Control Techniques for DC-DC Buck Converter with Improved Performance

The switched-mode dc-dc converters are some of the most widely used power electronics circuits for its high conversion efficiency and flexible output voltage. These converters used for electronic devices are designed to regulate the output voltage against the changes of the input voltage and load current. This leads to the requirement of more advanced control methods to meet the real demand. Many control methods are developed for the control of dc-dc converters. To obtain a control method that has the best performances under any conditions is always in demand. Conventionally, the dc-dc converters have been controlled by linear voltage mode and current mode control methods. These controllers offer advantages such as fixed switching frequencies and zero steady-state error and gives a better small-signal performance at the designed operating point. But under large parameter and load variation, their performance degrades. Sliding mode (SM) control techniques are well suited to dc-dc converters as they are inherently variable structure systems. These controllers are robust concerning converter parameter variations, load and line disturbances. SM controlled converters generally suffer from switching frequency variation when the input voltage and output load are varied. This complicates the design of the input and output filters. The main objective of this research work is to study different control methods implemented in dc-dc converter namely (linear controllers, hysteresis control, current programmed control, and sliding mode (SM) control). A comparison of the effects of the PWM controllers and the SM control on the dc-dc buck converter response in steady state, under line variations, load variations is performed

Modelling of a Buck converter with adaptive modulation and design of related driver stage

This thesis concerns the modelling of a buck converter with peak current mode control, and adaptive PWM/PFM (constant Ton) and provides a small signal model, derived from steady-state averaging, for all the operative regions of the converter, and used for stability analysis and parametric optimization. Eventually the design of a driver stage is proposed, with segmentation, dead time control and zero cross detection as main functionalities to improve efficienc

DC-DC Converters - Dynamic Model Design and Experimental Verification

To obtain high performance control of a dc-dc converter, a good model of the converter is needed. The load usually affects the dynamics and one way to take this into consideration is to regard the load as a part of the converter. The load is often the most variable part of this system. If the load current and the output voltage are measured there are good possibilities to obtain a good model of the load on-line. Adaptive control can then be applied to improve the control. In peak current-mode control, the output voltage and the inductor current are measured and utilized for control. In the author's licentiate thesis, analytic models were derived for the case where the load current is also measured and utilized for control. The control-to-output transfer function, the output impedance, and the audio susceptibility were derived for the buck, boost, and buck-boost converters operated in continuous conduction mode in the case of resistive load. The use of load current can be seen as gain scheduling in the case where the load is a resistor. Gain scheduling can be considered a special case of adaptive control. The majority of the results in the licentiate thesis were validated by comparing the frequency responses predicted by the analytic models and switched large-signal simulation models. In this thesis, additional results are presented for the buck converter. Experimental results obtained by means of a network analyzer verify the derived control-to-output transfer function and the audio susceptibility but not the output impedance at low frequencies. In the experimental buck converter there are stray resistances in the inductor, transistor, and diode but these stray resistances were not considered in the licentiate thesis. A new transfer function for the output impedance is derived where these stray resistances are considered and it is in good agreement with the experimental result also at low frequencies. If the current to the output capacitor is measured in addition to the output voltage and the inductor current, the load current can be calculated as the difference between the inductor and capacitor currents in the case of the buck converter. Hence, the measurement of the load current can be replaced by measurement of the capacitor current. If this possibility is utilized and the capacitor current is measured by means of a current transformer, a low-frequency resonance is introduced in the frequency responses according to experimental results. The reason for this resonance is due to the high-pass-filter characteristics of the current transformer. A new analytic model is derived which predicts the resonance

