Jos Arillaga

Electromagnetic transient simulation

This chapter discusses electromagnetic transient simulation. The simulation of electromagnetic transients associated with HVDC schemes is carried out to assess the nature and likely impact of overvoltages and currents, and their propagation throughout both the AC and DC systems. Transient simulation is also performed for the purpose of control design and evaluation. Transients can arise from control action, fault conditions and lightning surges.

The harmonic solution

This chapter describes the use of the Newton method to model the interaction between the converter and the AC and DC systems.

The AC-DC converter in steady state

This chapter describes a variety of steady-state AC-DC converter models with varying degrees of complexity. The starting case is the fundamental-frequency model based on symmetrical operation, with perfect AC-current filters and DC-voltage smoothing. This model is used in the power flow solution considered in Chapter 3. The removal of the symmetry constraint is considered next, and a three-phase model is developed for use in more detailed power-flow analysis, a subject described in Chapter 5. The perfect filter and smoothing assumptions are then removed and the AC-DC converter is considered as a frequency modulator. A small-signal transfer-function model is described, capable of direct analysis of cross modulation effects at any frequency. This technique is used to simulate the mechanism of harmonic instabilities. The use of convolutions in the harmonic domain avoids the problems of aliasing associated with numerical FFT calculations, or the complexity of Fourier analysis. An additional advantage of the convolution analysis is that all of the equations are differentiable when decomposed into real and imaginary components, a feature which enables a straightforward implementation of a Newtons method solution in Chapter 4.