Pritam Das

A Novel ZVZCS Full-Bridge DC/DC Converter Used for Electric Vehicles

This paper presents a novel ZVZCS full-bridge DC/DC converter, which is able to process and deliver power efficiently over very wide load variations. The proposed DC/DC converter is part of a plug-in AC/DC converter used to charge the traction battery (high voltage battery) in an electric vehicle. The key challenge in this application is operation of the full-bridge converter from absolutely no-load to full-load conditions. In order to confirm reliable operation of the full-bridge converter under such wide load variations, the converter should not only operate with soft-switching from full load to no-load condition with satisfactory efficiency for the full range of operation, but also the voltage across the output diode bridge needs to be clamped to avoid any adverse voltage overshoots arising during turn-OFF of the output diodes as commonly found in regular full bridge converters. In order to achieve such stringent requirements and high reliability, the converter employs a symmetric passive near lossless auxiliary circuit to provide the reactive current for the full-bridge semiconductor switches, which guarantees zero voltage switching at turn-ON times for all load conditions. Moreover the proposed topology is based on a current driven rectifier in order to clamp the voltage of the output diode bridge and also satisfy ZVZCS operation of the converter resulting in superior efficiency for all load conditions. In this paper operation of the converter is presented in detail followed by analytical design procedure. Experimental results provided from a 3KW prototype validate the feasibility and superior performance of the proposed converter.

A Comparative Study of a New ZCS DC–DC Full-Bridge Boost Converter With a ZVS Active-Clamp Converter

Pulse width modulation (PWM) current-fed full-bridge dc-dc boost converters are typically used in applications where the output voltage is considerably higher than the input voltage. In this paper, a comparison is made between two converter topologies of this type-the standard zero-voltage switching (ZVS) active-clamp topology and a new zero-current switching (ZCS) topology. This paper begins with a review of the operation of the ZVS active-clamp converter and that of ZCS converters in general; the advantages and disadvantages of each approach are stated. A new ZCS-PWM current-fed dc-dc boost full-bridge converter is then introduced. The operation of the new converter is explained and analyzed, and a procedure for the design of its key components is given and demonstrated with an example. Experimental results obtained from a prototype of a ZVS active-clamp converter and the new ZCS converter are presented. Finally, a comparison of the performance of the two converters is made and conclusion based on this comparison is stated.

A Nonisolated Bidirectional ZVS-PWM Active Clamped DC–DC Converter

Power electronic converter systems for applications such as telecom, automotive, and space can have dc voltage buses that are backed up with batteries or supercapacitors. These batteries or supercapacitors are connected to the buses with bidirectional dc-dc converters that allow them to be discharged or charged, depending on the operating conditions. Bidirectional dc-dc converters may be isolated or nonisolated depending on the application. A new soft-switched bidirectional dc-dc converter will be proposed in this letter. The proposed converter can operate with soft switching, a continuous inductor current, fixed switching frequency, and the switch stresses of a conventional pulsewidth modulation converter regardless of the direction of power flow. These features are due to a very simple auxiliary active clamp circuit that is operational regardless of the direction of power flow. In the letter, the operation of the converter will be discussed and its feasibility will be confirmed with experimental results obtained from a prototype.

Analysis and Design of a Nonisolated Bidirectional ZVS-PWM DC–DC Converter With Coupled Inductors

A new zero-voltage-switched bidirectional dc-dc converter with coupled inductors is proposed in the paper. The proposed converter can operate with a steep conversion ratio, soft switching, a continuous inductor current, and fixed switching frequency. It can also operate with the switch stresses of a conventional pulsewidth-modulation-tapped/coupled-inductor converter regardless of the direction of power flow and without any voltage spikes across the switches during turn-OFF. These features are due to a very simple auxiliary circuit that is operational regardless of the direction of power flow and absorbs energy from the leakage inductance of the coupled inductors during switch turn-OFF. In the paper, the operation and design of the converter are discussed and its feasibility is confirmed with experimental results obtained from a prototype.

A Comparative Study of Zero-Current-Transition PWM Converters

Zero-current-transition (ZCT) PWM converters are conventional PWM converters that use an active auxiliary circuit to turn off the main power switch with zero current switching. In the paper, the general operating principles behind all ZCT-PWM converters are reviewed, and the operation and properties of specific boost converters are discussed. The strengths and weaknesses of each converter are stated and a new and improved ZCT-PWM boost converter is proposed and compared with the other converters. Experimental results that confirm the superior performance of the new proposed converter are presented

A New Control Approach Based on the Differential Flatness Theory for an AC/DC Converter Used in Electric Vehicles

