Tan Ma

Protection of Autonomous Microgrids using Agent-Based Distributed Communication

This paper presents a real-time implementation of autonomous microgrid protection using agent-based distributed communication. Protection of an autonomous microgrid requires special considerations compared to large-scale distribution networks due to the presence of power converters and relatively low inertia. In this paper, we introduce a practical overcurrent and a frequency-selectivity method to overcome conventional limitations. The proposed overcurrent scheme defines a selectivity mechanism considering the remedial action scheme of the microgrid after a fault instant based on feeder characteristics and the location of the intelligent electronic devices (IEDs). A synchrophasor-based online frequency-selectivity approach is proposed to avoid pulse loading effects in low inertia microgrids. Experimental results are presented for verification of the proposed schemes using a laboratory-based microgrid. The setup was composed of actual generation units and IEDs using the IEC 61850 protocol. The experimental results were in excellent agreement with the proposed protection scheme.

Control of a Hybrid AC/DC Microgrid Involving Energy Storage and Pulsed Loads

This paper presents a real-time coordinated control of the hybrid ac/dc microgrids involving energy storage and pulsed loads. Grid-isolated hybrid microgrid applications require special considerations due to the intermittent generation, online energy storage control, and pulsed loads. In this study, we introduce a comprehensive frequency and voltage control scheme for a hybrid ac/dc microgrid consisting of a synchronous generator, solar generation emulator, and bidirectional (ac/dc and dc/dc) converters. A bidirectional controlled ac/dc converter with an active and reactive power decoupling technique is used to link the ac bus with the dc bus, while regulating the system voltage and frequency. A dc/dc boost converter with a maximum power point tracking function is implemented to maximize the intermittent energy generation from solar generators. Current-controlled bidirectional dc/dc converters are applied to connect each lithium-ion battery bank to the dc bus. Lithium-ion battery banks act as energy storage devices that serve to increase the system resiliency by absorbing or injecting power. Experimental results are presented for verification of the introduced hybrid ac/dc power flow control scheme.

Operation and protection of photovoltaic systems in hybrid AC/DC smart grids

In this paper, some of the aspects related to the design, control, operation and protection of photovoltaic (PV) systems are presented and investigated. The photovoltaic systems under study are integrating their power to the common DC bus of a hybrid AC/DC microgird in a smart grid infrastructure, where a communication layer is allowing wide area monitoring, control and protection of the whole system. These PV systems can be mainly operated either in a voltage control mode, when the DC side of the system is disconnected from the main AC grid, or in a maximum power point tracking (MPPT) mode when connected to the DC bus. The control of the power conditioning units interfacing the PV panels to the rest of the systems in these two modes of operation is investigated. Furthermore, the protection of these converters against different types of faults will be also investigated. Simulation and experimental results are included in the paper to justify the validity of the ideas and concepts discussed.

Control of hybrid AC/DC microgrid involving energy storage, renewable energy and pulsed loads

This paper proposes the coordinated control of a hybrid AC/DC power system with renewable energy source, energy storages and critical loads. The hybrid microgrid consists of both AC and DC sides. A synchronous generator and a PV farm supply power to the systems AC and DC sides, respectively. A bidirectional fully controlled AC/DC converter with active and reactive power decoupling technique is used to link the AC bus with the DC bus while regulating the system voltage and frequency. A DC/DC boost converter with a maximum power point tracking (MPPT) function is implemented to maximize the energy generation from the PV farm. Current controlled bidirectional DC/DC converters are applied to connect each lithium-ion battery bank to the DC bus. Lithium-ion battery banks act as energy storage devices that serve to increase the system stability by absorbing or injecting power to the grid as ancillary services. The proposed system can function in both grid-connected mode and islanding mode. Power electronic converters with different control strategies are analyzed in both modes in detail. Simulation results in MATLAB Simulink verify that the proposed topology is coordinated for power management in both AC and DC sides under critical loads with high efficiency, reliability, and robustness under both grid-connected and islanding modes.

Multiagent-Based Optimal Microgrid Control Using Fully Distributed Diffusion Strategy

This paper proposes a multiagent-based optimal microgrid control scheme using a fully distributed diffusion strategy. A two-level cooperative optimization multiagent system is adapted for distributed energy resources economic dispatch. The lower level implements an adaptive droop scheme based on online no-load frequency adjustments. The upper level implements distributed communication using diffusion between neighboring agents for optimal microgrid management. The proposed control scheme enables peer-to-peer communication among the agents without the necessity of a centralized controller, and simultaneously performs resource optimization while regulating the system frequency. The results are compared with centralized and consensus-based optimization algorithms. We have concluded that the proposed algorithm is superior over consensus algorithms in terms of convergence speed and utilizes reduced communication infrastructure compared to centralized controllers. Simulation demonstrations were conducted along with experimental results from a hardware-based microgrid using an industrial multiagent framework. The simulation and experimental results show that the proposed method and the agent framework can be deployed in real-world microgrids and offer superior decision making on optimal microgrid control.

