A harmonics elimination method using a novel three-winding transformer for HVDC transmission systems

Abstract

A high-voltage direct current (HVDC) transmission system including wind turbine generating systems has been proposed. In the system, the thyristor converter and inverter are used in the same way as in traditional HVDC transmission systems. Hence, the system is suitable for large-scale wind farms and it has high reliability. However, the traditional HVDC transmission systems cause a large number of harmonics in the sending-end grid current and the receiving-end grid current. In this paper, a novel harmonics elimination method using a three-winding transformer with negative leakage inductance for the HVDC transmission systems is proposed. The theory of the proposed method is discussed and the simulation model of the proposed system is developed first. The proposed method is confirmed to be effective when a resistance load is connected to the output terminal of the system. It is shown that the proposed method is useful to eliminate harmonic distortions generated at the inverter. Also, to obtain an accurate simulated result, the simulation model is modified to take in the effects of the excitation circuit of the transformer and its magnetic hysteresis loop. Finally, current waveforms and voltage waveforms of the transformer when receiving-end grid is connected to the output terminal of the system are discussed.

AC Filterless Flexible LCC HVDC With Reduced Voltage Rating of Controllable Capacitors

“…For commutation from TY1 to TY3 as discussed in previous section, the highest rate of current rise for i 3 takes place at the start of commutation, i.e., 3 1 Fig. 9 shows the highest rate of current rise for different values of L at two different values of firing angles according to (22). From Fig.…”

“…In parallel with the development of more efficient AC filters, other methods have been proposed to reduce the filtering requirements by modifying the converter bridges or converter transformers [19][20][21][22][23]. The method of DC ripple reinjection was originally proposed in [19] and has been subjected to various developments over the years [20].…”

“…Therefore the size of AC filters is not significantly reduced and it leads to higher cost and complexity of the converter stations compared with the method proposed in this paper. A new three-winding transformer with negative leakage inductance is proposed in [22] to eliminate AC harmonics. However the method is only effective when a resistive load is connected to the output of inverter system.…”