Voltage-sensorless control scheme for a grid connected inverter using disturbance observer

A grid connected inverter usually requires voltage and current measurements to control the active and reactive powers as well as the inverter output currents. While voltage sensors are essential to obtain reliable information on the phase angle, these additional components certainly increase the production costs and complexity. In this paper, a voltage-sensorless control scheme for a grid connected inverter using a disturbance observer (DOB) is presented. The grid voltages are estimated by DOB in the stationary reference frame using the current measurements and reference signals. Even though the DOB estimates the grid voltages with reasonable accuracy in the presence of the uncertainty such as the unbalanced condition and harmonic distortion, the resultant waveform shows a phase lag depending on the estimation bandwidth. To overcome this limitation, a phase lead compensation is introduced. By using these techniques, the phase angle of grid voltages can be completely restored even if the phase angle of grid is initially unknown. The proposed scheme is simple and straightforward. In addition, it does not require any additional hardware. The feasibility of the proposed voltage-sensorless control scheme is demonstrated through simulations and experiments using 2 kVA prototype inverter.