Design and control of three-phase four-wire inverters for v2g applications

Blas Perez, Miguel 2024. Design and control of three-phase four-wire inverters for v2g applications. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

An attractive power electronics inverter for electric vehicle (EV) chargers is based on a three-phase four-wire topology as it can handle unbalanced loads, supply neutral current, and provide balanced voltages. Moreover, wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride are suitable for EV technologies due to their electrical properties, allowing them to operate at high switching frequencies and voltages, leading in turn to power density improvement of power electronic converters. The main issue from these topologies arises from the generation of second-order ripple on the dc bus of the inverter due to imbalances in the three-phase system. To mitigate the magnitude of this ripple, large and expensive capacitors are required, leading to a low power density. This thesis presents a control design scheme for three-phase four-wire inverters for EV chargers for vehicle-to-grid applications. The control strategy enables the three-phase four-wire inverters to operate within isolated grids. The thesis also proposes a three-phase four-leg buck inverter based on SiC MOSFETs. It uses a decoupling controller to reduce the second-order ripple on the dc side of the inverter. The topology is configured as a dc/dc buck converter for each phase leg and the neutral leg. Moreover, the capacitance of the neutral leg is reduced by approximately eight times compared to that of the conventional neutral leg topology, thereby increasing power density and reducing overall cost. A final focus of the thesis is investigating a three-switch neutral leg for three-phase four-wire inverters to alleviate the second-order ripple on the dc side through control strategy. Additionally, this neutral leg mitigates the second-order harmonics on the ac side compared to conventional and four-leg buck inverters. Another advantage of the three-switch neutral leg is its versatility, providing an additional output source on the dc side and enabling voltage regulation with independent control in the neutral leg. In addition, this neutral leg is suitable for applications requiring high voltage ratios between the dc and ac sides. To provide confidence on the validity of the investigated topologies, their control schemes, and overall performance, experimental verification was conducted using laboratory prototypes of the presented topologies. Simulation and experimental results show a good agreement in inverter operation under balanced and unbalanced scenarios.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Engineering
Uncontrolled Keywords:	1). Three-phase four-wire inverter 2). EV charger 3). Neutral leg 4). Second-order ripple 5). Decoupling controller 6). Silicon carbide
Date of First Compliant Deposit:	21 August 2024
Last Modified:	24 Sep 2024 15:24
URI:	https://orca.cardiff.ac.uk/id/eprint/171509

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