Solid-state transformer (SST) is an emerging technology integrating with a transformer power electronics converters and control circuitry. This paper comprehensively reviews the SST topologies suitable for different voltage levels and with varied stages, their control operation, and different trends in applications. The paper discusses various SST configurations with their design and characteristics to convert the input to output under unipolar and bipolar operation. A comparison between the topologies, control operation and applications are included. Different control models and schemes are explained. Potential benefits of SST in many applications in terms of controllability and the synergy of AC and DC systems are highlighted to appreciate the importance of SST technologies. This review highlights many factors including existing issues and challenges and provides recommendations for the improvement of future SST configuration and development.

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State of the art of solid-state transformers: Advanced topologies, implementation issues, recent progress and improvements

In recent years, continuous depletion of conventional energy resources and the fluctuating fuel cost have motivated research on alternative source for power generation. To effectively harvest power from the green energy resources, extensive research have been carried out in literature. Solar energy being the foremost among all other renewable energy resources has evolved as a reliable substitute for the conventional power generation. Unlike other sources, real time research on Photovoltaic (PV) Systems is a difficult assignment as it necessitates an accurate PV emulator that can precisely replicate the nonlinear characteristics of a PV cell. PV Researchers have developed emulators of different type utilizing various configurations. This paper attempts to present a comprehensive review on different PV emulator topologies so as to gather all the research activities that are scattered in this arena under a common umbrella. Further this paper provides a detailed analysis of each technique emphasizing on its (i) Realization cost (ii) Accuracy (iii) Level of complexity (iv) Sensitiveness to varying environmental conditions (v) Hardware implementation and (vi) Efficiency.

Analysis on solar PV emulators: A review

Sustainable electrification planning for remote locations especially in developing countries is very complex in nature while considering different traits such as social, economic, technical, and environmental. To address these issues related to current energy needs depending upon the end user requirements, a coherent, translucent, efficient, and rational energy planning framework has to be identified. This paper presents a comprehensive generalized methodological framework based on the synergies of decision analysis and optimization models for the design of a reliable, robust, and economic microgrid system based on locally available resources for rural communities in developing nations. The framework consists of three different stages. First, decision analysis considering various criterions (technical, social, economic, and environmental) for the selection of suitable energy alternative for designing the microgrid considering multiple scenarios are carried out. Second, the optimal sizing of the various energy resources in different microgrid structures is illustrated. Third, hybrid decision analysis methods are used for selection of the best sustainable microgrid energy system. Finally, the framework presented is then utilized for the design of a sustainable rural microgrid for a remote community located in the Himalayas in India to illustrate its effectiveness. The results obtained show that decision analysis tools provide a real-time solution for rural electrification by binding the synergy between various criteria considering different scenarios. The feasibility analysis using proposed multiyear scalable approach shows its competence not only in determining the suitable size of the microgrid, but also by reducing the net present cost and the cost of electricity significantly.

A Novel Methodological Framework for the Design of Sustainable Rural Microgrid for Developing Nations

The photovoltaic (PV) emulator is a nonlinear power supply which has similar current-voltage (I-V) characteristic to the PV module In solar energy generation research, such as the maximum power point tracking (MPPT) and the PV inverter, the actual PV module and the high power controllable light source were used during the experimenting phase However, this method requires complex experiment setup, is highly inefficient, and can damage the PV module The PV emulator provides a simpler and more efficient solution compared to the actual PV module and the controllable light source while maintaining similar output produces by the actual PV module This paper provides a template for the researcher to design the PV emulator according to the requirements established from the tested system The PV emulator consists of three parts which are the PV model, the control strategy, and the power converter The PV model produces the I-V characteristic of the PV module The control strategy determines the operating point of the PV emulator on the I-V characteristics curve and produces the reference signal for the power converter The power converter follows the reference signal and generates a similar output as the actual PV module

