The major drawback of most control methods for uninterruptible power supply (UPS) inverters is complexity. In this study, a simple voltage sensorless multi-loop control method is proposed for the single-phase UPS inverter and the parameters are designed systematically based on a frequency domain method. The suggested control scheme uses two nested simple proportional controllers instead of proportional–integral/resonant controllers to regulate the output voltage and produce active resonance damping. In addition, a feedforward compensation of the reference voltage is used to enhance the performance of the control system. The proposed controller does not need any reference frame transformation or integration/derivation of measured quantities in its structure. To reduce the cost and at the same time to improve the reliability of the converter system, the output voltage sensor is replaced by a simple estimation algorithm based on the digital Kalman filter. Experimental results with a 500 VA prototype, as well as simulation results validate the excellent performance of the suggested estimation and control scheme.

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