Showing papers by "Dragan Maksimovic published in 2012"

Minimum Current Operation of Bidirectional Dual-Bridge Series Resonant DC/DC Converters

Abstract: This paper discusses the steady-state operation of phase-shift modulated dual-bridge series resonant converter (DBSRC) intended for dc/dc power bidirectional control over a wide range of input and output voltages. The analysis, developed here for the most general case of three independent phase-shift control angles, demonstrates the existence of minimum current trajectories in the 3-D control space along which the DBSRC cell can deliver any admissible power level with minimum tank circulating current. At nonunity conversion ratios, minimum current operation prevents the DBSRC output bridge from experiencing severe hard-switching losses, substantially reducing the effort normally required by auxiliary zero-voltage switching assistance circuitry, and outperforming the efficiency of conventional one-angle modulation approaches especially at light load. The developed approach is validated via computer simulations and experimental tests on a 1-kW DBSRC prototype. Tests performed at a nonunity voltage conversion ratio indicate a marked light-load efficiency improvement with respect to the conventional one-angle modulation, confirming the importance of the minimum current operation when the converter is expected to operate with programmable output voltages or under wide input voltage variations.

Codesign of PA, Supply, and Signal Processing for Linear Supply-Modulated RF Transmitters

Abstract: This paper presents a method for achieving high-efficiency linear transmitters by codesign of the RF power amplifier (PA), dynamic supply, and signal processing. For varying amplitude signals, the average efficiency of the PA is improved by adding a supply modulator with requirements derived from nonstandard PA modeling. The efficient PA and supply modulator both introduce signal distortion. A targeted linearization procedure is demonstrated with reduced complexity compared to standard digital predistortion. Experimental results on a 2.14-GHz 81% efficient 40-W peak power GaN PA illustrate the codesign method by achieving 52.5% composite power-added efficiency with high linearity for a W-CDMA signal with a 23-MHz supply modulator bandwidth.

Efficiency Optimization in Digitally Controlled Flyback DC–DC Converters Over Wide Ranges of Operating Conditions

Abstract: This paper presents an approach to efficiency optimization in digitally controlled flyback dc-dc converters over wide ranges of operating conditions. Efficiency is characterized and optimized based on power loss modeling and multivariable nonlinear constrained optimization over power-stage and controller parameters. A valley switching technique is adopted to reduce MOSFET turn-on switching loss in discontinuous conduction mode. An optimization procedure is formulated to minimize power loss weighted over a range of operating points, under a cost constraint. A lookup table-based digital controller is applied to achieve on-line efficiency optimization by programming switching frequencies and operating modes based on the efficiency optimization processes. The proposed on-line efficiency optimization approach is verified by experimental results on a low cost 65 W flyback dc-dc prototype.

Current Mode Control for Boost Converters With Constant Power Loads

Abstract: This paper describes how current mode control provides active damping for boost converters with constant power loads. Small-signal control-to-output transfer functions are derived for peak or valley current mode controlled boost converter with a downstream regulated converter modeled as constant power load. Furthermore, it is shown how load current feedforward presents an effective way to improve power load transient responses. Modeling and design approaches are validated by test circuit simulations, demonstrating stable operations using current mode control under constant power loads, and improved power step load transient responses based on load current feedforward.

Robust Gain-Scheduled Control of Switched-Mode DC–DC Converters

Abstract: This paper presents a robust control synthesis framework for switched DC-DC converters. The framework is based on an LMI formulation which can be solved automatically by efficient convex optimization algorithms. The method considers parameter-dependent Lyapunov functions such that it can take into account the uncertainty of converter parameters, nonlinear dynamics (such as state-dependence), as well as transient and steady-state performances that can be imposed beforehand. The result of the proposed synthesis method is a gain-scheduled controller that guarantees stability despite the accounted nonlinear dynamics and can provide excellent performances. Two different synthesis examples are shown for a DC-DC boost converter and their performance and robustness are compared with a standard control approach as current-mode control, both in nominal and non-nominal conditions. Finally, the proposed approach is verified with experimental results.

