Study On Impedance Network Electric Spring For Lowering DC Input Voltage

Renewable energy sources,such as solar energy and wind power,play an important role in the existing power system and will also be indispensable in the future.However,they will be influenced by natural conditions,such as weather.They have the personalities of the intermittent and volatility.In recent years,the ES,proposed from the perspective of the demand side,can compensate active and reactive power for renewable energy connected power systems,which well solves the power quality problem caused by the fluctuation of renewable energy to the power grid.ES has the advantages of small volume,fast compensation,and lower cost compared to traditional compensation methods.It can not only stabilize power grid voltage,but also implement functions such as power factor correction,but it still has the following disadvantages: Firstly,a larger DC input voltage is required,and it is normally achieved by connecting multiple batteries in series,which results in a higher cost and larger volume.Secondly,ES's inverter bridge arm will cause short-circuit problem due to improper setting of dead time,even the correct dead time setting will also cause voltage distortion,which will affect other devices.In order to solve these problems,the traditional solution is to use two stage boost ES,which specifically combining the traditional two stage boost inverter circuit with ES,it can boost the small voltage on the DC side,and then compensate the power grid,it just requires smaller energy storage battery and lower economic cost,but the problems of large power loss and shoot-through of the inverter bridge arm are still there.Therefore,this dissertation proposes a single stage impedance network electric spring to solve above problems.The main contributions of this dissertation are as follows.1.Elaborate and analyze the basic operating principle and topology of the existing ESs,and conclude their comparative advantages and disadvantages;2.The operating principle of traditional two stage boost ES is analyzed,then its shortages is revealed.Based on the shortcomings of existing ESs and two stage boost ES,a novel impedance network electric spring is proposed with detailed operating principle.It is followed with comparative analyses of two-stage ES and INES to illustrate feasibility,advantages and disadvantages of these two topologies in solving ES problems.Finally,it is verified that the proposed INES is superior;3.Mathematical model of INES is built up,and based on its equivalent circuit model,the circuit parameters affecting the stable operation of critical loads in the circuit are analyzed;4.Through the review of control strategies of ES and impedance network inverters,a novel control strategy of INES is proposed,and the corresponding electrical parameters of the INES circuit and the control circuit are designed,and the simulation model is built on MATLAB / Simulink software to verify it.Finally,an experimental prototype of INES is conducted for experimental verifications.