Transient Response Improvement For Multi-phase Voltage Regulators

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

Fixed-switching frequency sliding mode control applied to power converters

The application of the sliding mode control in power converters has a well-known inconvenient from the practical point of view, which is to obtain fixed switching frequency implementations. This thesis deals with the development of a hysteresis band controller in charge of fixing the switching frequency of a sliding motion in power electronics applications. The proposed control measures the switching period of the control signal and modifies the hysteresis band of the comparator in order to regulate the switching frequency of the sliding motion. The proposed structure becomes in an additional control loop aside from main control loop implementing the sliding mode controller. In the first part of the thesis, the switching frequency control system is modelled and a design criteria for the control parameters are derived for guaranteeing closed loop stability, under different approaches and taking into account the most expectable working scenarios. In the second part of the thesis, the proposed strategies are applied to several power converters prototypes. Specifically, DC-to-DC and DC-to-AC power converters are built and the experimental results are shown. In this part, the strategies used for implementing the controllers are also deeply discussed.La aplicación del control en modo deslizante en el ámbito de la electrónica de potencia presente una problemática ampliamente conocida, obtener aplicaciones a frecuencia fija de operación. Es esta tesis se estudia el desarrollo de un comparador con histéresis variable encargado de regular el periodo de conmutación de controladores bajo regímenes deslizantes en convertidores de potencia. La estructura propuesta mide el periodo de conmutación de la señal de control y actualiza, de manera adecuada, la banda de histéresis del comparador a tal fin de regular la frecuencia de conmutación al valor deseado. La solución propuesta forma un segundo lazo de control, además del lazo de control principal que implementa el controlador en modo deslizante. En la primera parte de la tesis, éste segundo lazo es modelado, haciendo posible el estudio de las condiciones de estabilidad bajo realizaciones en tiempo continuo y en tiempo discreto. Además, se estudian las condiciones típicas de trabajo de los controladores utilizados en convertidores de potencia, como son los esquemas de regulación y de seguimiento de señales variantes en el tiempo. La segunda parte de la tesis se centra en evaluar, de manera experimental, los desarrollos teóricos de los controladores propuestos en convertidores de potencia. Concretamente, en la tesis se presentan los resultados experimentales obtenidos con diversos convertidores DC-DC y DC-AC. Adicionalmente, las metodologías y técnicas de implementación de los controladores son, de igual modo, ampliamente descritas

Fixed-switching frequency sliding mode control applied to power converters

The application of the sliding mode control in power converters has a well-known inconvenient from the practical point of view, which is to obtain fixed switching frequency implementations. This thesis deals with the development of a hysteresis band controller in charge of fixing the switching frequency of a sliding motion in power electronics applications. The proposed control measures the switching period of the control signal and modifies the hysteresis band of the comparator in order to regulate the switching frequency of the sliding motion. The proposed structure becomes in an additional control loop aside from main control loop implementing the sliding mode controller. In the first part of the thesis, the switching frequency control system is modelled and a design criteria for the control parameters are derived for guaranteeing closed loop stability, under different approaches and taking into account the most expectable working scenarios. In the second part of the thesis, the proposed strategies are applied to several power converters prototypes. Specifically, DC-to-DC and DC-to-AC power converters are built and the experimental results are shown. In this part, the strategies used for implementing the controllers are also deeply discussed.La aplicación del control en modo deslizante en el ámbito de la electrónica de potencia presente una problemática ampliamente conocida, obtener aplicaciones a frecuencia fija de operación. Es esta tesis se estudia el desarrollo de un comparador con histéresis variable encargado de regular el periodo de conmutación de controladores bajo regímenes deslizantes en convertidores de potencia. La estructura propuesta mide el periodo de conmutación de la señal de control y actualiza, de manera adecuada, la banda de histéresis del comparador a tal fin de regular la frecuencia de conmutación al valor deseado. La solución propuesta forma un segundo lazo de control, además del lazo de control principal que implementa el controlador en modo deslizante. En la primera parte de la tesis, éste segundo lazo es modelado, haciendo posible el estudio de las condiciones de estabilidad bajo realizaciones en tiempo continuo y en tiempo discreto. Además, se estudian las condiciones típicas de trabajo de los controladores utilizados en convertidores de potencia, como son los esquemas de regulación y de seguimiento de señales variantes en el tiempo. La segunda parte de la tesis se centra en evaluar, de manera experimental, los desarrollos teóricos de los controladores propuestos en convertidores de potencia. Concretamente, en la tesis se presentan los resultados experimentales obtenidos con diversos convertidores DC-DC y DC-AC. Adicionalmente, las metodologías y técnicas de implementación de los controladores son, de igual modo, ampliamente descritas.Postprint (published version

Experimental investigation and CFD analysis of pressure drop in an ORC boiler for a WHRS implementation

Waste heat dissipated in the exhaust system of a combustion engine represents a major source of energy to be recovered and converted into useful work. The Waste Heat Recovery System (WHRS) based in an Organic Rankine Cycle (ORC) is an approach for recovering energy from heat sources, achieving a significant reduction in fuel consumption and, as a result, exhaust emissions. This paper studies pressure drop in an ORC shell-and-tubes boiler for a WHRS implementation experimentally and with computational simulations based on a 1-dimensional heat transfer model coupled with 3D calculations. An experimental database is developed, using ethanol in a pressure range of 10–15 absolute bar as working fluid, with mass fluxes inside the tubes in the range of 349.31 kg/s-m2 and 523.97 kg/s-m2, and inlet temperatures in the range of 60 °C and 80 °C. Thus, the friction factor of different regions of the boiler were estimated using both CFD simulations, experimental data, and bibliographic correlations. Simulations of operating points and the results of the experimental test bench showed good agreement in pressure drop results, with a mean absolute error of 15.47%, without a significant increment in the computational cost

