33 research outputs found
Analysis, Design and Control of a Modular Full-Si Converter Concept for Electric Vehicle Ultra-Fast Charging
L'abstract è presente nell'allegato / the abstract is in the attachmen
Modulation Strategy Assessment for 3-Level Unidirectional Rectifiers in Electric Vehicle Ultra-Fast Charging Applications
This paper proposes a complete analysis and comparison of the most significant pulse-width modulation (PWM)
strategies for unidirectional 3-level rectifiers. The basic operation of the converter is described and the stresses on the major
passive components (i.e. DC-link capacitors, differential-mode
inductors, common-mode chokes) are calculated, highlighting
the general performance trade-off of each modulation strategy.
This analysis is applied to a rectifier for electric vehicle (EV)
ultra-fast charging connected to the European low-voltage grid
(i.e. 50 Hz, 400 V line-to-line), adopting a 650 V DC-link. The
best candidates concerning different performance metrics are
identified and the most suitable strategy for EV battery charging
is selected
Optimal Design of Grid-Side LCL Filters for Electric Vehicle Ultra-Fast Battery Chargers
This paper proposes a complete design procedure for LCL filters intended for electric vehicle (EV) ultra-fast battery chargers. The basic modeling of LCL filters is reported and the optimal ratio between grid-side and converter-side inductance is discussed. The design methodology is based on the identification of all parameter constraints, which allow to graphically determine the filter design space. Once the available space is identified, the feasible design which minimizes the total required inductance is selected, since inductors dominate the overall LCL filter volume, loss and cost. The proposed design procedure is directly applied to a 50 kW, 20 kHz 3-level unidirectional rectifier for a modular EV ultra-fast charger. The performances of the selected design, in terms of harmonic filtering and current control dynamics, are verified by means of simulation in PLECS environment, proving the validity of the proposed design methodology
Optimal Design of Grid-Side LCL Filters for Electric Vehicle Ultra-Fast Battery Chargers
This paper proposes a complete design procedure for LCL filters intended for electric vehicle (EV) ultra-fast battery chargers. The basic modeling of LCL filters is reported and the optimal ratio between grid-side and converter-side inductance is discussed. The design methodology is based on the identification of all parameter constraints, which allow to graphically determine the filter design space. Once the available space is identified, the feasible design which minimizes the total required inductance is selected, since inductors dominate the overall LCL filter volume, loss and cost. The proposed design procedure is directly applied to a 50 kW, 20 kHz 3-level unidirectional rectifier for a modular EV ultra-fast charger. The performances of the selected design, in terms of harmonic filtering and current control dynamics, are verified by means of simulation in PLECS environment, proving the validity of the proposed design methodology
Design Space Optimization of a Three-Phase LCL Filter for Electric Vehicle Ultra-Fast Battery Charging
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 µH inductors and 15 µF 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
Digital Multi-Loop Control of an LLC Resonant Converter for Electric Vehicle DC Fast Charging
This paper proposes a digital control strategy for LLC resonant converters, specifically intended for EV battery charging applications. Two cascaded control loops, i.e. an external battery voltage loop and an internal battery current loop, are designed and tuned according to analytically derived expressions. Particular attention is reserved to the output current control analysis, due to its extremely non-linear behaviour. The well known seventh-order LLC small-signal model, derived with the extended describing function (EDF) method, is simplified to an equivalent first-order model at the resonance frequency. In theseconditions,whichareproventobethemostunderdamped, the current control loop is tuned taking into account the delays introduced by the digital control implementation. Moreover, the adoption of a look-up table (LUT) in the feed-forward path is proposed to counteract the system non-linearities, ensuring high dynamical performance over the full frequency operating range. Finally, the proposed control strategy and controller design procedure are verified both in simulation and experimentally on a 15 kW LLC converter prototype
Decoupled and Modular Torque Control of Multi-Three-Phase Induction Motor Drives
In recent years, the development of multi-three-phase drives for both energy production and transportation electrification has gained growing attention. An essential feature of the multi-three-phase drives is their modularity since they can be configured as three-phase units operating in parallel and with a modular control scheme. The so-called multi-stator modeling approach represents a suitable solution for the implementation of modular control strategies able to deal with several three-phase units. Nevertheless, the use of the multi-stator approach leads to relevant coupling terms in the resulting set of equations. To solve this issue, a new decoupling transformation for the decoupled torque control of multi-three-phase induction motor drives is proposed. The experimental validation has been carried out with a modular power converter feeding a 12-phase induction machine prototype (10 kW, 6000 r/min) using a quadruple three-phase stator winding configuration
Iterative Design of a 60 kW All-Si Modular LLC Converter for Electric Vehicle Ultra-Fast Charging
This paper proposes an iterative design procedure
for a high-power LLC resonant converter, taking part in a
60 kW modular DC/DC conversion stage for an electric vehicle
(EV) ultra-fast battery charger. The basics of operation of
the LLC converter are briefly recalled and the most relevant
analytical expressions are reported. Due to the high-power
requirement and the wide output battery voltage range (i.e.
