Experimental comparison of single-phase active rectifiers for EV battery chargers

An experimental comparison of single-phase active rectifiers for electric vehicle (EV) battery chargers is presented and discussed. Active rectifiers are used in on-board EV battery chargers as front-end converters to interface the power grid aiming to preserve the power quality. In this paper, four topologies of active rectifiers are compared: traditional power-factor-correction; symmetrical bridgeless; asymmetrical bridgeless; and full-bridge full-controlled. Such comparison is established in terms of the requirements for the hardware structure, the complexity of the digital control system, and the power quality issues, mainly the grid current total harmonic distortion and the power factor. Along the paper these comparisons are presented and verified through experimental results. A reconfigurable laboratorial prototype of an on-board EV battery charger connected to the power grid was used to obtain the experimental results.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013. This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation - COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015- POCI- 01-0145-FEDER-016434.info:eu-repo/semantics/publishedVersio

Integrated on-board battery chargers for EVs based on multiphase machines and power electronics

The concept of integration of an electric vehicle (EV) drivetrain’s components into the charging process is not novel. It has been considered over the years in both industry and academia, which resulted in a number of published papers and patents in this area. Possibilities of charging from single-phase and three-phase mains were both considered. In the former group the charging power rating cannot exceed the limit set by the single-phase mains. Therefore, the topologies are characterised with low charging powers, leading to a long duration of the charging process. Although the topologies supplied form three-phase mains are capable of achieving fast charging, they were considered to a much lesser extent. The main reason is the undesirable torque production in machines integrated into the charging process during the battery charging, which is unavoidable when a three-phase machine of either synchronous or induction type is used. The thesis investigates integrated on-board battery chargers for electric vehicles (EVs) based on multiphase machines and multiphase power electronics. At present, EVs rely on three-phase systems for machine propulsion. However, recent advances in multiphase drive technology have firmly established their potential advantages over their three-phase counterparts for this application. One of the most notable features of multiphase drive systems is their excellent fault tolerance, which is highly desirable in EVs since it enables realisation of the requirement for “limp-home” operation in the propulsion mode, in case of a fault. The thesis demonstrates that multiphase drives have an additional major advantage over three-phase systems in vehicular applications, which is related to the aspect of battery charging. It shows a clear superiority of multiphase over three-phase systems in designing integrated charging topologies for EVs. In order to support the statement, the thesis provides a multitude of novel charging solutions that incorporate multiphase machines and multiphase power electronics into the charging process. The developed solutions could contribute to achieve significantly faster and cost-free (or at a minimum additional cost) on-board chargers in the near future. The thesis demonstrates how additional degrees of freedom that exist in multiphase systems can be conveniently utilised to achieve torque-free charging operation. Therefore, although three-phase currents flow through machines’ stator windings, they are not capable of producing a torque; thus the machines do not have to be mechanically locked. The principal advantage is that either very few or no new elements are required in order to realise the charging process. Thus savings are made with regard to cost and weight, and available spare space in the vehicle is increased. The novel integrated charging solutions, developed in the thesis, are based on primarily five-phase, asymmetrical and symmetrical six-phase, and asymmetrical and symmetrical nine-phase systems. Solutions with other phase numbers are also considered. Thus, in essence, all the possible phase numbers are encompassed by the research and the solutions are valid for both induction and synchronous machines. A common attribute of all discussed topologies is that they do not require a charger as a separate device since the charging function is performed by the drivetrain elements, predominantly a multiphase machine and an inverter. Further, each topology is capable of operating in both charging and vehicle-to-grid (V2G) mode. Three types of voltage sources are considered as a power supply for the charging process, namely single-phase, three-phase, and multiphase. For each supply type, and each phase number, viability of torque-free charging operation is theoretically assessed. Mathematical models of multiphase rectifiers are developed. For each topology equivalent scheme in the charging/V2G mode of operation is constructed. A control scheme, which aims at achieving unity power factor operation and complete suppression of the low order grid current harmonics, is designed for each solution. Finally, the validity of theoretical considerations and control algorithms for the developed solutions is experimentally assessed in charging, V2G, and propulsion mode of operation. Experimental performances of all discussed topologies are compared, and advantages and shortcomings of each solution are identified and discussed

Full Digital Control and Multi-Loop Tuning of a Three-Level T-Type Rectifier for Electric Vehicle Ultra-Fast Battery Chargers

The rapid development of electric vehicle ultra-fast battery chargers is increasingly demanding higher efficiency and power density. In particular, a proper control of the grid-connected active front–end can ensure minimum passive component size (i.e., limiting design oversizing) and reduce the overall converter losses. Moreover, fast control dynamics and strong disturbance rejection capability are often required by the subsequent DC/DC stage, which may act as a fast-varying and/or unbalanced load. Therefore, this paper proposes the design, tuning and implementation of a complete digital multi-loop control strategy for a three-level unidirectional T-type rectifier, intended for EV ultra-fast battery charging. First, an overview of the operational basics of three-level rectifiers is presented and the state-space model of the considered system is derived. A detailed analysis of the mid-point current generation process is also provided, as this aspect is widely overlooked in the literature. In particular, the converter operation under unbalanced split DC-link loads is analyzed and the converter mid-point current limits are analytically identified. Four controllers (i.e., dq-currents, DC-link voltage and DC-link mid-point voltage balancing loops) are designed and their tuning is described step-by-step, taking into account the delays and the discretization introduced by the digital control implementation. Finally, the proposed multi-loop controller design procedure is validated on a 30 kW, 20 kHz T-type rectifier prototype. The control strategy is implemented on a single general purpose microcontroller unit and the performances of all control loops are successfully verified experimentally, simultaneously achieving low input current zero-crossing distortion, high step response and disturbance rejection dynamics, and stable steady-state operation under unbalanced split DC-link loading

