This paper provides a comprehensive review and analyses on the state-of-the-art and future trends for high-power conductive on-board chargers (OBCs) for electric vehicles. To provide a global context, a summary of global charging standards and electric vehicle (EV) related trends are presented, which demonstrates momentum toward the OBCs with higher power rating. High-power OBCs are either unidirectional or bidirectional, and they have either an integrated or non-integrated system architecture. Non-integrated high-power OBCs are studied both from industry and academia, and the former are used to illustrate the current state of the art. The latter are classified on the basis of the converter design approach, studied for their principle of operation, and compared over power density, weight, efficiency, and other metrics. In addition to non-integrated OBCs, recent advancements in propulsion-machine integrated OBC solutions are also presented. Other integrated OBC techniques, such as system integration with the EV's auxiliary power module and wireless charging systems, are also discussed. Finally, future charging strategies and functionalities in charging infrastructures are addressed, and global OBC trends are summarized.

Global Trends in High-Power On-Board Chargers for Electric Vehicles

Vehicle-to-Grid (V2G) is a promising technology that allows the batteries of idle or parked electric vehicles (EVs) to operate as distributed resources, which can store or release energy at appropriate times, resulting in a bidirectional exchange of power between the ac grid and the dc EV batteries. This bidirectional exchange of power is realized using bidirectional power electronic converters that connect the grid with the EV battery. Most research on bidirectional converters for V2G applications focuses on using two dedicated power conversion stages – a bidirectional ac-dc conversion stage that helps in power factor correction, followed by a bidirectional dc-dc conversion stage that provides voltage matching. However, a single bidirectional ac-dc conversion stage can also facilitate V2G and grid-to vehicle (G2V) active power transfers. This paper reviews and compares the various bidirectional ac-dc and dc-dc converter topologies that facilitate V2G and G2V active power flows. Moreover, the paper discusses the various classes of charger/discharger systems reported for V2G applications, like on-board/off-board, integrated/non-integrated and conductive/inductive, and a comparative statement is made based on certain proposed criteria. Further, the current trends in the application of wide band-gap devices in high power-dense V2G capable converters and integration of renewable energy sources into EV charging/discharging infrastructures have also been discussed.

Review of power electronics in vehicle-to-grid systems

A three-phase onboard charger, integrated with the propulsion system of a plug-in electric vehicle, is presented. It is constructed by connecting an add-on three-phase power electronics interface to the propulsion system. The propulsion motor is utilized as a coupled DC inductor for the charger. The charging power level of the proposed charger could be as high as that of the propulsion system. The charger topology is capable of three-phase power factor (PF) correction and battery voltage/current regulation. Detailed analyses of the circuit operation and modeling of the circuit are presented. Experimental results of a 3.3-kW three-phase integrated charger, using a permanent magnet synchronous machine (PMSM), are provided. A nearly unity PF and 4.77% total harmonic distortion are obtained with a maximum efficiency of 92.6%.

A Three-Phase Integrated Onboard Charger for Plug-In Electric Vehicles

This paper presents an innovative technique for synchronous rectification in a bidirectional CLLC converter with an integrated transformer for plug-in electric vehicle applications. To improve efficiency and power density, the integrated transformer is introduced and simulated using finite element analysis. In addition, synchronous rectification is implemented by controlling the turn- on and turn- off timings based on the phase difference between primary gate pulse and secondary resonant current. Furthermore, a simplified closed-loop design is discussed and implemented on a digital signal processor (TMS320F28335). The effectiveness of the control loop is verified through a 3.3 kW proof-of-concept prototype with peak efficiency of 97.5%.

Bi-Directional CLLC Converter With Synchronous Rectification for Plug-In Electric Vehicles

The recognition of driver's braking intensity is of great importance for advanced control and energy management for electric vehicles. In this paper, the braking intensity is classified into three levels based on novel hybrid unsupervised and supervised learning methods. First, instead of selecting threshold for each braking intensity level manually, an unsupervised Gaussian mixture model is used to cluster the braking events automatically with brake pressure. Then, a supervised Random Forest model is trained to classify the correct braking intensity levels with the state signals of vehicle and powertrain. To obtain a more efficient classifier, critical features are analyzed and selected. Moreover, beyond the acquisition of discrete braking intensity level, a novel continuous observation method is proposed based on artificial neural networks to quantitative analyze and recognize the brake intensity using the prior determined features of vehicle states. Experimental data are collected in an electric vehicle under real-world driving scenarios. Finally, the classification and regression results of the proposed methods are evaluated and discussed. The results demonstrate the feasibility and accuracy of the proposed hybrid learning methods for braking intensity classification and quantitative recognition with various deceleration scenarios.

