Search

A frequency-based approach is proposed in this paper to size a battery-supercapacitor energy storage system for maintaining power balance of an isolated system with high penetration of wind generation, thus to maintain the grid frequency stability with the stochastic wind power fluctuations being considered. The sizing method proposed makes full use of the combined technical merits of two types of energy storage systems, battery and supercapacitor, as their specific power/energy densities and the corresponding expected life cycle cost/year are different. The power imbalance between hourly dispatched wind power and the corresponding actual real-time wind power output is decomposed into different time-varying periodic components by use of the Fourier transformation. Then two different types of energy storage systems are applied to balance the low-frequency and intermediate-frequency component respectively. A computational procedure is developed in the paper for choosing the optimal cut-off frequencies in determining the range of low and intermediate frequency for sizing the hybrid energy storage system. Comparative studies of a real isolated system in China are presented in the paper to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Distribution system operators aim to improve hosting capacity (HC) of distribution networks (DNs) to accommodate more distributed rooftop photovoltaics (PVs). Although PV power generation delivers numerous benefits, power unbalance and voltage rise are two major obstacles that limit the network HC. To mitigate these issues, battery energy storage systems (BESSs) can be applied. Thus, this paper proposes a robustly optimal allocation method for BESSs, which aims to reduce the power unbalance and alleviate the voltage rise, and thus improve the HC of the unbalanced three-phase DNs. Considering that locations and capacities of distributed rooftop PVs are determined by customers, future PV installations are regarded as uncertainties. In addition, to deal with the uncertainties, the proposed BESS allocation problem is formulated as an adaptive robust optimization (ARO) model with integer recourse variables. Accordingly, a solution algorithm which integrates an alternating optimization procedure into a column-and-constraint generation algorithm is developed to efficiently solve the ARO model. With the proposed BESS allocation method, a new perspective on HC improvement is provided, which not only considers the worst power unbalance situation but also satisfies the allowed maximum PV capacity. The simulation results verify high efficiency and solution robustness of the proposed allocation method. [ABSTRACT FROM AUTHOR]

Displacement of conventional synchronous generators by non-inertial units such as wind or solar generators will result in reduced-system inertia affecting under-frequency response. Frequency control is important to avoid equipment damage, load shedding, and possible blackouts. Wind generators along with energy storage systems can be used to improve the frequency response of low-inertia power system. This paper proposes a fuzzy-logic based frequency controller (FFC) for wind farms augmented with energy storage systems (wind-storage system) to improve the primary frequency response in future low-inertia hybrid power system. The proposed controller provides bidirectional real power injection using system frequency deviations and rate of change of frequency (RoCoF). Moreover, FFC ensures optimal use of energy from wind farms and storage units by eliminating the inflexible de-loading of wind energy and minimizing the required storage capacity. The efficacy of the proposed FFC is verified on the low-inertia hybrid power system. [ABSTRACT FROM AUTHOR]

This paper proposes a restorability improvement strategy to accelerate system restoration through the implementation of a wind farm-battery energy storage system (WF-BESS) system. The concept of restorability is introduced and a restorability improvement model (RIM) is proposed and formulated as a mixed integer linear programming problem. To simulate the cylinder temperature drop during outages, the cranking time of a unit is modeled as a stepwise function of its startup time in the RIM. The WF might fail to meet its scheduled generation outputs optimized by the RIM due to the intermittency of wind. To tackle this problem, a linearized control strategy for the BESS (CSBESS) is proposed to minimize the difference between the scheduled wind power outputs and the combined power of the WF-BESS system. An iterative method is employed to efficiently solve the RIM and CSBESS by introducing optimality cuts. An actual power system case is employed to illustrate the effective performance of the proposed approach. [ABSTRACT FROM AUTHOR]

DC-bus voltage control is an important task in the operation of a dc or a hybrid ac/dc microgrid system. To improve the dc-bus voltage control dynamics, traditional approaches attempt to measure and feedforward the load or source power in the dc-bus control scheme. However, in a microgrid system with distributed dc sources and loads, the traditional feedforward-based methods need remote measurement with communications. In this paper, a nonlinear disturbance observer (NDO) based dc-bus voltage control is proposed, which does not need the remote measurement and enables the important “plug-and-play” feature. Based on this observer, a novel dc-bus voltage control scheme is developed to suppress the transient fluctuations of dc-bus voltage and improve the power quality in such a microgrid system. Details on the design of the observer, the dc-bus controller and the pulsewidth-modulation (PWM) dead-time compensation are provided in this paper. The effects of possible dc-bus capacitance variation are also considered. The performance of the proposed control strategy has been successfully verified in a 30 kVA hybrid microgrid including ac/dc buses, battery energy storage system, and photovoltaic (PV) power generation system. [ABSTRACT FROM AUTHOR]

