.

Design of robust SVC for voltage control in an isolated wind-diesel hybrid power system

This paper focuses on a new robust control design of static var compensator (SVC) for voltage control in an isolated wind-diesel hybrid power system. The proposed method is based on the Hinfin loop shaping technique and genetic algorithm (GA). The structure of the controller is a proportional integral (PI) controller with single input. In the design, system uncertainties are modeled by a normalized coprime factorization. The performance and robust stability conditions of the designed system satisfying the Hinfin loop shaping are formulated as the objective function in the optimization problem. The GA is applied to solve an optimization problem and to achieve control parameters. Simulation studies show the effectiveness and robustness of the proposed method.

Fuzzy logic PID-based SMES controller design using Bee Colony Optimization for stabilization of inter-area oscillation

This paper proposes a design of Fuzzy Logic based-Proportional-Integral-Derivative (FLPID) controller of Superconducting Magnetic Energy Storage (SMES) by a Bee Colony Optimization (BCO) for stabilization of inter-area oscillation in an interconnected power system. Conventionally, the scale factors, membership functions and control rules of FLPID are obtained by trial and error method or experiences of designers. To tackle this problem, the BCO is applied to simultaneously tune all control parameters of FLPID controller based on the minimization of the integral of time-multiplied absolute error of the generators speed difference between any two areas. Simulation results in a two-area four-machine power system show the superior stabilizing effect of the SMES with the proposed optimal FLPID controller in comparison with the SMES with conventional FLPID controller.

Robust frequency stabilization in a microgrid system

This paper proposes a new design of a robust control and monitoring system (RCMS) for robust stabilization of frequency fluctuation in a microgrid (MG) system. In MG system, the power sources consists of wind power (WP), photovoltaic (PV), microturbine (MT) and fuel cell (FC). Due to WP, PV and load fluctuations, the frequency stabilization of RCMS is performed by adjusting the power outputs of MT and electrolyzer system (ES) in both islanding and interconnected utility grid operations. The structure of MT and ES controllers is a proportional integral (PI). To enhance the robustness of designed controllers against system uncertainties, controller parameters of MT and ES are concurrently tuned by the particle swarm optimization based on a specified-structure H„ loop shaping control. Simulation results display the effectiveness and robustness of the proposed RCMS against system parameters variation and several operating conditions.

Design of robust control and monitoring system for microgrid stabilization

This paper proposes a design of the robust control and monitoring system (RCMS) for stabilization of microgrid (MG) system. The power sources in MG consists of wind power (WP), photovoltaic (PV), micro-turbine (MT) and fuel cell (FC). Due to intermittent powers from WP, PV and load fluctuations, the MG stabilization of RCMS is performed by controlling the power outputs of MT and electrolyzer system (ES) in both islanding and interconnected utility grid operations. The structure of MT and ES controllers is the proportional integral (PI). By taking system uncertainties into account, control parameters of MT and ES are simultaneously optimized based on the particle swarm optimization (PSO) based fixed-structure H∞ loop shaping control. Simulation results show the robustness and effectiveness of the proposed RCMS against the variation of system parameters and operating conditions.

Microgrid stabilization by SMES with SOC control

In the isolated microgrid with wind and photovoltaic power, the intermittent power produced from such power sources is an inevitable problem. In addition, under the occurrence of short circuits, the transient power swing may deteriorate the system stability. To deal with these problems, this paper focuses on the new power controller design of superconducting magnetic energy storage (SMES) considering the state-of-charge (SOC) control for microgrid stabilization. The structure of active and reactive power controllers of SMES is a proportional-integral (PI) controller. The optimization of PI parameters based on the minimization of the SOC deviation and the power output deviation of wind and PV sources is carried out. Simulation study confirms that the SMES with SOC control not only guarantees the stabilizing performance under normal and faulted conditions, but also prevents the over-charge and deep-discharge operations.