Control Schemes For PV Grid-connected Inverter Under Non-ideal Grid Conditions

The PWM voltage saurce converter(VSC) has been increasingly employed inrecent years owing to its advanced features including sinusoidal input current,small size of input and output filter,bi-directional power flow, high control abilityof grid-side active and reactive power, etc. Compear with L-type filter, LCL-filterhas higher attenuation ability of current harmonics at higher frequencies, so it hasbeen more and more employed in VSC system.In order to suppress the LCL filterthe harmonic resonance problem,this paper uses the capacitor current inner loop isto increase the system damping active damping method.The voltage of power grid harmonics in the case of grid-connected inverteroutput current distortion casued by the problem, this paper adopts two kinds ofcontrol methods:One is in the three-phase static coordinate system usingproportional resonant(PR) and harmonic compensation(HC) regulator controlstrategy combing;The other is the grid voltage PI regulator in the synchronousrotating coorrdinate syestem using state feedback control.Process of the grid,the grid containing the harmonic conditions,in order toobtain the three-phase PWM inverter control signals to achieve grid-connectedinverter active and reactive power independently controlled,the current was sinewave and the power factor is adjustable,you need to quickly and accurately learnthe grid side voltage phase and charge.In this paper,the PLL based on biquadgeneralized integrator software, it can not only quickly and accurately in thenon-ideal grid access to the grid voltage phase, but also can suppress the harmonicsof the system output, has a good frequencyadaptive characteristics, and a largenumber of simulation studies to verify the correctness of this method.Equivalent mathematical model LCL PV grid-connected inverter AC side ofthree-phase stationary coordinate system and the AC side of the synchronousrotating coordinate system under equivalent mathematical model.According to theirequivalent mathematical model to analyze the proportion of resonant three-phasestationary coordinate system (PR), and harmonic compensation (HC) to adjust thecombination of control strategies for the suppression of the grid voltage harmonicson the gridcurrent impact of rationality; At the same time the use of the equivalent transformation of the principle of detailed analysis of the synchronous rotatingcoordinate system using the ratio of the first derivative, the three states of thesecond-order differential feedback control strategy is correct, and were classifiedaccording to the harmonic number of different grid containsdifferent harmonicnumber of different state feedback strategy, the last simulation verifies thecorrectness of theoretical analysis.The paper built1.92kW grid-connected inverter prototype under thesynchronous coordinate system in the non-ideal grid voltage conditions, theexperiments of the corresponding state feedback control scheme for differentharmonic frequency. Consistent with experimental results and simulation analysisto verify the effectiveness of control programs.