Abstract
Harmonic simulations play a key role in studying and predicting the impact of nonlinear devices on the power quality level of distribution grids. A frequency-domain approach allows higher computational efficiency, which has key importance as long as complex networks have to be studied. However, this requires proper frequency-domain behavioral models able to represent the nonlinear voltage–current relationship characterizing these devices. The Frequency Transfer Matrix (FTM) method is one of the most widespread frequency domain modeling approaches for power system applications. However, others suitable techniques have been developed in the last years, in particular the X-parameters approach, which comes from radiofrequency and microwave applications, and the simplified Volterra models under quasi-sinusoidal conditions, that have been specifically tailored for power system devices. In this paper FTM, X-parameters and simplified Volterra approaches are compared in representing the nonlinear voltage –current relationship of a bridge rectifier feeding an ohmic-capacitive dc load. Results show that the X-parameters model reaches good accuracy, which is slightly better than that achieved by the FTM and simplified Volterra models, but with a considerably larger set of coefficients. Simplified Volterra models under quasi-sinusoidal conditions allows an effective trade-off between accuracy and complexity.
Highlights
Power electronics devices are widespread in electrical grids, thanks to the impressive advancement of high-power semiconductor devices
Others suitable techniques have been developed in the last years, in particular the X-parameters approach, which comes from radiofrequency and microwave applications, and the simplified Volterra models under quasi-sinusoidal conditions, that have been tailored for power system devices
When analyzing the performance of the Frequency Transfer Matrix (FTM) approach, it can be seen that its accuracy is worse with respect to the 11th degree Volterra model: in this case, the NRMSE is characterized by a mean value of 12% and a 95th percentile value of 20%
Summary
Power electronics devices are widespread in electrical grids, thanks to the impressive advancement of high-power semiconductor devices. Frequency-domain Volterra models represent the straightforward extension of the conventional frequency response function (FRF) to nonlinear time invariant (NTI) systems This approach can be employed to model power electronics converters [23], but the main drawback is that its complexity rapidly increases with the number of input harmonics and the considered nonlinearity degree. The three different frequency-domain nonlinear modeling approaches that have been previously introduced will be briefly recalled and applied to represent the current–voltage relationship of a diode rectifier feeding an ohmic-capacitive dc load These models can be integrated into a harmonic solver, for example, in order to study the power quality issues in a distribution grid. Performance reached by the three different nonlinear models are compared under realistic scenarios (random harmonics and off-nominal frequency conditions) and a detailed discussion is carried out
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