Kai Strunz

A Review of Hybrid Renewable/Alternative Energy Systems for Electric Power Generation: Configurations, Control, and Applications

Summary form only given. This paper, prepared by a special task force of the IEEE PES Renewable Energy Technologies Subcommittee, is a review of hybrid renewable/alternative energy (RE/AE) power generation systems focusing on energy sustainability. It highlights some important issues and challenges in the design and energy management of hybrid RE/AE systems. System configurations, generation unit sizing, storage needs, and energy management and control are addressed. Statistics on the current status and future trend of renewable power generation, as well as some critical challenges facing the wide-spread deployment of RE/AE power generation technologies and vision for future research in this area are also presented. The comprehensive list of references given at the end of the paper should be helpful to researchers working in this area.

Modeling Guidelines and a Benchmark for Power System Simulation Studies of Three-Phase Single-Stage Photovoltaic Systems

This paper presents modeling guidelines and a benchmark system for power system simulation studies of grid-connected, three-phase, single-stage Photovoltaic (PV) systems that employ a voltage-sourced converter (VSC) as the power processor. The objective of this work is to introduce the main components, operation/protection modes, and control layers/schemes of medium- and high-power PV systems, to assist power engineers in developing circuit-based simulation models for impact assessment studies, analysis, and identification of potential issues with respect to the grid integration of PV systems. Parameter selection, control tuning, and design guidelines are also briefly discussed. The usefulness of the benchmark system is demonstrated through a fairly comprehensive set of test cases, conducted in the PSCAD/EMTDC software environment. However, the models and techniques presented in this paper are independent of any specific circuit simulation software package. Also, they may not fully conform to the methods exercised by all manufacturers, due to the proprietary nature of the industry.

A Knowledge-Based Approach for Control of Two-Level Energy Storage for Wind Energy Systems

The percentage of wind energy in a generation mix will ultimately be limited by its intermittency and uncertainty as a source of power. However, the pairing of wind with energy storage systems could be utilized in order to produce dispatchable power. This paper considers a two-level energy storage system for application to wind energy systems. A knowledge-based management algorithm is proposed in order to schedule the power from the two levels. The system is tested for two possible power systems applications and its performance is compared with that of an alternate scheduling approach. Results demonstrate that the proposed algorithm requires a lower storage rating due to its ability to better coordinate operation of the two devices.

DC Microgrid for Wind and Solar Power Integration

Operational controls are designed to support the integration of wind and solar power within microgrids. An aggregated model of renewable wind and solar power generation forecast is proposed to support the quantification of the operational reserve for day-ahead and real-time scheduling. Then, a droop control for power electronic converters connected to battery storage is developed and tested. Compared with the existing droop controls, it is distinguished in that the droop curves are set as a function of the storage state-of-charge (SOC) and can become asymmetric. The adaptation of the slopes ensures that the power output supports the terminal voltage while at the same keeping the SOC within a target range of desired operational reserve. This is shown to maintain the equilibrium of the microgrids real-time supply and demand. The controls are implemented for the special case of a dc microgrid that is vertically integrated within a high-rise host building of an urban area. Previously untapped wind and solar power are harvested on the roof and sides of a tower, thereby supporting delivery to electric vehicles on the ground. The microgrid vertically integrates with the host building without creating a large footprint.

Electric Vehicle Battery Technologies

This chapter aims at bridging the gap between chemistry scientists and electrical engineers on electric vehicle (EV) batteries. The power and energy of electric propulsion are first reviewed in Sect. 2.2. Commonly used terms to describe battery performance and characterization are then introduced in Sect. 2.3, followed by the review of various battery charging methods and EV charging schemes in Sect. 2.4. The fundamentals of EV battery technologies are addressed in Sect. 2.5. Two currently most common EV battery technologies, namely, nickel metal hydride (NiMH) and lithium-ion (Li-ion), are covered. It is targeted for giving power engineers a basic understanding of battery chemistry. The EV battery modeling is introduced in Sect. 2.6. It is important for power engineers to appreciate the fundamentals of battery chemistry and battery modeling and use it for power electronic interfacing converter design, battery management, and system level studies. Section 2.7 covers the topic on battery characterization including battery model parameter estimation, state of charge (SOC), and state of health (SOH) estimation. The battery aggregation for power grid applications is discussed in Sect. 2.8. The concept of virtual power plant (VPP) for battery aggregation is introduced to support EV’s participation in power markets.