Light-load power management in differential power processing systems

Series stacking is used as a means of implicitly raising DC bus voltages without additional power processing and has been explored widely in the context of photovoltaic sources and batteries in the past. More recently it has also been explored in the context of server loads and microprocessor cores. Supplying power at a higher voltage supports a reduction in conduction losses and reduces complexity in power supply design related to the high current at low voltage nature of microprocessor loads. However, series stacking of DC voltage domains forces the dc voltage domains to share the same currents. In the context of series stacked loads, this would lead to failure of voltage regulation of individual dc voltage domains. Additional power electronics, commonly referred to as differential power processing (DPP) units are required to perform this vital task. The idea is to let the DPP converters (which need to have bidirectional capability) process the difference between currents of adjacent voltage domains, so that the load voltages are regulated. Although series stacking and DPP has been explored in significant detail, the importance of light load efficiencies of these DPP converters has not been highlighted enough in the past. In this document we discuss the importance of light load control in common series stacked systems with DPP and propose a light load power management scheme for bidirectional buck-boost converters (which is the building block of most DPP converter topologies). Extending efficient operation load range of converters (to process higher power in rare heavily mismatched conditions and to maintain good light load efficiencies at the same time) with multiphase converters and asymmetric current sharing is also discussed in the context of DPP converters. We finally propose to build a series stacked system of low voltage loads and DPP regulators to demonstrate the advantages of series stacking as opposed to the conventional parallel connection

State Space Modelling of Current-Mode Control and its Application to Input Impedance Shaping of Power Electronic Constant-Power Loads

Distributed DC power systems offer many benefits over AC line distribution systems such as improved energy conversion efficiency and reduced mass due to high-frequency isolation. Unfortunately, distributed DC systems with regulated bus voltages suffer from destabilising effects from loading by downstream power electronic converters behaving as constant-power loads. Power electronic constant-power loads present a negative incremental input impedance to the main bus, which may result in negative impedance instability. Avoiding the effects of negative impedance instability is most often achieved by following impedance ratio criteria, such as the Middlebrook stability criterion which has the drawback of imposing conservative constraints on the design of the power system components. Such conservative criteria can also result in the over-design of converter input filters and artificially imposing limits on the bandwidths of the load power electronic converters. Through the use of a current-mode controlled pre-regulator, the input impedance of power electronic constant-power loads can be shaped to interact with the main bus impedance in a stable manner while optimising converter bandwidth and line rejection. A new state space based approach is developed to model peak and valley current-mode control. Following this new approach, models for all basic DC-DC converter topologies are created (Buck, Boost and Flyback). This new model allows for an accurate analysis of a pre-regulator and its straight forward design

HA 컨버터를 응용한 AC-DC 및 DC-AC 전력 변환

학위논문 (박사)-- 서울대학교 대학원 : 전기공학부, 2013. 2. 조보형.This dissertation proposes a new topology H-bridge converter with additional switch legs (HA converter). The proposed topology has simple circuit structure with expandability and flexibility. With six semiconductor devices and single inductor, the topology is capable of operating as buck, boost, and buck-boost converter. Theoretically, it demonstrates low common mode current and electromagnetic interference (EMI) by solidly connecting grounds of input and output terminals. The proposed topology is advantageous not only in grid-connected power conversion application but also in stand-alone power system such as electric vehicle, because these systems include large parasitic capacitances and are prone to high common mode EMI due to the wide mechanical structure of the conductor. Among many offspring circuits of the HA converter, a boost-buck-boost (B3) rectifier for off-line power supply with active power factor correction and a buck-buck-boost (B3) inverter for grid-connected photovoltaic system are proposed as two practical examples. Principle of operations, dedicated control algorithms, and filters for the new circuits are analyzed and designed in detail. Experimental results based on the laboratory prototype hardware prove that the proposed circuits outperform their conventional counterparts by showing low common mode noise and comparable efficiency.Abstract............................i Contents...........................ii List of Figures....................iv List of Tables......................x 1. Introduction.....................1 1.1. Motivations and Backgrounds....1 1.2. Objectives.....................2 1.3. Dissertation Outlines..........4 2. H-bridge Converter with Additional Switch Legs (HA Converter)......................7 2.1. Review of Common Mode EMI......7 2.1.1. In Off-line AC-DC Rectifier.11 2.1.2. In Grid-connected DC-AC PV Inverter...........................16 2.2. Topology Derivation...........24 2.2.1. Dual H-bridges..............29 2.2.2. HA Converter................31 2.3. Feature of HA Converter.......34 3. B3 Rectifier for AC-DC Conversion.........................40 3.1. Advantage of B3 Rectifier.....40 3.2. Operation.....................43 3.3. Control.......................45 3.3.1. Power Imbalance in a Line Cycle..............................47 3.3.2. Inductor Current Reference Calculation........................51 3.3.3. Compensator Design..........56 3.4. Differential Input Filter Design.............................67 3.5. Experiments...................75 3.5.1. Implementations.............75 3.5.2. Results and Discussions.....81 4. B3 Inverter for DC-AC Conversion.........................88 4.1. Advantage of B3 Inverter...........................88 4.2. Operation.....................91 4.3. Control.......................93 4.3.1. Inductor Current Reference Calculation........................93 4.3.2. Compensator Design..........98 4.4. Differential Output Filter Design............................104 4.5. Experiments..................111 4.5.1. Implementations............111 4.5.2. Results and Discussions....117 5. Flexibility of HA Converter.........................125 6. Conclusion and Further Works...134 Appendix..........................137 A.1. Correction Factor of B3 Rectifier in Small Signal Model.............................137 A.2. Input Impedances of Boost and Buck-boost Converter.........................139 A.3. Loss Estimation of B3 Rectifier Switches..........................144 A.4. H5 and HERIC Inverter Operations........................153 References........................160 국문 초록.........................168 감사의 글.........................169Docto

