A Constant Grid Interface Current Controller for DC Microgrid

With the increased percentage of distributed renewable energy sources (RES) connected to the power network, it is challenging to maintain the balance between the power generation and consumptions against the unpredictable renewable energy generation and load variations. Considering this, this study proposed a new DC microgrid control strategy to reduce the disturbance to the main power grid from the distributed generation and load variations within the DC microgrid. The DC microgrid model used in this study includes an energy storage unit (battery), a distributed generation unit (PV) and loads. A fuzzy logic controller (FLC) is used to actively regulate the battery charging/discharging current to absorb the power variation caused by PV generation and load changes. The proposed control strategy is validated by simulation in MATLAB/Simulink

Impact of Coil Misalignment in Data Transmission over the Inductive Link of an EV Wireless Charger

The penetration rate of electric vehicles (EVs) will experience a relative increment in the future, so easy to use ways to recharge will be demanded. In this sense, wireless charging represents a safe charging method that minimises user intervention. In a similar way to conductive charge, wireless charging requires some information exchange between the charger primary side and secondary side (battery) for safety and operational reasons. Thus, wireless chargers depend on a communication system for their controlled and correct operation. This paper analysed the communication performance of a wireless EV charger in which the communiction device is part of the wireless power transfer system. Particularly, this work studies how the communication system reacts to power coil displacements, which commonly occur in their conventional performance. The results show that the compensation topology selected to ensure the resonant operation clearly impacts on the communication performance. In particular, the theoretical model and the simulation results demonstrate that the asymmetrical compensation topologies are more stable in terms of the wireless communication channel capacity

Active DC bus signaling control method for coordinating multiple energy storage devices in DC microgrid

Management of multiple energy storage devices in a DC microgrid is a challenge. Conventional method, such as droop control, cannot ensure accurate current sharing in coordinating multiple battery banks, which limits the DC microgrid system performance. This paper proposed an active DC bus signaling (ADBS) method to coordinate multiple battery banks in a DC microgrid. It has the advantages of accurate current sharing. Using the proposed ADBS method, the master controller can collect State of charge (SoC) of each slave battery bank by actively varying the DC bus voltage levels and monitoring the current change. The master module then sets a working voltage level after decision-making. The proposed method was experimentally evaluated, and the experimental results show that all the possible working voltage levels can be reached and the accuracy of current sharing is guaranteed

Power maximised and anti-saturation power conditioning circuit for current transformer harvester on overhead lines

The current transformer (CT) harvester is an effective and efficient solution due to its higher reliability and power density compared to other techniques. However, the current of overhead conductor fluctuates from tens of to thousands of amperes, which brings two challenges for the CT harvester design. First, the startup current, above which the harvester can independently power the monitoring devices, should be as low as possible, so that the battery capacity can be reduced; secondly, the magnetic core should be ensured unsaturated in high current condition. This paper proposes a power conditioning circuit with comprehensive control to maximize the output power and prevent the core from saturation. A prototype that can deliver 22.5 W power with 200 A is designed, and a control strategy based on the finite-state machine is implemented. Experimental results show that the startup current for 2 W load is about 30 A, and the core power density at 60 A is 45.96 mW/cm3, both of which are markedly improved compared to the reported results of the same condition

Novel communication method between power converters for DC micro-grid applications

Communication between power converters is vital for high performance DC micro-grids controls. However, for residential DC micro-grid applications, using external communication link would increase the system cost, and reduce the system flexibility and reliability. This paper presents a novel method to enable the conventional DC/DC converters to transmit data via the common DC Bus. With this technology, cost-effective low bandwidth communication links between power converters can be established within a DC micro-grid, and advanced distributed control algorithms can be developed. A reliable communication with 2 kbps transmission rate has been implemented between the Boost converters through the common input DC bus

Accelerated Particle Swarm Optimization for Photovoltaic Maximum Power Point Tracking under Partial Shading Conditions

This paper presents an accelerated particle swarm optimization (PSO)-based maximum power point tracking (MPPT) algorithm to track global maximum power point (MPP) of photovoltaic (PV) generation under partial shading conditions. Conventional PSO-based MPPT algorithms have common weaknesses of a long convergence time to reach the global MPP and oscillations during the searching. The proposed algorithm includes a standard PSO and a perturb-and-observe algorithm as the accelerator. It has been experimentally tested and compared with conventional MPPT algorithms. Experimental results show that the proposed MPPT method is effective in terms of high reliability, fast dynamic response, and high accuracy in tracking the global MPP

Multifunctional control design for modular plug-and-play battery storage in DC microgrids

Plug-and-Play (P&P) performance facilitates the modularity of DC microgrids. The realization of P&P operation relies on the control design of DC microgrids. Conventional control methods are normally designed for steady operation of a DC microgrid, neglecting or partially sacrifices the availability of P&P operations. Some bottom layer’s control designs such as droop control, from a hierarchical control scheme perspective for example, are inherently able to realize P&P operations. However, such methods have limitations in terms of power sharing accuracy. This paper proposes a control scheme that reconfigures hierarchical control and makes it more compatible for different P&P operation situations in DC microgrids. In this control scheme, Automatic Mater-Slave (AMS) control is implemented in the secondary control layer to automatically respond to those cases in the absence of communication or the failure of the master module. The proposed control scheme is validated by MATLAB/Simulink simulation

Design and Assessment of an Electric Vehicle Powertrain Model Based on Real-World Driving and Charging Cycles

In this paper, an advanced analytical model for an electric vehicle (EV) powertrain has been developed to illustrate the vehicular dynamics by combining electrical and mechanical models in the analysis. This study is based on a Nissan Leaf EV. In the electrical system, the powertrain has various components including a battery pack, a battery management system, a dc/dc converter, a dc/ac inverter, a permanent magnet synchronous motor, and a control system. In the mechanical system, it consists of power transmissions, axial shaft, and vehicle wheels. Furthermore, the driving performance of the Nissan Leaf is studied through the real-world driving tests and simulation tests in MATLAB/Simulink. In the analytical model, the vehicular dynamics is evaluated against changes in the vehicle velocity and acceleration, state of charge of the battery, and the motor power. Finally, a number of EVs involved in the power dispatch is studied. The greenhouse gas emissions of the EV are analyzed according to various energy power and driving features, and compared with the conventional internal combustion engine vehicle. In this case, Nissan Leaf is a pure EV. For a given drive cycle, Nissan Leaf can reduce CO2 emissions by 70%, depending on the way electricity is generated and duty cycles