Xiaokang Xu

Application and modeling of battery energy storage in power systems

This paper presents engineering experiences from battery energy storage system (BESS) projects that require design and implementation of specialized power conversion systems (a fast-response, automatic power converter and controller). These projects concern areas of generation, transmission, and distribution of electric energy, as well as end-energy user benefits, such as grid frequency regulation, renewable energy smoothing and leveling, energy dispatching and arbitrage, power quality and reliability improvements for connected customers, islanding operations, and smart microgrid applications. In general, a grid level BESS project sends an interconnect request to utility power grids in the project development stage. Simulation models of equipment are then sent for a system impact study (e.g., power flow and/or stability analysis), based on utility grid code requirements. The system study then determines the connections technical feasibility and impact of the project on the power grid. In this paper, a set of new BESS models is presented that are configured and parameterized for use in system impact studies as well as transmission planning studies. The models, which have been recently approved and released by the U.S. Western Electricity Coordinating Council (WECC), represent the steady state and dynamic performance of the BESS in several software platforms for power system studies based on operating project performance experience. Model benchmarking results as well as a real system case study are also included in the paper to show that the parameterized and tuned models respond correctly and as expected when system operating conditions change following contingency events. Finally, this paper provides useful guidelines in the use of new models to represent a BESS for power system analysis.

A New Control Strategy for Distributed Static Compensators Considering Transmission Reactive Flow Constraints

This paper presents a new control strategy for a distributed static compensator (also known as distributed STATCOM or DSTATCOM), configured to regulate the reactive (VAr) flow at a point in a transmission system. This new control strategy takes into account the operating VAr limits of that reactive flow in determining the steady-state output of the DSTATCOM. The new control strategy applies a slow reset regulator (SRR) to slowly bias the VAr set point of the DSTATCOM master controller to maintain its steady-state output within a target bandwidth. The operating result maintains an appropriate VAr reserve level from the DSTATCOM for dynamic events in the system. This paper also presents a new algorithm to calculate the operating constraints of the SRR that reflect the VAr flow at the local or remote point in the transmission system and the allowable VAr thresholds for that flow. These allowable thresholds can be utilized to the full extent to lower the steady-state output of the DSTATCOM, maximize its VAr reserve for dynamic events and reduce equipment and associated system operating losses. Modeling, implementation, and simulation of an engineering project show that the new control strategy and algorithm are functioning properly as expected.

Transmission voltage support using distributed static compensation

FACTS devices such as static var compensators (SVC) or static compensators (STATCOM) are often examined in transmission planning studies and applied in transmission systems for reactive power control and voltage support. For some transmission applications and also for smaller utilities that need to deal with voltage issues at the distribution system level, a distributed approach to reactive power control and voltage support with STATCOM systems in multiple locations where voltage and reactive issues exist can be more effective than a centralized solution. This STATCOM system design is called Distributed Static Compensation. This distributed approach also achieves higher reliability with the redundancy, which eliminates the operational risk of the total loss of reactive power support in the area in the event of a large centralized unit being out of service. The Distributed STATCOM system has a high short-time rating. This unique short-time rating can be applied to support voltage recovery during significant dynamic events. This paper presents and discusses two real system case studies on application of Distributed STATCOMs for voltage support in North American transmission systems. Modeling aspects of the Distributed STATCOM systems are also discussed.

Development and planning of solar power in China

Solar energy is becoming the third most important renewable source in terms of globally installed capacity, after hydro and wind power. China is experiencing a rapid expansion in the solar power industry. This paper provides a good overview of the current status and future development of solar generation in China. This paper discusses medium and long-term planning goals of solar power in China including interconnection and grid planning challenges. Interconnection rules, government regulations, financial incentive and subsidy programs, tariffs and tax issues with regards to solar power development are also discussed. Specific numbers are given with regards to nationwide installed solar power capacity at the present and in the future. The paper shares the Chinese solar power development experience with the world solar power industry and contributes to the area of generation mix strategies, planning and interconnection.

