Majid Pahlevaninezhad

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 Load Adaptive Control Approach for a Zero-Voltage-Switching DC/DC Converter Used for Electric Vehicles

This paper presents a load adaptive control approach to optimally control the amount of reactive current required to guarantee zero-voltage switching (ZVS) of the converter switches. The proposed dc/dc converter is used as a battery charger for an electric vehicle (EV). Since this application demands a wide range of load variations, the converter should be able to sustain ZVS from full-load to no-load condition. The converter employs an asymmetric auxiliary circuit to provide the reactive current for the full-bridge semiconductor switches, which guarantees ZVS at turn-on times. The proposed control scheme is able to determine the optimum value of the reactive current injected by the auxiliary circuit in order to minimize extra conduction losses in the power MOSFETs, as well as the losses in the auxiliary circuit. In the proposed approach, the peak value of the reactive current is controlled by controlling the switching frequency to make sure that there is enough current to charge and discharge the snubber capacitors during the deadtime. In addition, some practical issues of this application (battery charger for an EV) are discussed in this paper. Experimental results for a 2-kW dc/dc converter are presented. The results show an improvement in efficiency and better performance of the converter.

Analysis and Implementation of a Single-Stage Flyback PV Microinverter With Soft Switching

This paper presents a novel zero-voltage switching (ZVS) approach to a grid-connected single-stage flyback inverter. The soft-switching of the primary switch is achieved by allowing negative current from the grid side through bidirectional switches placed on the secondary side of the transformer. Basically, the negative current discharges the metal-oxide-semiconductor field-effect transistors output capacitor, thereby allowing turn on of the primary switch under zero voltage. To optimize the amount of reactive current required to achieve ZVS, a variable-frequency control scheme is implemented over the line cycle. In addition, the bidirectional switches on the secondary side of the transformer have ZVS during the turn- on times. Therefore, the switching losses of the bidirectional switches are negligible. A 250-W prototype has been implemented to validate the proposed scheme. Experimental results confirm the feasibility and superior performance of the converter compared with the conventional flyback inverter.

Composite Nonlinear Feedback Control and Stability Analysis of a Grid-Connected Voltage Source Inverter With

In this paper, the stability analysis of a grid-connected voltage source inverter with an LCL filter is presented. The Poincaré map is used to analyze the stability of the system from a geometric point of view and provides a better understanding of the system performance. In addition, a composite nonlinear feedback (CNF) control is proposed in order to improve the transient and steady-state performance of the control system. Simulation and experimental analysis verify the validity of the analysis and also show the superiority of the CNF-based controller compared to the conventional proportional-resonant controller during transients and steady-state operation.

LCL

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.

Filter

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.

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

Power factor correction (PFC) is an essential part of ac/dc converters in order to improve the quality of the current drawn from the utility grid. The PFC closed-loop control system requires a precise measurement of the boost inductor current in order to tightly shape the input current. Current sensors are widely used in the PFC closed-loop control system to measure the boost inductor current. Current sensors introduce delay and noise to the control circuitry. Also, they significantly contribute to the overall cost of the converter. Therefore, they make the implementation of the PFC converter complicated and costly. Current sensorless control techniques can offer a cost-effective solution for various applications. The unique structure of the boost PFC converter makes it challenging to robustly estimate the inductor current due to the nonlinear structure of the converter. Also, it is shown in this paper that the system loses observability at some singular operating points, which makes the observer design more challenging. In addition, the load value is unknown in most applications. Thus, the observer should be able to estimate the inductor current in the presence of uncertainties in the load and other parameters. This paper presents an adaptive nonlinear observer for the boost PFC, which is able to accurately estimate the inductor current. The adaptive structure of the converter allows the robust and reliable performance of the observer in the presence of parameter uncertainties, particularly load variations. Also, an auxiliary compensation is integrated into the observer to circumvent the singular operating points and provide a precise estimation for the entire range of operation. Experimental results are presented to verify the feasibility of the proposed sensorless control approach.

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

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.

ADAPTIVE NONLINEAR CURRENT OBSERVER FOR BOOST PFC AC/DC CONVERTERS

Presently, there is an immense impetus in the automotive industry to develop plug-in electric vehicles (PIEVs) to reverse the ever increasing green house gas emissions from fossil fuels and depleting fossil fuel resources. High-frequency ac-dc converters with an isolated output are one of the essential building blocks for transferring power from utility mains to the traction battery packs which store energy for propelling the EV. Generally, the ac/dc converters used in EVs include a PFC stage at the input side and an isolated dc/dc converter at the battery side. Due to the switching nature of the converter, electromagnetic compatibility (EMC) of these converters is an essential requirement, to ensure not only its own operation but also the safe and secure operation of surrounding electrical equipment. EVs possess a lot of sophisticated electronic circuits in the vicinity of the battery charging power converters. Thus, strict EMC standards of the on-board power converters must be met according to the CISPR 12 or SAEJ551/5 relevant EMC standards. Conventional passive filters used for EMI mitigation in power converters, comes at the expense of cost, size and weight, power losses, and printed circuit board real estate. In this paper, an electromagnetic interference (EMI) filter embedded into the main high-frequency planar transformer used in the dc/dc converter is proposed as a very cost-effective and efficient solution for EVs. The proposed structure is able to significantly suppress the common-mode (CM) EMI noise generated in the dc/dc converter. Experimental results have been obtained from a 3-kW prototype in order to prove the feasibility and performance of the proposed EMI filter. The results show that the proposed embedded EMI filter can effectively suppress the CM noise particularly for high switching frequency power converters. The proposed structure can be a very simple and cost-effective EMI filtering solution for future PIEVs.

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

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.