Average Inductor Current Sensor for Digitally Controlled Switched-Mode Power Supplies

Abstract: Current-mode control in digitally controlled switched-mode power supplies typically requires analog-to-digital (A/D) conversion of at least two signals, voltage, and current. The complexity of voltage A/D converters can be reduced using window A/D techniques. In conventional current A/D conversion, however, relatively high resolution is required over a wide range of signals, which results in increased complexity, power consumption, and cost of the controller. This paper proposes a very simple feedback sensor capable of high-resolution average inductor current sensing using two analog comparators and an analog low-pass filter. The approach requires very few external components and employs minimal digital hardware resources. A dynamic model and performance of the average inductor current sensor are experimentally verified on a 12-V input, 19-V output, 50-W boost converter prototype. The applicability of the proposed sensor is demonstrated in a digitally controlled 400-W, 400-V output Boost power factor preregulator.

Personalized driving behavior monitoring and analysis for emerging hybrid vehicles

Abstract: Emerging electric-drive vehicles, such as hybrid electric vehicles (HEVs) and plug-in HEVs (PHEVs), hold the potential for substantial reduction of fuel consumption and greenhouse gas emissions. User driving behavior, which varies from person to person, can significantly affect (P)HEV operation and the corresponding energy and environmental impacts. Although some studies exist that investigate vehicle performance under different driving behaviors, either directed by vehicle manufacturers or via on-board diagnostic (OBD) devices, they are typically vehicle-specific and require extra device/effort. Moreover, there is no or very limited feedback to an individual driver regarding how his/her personalized driving behavior affects (P)HEV performance. This paper presents a personalized driving behavior monitoring and analysis system for emerging hybrid vehicles. Our design is fully automated and non-intrusive. We propose phone-based multi-modality sensing that captures precise driver---vehicle information through de-noise, calibration, synchronization, and disorientation compensation. We also provide quantitative driver-specific (P)HEV analysis through operation mode classification, energy use and fuel use modeling. The proposed system has been deployed and evaluated with real-world user studies. System evaluation demonstrates highly-accurate (0.88-0.996 correlation and low error) driving behavior sensing, mode classification, energy use and fuel use modeling.

10 MHz large signal bandwidth, 95% efficient power supply for 3G-4G cell phone base stations

Abstract: To improve the efficiency of cell phone base station transmitters, it is desirable to run the RF Power Amplifier (RFPA) with an envelope modulating power supply that provides the RFPA with the voltage and current needed for maximum efficiency. However, cell phone transmission varies the RF output power considerably over short periods, with the average power significantly less than the peak transmission power, which is difficult for traditional power supplies to support efficiently. This paper describes a switched-mode 8-phase buck envelope modulating power supply with a lookup table that varies the duty cycle and operating frequency to maintain soft switching under all operating conditions, and with dynamic timing correction to keep the phases uniformly distributed in time except when tracking signal dynamics that require simultaneous switching of multiple phases. The power supply does not require active compensation to keep the phase currents balanced. The experimentally demonstrated power supply provides 10 MHz large signal bandwidth, >40 A/μsec current slew rate, with switching frequency of up to 15 MHz at 95% efficiency. The supply is suitable for 2-carrier WCDMA and LTE cell phone base stations.

Discrete-time small-signal modeling of a 1 MHz efficiency-optimized dual active bridge converter with varying load

Abstract: A discrete-time, small-signal model is developed for the dual active bridge (DAB) converter which considers the effects of zero-voltage switching (ZVS) intervals on converter dynamics. The model is applied to the converter operating under phase-shift modulation, and is shown to be valid across a full range of load values constituting multiple operating modes of the converter. Finally, the model is applied to the case of an unregulated converter to show that output voltage variation that results in improved efficiency over wide range of loads can also lead to simplified control and compensation requirements across the full load range

Circuit-oriented modeling of nonlinear device capacitances in switched mode power converters

Abstract: The existence of parasitic capacitances surrounding switching devices has been well established in the field. These capacitances are capable of having significant impact on the analysis, design, and performance of switched mode power supplies through increased switching loss or altered converter dynamics in the soft-switched case. As power converters continue to move to higher frequency, these effects become more pronounced and must be taken into account in converter design and analysis. This paper examines the nonlinear voltage-dependence of switching device capacitances and proposes a circuit-oriented analysis technique that allows the parasitic capacitances to be replaced with linear equivalents. The developed linear equivalents are then used with traditional circuit analysis to experimentally confirm their ability to accurately model converter operation of an example converter which exhibits significant loss and dynamic effects from device capacitances.

