Improvement of Stability and Load Sharing in an Autonomous Microgrid Using Supplementary Droop Control Loop

Abstract

This paper investigates the problem of appropriate load sharing in an autonomous microgrid. High gain angle droop control ensures proper load sharing, especially under weak system conditions. However it has a negative impact on overall stability. Frequency domain modeling, eigenvalue analysis and time domain simulations are used to demonstrate this conflict. A supplementary loop is proposed around a conventional droop control of each DG converter to stabilize the system while using high angle droop gains. Control loops are based on local power measurement and modulation of the d-axis voltage reference of each converter. Coordinated design of supplementary control loops for each DG is formulated as a parameter optimization problem and solved using an evolutionary technique. The supplementary droop control loop is shown to stabilize the system for a range of operating conditions while ensuring satisfactory load sharing.

Conventional P-ω/Q-V Droop Control in Highly Resistive Line of Low-Voltage Converter-Based AC Microgrid

“…Substituting Equation (27) into Equation (2) in terms of V, the output reactive power of DG is given by:…”

“…In highly resistive line, the control strategies without communication are generally divided into three categories: the P-V droop with Q-f boost (VPD/FQB) method [14][15][16][17][18][19], the virtual impedance methods [20][21][22][23][24], and the variants of droop control [25][26][27]. The detail advantages and disadvantages of these methods [14][15][16][17][18][19][20][21][22][23][24][25][26][27] can be found in our latest review [17].…”

“…The detail advantages and disadvantages of these methods [14][15][16][17][18][19][20][21][22][23][24][25][26][27] can be found in our latest review [17].…”

“…Although the intelligent control structure carefully tracks the GDC dynamic behavior, and exhibits desirable performance for different load change scenarios, the ANFIS controller is slightly complex. In further investigation of the droop concept, power-angle droop control is proposed for rural low voltage networks in [26,27]. The angle droop can improve load power sharing among DGs without a frequency drop.…”

Improving Voltage Profile of Islanded Microgrid using PI Controller

“…In a microgrid (islanding) mode, the profile of voltage and frequency have to be maintained by the microgrid itself, if not the system will malfunction due to the nature of the attached DG units and the power converter [12]. An appropriate method for load sharing among the DG units must be selected for sharing the load [13], [14]. The problem of voltage during islanding operation of microgrid is similar to voltage drop deviations in emergency conditions by connecting DVR (Dynamic Voltage Restorer) which is custom power device in existing distribution system [15], [16].…”