Yih-Der Lee

Bio: Yih-Der Lee is an academic researcher from Atomic Energy Council. The author has contributed to research in topics: Microgrid & Fault (power engineering). The author has an hindex of 4, co-authored 14 publications receiving 73 citations.

A novel fault protection system using communication-assisted digital relays for AC microgrids having a multiple grounding system

Abstract: This paper develops a novel fault protection system for AC microgrids having a multiple grounding system. Communication-supported digital relays which have different protection modules are used for this novel microgrid protection system. The protection modules in a digital relay have various functionalities to protect AC microgrids from various fault types, such as: low/high-impedance ground faults and short-circuits. To effectively use the developed novel microgrid protection system, the first step is to reconfigure different microgrid structures into a standard microgrid configuration having a multiple-grounding system through using delta/wye-grounded or wye-grounded/wye-grounded transformers. Then, a fast–dependable–adaptable (FDA) fault protection algorithm is developed to protect AC microgrids from faults occurring at trunk lines, common buses or branch lines. At an islanded operation mode of AC microgrids, by using digital relays, a new protection module is designed to detect, locate, and classify the faults occurring at trunk lines and common AC buses, while other protection modules can use the existing protection methodologies (e.g. directional/non-directional overcurrent protection principles, etc.) to detect and clear the faults at source branches or load branches of the microgrids. At a grid-connected operation mode, standard overcurrent protection modules are applied for the FDA fault protection system. Simulation and experiment results obtained from various fault cases at a real low-voltage AC microgrid have validated the effective operation of the FDA fault protection system.

Investigation on transient behaviours of a uni-grounded low-voltage AC microgrid and evaluation on its available fault protection methods: Review and proposals

Abstract: In a general microgrid (MG), a step-up distribution transformer is used to facilitate integration of the low-voltage (LV) AC microgrid into a medium-voltage distribution system. On the other hand, isolation transformers are placed between distributed energy resources (DERs) (e.g. non-renewable/renewable energy resources and energy storage devices) and common AC buses/lines to eliminate DC-current components and to configure 3-phase & 4-wire, 3-phase & 3-wire, 1-phase & 2-wire, or 1-phase & 3-wire AC microgrids. When all neutral points of isolation transformers are grounded through a unique grounding system of the step-up distribution transformer, a uni-grounded AC microgrid structure is configured. This paper not only mentions advantages and shortcomings of the uni-grounded LVAC microgrid operation, but also investigates its transient operation characteristics. Transient simulation results of the uni-grounded LVAC MG are surveyed through various fault situations and operation transition tests between the grid-connected mode and the islanded mode of the microgrid. Available fault protection methods of a uni-grounded LVAC microgrid are considered. Transient simulation results from PSCAD software are used to validate the fault protection solutions developed for the uni-grounded LVAC microgrid. Last, a generalised fault protection system of uni-grounded LVAC microgrids is proposed in the paper.

Ancillary voltage control for a distribution feeder by using energy storage system in microgrid

Abstract: This paper presents ancillary voltage control for a distribution feeder by using energy storage system (ESS) in microgrid. The microgrid consists of photovoltaic, wind power, and distribution generator. The active and reactive power control, voltage and frequency droop control for the power converter of ESS are proposed to reduce microgrid impact on the distribution feeder. The voltage variation along the feeder due to change of renewable power generation is derived by executing power flow analysis. The actual voltage fluctuation on the microgrid is measured, which is used to control active and reactive power output of the power converter via energy management system in the microgrid SCADA platform. Three operation scenarios of the microgrid with ESS are tested to verify the effectiveness of the proposed control method. It is found that the power output of ESS can be well regulated to reduce voltage fluctuation on the microgid, which is complied with grid connect code to achieve better voltage control performance for the distribution feeder.

A Study on Control Strategy of PV inverter for Harmonic Mitigation in A Microgrid

Abstract: This paper presents a study of the control strategies of three-phase grid-connected photovoltaic (PV) inverter to mitigate its harmonic current output and improve the power quality of the grid. The operation principle and topology of the PV inverter is analyzed by establishing the state-space mathematical model based on the adaptation of proportional resonant (PR) and quasi-proportional resonant (QPR) controllers. According to the characteristics of the PR ad QPR controllers, the theories for mitigating harmonic currents are reviewed. A three-phase ac microgrid with grid-connected inverter systems is then built on Matlab/Simulink and the performances of the inverter controllers for harmonic mitigations are verified by comparing the simulation results.