Model predictive control of a single-phase five-level VIENNA rectifier

Power converters and control strategies are very vital for the increasing sustainability of the power grid targeting smart grids. In these circumstances, it is proposed a novel single-phase five-level (SP5L) VIENNA rectifier digitally controlled by a model predictive control (MPC) with fixed switching frequency, which can be useful for a variety of applications with a robust current tracking. The proposed SP5L VIENNA rectifier is an advancement of the classical three-level VIENNA rectifier, also contributing to preserve power quality, and exhibiting the advantage of operating with more voltage levels at the expense of few additional switching devices. The proposed topology is introduced and correlated with the classical solutions of active rectifiers. The operation principle is introduced and used to describe the MPC, which is given in detail, as well as the necessary modulation strategy. The results were obtained for a set of various operating conditions, both in terms of reference of current and grid-side voltage, as well as in steady-state and transient-state, proving the benefits of the proposed SP5L VIENNA rectifier and the accurate and precise use of the MPC to control the grid-side current.This work has been supported by FCT -Fundacao para a Ciencia e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017, and by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT

A novel fixed switching frequency control strategy applied to an improved five-level active rectifier

A novel fixed switching frequency control strategy applied to an improved five-level active rectifier (iFLAR) is proposed. The operation with fixed switching frequency represents a powerful advantage, since the range of the produced harmonics is well identified, and it is possible to design passive filters to mitigate such harmonics. The experimental validation shows that the control strategy allows attaining an ac-side current with reduced total harmonic distortion and high power factor, which is an attractive influence for grid-connected electrical appliances. This contribution is even more relevant with the new paradigm of smart grids where higher levels of power quality are required. A theoretical analysis of the control strategy and the details of its implementation in a digital signal processor are presented. The control scheme and the developed iFLAR were experimentally confirmed using a laboratorial prototype, showing its benefits in terms of accuracy, reduced total harmonic distortion and high power factor.This work has been supported by COMPETE: POCI-010145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013. This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation – COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT – Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015 – POCI – 01–0145–FEDER–016434. Mr. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by the Portuguese FCT agency. This work is part of the FCT project 0302836 NORTE-01-0145-FEDER-030283.info:eu-repo/semantics/publishedVersio

Comprehensive analysis and cost estimation of five-level bidirectional converters for electric vehicles operation in smart cities context

A comprehensive analysis, comparison and cost estimation of five-level bidirectional converters for the electric vehicle (EV) operation in smart cities context is presented in this paper. Nowadays, five-level converters are widely used with success to interface between the power grid and renewable energy sources, as well as, to operate as motor drivers. Therefore, with the EV introduction into the power grids arises a new opportunity to use such five-level converters as interface between the power grid and the EV batteries, i.e., in on-board charger applications. Moreover, considering the future scenarios of smart grids and smart cities, the five-level bidirectional converters will be essential for the operation modes grid-to-vehicle (G2V, charging the batteries from the power grid) and vehicle-to-grid (V2G, returning energy from the batteries to the power grid). In this context, this paper presents an aggregation of the most important five-level bidirectional converter topologies that can be applied for on-board EV chargers in smart cities context. Along the paper it is presented a detailed description of the hardware and control algorithms of the five-level converters, and are also presented and explained simulation results performed under realistic operating conditions. Finally, it is presented the cost estimation for a real application considering the hardware requirements for each one of the converters.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013 and by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation Ǧ COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT Ǧ Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015-POCI-01-0145-FEDER-016434.info:eu-repo/semantics/publishedVersio

Sliding mode control of an innovative single-switch three-level active rectifier

This paper presents the sliding mode control (SMC) applied to an innovative active rectifier. This proposed active rectifier is constituted by a single-switch, and operates with three voltage levels, evidencing a set of advantages when compared with conventional approaches of power factor correction topologies. Taking into account the diversity of applications for this type of power converter, the SMC is used in order to obtain a robust current tracking. Since the active rectifier is controlled according to the ac grid-side current, the error between such current and its reference is determined, and by employing the SMC, this error is minimized during each sampling period with the objective of selecting the state of the single-switch. A comprehensive description about the SMC implementation, supported by the overall operation of the active rectifier, is presented throughout the paper. The obtained computational results for a set of different operating conditions, comprising significant power ranges and sudden variations, confirm the accurate application of the SMC when applied to the proposed single-switch three-level active rectifier. A comparison is also established with other current control, allowing to confirm the precise application of the SMC strategy.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work has been supported by FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017, and by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT