Coordination Control Of Hybrid Energy Storage Devices

With the growing numbers of distributed generation in future's power system,energy storage technology is becoming more and more inportant in improving system stability and power quality.In general,storage unit about energy type like lead-acid battery has higher energy density and lower power density;however,storage unit about power type like supercapacitor has lower energy density and higher power density,so they have many complementary advantages.In such case,a hybrid energy storage system will have more advantages than a single energy storage system,and its coordinated control strategy has become a research hotspot.Compared with conventional control strategy based on master-slave control,this paper aims at the coordinated control strategy of hybrid energy storage device,which is suitable for DC microgrid with distributed characteristics,and the control strategy needs to make sure that devices about energy&power type can work well by using their own local information,i.e.operate in "plug and play" mode.This paper will mainly focus on the following aspects to research parallel technology among energy storage devices.This paper chooses a suitable energy storage structure and a sinplified equivalent circuit models of storage units.The principle of the bi-directional buck-boost converter and its process about mode switching are described,and the principle of two typical control—voltage and current control are analyzed.For the mathematical model of the energy storage device,the energy storage unit and bi-directional converter are modeled in boost direction,and the open-loop transfer function of the energy storage device is derived.The principle of the current voltage(I-U)droop control and current voltage(U-I)droop control are analyzed,and their equivalent parameters about how to get the same output results are derived.That I-U droop control can be achieved by using inductive side current is verified by mathematical method.The idea about how to use the droop control to realize the hybrid energy storage technology is proposed.An improved parallel control strategy based on I-U droop control is proposed.In the droop control used by device about energy type,the virtual inductance control is introduced to reduce the high frequent component of the response power,and the current feed-forward control is introduced in the droop control used in device about power type to increase the high frequent response power.The operation principle of this two kinds of control is analyztd.According to the bode diagram of their output impedance,the operation principle of virtual inductance and current feed-forward on the response curve of the energy storage device is analyzed in detail Finally,this paper also puts forward the method about how to select the parameter of the coord inated control strategy.Another parallel control strategy based on U-I droop control is proposed.In the droop control used by device about energy type,the first-order inertial is introduced to improve the stability of control;the device about power type adopts the voltage change rate current(U-I)droop control,and the first-order inertial is also introduced to irnprove the stability of its control.The operation principle of this two kinds of control is analyzed.According to the bode diagram of their output impedance,the operation principle of virtual conductance and first-order inertial on the response curve of the energy storage device is analyzed in detail.Finally,coordinated control strategies of hybrid energy storage proposed in(3)and(4)are compared in some way.After finished the theoretical research mentioned above,the effectiveness and correctness of the theoretical analysis and control strategy are verified by simulation model in Matlab/Simulink and hardware-in-the-loop simulation platform based on dSPACE1103.