1,375 research outputs found

    Modeling and Design of High-Performance DC-DC Converters

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    The goal of the research that was pursued during this PhD is to eventually facilitate the development of high-performance, fast-switching DC-DC converters. High-switching frequency in switching mode power supplies (SMPS) can be exploited by reducing the output voltage ripple for the same size of passives (mainly inductors and capacitors) and improve overall system performance by providing a voltage supply with less unwanted harmonics to the subsystems that they support. The opposite side of the trade-off is also attractive for designers as the same amount of ripple can be achieved with smaller values of inductance and/or capacitance which can result in a physically smaller and potentially cheaper end product. Another benefit is that the spectrum of the resulting switching noise is shifted to higher frequencies which in turn allows designers to push the corner frequency of the control loop of the system higher without the switching noise affecting the behavior of the system. This in turn, is translated to a system capable of responding faster to strong transients that are common in modern systems that may contain microprocessors or other electronics that tend to consume power in bursts and may even require the use of features like dynamic voltage scaling to minimize the overall consumption of the system. While the analysis of the open loop behavior of a DC-DC converter is relatively straightforward, it is of limited usefulness as they almost always operate in closed loop and therefore can suffer from degraded stability. Therefore, it is important to have a way to simulate their closed loop behavior in the most efficient manner possible. The first chapter is dedicated to a library of technology-agnostic high-level models that can be used to improve the efficiency of transient simulations without sacrificing the ability to model and localize the different losses. This work also focuses further in fixed-frequency converters that employ Peak Current Mode Control (PCM) schemes. PCM schemes are frequently used due to their simple implementation and their ability to respond quickly to line transients since any change of the battery voltage is reflected in the slope of the rising inductor current which in turn is monitored by a fast internal control loop that is closed with the help of a current sensor. Most existing models for current sensors assume that they behave in an ideal manner with infinite bandwidth and ideal constant gain. These assumptions tend to be in significant error as the minimum on-time of the sensor and therefore the settling time requirements of the sensor are reduced. Some sensing architectures, like the ones that approximate the inductor current with the high-side switch current, can be even more complex to analyze as they require the use of extended masking time to prevent spike currents caused by the switch commutation to be injected to the output of the sensor and therefore the signal processing blocks of the control loop. In order to solve this issue, this work also proposes a current sensor model that is compatible with time averaged models of DC-DC converters and is able to predict the effects of static and transient non-idealities of the block on the behavior of a PCM DC-DC converter. Lastly, this work proposes a new 40 V, 6 A, fully-integrated, high-side current sensing circuit with a response time of 51 . The proposed sensor is able to achieve this performance with the help of a feedback resistance emulation technique that prevents the sensor from debiasing during its masking phase which tends to extend the response time of similar fully integrated sensors

    A Novel Boost Converter Based LED Driver Chip Targeting Mobile Applications

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    abstract: A novel integrated constant current LED driver design on a single chip is developed in this dissertation. The entire design consists of two sections. The first section is a DC-DC switching regulator (boost regulator) as the frontend power supply; the second section is the constant current LED driver system. In the first section, a pulse width modulated (PWM) peak current mode boost regulator is utilized. The overall boost regulator system and its related sub-cells are explained. Among them, an original error amplifier design, a current sensing circuit and slope compensation circuit are presented. In the second section – the focus of this dissertation – a highly accurate constant current LED driver system design is unveiled. The detailed description of this highly accurate LED driver system and its related sub-cells are presented. A hybrid PWM and linear current modulation scheme to adjust the LED driver output currents is explained. The novel design ideas to improve the LED current accuracy and channel-to-channel output current mismatch are also explained in detail. These ideas include a novel LED driver system architecture utilizing 1) a dynamic current mirror structure and 2) a closed loop structure to keep the feedback loop of the LED driver active all the time during both PWM on-duty and PWM off-duty periods. Inside the LED driver structure, the driving amplifier with a novel slew rate enhancement circuit to dramatically accelerate its response time is also presented.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

    Digital Controlled Multi-phase Buck Converter with Accurate Voltage and Current Control