Distributed control of hybrid AC-DC microgrid with solar energy, energy storage and critical load

In this paper, a novel power flow control method for a hybrid AC-DC microgrid with solar energy, and energy storage is proposed for the integration of a pulse load. This micro grid works in islanding mode with a synchronous generator and PV farm supplying power to the systems AC and DC sides, respectively. A bidirectional AC-DC inverter is used to link the AC and DC sides by controlling the active and reactive power flow between them. The PV farm is connected to the DC bus through a DC-DC boost converter with maximum power point tracking (MPPT) functionality. A Battery bank is connected to the DC bus through a bidirectional DC-DC converter. The system is tested with a pulse load connected to the AC side. Simulation results verify that the proposed topology is coordinated for power management in both the AC and DC sides under critical loads with high efficiency, reliability and robustness in islanding modes.

Fuzzy logic based power and thermal management system design for multi-cell lithium-ion battery bank protection and operation

Batteries used as energy storage devices will play an important role in future power systems due to the growing popularity of micro grids (MG) and plug-in hybrid electric vehicles (PEVs). The performance of the MGs and PEVs strongly relies on their battery bank management systems, which always consists of multiple cells connected together in series and in parallel. The energy conversion efficiency of the battery bank system is influenced by a single battery cells state of charge (SOC) and temperature variations. Thermal and SOC imbalances increase the risk of catastrophic faults in the battery bank system. In this paper, the design of a novel fuzzy logic based battery bank management system is presented. The battery bank management system will have self-healing capabilities to protect itself from SOC and thermal imbalances. The proposed design is validated by using MATLAB Simulink to present a battery management system that balances the SOC and temperature of a battery module consists of a 6 × 3 configuration of lithium-ion cells connected in series and parallel. The proposed battery bank power and thermal management system can effectively regulate the temperature and balance the SOCs of the cells in the battery bank during the charging and discharging process, which will largely increase the safety of the whole system.

Optimal renewable energy farm and energy storage sizing method for future hybrid power system

This paper proposes a novel optimization method for sizing a renewable energy farm consisting of batteries and ultra-capacitors in a hybrid power system. The combination of ultra-capacitors with batteries is an emerging practice in advanced power electronic systems and a superior configuration scheme is crucial to deploy them effectively with the high penetration of renewable energy sources and critical loads in future power systems. The proposed sizing method fully utilizes the energy generated from the renewable energy farm and limits power fluctuation within the utility grid, improving grid stability and reducing construction and maintenance costs. This two-step optimization process appropriately sizes the renewable energy farm and the energy storage system by using a genetic algorithm (GA). Regional historical data of the solar irradiance, wind speed, and local load profile of Key West, Florida is used to establish the first cost function for optimizing the combination of PV and wind power based on the entire years daily energy difference between the renewable energy farm and twenty percent of the local load. With the optimized renewable energy farm size, a second cost function is designed to get the optimal combination of battery and ultra-capacitor sizes to smooth the impact caused by the renewable energy farm. A case study of a hybrid power system located in Key West, Florida is presented to verify the advantages of the proposed optimal sizing method.

Aggregated active distribution networks for secondary control of islanded power systems

Future distribution networks with high penetration of renewable resources and energy storage can provide ancillary services such as frequency regulation. This study proposes a secondary frequency control scheme based on aggregated active distribution networks. The proposed method is based on hierarchical coordinated control of bidirectional controlled energy storages under islanding situations. The constitution of under-generated islanding, where total initial generation is less than the total load and the over-generated island with an initial excess generation scenarios are investigated with secondary control support. Experimental results clearly demonstrates the effectiveness of the proposed aggregated control in a laboratory based testbed involving actual generators, energy storage and phasor measurement units.

Plug-in vehicles car park photovoltatic farm construction for cost and emission reductions

In this paper, a photovoltatic (PV) farm construction plan for charging plug-in electric vehicles (PEVs) in a workplace parking lot is proposed. The system involves a developed smart power charging controller, an under construction PV farm and a DC distribution bus connected to the AC utility grid. In order to produce enough energy for the daily consumption of a certain number of PEVs at the same time limit the construction cost of the PV farm, the scale of the PV farm should be optimized. A stochastic model of PEVs daily energy consumption is used together with the historical solar irradiance data in this area to find the best scale of the PV farm through genetic algorithm (GA) optimization. Since the output power from the PV farm varies in different environmental situations, energy forecasting and distribution is achieved by using the smart power flow controller. One day period simulation of the hybrid PEVs charging system is done to demonstrate that the proposed plan can effectively support enough power for a certain number of PEVs with the maximum utilization of renewable energy and minimum grid impact.