Flexible HVDC Transmission Technology Piloted by China Southern Power Grid

Initiated by China Southern Power Grid as one of the major R&D projects under “The Thirteenth Five-Year Plan”, the “Key Technology Research and Engineering Demonstration Application for High Voltage and Large Capacity Flexible Direct Current Transmission Project” has been approved recently by experts organized by the Ministry of Industry and Information Technology. Aiming to achieve a breakthrough in extra-high voltage, large capacity, long distance, overhead wiring and hybrid DC transmission technology, this project stands for the future of DC transmission and is going to upgrade the structure of traditional power grid.

It is reported that the “Key Technology Research and Engineering Demonstration Application for High Voltage and Large Capacity Flexible Direct Current Transmission Project”, as one national key R&D project of 2016, will be performed by China Southern Power Grid and other 16 companies together, where the following listed aspects are on the agenda, namely, the agile access technology for flexible DC transmission, the extra-high voltage, large capacity, long distance, overhead wiring and hybrid DC transmission technology, the R&D of converter valve for ±800kv/5,000mw extra-high voltage flexible DC transmission, key control and protection technologies for extra-high voltage flexible DC transmission and the engineering technology for demonstration and application and so on.

Long-term technological accumulation and engineering experience

It is learned that the technical team of China Southern Power Grid enjoys a quite mature technology accumulation and rich engineering experience in flexible DC transmission field and has been measuring itself up to world advanced standards. As early as in 2011, the China Southern Power Grid has offered technological support to establish the CNOOC Wenchang Flexible DC Transmission Project where the two-level converter was applied. By the end of 2011, the Ministry of Science and Technology of the PRC issued the project assignment of “Large-scale Wind Power Flexible DC Transmission Access Technology Research and Development” under the National High-tech R&D Program (863 Program) and the technical team of China Southern Power Grid was the very core to perform this project. With the achievements from 863 project research, China Southern Power Grid built up a three-terminal flexible DC transmission project of ±160kv/200mw/100mw/50mw and had it put into production in December 25, 2013 at Guangdong Nan’ao Wind Power Base, which was also the first multiple-terminal flexible DC transmission project in the world.

Ever since the operation of Nan’ao project, it has survived such conditions as severe typhoon, full power operation, three-terminal reactive support and AC system fault etc. and has become the main stable channel to transmit Nan’ao wind power. Meanwhile, we have observed an obvious improvement in Nan’ao wind power’s utilization ratio and economic effect without the occurrence of power-fan cut off and stored power being hold back. Up till September 29, 2016, this project has transmitted 524 million kwh and reached an economic effect of RMB 325 million with an electric charge of RMB 0.62/kwh, which, according to the latest standard coal consumption rate (326g/kwh)for power supply of 6,000kw and above issued by National Energy Administration, indicates that as many as 170,800 tons of coals and 425,300 tons of carbon dioxide emissions have been saved and reduced respectively. So, the overall technical achievement of Nan’aomultiple-terminal flexible DC transmission project has been granted the 2015 China Southern Power Grid Special Award of Progress for Science and Technology and the First Prize of 2015 Science and Technology Award of China Machinery Industry.

To lead the world

On September 30, 2015, the Ministry of Science and Technology of the PRC approved the establishment of a national key laboratory based on DC transmission technology of China Southern Power Grid, which, on the one hand, stands for a full recognition to the latter from specialists all over the country; on the other hand, is going to further upgrade the latter’s R&D strength in this field.

On August 29, 2016 when the last item of system commissioning is finished for Luxi back-to-back DC asynchronous interconnection project of Yunnan Power Grid and China Southern Power Grid, the whole project is put into operation with multiple world leading technologies, including the highest flexible DC voltage level (±350kv), the largest flexible DC capacity (1000mw±300megavar), being the first to apply flexible DC transmission technology to backbone grid and the first converter station to coordinate flexible DC unit and conventional DC unit in the world.

Ever since the establishment of the flexible DC unit of this project, it has been the common topic for experts of this field home and abroad. For example, it was particularly presented in the keynote speech on the opening ceremony of the 2016 International Conference on Large High Voltage Electric System held in Paris, which declares that China is leading the world in the development of flexible DC transmission technology and its equipment manufacturing and engineering application. And it is the technical team of China Southern Power Grid who has finished the systematic research, design and on-site commissioning for this project and will continue to make its contribution in this field.

More innovation for more promising future

Experts of this field believe that the rapid development of new energy and cross-regional power interconnection is definitely going to expand the market demand of high voltage and large capacity flexible DC transmission technology. It is preliminarily estimated that the domestic flexible DC transmission capacity within “The Thirteenth Five-Year Plan” is about to reach 15,000mw, including its application in long distance and main power grid transmission, which will, according to the international standards of RMB 150 million/100mw, stimulate an industry investment of RMB 22.5 billion.

China Southern Power Grid says that deeper and further systematic research shall be conducted in such aspects as the capacity scale, long distance transmission and application in bulk power grid. As the core of this key R&D project under “The Thirteenth Five-Year Plan”, China Southern Power Grid will go all out to fulfill the “Made in China 2025” plan where priority is given to innovation, top-notch quality and green development so as to promote the high-end equipment manufacturing for flexible DC transmission technology, enhance the core-competitiveness of China’s electric power equipment enterprises, win a dominating position for domestic flexible DC transmission technology and upgrade it to a brand new level as a whole.