Ali Ramezani
PhD Electrical Engineering
Publications
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In this paper, a new five-level voltage source inverter is proposed for high-power applications. The proposed inverter is competitive in performance, component count, and control complexity compared with the conventional multilevel inverters. Also, the proposed inverter has a simple structure as it does not have any dc-link neutral points, unlike hybrid converters. Furthermore, the proposed topology can be connected in back-to-back due to the presence of a common dc-link. Also, there is no need of isolated dc source and complex phase-shifting transformer. In addition, a simple voltage balancing approach based on level-shifted carrier pulse width modulation scheme is proposed to control the flying capacitor voltages. The proposed approach will make use of the redundancy switching states to balance the flying capacitor voltages in the proposed inverter. The steady-state and transient performance of the proposed five-level voltage source inverter and voltage balancing approach is validated through MATLAB simulation studies at different power factors and modulation indices. The simulation studies are further evaluated experimentally by a scaled-down laboratory prototype. Furthermore, the feasibility of the proposed topology is analyzed under the performance indices of voltage and current harmonic distortion, flying capacitor voltage ripples, converter power losses, and converter efficiency.
Optimized Electric Vehicle Wireless Chargers with Reduced Output Voltage Sensitivity to Misalignment
Journal paperIEEE Journal of Emerging and Selected Topics in Power Electronics
In this paper, an optimized design of wireless charger for Electric Vehicle (EV) applications is presented to reduce the misalignment effect on the output voltage and efficiency of the wireless charger system. The existing methods to regulate the output voltage require either the communication link between the EV and charging station to control the charging station converter or a DC-DC converter on the EV. This paper provides a solution to optimize compensation networks to reduce output voltage sensitivity with respect to misalignment and improve the efficiency of the overall system. Four topologies are studied in details and optimized compensation network is developed for each topology. The compensation networks are also designed to satisfy Zero Voltage Switching (ZVS) for a wide range of misalignments. The performance of the optimized circuits is compared in detail in terms of efficiency, output voltage performance, size of the resonant network, and power loss distribution. This paper also shows that LCCLCC and LCC-Series are the best candidates for operation in a wide range of misalignments. A 500W/ 85kHz prototype charger is built for each topology and the performance of the optimized resonant networks are evaluated experimentally.
A New Wireless EV Charging System with Integrated DC-DC Magnetic Element
Journal paper IEEE Transactions on Transportation Electrification, 2019
A DC-DC conversion stage is commonly used for a wireless electric vehicle (EV) battery charging system. The DC-DC stage requires a bulky inductor to charge the battery either in constant voltage (CV) or constant current (CC) modes. In this paper, a new magnetic structure for a wireless EV charging system is proposed to integrate the DC-DC inductor with the receiver coil on the vehicle side. The proposed structure utilizes the existing core material in the wireless power circuit pads and provides a more compact design and efficient wireless charger system for EV applications. The proposed magnetic structure is modeled in 3D, FEA results are presented and compared with measurements. Moreover, the effect of the proposed integration method on the wireless charging system performance is investigated and the results are presented. A 3.3 kW/85 kHz wireless charger is optimally designed and built to evaluate the proposed configuration. Furthermore, the efficiency and output voltage of the wireless charging system are also measured and compared with the simulation results. The simulation and experimental results show the performance of the proposed structure.
A New 5–Level Voltage Source Inverter
Conference paper2019 IEEE Applied Power Electronics Conference and Exposition (APEC)
This paper presents a new 5-level voltage source inverter for medium-voltage, high-power applications. The proposed topology uses a less number of active components in comparison with classical 5-level topologies. In the proposed inverter, the flying capacitors voltage needs to be regulated at 1/4 of the net dc-link voltage to generate a 5-level voltage waveform at the output. In order to control the output voltage and flying capacitors voltage, a space vector modulation (SVM) scheme is developed. This technique utilizes the redundancy switching states to generate a desired output voltage and regulate the flying capacitors voltage at their nominal value, simultaneously. The steady-state and transient performance of the proposed inverter are verified through MATLAB simulations.
