Design of Efficient, Fast and Accurate Emulators for Photovoltaic Systems

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Photovoltaic systems (PVSs) continue to face ongoing challenges, such as the reliability of power electronic systems and the effective integration of energy storage. A PV emulator (PVE) provides a testing and analysis platform for PVSs, such as maximum power point tracking and partial shading effect, independent of weather conditions and ease of scaling. Many researchers have proposed different PVE topologies to mimic the real PVSs. A good PVE requires fast computing and power converters with a wide output range. However, the controller bandwidth restricts the emulator's response time, and it must stabilize the converter for many different operating points for a given insolation level. Hence, converter-based solutions generally have a slower response time than real PVSs. The study's first phase is to devise a simple, reliable, effective circuit-based PVE based on the equivalent PV stacked cells that are cost-effective and perform close to a real PV source. A PVE that physically models a single-diode analytical model is studied. Due to its simplicity, the proposed PVE shows a better dynamic response and shorter settling time than several benchmarked commercial products, where a few power diodes and two resistors are used. Furthermore, the thermal characteristic of the PVE is identified and solved by adding a variable speed fan cooling system. Phase two proposes a constant current source DC/DC converter (CCSC) for the PVE applications based on a cost-effective and straightforward method. The CCSC simplifies the converter and controller designs as it operates at a fixed point for each insolation level compared with a converter-based solution that requires a voltage-source converter with wide output operating ranges. Even using a variable speed fan to control the operating temperature of the power semiconductor string, the overall system efficiency is low. The third phase of the study involves the proposed redesign of a PVE, using two new hybrid solutions that consist of a switching circuit (SC) is inserted parallel with the semiconductor string to manage the thermal behaviour of the emulator system. When the operating point of the PVE moves from the current source region to the voltage source region, the more efficient converter switches in to replace the semiconductor string seamlessly to maintain the circuit operation of the emulator. The SC is only required to handle a narrow operating voltage range than a conventional pure switching converter-based solution. The experimental results show a high performance in terms of temperature, efficiency, and dynamic response.
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