Passive Islanding Detection Technique for Integrated Distributed Generation at Zero Power Balanced Islanding

Renewable power generation systems have more advantages in the integrated power system compared to the generation due to fossil fuels because of their advantages like reliability and power quality. One of the important problems due to such renewable distributed generation (DG) system is an unintentional islanding. Islanding is caused if DG supplies power to load after disconnecting from the grid. As per the DG interconnection standards, it is required to detect the islanding within two seconds after islanding with the equipments connected to it. In this paper a new passive islanding detection method is presented for wind DG integrated power system with rate of change of positive sequence voltage (ROCOPSV) and rate of change of positive sequence current (ROCOPSC). The islanding is detected if both the values of ROCOPSV and ROCONSV are more than a predefined threshold value. The test system results carried on MATLAB shows the performance of the proposed method for various islanding and non islanding events with different power imbalances. The results conclude that, this method can detect islanding even at balanced islanding with zero non detection zone (NDZ)

PWM Harmonic Signature Based Islanding Detection for a Single-Phase Inverter with PWM Frequency Hopping

Distributed generation (DG) has gained popularity in recent years due to the increasing requirement for renewable power sources. A problem that exists with DG systems is the islanding of DG units that creates safety issues for personnel as well as the potential for damage to utility infrastructure. Therefore, islanding detection methods are utilized to mitigate the risk of islanded operation of DG units. A new passive method of islanding detection based on the signature of the PWM voltage harmonics is proposed. The viability of the algorithm is investigated with the use of an analytical and time domain model of the inverter and further validated with experimental results. Furthermore, an extension of the detection scheme is proposed for use in multiinverter scenarios composed of adaptive frequency hopping to eliminate unwanted tripping

Reconfigurable control scheme for a PV microinverter working in both grid connected and island modes

In this paper, a photovoltaic (PV) microinverter capable of operating in both island mode and grid-connected mode by means of a reconfigurable control scheme is proposed. The main advantage of control reconfiguration is that in grid-connected mode, the microinverter works as a current source in phase with the grid voltage, injecting power to the grid. This is the operation mode of most commercial grid-connected PV microinverters. The idea is to provide those microinverters with the additional functionality of working in island mode without changing their control algorithms for grid-connected mode, which were developed and refined over time. It is proposed that in island mode, the microinverter control is reconfigured to work as a voltage source using droop schemes. These schemes consist in implementing P/Q strategies in the inverters, in order to properly share the power delivered to the loads. The aim of the paper is to show that the proposed control reconfiguration is possible without dangerous transients for the microinverter or the loads. Simulation and experimental results on an 180-W PV microinverter are provided to show the feasibility of the proposed control strategy.This work was supported by the Spanish Ministry of Science and Innovation under Grant ENE2009-13998-C02-02.Trujillo Rodríguez, CL.; Velasco De La Fuente, D.; Garcerá, G.; Figueres Amorós, E.; Guacaneme Moreno, JA. (2012). Reconfigurable control scheme for a PV microinverter working in both grid connected and island modes. IEEE Transactions on Industrial Electronics. 59:101-111. https://doi.org/10.1109/TIE.2011.2177615S1011115

An islanding detection method for multi-DG systems based on high-frequency impedance estimation

Active islanding detection methods are generally employed for grid-connected inverter-based Distributed Generation (DG). However, there might be mutual influences and power quality issues caused by the disturbance signal when multiple inverters are involved. To address those problems, this paper analyzes the potential failure mechanism of the f-Q (frequency-reactive power) drifting active method in multiple-DG situations. Then, a novel high frequency transient injection based islanding detection method that is suitable for both single and multiple-DGs is proposed. Compared with the conventional injection methods, a high frequency impedance model for DG is provided for better theoretical analysis. By means of the intermittent Time Domain Low Voltage Condition (TDLVC) injection control, this method can achieve good accuracy and reduce disturbances to power system

Flexible grid connection and islanding of SPC-based PV power converters

Peer ReviewedPostprint (author's final draft

An Islanding Detection Method for Micro-Grids With Grid-Connected and Islanded Capability

