The implementation and effectiveness of linear interpolation within digital simulation

The greater use of detailed models and the increasing size and complexity of system studies in power system digital simulation. has resulted in the need to re-examine the ability of digital computations performed at finite time intervals to accurately represent the actual system. These concerns are manifested in two distinct areas. The first is the ability to switch elements at a specific point in time. Traditional digital simulation techniques allow switching elements to change state only at discrete computation times, whereas in reality switching can occur at any instant in time. The second area of concern is in the ability to accurately represent detailed control systems. These concerns are of particular importance in simulations containing a large number of controlled switching devices, such as HVdc systems or ac systems containing FACTs devices. This paper presents a discussion of the implementation and effectiveness of linear interpolation techniques in a digital simulation program. The paper addresses interpolation in both the network solution and the control system. The CIGRE HVdc Benchmark Model (Szechtman, M. et al., Electra, 1991, 135 and Wess, T. and Ring, H., CIGRE Report, WG 14-02, 1988) with detailed control models is used to demonstrate how linear interpolation is implemented and its effectiveness. All simulation results presented were generated using EMTDC (Nayak, O. et al., IEEE Computer Applications in Power, 1995, 8(1)), but the techniques discussed can be applied to any electromagnetic transients program. (C) Elsevier Science Ltd.