| With the rapid development of China’s economy and the uneven distribution of energy and load determines that the HVDC transmission system still has broad application prospect. Tri-pole HVDC transmission technology using current modulation control mode can take the advantages of HVDC and use the three-phase conductors to transmit power, it can upgrade the DC transmission capacity fifty percent more than the capacity of the original AC line. Therefore, the tri-pole HVDC transmission technology is one of the potential solutions to increase power transmission capacity. At present, there is no study on the harmonic of tri-pole HVDC transmission system, so it is of great significance in researching the harmonic and its suppression measures of tri-pole HVDC system.First of all, this paper introduces the main circuit topology, the current modulation control mode and the operating modes. Then based on the switching function and the linear modulation theory which are suitable for analyzing the harmonic of tri-pole HVDC transmission system, the characteristics of tri-pole HVDC harmonics are got.Based on the characteristics of tri-pole HVDC system, the inter-harmonic component is added to the 3-pulse harmonic model. With the switching function method the advanced 3-pulse harmonic model is deduced which reflects periodical change of the voltage in the 3th pole. Then this paper introduces the equivalent disturbing current and harmonic models of the main circuit in HVDC transmission system. Using the parameters of San-chang HVDC engineering, the equivalent disturbing currents in every pole are calculated. From the calculation result, it can be seen that the equivalent disturbing currents in every pole are all in the moderate range. Therefore, there is no need to study the harmonic suppression measures of tri-pole HVDC transmission system exclusively, they can be the same with the HVDC transmission system. |
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