With the increasing prevalence of renewable energy and distributed generation (DG) in distribution systems, micro-grids are becoming more popular and an attractive option for enhancing system operation and reliability. This can be attributed to the micro-grid ability to operate in both connected and disconnected modes. Equally important, micro-grids are the best solution to meet the increasing demand of electric power in a cost effective manner due to the close proximity to the load demand and thus minimizing system losses. Islanding detection methods have been proposed for inverter based distributed generation with only grid-connected capability. Micro-grids are composed of DGs that are capable of operating in two modes: grid connected and islanded. This thesis introduces and proposes the concept of micro-grid transition detection where the status of the micro-grid is detected based on adaptively modifying the droop slope. The droop coefficient is chosen such that the micro-grid is stable while grid connected and in the contrary Unstable once an islanded micro-grid operation is initiated. The droop coefficient is adaptively modified, once the micro-grid transitions from grid-connected to islanded operation, to stabilize the micro-grid for the islanded mode of operation. The proposed method is capable of detecting micro-grid transition in less than 600 ms under various active and reactive power mismatches. The proposed micro-grid transition detection method is tested on a micro-grid equipped with inverter based DGs controlled using the droop approach. The main objective of this thesis is to develop a novel islanding detection method for micro-grids with grid connected and islanded capability. A micro-grid model was developed using power system computer aided design/ electromagnetic transient and DC (PSCAD/EMTDC) as a platform for testing the proposed method. Simulation results were conducted considering the Institute of Electrical and Electronics Engineers Standard 1547(IEEE Std. 1547) standard islanding detection testing procedure

Review on Control of DC Microgrids and Multiple Microgrid Clusters

This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors' point of view, are also provided in the final concluding part

Islanding Detection and Seamless Transfer for Grid-connected PWM Converters of Distributed Generation Units

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 2. 설승기.본 논문에서는 분산 전원용 계통 연계형 컨버터의 단독 운전 검출 및 무순단 절환을 위한 제어 방식에 대해 다룬다. 분산형 전원은 기존의 화석 연료를 대체할 수 있는 새로운 에너지원인 신재생 에너지를 바탕으로 하여 소규모로 전력 소비 지역 부근에 배치 가능한 전원으로써 원거리 전력 전송에 따른 손실을 감소 시키고 기존의 계통 개발 비용을 저감 시키며 계통 신뢰성 및 전력 품질 향상 등의 장점을 가진 미래의 배전 계통 구성 요소이다. 하지만 이러한 분산형 전원의 특성에도 불구하고 기존 계통과의 연계 운용에 있어서는 해결해야 할 기술적인 문제들이 많이 남아 있다. 그 가운데에는 분산형 전원의 계통 연계 운전을 담당하는 컨버터의 제어 기술이 자리 잡고 있다. 이러한 컨버터의 운전 기술 중에서 가장 특징적인 성능 중의 하나는 계통으로부터 분리된 상태에서도 운전할 수 있다는 것이다. 즉, 분산형 전원이 부하에 충분한 전력을 공급할 수 있을 정도의 발전양을 가지고 있을 때에는, 계통에 문제가 발생하더라도 독립적인 운전이 가능하여 효과적으로 부하의 전원 품질을 보장할 수 있다. 따라서 최근에는 이와 같은 분산형 전원의 장점을 적극적으로 활용하고 수용하기 위해 컨버터의 계통 연계 운전과 계통 분리 운전에 대해 활발한 연구가 진행되고 있다. 통상적으로 계통 연계 운전에서는 분산형 전원의 발전양을 제어하기 위하여 컨버터는 전류 제어 모드로 구동하고, 계통 분리 운전에서는 중요 부하에 일정 품질 이상의 전원을 공급하기 위해 전압 제어 모드로 동작한다. 하지만 이러한 두 가지의 운전 모드 사이의 전환 과정에서는 부하 전압에 과도 상태가 발생하거나 계통 혹은 컨버터에 정격 크기 이상의 돌입 전류가 흐를 위험이 존재한다. 따라서 분산형 전원의 계통 연계 운전과 계통 분리 운전 사이의 전환을 부드럽게 이어주는 컨버터의 무순단(Seamless) 절환 성능이 매우 중요한 문제로 인식되고 있다. 분산형 전원이 계통 분리 운전으로 전환되는 경우는 크게 두 가지로 나눌 수 있다. 첫번째는 지락 사고(Ground fault)와 같은 송배전 계통에서의 사고에 의해 계통 전원의 품질이 저하되어 분산형 전원 시스템이 스스로 계통과 차단한 후 계통 분리 운전으로 전환하는 경우이며 두번째는 계통단의 수리 및 점검 등의 이유로 단독 운전(Islanding)이 발생하게 되어 계통 분리 운전으로 전환하는 경우이다. 따라서 두 가지 경우에 대하여, 중요 부하의 안정적인 전원 수급을 가능하게 하는 무순단 절환 전략이 요구된다. 본 논문에서는 단독 운전 검출 성능을 포함하여 계통 연계 운전 모드와 계통 분리 운전의 부드러운 전환 제어 방식을 제안한다. 제안된 무순단 절환 전략의 성능을 5kW 용량의 전력 변환 장치 2대와 에너지 저장 장치(Energy Storage System, ESS)를 이용한 실험을 통해 검증하였다.초록 i 목차 iii 제 1 장 서론 1 1.1 연구 배경 1 1.2 연구 목표 3 1.3 논문의 구성 7 제 2 장 계통 연계형 컨버터의 전류 제어 – LCL 필터의 능동 댐핑 제어 9 2.1 시스템 구성 및 모델링 10 2.2 전류 제어기 설계 11 2.3 기존의 LCL 필터의 공진 억제 방식 14 2.3.1 기존의 수동 댐핑 방법 15 2.3.2 기존의 능동 댐핑 방법 19 2.4 제안된 LCL 필터의 공진 억제 방식 21 2.5 실험 결과 28 제 3 장 단독 운전 검출 37 3.1 단독 운전 시험 회로 39 3.2 기존의 단독 운전 검출 방식 42 3.2.1 직접 검출 방식 43 3.2.2 간접 검출 방식 45 3.3 제안된 단독 운전 검출 방식 73 3.3.1 부하 조건 76 3.3.2 주입할 무효 전력 설계 92 3.4 실험 결과 105 3.4.1 부하 시험 106 3.4.2 단독 운전 검출 시험 108 제 4 장 계통 연계 운전과 계통 분리 운전의 무순단 절환 120 4.1 기존의 운전 모드 절환 방식 122 4.2 제안된 자립 운전으로의 전환 방식 128 4.2.1 전압 제어기 구성 128 4.2.2 전압 제어기 설계 130 4.2.3 전압 제어기 전향 보상 134 4.3 제안된 계통 재병입 방식 135 4.4 실험 결과 137 제 5 장 결론 및 향후 과제 150 5.1 연구 결과 150 5.2 향후 과제 153 부록 A. 분산형 전원 관련 기술 및 연계 사항 155 A.1 중요 용어 정리 155 A.2 기술 요건 세부 사항 159 A.2.1 계통 연계 운전 159 A.2.2 단독 운전 161 A.2.3 자립 운전 162 참고 문헌 165 Abstract 174Docto

