A Novel Accurate Power Sharing Method Versus Droop Control In Autonomous Microgrids With Critical Loads

Abstract

In autonomous microgrids, the well-known frequency and voltage droop control are extensively used to share active and reactive powers among parallel inverters without using any communication infrastructure. However, power sharing is performed at the expense of altering the voltage and frequency of the system. To restore the voltage and frequency to their nominal amounts, a secondary control loop is often augmented to the system using communication links. To avoid using these complex hierarchical controls, this paper proposes a novel method for power sharing in parallel inverters providing constant frequency and nominal voltage operation for critical loads. The proposed method uses a simple structure based on communication links utilization. The simulation results show that the active and reactive powers are accurately shared with an acceptable transient response. Furthermore, the results are compared with the conventional droop control to show the superiority of the proposed method over the conventional one. INDEX TERMS Autonomous microgrid, active and reactive power sharing, constant frequency operation, critical loads.

Robust Power Sharing and Voltage Stabilization Control Structure via Sliding-Mode Technique in Islanded Micro-Grid

“…Figures 4-6 show the system dominant root locus with respect to the variations of droop parameters (m and n), TSMC controller parameters (c 1 and c 2 ) and the feedback parameter (k e ), respectively. The value of m is varied in the range of [1 × 10 −6 , 1] in Figure 4a; the value of n is varied in the range of [1 × 10 −6 , 1 × 10 −1 ] in Figure 4b; the value of c 1 is varied in the range of [1, 10,000] in Figure 5a; the value of c 2 is varied in the range of [1, 10,000] in Figure 5b; the value of k e is varied in the range of [1,50] in Figure 6. As can be seen from Figure 4a, when the value of m is relatively small, the system presents a nearly second-order underdamped behavior with a pair of conjugate complex dominant roots and a too small value of m will lead to a poor stability margin.…”

“…However, a too big value of n will lead to the system oscillation. Figure 5 shows the system dominant root locus when the TSMC controller parameters (c 1 and c 2 ) vary in the range of [1,10,000]. As can be seen from Figure 5, the system presents a second-order underdamped behavior with a pair of conjugate complex roots.…”

“…As with the control technology for parallel-connected inverters, the droop control has been widely used in the micro-grid (MG) [1][2][3][4]. Especially for the islanded operation mode, the droop control can maintain the voltage amplitude/frequency stability and adjust the power allocation proportion among multiple inverters simultaneously [5].…”

Multiloop low bandwidth communication-based power sharing control for microgrids

“…The voltage drop across the feeders and power-sharing deviations are addressed in [26,27]. The mathematical expression for Voltage drop is given as: (5) Where the RP and XQ are the resistance and reactance of the P and Q respectively and V o , the output voltage of the DG unit. Considering two DG inverters DG1 and DG2 the above equation can be written as:…”

“…The switching from one mode to another mode could be manual or autonomous [2]. In case of automatic islanding, the power-sharing accuracy especially the reactive power sharing accuracy, voltage and frequency adjustments are achieved by improved droop-based control schemes which are decentralized and communication free control scheme [3][4][5]. Droop control takes the local measurements, and it can be implemented very easily, but the mismatch in the feeder's impedance of the parallel-connected DG inverters cause reactive power sharing errors and voltage deviations.…”