This paper presents a high-performance control strategy to support an optimised transient performance for a hybrid AC/DC microgrid system based on an improved virtual synchronous generator (VSG). The standard VSG is modified and an improved control strategy is developed. A pre-synchronization controller is embedded within the improved VSG controller for grid-connection use. In addition, this paper builds the small-signal model for the improved VSG controller in order to analyse the system's stability. A controller for the battery energy storage system is developed in order to assist the power output of the hybrid microgrid. The microgrid system is designed in a MATLAB/SIMULINK simulation environment based on the under-construction hybrid AC/DC microgrid system at Griffith University, Australia. A comparative study of droop control, conventional VSG control, and the improved VSG control is carried out under different possible transient cases. The pre-synchronization method is also tested. The simulation results show that the improved VSG control strategy is evidently able to ensure smooth variations in frequency, voltage and active power during transient cases.

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In recent years, the penetration level of distributed energy resources (DER) in the low voltage (LV) networks are increasing rapidly which has resulted in causing the voltage rise problem, even at the far end customer point in distribution networks (DNs). This paper presents a coordinated hierarchical controls selection method for mitigating the overvoltage problem using available resources in DNs, for example, static synchronous compensators (STATCOM) and battery energy storage (BES) systems. The proposed method recommends the installation of new control devices, such as photovoltaic (PV) smart voltage source inverter (VSI) with reactive power compensation capability, residential BES installations, and power sharing among neighboring distributed generator (DG) units depending on PV penetration levels at the LV network. The requirements of the proposed installation of the compensation devices are based on three criteria: (i) higher PV penetration scenarios; (ii) satisfying relevant standards; and (iii) economic perspectives. The interactions among standard VSI (operated at unity power factor (pf)) and smart VSI (variable pf) are also considered in the proposed method to mitigate the voltage rise problems. The results show that only after exceeding certain PV penetrations, the LV network requires a coordinated operation from STATCOM/BES and advanced compensation devices to sustain terminal voltages within permissible (±6%) limits. The proposed method is verified with extensive case studies utilizing real PV irradiance and customer loads data with nonlinear dynamic DER models connected with an urban LV network in the PSCAD/ EMTDC software environment.

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In this paper, an Internet of Things (IoT) platform is proposed for Multi-Microgrid (MMG) system to improve unbalance compensation functionality employing three-phase four-leg (3P-4L) voltage source inverters (VSIs). The two level communication system connects the MMG system, implemented in Power System Computer Aided Design (PSCAD), to the cloud server. The local communication level utilizes Modbus Transmission Control Protocol/Internet Protocol (TCP/IP) and Message Queuing Telemetry Transport (MQTT) is used as the protocol for global communication level. A communication operation algorithm is developed to manage the communication operation under various communication failure scenarios. To test the communication system, it is implemented on an experimental testbed to investigate its functionality for MMG neutral current compensation (NCC).To compensate the neutral current in MMG, a dynamic NCC algorithm is proposed, which enables the MGs to further improve the NCC by sharing their data using the IoT platform. The performance of the control and communication system using dynamic NCC is compared with the fixed capacity NCC for unbalance compensation under different communication failure conditions. The impact of the communication system performance on the NCC sharing is the focus of this research. The results show that the proposed system provides better neutral current compensation and phase balancing in case of MMG operation by sharing the data effectively even if the communication system is failing partially.Energies 2018, 11, 3102 2 of 22 control the neutral current directly [3], where the 3P-4L voltage source inverter (VSI) provides better unbalance compensation than other active and passive methods [4]. Traditionally, a fixed portion of the 3P-4L converter capacity is specified to compensate the neutral current. However, the drawback of this method is in case of higher neutral current compensation (NCC) necessity, where it can lead to increased capacity of the 3P-4L compensator [5]. Authors in Reference [6] employed the 3P-4L VSI with PV installation to compensate for the neutral current but case scenarios for network interaction with different loads are not presented. A fixed capacity neutral current compensation method employing 3P-4L VSI under various load scenarios for network contingencies cases is proposed in Reference [7]. Furthermore, the 3P-4L VSI is used to eliminate the leakage current from PV installations [8]. However, none of these researches have considered higher capacity requirement. Authors in Reference [9] propose a dynamic capacity distribution method to compensate for the neutral current utilizing the maximum capacity of the VSI in a Microgrid (MG) but no communication system in presented. Authors in References [10,11] have employed conservative power theory to share the residual neutral current among the VSIs in an MG. Although a communication system have been employed, its operational details are not presented. Cloud-based Internet of Things (IoT) platforms to manage energy of building...