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Hybrid-Learning-Based Classification and Quantitative Inference of Driver Braking Intensity of an Electrified Vehicle

This paper proposes a new methodology to control a three-phase boost power factor correction (PFC) using a single dc output voltage sensor. Typically, a PFC control technique requires measurement from five independent sensors, i.e., two input voltages, one output dc voltage, and two input phase currents. Elimination of four sensors in the control system of a PFC converter is theoretically feasible and implementable without compromising stability and power quality of the converter, as analyzed and presented in this paper. The proposed control technique uses the ripple information of the measured dc-link voltage, converter dynamics, and switching states at a preceding sample in order to estimate the present state of four other unknown state variables and, thus, establishes the control method. A 2.2-kW experimental prototype of a three-phase boost PFC is developed and tested to verify the accuracy and applicability of the proposed control logic at different line and load conditions. According to the experimental measurements, conversion efficiency more than 98%, total harmonic distortion as low as 4.3%, and an output voltage ripple of ±2% are achieved at 2.2-kW output power.

Control of a Three-Phase Boost PFC Converter Using a Single DC-Link Voltage Sensor

This paper presents a methodology to control a phase-shifted full-bridge (PSFB) dc/dc converter with variable switching frequency, as a function of the output load power. The main objective of such control is to maximize the conversion efficiency at a wide range of load power levels. By tuning the switching frequency, the net phase of the input impedance of the converter can be manipulated, and thus, at the lower load power operation, the net input impedance can be made highly inductive to achieve zero-voltage switching (ZVS) at the primary-side switches. This paper proposes an efficiency maximization method, which derives an optimum switching frequency based on the load power from a loss-minimization model. In addition, a state-feedback-based control method is proposed for maintaining a tight dynamic regulation over the converter output under a load transient. A 6-kW laboratory prototype of the PSFB converter is developed and designed to validate the proposed control algorithm. The experimental results show a conversion efficiency of 98% at full load and output voltage ripple of ±1%, while ensuring ZVS at all operating points between 100 W and 6 kW.

Variable-Switching-Frequency State-Feedback Control of a Phase-Shifted Full-Bridge DC/DC Converter

This paper proposes an input voltage sensorless control algorithm for three-phase active boost rectifiers. Using this approach, the input ac-phase voltages can be accurately estimated from the fluctuations of other measured state variables and preceding switching state information from converter dynamics. Furthermore, the proposed control strategy reduces the input current harmonics of an ac–dc three-phase boost power factor correction (PFC) converter by injecting an additional common-mode duty ratio term to the feedback controllers’ outputs. This additional duty compensation term cancels the unwanted input harmonics, caused by the floating potential between ac source neutral and dc link negative, without requiring any access to the neutral point. A 6-kW (continuous power)/10-kW (peak power) three-phase boost PFC prototype using SiC-based semiconductor switching devices is designed and developed to validate the proposed control algorithm. The experimental results show that an input power factor of 0.999 with a conversion efficiency of 98.3%, total harmonic distortion as low as 4%, and a tightly regulated dc-link voltage with 1% ripple can be achieved.

Input Voltage Sensorless Duty Compensation Control for a Three-Phase Boost PFC Converter

This paper proposes a systematic approach to model and optimize an integrated transformer for on-board chargers in electric vehicles. The proposed approach includes a comprehensive transformer loss model with accurate electromagnetic description of leakage inductance and optimization process. The multiobjective optimization using genetic algorithm is presented to optimize the performance-space variables, i.e., volume, weight, and losses, by appropriate selections of design-space parameters, i.e., winding specifications and core candidacies. Four sets of integrated transformers are optimally designed and compared in terms of the theoretical analyses; finite-element analyses and experimental performance. As verification to the proof-of-concept, the integrated transformers are implemented and tested on a 3.3-kW on-board charger prototype. It has been shown that the measured losses agree with the theoretical computation. The peak efficiency of CLLC stage with the optimal selection of transformer reaches 98.2%, achieving efficiency enhancement and temperature improvement in comparison to other feasible candidates.

Ayan Mallik

Papers

Bi-Directional CLLC Converter With Synchronous Rectification for Plug-In Electric Vehicles

Control of a Three-Phase Boost PFC Converter Using a Single DC-Link Voltage Sensor

Variable-Switching-Frequency State-Feedback Control of a Phase-Shifted Full-Bridge DC/DC Converter

Input Voltage Sensorless Duty Compensation Control for a Three-Phase Boost PFC Converter

Modeling and Optimization of an Integrated Transformer for Electric Vehicle On-Board Charger Applications