Analysis of Power Redistributors for Low-Voltage Distribution Grids
A.K. Iyer (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Thiago Bastia Soeiro – Mentor (TU Delft - DC systems, Energy conversion & Storage)
Pavol Bauer – Graduation committee member (TU Delft - DC systems, Energy conversion & Storage)
A. Lekic-Vervoort – Graduation committee member (TU Delft - Intelligent Electrical Power Grids)
Marco Stecca – Mentor (TU Delft - DC systems, Energy conversion & Storage)
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Abstract
The phenomenon of phase unbalance is prevalent in the low voltage distribution grid due to the presence of single-phase loads. The unbalance can cause issues such as capacity underutilisation, transformer losses and problems with induction motors. To ensure the reliability of the upstream grid, it is important to maintain balanced three-phase power. This becomes more relevant with the proliferation of Distributed Energy Resources (DERs) and storage. This thesis explores the use of power electronic devices as a power redistributor.
To begin with, different topologies of a converter are discussed. These topologies have their own sets of advantages and disadvantages. Based on various operating and design parameters, a comparison between these topologies is made.
Subsequently, different control strategies for the converter are analysed. Among these, the current control strategy ensures supply of balanced and sinusoidal current to the loads with low computational burden, and is hence chosen. This strategy involves the control of sequence components independently in the double synchronous reference frame.
Low-frequency harmonics occur in the DC-link as a result of the compensation of negative-and zero-sequence components by the converter. The magnitude of this low-frequency harmonic and the overall harmonic Root Mean Square (RMS) current in the DC-link are derived mathematically and validated by simulations to represent this converter. It is observed that the DC-link sizing is mainly dependent on the low-frequency harmonics and thus, their accurate estimation will help in better sizing of the DC-side components.
The various configurations of the converter under consideration are benchmarked against each other on parameters such as Total Harmonic Distortion (THD), Power Losses, and DC-Link Sizing.