Journal of Power Electronics

The Korean Institute of Power Electronics (전력전자학회)
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Current Harmonics Rejection and Improvement of Inverter-Side Current Control for the LCL Filters in Grid-Connected Applications

  • Xu, Jinming (College of Automation Engineering, Nanjing University of Aeronautics and Astronautics) ;
  • Xie, Shaojun (College of Automation Engineering, Nanjing University of Aeronautics and Astronautics) ;
  • Zhang, Binfeng (College of Automation Engineering, Nanjing University of Aeronautics and Astronautics)
  • Received : 2016.09.09
  • Accepted : 2017.08.28
  • Published : 2017.11.20
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Abstract

For grid-connected LCL-filtered inverters, the inverter-side current can be used as the control object with one current sensor for both LCL resonance damping and over-current protection, while the grid-voltage feedforward or harmonic resonant compensator is used for suppressing low-order grid current harmonics. However, it was found that the grid current harmonics were high and often beyond the standard limitations with this control. The limitations of the inverter-side current control in suppressing low-order grid current harmonics are analyzed through inverter output impedance modeling. No matter which compensator is used, the maximum magnitudes of the inverter output impedance at lower frequencies are closely related to the LCL parameters and are decreased by increasing the control delay. Then, to improve the grid current quality without complicating the control or design, this study proposes designing the filter capacitance considering the current harmonic constraint and using a PWM mode with a short control delay. Test results have confirmed the limitation and verified the performance of the improved approaches.

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References

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