Average Current Mode Control of Grid Connected Voltage Source Inverters with LCL Filter

This paper presents the average current mode control of single-phase grid-connected inverters without explicitly using an analog loop filter. The reference and the feedback inverter currents are given to a comparator instead of a subtractor. The duty cycle of the comparator output waveform is then estimated and compared against a reference duty cycle of 50% to obtain the error signal for the PI current controller. The PI controller output added with the grid voltage feed-forward term drives the PWM module to generate H-bridge switching pulses. The paper analyses the effect of using the comparator and associated logic instead of directly employing a subtractor to generate a current error signal for the control loop. The proposed method provides a robust current sensing scheme, shielding the current control loop from high-frequency common mode leakage currents and switching harmonics, and delivers grid current with a low THD of 0.83%. A scheme to further reduce the THD of the grid current by compensating for the dead-time is also investigated and the THD of the grid current could be further lowered to 0.17%.