| With the rapid development of national economy,the electric power demand in our country is getting much higher.However,with the acceleration of modern industrial process,the power quality requirements of electrical equipment are also enhancing.Therefore,how to ensure the stability and efficiency of power supply system has become a hot topic in the field of power research.The unified power quality controller(UPQC)is mainly composed of a shunt active power filter,a series active power filter and a DC side energy storage unit.The UPQC has the functions of dynamic voltage restoration,reactive power compensation,and voltage and current harmonics elimination.It is a comprehensive power quality control device.Whereas,the load voltage often has phase jump after compensated and the compensation capacity of series and parallel units is always very large in the conventional UPQC.Moreover,the insufficient energy storage on dc side of conventional UPQC limits its operation function.In view of the above problems,the specific work of this paper is as follows:(1)By analyzing the advantages and disadvantages of UPQC common voltage compensation strategies and topological structures,the full compensation strategy of load voltage is combined with the energy storage UPQC,which makes it possible to realize load voltage full compensation,while the UPQC compensation capacity is reduced.Then,the working principle of the energy storage UPQC is analyzed,its single-phase equivalent circuit diagram is drawn,and the mathematical models of series unit,parallel unit and dc energy-storing unit are established based on the switch function.(2)Facing the compensation problem of ignoring load voltage phase while utilizing the conventional UPQC voltage compensation strategy,the full compensation strategy of load voltage amplitude and phase is analyzed based on the reference of load nominal voltage under system normally operating.By combining the concept of amplitude changing rate of series voltage compensation,the amplitude changing range of compensation voltage and current is analyzed,and the analysis shows that the full compensation of load voltage is more suitable for energy storage UPQC.(3)In order to achieve coordinated power distribution between series and parallel units,the compensation strategy of conventional energy storage UPQC will cause phase jump of load voltage after compensation,which has a bad effect on the phase jump sensitive load.Therefore,this paper proposes a capacity configuration strategy with full compensation of load voltage amplitude and phase for UPQC energy storage system.The proposed strategy enables the load voltage to be fully compensated.Combining with the energy storage unit,the appropriate parallel compensation current of UPQC is selected and its amplitude is kept constant,which reduces the amplitude of the power supply current after compensated.Thus,the compensation capacity of the series unit is kept low,and the capacity configuration of the series unit of UPQC is reduced.Simulations have been carried out,and the results shows that the proposed strategy achieves full compensation of load voltage and reduces the compensation capacity of UPQC series unit.(4)The main circuit of UPQC is designed in this paper,which includes the selection of series transformer and power switching device.The calculation methods of parameters such as series filter inductor,series filter capacitor,parallel filter inductor,parallel filter capacitor and DC side capacitor are also introduced in this paper.The series and parallel units of the UPQC and the uninterrupted power supply function are simulated in MATLAB.The simulation results show that the UPQC system designed in this paper can maintain the load voltage quality and the grid current quality.The simulation results also show the effectiveness of the uninterrupted power supply function. |
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