Research On The Key Control Techniques Of Hybrid Controller For Power Quality And Fault Current

With the development of economy,China's dependence on electricity is getting stronger and stronger,power as the national economic development and the protection of people's lives by the government's attention.However,in recent years,the power grid structure is increasingly complex,power electronic devices constitute the equipment continue to access the power grid,resulting in frequent power quality problems.At the same time,the scale of the power grid has been expanded to cause a significant increase in short-circuit capacity,which directly threatens equipment and system safety.Therefore,the power quality control and short circuit fault current limit,is the current power research workers need to overcome the difficulties.Aiming at the problem that the traditional power quality control equipment and the fault current limiting device are simple and inefficient,this paper presents a new type of Hybrid controller for power quality and fault current system(HPQFC system),It can not only manage the power quality,but also can limit the short circuit fault current,overcome the traditional power quality control equipment in the short circuit fault can not achieve their own protection,and the traditional fault current limiting device function is single,the use of low efficiency.In this paper,a new type of Hybrid controller for power quality and fault current system is proposed.It combines the power quality regulation with the fault current limiting.When the grid is working normally,it can control the power quality.When the short circuit fault occurs,Can limit the size of the fault current limit.In this paper,the working principle of HPQFC system is introduced in detail,and the basic control strategy of the HPQFC system is introduced.The compound control strategy,the series side compound control strategy and the fault current limiting compound control strategy are respectively Description.Based on the instability of the pre-stage PWM rectifier in the HPQFC system,the load capacity of the PWM rectifier is deduced theoretically,and the maximum load capacity of the PWM rectifier is obtained.When HPQFC system working in governancing power quality model,If the voltage compensation depth is not enough,it will bring phenomenon of loss level.the essence of loss level is modulation ratio is low.so the relationship between the number of levels and the modulation ratio of CPS-SPWM modulation strategy is analyzed in detail,and the relationship between the output ratio and the modulation ratio is obtained.Based on analysis of compensation performance affected by system parameters,concept of system parameter impact factor is put forward as reference variable to determine whether a system falls in satisfaction area,the maximum level control strategies of HPQFC system was put forward.Aiming at the unsatisfactory effect of the current limiting effect of the filter,the equivalent circuit of the current limiter and the equivalent mathematical model Was established.Based on the analysis of the influence of thyristor triggering phase on current waveform,this paper puts forward the active regulation of the fault current of grid based on HPQFC thyristor adjustment.Based on the analysis of the influence of thyristor triggering phase on current waveform,this paper puts forward the equivalent circuit and equivalent mathematical model of current limiter.The simulation results show that the proposed control strategy can limit the short circuit fault current to a reasonable level by adjusting the thyristor conduction angle according to the system requirements.