Recently, the scientific and technological achievement appraisal meeting for "Key Technology of Large Capacity DC Breaking and Development of HV, MV and LV Series DC Circuit Breakers" jointly organized by the Chinese Society of Electrical Engineering and China Machinery Industry Federation was held in an "online + offline" form. More than 40 people including experts from the appraisal committee, special guests, representatives from the Chinese Society of Electrical Engineering and the China Machinery Industry Federation, as well as representatives from Tsinghua University, Tsinghua Sichuan Energy Internet Research Institute, Beijing Power Equipment Group Co., Ltd., Shandong Taikai High Voltage Switchgear Co., Ltd., Zhuzhou CRRC Times Semiconductor Co., Ltd., Power Research Institute of State Grid Jibei Power Co., Ltd., Guangdong Power Grid Co., Ltd. and other project completing units attended the online and offline meeting. The meeting was presided over by Lu Shujun, vice chairman of the Chinese Society of Electrical Engineering.

Photo: Online participants

Photo: Offline participants

The chairman of the appraisal committee is Academician Li Licheng of China Southern Power Grid Corporation, the vice chairmen are Academician Chen Weijiang of State Grid Corporation of China, Academician Luo An of Hunan University, and Academician Tang Guangfu of Global Energy Internet Research Institute, and the members are Professor Ding Lijian of Hefei University of Technology, Chief Engineer Li Chongjian of CISRI Automation Research and Design Institute of Metallurgical Industry, Professor He Junjia of Huazhong University of Science and Technology, Professor Rong Mingzhe of Xi’an Jiaotong University, Chief Expert Yao Sili of Xi’an HV Apparatus Research Institute, Professor Senior Engineer Nie Dingzhen of State Power Economic Research Institute, Professor Cui Xiang of North China Electric Power University, Professor Senior Engineer Zeng Nanchao of China Electric Power Research Institute, and Professor Liao Ruijin of Chongqing University.

Academician Han Yingduo and Dean Kang Chongqing of the Department of Electrical Engineering and Applied Electronics of Tsinghua University, and Deputy Director Liu Qianwei of the Science and Technology Division of State Grid Corporation were also invited to the meeting.

Professor Zeng Rong and Associate Professor Yu Zhanqing of Tsinghua University respectively made a work report and technical report on behalf of the project completing units, and comprehensively reported the status of the project to the appraisal committee. For ten years since 2011, facing the challenge of “large-capacity DC breaking” in the DC grid and relying on the "One-Department & Two-Institute" platform of the Department of Electrical Engineering of Tsinghua University, Energy Internet Innovation Research Institute and Tsinghua Sichuan Energy Internet Research Institute, the DC technology research team led by Professor Zeng Rong, Associate Professor Yu Zhanqing, and Associate Professor Huang Yulong of Tsinghua University, has been working tirelessly and cooperated closely with Beijing Electric Power Equipment General Factory, Shandong Taikai High Voltage Switchgear Company, Zhuzhou CRRC Times Semiconductor Company, Power Research Institute of State Grid Jibei Power Co., Ltd., Guangdong Power Grid Co., Ltd. and some other units, successfully developed IGCT plus devices with a breaking capacity of 10,000 amperes, overcome the high current breaking and coupled negative voltage commutation of power electronic multi-stage series switchgears, and manufactured a series of HV, MV and LV DC circuit breakers with original schemes and superior performance, which have been applied in multi-scenario projects such as DC power grids, data centers, and electrified transport, making China internationally leading in the DC circuit breaker technology.

Photo: Project team members are reporting the research progress

Innovative Achievement 1: Successfully developed fully-independently produced IGCT Plus devices with a breaking capacity of 10,000 amperes

Large-capacity single-breaking power electronic devices are critical for the performance and cost of DC circuit breakers. To satisfy the demand for high-current breaking, the project team proposed a new GCT chip longitudinal doping structure and cell arrangement method, broke through the low-impedance fast commutation gate drive technology, mastered the cell current sharing technology of large-size devices, and jointly developed an IGCT Plus device with current breaking capacity of 10,000 amperes with Zhuzhou CRRC Times Semiconductor Co., Ltd.

