Iterative learning control with filter-capacitor current compensation for a three-phase four-wire inverter

This paper presents an iterative learning control with filter-capacitor current compensation for a three-phase four-wire inverter, which is adopted to uninterruptible power supply (UPS) applications. It can supply unbalanced, linear and rectified loads. With the proposed iterative learning control, the steady-state error can be reduced significantly cycle by cycle, and it is allowed to have wide inductance variation, reducing core size significantly. Additionally, the compensation for the filter-capacitor current is also considered in the control, which can help to shape output voltage waveform more accurately. In the design and implementation, the inverter inductances corresponding to various inductor currents are measured off-line and tabulated into a single-chip microcontroller for tuning loop gain every switching cycle, ensuring system stability. Experimental results measured from a 10 kVA inverter have verified the analysis and discussion.