Research On Power Quality Analysis And Control Measures Of DC Distribution Network

Recently,with the vigorous development of power electronics technology,and the larger number of DC loads and DC power sources,the source-load characteristics of the distribution network tend to be DC,the DC distribution network has become an effective way to consume distributed energy and supply DC loads with power,which has broad prospects for development and application.With the large increase of sensitive loads,the requirements of enterprises and users for power quality are becoming more and more strict,which is one of the key issues affecting the development of DC distribution network applications.Compared with the AC system,the DC system has no reactive power and frequency,while the DC system has less damping and the poor ability of anti-interference,which make the AC and DC power quality problems have differences.Therefore,the study of DC power quality is of great significance to promote the construction and popularization of DC distribution networks.Aiming at the problem of DC power quality,this paper analyzes it in detail and provides DC power quality management strategies.The main work and achievements completed are as follows:(1)The classification of DC power quality is discussed in detail.The DC power quality problem is divided into stable power quality and transient power quality.The stable power quality includes DC voltage fluctuation and flicker,ripple,DC voltage deviation,and DC voltage imbalance(bipolar DC distribution network).The transient power quality includes DC voltage rise,fall,and short-term interruption.The indicators for evaluating power quality problems are analyzed,and the causes and manifestations of steady-state and transient power quality are given.(2)In order to suppress DC voltage deviation,a comprehensive control of the controllable load and battery energy storage system(BESS)is proposed in this paper.when the voltage fluctuation is small,the controllable load can be used to suppress the DC voltage fluctuation,which can reduce the capacity of the battery and reduce its charge and discharge times,which improves the economical efficiency of BESS.When the voltage fluctuation is big,due to the limited capacity of the controllable load,comprehensive control is required with BESS,and the parameters of both are designed.It reduces DC voltage transient fluctuations using feedforward control based on disturbance observer(DO).(3)Aiming at the problem of DC transient power quality,a super-capacitor(SC)management strategy based on sliding mode control(SMC)is proposed in this paper.Firstly,the advantages of SC for DC transient power quality problems are explained.Secondly,the parameters of SC are designed.Then,according to the model of SC management device,a sliding mode control based on Super-Twisting algorithm is designed,which also has strong robustness when the system parameters change,and finally provides a recovery strategy for SC.