Exact Feedback Linearisation for a Grid-Connected PV Microinverter with Battery–Ultracapacitor Storage

Photovoltaic microinverters operating under rapidly varying irradiance are subject to large changes in input voltage and power flow, for which controllers designed from a single operating-point linearisation may lose their intended dynamic properties. This paper develops an exact feedback linearisation framework for a grid-connected photovoltaic microinverter equipped with a hybrid energy storage system comprising a battery and an ultracapacitor. Exact feedback linearising laws are derived for the current-control loops of the photovoltaic boost converter and of the bidirectional battery and ultracapacitor converters. An admissible operating region is obtained explicitly, ensuring that the control actions remain within modulation limits. The resulting inner-loop dynamics become independent of the operating point and of input-voltage variations. The proposed method is evaluated through detailed simulations under severe irradiance transients and is further validated on a laboratory-scale prototype. For an input-voltage step to 12.1V, the proposed controller reduces the current-tracking charge deficit from 5.72 A·ms to 0.0224 A·ms over a 5ms interval when compared with a conventional small-signal design. During the most demanding irradiance transient, the peak-to-peak deviation of the dc-link voltage stays below 16% while the ultracapacitor supplies up to 2.8 A. The model agrees well with the experimental results at steady state and at the extremes of the dc-link, but it overestimates the transient deviation of the dc-link by 27%, the peak current of the ultracapacitor by 69%, and its switching ripple by 63%.