224 research outputs found
Bridgeless Step/Up Unity Power Factor Rectifier for High Voltage Applications
Power electronic devices with front- end rectifier are widely used in computer, communication and electric vehicle industries. These rectifiers are nonlinear in nature and generate current harmonics which pollute utility power. International harmonic standards (e.g., IEC 61000-3-2 and EN 61000-3-2) have been put in place to confine power pollution. These standards limit the current harmonics generated by loads to a specified threshold depending on load power and application. In other words, a high power factor is required.
Power supplies with active power factor correction (PFC) techniques are becoming necessary for many types of electronic equipment to meet the harmonic regulations and standards. However, classical PFC schemes have lower efficiency due to significant losses in the diode bridge. Several bridgeless topologies have been introduced to decrease diode bridge conduction losses. Most of the step-up PFC rectifiers utilize boost converter at their front end due to its natural PFC capability.
In this thesis, a new bridgeless PFC topology based on Cuk converter is presented. Similar to Cuk converter, the proposed topology offers several advantages in PFC applications, such as easy implementation of transformer isolation, inherent inrush current limitation during start-up and overload conditions, and lower electromagnetic interference (EMI). These advantages make the proposed topology a viable solution for high voltage DC loads such as electric vehicle battery charger.
Chapter III presents steady state analysis for the proposed rectifier. The rectifier is analyzed only during the positive half of the line frequency due to symmetry. Design procedure, simulation and measurements to verify the capability of the rectifier are presented in Chapter IV. Harmonics content and efficiency of the proposed rectifier versus conventional Cuk full bridge PFC rectifier are also presented
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
A High Frequency, High Efficiency, High Power Factor Isolated On-board Battery Charger for Electric Vehicles
In this paper, a high frequency, high efficiency and high power factor isolated on-board battery charger is proposed. The proposed topology includes two parts, AC/DC power factor correction (PFC) circuit unit and DC/DC converter unit. For the PFC circuit, SiC based totem-pole interleaved bridgeless PFC is selected, the diode bridge rectifier is eliminated. In addition, it can operate in continuous conduction mode (CCM) thanks to the low reverse recovery losses of the SiC MOSFETs. Besides, the interleaved technology minimizes the input current ripple. The DC/DC converter unit is composed of two LLC resonant converters sharing the same full-bridge inverter with constant switching frequency. The outputs of two LLC resonant converters are connected in series. One of the LLC resonant converter is operating at the resonant frequency, which is the highest efficiency operation point; while magnetic control is adopted for the second LLC resonant converter to fulfill the duty of providing closed-loop control for constant voltage (CV) and constant current (CC) charge modes. The proposed topology can achieve zero voltage switching (ZVS) for all primary switches and zero current switching (ZCS) for all secondary diodes during both CC and CV modes. Furthermore, the constant switching frequency is simplified the electromagnetic interference (EMI) filter design. Simulation studies for 3.3kW power level and 100kHz switching frequency are performed, the simulation results are presented to verify the feasibility and validity of the proposed topology
Soft-Switched Step-Up Medium Voltage Power Converters
With a ten-year average annual growth rate of 19 percent, wind energy has been the largest source of new electricity generation for the past decade. Typically, an offshore wind farm has a medium voltage ac (MVac) grid that collects power from individual wind turbines. Since the output voltage of a wind turbine is too low (i.e., typically 400 690 V) to be connected to the MVac grid (i.e., 20 40 kV), a heavy line-frequency transformer is used to step up the individual turbines output voltage to the MV level. To eliminate the need for bulky MVac transformers, researchers are gravitating towards the idea of replacing the MVac grid with a medium voltage dc (MVdc) grid, so that MV step-up transformers are replaced by MV step-up power electronic converters that operate at the medium frequency range with much lower size and weight.
This dissertation proposes a class of modular step-up transformerless MV SiC-based power converters with soft-switching capability for wind energy conversion systems with MVdc grid. This dissertation consists of two parts: the first part focuses on the development of two novel groups of step-up isolated dc-dc MV converters that utilize various step-up resonant circuits and soft-switched high voltage gain rectifier modules. An integrated magnetic design approach is also presented to combine several magnetic components together in the modular high voltage gain rectifiers. The second part of this dissertation focuses on the development of several three-phase ac-dc step-up converters with integrated active power factor correction. In particular, a bridgeless input ac-dc rectifier is also proposed to combine with the devised step-up transformerless dc-dc converters (presented in the first part) to form the three-phase soft-switched ac-dc step-up voltage conversion unit. In each of the presented modular step-up converter configurations, variable frequency control is used to regulate the output dc voltage of each converter module. The operating principles and characteristics of each presented converter are provided in detail. The feasibility and performance of all the power converter concepts presented in this dissertation are verified through simulation results on megawatts (MW) design examples, as well as experimental results on SiC-based laboratory-scale proof-of-concept prototypes
Totem-pole bridgeless boost PFC rectifier using series-parallel resonant network
A new series-parallel resonant bridgeless boost (SPBBR) power factor correction (PFC) rectifier is proposed in this paper. It is based on a totem-pole bridgeless boost (TPBLB) configuration which allows bi-directional current to flow during resonance to provide soft-switching for all semiconductor devices. Therefore, no additional active switch is needed. The resonant is produced by a resonant network which is placed before the output capacitor. A detailed analysis of the converter operation and control is presented. Design considerations and parameter values determination are also given. Simulation results is used to verify the theoretical analysis of the SPBBR
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