Real Time Digital Simulator Environment Research Articles

Development of Control Strategies for Operation of Cluster of Interconnected Hybrid Microgrids in Islanded Mode

This article presents the architecture and control techniques for interconnections of islanded hybrid smart microgrids (MGs, both dc and ac), for transferring the bidirectional power between different MGs. Three ring-type MGs, i.e., one ac microgrid (acMG) and two dc microgrids (dcMGs) operating at different voltages are interconnected to form a power park. A bidirectional dc–dc converter has been used to interconnect two dcMGs, and bidirectional three-phase voltage source converter (VSC) is used to interconnect the dcMG and acMG. The control techniques of these bidirectional VSCs are also proposed to control the operation of interconnected MGs system. The feedforward and feedback control signals are suggested in the proposed control techniques. The objectives of the proposed control techniques are to control the bidirectional power flow between the interconnected MGs, and to establish the constant rated voltages of all MGs, under islanded mode, for various operating scenarios. To check the effectiveness and robustness of the developed interconnected MGs system and proposed control techniques, the simulations have been carried out for the different operating conditions, in the real-time digital simulator environment.

Programmable Crypto-Control for IoT Networks: An Application in Networked Microgrids

In collaborative networked microgrids (NMs), distributed energy resources (DERs) utilize intelligent IoT based controllers to coordinately support various smart community functions. Meanwhile, privacy and security issues occur when IoT-based controllers interact with each other. This paper presents a cryptography-based, programmable control (crypto-control) scheme to provably preserve the privacy of DERs while ensuring fast, flexible distributed control in NMs. Specifically, it makes the following contributions: 1) a programmable crypto-control-based NMs (PCNMs) architecture, where crypto-controllers are fully virtualized, is devised; 2) a novel dynamic encrypted weight addition (DEWA) approach, which integrates an enhanced partial homomorphic encryption and a secret sharing scheme, is devised to ensure privacy preserving of distributed controls; 3) the DEWA privacy-preserving property is mathematically analyzed; and 4) a real-time DEWA-based PCNMs testbed is deployed by incorporating DEWA, real software defined networking switches, and IoT devices. The deployable crypto-control scheme is interfaced with and thoroughly verified in a Real-Time Digital Simulator environment, and the experimental results validate the effectiveness, benefits, and superiority of DEWA-based PCNMs. The inherent resilience of the DEWA-based PCNMs is validated by small signal stability analyses.

A Dual-Time Transform Assisted Intelligent Relaying Scheme for the STATCOM-Compensated Transmission Line Connecting Wind Farm

The fixed-impedance-based distance relaying schemes find limitation in providing reliable protection to transmission lines connecting doubly fed induction generator based large capacity wind farms and compensated with static synchronous compensator (STATCOM). In this article, the performance of the distance relay protecting such transmission lines is investigated and proposes an advanced protection scheme where the fault detection and fault section identification task is performed using the signs of the superimposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> -aerial components of the measured currents at the line ends and STATCOM location. Furthermore, suitable features are extracted from the relay end measured currents using dual-time transform (TT) and subsequently utilized by decision tree classifier for fault classification. Finally, the single-end traveling wave-based technique is employed using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> -aerial current waves for estimating the fault location. The performance of the proposed protection scheme is evaluated on different fault and nonfault cases generated on a two-bus test power system through MATLAB/Simulink and OPAL-RT (OP4510) manufactured real-time digital simulation environment. The performance of the proposed protection scheme is also compared with some earlier reported works. The demonstrated results justify the effectiveness of the proposed scheme for protecting such complex transmission networks.

