Research On System Topology And Control Strategy Of Megawatt Power Grid Simulator

With more and more distributed generation systems connected to the public grid,the grid has put forward higher performance requirements for new energy power electronic equipment.Therefore,before the new energy power electronic equipment is connected to the grid,it is urgent to test the adaptability of the grid simulator.However,most of the existing power grid simulators can only simulate voltage sags,frequency offsets,threephase imbalances and other common grid states,and lack of simulation of grid inertia and line impedance.At the same time,the low control bandwidth of high-power grid simulator limits the accurate simulation of high-order harmonics.In view of the above problems,this paper proposes the topology scheme of megawatt power grid simulator based on power combination.On this basis,the harmonic voltage simulation strategy,synchronous generator characteristic simulation strategy and line impedance characteristic simulation strategy are studied respectively,which is conducive to improving the completeness of power grid simulator function.The main research work and innovation are as follows:1)Aiming at the problem of low control bandwidth caused by low switching frequency of high power grid simulator,a topology scheme of megawatt power grid simulator based on power combination is proposed.By adopting the series structure of coupling fundamental wave unit with high power and low switching frequency and harmonic unit with low power and high switching frequency,the independent control of fundamental wave and harmonic wave is realized,and the control bandwidth of the system is improved.2)Aiming at the problem of accurate simulation of harmonic in power grid simulator,the mathematical model of megawatt level power grid simulator system is established,the simulation principle of single harmonic and combined harmonic is described,and the performance of typical harmonic amplitude detection algorithm is compared and analyzed.Based on this,the harmonic voltage simulation strategy based on amplitude and phase control is proposed to realize the accurate simulation of harmonic voltage.3)Aiming at the problem that the existing power grid simulator does not have the power grid inertia simulation,the paper analyzes the simulation principle of the synchronous generator characteristics,and puts forward two inertia simulation schemes: constant inertia and variable inertia.By adding the inertia and damping characteristics of the synchronous generator into the system control,the power grid simulator has the steady and dynamic performance comparable to the synchronous generator.In addition,the small signal model of the system is established and its stability is analyzed.4)Aiming at the problem of simulating line impedance change in power grid simulator,this paper studies the equivalent model and simulation principle of line impedance,puts forward two line impedance simulation schemes of pure inductance and resistance inductance,and analyzes the effectiveness of the two schemes.By reshaping the output impedance of power grid simulator,the flexible simulation and regulation of line impedance are realized.5)The experiment platform of 2MW full power electronic power grid simulator system is set up.The design process of hardware circuit and software program of the platform is introduced in detail.The basic function of megawatt power grid simulator,harmonic voltage simulation strategy,synchronous generator characteristic simulation strategy,line impedance characteristic simulation strategy and system fault protection are studied in turn.The experimental results verify the correctness and effectiveness of the proposed control strategy.