Multifrequency Averaging of Hysteresis-Current-Controlled DC-DC Converters

Multifrequency averaging is one of the widely used modeling and simulation techniques today for the analysis and design of power electronic systems. This technique is capable of providing the average behavior as well as the ripple behavior of power electronic systems. Hysteresis current control has fast response and internal current stability through controlling switches to maintain the current within a given hysteresis band of a given current command. However the state space variables in a hysteresis controlled system cannot be directly approached by multifrequency averaging method because of time varing switching frequency. In this thesis, a method of applying multifrequency averaging to hysteresis current controlled dc-dc converters is proposed. A dc-dc converter model with the application of this method has been successfully developed and validated both in simulation and experiment

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

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

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

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

High performance control of VRM circuits

Master'sMASTER OF ENGINEERIN

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

Toward high-efficiency high power density single-phase DC-AC and AC-DC power conversion - architecture, topology and control

Power conversion between the single-phase AC grid and DC sources or loads plays an indispensable role in modern electrical energy system for both generation and consumption. The renewable resources and electrical energy storage are integrated to the grid through inverters. Telecoms, data centers and the rest of the digital world is powered by the grid through rectifiers. Existing and emerging applications all demand the DC-AC and AC-DC systems to be not only more efficient to reduce energy consumption, but also more compact to reduce cost and improve portability. Therefore, new AC-DC and DC-AC converter designs that improve the efficiency and power density of the system is a critical area of research and is the focus of this dissertation. The recent development of wide band-gap devices stimulates a new round of improvement on efficiency and power density of AC-DC converters. However, despite the new transistors used, the fundamental system architecture and topology remain relatively unchanged, which is becoming the bottleneck for further improvement. This dissertation explores new architecture, topology and control to overcome this bottleneck, targeting an order-of-magnitude improvement on power density and comparable efficiency to the conventional design. The proposed solutions build on two key innovations: the series-stacked buffer architecture for twice-line-frequency power pulsation decoupling in single-phase AC-DC and DC-AC conversion, and the flying capacitor multilevel topology for power transfer and waveform conversion between AC and DC. This work provides complete solutions for these ideas, including the theoretical development, design procedure, control method, hardware implementation and experimental characterization

A new switching technique for minimisation of DC-link capacitance in switched reluctance machine drives.

In a switched reluctance (SR) drive, the transfer of the de-fluxing energy in stator windings back to the dc-link results in a large dc-link capacitance. This limits its applications where weight and size of the drive are restricted. This thesis describes a control technique for the dc-link capacitance minimisation in an SR drive. The proposed control technique maintains the constant power transfer between the de supply and the H-bridge converter. The average dc-link current over a switching period is kept constant. When the output of the integrator, i.e., the average dc-link current, reaches a predefined value proportional to the torque demand, appropriate switching takes place. This is achieved by integrating the dc-link current in each switching period. This technique is called dc-link current integration control (DLCIC). The de-fluxing current from the outgoing phase is not fed back to the dc-link capacitor. Instead, it is transferred to the incoming phase to prevent a negative dc-link current, which causes a fluctuation in the capacitor voltage. Extensive simulation studies of the DLCIC and other techniques reported in literature have been performed and the simulation results from DLCIC are compared with those from other techniques such as Hysteresis Current Control (HCC) and Pulse Width Modulation Current Control (PWMCC). It has been shown that the peak-to-peak voltages across the dc-link capacitor from DLCIC are the lowest amongst other techniques. The operational speed range of the DLCIC is determined and the optimal turn-on and turn-off angles are proposed. Filter components under the DLCIC operation has been designed and compared with the filter for HCC. It is shown that the weight of the filter for DLCIC is far lower than that for HCC. The proposed control technique have been validated by experiments. The experimental results show that at the dc-link voltage ripple which results from DLCIC is much lower than that from HCC. This demonstrates that DLCIC can minimise the dc-link capacitance in an SR machine drive