Elyas Rakhshani

Bio: Elyas Rakhshani is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Electric power system & Control theory. The author has an hindex of 18, co-authored 87 publications receiving 1102 citations. Previous affiliations of Elyas Rakhshani include Islamic Azad University & Polytechnic University of Catalonia.

Inertia Emulation in AC/DC Interconnected Power Systems Using Derivative Technique Considering Frequency Measurement Effects

Abstract: Virtual inertia is known as an inevitable part of the modern power systems with high penetration of renewable energy. Recent trend of research is oriented in different methods of emulating the inertia to increase the sustainability of the system. In the case of dynamic performance of power systems especially in Automatic Generation Control (AGC) issue, there are concerns considering the matter of virtual inertia. This paper proposes an approach for analyzing the dynamic effects of virtual inertia in two-area AC/DC interconnected AGC power systems. Derivative control technique is used for higher level control application of inertia emulation. This method of inertia emulation is developed for two-area AGC system, which is connected by parallel AC/DC transmission systems. Based on the proposed technique, the dynamic effect of inertia emulated by storage devices for frequency and active power control are evaluated. The effects of frequency measurement delay and phase-locked loop effect are also considered by introducing a second-order function. Simulations performed by MATLAB software demonstrate how virtual inertia emulation can effectively improve the performance of the power system. A detailed eigenvalue analysis is also performed to support the positive effects of the proposed method.

Analysis of derivative control based virtual inertia in multi-area high-voltage direct current interconnected power systems

Abstract: Due to increasing level of power converter-based component and consequently the lack of inertia, automatic generation control (AGC) of interconnected systems is experiencing different challenges. To cope with this challenging issue, a derivative control-based virtual inertia for simulating the dynamic effects of inertia emulations by HVDC (high-voltage direct current) interconnected systems is introduced and reflected in the multi-area AGC system. Derivative control technique is used for higher level applications of inertia emulation. The virtual inertia will add an additional degree of freedom to the system dynamics which makes a considerable improvement on first overshoot responses in addition to damping characteristics of HVDC links. Complete trajectory sensitivities are used to analyse the effects of virtual inertia and derivative control gains on the system stability. The effectiveness of the proposed concept on dynamic improvements is tested through Matlab simulation of two-area test system for different contingencies.

Virtual Synchronous Power Strategy for Multiple HVDC Interconnections of Multi-Area AGC Power Systems

Abstract: Automatic generation control (AGC) in multi-area interconnected power systems is experiencing several adaptions due to increasing level of power converter based components in the system. The concept of virtual synchronous power (VSP) to simulate the dynamic effects of virtual inertia emulations by HVDC links for higher level control applications is introduced and reflected in the multi-area AGC model. By using this proposed combination in the AGC model, the dynamic performance of the studied system shows a significant improvement. The proposed formulation is generalized for multi-area systems with multiple HVDC links. The active power loop control in VSP-based HVDC links has a second-order characteristic, which makes a simultaneous enabling of damping and inertia emulations into the system. Trajectory sensitivities are also used to analyze the effects of VSP's parameters on the system stability. The effectiveness of the proposed concept on dynamic improvements is tested through MATLAB simulation of a four-area system.

Foundations and Challenges of Low-Inertia Systems (Invited Paper)

Abstract: The electric power system is currently undergoing a period of unprecedented changes. Environmental and sustainability concerns lead to replacement of a significant share of conventional fossil fuel-based power plants with renewable energy resources. This transition involves the major challenge of substituting synchronous machines and their well-known dynamics and controllers with power electronics-interfaced generation whose regulation and interaction with the rest of the system is yet to be fully understood. In this article, we review the challenges of such low-inertia power systems, and survey the solutions that have been put forward thus far. We strive to concisely summarize the laid-out scientific foundations as well as the practical experiences of industrial and academic demonstration projects. We touch upon the topics of power system stability, modeling, and control, and we particularly focus on the role of frequency, inertia, as well as control of power converters and from the demand-side.

Hydrogen energy systems: A critical review of technologies, applications, trends and challenges

Abstract: The global energy transition towards a carbon neutral society requires a profound transformation of electricity generation and consumption, as well as of electric power systems. Hydrogen has an important potential to accelerate the process of scaling up clean and renewable energy, however its integration in power systems remains little studied. This paper reviews the current progress and outlook of hydrogen technologies and their application in power systems for hydrogen production, re-electrification and storage. The characteristics of electrolysers and fuel cells are demonstrated with experimental data and the deployments of hydrogen for energy storage, power-to-gas, co- and tri-generation and transportation are investigated using examples from worldwide projects. The current techno-economic status of these technologies and applications is presented, in which cost, efficiency and durability are identified as the main critical aspects. This is also confirmed by the results of a statistical analysis of the literature. Finally, conclusions show that continuous efforts on performance improvements, scale ramp-up, technical prospects and political support are required to enable a cost-competitive hydrogen economy.

A Review of Passive Power Filters for Three-Phase Grid-Connected Voltage-Source Converters

Abstract: In order to reduce size and cost, high-order passive filters are generally preferred in power converters to cancel out high-frequency harmonics caused by pulsewidth modulation. However, the filter resonance peaks may require the use of passive dampers to stabilize the interactions between the load and source impedances. Furthermore, the stabilizing effect is more difficult to be guaranteed for cost-optimized filters, which are characterized by low-inductance and high-capacitance passive components. In this paper, several passive filter topologies used to interface voltage-source converters with the utility grid are reviewed and evaluated in terms of damping capability, stored energy in the passive components, and power loss in the damping circuit. In addition, the influences of different switching frequencies of power converters on the passive filter design are discussed in the range 1–15 kHz. Illustrative design examples of the passive filters and experimental data are also provided.

Delay-Dependent Robust Load Frequency Control for Time Delay Power Systems

Abstract: The usage of communication channels introduces time delays into load frequency control (LFC) schemes. Those delays may degrade dynamic performance, and even cause instability, of a closed-loop LFC scheme. In this paper, a delay-dependent robust method is proposed for analysis/synthesis of a PID-type LFC scheme considering time delays. The effect of the disturbance on the controlled output is defined as a robust performance index (RPI) of the closed-loop system. At first, for a preset delay upper bound, controller gains are determined by minimizing the RPI. Secondly, calculation of the RPIs of the closed-loop system under different delays provides a new way to assess robustness against delays and estimate delay margins. Case studies are based on three-area LFC schemes under traditional and deregulated environments, respectively. The results show that the PID-type controller obtained can guarantee the tolerance for delays less than the preset upper bound and provide a bigger delay margin than the existing controllers do. Moreover, its robustness against load variations and parameter uncertainties is verified via simulation studies.