Abstracts:The market for partly or fully electrified vehicles is expanding fast. The number of sources and loads that are connected to the vehicles traction voltage systems (TVS) increase and thus also the ElectroMagnetic Compatibility (EMC) requirements on these sources and loads. These requirements should make sure that neither function nor lifetime of any source or load is severely affected by another. The EMC requirements include both Common Mode (CM) and Differential Mode (DM) voltages and currents created by the modulation of the various power electronic converters involved as well as intentional and parasitic impedances of the TVS and reach up to at least 10 MHz for CM and 100 kHz for DM. This article presents a theory for the dimensioning of CM-capacitances in an Electric Machine Drive (EMD) that is confirmed by measurements on a commercial electrical Volvo truck. The conclusions point out a recommendation for selection of the CM-capacitances of the EMD vs. the CM capacitance of the Electrical traction Machine (EM). As a rule of thumb the recommendation is that the CM-capacitance of the EMD is around 50 times the CM-capacitance of the EM and mounted inside the EMD to avoid big loops of CM currents in the vehicle.

Abstracts:In this article, the modeling of an optimum fast charging profile for lead-acid batteries (LABs) is proposed. The proposed profile is a multi-step constant current (MSCC) where various current magnitudes in a descending manner are applied to the battery; therefore, it prevents the over-voltage and gassing phenomenon at the end of charging process, and shortens the charging time at the same time. Using an electro-thermal model of a LAB, an optimization problem containing charging time, battery temperature during the process, and battery's terminal voltage as objective functions is defined. The magnitude and duration of all charging steps are taken into account as control variables to be optimized for minimizing the objective functions using a particle swarm optimization (PSO) algorithm. A comparison between different conventional charging profiles for LABs is also provided in terms of charging time and battery's temperature and voltage. The simulation results carried out by MATLAB/Simulink show that the proposed profile reduces the charging time, while keeps the battery's temperature and voltage during the charging process within allowable range. The impacts of model's uncertainties on the proposed approach is evaluated. A comprehensive comparison is also provided to confirm the benefits of the proposed method over MSCC profiles reported in the literature. The effectiveness of the proposed approach is finally validated using the experimental implementation for a 12 V 200Ah lead-acid battery.

Abstracts:Multi-port power converters are widely used in managing multiple energy sources and loads. To that end, a dual-input single-output dc-dc converter is proposed in this article. The converter integrates two low-voltage dc sources into a dc bus. Pulse width modulation is used to control the transfer energy from the input ports to the output port. The soft-switching operation in the primary side switches is achieved with the help of the secondary side modulation and the discontinuous conduction mode (DCM) operation of the primary inductors. Moreover, the DCM operation helps avoid the high-frequency transformer saturation even when the two input voltages have different magnitudes. Detailed analysis of the proposed dc-dc converter is presented in this article. The steady-state operation, the dynamic performance at the output load variation and input voltage disturbances, and maximum power point operation of the converter are validated through the simulation and experimental results obtained from a 200 W hardware prototype.

Abstracts:In this article, the static and dynamic characterizations for semiconductors with different materials, including silicon (Si), silicon carbide (SiC), and gallium nitride (GaN), are evaluated and compared at room temperature and cryogenic temperature (liquid nitrogen temperature). For static characterizations, the on-state resistance and threshold voltage are evaluated. For dynamic characterizations, the turn-on switching loss, turn-off switching loss, and dynamic on-state resistance (<italic>R</italic>_ds(on)) are evaluated. The results demonstrate that Si and GaN based semiconductors have improved performances with lower on-state resistance and faster switching speed at low temperature operations. For SiC based semiconductors, the on-state resistance increases significantly at cryogenic temperature. The switching speed is reduced dramatically for the evaluated 1.2 kV SiC metal oxide semiconductor field effect transistors (MOSFETs) at cryogenic temperature. This makes it less attractive for cryogenic applications. For the evaluated 650 V and 900 V SiC MOSFETs, the switching speed remains almost unchanged at low temperature. GaN high electron mobility transistor (HEMT) demonstrates a fast turn-on switching speed at low temperature, where the device&#x0027;s <italic>dv&#x002F;dt</italic> and <italic>di&#x002F;dt</italic> are almost doubled when compared with room temperature. In addition, the dynamic <italic>R</italic>_ds(on) of the evaluated GaN HEMTs also decreases at low temperatures. The evaluation results can serve as guidelines for cryogenic power electronics applications. Meanwhile, the future work for semiconductors cryogenic characterizations is discussed.

Abstracts:This article proposes a comprehensive steady-state analysis for a front-end Modular Multi-Parallel Rectifiers (MMR) system with a shared DC-link. A generalised mathematical representation for an n-number of parallel rectifiers is proposed. The MMR is analysed for both Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). In addition, the CCM and DCM boundary of the MMR is identified mathematically. The impact of parasitic elements on the mode of operations is studied. In addition, the impact of different ASD scenarios on the mode of operation is studied. A 200 W Simulink model for the MMR is utilised to confirm the proposed steady-state mathematical modelling equations. A 200 W practical setup is implemented in a laboratory to validate the proposed mathematical equations.