A high-efficiency bidirectional buck-boost DC-DC converter

Abstract: This paper presents efficiency optimization and implementation of a bidirectional DC-DC converter based on the four-switch, non-inverting buck-boost configuration. The converter is intended for DC power systems to interface different sources or loads to a common DC bus, operating over a wide range of voltages. The number of converter phases, switching frequency, and inductor parameters are determined by an iterative efficiency optimization approach. The experimental 500W bidirectional converter operates from 12–38V at the source/load port to 21–32V at the bus port, with up to 97% efficiency.

Automatic voltage and dead time control for efficiency optimization in a Dual Active Bridge converter

Abstract: A control scheme is developed in which efficiency is optimized over a wide range of loads for a Dual Active Bridge (DAB) converter. A simple control strategy is proposed to adjust both the converter conversion ratio and switching dead times to maintain high efficiency in the presence of varying loads. To demonstrate feasibility of the proposed control method, experimental results are presented for a 150-to-12 V, 120 W, 1 MHz prototype converter which has 97.4% peak efficiency and maintains greater than 90% efficiency over a load range between 20 W and 120 W.

Electric vehicle DC charger integrated within a photovoltaic power system

Abstract: Mitigation of the variability in output power of renewable generators such as solar photovoltaic (PV) systems is a growing concern as these generators reach higher penetrations on electric grids. This paper presents a system where a bidirectional, highly efficient, DC-DC electric vehicle (EV) charger is placed between the high-voltage DC bus of a PV system and the EV battery. In addition to providing fast charging for the EV battery from PV or from the grid, the charger is capable of diverting fast changes in PV power output to the battery, thereby reducing the rate of change of inverter output power to a level below the ramp rate of existing grid resources. The paper addresses sizing of the charger and energy storage based on the PV system rating, the desired maximum ramp rate, and site insolation characteristics. Analysis suggests that small amounts of energy storage can accomplish large reductions in output power ramp rate. Experimental results are shown for a 10 kW, 98% efficient DC-DC charger based on bidirectional four-phase zero-voltage-switching converter.

Gain-scheduled control of multi angle phase shift modulated dual active bridge series resonant DC/DC converters

Abstract: This paper describes a feedback control approach for dual active bridge series resonant converters that makes use of gain-scheduling to improve the dynamic response of such topologies. The proposed approach uses recently developed small signal models to allow the dual active bridge series resonant converter to maintain phase margin and gain margin requirements over the entire operating range. The proposed method and its application are described, and a controller design example and experimental results are provided for a prototype 1 kW dual active bridge series resonant converter. Verification that the controller satisfies the design constraints is presented, and the gain-scheduling controller performance is compared to that of a constant gain feedback controller.

Photovoltaic power system with integrated electric vehicle DC charger and enhanced grid support

Abstract: This paper describes a photovoltaic (PV) power system with integrated bidirectional electric vehicle (EV) DC charger. The system enables fast and efficient EV battery charging while providing enhanced grid support by limiting the ramp rate of the PV inverter output power. Charger operation is described in three distinct modes: charging only, charging with grid support, and grid support only. A prototype system consists of a 15 kW grid-tied PV system, a 10 kW, 98% efficient bidirectional DC charger, and a 10 kWh EV battery. Experimental results demonstrate the operating modes, start-up routine, battery state-of-charge (SOC) estimation, and system operation. Simulation results are presented for a worst-case scenario of highly fluctuating PV power output; the vehicle battery is charged in less than 90 minutes while simultaneously reducing the maximum ramp rate of the inverter output power by 30% and the average ramp rate by 93%.

Architecture and control of PV modules with submodule integrated converters

Abstract: This paper describes a PV module architecture with submodule integrated converters (subMICs) that improve efficiency of energy capture in the presence of partial shading or other mismatch conditions. Replacing standard bypass diodes, the subMICs are bidirectional dc-dc converters capable of injecting or subtracting currents to balance the module substring voltages. When no mismatches are present, the subMICs are simply shut down, presenting no insertion losses. A simple distributed control approach is described that allows autonomous subMIC control without the need for a central controller or any communication among the subMICs. It is shown that this control approach is close to optimal. Besides, this distributed control approach allows to isolate the secondary port of subMICs from the module output. The isolated-port architecture has additional advantages in its implementation and integration within arrays of PV modules. Simulation and experimental results demonstrating effectiveness of the proposed architectures and the control approach are shown for a typical PV module with 3 substrings.