The distribution system asset (DSA) planning process for a new or existing subdivision involves a comparison of several feasible plans and selection of the least costly plan. The costs comprise the cost of new assets and their replacements, operation and maintenance costs, as well as reliability costs. DSA planning tools have been used for distribution utilities for decades, so that mature methods are available for traditional distribution systems. However, most of the DSA planning tools fail to include battery energy storage systems (BESS) as an asset solution for systems with high penetration of renewable energy sources. In addition, minimizing the investment cost and maximizing the reliability performance, which can be measured by the system average interruption duration index (SAIDI), are contradicting objectives. With a large investment, the system will have a small SAIDI, and vice versa. In this paper, a multi-objective algorithm that uses fuzzy optimization technique to handle these contradicting objectives is proposed. The algorithm includes traditional types of assets as well as BESS. One of the main advantages of the proposed method is that the customer interruption costs are not explicitly necessary, as these values cannot be precisely determined for all loads. In the tool, the annual investment cost and SAIDI are minimized, and the optimal size of BESS is obtained. Its performance is demonstrated on a 33-bus distribution system and the results are compared with other methods available in the literature. [ABSTRACT FROM AUTHOR]

This paper combines three different methods for the analysis of a self-oscillating bidirectional dc–dc converter under hysteresis control. First, the describing function method is used to predict the steady-state limit cycle, along with its oscillation amplitude and frequency. Second, the Tsypkin method is applied to provide more precise information on the dynamical behavior of the system. To complete the study, a sliding-mode approach is used to provide more insight into the system response in terms of its parameters. A comparative study among the results obtained from the different approaches in the frequency and time domain is given. Finally, an experimental prototype validates the theoretical and the numerical predictions. [ABSTRACT FROM AUTHOR]

The battery energy storage system is an essential enabling device of the smart grid, because it helps grid connection of massive renewable energy resources. This paper has a brief discussion on a battery energy storage system based on a multilevel cascade pulsewidth-modulated (PWM) converter for its practical use. The active-power control of individual converter cells is presented to make it possible to charge and discharge the battery units at different power levels while producing a three-phase balanced line-to-line voltage. This results in the maximum utilization of battery energy even when the power-handling capabilities of the battery units differ. Experimental results obtained from a 200-V, 10-kW, 3.6-kWh battery energy storage system verify the effectiveness of the presented active-power control. [ABSTRACT FROM AUTHOR]

This paper deals with a new control algorithm for a voltage and frequency controller (VFC) of an isolated wind energy conversion system (IWECS) using an isolated asynchronous generator to feed three-phase four-wire consumer loads. The reference source currents are estimated for the indirect current control of a voltage source converter (VSC) using the single-phase PQ theory to control the voltage and frequency of IWECS. A three-leg VSC with a battery energy storage system is used as a VFC for an IWECS. A nonisolated star-polygon transformer is used to provide a neutral terminal for four-wire loads and to compensate the neutral current resulting in reduction in rating of VSC. The proposed VFC is implemented using a DSP. Experimental results are presented to demonstrate the additional capabilities of VFC as a load leveler, a load balancer, a harmonic eliminator, and a neutral current compensator. [ABSTRACT FROM AUTHOR]

This paper presents a method for optimal sizing and operation of a battery energy storage system (BESS) used for spin-fling reserve in a small isolated power system. Numerical simulations are performed on a load-frequency control (LFC) dynamic simulator of the isolated network. A novel control algorithm using adjustable state of charge limits is implemented and tested on a BESS dynamic model. An optimal sizing procedure of the BESS is developed for an isolated power system in order to achieve highest expected profitability of the device. The BESS can increase significantly the power system stability, the grid security, and the planning flexibility for a small isolated power system with tow grid inertia. Meanwhile, it fulfills the frequency control requirements with a high expected economic profitability. [ABSTRACT FROM AUTHOR]

This article presents an interleaved bidirectional chopper with auxiliary converters for onboard energy storage systems that is capable of achieving a significant reduction in the mass and volume of the current-smoothing inductors. The proposed chopper consists of multiple interleaved subconverters, where each subconverter consists of a bidirectional chopper cell, a current-smoothing inductor at the low-voltage side, and an auxiliary converter that is formed by the cascade connection of multiple full-bridge cells. Each auxiliary converter is connected in series with its respective inductor to suppress the ac voltage component that produces ripple current in the inductor of each subconverter; hence, a smaller inductor can be used to meet the ripple current requirement when compared with the conventional bidirectional chopper. In addition, auxiliary converters can be used as dc-circuit breakers to protect the low-voltage side against faults in the power devices of the bidirectional chopper cells. This article discusses the operating principles and control method of the proposed chopper, followed by experiments using a downscaled experimental model. [ABSTRACT FROM AUTHOR]