Tarak Saha

A novel position sensorless power transfer control of lumped coil-based in-motion wireless power transfer systems

Traditional in-motion (dynamic) wireless power transfer (WPT) is based on elongated power transmitting tracks. It suffers from low efficiency, having complex and not fully utilized magnetic structures, among other drawbacks. In the case of lumped transmitter coils commeasurable in size with the receiver coil, which has been recently proposed for the in-motion WPT, the power transfer is intermittent with variable power transfer efficiency. Although it is characterized by a very high efficiency when the pads are aligned (>90%), high efficiency of the overall energy transfer will be maintained only if the transmitter coil is energized in a proper, synchronized manner with respect to the position of the receiver coil. Considering the actual state of communication and sensing technology, identification of the actual position of the receiver pad in realtime would be a very challenging task and no reliable solution has been proposed so far in the WPT arena. This paper provides a thorough analysis of the power transfer characteristics of an in-motion system with lumped coils, meaning the analytic description of time-varying power transfer and efficiency profiles. Possible compensation topologies are studied and the most suitable structure is selected. A control algorithm is proposed to control the amount of energy transferred to the receiver, without the utilization of any position detection system. The energizing profiles are designed to maximize energy efficiency, while at the same time transferring the required amount of energy to the receiver. The control algorithm is analyzed by using analytical modeling of the WPT system and then verified by MATLAB-Simulink simulation tool. A scaled-down hardware prototype is developed and employed to test the operation of the control algorithm for different transferred energies.

Control of series connected resonant converter modules in constant current dc distribution power systems

Applications such as undersea power prefer constant current dc distribution in a series trunk cable connection over dc voltage distribution in order to provide robustness against cable impedance and faults. Power converter modules employed in these architectures are connected in series and have a constant current input. In this paper, steady state analysis and a control strategy are presented for series connected resonant converter modules in a constant current dc distributed power system. The control strategy is developed to achieve stable operation of the system with no communications required among modules. Hardware results are provided for a system consisting of two series connected 100 kHz 500 W SRCs with 1 A trunk current and regulated output current.

Design considerations for series resonant converters with constant current input

Applications such as under-sea power prefer dc current distribution in a series cable connection instead of dc voltage distribution due to the long distance and cable loss. Power converter modules employed in these scenarios have a constant current input. In this paper, steady state analysis and unique design considerations are presented for the series resonant converter topology with constant current input. Constraints on the resonant tank component selection and operating frequency are developed to achieve the desired load range for the given input current. Hardware results are provided based on an under-sea dc distribution scenario to verify the benefits of the analysis and design considerations for a 400 kHz, 500 W SRC with 1 A input current and 330 mA output current.

Analysis and design of a series resonant converter with constant current input and regulated output current

Constant current dc distribution to series connected loads has been preferred for long distance high reliability systems such as undersea cabling for telecommunications and observation networks. In addition, some loads require constant current output, creating a need for high efficiency power supplies that provide a regulated current gain from input current to output current. Series resonant converters (SRCs) are a good candidate with the potential for high output impedance current source output behavior. However, SRCs behave differently with constant current input compared to traditional constant voltage input, a behavior that has not been well studied in the literature. This work presents detailed analysis and design considerations for SRCs operated with constant current input and regulated to provide a constant current output. The converter control method, zero-voltage-switching (ZVS) realization, and approaches to maintain SRC operation at resonance are discussed. The current source property of the SRC offers many advantages such as independence of load voltage, parallel operation and short circuit output protection. Hardware results are presented for a 380 kHz, 450 W prototype SRC with 1 A input current and 0.33 A regulated output current.

Analysis of zero voltage switching requirements and passive auxiliary circuit design for DC-DC series resonant converters with constant input current

Constant current distribution systems such as under-sea power distribution systems use power converters with a constant input current as a source of input power. This paper analyzes minimum requirements for passive zero-voltage-switching (ZVS) components of dc-dc series resonant converters (SRCs) in dc distribution systems. A steady state analysis of the technique shows that the input voltage varies with the output power of the converter when using a constant input current source. Thus, ZVS requirements deviate from traditional solutions as commonly used for SRCs with a constant input voltage. Design guidelines for selecting the ZVS assisting inductor are presented to achieve ZVS for all active switches over a wide load range without significantly increasing the overall conduction losses. The approach is validated using experimental results for a 400 kHz 450 W SRC with 1 A constant input current and 0.33 A output current.

Impedance-based stability analysis and design considerations for DC current distribution with long transmission cable

Stability is a major concern for dc distribution systems because the integrated system may become unstable even though the subsystems are stable individually. Significant analysis and design has been applied to dc voltage distribution systems, while stability and related control design are not well studied for dc current distribution systems, especially for the scenarios with long transmission cables. In this paper, impedance expressions for long transmission cables are derived and applied to analyze stability of power converters in dc current distribution systems. The relation between converter closed-loop and open-loop input impedance is discussed by taking a series resonant converter (SRC) with constant current input and regulated output current as an example. Impedance-based stability analysis and design considerations are proposed by employing the Nyquist plot of the system minor loop gain. The stability analysis and design presented are validated through experimental results based on a system with a 1 A current source, a 100 km cable emulator and a 500 W SRC.

Zero voltage switching assistance design for DC-DC series resonant converter with constant input current for wide load range

In under-sea dc power distribution systems, constant current feed is preferred over constant voltage feed for robustness against long distance cable impedance. The input voltage of each power converter module in a series connected dc power distribution system varies over a wide range as a function of the load power. This behavior brings unique challenges to maintaining zero voltage switching (ZVS) for series resonant converters (SRCs), making simple passive techniques impractical for applications with a wide load range. Hence, active ZVS assisting circuits are preferred to achieve ZVS over the resulting wide input voltage range. In this paper, design guidelines are provided for active ZVS assisting circuits in such systems. Limitation of active ZVS circuits and methods to overcome them are also presented. The analysis is verified by hardware testing of an SRC operating at 250 kHz from a constant input source of 1 A with regulated output current of 0.33 A, and a power level of 1 kW.

Design of Hybrid Energy Storage Systems for Wirelessly Charged Electric Vehicles

Emerging Wireless Power Transfer (WPT) technology employed to dynamically charge Electric Vehicles (EVs) has the potential to overcome the limitations of EVs by extending vehicle driving range, making them lighter and less expensive. However, while moving over road-embedded pads during a regular driving and charging routines, the vehicle energy storage system is exposed to short-duration, high- energy bursts delivered from the road-embedded equipment. To manage energy storage and distribution inside a vehicle, a hybrid energy storage system is proposed, consisting of a battery and supercapacitor modules actively connected to an internal DC bus while supplying the inverter-motor drivetrain. Considering the specificity of the wireless charging system as a power delivery infrastructure, as well as the operational constrains of supercapacitor and battery storage units, we formulated the requirements and proposed a new energy management system (EMS). The proposed EMS strategy was verified for selected battery and supercapacitor modules through simulations over the downscaled standardized ECE-15 Urban Drive Cycle (UDC) and for various layouts of wireless charging infrastructure. Simulation results have proved the effectiveness of the proposed hybrid energy storage and superimposed EMS algorithm.