A study of passive harmonic filter planning for an AC microgrid

Abstract: A microgrid usually consists of small-scale of thermal generation sources and other distributed energy resources (DER) such as photovoltaic, wind power, and fuel cells to serve its loads. The microgrid can increase DER penetrations and operation reliability through appropriate control schemes and energy management. When the inverter-based DERs supply electric energy to nonlinear loads in the microgrid, harmonic currents are produced and resonances in the grid may occur and causes negative impacts on some critical loads or other equipment, as well as extra power losses. To mitigate the undesired harmonic effects and improve the microgrid performance, this paper presents a study of planning single-tuned passive harmonic filters for the microgrid. Simulation results show that the designed filters can effectively mitigate the harmonic currents in the microgrid.

Reactive Power Management in Renewable Rich Power Grids: A Review of Grid-Codes, Renewable Generators, Support Devices, Control Strategies and Optimization Algorithms

Abstract: Power electronic converter (PEC)-interfaced renewable energy generators (REGs) are increasingly being integrated to the power grid. With the high renewable power penetration levels, one of the key power system parameters, namely reactive power, is affected, provoking steady-state voltage and dynamic/transient stability issues. Therefore, it is imperative to maintain and manage adequate reactive power reserve to ensure a stable and reliable power grid. This paper presents a comprehensive literature review on the reactive power management in renewable rich power grids. Reactive power requirements stipulated in different grid codes for REGs are summarized to assess their adequacy for future network requirements. The PEC-interfaced REGs are discussed with a special emphasis on their reactive power compensation capability and control schemes. Along with REGs, conventional reactive power support devices (e.g., capacitor banks) and PEC-interfaced reactive power support devices (e.g., static synchronous compensators) play an indispensable role in the reactive power management of renewable rich power grids, and thus their reactive power control capabilities and limitations are thoroughly reviewed in this paper. Then, various reactive power control strategies are reviewed with a special emphasis on their advantages/disadvantages. Reactive power coordination between support devices and their optimal capacity are vital for an efficient and stable management of the power grid. Accordingly, the prominent reactive power coordination and optimization algorithms are critically examined and discussed in this paper. Finally, the key issues pertinent to the reactive power management in renewable rich power grids are enlisted with some important technical recommendations for the power industry, policymakers, and academic researchers.

Distributed Energy Resources Based Microgrid: Review of Architecture, Control, and Reliability

Abstract: To accomplish feasible large-scale integration of distributed energy resources (DER) into the existing grid system, microgrid implementation has proven to be the most effective. This article reviews the vital aspects of DER based microgrid and presents simulations to investigate the impacts of DER sources, electric vehicles (EV), and energy storage system (ESS) on practicable architectures’ resilient operation. The focus is primarily on the concept and definition of microgrid, comparison of control strategies (primary, secondary, and tertiary strategies), energy management strategies, power quality (PQ) issues associated with DER based microgrid, and state-of-the-art entities such as ESS and EV's applications toward microgrid reliability. Following discussion on the different attributes of DER sources-based microgrid, simulations are performed to verify the results of the past works on the effects of solar, wind energy sources, ESS, and EVs on the microgrid frequency response. Additional simulations are conducted to assess the influences of DERs, ESS, EVs, and their operational strategies on the microgrid reliability aspects.

Protection IssuesinMicrogridswithMultiple Distributed Generation Units

Abstract: WWW: http://www.esat.kuleuven.be/electa Abstract --Theapplication oflocal generators in distribution gridshasconsequences fortheprotection system.In thispaper,protection issuesconcerning distributed generation arediscussed, followed by a discussion oftheresults ofsimulations. Thesesimulations concerntheeffect of localinduction generators on protection selectivity inasystem withparallel distribution feeders andtheeffect onfault detection. Itisfoundthatlocal induction generator canposea selectivity problem inasystem withparallel feeders whena line-to-line fault ora doubleline-to-ground fault occurs. Regarding thefault current detected atthebeginning ofa feeder, detected current islowest whenaline-to-line fault or a line-to-ground faultoccurs. Depending on therelay settings, this canresult inadetection problem. IndexTerms--Distributed generation, powersystem protection, selectivity, induction generator, powersystem simulation, short-circuit current.

AC microgrid protection – A review: Current and future prospective

Abstract: Microgrid is an important component of the evolving smart-grid. It has the ability to increase reliability, decrease costs, and enlarge penetration rates for distribution generation systems. However, the protection coordination may get badly affected due to the bi-directional/variable power flow associated with microgrid system and increasing penetration rates of distributed energy resources. Therefore, a proper protection strategy is highly required to decrease the complexities associated with microgrid system. In this paper, a widespread literature review on the current research and progression in the field of AC-microgrid protection is presented. The prime objective of this survey is to extend the researcher’s database comprising relevant reference points which could be highly beneficial to their future research work. This work comprises of the current status, major hitches and existing research efforts focussed in the direction of providing a smooth relaying system under diverse MG operating conditions. Moreover, the work concentrates on analysing the intelligent approaches/devices that help transform the present protection schemes to become smarter.