Novel Compensation Methods Using Energy Storage System (ESS) in Islanded Unbalanced Single-/Three-Phase Multi microgrids

 Abstract

The integration of single-phase microgrids (MG) and unbalanced loads to three-phase MGs results in power quality issues at the point of common coupling (PCC). These issues include unbalanced voltage, unequal power flow, and inaccurate reactive power sharing. In this article, an energy storage system (ESS) has been proposed with novel control methods to help mitigate unbalance issues in these islanded multimicrogrids (MMGs). Itpresents two novel control methods: modified reverse droop control and multifunction control to compensate the reactive power of the MMGand generate the needed active and reactive power references of the ESS. The developed control methods mitigate PCC voltage and power unbalance of theMMGand also achieve the load power sharing proportionally among different rated photovoltaics (PV) inverters. In addition, the system stabilitywith the proposed control is also presented under different scenarios. The proposed multifunction controller operation is validated using Opal-RT real-time simulator and experimentally using control hardware-in-the-loop. The results demonstrate that the PCC unbalanced voltage and power are reduced significantly by 97.8%, and the proper reactive power sharing is achieved among the different PV inverters in the proposed system.

Index Terms :Current-controlled energy storage system (ESS), power sharing, photovoltaics (PV) islanded, reactive power compensation (RPC), single-three-phase microgrid (MG), stability analysis, unbalanced voltage compensation

Block Diagram

Fig.1. Block diagram of the proposed MRDC scheme

Expected Simulation Results:

Fig. 2. Reactive power responses with different RPC and RPSA coefficients under load step change. (a) with lower coefficients. (b) with higher coefficients.

Fig. 3. Output voltage of PCC (a) before, (b) after implementing RPCA, and (c) VUF of PCC voltage.

Fig. 4. (a) Reactive power sharing performance between PV inverters. (b) Active power and (c) reactive power for each phases at the three-phase PCC terminal.

CONCLUSION

This article presents coordinated control of an ESS connected to a single-phase PVinverter and a load in parallel to improve the unbalanced voltage at the PCC terminal in an unbalanced MMG. The proposed control methods help mitigate voltage unbalance, reduce power unbalance at three-phase PCC, and share the reactive power proportionally between the PV inverters. In addition to the proposed control, stability analysis of the proposed system is presented. The effectiveness of the proposed controllers has been validated using Opal-RT real-time simulation and CHIL under an unbalanced MMG. The simulation results not only improved the power quality by 97.8%, but also the reactive power sharing between single-phase and three-phase inverters proportionally.

REFERENCES

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