Design and Control of On-board Bidirectional Battery Chargers with Islanding Detection for Electric Vehicle Applications

Electric vehicles have gained popularity over the last decade due to concerns regarding climate change as well as depleting fossil fuel reserves. One of the important components of electric vehicles is the battery charging system that has been the focus of recent research interest in terms of vehicle to grid (V2G) power transfer with the aim of providing peak load levelling for the grid as well as a buffer for excess renewable energy. The research addressed in this thesis is focused on single-phase on- board bidirectional chargers for electric vehicle applications where emphasis is given to the design, control and islanding detection aspects. A comparative study between a low frequency transformer based and high frequency DAB based bidirectional charging system is carried out and the weight, cost and efficiency between the two topologies compared. An optimised LCL filter design method for the two converters is presented which characterises the high frequency current ripple as well as the losses in the damping resistor. Controller design, simulation and experimental validation of the two converters are also presented. The impact of 3rd harmonics on the performance of second order generalised integrator (SOGI) phase locked loops (PLLs) is investigated through an analytical method to predict the resulting output harmonic magnitudes. Two modified SOGI PLLs are presented where the harmonic rejection performance has been improved. A new PLL structure based on the novel IIR filter proposed by Ed Daw et al. is investigated for application in grid converters. The new PLL is evaluated with hardware-in-the-loop (HIL) simulations for transient and abnormal grid conditions and compared with the SOGI PLL for performance evaluation as well as computational requirements. The new PLL is validated in bidirectional charger hardware. A new islanding detection algorithm based on the detection of high frequency switching harmonic signature with frequency hopping is presented which has the advantage of multi-inverter compatibility. The difficulty in detection for PWM harmonic based methods when capacitive loads are present is analysed. Furthermore, the algorithm is validated in hardware