Leakage current minimisation in transformer-less wide operating range interleaved minimum phase hybrid converter with improved AC output quality

This study proposes a transformer-less interleaved minimum phase hybrid converter, which is capable of delivering both AC and DC outputs, with reduced leakage current for photovoltaic applications. As the conventional transformer-less hybrid converters have the limitation of strong common-mode leakage current, when they are connected to the grid or their neutral point is grounded, a hybrid unipolar-based sinusoidal pulse-width modulation technique is used in the proposed hybrid converter to minimise the total common-mode voltage during its operation. Moreover, the proposed hybrid converter has a wide operating range of duty ratio (D) and modulation index ($M_i$Mi), i.e. it can operate at both the conditions $D + M_i \ge 1$D+Mi≥1 and $D + M_i \le 1$D+Mi≤1, unlike the conventional hybrid converters. Furthermore, the proposed hybrid converter exhibits minimum phase behaviour; which results in simpler controller design, high loading capability and fast dynamic response. In addition, it has improved output AC voltage quality because of operation at high $M_i$Mi values. The proposed hybrid converter also exhibits superior cross-regulation during dynamic load change conditions. The performance of the proposed converter is compared with other similar topologies to bring out its advantages. Detailed mathematical modelling is carried out and a 900 W laboratory prototype is developed to verify its performance.