ARI and ARID control of virtual synchronous generator for frequency response improvement

The modern power system is progressing from a centralised generation having synchronous generators to the distributed generation having the large-scale integration of renewable energy sources. These renewable energy sources are interfaced with the system through the inverter. Due to the inertia-less nature of inverter, the system becomes prone to frequency instability. The virtual synchronous generator control is used to enhance the frequency stability by introducing virtual inertia in the inverter control. The virtual synchronous generator technique provides flexibility to the researchers to regulate swing equation parameters in real-time. Based on this concept, this paper proposes an auto-regulated inertia control as the first contribution to improve the damping effect of virtual synchronous generator control. In the literature, the primary focus is on the inertia control and negligible importance is given to the damping factor control. Therefore, to show the effect of dynamic damping factor, together with dynamic virtual inertia, on the transient stability; an auto-regulated inertia and damping factor control of virtual synchronous generator is proposed as the second contribution. Simulation results of the proposed techniques are compared with the various virtual inertia control techniques in the real-time digital simulator environment. The results show that auto-regulated inertia and damping factor control is the most effective method to provide dynamic frequency support to the microgrid.

A New Approach for Protecting TCSC Compensated Transmission Lines Connected to DFIG-Based Wind Farm

Thyristor-controlled series capacitor (TCSC) compensated transmission lines (TLs) are increasingly used in recent years for transmission of bulk power generated by doubly fed induction generator (DFIG) based large scale wind farms. However, the typical fault characteristics of DFIG and TCSC affect the performance of conventional distance relays. To solve the problem, in this article, a new relaying algorithm is proposed that utilizes sign of the half-cycle superimposed positive-sequence current for fault detection, empirical mode decomposition assisted random forest classifier for fault classification and modified impedance approach for fault location estimation. The performance of the proposed relaying algorithm is evaluated on various fault and nonfault cases generated on a test power system using MATLAB/Simulink and OPAL-RT (OP4510) manufactured real-time digital simulator environment. Also, compared with few existing approaches. The demonstrated results justify the merits of the proposed relaying algorithm for protecting the TCSC compensated TL connected with DFIG-based wind farm.

A Test-Bed for Researching the Interactions of Underexcitation and Overexcitation Limiters of Synchronous Generators with Protection Functions

A test-bed implemented in a real-time digital simulation environment is presented in this article to perform coordination studies between protection functions and excitation limiters of automatic voltage regulators of synchronous generators. A hardware-in-the-loop simulation is implemented in laboratory to test and evaluate several protection schemes during underexcited and overexcited events. The interactions among the underexcitation and overexcitation limiters (UEL and OEL) with these protection functions are investigated, and the best settings for their coordination are proposed. This article increases the scope of [1] and [2] by including the interactions among the protection functions ANSI 24 (V/Hz), ANSI 59 (overvoltage), and ANSI 81 (underfrequency and overfrequency) with the OEL, and the interactions among the protection functions ANSI 21 (distance) and ANSI 27 (undervoltage) with the UEL in addition to the coordination between the protection function ANSI 40 (loss of excitation) and the UEL. Thus, the appropriate settings for these protection and controls are proposed for the excitation system developed. The main results are presented and discussed.

A robust firefly–swarm hybrid optimization for frequency control in wind/PV/FC based microgrid

This paper presents frequency regulation in a microgrid consisting of wind, photovoltaic (PV), fuel cell (FC) and diesel engine generator (DEG) along with the energy storage system such as flywheel energy storage (FES) and battery energy storage (BES). In this study, firefly and particle swarm (FF–PSO) based hybrid optimization technique is proposed to tune parameters the proportional–integral–derivative (PID) controller to minimize the frequency deviation in microgrid system under different operating conditions such as variation in wind speed, and load demand. Further, a comparative analysis for tuning of the PID controller is performed using particle swarm optimization (PSO), and firefly algorithms (FFA) to minimize the deviation in frequency. The power management as well as frequency control in microgrid is studied with the help of the performance indices; integral absolute errors (IAE), peak overshoots, settling times and standard deviation (SD). In addition, the effect of communication delay with higher non-linearity is tested to assess the performance of the controllers. Further, the frequency control is validated in real-time digital simulation environment using OPAL-RT. The qualitative, quantitative and real-time analysis reflects the improvements in frequency deviation in microgrid using the proposed hybrid FF–PSO optimized PID as comparison to the PSO/FF optimized PID controllers.

