Renewable-energy-based microgrids are a better way of utilizing renewable power and reduce the usage of fossil fuels. Usage of energy storage becomes mandatory when such microgrids are used to supply quality power to the loads. Microgrids have two modes of operation, namely, grid-connected and islanding modes. During islanding mode, the main responsibility of the storage is to perform energy balance. During grid-connected mode, the goal is to prevent propagation of the renewable source intermittency and load fluctuations to the grid. Energy storage of a single type cannot perform all these jobs efficiently in a renewable powered microgrid. The intermittent nature of renewable energy sources like photovoltaic (PV) demands usage of storage with high energy density. At the same time, quick fluctuation of load demands storage with high power density. This paper proposes a composite energy storage system (CESS) that contains both high energy density storage battery and high power density storage ultracapacitor to meet the aforementioned requirements. The proposed power converter configuration and the energy management scheme can actively distribute the power demand among the different energy storages. Results are presented to show the feasibility of the proposed scheme.

The power output and the dynamic performance of PWM (pulse width modulated) controlled AC motor drives can be improved by increasing the inverter output voltage through overmodulation. Two different solutions are proposed to increase the output voltage in a continuously controllable fashion up to maximum possible value, which is reached in the six-step mode. The solutions differ in their approaches. A space vector strategy is used for high dynamic performance, high switching frequency drives, while a field-oriented PWM method is used for low switching frequency, high power inverters. Experimental results are presented.< >

Multilevel inverters are increasingly being used in high-power medium voltage applications due to their superior performance compared to two-level inverters. Among various modulation techniques for a multilevel inverter, the space vector pulsewidth modulation (SVPWM) is widely used. However, the implementation of the SVPWM for a multilevel inverter is complicated. The complexity is due to the difficulty in determining the location of the reference vector, the calculation of on-times, and the determination and selection of switching states. This paper proposes a general SVPWM algorithm for multilevel inverters based on standard two-level SVPWM. Since the proposed multilevel SVPWM method uses two-level modulation to calculate the on-times, the computation of on-times for an n-level inverter becomes easier. The proposed method uses a simple mapping to achieve the SVPWM for a multilevel inverter. A general n-level implementation is explained, and experimental results are given for three-level and five-level inverters

This paper presents a multiagent system (MAS) for real-time operation of a microgrid. The proposed operational strategy is mainly focused on generation scheduling and demand side management. In generation scheduling, schedule coordinator agent executes a two-stage scheduling: day-ahead and real-time scheduling. The day-ahead scheduling finds out hourly power settings of distributed energy resources (DERs) from a day-ahead energy market. The real-time scheduling updates the power settings of the distributed energy resources by considering the results of the day-ahead scheduling and feedback from real-time operation of the microgrid in real-time digital simulator (RTDS). A demand side management agent performs load shifting before the day-ahead scheduling, and does load curtailing in real-time whenever it is necessary and possible. The distributed multiagent model proposed in this paper provides a common communication interface for all components of the microgrid to interact with one another for autonomous intelligent control actions. Furthermore, the multiagent system maximizes the power production of local distributed generators, minimizes the operational cost of the microgrid, and optimizes the power exchange between the main power grid and the microgrid subject to system constraints and constraints of distributed energy resources. Outcome of simulation studies demonstrates the effectiveness of the proposed multiagent approach for real-time operation of a microgrid.

In order to actively control the power flow between the load and ultracapacitor, a dual-active-bridge converter can be utilized. Conventional phase-shift modulation (PSM) has difficulties in working with a wide range of source voltage levels and load power levels. In addition, a traditional PI controller does not provide satisfactory behavior as the relation between the control variable and output voltage is nonlinear. In this paper, a hybrid modulation scheme is proposed to extend the power range of operation from 100% to 16.67% instead of 100% to 58.33% that is achieved by conventional PSM. A feedback-linearized controller is also designed to achieve a better dynamic response under various load conditions. The details of the modulation principle and controller design are given, and the experimental results verify the proposed modulation and control scheme.