Search

Hybrid ac/dc microgrid (HMG) comprises ac and dc microgrids (MGs) interconnected through an interlinking converter (IC). In islanded operation mode of HMG, a coordinated control structure must be implemented to realize voltage and frequency control in ac MG, voltage control in dc MG, active and reactive power sharing among ac sources, active power sharing among dc sources, global active power sharing among dc and ac sources, and reactive power sharing among ac sources and IC. To realize these objectives, a new coordinated control based on master–slave approach is proposed in this paper. In this method, the master source of each MG broadcasts its relative power loading as a common signal to the slave sources of the same MG and IC through a unidirectional low-bandwidth communication network. Based on this information, the slave sources and the IC adjust their operating point. The proposed method provides accurate power sharing as well as zero voltage and frequency deviation. It does not require a centralized control unit and features plug and play capability. The derivation of the proposed method is thoroughly discussed in this paper. Time domain simulation results based on CIGRE benchmark MG are presented to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

Interconnection of microgrids (MGs) provides the opportunity of increasing loadability and enhancing reliability by allowing power exchange among individual MGs. Control of networked MGs requires coordination of distributed energy resources (DERs) within each MG such that the sum of the MG’s load and exported power is shared proportionally among DERs while maintaining power quality. This paper proposes a new hierarchical control scheme for accurate load sharing and power quality enhancement in networked MGs with unbalanced load currents. The proposed scheme is comprised of local DER controllers, MG control units, and Networked MG control center. The MG control units adjust the power exchange at the value specified by the control center and regulate the voltage at the point of common coupling (PCC) by means of a secondary control signal. At the DER level, droop control is adopted to enable load sharing with fast dynamic response. The droop controller output is combined with the secondary control signal and a correction voltage which eliminates the effect of line impedances on the current sharing accuracy. This way, accurate sharing of individual phase currents is realized without requirement of data exchange among DERs. Simulation and experimental results showcase the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

The increasing penetration of dc distributed energy resources (DERs) and dc loads has motivated the utilization of dc microgrids (MGs). In this paper, a new two-level control scheme is proposed for accurate power sharing and appropriate voltage regulation in dc MGs during islanded operation mode. In the primary control level, a P − V droop method is proposed to eliminate the dependency of power sharing among DERs on line resistances. Since the P − V droop deviates the voltage derivative to a nonzero value, a voltage derivative restoration mechanism is adopted in the secondary control level to provide voltage stability. The secondary control level also compensates the voltage deviations by cascading an outer voltage control loop with the inner voltage derivative restoration loop. The secondary control signal is broadcasted to each DER via a unidirectional low-bandwidth communication link. Small signal stability of the proposed scheme is analyzed by studying the locus of the system eigenvalues. To verify the efficacy of the proposed method and compare it with the conventional scheme, real-time simulations in OPAL-RT lab setup are provided. [ABSTRACT FROM AUTHOR]

This paper proposes a new decentralized power management and load sharing method for a photovoltaic based islanded microgrid consisting of various photovoltaic (PV) units, battery units and hybrid PV/battery units. Unlike the previous methods in the literature, there is no need to communication among the units and the proposed method is not limited to the systems with separate PV and battery units or systems with only one hybrid unit. The proposed method takes into account the available PV power and battery conditions of the units to share the load among them. To cover all possible conditions of the microgrid, the operation of each unit is divided into five states and modified active power–frequency droop functions are used according to operating states. The frequency level is used as trigger for switching between the states. Efficacy of the proposed method under different load, PV generation, and battery conditions is validated experimentally in a microgrid lab prototype consisting of three units. [ABSTRACT FROM AUTHOR]