250-1000 V), a modular design approach is adopted, leveraging
the split input DC-link structure provided by a 3-level active
front-end. A total of four modules, with at 15 kW nominal
power and a 250-500 V output voltage regulation capability, are
designed with a straightforward iterative procedure based on
the first-harmonic approximation (FHA). Finally, the proposed
methodology is verified experimentally on a 15 kW LLC converter prototype directly resulting from the design procedure
Optimal Air Gap Length Design in Powder Core Inductors
The main requirements of magnetic components for power electronics applications are high power density and low power losses, driven by the need for more compact and more efficient power converters. Metal powder materials are a common choice for high-power and high-frequency inductors subject to a large magnetic field bias, since they feature high saturation flux density and low magnetic permeability (i.e., a “distributed” air gap), allowing for the adoption of un-gapped cores. Despite this, under high values of magnetomotive force (i.e., deep core magnetic saturation), the insertion of a concentrated air gap can lead to higher core inductance factor values with respect to an un-gapped configuration. In this context, this paper proposes a straightforward procedure to maximize the inductance factor of metal powder magnetic cores by identifying the optimal air gap length for a specified design operating point. In particular, the procedure completely relies on information available in the core manufacturer’s datasheet and does not require experimental characterization of the core itself, dramatically simplifying the inductor design procedure. The proposed methodology is theoretically described and then experimentally validated on an XFlux® 60 core from Magnetics
Three-Level Unidirectional Rectifiers under Non-Unity Power Factor Operation and Unbalanced Split DC-Link Loading: Analytical and Experimental Assessment
Three-phase three-level unidirectional rectifiers are among the most adopted topologies
for general active rectification, achieving an excellent compromise between cost, complexity and
overall performance. The unidirectional nature of these rectifiers negatively affects their operation,
e.g., distorting the input currents around the zero-crossings, limiting the maximum converter-side
displacement power factor, reducing the split DC-link mid-point current capability and limiting the
converter ability to compensate the low-frequency DC-link mid-point voltage oscillation. In particular, the rectifier operation under non-unity power factor and/or under constant zero-sequence
voltage injection (i.e., when unbalanced split DC-link loading occurs) typically yields large and
uncontrolled input current distortion, effectively limiting the acceptable operating region of the
converter. Although high bandwidth current control loops and enhanced phase current sampling
strategies may improve the rectifier input current distortion, especially at light load, these approaches
lose effectiveness when significant phase-shift between voltage and current is required and/or a
constant zero-sequence voltage must be injected. Therefore, this paper proposes a complete analysis and performance assessment of three-level unidirectional rectifiers under non-unity power
factor operation and unbalanced split DC-link loading. First, the theoretical operating limits of
the converter in terms of zero-sequence voltage, modulation index, power factor angle, maximum
DC-link mid-point current and minimum DC-link mid-point charge ripple are derived. Leveraging
the derived zero-sequence voltage limits, a unified carrier-based pulse-width modulation (PWM)
approach enabling the undistorted operation of the rectifier in all feasible operating conditions is
thus proposed. Moreover, novel analytical expressions defining the maximum rectifier mid-point
current capability and the minimum peak-to-peak DC-link mid-point charge ripple as functions of
both modulation index and power factor angle are derived, the latter enabling a straightforward
sizing of the split DC-link capacitors. The theoretical analysis is verified on a 30 kW, 20 kHz T-type
rectifier prototype, designed for electric vehicle ultra-fast battery charging. The input phase current
distortion, the maximum mid-point current capability and the minimum mid-point charge ripple
are experimentally assessed across all rectifier operating points, showing excellent performance and
accurate agreement with the analytical predictions