Resonant pulse-shaping power supply for radar transmitters

Abstract: The final radiofrequency power amplifier (PA) of a radar transmitter module is a large factor in system efficiency. Typical radar transmitter signals are frequency-modulated with constant-amplitude pulse envelopes in order to optimize efficiency, resulting in spectral broadening and power radiated outside of the radar frequency band. This paper demonstrates a PA with a dynamic power supply which enables high efficiency while reducing the spectral emissions. The resonant pulse-shaping power supply generates a raised-cosine pulse envelope waveform with efficiency greater than 90% and peak envelope power around 6 W. Measured results with a 2.14-GHz GaN power amplifier with an efficiency of 76% at peak power demonstrate over 67% transmitter efficiency.

Efficient and Linear Amplification of Spectrally Confined Pulsed AM Radar Signals

Abstract: This letter presents a pulsed high-efficiency power amplifier with increased spectral purity obtained by supply modulation of the pulse envelope. The PA operates at 2.14 GHz with 78% efficiency at 6 W peak power, and with 66.4% average efficiency over a 14.7 μs pulse with a 4.1 dB PAR shaped by a 90% efficient resonant-pulse envelope supply modulator. For PARs greater than 4.1 dB, the signal envelope can be split between the supply modulator and the PA drive, with up to 25% improvement in composite efficiency.

Analysis of solar irradiance intermittency mitigation using constant DC voltage PV and EV battery storage

Abstract: The increasing presence of photovoltaic(PV) renewable power generation and plug-in hybrid electric vehicles (PHEV) in the national infrastructure leaves utilities, Solar PV owners, and both PV-inverter and Battery Charger manufacturers searching for means to mitigate the potentially destabilizing effects of intermittent renewables and battery charging loads on traditional utility grids, and particularly distribution feeders. Small amounts of battery storage can be interfaced to the PV-inverter system's dc-link to effectively filter the fast transient changes in PV output power, thus enabling a greater presence of grid-interactive PV generation and providing a means of alleviating the grid from growing demands of battery charging loads and the challenges of intermittent distributed resources.

Simulation and characterization of GaN HEMT in high-frequency switched-mode power converters

Abstract: High switching frequencies can lead to converters with reduced size and high power density. Using RF/microwave devices, microwave design techniques can be applied to allow soft-switching of devices and thus high efficiency operation, at the cost of higher complexity and component count. This paper explores the use of microwave GaN High Electron Mobility Transistors (HEMT) to realize power conversion in the 10–100 MHz range using conventional PWM techniques that may enable simple, small and efficient converters. Several driver and test circuits are described, simulated and tested, and experimental results are also provided for a floating buck converter operating at 20 MHz and controlled using conventional PWM techniques.

Mismatch-Error Shaping-Based Digital Multiphase Modulator

Abstract: This paper introduces a digital multiphase modulator (MPM) using mismatch-error shaping techniques based on a digital-to-analog converter view of multiphase power converters. The proposed modulator has relatively simple implementation requiring no explicit pulsewidth modulation and generates control pulses for any number of phases using a single, low-frequency clock. Advantages and disadvantages of the mismatch-error shaping MPM are examined through analysis, simulations, and experimental results. The proposed MPM is particularly well suited for multilevel envelope-tracking amplifiers supplying power to linear RF power amplifiers. Results are shown for an experimental eight-phase buck converter in an envelope-tracking application.

A methodology for characterizing and modeling inverters for grid integration studies using Power Hardware-in-the-Loop

Abstract: A methodology is proposed and executed to characterize and model inverters for grid integration studies using Power Hardware-in-the-Loop. A Hardware-in-the-Loop system is configured using a Real-Time Data System (RTDS), grid simulator, load bank, photovoltaic inverter, DC power supply and bus system. A characterization scheme is developed on the RTDS that is based on the abnormal grid conditions and tests outlined in IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems. It was found that it is possible to characterize the inverter's grid protection controller's response to abnormal voltage, abnormal frequency and islanding conditions without prior knowledge of intimate control algorithms or hardware configuration. A model of the system was then created in Matlab Simulink using the data obtained from the characterization process. The inverter model is developed such that the detection and response to the stated abnormal grid conditions of the model emulates that of the actual inverter.

