Hamid Behjati

A Multiple-Input Multiple-Output DC–DC Converter

A multiple-input multiple-output dc-dc converter topology is proposed. This converter is able to accommodate an arbitrary number of sources and loads. The steady-state and dynamic characteristics of the proposed converter are analyzed. A controller scheme is proposed that enables budgeting the input powers coming from different energy sources, in addition to regulating the output voltages. Loss and efficiency modeling and sensitivity analysis to the underlying parameters are performed. Several case studies are presented to verify the analytical models and evaluate the performance of the proposed converter.

Modular DC–DC Converters on Graphs: Cooperative Control

Modular dc-dc converters are popular in dc-power systems due to their advantageous characteristics such as fault tolerance, ease of thermal management, reducing voltage/current stress of the components, and modularity. In this paper, the concept of cooperative control in multiagent systems is introduced for modular dc-dc converters. Each constituent converter is represented by a node in a directed communication graph that models the information flow among converters. The proposed cooperative control scheme enjoys structural modularity, plug-and-play capability, fault tolerance against random failures in the converters and/or communication links, and satisfactory dynamic performance. This paper provides a general analytical framework to study modular dc-dc converters with an arbitrary communication graph. Hence, the designer has the freedom to choose among the various types of graphs based on the available communication resources and the desired level of reliability and fault tolerance. The dynamic model of the cooperative multiconverter system is developed and analyzed. Hardware measurements are presented to verify the plug-and-play capability, fault tolerance in both cyber and physical domains, and dynamic performance of the proposed cooperative control scheme.

A multi-port dc-dc converter with independent outputs for vehicular applications

A multi-port multiple-output topology is presented to efficiently interface independent dc loads with diverse dc sources in electric vehicles. The main characteristics of this new circuit topology are, namely, ability to convert power from any number of energy resources to any number of loads, to supply output voltages that are greater than maximum input voltage or lower than minimum input voltage, avoiding bulky transformer, and minimum possible storage elements (a single inductor). Different operation modes of the circuit are characterized, analyzed, and verified by detailed switch-level simulation for all operational modes.

Reliability Analysis Framework for Structural Redundancy in Power Semiconductors

Parallel and standby configurations can be applied to semiconductor switches to improve the reliability of power electronic converters in mission-critical applications. In this paper, the reliability models of both configurations are developed based on the Markov process. The mean time to failure (MTTF) of each configuration is derived in terms of the underlying parameters. It is demonstrated that there is a boundary condition in which both configurations have the same MTTF. This boundary condition is expressed in terms of the junction temperature of the semiconductor switch in the steady state. The temperature range in which the parallel configuration is more reliable is formulated for different types of power semiconductor switches including MOSFETs, bipolar junction transistors, SCRs, triacs, regular diodes, and Schottky diodes. Case studies are presented to determine the more reliable configuration for a laboratory-scale buck converter.

Alternative Time-Invariant Multi-Frequency Modeling of PWM DC-DC Converters

A time-invariant multi-frequency modeling technique is proposed for pulse-width-modulated (PWM) dc-dc converters. The proposed methodology distinguishes between different types of modulation carrier signals (e.g., sawtooth and isosceles triangle carriers). A straightforward systematic procedure is proposed to automatically convert the conventional state-space time-variant model to the proposed time-invariant model. Hence, high-order time-invariant models can be easily developed for system design and stability analysis purposes. Closed-loop time-domain and open-loop frequency-domain responses extracted from a laboratory-scale Cuk converter have verified the proposed methodology.

Reduced-Order Dynamic Modeling of Multiple-Winding Power Electronic Magnetic Components

Dynamic high-fidelity magnetic equivalent circuits (HFMEC) are viable tool for accurate, physics-based modeling of magnetic components. However, such model formulation typically requires hundreds or thousands of state variables to accurately represent the eddy current dynamics. A reduced-order HFMEC modeling approach has been recently introduced for single-winding systems, e.g., inductors. This letter extends the HFMEC approach to multiple-winding power-electronic transformers. First, a general full-order HFMEC model of the multiple-winding system is developed that incorporates magnetic saturation and the eddy current dynamics. Then, multiple-input/multiple-output linear and nonlinear order-reduction techniques are used to extract the desired essential system dynamics while preserving the model accuracy and gaining computational efficiency. The proposed methodology is validated on a typical power electronic transformer with both pulse width modulation and sinusoidal excitations using numerical simulations and experimental measurements.

A MIMO topology with series outputs: An interface between diversified energy sources and diode-clamped multilevel inverter

A new multiple-input multiple-output (MIMO) dc-dc converter topology is presented. The proposed topology can interface between diversified energy sources and diode-clamped multilevel inverter. Regulating series output voltages for the dc-link of the diode-clamped multilevel inverter, diversifying energy sources, improving availability of the energy source, employing a single inductor, and cost effectiveness are the advantages of the proposed MIMO converter. The steady state operation of the converter is characterized and verified by numerical switch-level simulation.

Power Budgeting Between Diversified Energy Sources and Loads Using a Multiple-Input Multiple-Output DC–DC Converter

A single-stage multiple-input multiple-output dc-dc converter topology is proposed. The proposed converter can employ arbitrary number of energy sources and can supply arbitrary number of loads. The ability of the converter to regulate the input powers coming from different energy sources, in addition to regulating the output voltages, stands out. A specific switching scheme is proposed, and the dynamic model of the converter is developed based on the designated switching scheme. An appropriate control algorithm is presented, based on which the input powers and output voltages are regulated. Several hardware measurements and numerical simulations are presented to verify dynamic characterizations and to demonstrate the converters performance.

Comparative reliability study of hybrid energy storage systems in hybrid electric vehicles

Hybrid energy storage system (HESS), consisting of battery, ultracapacitor, and the converter interface, is one of the fundamental components in hybrid electric vehicles (HEVs). This paper presents a comparative reliability study between the state-of-art HESS topologies used in HEVs. The operational principles of different HESS topologies are briefly explained, and Markov-based reliability model of each topology is developed. The mean time to failure (MTTF) of each topology is derived in terms of the failure rates of its building blocks. The MTTFs of different topologies are compared and the most reliable topologies are identified. HESS topologies are arranged based on their reliability rankings from the most reliable to the least reliable.

Sculpting the dynamic response of PWM dc-dc converters in an arbitrary shape using WPI control technique

Weighted proportional integral (WPI) control method is introduced for pulse-width-modulated (PWM) dc-dc converters. Although WPI control is computationally similar to the conventional PI control, it offers direct step response assignment, which allows the designer to satisfy any desired design specification. The WPI control method is explained for a PWM dc-dc converter of an arbitrary order, n, and numerical simulations are presented to compare the performance indices of the proposed control method with those of the conventional PI controllers.