1949-3053 (c) 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TSG.2017.2741668, IEEE Transactions on Smart Grid 1 Voltage and Frequency Regulation of Microgrid With Battery Energy Storage Systems Huiying Zhao, Student Member, IEEE, Mingguo Hong, Member, IEEE, Wei Lin, Senior Member, IEEE and Kenneth A. Loparo, Life Fellow, IEEE Abstract—This paper presents a novel primary control strategy based on output regulation theory for voltage and frequency regulations in microgrid systems with fast-response battery energy storage systems (BESS). The proposed control strategy can accurately track voltage and frequency set points while mitigating system transients in the presence of disturbance events. Therefore, it overcomes the key weaknesses of droop- based control methods such as large steady-state voltage and frequency deviations and poor transient performance. Through- out this work, four control schemes are derived with trade- offs between communication requirement and system dynamic performance. Their effectiveness is validated through Matlab SIMULINK simulation studies involving a medium-voltage (MV) microgrid with both synchronous generation resources and BESS. Although the proposed control schemes are centralized, practical implementation is possible with available communication links in microgrids and embedded hardware technologies. Index Terms—microgrids, voltage and frequency regulation, output regulation theory, droop control, battery energy storage systems, power electronic converters. NOMENCLATURE δ DGi Synchronous generator internal voltage angle of mi- crogrid MG i (radian) δ CNVi Phase angle of converter in MG i (radian) γ dqi Integration of the current difference at the current controller λ i Actual eigenvalues of the closed loop system in con- trol scheme II λ ∗ i Desired eigenvalues of the closed loop system in control scheme II ω com Rotor speed of common reference frame (radian/s) ω DGi Synchronous generator rotor speed of MG i (radian/s) Φ i Integration of the q-axis voltage of the phase lock loop τ t ,τ g Time constants of generator turbine governor(s) C fi LC filter capacitance of converter in MG i D Generator damping coefficient E fi Excitation voltage of generator in MG i E dqi Transient EMF of generator in MG i i dqLDi Load current of microgrid MG i i dqLDk Load current at network bus k i dqLNl Current of network line l i dqXFi Current of transformer for MG i i ldqCNV i Output current of pulse-width modulation in MG i i ∗ ldqCNV i Output current set points of pulse-width modulation in MG i The authors are with the Department of Electrical Engineering and Com- puter Science, Case Western Reserve University, Cleveland, OH 44106, USA. i odqCNV i Output current of converter in MG i k d Droop constant of generator turbine governor K pc ,K ic PI parameters of converter current controller K P ,K I PI parameters of generator excitation system K p ,K i PI parameters of converter phase lock loop L ci Inductance of converter coupling inductor in MG i L fi LC filter inductance of converter in MG i M Generator moment of inertia MG i The ith microgrid, i=1, 2 and 3 P ei Electrical power output of generator in MG i P mi Prime mover mechanical power of generator in MG i P refi Active power set point of generator in MG i r di Ground resistance of converter in MG i R LDi ,L LDi Resistance and inductance of the load in MG i R LDk ,L LDk Resistance and inductance of the RL load at network bus k R LNl ,L LNl Resistance and inductance of the network line l R XFi ,L XFi Resistance and inductance of transformer for MG i T ′ dq0 Generator transient time constant(s) T R ,T s Time constants of the excitation system(s) V Ai , V Bi Excitation system states of generator in MG i v cdqCNV i LC filter voltage of converter in MG i v dqn Voltage of bus i in reference frame of the system v dqPCCi PCC voltage in reference frame of the system v idqCNV i Actual voltage of the pulse-width modulation v ∗ idqCNV i Demand voltage of the pulse-width modulation V refi Terminal voltage set point of generator in MG i X ′ dqi Transient reactance of generator in MG i p.u. Per unit PCC Point of common coupling PWM pulse-width modulation I. I NTRODUCTION M icrogrids as small-scale power systems capable of op- erating in both the grid-connected and islanded modes, can provide important operational benefits with enhanced energy security and grid resiliency [1], [2]. They will play an important role in the development of the next generation electric power grid [3]. Some important challenges exist for microgrid operation, however, especially in the area of power quality management when microgrids are operating in the islanded mode. The challenges are primarily associated with the relative low system inertia to absorb network disturbances, high resistance to reactance ratios (R/X) of distribution lines, and the coupling between active and reactive power of voltage