Abstracts:Short-circuit protection is critical and indispensable for resonant switched-capacitor converter (RSCC) to improve the reliability. Based on comparison of frequency control, duty ratio control and traditional variable frequency variable duty ration control (VFVDC-I), a novel variable frequency variable duty ratio control (VFVDC-II) is proposed for RSCC to suppress the short-circuit current. By analyzing the operation principle and short-circuit mechanism, the RSCC steady-state characteristics as well as the soft switching conditions under four methods are discussed. Then, the resonant characteristics of four methods are compared through state trajectory analysis. At last, the experiments are carried out to verify the correctness of theoretical analysis and feasibility of proposal method. The experimental results demonstrate that the proposed VFVDC-II avoids the voltage oscillation caused by narrow pulse and achieves the shortest transient response and the lowest peak resonant current at short circuit. Moreover, zero voltage switching is realized during turning on, which helps reduce the switching loss.

Abstracts:This article presents a methodology to control the internal energy balance of a modular multilevel cascade converter (MMCC) with distributed energy resources. The converter is characterized by a high voltage multi-terminal DC link connected to a three-phase MMCC with distributed photovoltaic arrays. Each modular arm structure is composed of bidirectional cascaded chopper cells with floating capacitors connected to the photovoltaic array through a DC/DC converter. Based on the power flow equations developed for the individual cells, a control methodology is applied to maintain the internal energy balance of the MMCC under power imbalance between the cells. The operation at different levels of irradiance is discussed to allow the operation with individual cells with zero energy generated from the photovoltaic array. Zero power cells are used to maintain three-phase output voltage and stable MMCC operation. Power balance between the arms is achieved through of the AC circulating currents in the MMCC arms without affecting the DC link and AC output currents. This converter topology and control methodology is suitable for hybrid renewable energy systems such as wind-solar power systems. Comprehensive experimental results are presented to validate operating principles and control methodology.

Abstracts:Parallel connected multi-MW three-level neutral point clamped power converters (3L-NPC) are widely preferred in large-rated variable speed pumped storage unit as it improves operating efficiency and reliability. During open circuit fault conditions&#x002F;gate drive malfunction, the entire unit must be shut down to ensure the safety of other healthier components. This article proposes reactive power circulation-based fault tolerance control strategies for grid side converter (GSC) during inner and outer switch fault conditions. In case of an open-circuit fault in outer switches, the normal sinusoidal currents are achieved in GSC by circulating reactive power among the healthy to faulty power converters. In case of an open-circuit fault in inner switches, the reactive power is circulated between healthy converters and a doubly fed induction machine (DFIM). In addition, neutral-point (NP) voltage oscillations are suppressed by injecting a zero-sequence signal into the reference voltage. The feasibility study and performance analysis of the proposed fault tolerance control strategies are carried out in the MATLAB&#x002F;Simulink 2014a environment for the 250 MW DFIM unit. Furthermore, experimental validation is carried out in 3HP DFIM scale-down laboratory prototype with three parallel connected converters.

Abstracts:Solid State Transformer (SST) is expected to be a key component in future smart grid systems, which integrates MVAC grid with LV DC/AC grid. For a three stage SST, resonant converter is a potential candidate as the DC-DC stage due to its high conversion efficiency. However, it exhibits an oscillation of 100 Hz (double line frequency) in the high frequency (HF) link current, which increases device current stress and conduction loss. This paper proposes an analytical model which determines the magnitude of this oscillation at different power factor operations. The obvious solution to minimize this oscillation is to keep a high value of capacitor at each MVDC bus, but it reduces the power density of the system. Therefore, this paper proposes an improved solution with a combination of inductor and capacitor at the LVDC bus. The proposed filter reduces the RMS value of the HF link current by 29&#x0025; at unity power factor operation. The dynamics of the proposed filter is also included in the control system design by deriving a dynamic equivalent circuit in this paper. The design is verified in a laboratory prototype of 8 kVA, 1.65 kV/300 V solid state transformer.

Abstracts:Wide variations in voltage conversion ratio and loading are the most important parameters to consider when designing off-board EV chargers to achieve high power density and efficiency. Dual phase shift (DPS) modulation provides a better way for dual active bridge (DAB) DC-DC converter operation when load side parameter variation is utmost important. To accomplish this, conventional DPS control is modified to ensure zero voltage switching (ZVS) across the entire load range despite wide variations in voltage conversion ratio. The designed control provides ZVS of all FETs as compared to the conventional DPS control over full loading range. For this, magnetizing inductance of HF isolation transformer is utilized and designed to shape the secondary side current for getting ZVS for both active legs. The light loading performance of the converter is improved with the bidirectional conduction angle control. The hybrid utilization of DPS control is incorporated with minimum peak current stress considerations. A Karush-Kuhn-Tucker (KKT) method based on Lagrange&#x0027;s multipliers is used for mathematical derivation of optimized solution of both control parameters. Performance of designed control is verified using experimental results for wide variation in battery terminal voltage. For validation, a 1250 W laboratory prototype is developed. A comparison of ZVS regions among the conventional and designed modulation technique, shows the effectiveness under wide voltage and loading scenarios.