High Misalignment Tolerant Wireless Charger Designs for EV Applications
Conference paper2019 IEEE Transportation Electrification Conference and Expo (ITEC)
This paper presents a new optimal design of the resonant networks in terms of output voltage sensitivity respect to misalignment. For both stationary and dynamic electric vehicle charging applications, the misalignment which is the variation of mutual coupling is inevitable. The variation of coupling factor affects the output voltage and efficiency of the wireless charger system. Therefore, output voltage sensitivity respect to the variations of the coupling factor is one of the major system performance indexes. The other main parameter is the efficiency of the wireless charger system in a wide range of coupling variations. In this paper, two different objective functions are defined to address the desired design requirements. Moreover, a framework for the design and optimization of the compensation topologies is presented. Efficiency and output voltage of each topology is compared for each objective function. Finally, the best candidates for each case are selected.
A Dynamic Wireless Charging System with a Robust Output Voltage Respect To Misalignment
Conference paper2019 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW), London, UK
In a dynamic wireless charging application, the mutual inductance of the secondary side coil and primary side coils is a time-dependent variable. Therefore, the induced voltage on the vehicle side coil will be changed by the variation of the mutual inductance. In this paper, the effect of the coupling factor (k) variation on the output voltage of an LCC-S compensated topology is analyzed and sensitivity function is defined. In order to reduce the effect of the variation of k on the output voltage and efficiency, an optimization problem is defined. Moreover, to achieve high efficiency for a wide range of k, desired constraints are considered in the problem. As a case study, a 500 W/85 kHz system is optimized and variation of the output voltage under different coupling factors are simulated. The effectiveness of the design is validated by experimental measurements.
Optimized LCC-Series Compensated Resonant Network for Stationary Wireless EV Chargers
Journal paperIEEE Transactions on Industrial Electronics, 2018
In this paper, an optimal design procedure for LCC-series compensation network is proposed for a stationary wireless Electric Vehicle (EV) charger. Main focus of this paper is to optimize the resonant network suitable for a wide range of operation from no-load to full power operation. The conventional methods only consider the full load condition to design the resonant network; in contrast, the proposed method employs a Time-Weighted Average Efficiency (TWAE) for different coupling conditions to achieve high efficiency over a wide load range including light-load and no-load operation. The resonant network is tuned to realize Zero Voltage Switching (ZVS) for the primary side inverter. Moreover, a Finite Element Analysis (FEA) is performed to calculate self and mutual inductances as well as core losses for magnetic couplers. In order to validate the feasibility of the proposed design, a 1 kW/85 kHz prototype with circular magnetic couplers is implemented. According to simulations and experiments, flat profiles for both efficiency and output voltage against output power variations are achieved. Experimental results demonstrate a 94.8% peak efficiency for the full-load operating.
A Wireless Power Transfer System with Reduced Output Voltage Sensitivity for EV Applications
Conference paper2018 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (Wow)
This paper presents a design procedure for LCC-Series compensation network for Wireless Power Transfer (WPT) system for Electric Vehicle (EV) applications. DC-link voltage variations is common in the gird connected power converters due to using diode rectification. These voltage variations could be reflected to the load side in a WPT system. The main focus of this paper is to design the resonant circuit to minimize the output voltage sensitivity respect to the input voltage variations. The resonant network is also tuned to realize Zero Voltage Switching (ZVS) for the primary side inverter to minimize the switching losses. Furthermore, a Finite Element Analysis (FEA) is performed to calculate self and mutual inductances as well as core losses for magnetic couplers. In order to validate the feasibility of the proposed design, a 22 kW/85 kHz WPT system with circular magnetic couplers is simulated. According to the frequency domain analysis the proposed circuit has 32% less sensitivity to the input voltage variations in comparison with the conventional design.
High efficiency wireless power transfer system design for circular magnetic structures
Conference paper2016 7th Power Electronics and Drive Systems Technologies Conference (PEDSTC), Tehran, Iran, 2016, pp. 565-570.
In this paper, a new approach is proposed to achieve maximum coupling coefficient for the windings in circular Wireless Power Transfer (WPT) systems. The designed magnetic structure has the maximum magnetic coupling coefficient in a specific air gap in order to maximize the system efficiency. Series resonant compensator network is analyzed in frequency domain and proper operating point is selected to achieve constant voltage gain in different loads. This system controls output voltage through a closed loop control via controlling inverter’s duty cycle. The design procedure is explained for a 5 kW system. This system can transfer power from 100mm to 200mm air gap by resonant network and magnetic circular coupling that has a 480mm diameter. Efficiency results for output power in various air gaps are presented, where efficiency of the nominal load for 150mm air gap is 93%.