Optimal Distribution System Horizon Planning–Part I: Formulation

This paper is the first of a two-part paper on optimal distribution system planning. The horizon distribution planning problem and optimal distribution system model formulation are described. The horizon planning mission is to minimize future costs by determining optimal design parameters given assumptions about the future. Prior work addressed short-range and expansion planning of subsets or combinations of design parameters. The many distribution requirements and associated constraints inhibited an all-inclusive evaluation of total horizon design requirements for the 20+ year period. The proposed model and optimization formulation provides a generalized horizon planning approach and introduce a fully functioning comprehensive horizon planning model using a perspective that encompasses all necessary parameters and constraints. Parameters include: substation and distribution transformer capacities; number, size, and lengths of distribution feeders and secondary conductors; and primary voltage class. Optimal design voltage drops and reliability indices are determined. The horizon planning optimization application is described and solved in the second companion paper using continuous constrained nonlinear programming methods. The application is demonstrated with Snohomish PUD case studies

Interfacing Issues in Real-Time Digital Simulators

This paper deals with the current state-of-the-art in interfacing issues related to real-time digital simulators employed in the simulation of power systems and power-electronic systems. This paper provides an overview of technical challenges encountered and their solutions as the real-time digital simulators evolved. Hardware-in-the-loop interfacing for controller hardware and power apparatus hardware are also presented.

Stochastic formulation of SPICE-type electronic circuit simulation with polynomial chaos

A methodology for efficient tolerance analysis of electronic circuits based on nonsampling stochastic simulation of transients is formulated, implemented, and validated. We model the stochastic behavior of all quantities that are subject to tolerance spectrally with polynomial chaos. A library of stochastic models of linear and nonlinear circuit elements is created. In analogy to the deterministic implementation of the SPICE electronic circuit simulator, the overall stochastic circuit model is obtained using nodal analysis. In the proposed case studies, we analyze the influence of device tolerance on the response of a lowpass filter, the impact of temperature variability on the output of an amplifier, and the effect of changes of the load of a diode bridge on the probability density function of the output voltage. The case studies demonstrate that the novel methodology is computationally faster than the Monte Carlo method and more accurate and flexible than the root-sum-square method. This makes the stochastic circuit simulator, referred to as PolySPICE, a compelling candidate for the tolerance study of reliability-critical electronic circuits.

Optimal Distribution System Horizon Planning–Part II: Application

This is the second part of a two-part paper in which application methods to enhance distribution horizon planning for a 20+ year period are described. The optimal horizon planning model encompasses all distribution design requirements for primary and secondary systems. The model formulation is described in the companion paper Part I. The model makes use of a generalized feeder layout viewed as a tree-like circuit serving a circular sector of a round or hexagonal service area of uniform load density. The horizon model optimization objective cost function and constraint equation applications are described in this paper. The horizon planning model is validated with analysis of case studies and sensitivity evaluations for input and output variables. The case studies are assessed under various conditions such as changing consumer density, consumer characteristics, cost of energy, and economic assumptions. The application of the model is demonstrated using Snohomish PUD future expansion assumptions with case studies to examine impacts of horizon assumptions on future conductor sizes, primary voltage classes, voltage drop designs, reliability, and consumer cost of service

Real-Time Simulation Technologies for Power Systems Design, Testing, and Analysis

This task force paper summarizes the state-of-the-art real-time digital simulation concepts and technologies that are used for the analysis, design, and testing of the electric power system and its apparatus. This paper highlights the main building blocks of the real-time simulator, i.e., hardware, software, input-output systems, modeling, and solution techniques, interfacing capabilities to external hardware and various applications. It covers the most commonly used real-time digital simulators in both industry and academia. A comprehensive list of the real-time simulators is provided in a tabular review. The objective of this paper is to summarize salient features of various real-time simulators, so that the reader can benefit from understanding the relevant technologies and their applications, which will be presented in a separate paper.