Forced oscillation source location in power systems using system dissipating energy

A dissipating energy-based technique is proposed to locate the source of forced oscillations (FOs) in power systems. The network and load information is incorporated into the developed algorithm and continuously updated using supervisory control and data acquisition (SCADA) measurement. The effect of electromechanical damping on system response in FO scenario is discussed; and therefore, the efficiency of the proposed technique to locate the source has been investigated. The proposed methodology is tested and verified for different simulation test cases and for different scenario viz. for single and multiple sources of disturbances. In the case of multiple sources of disturbances with different time of initiation of the disturbance, the proposed technique successfully locates all sources in their time durations of disturbance. Different load models have been evaluated for their impact on the success of the proposed algorithm in a real-time digital simulation environment. The proposed technique is successfully verified for the test cases reported by the IEEE PES Task Force on Oscillation Source Location.

Development and Testing of New Equipment for Faulty Phase Earthing by Applying RTDS

In neutral-isolated medium-voltage (MV) networks, the earth fault arc is typically extinguished by an automatic reclosing function. It causes a short interruption for the feeder in question. The earth fault arc can also be extinguished by using a shunt circuit breaker (SCB) to earth the faulty phase temporarily at the feeding, typically the 110/20 kV substation. The functioning of the SCB does not change phase-to-phase voltages of the MV system. Therefore, voltage breaks or dips to customers or distributed-generation units can be avoided. The SCB is used for reducing the harmful short interruptions experienced by the customers and electricity producers connected to MV or low-voltage networks. This paper describes the development of the modern SCB equipment. Main attention was paid to the development, testing, and prototyping of the novel SCB. The developed algorithm for the faulty phase selection was implemented to the feeder terminal. The prototype equipment, including the SCB, the programmable logic controller, and intelligent electronic device was tested by applying the real-time digital simulator environment. The prototype has also been installed and tested with artificial earth faults in the real network.

Type 2 fuzzy logic-based robust control strategy for power sharing in microgrids with uncertainties in operating conditions

Summary Accurate power sharing in a microgrid with distributed generations is a challenging task because of various uncertainties in the network operating conditions. This article proposes a new control scheme for power sharing in a microgrid comprising doubly fed induction generator–based wind energy system, a photovoltaic system, and a battery storage, operating in both grid-connected and islanding conditions. A robust intelligent controller is designed for power sharing to counter the effects of nonlinearities in the model and uncertainties in the operating conditions. The third dimension of type 2 membership functions (MFs) and the footprint of uncertainty together provide an additional degree of freedom in the controller design that enables it to directly model and handle the uncertainties associated with the rules and MFs. The performance of the proposed scheme is verified through a comparative analysis with the conventional Proportional Integral (PI) controller, considering the IEEE-34 bus system as a microgrid, under various network disturbances. Further, the feasibility of the controller for real-time applications is demonstrated through hardware-in-loop simulations in the real-time digital simulator environment.

Implementation of an Intelligent Reconfiguration Algorithm for an Electric Ship's Power System

In all-electric navy ships, severe damage or faults may occur during battle conditions. This might even affect the generators, and as a result, critical loads might suffer from power deficiencies for a long time, ultimately leading to a complete system collapse. A fast reconfiguration of the power path is therefore necessary in order to serve the critical loads and to maintain a proper power balance in the ship's power system. A fast intelligent reconfiguration algorithm based on small-population-based particle swarm optimization (PSO) (SPPSO) is presented in this paper. The reconfiguration of the electric ship's power system is formulated as a single objective as well as a multiobjective optimization problem. In the case of multiobjective optimization, the Pareto optimal solutions are obtained by SPPSO from two conflicting objective functions. From the Pareto set, the final solution is chosen depending on users' preferences regarding the mission of the navy ship. SPPSO is a variant of PSO having fewer numbers of particles and regenerating new solutions within the search space every few iterations. This concept of regeneration in SPPSO makes the algorithm fast and greatly enhances its capability. The strength of the proposed reconfiguration strategy is demonstrated on a real-time digital simulator environment.