| In recent years,with the large-scale access of new energy sources and the updating of electrical equipment,users' demand for electrical energy has become more and more diversified,and power quality problems have attracted great attention.Static Synchronous Compensator(STATCOM)is a dynamic reactive power compensation device with advanced technology,convenient use and good economic performance.It has good bidirectional continuous adjustment compensation current capability,high flexibility,and can adapt to the power system for various working conditions.It can also compensate the reactive power and harmonics of the system and improve the power quality.This paper taken the three-phase three-wire STATCOM as the research object,and the work done was as follows:Firstly,the main circuit structure and working principle of STATCOM were analyzed,and three mathematical models of STATCOM in three-phase stationary coordinate system,two-phase stationary coordinate system and two-phase rotating coordinate system were established.The SVPWM modulation principle was analyzed for the modulation strategy of STATCOM.Secondly,in order to compensate the characteristic harmonics,the current detection method based on multi-synchronous harmonic rotating coordinate system and the harmonic current detection method based on SOGI were studied.The control method of the improved reactive current was studied,and the current inner loop control method was used to realize the decoupling control.The mathematical model of STATCOM in multi-synchronous harmonic rotating coordinate system was established,and the PI control strategy in multi-synchronous harmonic rotating coordinate system was studied.The STATCOM controller based on PI control was designed.Then,the basic theory of the repetitive controller was studied,and the connection between the repetitive controller and the infinite number of resonant controllers was derived.The implementation of the repetitive controller in thedigital domain was explained,and the stability of the embedded composite controller using the repetitive control and the PI control was studied,and the range of parameters was obtained.A composite controller based on repeat-PI control suitable for STATCOM was designed to realize the function of compensating for characteristic harmonics.Finally,a three-phase three-wire STATCOM simulation model was built in MATLAB/Simulink simulation software.The effectiveness of characteristic harmonic compensation was verified by controller based on PI control and compound controller based on repeat-PI control.The results show that the composite controller based on repeat-PI control has better tracking compensation for characteristic harmonics. |
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