Study On Three Phase Voltage Source Inverter Harmonic Compensation Technology

Distributed Generation (DG) based on the wind and solar energies is one of importantparts of national strategies for the sustainable energy development. In general, powerelectronic converters are the necessity for DG operation for energy conversion in thegrid-connected mode. Typically, a grid-connected inverter is utilized to provide an interfacebetween DG and grid. IEEE Std.1547specifies that the total harmonic distortion of theinverter output current should not be greater than5%. It is mainly because the harmoniccurrent injection into the grid will lead to the harmonic voltage drop across the line impedance,which may deteriorate the power quality of the terminal voltage and cause the devicemalfunction. Therefore, the output current waveform of the grid-connected inverter isgenerally sinusoidal with low level of harmonics. In practice, however, the voltage distortionis still an issue, which results from the nonlinear loads in the grid. In order to solve theproblem, the harmonic compensation function is integrated into the grid-connected inverter. Itcan achieve the power generation and power quality enhancement as well.First of all, the mathematic model of three phase voltage-source inverter is developed,and then the current controller parameters are designed from the viewpoint of the systembandwidth. The operating principle and linear model of the phase-locked loop is analyzed. Theeffect of the voltage distortion on its accuracy is discussed. Simulations are carried out underthe linear and nonlinear loads. The results indicate that the conventional sinusoidal currentcontrol with nonlinear loads may result in the voltage and current distortions in the grid side.In order to settle the abovementioned problem, the harmonic compensation function isintegrated into the control system. Two compensation schemes are analyzed. One is based onthe load current detection, and the other is based on the voltage detection at the point ofcommon coupling. Simulation results reveal that the former scheme has better compensationperformance at the expense of the additional sensors for the load current detection. On theother hand, the latter scheme can achieve partial compensation, but it needs not such additionalsensors as the former one. Finally, an improvement based on the latter scheme is discussed andsimulation verifications are carried out.In order to further verify the scheme, the system hardware and software are developedbased on the TMS320F2812DSP. The tests are carried out in the experimental platform, andresults indicate that integration of harmonic compensation function into the control system ofthe grid-connected inverter enables both the power generation and power quality enhancement.