Real-time electromagnetic electromechanical hybrid transient simulation for large power systems

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Real-time electromagnetic electromechanical hybrid transient simulation for large power systems

 

Author: Su, Hongtian
Title: Real-time electromagnetic electromechanical hybrid transient simulation for large power systems
Degree: Ph.D.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations.
Electric power system stability.
Transients (Electricity)
Electromagnetism -- Measurement.
Hybrid computer simulation.
Department: Dept. of Electrical Engineering
Pages: xxi, 221 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1896754
URI: http://theses.lib.polyu.edu.hk/handle/200/1596
Abstract: In this research a new hybrid real-time fully digital simulator capable of simulating both electromagnetic and electromechanical transients over a broad range of frequencies was developed. This simulator is capable of performing transient stability studies over a wide range of contingencies, including asymmetrical faults and mal-operation of power electronic systems. This type of simulator will play an increasing role in power system operations, and will contribute towards the enhancement of power system security. The research was motivated by the profound effect of deregulation on the planning and operation of interconnected power systems leading to the virtual elimination of integrated generation and transmission least-cost planning and traditional economic-dispatch-based unit commitment. The new environment is characterized by rapid reconfigurations of the transmission systems, with consequent increasing uncertainty related to system security. Furthermore the increasing demands on transmission resulting from limited expansion of transmission systems has led to the proliferation of novel approaches to increase transmission capability, notably the utilization of power electronic systems. This has placed increasing demands on improved dynamic security assessment, and it is here where modern real-time or accelerated-time hybrid simulators have an increasingly important role. These simulators, coupled with real-time data acquisition, will have the ability to capture system behaviour at any instant of time, and will allow operators to study an increasingly comprehensive contingency list (including mal-operation of power electronic systems) and "what if" scenarios for different system conditions and configurations, with the obvious benefit of increasing system security. The hybrid simulator includes both Electromagnetic Transients (EMT) and Transient Stability (TS) simulators within an integrated analysis tool operating on a UNIX based multi-processor server, and is, capable of effective simulation of large- size networks, while providing accurate representation of highly nonlinear components, such as FACTS devices and HVDC links. Real-time operation was realized on a Silicon Graphics (SGI) multi-processor server simultaneously running a real-time EMT program called HYPERSIM (developed by the Hydro Quebec Research Institute) and a comprehensive transient stability program developed by the author. In this research the difficulties related to the interface of two very different programs were overcome. EMT is normally aimed at detailed studies of relatively small networks; however, the mandatory small time step results in a computationally intensive simulator, impracticable for the simulation of very large systems. On the other hand, TS simulators are aimed at solving the electromechanical equations of very large systems where the solution is usually based on a single phase equivalent and as such contingencies such as asymmetrical faults are somewhat difficult to deal with. Furthermore their large time steps preclude modelling of power electronic systems at the device level: FACTS equipment and HVDC converters have to be represented as relatively simple mathematical models. Consequently it is not practicable to study such contingencies as unbalanced and/or mal-operation of power electronic equipment in a TS program. In the hybrid simulator, the EMT and TS simulators each take responsibility for one part of power system: the EMT simulator models a detailed system (such as a FACTS system) and the TS simulator models the rest, referred to as the external system. Each simulator sees the other as an equivalent, and both simulators proceed in parallel and communicate with each other at specified time intervals. The communication between the detailed and external systems is maintained through a well-defined common interfacing location. The two simulators have different integration time steps and component modelling techniques, and this mandated the development of a novel parallel interaction protocol in order to coordinate the variables transferring between the two simulators while being compatible with real-time operation. Significant problems had to be overcome, for example the EMI simulator must run continuously while the TS simulator must perform iterations. Consequently the TS simulator must perform some of its iterations with incomplete data from EMI, and to overcome this problem a prediction scheme was developed and incorporated into the TS simulator. Based on the parallel implementation of protocol, a parallel hybrid simulation was built employing multi-thread techniques. Several case studies were run on two different multi-processor computers to verify the operation of the hybrid simulator. Performance studies were made based both on serial and parallel protocol implementation, and the results compared well. Visual comparisons were made between the hybrid simulation and benchmark cases run on conventional simulators, again with good results. A case study involving a commutation failure of a FACTS system on a 39 bus system showed the system to be unstable following this contingency: this case could not have been run on a conventional TS simulator.

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