Sensorless Control of Series Stacked Buffer Converter in a Two-Stage Microinverter for PV Applications

The series stacked buffer converter (SSBC) is a promising solution for power pulsation decoupling in single-phase converters due to its low power processing and voltage stress compared to its counterparts. However, its practical adoption is limited by the need for more expensive voltage and current sensors, which increase system cost and complexity. This paper proposes a novel sensorless control strategy for the SSBC in a two stage microinverter for photovoltaic (PV) applications. The novel sensorless approach is based on acquiring the average power, DC bus voltage, and input energy port voltage of the SSBC. The proposed approach estimates these quantities from existing control loops, including: the maximum power point tracking (MPPT) loop, the DC bus voltage regulation loop for downstream inverter, and isolated-port voltage from the submodule-integrated converters (subMICs). This eliminates the need for dedicated expensive current and voltage sensors, significantly reducing both the cost and complexity of the SSBC. The paper presents the design guidelines of the sensorless controller, where a proposed feed-forward term is combined with a novel small-signal feedback compensation. The approach has excellent ripple mitigation properties at the DC bus, and it is robust to mismatches in the real circuit data and capacitor tolerance. The proposed approach is validated through simulations and experiments using a 300 W microinverter prototype connected to a 180 W, 72-cell commercial PV module. The sensorless control achieves a DC bus ripple of just 95% with a 20 μF film capacitor.