Frequency-Based Decentralized Conservation Voltage Reduction Incorporated Into Voltage-Current Droop Control for an Inverter-Based Islanded Microgrid

Hyeon-Jin Moon,Young-Jin Kim,Seung-Il Moon

doi:10.1109/access.2019.2943538

Abstract

Conservation voltage reduction (CVR) aims to decrease load demands by regulating bus voltages at a low level. This paper proposes a new strategy for decentralized CVR (DCVR), incorporated into the current-based droop control of inverter-interfaced distributed energy resources (IDERs), to improve the operational reliability of an islanded microgrid. An I dq controller is developed as an outer feedback controller for each IDER, consisting of Id-V controllers for the DCVR and I d -ω and I q -V controllers for power sharing. In particular, the I d -V controllers adjust the output voltages of the IDERs in proportion to the frequency variation determined by the I d -ω controllers. This enables the output voltages to be reduced by the same amount, without communication between the IDERs. The I q -V controllers are responsible for reactive power sharing by adjusting the voltages while taking into account the Id-V controllers. Small-signal analysis is used to verify the performance of the proposed DCVR with variation in the I d -ω and Iq-V droop gains. Case studies are also carried out to demonstrate that the DCVR effectively mitigates an increase in the load demand, improving the operational reliability, under various load conditions determined by power factors and load compositions.

Highlights

Microgrids (MGs) are self-contained local entities including distributed energy resources (DERs) and loads [1]
CASE STUDIES AND RESULTS The MG test bed, shown in Fig. 1, was implemented using Matlab/Simulink to analyze the real-time performance of the proposed decentralized CVR (DCVR) strategy with variation in the load demand, FIGURE 6. (a) Active and (b) reactive power outputs of the interfaced DERs (IDERs) for nId = 5%
This paper proposed a new DCVR strategy incorporated with current-based droop control to improve the operational reliability of an inverter-based islanded MG

Summary

INTRODUCTION

Microgrids (MGs) are self-contained local entities including distributed energy resources (DERs) and loads [1]. DERs, controllable loads, and voltage-regulating devices such as capacitor banks These centralized schemes have advantages in terms of determining global or near-global optimal operations of MGs, based on full observation of the operating conditions of DERs. a large amount DER-related data must be transferred in real time via communications links, making it difficult to implement such centralized schemes in practice [5]. The P–ω and Q–V droop control schemes have been widely adopted [13]–[17], so that the total power generation can be shared among the DERs for real-time frequency and voltage regulations. Simulation case studies are carried out to validate that the proposed DCVR improves the transient response of the IDERs and enables regulation of bus voltages at the lower level, further reducing the load demand, under various load conditions, which are characterized by load power factors and compositions

DESCRIPTION OF MG TEST BED AND PROPOSED DCVR

FREQUENCY-BASED DCVR WITH CURRENT-BASED DROOP CONTROL

CASE STUDIES AND RESULTS

CONCLUSION