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    abstract: A 4-phase, quasi-current-mode hysteretic buck converter with digital frequency synchronization, online comparator offset-calibration and digital current sharing control is presented. The switching frequency of the hysteretic converter is digitally synchronized to the input clock reference with less than ±1.5% error in the switching frequency range of 3-9.5MHz. The online offset calibration cancels the input-referred offset of the hysteretic comparator and enables ±1.1% voltage regulation accuracy. Maximum current-sharing error of ±3.6% is achieved by a duty-cycle-calibrated delay line based PWM generator, without affecting the phase synchronization timing sequence. In light load conditions, individual converter phases can be disabled, and the final stage power converter output stage is segmented for high efficiency. The DC-DC converter achieves 93% peak efficiency for Vi = 2V and Vo = 1.6V.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

    Current measurement in power electronic and motor drive applications - a comprehensive study

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    Current measurement has many applications in power electronics and motor drives. Current measurement is used for control, protection, monitoring, and power management purposes. Parameters such as low cost, accuracy, high current measurement, isolation needs, broad frequency bandwidth, linearity and stability with temperature variations, high immunity to dv/dt, low realization effort, fast response time, and compatibility with integration process are required to ensure high performance of current sensors. Various current sensing techniques based on different physical effects such as Faraday\u27s induction law, Ohm\u27s law, Lorentz force law, magneto-resistance effect, and magnetic saturation are studied in this thesis. Review and examination of these current measurement methods are presented. The most common current sensing method is to insert a sensing resistor in the path of an unknown current. This method incurs significant power loss in a sense resistor at high output currents. Alternatives for accurate and lossless current measurement are presented in this thesis. Various current sensing techniques with self-tuning and self-calibration for accurate and continuous current measurement are also discussed. Isolation and large bandwidth from dc to several kilo-hertz or mega-hertz are the most difficult, but also most crucial characteristics of current measurement. Electromagnetic-based current sensing techniques, which are used to achieve these characteristics, are analyzed. Many applications require average current information for control purposes. Different average current sensing methods of measuring average current are also reviewed. --Abstract, page iii

    Current Sensing for Automotive Electronics -- A Survey

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    Current sensing is widely used in power electronic applications such as dc-dc power converters and adjustable-speed motor drives. Such power converters are the basic building blocks of drivetrains in electric, hybrid, and plug-in hybrid electric vehicles. The performance and control of such vehicles depend on the accuracy, bandwidth, and efficiency of its sensors. Various current-sensing techniques based on different physical effects such as Faraday\u27s induction law, Ohm\u27s law, Lorentz force law, the magnetoresistance effect, and the magnetic saturation effect are described in this paper. Each technique is reviewed and examined. The current measurement methods are compared and analyzed based on their losslessness, simplicity, and ease of implementation

    Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

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    Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics

    Controller Modeling and Stability Analysis of Multiple Input Single Output DC-DC Converter

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    This thesis entails the stability analysis of the Multiple Input Single Output (MISO) DC-DC converter developed for the DC House Project at Cal Poly. A frequency domain control system model of the MISO converter was designed and constructed using MATLAB Simulink. Transfer functions were derived and modeled for each stage of the converter to best fit the converter circuit system used in the original MISO circuit. Stability metrics such as overshoot, undershoot, rise time, phase margin and gain margin were measured to evaluate and analyze the stability of the converter. These metrics were measured with the original model including the current sharing network that allows load sharing between multiple MISO modules. The simulation results demonstrate that based on the existing model, the system is stable with a gain margin of infinity and phase margin of around 40 degrees at crossover frequency of 47kHz with nominal input voltage of 24V. Another compensator was proposed to overcome the shortcomings of the original compensator model with respect to the overshoot and phase margin. The new compensator model improved the phase margin at the same crossover frequency with a higher rise time and lowered percent overshoot. Additional improvements and tradeoffs are further discussed to help with the decision when designing a compensator for DC-DC converter that uses the current mode control technique

    Analysis of an On-Line Stability Monitoring Approach for DC Microgrid Power Converters

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    An online approach to evaluate and monitor the stability margins of dc microgrid power converters is presented in this paper. The discussed online stability monitoring technique is based on the Middlebrook's loop-gain measurement technique, adapted to the digitally controlled power converters. In this approach, a perturbation is injected into a specific digital control loop of the converter and after measuring the loop gain, its crossover frequency and phase margin are continuously evaluated and monitored. The complete analytical derivation of the model, as well as detailed design aspects, are reported. In addition, the presence of multiple power converters connected to the same dc bus, all having the stability monitoring unit, is also investigated. An experimental microgrid prototype is implemented and considered to validate the theoretical analysis and simulation results, and to evaluate the effectiveness of the digital implementation of the technique for different control loops. The obtained results confirm the expected performance of the stability monitoring tool in steady-state and transient operating conditions. The proposed method can be extended to generic control loops in power converters operating in dc microgrids

