Showing papers by "Dragan Maksimovic published in 2011"

Electric vehicle charge optimization including effects of lithium-ion battery degradation

Abstract: This paper presents a method for minimizing the cost of electric vehicle (EV) charging given variable electricity costs while also accounting for estimated costs of battery degradation using a simplified lithium-ion battery lifetime model. The simple battery lifetime model, also developed and presented here, estimates both energy capacity fade and power fade due to temperature, state of charge profile, and daily depth of discharge. This model has been validated by comparison with a detailed model [6], which in turn has been validated through comparison to experimental data. The simple model runs quickly in a MATLAB script, allowing for iterative numerical minimization of charge cost. EV charge profiles optimized as described here show a compromise among four trends: charging during low-electricity cost intervals, charging slowly, charging towards the end of the available charge time, and suppression of vehicle-to-grid power exportation. Finally, simulations predict that batteries charged using optimized charging last longer than those charged using typical charging methods, potentially allowing smaller, cheaper batteries to meet vehicle lifetime requirements.

GaN-FET based dual active bridge DC-DC converter

Abstract: This paper describes a high step-down unregulated, fixed-ratio DC-DC converter (DCX) based on the dual active bridge (DAB) power stage operating at high switching frequency using enhancement-mode Gallium-Nitride-on-Silicon (GaN) transistors. The DAB power stage design as well as a comparison of losses using GaN and silicon MOS devices is based on a detailed state-plane analysis of resonant transitions. Experimental results are presented for a 150 W, 150-to-12 V prototype DCX operating at 1 MHz switching frequency.

A Simple Digital Power-Factor Correction Rectifier Controller

Abstract: This paper introduces a single-phase digital power-factor correction (PFC) control approach that requires no input voltage sensing or explicit current-loop compensation, yet results in low-harmonic operation over a universal input voltage range and loads ranging from high-power operation in continuous conduction mode down to the near-zero load. The controller is based on low-resolution A/D converters and digital pulsewidth modulator, requires no microcontroller or DSP programming, and is well suited for a simple, low-cost integrated-circuit realization, or as a hardware description language core suitable for integration with other power control and power management functions. Experimental verification results are shown for a 300-W boost PFC rectifier.

Small signal phasor modeling of dual active bridge series resonant DC/DC converters with multi-angle phase shift modulation

Abstract: This paper presents an approach for generating small signal models of resonant converters focusing on the transformer-isolated dual active bridge series resonant converter (DABSRC) topology. The presented approach can be generalized to other active bridge resonant converters with one or more phase shift control inputs. Both steady state analysis and small signal modeling of the DABSRC are shown, and the resulting models are experimentally verified using a 1 kW prototype converter.

Autotuning of Digitally Controlled Boost Power Factor Correction Rectifiers

Abstract: This paper presents a robust autotuning technique for digitally controlled boost power factor correction (PFC) rectifiers. The proposed tuning approach perturbs the PFC current and voltage control loops through injection of digital perturbation signals, and achieves the desired crossover frequencies and phase margins for wide ranges of operating conditions and power-stage parameters through simple compensator gain adjustments. An added benefit of the proposed approach is a precise estimation of the filter inductance and capacitance values, therefore facilitating accurate continuous/discontinuous conduction mode (CCM/DCM) boundary detection, which minimizes transition effects and further reduces the input current harmonic distortion. The proposed approach is verified by experimental results on a 300-W digitally controlled boost PFC rectifier prototype.

A microgrid modeling and simulation platform for system evaluation on a range of time scales

Abstract: This paper presents a simulation platform for the modeling and study of microgrid (MG) power systems. Using MathWorks Simulink modeling software, the platform provides a library of tools for designing and simulating the behavior of an MG on time scales from seconds to days. The library includes a collection of power system and power electronics components (sources, loads, switches, etc.) that may be arbitrarily configured. The platform also facilitates the study of energy management systems (EMS), which optimize the behavior of certain controllable sources and loads according to programmed algorithms. User-generated EMS routines can be integrated into an MG model.

Zero voltage switching technique for bi-directional DC/DC converters

Abstract: This paper proposes a zero-voltage switching (ZVS) technique for bi-directional DC/DC converters. The DC/DC unit considered consists of two distinct bi-directional DC/DC cells paralleled at both input and output and whose two input bridges are coupled by means of passive inductive branches. A multi-angle phase-shift modulation method is proposed which simultaneously achieves bi-directional power control, power sharing and ZVS of all the electronic devices over the full power range without the need for auxiliary switches. Simulation and experimental results are reported for a 2.4 kW DC/DC unit consisting of two paralleled 1.2 kW bi-directional Dual-Bridge Series Resonant Converter (DBSRC) cells.

Modeling and digital control of LCLC resonant inverter with varying load

Abstract: This paper presents modeling and design techniques to control the output power of an LCLC resonant inverter over a wide range of loads. A small signal model that relates the output power to the phase shift command is developed using the envelope modeling technique. The model is used to design a digital power control loop for the resonant inverter with the load varying over 5∶80 Ω range. The results are verified through simulations and experiments on a prototype 200 W LCLC resonant inverter.

On-line efficiency optimization in flyback dc-dc converters over wide ranges of operating conditions

Abstract: This paper presents a look-up table based digital control approach to on-line efficiency optimization over wide ranges of operating conditions. The proposed digital controller allows programmable modes of operation based on off-line efficiency characterization and optimization. Applied to a flyback dc-dc converter, the controller adopts valley switching in discontinuous conduction mode (DCM), which significantly reduces the MOSFET turn-on switching loss. Furthermore, solutions to the problem related to undesirable frequency hopping, commonly observed in other valley-switching control schemes, are presented. Dynamic operation of the controller demonstrates smooth mode transitions and consistent transient responses over various operating conditions. Experimental results show that efficiency of a low-cost 65-W flyback prototype exceeds 92% at all operating points over approximately 3:1 range of input voltages and 10:1 range of loads.

Specifications-driven design space boundaries for Point-of-Load converters

Abstract: This paper derives physical constraints for the output filter of a Point-of-Load (POL) converter. Time-optimal control theory is employed to translate the POL static and dynamic specifications into boundaries in the L-C design space, ultimately defining a set Σ of L and C values compatible with the application requirements. Outside the identified set Σ, no controller is capable of meeting the POL specifications; inside the identified set Σ, various degrees of approximation of the time-optimal response are possible, depending on the specific control approach in the field application. The identified set shows the minimum possible values of L and C such that the specifications can be met, which allows the designer to evaluate the impact of a practical controller implementation on the size of the output filter. The design space and boundaries for a digital PID controller are derived, leading to a combined L-C filter and controller design approach. Experimental results validating the design space boundaries are presented for a 12V-to-1 V, 20 A POL converter.