Photo: IGCT Plus device

Innovative Achievement 2: Broke through the key technology of high-current breaking of power electronic multi-stage series switchgears

The modularized power electronic multi-stage direct series switchgear is the core component for DC circuit breaker to break the current. The project proposed a multi-stage series connection method for clamp type power electronic switchgear based on discrete metal oxide varistors, which solves the voltage balance problem of multi-stage series units; a two-way flow-through topology of bridge-type power electronic units based on conventional recovery speed diodes, which can effectively suppress the self-excited oscillation generated in diode recovery and save about 40% of the device cost compared with the traditional anti-series solution; a hybrid power electronic switchgear DC breaking technology integrated with the high breaking and surge withstand capabilities of the two different IGBT/IGCT devices, which can save the cost by about 60% to 70% compared with the single IGBT direct-series solution.

Photo: DC series valve group

Innovation Achievement 3: Proposed a DC circuit breaker commutation method based on coupled negative voltage technology

High-speed and reliable current transfer is the prerequisite for the successful breaking of the DC circuit breaker. To satisfy the requirement for high-speed and reliable current transfer of DC circuit breakers, the research team proposed a hybrid DC circuit breaker commutation technology based on a coupled negative voltage circuit, the main current branch loss is nearly zero, and water cooling is not required; it breaks through the key technologies such as single-break 100kV fast mechanical switchgear, low-inductance and large-capacity tightly coupled reactors and high-power pulsed power supplies, and can complete current transfer in 400μs~800μs.

Figure: Commutation process

Based on the above technological breakthroughs, the DC technology research team of Tsinghua University proposed different types of DC breaking topology innovation solutions for different voltage levels, application scenarios and technical requirements in the fields of DC power grids, data centers, and electrified transport, manufactured a series of HV, MV and LV DC circuit breakers with Beijing Electric Power Equipment Group Co., Ltd. and Shandong Taikai HV Switchgear Co., Ltd., and realized the large-scale engineering application.

① For HV DC power grid scenarios, a 535kV/25kA hybrid DC circuit breaker was developed and applied in Zhangbei 500kV flexible DC grid project, and passed the on-site short-circuit test.

② For MV DC application scenarios, a 10kV/10kA hybrid DC circuit breaker was developed and applied in Dongguan DC distribution grid project; a 10kV/3kA hybrid DC load switchgear was developed for Suzhou DC distribution grid project.

③ For multi-terminal DC breaking application scenarios, a 10kV/10kA three-terminal hybrid DC circuit breaker was developed and applied in Zhuhai DC distribution grid project.

④ For LV high-speed protection application scenarios, a 375V/5kA 100 microseconds solid-state DC circuit breaker was developed and applied in the DC power supply project of Dongguan Data Center; a 480V solid-state DC circuit breaker was developed for Huawei and applied in its communication test platform.

⑤ For independent all-electric system scenarios such as rail transit, a 10kV/60kA hybrid DC circuit breaker and a 3kV natural commutation hybrid DC circuit breaker are developed based on hybrid power electronic switchgears.

Figure: Multi-scenario application of DC circuit breakers

Experts of the appraisal committee believe that the project has overcome a number of key technical problems for large-capacity DC switching, and the achievements have been successfully applied in Zhangbei flexible DC power grid project, Dongguan AC/DC hybrid power distribution project, and Zhuhai "Internet + Smart Energy" demonstration project of the National Energy Administration, returned significant social and economic benefits, ran normally and can be generalized in extensive scenarios. Experts from the project appraisal committee agreed that "the project has achieved a number of innovative achievements, and reached the international leading level in general".

Specially invited experts, Academician Han Yingduo and Deputy Director Liu Qianwei, also spoke highly of the project achievements and suggested that they should be generalized in more fields as soon as possible. On behalf of the project completing units, Professor Kang Chongqing, Dean of EEA, delivered a speech of appreciation to academicians and experts for their suggestions, as well as the Chinese Society of Electrical Engineering, China Machinery Industry Federation, and project partners for their support to the project.

Lu Shujun, Vice Chairman of the Chinese Society of Electrical Engineering, made a summary of the meeting. He confirmed that the appraisal committee gave a realistic, objective and fair assessment conclusion on the project, and the valuable suggestions put forward will also play a major role of guide in the follow-up work of the project units.