Simple Digital Pulse Width Modulator with 60 picoseconds resolution using a low-cost FPGA

Abstract: This paper describes a very simple Digital Pulse Width Modulator (DPWM), with under 100 picoseconds resolution capability in low-cost field-programmable gate arrays (FPGA). The DPWM implementation is based on internal carry chains and internal logic resources which are present in most FPGA families. The proposed approach does not require manual routing or placement, consumes few hardware resources, and does not rely on specialized phase locked loop or clock management resources. The DPWM is capable of supporting high switching frequencies for digitally controlled switched-mode power converters. A 50 MHz switching frequency DPWM with 60 picoseconds resolution and a 1 MHz switching frequency DPWM with 90 picoseconds resolution are experimentally demonstrated, with monotonicity and excellent linearity.

Average current-mode control of Boost converters with bidirectional power transfer capabilities

Abstract: This paper addresses a potential instability that can take place in Boost converters with average inductor current control. When the output of a Boost converter is attached to a load having bidirectional power capabilities or to an energy source such as a photovoltaic (PV) panel, instability conditions exist which prevent the design of a wide-bandwidth inductor current control. This paper discusses such instability conditions and their physical interpretation, and proposes an alternative control approach solving the problem. Simulation and experimental analyses for a non-inverting buck-boost converter interfacing a 85 W PV module are provided to demonstrate the instability condition as well as to validate the proposed alternative control solution.

A large-scale study of PHEV charging

Abstract: Addressing challenges related to transportation electrification and grid integration of electric and plug-in hybrid electric vehicles (PHEV), this paper presents results from a large-scale study of real-world PHEV driving and charging patterns The dataset is based on over 100 PHEVs deployed in various scenarios across the US, including more than 39,500 driving trips, over 700,000 km driving distance, and over 7,400 charging events Data analysis results indicate suboptimal utilization of PHEVs due to insufficient charging Implications of PHEV proliferation on the power grid both in terms of power demand and the need for charging infrastructure are examined, highlighting the importance of user-vehicle-grid interactions

Simplified sensing and A/D conversion for digitally controlled flyback DC-DC converters with on-line efficiency optimization

Abstract: This paper presents simplified sensing and analog-to-digital (A/D) conversion techniques, targeting low-cost, low-pin-count controller implementation for digitally controlled flyback DC-DC converters with on-line efficiency optimization. Precise output voltage regulation is accomplished by sensing an auxiliary winding voltage on the primary side at the end of the diode conduction interval, thus eliminating the need for secondary-side circuitry and isolation in the feedback path. Furthermore, simple single-comparator analog-to-digital (A/D) conversion techniques are adopted for input current and input voltage sensing, allowing implementation of on-line efficiency optimization over wide ranges of operating points. Experimental results are shown for a digitally controlled 65-W flyback prototype.

A design-oriented optimization framework for envelope trackers: Application to a sliding-mode control buck converter for EDGE

Abstract: Due to the increase of required bandwidth, the newer generation of communication systems uses spectrum-efficient digital modulations that involve non-constant envelope RF signals. RF transmitter architectures that potentially can concurrently provide high efficiency and linearity consider wideband adaptive RF PA supplies based of switching power converters. In this work, a behavioral system-level characterization of how circuit-level effects (namely limited bandwidth and switching effects) affect the overall communication system performance metrics (characterized by spectra, eye diagrams, signal constellations, EVM and BER) of an EDGE communication system is presented, and particularized to optimize the performance of a sliding-mode controlled buck converter based envelope tracker.

Data Conversion Pulse-Width Modulators for Switch-Mode Power Converter Digital Control

Abstract: This chapter presents a survey and classification of architectures for integrated circuit implementation of digital pulse-width modulators (DPWM) targeting digital control of high-frequency switching DC-DC power converters. In order to optimize circuit resources in terms of occupied area and power consumption, architectures based on tapped delay lines are studied, which includes segmentation of the input digital code to drive binary-weighted delay cells and thermometer-decoded unary delay cells. Integrated circuit design of a particular example of the segmented DPWM is described.