Maximum Available Power Of Renewable-energy Gridconnected Converter Under Weak Grid Conditions And Optimal Design Of Controller Parameters

Excessive use of fossil fuels causes global warming,energy depletion and other issues have captured widespread attention,and renewable energy has become the main energy field explored by all countries for sustainability and clean.With the increasing penetration of wind,PV and other renewable energy in the power system,the power electronic complexity of the system is deepened,and the renewable energy grid connected converter is the core power electronic equipment of renewable energy power system.The large scale and high concentration of renewable energy in China is carried out by HVDC transmission over a long distance which makes the public grid usually exhibits the weak grid characteristics.The stability of the renewable energy grid-connected converter has a key impact on the safe and stable operation of power system under weak grid conditions.As a power conversion device,the power that can be converted by the renewable energy grid-connected converter is not only related to the capacity of the device itself,but also related to maximum available power(MAP).The DC-side power and AC-side power of renewable energy grid-connected converter are unbalanced when there is disturbance in the power system,and the state of the energy storage element and the controller will change which causes the small signal stability problem of the power system.From the point of unbalance of DC-side power and AC-side power,this paper studies the stability of the new energy grid-connected converter under weak grid conditions and MAP of the new energy grid-connected converter.At the same time,the controller parameters are designed to improve the MAP,and the applicability of the designed controller parameters under different short-circuit ratios is analyzed.The details are as follows:(1)For the typical single-machine infinite-bus system consist of the new energy gridconnected converter,the theoretical MAP of the grid-connected converter which ignores all the control loop dynamics is given,and the theoretical MAP increases with the increase of the short circuit ratio.Furthermore,the mathematical model of the renewable energy grid-connected converter that ignores the dynamic characteristics of the current inner loop and PLL is established to reveal the constraint of the DC voltage outer loop on the static stability interval,and the stability criterion of the working point on the power characteristic curve is given.Finally,the theoretical derivation is verified by simulation.(2)The full-order state space model of the renewable energy grid-connected converter considering the dynamics of all control loops under weak grid conditions is established to figure out the actural MAP of the renewable energy grid-connected converter under different short circuit ratios through the characteristic root analysis method.The actual MAP of the renewable energy grid-connected converter can reach the theoretical MAP only at certain SCRs when the typical controller parameters are used.It is pointed out that whether the actual MAP of the renewable energy grid-connected converter can reach the theoretical MAP is related to the unstable form at the actual MAP.Finally,the theoretical analysis is verified by simulation.(3)Considering the interaction between the control loops,the controller parameters are designed at specific SCR when the actual MAP cannot reach the theoretical MAP,aiming to improve the actual MAP.It is pointed out that the optimal design of controller parameters at specific SCR can only improve the actual MAP near the SCR,therefore the design of controller parameters should be combined with the actual system operation conditions.Finally,the feasibility of controller parameter design is verified by simulation.