Power Loss Reduction for PV Emulator Using Transistor-based PV Model

Recently, a photovoltaic (PV) emulator based on a combination of a constant current source and a semiconductor string, i.e., transistors or diodes, has demonstrated much faster dynamics than switching mode power supply (SMPS) based solution and shown also compatible performance with that of a real PV system. While it has high power efficiency at the maximum power point (MPP), the power loss of the emulator increases beyond the MPP and is at the highest at the open-circuit voltage (OCV) operation condition. This paper presents a hybrid solution where the semiconductor string works in the current-source region of the I-V curve and a new switching circuit, which sits in parallel with the semiconductor string, activates in the voltage-source region. Experimental results show that the efficiency and temperature of the PV emulator based on transistor string alone configuration reach 4.8% and 93.5°C, respectively, in the worst-case scenario, i.e., OCV condition, compared to 88.3% and 26.3°C, respectively, for the proposed solution. The switching circuit handles only a fraction of the rated emulator power and has much narrower control bandwidth requirement than pure switching converter based solution. A new control algorithm is proposed to manage the transition between the two regions seamlessly.