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Improved inverter-side current control for grid-connected ZCZ-filtered inverter with low grid current distortion and high robustness

For the grid-connected LCL-filtered inverter in the distributed generations, the current control with one current feedback only is attracting a wide attention for the use of minimal sensors. Even though, it is found that the typical inverter-side current control with the filter-based active damping faces several problems, including 1) a contradiction between high bandwidth and stability, 2) a poor robustness under parameters variations and 3) a weak rejection of grid current low-order harmonics. To solve these problems while reserving the merit of using minimal number of sensors, this study proposes an inverter-side current control with reduced control delay and improved grid-voltage feedforward. By placing the PWM reference reloading instant at the moment the computation of control algorithm is finished, the digital control delay time is negligible so that the mentioned contradiction and the poor robustness are solved. With an extra first-order derivative feedforward of grid voltage, the limitation of inverter output impedance magnitude no longer exists so that the rejection of grid current low-order harmonics can be much strengthened. Finally, simulations and experiments prove that the improved inverter-side current control works much better than the typical inverter-side current control.