AC/DC converters used for charging high-voltage battery banks in electric vehicles from the utility mains, generally, consist of two stages. The first is a power factor correction (PFC) ac/dc boost converter to reduce the input current harmonics injected to the utility grid and convert input ac voltage to an intermediate dc voltage (dc-bus voltage). The second part is an isolated dc/dc converter for providing high-frequency galvanic isolation. This paper presents a novel intelligent control law based on the differential flatness theory to control the input power of the PFC stage which is determined by the charging characteristics of the high-energy battery bank, instead of controlling the intermediate dc-bus voltage at a constant value as done in the conventional controller. Application of the proposed control law to such an ac/dc converter helps improve the dynamic behavior of the input PFC stage compared to the conventional controller and also achieve load adaptive regulation of the intermediate dc-bus voltage. Such load-adaptive dc-bus voltage regulation allows the dc/dc full-bridge converter to operate optimally from no-load to full-load conditions unlike the conventional controller with constant dc-bus voltage which forces the dc/dc full-bridge to operate with very low duty ratios at no-load conditions. Experimental results from a 3-kW ac/dc converter are presented in the paper to validate the proposed control method. The improved converter performance and increased efficiency as compared to the conventional control method proves the superiority of the proposed technique.

A Nonlinear Optimal Control Approach Based on the Control-Lyapunov Function for an AC/DC Converter Used in Electric Vehicles

AC/DC converters used in electric vehicles generally consist of two stages: an input power factor correction (PFC) boost AC/DC stage that converts input AC voltage to an intermediate DC voltage and reduces input current harmonics injected to the grid, and a DC/DC converter that provides high-frequency galvanic isolation. Since there is a low-frequency ripple (second harmonic of the input ac line frequency) in the output voltage of the PFC AC/DC boost converter, the voltage loop in the conventional control system typically has a very low bandwidth to avoid distorting the input current waveform. This causes the conventional PFC controller to have slow dynamics against load variations. This paper presents a new control approach that regulates the input power of the converter instead of the output voltage by using an optimal nonlinear control approach based on the Control-Lyapunov Function (CFL). In this paper, it is shown that the proposed controller is able to eliminate the low bandwidth voltage control loop in the conventional PFC controller, thus allowing the front-end AC/DC boost PFC converter to operate with faster dynamic response than with the conventional controller approach. Experimental results from a 3 kW AC/DC converter are presented in the paper to validate the proposed control method and its superior performance.

An Improved AC–DC Single-Stage Full-Bridge Converter With Reduced DC Bus Voltage

A new ac-dc single-stage voltage-fed pulsewidth-modulation (PWM) full-bridge converter is proposed in this paper. The converter can simultaneously perform input power factor correction and dc-dc conversion using conventional phase-shift PWM and can maintain a primary-side dc bus voltage of less than 450 V even at a high input line voltage of 265 Vrms. This is a combination of features that few, if any, other converters of the same type have. The proposed converter has these features due to the novel implementation of an asymmetrical auxiliary transformer winding that is placed in series with the input inductor and acts as a boost switch. In this paper, the operation of the proposed converter is explained in detail, its outstanding features are discussed, and a detailed design procedure is given and demonstrated with an example. Experimental results that confirm the feasibility of the converter and its ability to meet IEC1000-3-2 Class D standards for electrical equipment are also presented in this paper.

Analysis and Design of a New AC–DC Single-Stage Full-Bridge PWM Converter With Two Controllers

Single-phase power factor correction (PFC) ac-dc converters are widely used in the industry for ac-dc power conversion from single phase ac-mains to an isolated output dc voltage. Typically, for high-power applications, such converters use an ac-dc boost input converter followed by a dc-dc full-bridge converter. A new ac-dc single-stage high-power universal PFC ac input full-bridge, pulse-width modulated converter is proposed in this paper. The converter can operate with an excellent input power factor, continuous input and output currents, and a non-excessive intermediate dc bus voltage and has reduced number of semiconductor devices thus presenting a cost-effective novel solution for such applications. In this paper, the operation of the proposed converter is explained, a steady-state analysis of its operation is performed, and the results of the analysis are used to develop a procedure for its design. The operation of the proposed converter is confirmed with results obtained from an experimental prototype.

A Nonlinear Controller Based on a Discrete Energy Function for an AC/DC Boost PFC Converter

AC/DC converter systems generally have two stages: an input power factor correction (PFC) boost ac/dc stage that converts input ac voltage to an intermediate dc voltage while reducing the input current harmonics injected to the grid, followed by a dc/dc converter that steps up or down the intermediate dc-bus voltage as required by the output load and provides high-frequency galvanic isolation. Since a low-frequency ripple (second harmonic of the input ac line frequency) exists in the output voltage of the PFC ac/dc boost converter due to the power ripple, the voltage loop in the conventional control system must have a very low bandwidth in order to avoid distortions in the input current waveform. This results in the conventional PFC controller having a slow dynamic response against load variations with adverse overshoots and undershoots. This paper presents a new control approach that is based on a novel discrete energy function minimization control law that allows the front-end ac/dc boost PFC converter to operate with faster dynamic response than the conventional controllers and simultaneously maintain near unity input power factor. Experimental results from a 3-kW ac/dc converter built for charging traction battery of a pure electric vehicle are presented in this paper to validate the proposed control method and its superiority over conventional controllers.