Abstract
The application of power electronics can introduce flexibility into power systems, but it can also cause harmonic problems. As a typical application of power electronics, high-voltage direct current (HVDC) transmission exhibits very prominent harmonic problems. In recent years, many HVDC protection maloperation events caused by harmonic problems have occurred in the field. The phenomena of harmonic transfer and amplification in HVDC transmission have an undeniable impact on the overall operation of a power system. Previous studies of these phenomena have relied mainly on detailed electromagnetic transient simulations. However, these simulations normally suffer from a large computational burden and low efficiency due to the complexity of the models and the small simulation time steps used. Therefore, an efficient analysis model of harmonics for various HVDC operating modes is presented in this paper. This model is based on port theory; every part of the HVDC transmission system is represented by an equivalent two-port component to construct a unified equivalent circuit. The proposed model is simple to calculate, and only the connections of the two-port components need to be changed to model different operation modes. The proposed two-port model is applied for the harmonic analysis of an HVDC transmission system, and the validity and accuracy of the model are confirmed by detailed electromagnetic simulations. Moreover, the model can be easily applied to HVDC systems for harmonic transfer and amplification, and the effects of the HVDC transmission power and smoothing reactor on harmonic transfer and amplification are analyzed.
Highlights
The proportion of power electronics apparatuses in power systems has grown in recent years, and harmonic problems are becoming increasingly prominent in power systems [1]–[3]
In the two-port model proposed in this paper, the transformer, converter, smoothing reactor and filter, and DC line in the high-voltage direct current (HVDC) transmission system are equivalent to one two-port network
This paper presents an analysis to show the influence of the HVDC transmission power and smoothing reactor on harmonic transmission and amplification
Summary
The proportion of power electronics apparatuses in power systems has grown in recent years, and harmonic problems are becoming increasingly prominent in power systems [1]–[3]. A new approach for modeling line-commutated AC/DC/AC conversion systems based on modulation function theory was presented and discussed in [24] This new approach considers the DC-side harmonics caused by the impedance time variance. To cover the different HVDC operation modes, the HVDC system is modeled in detail, including DC smoothing reactors and filters These complex situations were not modeled in the work presented above. In the two-port model proposed in this paper, the transformer, converter, smoothing reactor and filter, and DC line in the HVDC transmission system are equivalent to one two-port network. This paper presents an analysis to show the influence of the HVDC transmission power and smoothing reactor on harmonic transmission and amplification.
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