Study Of Power Quality Optimization Control Strategy Of Islanded Power Generation Systems With Multiple Converters

With the increased development and utilization of renewable energy,distributed generation technology has received more and more attention.Especially,distributed islanded power generation systems are particularly important in islands and remote poverty-stricken areas where power grids cannot reach.Hence,ensuring the stable operation of power generation systems and improving the output power quality of power generation systems are the hotspots of the researches about the islanded power generation systems.In this paper,the islanded power generation system with multiple converters will be developed from the following four aspects:(1)The control strategy,modeling and parameter design of the single-phase inverter are investigated.In order to solve the problems of the steady-state error and the resonance of the single-phase inverters,the PI controller in synchronous reference frame is introduced to design the hybrid reference frame-based voltage and current dual loop control strategy.With the consideration of the control delay of the system,the transfer function model of the single-phase inverter based on the hybrid reference frame-based voltage and current dual loop control strategy is established.Moreover,an optimal control parameter design guideline is proposed for the single-phase inverters with the hybrid reference frame-based voltage and current dual loop control strategy.Under the control delay consideration,this method designs a satisfactory region,which is specified by the phase margin(PM)and the gain margin(GM).With this predefined region,the control parameters of the system can be obtained,and it is more convenient and explicit to optimize the system performance according to the satisfactory region.Finally,the simulation model is built in the PLECS to verify the validity of the control strategy and the proposed parameter design method,which lays a foundation for the study of the islanded power generation systems with multiple converters.(2)The coordinate control strategy of the islanded power generation systems with multiple converters is studied.To maintaining the amplitude and frequency of the output voltage and sharing the output power of the inverters accurately,an improved droop control strategy based on the high-pass filters is established.The equivalence between the improved droop control strategy and the traditional hierarchical control strategy is analyzed,which indicates that the dynamic response of the power generation system can be improved by reducing the communication of the system while maintaining the voltage frequency and amplitude of the system.In order to guarantee the accurate reactive power sharing under the inconsistent line impedance condition,a reactive power sharing control strategy based on the average power voltage compensation(APVC)is established.The response ability of the consensus algorithm under different topologies and the weight factors is studied,and the fastest response scheme of the algorithm is selected.Moreover,combined with the hybrid reference frame-based voltage and current dual loop control strategy,this paper proposes an optimal power quality coordinated control strategy based on APVC + high-pass filter,which can maintain the voltage frequency and amplitude of power generation system and ensure the accurate power sharing of the system.Finally,PLECS is used to simulate and verify the proposed control strategy under the load disturbance condition,feeder disturbance condition,different line impedance condition and the different DC voltage condition.(3)The harmonic suppression method and model establishment of the islanded power generation system are studied.Aiming at the harmonic problem of power generation system,an improved harmonic suppression strategy based on the moving average filter phase-locked loop is proposed.This strategy introduces the phase-locked loop,which is commonly used in the grid-connected system,to extract the fundamental component under the nonlinear load condition and obtain the harmonic components of the voltage.Then,the obtained harmonic components are compensated to the modulated signals of the inverters of the power generation system to achieve the harmonic suppression.Meanwhile,the detailed model and analysis of the single-phase islanded power generation system are carried out with the small-signal analysis method,and the state-space equations are established,which include the average power voltage compensation-based reactive power sharing strategy,the improved droop control strategy based on the high-pass filter,the hybrid reference frame-based voltage and current dual-loop control strategy and the main circuit of the power generation system.Finally,the simulation model is built in the PLECS to verify the effectiveness of the proposed harmonic suppression strategy under linear and nonlinear load conditions.(4)An experimental platform of the single-phase inverter is built to verify the validity of the optimization control parameter design method proposed in this paper under the load disturbance condition,feeder disturbance condition and the nonlinear load condition with the change of the control parameters.Then,the experimental platform of the islanded grid power generation system composed of two parallelled inverters is built to verify the effectiveness of the proposed power quality coordinated optimal control strategy under the load disturbance and feeder disturbance conditions.