Research On Harmonic Suppression Technology Of Multi-inverter Grid-connecting System

Grid-connected inverter is a transport hub from renewable resource of energy to the grid. Harmonic content of the output current is an important criterion for the grid-connected inverter quality.Firstly, establish the mathematical model of grid-connected inverter in different coordinate systems separately. Select the model based on two-phase rotating coordinate system and analysis the stability of two kind of current feedback program in LCL filter comparatively. Take into account the two harmonic sources of current loop:PWM signal generator and the grid voltage. Firstly, with the double Fourier integration analysis harmonic characteristics of inverter output voltage PWM process generated. On the grid voltage imbalance applied mathematical model based on positive and negative sequence rotating coordinate system with symmetrical components law and divide into two sections to discuss. One is the impact of unbalanced grid voltage to inverter output characteristics; the second is the power imbalance makes the influence of traditional software PLL. And give equations for inhibiting negative sequence current and suppressing the second harmonic component of grid power. For the problem of traditional phase locked loop not working, proposes a phase locked loop design based on two synchronous coordinates. Finally, test and verify the effectiveness.In multi-inverter grid-connecting system, establish model system and analysis the coupling relationship between inverter and grid impedance for their impact on current harmonics to the network. To suppress harmonic current amplification problem, propose passive damping and active damping method to inhibit resonant perk of single inverter grid system. Passive damping law were added to the resistance in different locations LCL filter, analysis the transfer function through its Bode diagram to determine the impact on the system. The active damping method joining the capacitor voltage feedback builds a "notch" structure in the current ring to suppress resonance peaks. Use such a control strategy in multi-inverter grid-connecting system, test and verify the correctness of above theory.