http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

http://www.paredox.com/foswiki/pub/Luichart/RedoxTechnicalPapers/Battery_energy_storage_technology_for_power_systemsAn_overview.pdf

Battery Energy Storage Technology for power systems-An overview

This paper gives an overview of medium-voltage (MV) multilevel converters with a focus on achieving minimum harmonic distortion and high efficiency at low switching frequency operation. Increasing the power rating by minimizing switching frequency while still maintaining reasonable power quality is an important requirement and a persistent challenge for the industry. Existing solutions are discussed and analyzed based on their topologies, limitations, and control techniques. As a preferred option for future research and application, an inverter configuration based on three-level building blocks to generate five-level voltage waveforms is suggested. This paper shows that such an inverter may be operated at a very low switching frequency to achieve minimum on-state and dynamic device losses for highly efficient MV drive applications while maintaining low harmonic distortion.

Medium-Voltage Multilevel Converters—State of the Art, Challenges, and Requirements in Industrial Applications

This paper reviews methods to fix a number of hidden neurons in neural networks for the past 20 years. And it also proposes a new method to fix the hidden neurons in Elman networks for wind speed prediction in renewable energy systems. The random selection of a number of hidden neurons might cause either overfitting or underfitting problems. This paper proposes the solution of these problems. To fix hidden neurons, 101 various criteria are tested based on the statistical errors. The results show that proposed model improves the accuracy and minimal error. The perfect design of the neural network based on the selection criteria is substantiated using convergence theorem. To verify the effectiveness of the model, simulations were conducted on real-time wind data. The experimental results show that with minimum errors the proposed approach can be used for wind speed prediction. The survey has been made for the fixation of hidden neurons in neural networks. The proposed model is simple, with minimal error, and efficient for fixation of hidden neurons in Elman networks.

/pdf/review-on-methods-to-fix-number-of-hidden-neurons-in-neural-22240krax1.pdf

Review on Methods to Fix Number of Hidden Neurons in Neural Networks

The battery energy storage station (BESS) is the current and typical means of smoothing wind- or solar-power generation fluctuations. Such BESS-based hybrid power systems require a suitable control strategy that can effectively regulate power output levels and battery state of charge (SOC). This paper presents the results of a wind/photovoltaic (PV)/BESS hybrid power system simulation analysis undertaken to improve the smoothing performance of wind/PV/BESS hybrid power generation and the effectiveness of battery SOC control. A smoothing control method for reducing wind/PV hybrid output power fluctuations and regulating battery SOC under the typical conditions is proposed. A novel real-time BESS-based power allocation method also is proposed. The effectiveness of these methods was verified using MATLAB/SIMULINK software.

Battery Energy Storage Station (BESS)-Based Smoothing Control of Photovoltaic (PV) and Wind Power Generation Fluctuations

This paper proposes an improved optimal sizing method for wind-solar-battery hybrid power system (WSB-HPS), considering the system working in stand-alone and grid-connected modes. The proposed method is based on the following principles: a) high power supply reliability; b) full utilization of the complementary characteristics of wind and solar; c) small fluctuation of power injected into the grid; d) optimization of the battery's charge and discharge state; e) minimization of the total cost of system. Compared with the traditional methods, the proposed method can achieve a higher power supply reliability while require less battery capacity in stand-alone mode. And in grid-connected mode, the optimization strategy based on energy filter is further utilized to achieve the optimal battery capacity. Thus, the proposed method can achieve a much smaller fluctuation of power injected into the grid. In addition, the battery's charge and discharge state can be optimized thanks to the consideration of the battery's depth of discharge (DOD), the charge/discharge current, rate and cycles, which will prolong the battery's lifetime. A case study of WSB-HPS located in Hohhot, China is presented to verify the advantages of the proposed optimal sizing method.

An Improved Optimal Sizing Method for Wind-Solar-Battery Hybrid Power System

This paper presents the use of battery energy storage system for power smoothing in generation systems in which power flow variations can occur. These variations are the norm in wind energy generation. A simulation model for a battery energy storage system and a wind farm using squirrel cage induction generators magnetized with fixed capacitor banks are presented. And a decoupling and feed forward compensating control strategy is proposed. Simulations have been carried out and demonstrate that the BESS has the potential to significantly improve the wind farm's performance. Through control of the charging and discharging of the BESS using a power electronic interface, it is shown that the wind farm's output power can be controlled to a constant value. In addition, there is an overall improvement in the transient and dynamic response of the system.

Use of Battery Energy Storage System to Improve the Power Quality and Stability of Wind Farms

This paper presents the design and development of a three-phase 10-kV/400-V 500-kVA electronic power transformer (EPT). The power circuit is designed in a modular fashion, i.e., the main circuit consists of many identical ac–dc–dc–ac modules (abbreviated as power modules). Each power module consists of a high-voltage power cell, a low-voltage power cell (LVPC), a medium-frequency isolation transformer, and a filter. The corresponding control and protection system is developed. A special three-stage startup strategy is designed to shorten the startup time and reduce the startup inrush current. The negative-sequence current compensation is introduced in the input stage to handle the unbalanced loads. To keep the dc-link voltages balanced, an individual dc voltage balancing controller based on regulating the output power of each parallel LVPC is proposed. The detailed control hardware design and software implementation are discussed. The functions of this 10-kV EPT prototype are verified through the laboratory and field tests. The results are shown in this paper. Currently, the prototype is operating in the industrial power grid.

A 10-kV/400-V 500-kVA Electronic Power Transformer

This study presents a novel fundamental modulation strategy with selective harmonic elimination (SHE) for multilevel inverters. Compared with conventional schemes, more kinds of stepped waveforms can be adaptively synthesised and it is more possible to obtain the optimal solutions for the SHE problem, especially at low-modulation indices. The control purpose, SHE and fundamental voltage control, for a cascaded 11-level inverter is formulated as multi-objective optimisation problem which is solved by using shuffled frog leaping algorithm in this study. The theoretical and experimental results are presented to confirm the validity of the proposed modulation scheme.

Fundamental modulation strategy with selective harmonic elimination for multilevel inverters

Dynamics of vehicle-to-grid service to frequency regulation may suffer from the uncertainties arising from the spatial and temporal diversities of the large-scale plug-in vehicles (PEVs). Communication delays incurred both in the aggregation of the PEVs and in load frequency control (LFC) loop also degrade the dynamics and even destabilise the system. This study designs the LFC scheme considering those uncertainties. First, a dynamic model of individual PEV based on equivalent circuit and an aggregated model for PEVs group considering driving behaviours, battery characteristics, and delays are developed. Then, a state-space model with time delays and uncertainties is constructed to model the closed-loop LFC scheme with PEVs in primary control loop. After constructing the relationships among control gains, robust performances, and delays, a robust proportional–integral–derivative-type LFC scheme design method is developed by using linear matrix inequality and particle swarm optimisation algorithm. Case studies based on a three-area LFC system demonstrate that the PEVs contribute to the frequency regulation under different load disturbances and that the proposed LFC scheme successfully suppresses frequency fluctuations in the presence of delays and provides robustness against the uncertainties arising from the PEVs.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2016.0108

Chengxiong Mao

Papers

An Improved Optimal Sizing Method for Wind-Solar-Battery Hybrid Power System

Use of Battery Energy Storage System to Improve the Power Quality and Stability of Wind Farms

A 10-kV/400-V 500-kVA Electronic Power Transformer

Fundamental modulation strategy with selective harmonic elimination for multilevel inverters

Frequency regulation of multi-area power systems with plug-in electric vehicles considering communication delays