Active Fault Tolerant Control of Grid-Connected DER: Diagnosis and Reconfiguration Behnam Khaki Smart Grid Energy Research Center Department of Mechanical Engineering University of California Los Angeles, California 90095 Email: behnamkhaki@ucla.edu Heybet Kilic ¸ Department of Electric Power and Energy Dicle University Diyarbakir, Turkey 21280 Email: heybet.kilic@dicle.edu.tr Musa Yilmaz Department of Electronics and Telecommunication Engineering Batman University Batman, Turkey 72100 Email: musa.yilmaz@batman.edu.tr Miadreza Shafie-khah School of Technology and Innovations University of Vaasa 65200 Vaasa, Finland Email: miadreza@gmail.com Mohamed Lotfi, Jo˜ ao P. S. Catal˜ ao Faculty of Engineering University of Porto and INESC TEC Porto 4200-465, Portugal Emails: mohd.f.lotfi@gmail.com, catalao@fe.up.pt Abstract—In this paper, we propose an active fault tolerant control (FTC) to regulate the active and reactive output powers of a voltage source converter (VSC) in the case of actuator failure. The active fault tolerant controller of the VSC which connects a distributed energy resource to the distribution power grid is achieved through the fault diagnostic and controller reconfig- uration units. The diagnostic unit reveals the actuator failure by comparing the known inputs and measured outputs of VSC with those of the faultless model of the system and testing their consistency. In the case of actuator failure, the reconfiguration unit adapts the controller to the faulty system which enables the VSC to track the desired active and reactive output powers. The reconfiguration unit is designed using the virtual actuator which does not interfere with the regular controller of the VSC. The effectiveness of the proposed active FTC is evaluated by the numerical simulation of a VSC connected to the AC distribution grid. Index Terms—Voltage source converter, grid-connected dis- tributed energy resource, fault diagnosis, virtual actuator. I. I NTRODUCTION Conventional power grids with top-down structure rely on the large fossil fuel-based power stations emitting CO 2 . Also, they are experiencing considerable power loss, voltage fluctu- ation, and feeder congestion due to increasing load demand. To overcome these issues, distributed energy resources (DERs) with efficient power electronic converters can be deployed [1]- [3], as they are mostly based on renewable energies (such as solar, wind, and fuel cell) and located close to the electricity consumers. DER deployment can also increase load reliability as in the case of power outage, the load demands can be satisfied through the operation of DERs in islanded mode. Nevertheless, inherent intermittency and uncertainty of output power are considered the main disadvantages of DERs [4]. The solution is the controller for the power electronic interfaces of DERs which is robust against the faults in sensors and actuators, and it and can drive DER output power toward the desired value. The focus of this paper is to design an active PLL V dc Three Phase VSC Rs L s Rs L s R s L s AC Grid PCC V sa Vtb V tc V sb Vsc I a I b I c V ta Power Source abc dq Controller I dq P ref Qref mdq Q s Ps Fig. 1. Schematic diagram of grid-connected DER. fault-tolerant control (FTC) consisting of diagnosis and and reconfiguration units. Although a variety of methods have been proposed for fault detection, isolation, and tolerance in DERs and power grids [5]- [12], there are a few studies on a comprehensive actuator fault detection and controller reconfiguration. Most of the present studies are on the short circuit and sensor faults detection [5]- [7]. As some cases in point, two sensor fault detection methods, which are observer-based, for power system load frequency control loops are presented in [8]- [9]. In [10]- [11], the authors propose an observer-based fault tolerant control method for the sensor fault in the DERs. Also, a virtual actuator (VA) based FTC method for wide-are control of power systems is investigated in [12], and a model based framework to estimate and accommodate the actuator fault in a solid oxide fuel cell is proposed in [13]. In the former research, the authors do not provide any fault estimation approach, and in the latter, the authors design a controller working based on a switching rule to accommodate actuator failure. To address the lack of a comprehensive actuator fault detection and control reconfiguration for DERs, a VA-based 978-1-7281-4878-6/19/$31.00 ©2019 IEEE 3987