The Research And Implementation Of STATCOM With Energy Storage Suppressing Commutation Failure

High voltage direct current(HVDC)transmission technology is an effective technical means to solve the imbalance between supply and demand of energy resources in China.When the commutation voltage of the HVDC system dips,caused by the breakdown happened in the AC receiving-end system,the commutation failure will happen.It will cause the power derating,and even cause the HVDC transmission system block when it is serious.Static synchronous compensator(STATCOM)can quickly regulate the reactive power of the system,and support the power grid voltage.When it is used in HVDC transmission projects,the probability of commutation failure will be reduced.However,when large reactive power is needed for compensation,the DC voltage of traditional STATCOM is more likely to fluctuate,which will reduce its output capacity and will emerge a large number of harmonics in its output current.All this will weak its ability of commutation failure suppression.The STATCOM with energy storage is put forward to solve this issue in this paper,which can keep the DC voltage more stable,improve its output current,and increase its output reactive power capacity.This paper has mainly done the following research:(1)The research background and application of reactive power compensation are introduced.The strengths and weaknesses of existing reactive power compensation devices in the commutation failure suppression are summarized.When large reactive power is needed for compensation,the DC voltage of traditional STATCOM is prone to fluctuate,which will affect the accuracy of the DC voltage control and make the DC voltage fluctuate in a wide range.The STATCOM with energy storage is put forward to make the DC voltage more stable,improve its output current,increase its output reactive power capacity,and then suppress the commutation failure more effectively.(2)According to the mechanism of commutation failure,a comparison has been made between the traditional STATCOM and the STATCOM with energy storage in compensating performance,the commutation failure suppression principle of the STATCOM with energy storage is analyzed.The main circuit topology of STATCOM with energy storage based on a two-stage transformation is given,the mathematical model of the main circuit is deduced,the system control strategy is studied,the design of the main circuit parameters and control system is analyzed,a nd finally the device of STATCOM with energy storage is developed.(3)In the PSCAD/EMTDC simulation environment,the HVDC model of the International Great Grid Conference is used to test the commutation failure suppression.The results verify that the STATCOM with energy storage is more effective in suppressing commutation failure.The simulation platform of 1600 V HVDC transmission system is built in the experimental environment.The STATCOM with energy storage is operated in this platform,and the commutation failure suppression experiment is carried out to demonstrate the feasibility of the studied device.