Research And Design Of VSG Reactive Power-Voltage Loop Based On Small Signal Model

With the rapid development of national economy and the demand of environmental protection,distributed power generation composed of renewable energy has attracted more and more attention.Inverter,as a converting unit of distributed generation connected to microgrid,has become a hot topic for scholars to study and discuss.However,the characteristics of power electronic devices will lead to the disadvantages of poor stability,small inertia and disturbance-prone oscillation of the inverter system.Virtual Synchronous Generator(VSG)technology can effectively simulate the stator impedance,primary frequency/primary voltage regulation and inertia characteristics of synchronous generator,and can effectively control the frequency and amplitude of the output voltage of the inverter.These characteristics make VSG a widely concerned inverter controller.Robust droop VSG,which introduces integral term in reactive power-voltage loop.This not only improves the accuracy of reactive power distribution,but also can be regarded as a special case of the classical droop control without integral link or voltage amplitude term.Therefore,the selection of robust droop VSG is representative.Voltage parameter is an important index in power system.It has guiding significance for power quality of power system.Voltage in power system is generally closely related to reactive power of system.However,there are few studies on the parameter design of the reactive power-voltage loop,so this paper focuses on the parameter design of the reactive power-voltage loop.In order to study the parameter design of reactive power-voltage loop,a representative mathematical model of robust sagging VSG is established firstly.Based on this model,a small signal model between terminal voltage setting(Bus Voltage Settings)value and its output reactive power-voltage is obtained.Then,the decoupling of reactive power-voltage loop and active-power loop is realized by gain comparison analysis,and the second-order mathematical model of VSG reactive power-voltage loop is obtained.Referring to the parameters design basis of synchronous generator(SG)excitation system recommended by IEEE and IEC,the parameters of VSG reactive power-voltage loop are designed.Considering that the complex conditions that VSG system may encounter in operation are beyond the design scope,and the parameters of VSG system,such as line impedance,control strategy parameters,will change with the actual situation.If the dynamic response of the reactive power and voltage link of the inverters with arbitrary system parameters is simulated,the process is too complicated.BP neural network can infinitely approximate the internal structure of any system.Therefore,it has certain advantages to select BP neural network for training and learning VSG related parameters and simulation data,and the obtained BP training network can directly judge the operation state of the system after disturbance according to the system parameters.Experiments and simulation results show that the design method of reactive power and voltage parameters proposed in this paper has application value,and the research results are helpful to improve the parameter design of VSG.