Observer-Based Capacitor Current Sensorless Control Applied to a Single-Phase Inverter System With Seamless Transfer

In this paper, capacitor current sensorless control by using an observer is applied in a seamless transfer single-phase inverter. The proposed control system is a multiloop control system. The control loop is composed of a capacitor voltage outer control loop and capacitor current inner control loop for stand-alone mode. For on-grid mode, the grid current outer loop controller is combined with the stand-alone control structure to form a simple controller structure for mode switching. The capacitor current feedback signal is calculated using the observer in the discrete-time domain and thus sensors are not required. Use of the proposed observer for the inverter with capacitor current control has many advantages, such as sensorless capacitor current calculation, one-sample-ahead data prediction for sampling delay compensation, and an average capacitor current without ripple components. Verification of the theoretical analysis is presented through simulation and experiment. A 5-kW single-phase inverter prototype combined with a Li-ion battery is set up with a digital controller using a TI TMS320F28377D microcontroller unit to confirm the feasibility of the system.