Research On Mechanism And Suppression Measures Of Sub-synchronous Oscillation Of Large-scale Photovoltaic Series Compensation System

With the rapid development of new energy generation,the proportion of installed capacity of photovoltaic(PV)power generation in the power system is constantly increasing.In China,the large-scale PV power generation bases are built in Qinghai,Neimenggu and other regions.These PV power generation bases are far away from the load center.In order to realize the highcapacity and long-distance transmission of PV power generation,it is planned to adopt series compensation technology to transmit large-scale PV power generation to the load center.However,there is a risk of sub-synchronous oscillation(SSO)induced by the dynamic interaction between the series compensation line and the power electronic equipment such as the PV gridconnected converter,of which the specific mechanism is not clear.In order to ensure the stable operation of large-scale PV power generation bases,it is urgent to reveal the specific mechanism of the SSO of large-scale PV power generation with series compensation line,and propose the SSO suppression measures.In view of the above issues,the small signal analysis and time domain simulation analysis are carried out to study the mechanism and suppression measures of SSO induced by the interaction between large-scale PV power generation bases and series compensation line:(1)The small-signal state space model of the PV series compensation system is established.The influence of the control parameters of PV converter on the SSO modes of PV series compensation system is analyzed by eigenvalue method.The results show that the parameters of the phase locked loop(PLL)and the current loop can increase or decrease the SSO mode damping,which are the dominant parameters.The response process of the PV converter control system to the sub-synchronous frequency component of the PV series compensation system is derived in the time domain.The results further show that the amplification effect of PLL and current loop parameters on the amplitude of disturbance component is significant when certain conditions are satisfied.The accuracy of the above theoretical analysis is verified by time domain simulation.(2)According to the analysis of the SSO mechanism of the PV series compensation system,two kinds of SSO suppression measures are proposed on the side of PV power generation unit: 1)Embedding a band-pass filter in the voltage and current feedback loop on the AC side of the PV converter to block the sub-synchronous frequency component feeding into the converter;2)Adding damping control at the inner dq axis current loop to counteract the negative damping effect of the sub-synchronous frequency component.The effectiveness of two SSO suppression measures are verified by time domain simulation,respectively.