Consensus-Based Droop Control of Isolated Micro-Grids by ADMM Implementations

Due to low inertia, high penetration of renewable generators in isolated micro-grids may result in poor frequency and voltage response under large disturbances. In order to overcome this difficulty, the distributed average consensus algorithm has been studied recently by extending local droop control mechanisms of power converters into distributed droop control. However, its convergence rate and the resilience to noises are still not satisfactory. In this paper, two implementations of consensus-based distributed droop control by the alternating direction multipliers method are proposed. It can be shown that the closed-loop system is described by the second-order vector differential equation, and the stability of every trajectory can be analyzed by the energy function approach under certain mild conditions. Real-time digital simulations are performed to validate the effectiveness of the proposed distributed droop control mechanism.

I. Introduction

Micro-grid (MG) systems have been demonstrated as an effective technology to integrate the increasing distributed energy resources (DERs) into the existing AC power grid in the past decade [1], [2]. In order to enable the interoperability of various controllers and components in MG operations, the hierarchical control of electronically coupled DER units by DERs interface converters (DICs) plays a critical role for MG operations and control [2]. According to the time frame of operations and infrastructure requirements, the conventional hierarchical control, as shown in Fig. 1, consists of three distinct levels: (i) Primary control utilizes local measurements to synthesize local control actions; (ii) Secondary control is responsible for reliable, secure, and economical operations of MGs. Since the primary control may introduce steady state errors in frequency deviations and voltage magnitudes, these errors will be restored by secondary control actions; (iii) Tertiary control will set the optimal operational conditions and is responsible for coordinating the operation of multiple DICs, and communicating needs or requirements from the main power grid. Fig. 1.

DICs in an isolated AC MG with various control levels.