Implementation of a Cascade Fault Tolerant Control and Fault Diagnosis Design for a Modular Power Supply

The main objective of this research work was to develop reliable and intelligent power sources for the future. To achieve this objective, a modular stand-alone solar energy-based direct current (DC) power supply was designed and implemented. The converter topology used is a two-stage interleaved boost converter, which is monitored in closed loop. The diagnosis method is based on analytic redundancy relations (ARRs) deduced from the bond graph (BG) model, which can be used to detect the failures of power switches, sensors, and discrete components such as the output capacitor. The proposed supervision scheme including a passive fault-tolerant cascade proportional integral sliding mode control (PI-SMC) for the two-stage boost converter connected to a solar panel is suitable for real applications. Most model-based diagnosis approaches for power converters typically deal with open circuit and short circuit faults, but the proposed method offers the advantage of detecting the failures of other vital components. Practical experiments on a newly designed and constructed prototype, along with simulations under PSIM software, confirm the efficiency of the control scheme and the successful recovery of a faulty stage by manual isolation. In future work, the automation of this reconfiguration task could be based on the successful simulation results of the diagnosis method.This research was funded by the Tunisian Ministry of Higher Education and Scientific Research

Integrated Circuits and Systems for Smart Sensory Applications

Connected intelligent sensing reshapes our society by empowering people with increasing new ways of mutual interactions. As integration technologies keep their scaling roadmap, the horizon of sensory applications is rapidly widening, thanks to myriad light-weight low-power or, in same cases even self-powered, smart devices with high-connectivity capabilities. CMOS integrated circuits technology is the best candidate to supply the required smartness and to pioneer these emerging sensory systems. As a result, new challenges are arising around the design of these integrated circuits and systems for sensory applications in terms of low-power edge computing, power management strategies, low-range wireless communications, integration with sensing devices. In this Special Issue recent advances in application-specific integrated circuits (ASIC) and systems for smart sensory applications in the following five emerging topics: (I) dedicated short-range communications transceivers; (II) digital smart sensors, (III) implantable neural interfaces, (IV) Power Management Strategies in wireless sensor nodes and (V) neuromorphic hardware

Metering of two-phase slug flow

This thesis describes the development of a novel system, for metering of two-phase (gaswater) slug flows. The approach combines a model for stable slug flow, a non-intrusive set of conductance sensors, and appropriate closure relationships. This system allows each of the parameters in the model to be determined. The slug flow model is analysed, to determine the sensitivity of the phase flowrates to each measurement parameter. A metering system is then proposed which combines ring-shaped electrodes, electronic instrumentation, and processing software. The ring electrodes are optimised, for the measurement of the phase fraction and the translation velocity. New instrumentation is developed to activate the electrodes, with high measurement accuracy and a wide bandwidth. Analysis software is developed, to process the sensor data, provide suitable closure relations, and deliver the flowrates. A unique feature of this software is its ability to calculate uncertainty margins in the predicted flowrates. The NEL multiphase facility is used, to obtain data for developed, horizontal, gas-water slug flow in a 4-inch pipe. The data span the range of liquid phase superficial velocities 0.1 m s⁻¹ to 1.0 m s⁻¹ , and gas phase superficial velocities 0.6 m s⁻¹ to 6.0 m s⁻¹. The analysis software is used to obtain the flowrate predictions and estimates for the uncertainty margins. The stable slug flow model does not give good results. The relative error in the gas phase prediction is between 10% and 100%, and for the liquid phase prediction, between 50% and 500%. The uncertainty margins are also of comparable magnitude. Proposals for improving the accuracy of the translation velocity measurement, and for directly measuring the local velocities in the slug body (using a pressure transducer) are presented. These proposals aim to reduce the uncertainty that is caused by the use of the empirical closure relationships in the model.This thesis describes the development of a novel system, for metering of two-phase (gaswater) slug flows. The approach combines a model for stable slug flow, a non-intrusive set of conductance sensors, and appropriate closure relationships. This system allows each of the parameters in the model to be determined. The slug flow model is analysed, to determine the sensitivity of the phase flowrates to each measurement parameter. A metering system is then proposed which combines ring-shaped electrodes, electronic instrumentation, and processing software. The ring electrodes are optimised, for the measurement of the phase fraction and the translation velocity. New instrumentation is developed to activate the electrodes, with high measurement accuracy and a wide bandwidth. Analysis software is developed, to process the sensor data, provide suitable closure relations, and deliver the flowrates. A unique feature of this software is its ability to calculate uncertainty margins in the predicted flowrates. The NEL multiphase facility is used, to obtain data for developed, horizontal, gas-water slug flow in a 4-inch pipe. The data span the range of liquid phase superficial velocities 0.1 m s⁻¹ to 1.0 m s⁻¹ , and gas phase superficial velocities 0.6 m s⁻¹ to 6.0 m s⁻¹. The analysis software is used to obtain the flowrate predictions and estimates for the uncertainty margins. The stable slug flow model does not give good results. The relative error in the gas phase prediction is between 10% and 100%, and for the liquid phase prediction, between 50% and 500%. The uncertainty margins are also of comparable magnitude. Proposals for improving the accuracy of the translation velocity measurement, and for directly measuring the local velocities in the slug body (using a pressure transducer) are presented. These proposals aim to reduce the uncertainty that is caused by the use of the empirical closure relationships in the model

High performance control of VRM circuits

Master'sMASTER OF ENGINEERIN