Performance Improvement of AC-DC Power Factor Correction Converters For Distributed Power System

In present situation, the increase in the utilization of computers, laptops,uninterruptable power supplies, telecom and bio-medical equipments has become uncontrollable as its growth is rising exponentially. Hence, increase in functionality of such equipments leads to the higher power consumption and low power density which provided a large market to distributed power systems (DPS). The development of these DPS posed challenges to power engineers for an efficient power delivery with stringent regulating standards; this is the motivation and driving force of this research work. The objective is to minimize the switching losses of front-end converters employed in DPS, with the primary aim of achieving nearly unity power factor operation of converters.Single-phase and three-phase rectifiers are increasingly used in the field of alternating current – direct current (AC-DC) power converters as front-end converters in DPS. For power factor correction (PFC) stage, conventional single-phase AC-DC PFC boost converter is the most suitable topology because of its inherent advantages. These PFC boost converters exhibit poor dynamic regulation of output voltage owing to low pass filter in the voltage feedback loop. Research effort has been made to mitigate this problem of AC-DC PFC boost converters. An extended pulse width modulation switching technique has been investigated and proposed especially for single-phase and three-phase AC-DC PFC boost converters to improve the dynamic response of output voltage during transient periods

High gain non-isolated DC-DC converter topologies for energy conversion systems

PhD ThesisEmerging applications driven by low voltage level power sources, such as photovoltaics, batteries and fuel cells require static power converters for appropriate energy conversion and conditioning to supply the requirements of the load system. Increasingly, for applications such as grid connected inverters, uninterruptible power supplies (UPS), and electric vehicles (EV), the performance of a high efficiency high static gain power converter is of critical importance to the overall system. Theoretically, the conventional boost and buck-boost converters are the simplest non-isolated topologies for voltage step-up. However, these converters typically operate under extreme duty ratio, and severe output diode reverse recovery related losses to achieve high voltage gain. This thesis presents derivation, analysis and design issues of advanced high step-up topologies with coupled inductor and voltage gain extension cell. The proposed innovative solution can achieve significant performance improvement compared to the recently proposed state of the art topologies. Two unique topologies employing coupled inductor and voltage gain extension cell are proposed. Power converters utilising coupled inductors traditionally require a clamp circuit to limit the switch voltage excursion. Firstly, a simple low-cost, high step-up converters employing active and passive clamp scheme is proposed. Performance comparison of the clamps circuits shows that the active clamp solution can achieve higher efficiency over the passive solution. Secondly, the primary detriment of increasing the power level of a coupled inductor based converters is high current ripple due to coupled inductor operation. It is normal to interleaved DC-DC converters to share the input current, minimize the current ripple and increase the power density. This thesis presents an input parallel output series converter integrating coupled inductors and switched capacitor demonstrating high static gain. Steady state analysis of the converter is presented to determine the power flow equations. Dynamic analysis is performed to design a closed loop controller to regulate the output voltage of the interleaved converter. The design procedure of the high step-up converters is explained, simulation and experimental results of the laboratory prototypes are presented. The experimental results obtained via a 250 W single phase converter and that of a 500 W interleaved converter prototypes; validate both the theory and operational characteristics of each power converter.Petroleum Technology Development Fund (PTDF) Nigeri