    Transient Response Improvement For Multi-phase Voltage Regulators

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    Next generation microprocessor (Vcore) requirements for high current slew rates and fast transient response together with low output voltage have posed great challenges on voltage regulator (VR) design . Since the debut of Intel 80X86 series, CPUs have greatly improved in performance with a dramatic increase on power consumption. According to the latest Intel VR11 design guidelines , the operational current may ramp up to 140A with typical voltages in the 1.1V to 1.4V range, while the slew rate of the transient current can be as high as 1.9A/ns [1, 2]. Meanwhile, the transient-response requirements are becoming stringer and stringer. This dissertation presents several topics on how to improve transient response for multi-phase voltage regulators. The Adaptive Modulation Control (AMC) is a type of non-linear control method which has proven to be effective in achieving high bandwidth designs as well as stabilizing the control loop during large load transients. It adaptively adjusts control bandwidth by changing the modulation gain, depending on different load conditions. With the AMC, a multiphase voltage regulator can be designed with an aggressively high bandwidth. When in heavy load transients where the loop could be potentially unstable, the bandwidth is lowered. Therefore, the AMC provides an optimal means for robust high-bandwidth design with excellent transient performance. The Error Amplifier Voltage Positioning (EAVP) is proposed to improve transient response by removing undesired spikes and dips after initial transient response. The EAVP works only in a short period of time during transient events without modifying the power stage and changing the control loop gain. It facilitates the error amplifier voltage recovering during transient events, achieving a fast settling time without impact on the whole control loop. Coupled inductors are an emerging topology for computing power supplies as VRs with coupled inductors show dynamic and steady-state advantages over traditional VRs. This dissertation first covers the coupling mechanism in terms of both electrical and reluctance modeling. Since the magnetizing inductance plays an important role in the coupled-inductor operation, a unified State-Space Averaging model is then built for a two-phase coupled-inductor voltage regulator. The DC solutions of the phase currents are derived in order to show the impact of the magnetizing inductance on phase current balancing. A small signal model is obtained based on the state-space-averaging model. The effects of magnetizing inductance on dynamic performance are presented. The limitations of conventional DCR current-sensing for coupled inductors are addressed. Traditional inductor DCR current sensing topology and prior arts fail to extract phase currents for coupled inductors. Two new DCR current sensing topologies for coupled inductors are presented in this dissertation. By implementation of simple RC networks, the proposed topologies can preserve the coupling effect between phases. As a result, accurate phase inductor currents and total current can be sensed, resulting in excellent current and voltage regulation. While coupled-inductor topologies are showing advantages in transient response and are becoming industry practices, they are suffering from low steady-state operating efficiency. Motivated by the challenging transient and efficiency requirements, this dissertation proposes a Full Bridge Coupled Inductor (FBCI) scheme which is able to improve transient response as well as savor high efficiency at (a) steady state. The FBCI can change the circuit configuration under different operational conditions. Its flexible topology is able to optimize both transient response and steady-state efficiency. The flexible core configuration makes implementation easy and clear of IP issues. A novel design methodology for planar magnetics based on numerical analysis of electromagnetic fields is offered and successfully applied to the design of low-voltage high power density dc-dc converters. The design methodology features intense use of FEM simulation. The design issues of planar magnetics, including loss mechanism in copper and core, winding design on PCB, core selections, winding arrangements and so on are first reviewed. After that, FEM simulators are introduced to numerically compute the core loss and winding loss. Consequently, a software platform for magnetics design is established, and optimized magnetics can then be achieved. Dynamic voltage scaling (DVS) technology is a common industry practice in optimizing power consumption of microprocessors by dynamically altering the supply voltage under different operational modes, while maintaining the performance requirements. During DVS operation, it is desirable to position the output voltage to a new level commanded by the microprocessor (CPU) with minimum delay. However, voltage deviation and slow settling time usually exist due to large output capacitance and compensation delay in voltage regulators. Although optimal DVS can be achieved by modifying the output capacitance and compensation, this method is limited by constraints from stringent static and dynamic requirements. In this dissertation, the effects of output capacitance and compensation network on DVS operation are discussed in detail. An active compensator scheme is then proposed to ensure smooth transition of the output voltage without change of power stage and compensation during DVS. Simulation and experimental results are included to demonstrate the effectiveness of the proposed scheme
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