A comprehensive review on photovoltaic emulator

One of the most available energy sources in the world is solar energy, while in the category of renewable and nonrenewable energies is in the first group. Power generation of a photovoltaic (PV) system is a technique which is possible by using solar cells. Since photovoltaic systems cannot force solar cells to operate at MPP, a controller is needed to do so. If the controller can operate more accurately, or in other words, be optimized, the system will have an appropriate output. Many papers have been presented on maximum power point tracking algorithms. This paper intends to review the previous articles and provide a proper division, performance method. This explains the performance, application, advantages and disadvantages of algorithms to be a good reference for selecting the appropriate algorithm. Algorithms in this paper are divided into four categories methods based on measurement, calculation, intelligent schemes and hybrid schemes. The exhibition of new algorithms and the optimization of previous algorithms have led to the number of articles in this field over the years. In order to review the methods a comparative table is also provided. Finally, a PV system has been controlled by using three algorithms P&O, IC and Fuzzy-PI. The outputs control signals from the MPPT have been applied by Boost and SEPIC converters, and the outputs have been compared. Simulations have been performed in MATLAB/Simulink software.

A comprehensive review and classified comparison of MPPT algorithms in PV systems

Design and development of a model-based hardware simulator for photovoltaic array

Decoupled control of grid connected inverter with dynamic online grid impedance measurements for micro grid applications

This paper presents an overview of current control practices for three phase power converter acting as an asynchronous interface between a synchronous voltage source and a power electronic controlled voltage source. The paper starts with glimpse of the common topologies, and branches out to the control techniques from linear to non-linear, dc loops to ac loops, stationary frame to synchronous reference frame, predictive to hysteresis etc. The surveys of these controllers under faulty as well as distorted grid conditions and a few possible future trends in control were also presented as a concluding section.

Topologies and control of grid connected power converters

This paper presents a non-iterative maximum power point tracking (MPPT) technique for solar photovoltaic (PV) panels. The non-iterative MPPT is realised using online measured open circuit voltage and short circuit current along with the Fill Factor extracted from the datasheet parameters of PV panel. The proposed MPPT returns a power reference, which is directly used in the inverter control loop. This non-iterative MPPT algorithm is implemented in a single-stage three-phase inverter feeding power to grid with a hysteresis current controller. Restructuring of the Converter power circuit is proposed to facilitate the online measurements of the dynamic panel values. DC link energy storage is provided to maintain power delivery to grid during momentary disconnection of the panel due to measurement. The design procedure and selection of all the ancillary components for the restructured power circuit are presented in detail. The system implemented in hardware for a power rating of 0.5 kW is tested under steady and dynamic states of possible irradiance including partial shading. The proposed non-iterative MPPT is found to be far superior in performance to the regular iterative MPPTs.

A non-iterative MPPT of PV array with online measured short circuit and open circuit quantities

This paper presents a method for online dynamic measurement of the grid impedance that may prevail in an electrical network at any instant of time. Here the grid resistance and inductance are measured during the operation using a non-characteristic frequency current continuously injected into the grid, and subsequently calculating the impedance using discrete Fourier transforms. The proposed measurement is implemented in d-q reference frame so that the computational overhead on the microcontroller is relatively reduced. The continuous injection of non-characteristic current at 75 Hz avoids the injection of inter-harmonics into the grid during measurements. The resulting grid impedance value can be used for many purposes viz. knowing the status of the independent generations in micro-grids, controller tuning in converter systems, islanding detection etc. The proposed dynamic measurement of grid impedance is tested through simulation studies and experimentally. The experiments are conducted with the proposed controller on a scaled down laboratory model of micro-grid with a 1 kVA solar inverter, and the consolidated results of both simulation and experiments are presented.

A. Vijayakumari

Papers

Design and development of a model-based hardware simulator for photovoltaic array

Decoupled control of grid connected inverter with dynamic online grid impedance measurements for micro grid applications

Topologies and control of grid connected power converters

A non-iterative MPPT of PV array with online measured short circuit and open circuit quantities

Dynamic grid impedance calculation in D-Q frame for micro-grids