Design Space Optimization of a Three-Phase LCL Filter for Electric Vehicle Ultra-Fast Battery Charging

Davide Cittanti, Fabio Mandrile, Matteo Gregorio and Radu Bojoi
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Davide Cittanti: Energy Department “Galileo Ferraris”, Politecnico di Torino, 10129 Torino, Italy
Fabio Mandrile: Energy Department “Galileo Ferraris”, Politecnico di Torino, 10129 Torino, Italy
Matteo Gregorio: Energy Department “Galileo Ferraris”, Politecnico di Torino, 10129 Torino, Italy
Radu Bojoi: Energy Department “Galileo Ferraris”, Politecnico di Torino, 10129 Torino, Italy

Energies, 2021, vol. 14, issue 5, 1-26

Abstract: State-of-the-art ultra-fast battery chargers for electric vehicles simultaneously require high efficiency and high power density, leading to a challenging power converter design. In particular, the grid-side filter, which ensures sinusoidal current absorption with low pulse-width modulation (PWM) harmonic content, can be a major contributor to the overall converter size and losses. Therefore, this paper proposes a complete analysis, design and optimization procedure of a three-phase LCL filter for a modular DC fast charger. First, an overview of the basic LCL filter modeling is provided and the most significant system transfer functions are identified. Then, the optimal ratio between grid-side and converter-side inductance is discussed, aiming for the maximum filtering performance. A novel design methodology, based on a graphical representation of the filter design space, is thus proposed. Specifically, several constraints on the LCL filtering elements are enforced, such that all feasible design parameter combinations are identified. Therefore, since in low-voltage high-power applications the inductive components typically dominate the overall filter volume, loss and cost, the viable LCL filter design that minimizes the total required inductance is selected. The proposed design procedure is applied to a 30 kW, 20 kHz 3-level unidirectional rectifier, employed in a modular DC fast charger. The performance of the selected optimal design, featuring equal grid-side and converter-side 175 μ μ H inductors and 15 μ μ F capacitors, is verified experimentally on an active front-end prototype, both in terms of harmonic attenuation capability and current control dynamics. A current total harmonic distortion (THD) of 1.2% is achieved at full load and all generated current harmonics comply with the applicable harmonic standard. Moreover, separate tests are performed with different values of grid inner impedance, verifying the converter control stability in various operating conditions and supporting the general validity of the proposed design methodology.

Keywords: LCL filters; grid-connected converters; active front-end (AFE); power factor corrector (PFC); battery charging; ultra-fast charging (UFC); electric vehicles (EVs) (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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