Research On Key Technologies Of Power-type Energy Storage Systems In DC Micro-grid Operation And Control

In recent years,with the development of distributed generation(DG)and power electronics,more and more sorces and loads are inherently DC.Compared with AC Microgrids(MGs),DC MGs are better suited for integrating distributed renewable energy sources(RESs)and DC loads.As a result,the interest in DC MGs has increased significantly.As an indispensable compenent of DC MGs,power-type energy storage systems(ESSs)play an important role on the operation and control of DC MGs.In order to solve the existed problems of DC MG control,control techniques of power-type ESSs are systemically studied in this paper.The main contents of the research are as follows:(1)In order to improve the performance of the DC-DC converter in power-type ESSs,and to further improve the output quality of power-type ESSs,multi-phase DC-DC converters are researched.The current imbalance of each phase in multi-phase DC-DC converter is analyzed,based on which a improved current sharing method is proposed.In the proposed method,an additional current sensor is added to the circuit and the pulse-mode modulation(PWM)signals are reajusted based on the traditional passive current method.The unbalanced current caused by the differences of parasitic resistance in each phase is alleviated.As a result,current in each phase in the bidirectional DC-DC converter in power-type ESSs is well controlled.(2)To improve the dynamic response ability and the anti-jamming ability of power-type ESSs,the active disturbance rejection control technique(ADRCT)is researched.And the nonlinear control method is applied to the control of power-type ESSs.Results have shown that this method can obviously improve the anti-disturbance capability and dynamic performance of power-type ESSs,and make power-type ESSs more suitable for the control and regulation of DC MGs.(3)In order for overcoming the instability problems of DC MGs caused by constant power loads(CPLs),the stability criteria of DC MGs is analyzed.After that,an active damping method based on power-type ESSs is proposed to deal with the voltage fluctuations induced by CPLs.A virtual resistance is introduced to the control of the ESSs and the damping of the DC MGs is regulated.As a result,the system oscillations are suppressed and the system stability is improved.(4)The power-type ESSs are researched to be applied to inhibit the voltage fluctuations on the DC bus in DC MGs under transient conditions.The controller of the power-type ESSs is improved by introducing the charging power of the filter capacitor on the DC bus.This method makes power-type ESSs capable of compensating the power unbalance on the DC bus quickly under different system operation modes.(5)A control platform of power-type ESSs is built in laboratory,and the above control algorithms and control methods are tested and verified.The research results of this paper can obviously improve the performance of power-type ESSs,and can further improve the control effects and sytem stability of DC MGs.