Dynamic modeling and simulation of distributed static compensators in system impact studies

This paper discusses dynamic modeling and simulation of distributed static compensators (DSTATCOM) in system impact studies involving renewable applications, e.g., wind or solar power plants. Two dynamic simulation models of the DTSTACOM are presented and discussed. Dynamic simulations are presented to show that a reactive compensation system (RCS) assembled with the DSTATCOM as a master controller complies with reactive power, voltage control, and low voltage ride-though requirements for a wind power plant. Benchmark and real system models integrate the mechanically switched capacitors and the wind turbine generator reactive power capability into the total RCS system. The reactive characteristics of the DSTATCOM are also discussed.

Application of Distributed Static Compensators in Wind Farms to Meet Grid Codes

This paper discusses application of distributed static compensators (DSTATCOM) in wind farms to meet grid codes. Grid codes include many system performance requirements. This paper reviews voltage performance, reactive and power factor control and low voltage ride-through (LVRT) aspects of these requirements. The paper includes an overview of the status and future development of wind power in China and the U.S. and the needs in the fast-growing wind power industry in China. Regulations and grid codes for interconnection of wind generation in both countries are briefly described. The reactive power characteristics of wind turbine generators (WTGs) and DSTATCOM are discussed. The paper also includes real system application cases in which the DSTATCOM is being used in wind farms to comply with grid codes.

Probabilistic Reliability Methods and Tools for Transmission Planning and System Analysis

This paper discusses several probabilistic analytical methods and tools such as contingency enumeration, multi-area reliability assessment, and Monte Carlo simulation that can be used for transmission planning, generation expansion and system reliability assessment. The paper includes some case study results of applying these probabilistic methods and tools to real system planning and analysis. One study quantifies network probabilistic reliability measures with respect to various system problems, including branch overloads, loss of loads, voltage limit violations, and voltage collapse conditions as identified in contingency analysis for an EHV electric grid. The probabilistic measures complement the deterministic contingency results

A simulation tool for calculating energy prices in competitive electricity markets

This paper presents a software tool, PSStradeLMP , for simulating true energy market operation conditions and prices using security-constrained unit commitment and security-constrained economic dispatch. PSStradeLMP has been integrated with Siemens PTIs world-wide used transmission planning tool, PSStradeE, allowing for full transmission network modeling and providing a fundamental and essential foundation for LMP analysis. PSStradeLMP analyzes the effects of network conditions and determines LMP at each node as well as energy production cost components. The core function of PSStradeLMP is a 24-hour simulation for LMP-based electricity markets or energy price forecasting. Simulation results can be viewed as tables, displayed on a diagram of the network, or presented as a time-series plot. In conjunction with PSStradeE, PSStradeLMP can be used as a complimentary tool for market-based transmission planning.

Practical Application of Wind Power Models in System Analysis

This paper presents and discusses several wind power models available from Siemens PTIs (power technologies international) software package PSS/E. These models merge groups of individual identical units into one or more equivalent machines. These equivalent machines are placed along with their step-up transformers at collector buses designated by the user, assuming the configuration between these collector buses and the system interconnection point(s) have been defined. The models include load flow models and generic generator models with manufacturer specific controller models of elements of wind turbines for application in stability simulations. The paper also includes case studies and results.

Validation of a static VAr system model for a renewable project for grid code compliance

Power system dynamic models are the foundation for transient stability simulations which are usually part of transmission planning studies. Accurate dynamic simulations are crucial for reliable and secure operation of a transmission system and the precision of power system stability analysis depends on the accuracy of the models used to represent system equipment. Therefore, the validation of power system dynamic models is critical for producing correct simulation results. Comparison of dynamic simulations with field measurements is necessary to validate the quality of a dynamic model. This paper presents the validation process for a Static VAr System (SVS) model with field measurements for a transmission system application. The SVS under consideration includes a STATCOM (a FACTS device) and coordinated mechanically switched shunt elements. This SVS was designed and installed for a renewable project for grid code compliance. The control parameters of this model were first estimated and then tuned based on the actual equipment control parameters to fit simulations to field measurements from the transmission system. Comparison of the model simulation results with the field measurements shows that the validated model generates responses very close to the field test results. The SVS model validation and submission to the transmission system operator is a requirement of the grid code. The validated SVS model has been successfully used for several transmission planning studies and is appropriate and accurate for these types of studies.