Low Voltage Regulator Modules and Single Stage Front-end Converters

Evolution in microprocessor technology poses new challenges for supplying power to these devices. To meet demands for faster and more efficient data processing, modem microprocessors are being designed with lower voltage implementations. More devices will be packed on a single processor chip and the processors will operate at higher frequencies, exceeding 1GHz. New high-performance microprocessors may require from 40 to 80 watts of power for the CPU alone. Load current must be supplied with up to 30A/µs slew rate while keeping the output voltage within tight regulation and response time tolerances. Therefore, special power supplies and Voltage Regulator Modules (VRMs) are needed to provide lower voltage with higher current and fast response. In the part one (chapter 2,3,4) of this dissertation, several low-voltage high-current VRM technologies are proposed for future generation microprocessors and ICs. The developed VRMs with these new technologies have advantages over conventional ones in terms of efficiency, transient response and cost. In most cases, the VRMs draw currents from DC bus for which front-end converters are used as a DC source. As the use of AC/DC frond-end converters continues to increase, more distorted mains current is drawn from the line, resulting in lower power factor and high total harmonic distortion. As a branch of active Power factor correction (PFC) techniques, the single-stage technique receives particular attention because of its low cost implementation. Moreover, with continuously demands for even higher power density, switching mode power supply operating at high-frequency is required because at high switching frequency, the size and weight of circuit components can be remarkably reduced. To boost the switching frequency, the soft-switching technique was introduced to alleviate the switching losses. The part two (chapter 5,6) of the dissertation presents several topologies for this front-end application. The design considerations, simulation results and experimental verification are discussed

A Single-Stage LED Driver Based on ZCDS Class-E Current-Driven Rectifier as a PFC for Street-Lighting Applications

This paper presents a light-emitting diode (LED) driver for street-lighting applications that uses a resonant rectifier as a power-factor corrector (PFC). The PFC semistage is based on a zero-current and zero-derivative-switching (ZCDS) Class-E current-driven rectifier, and the LED driver semistage is based on a zero-voltage-switching (ZVS) Class-D LLC resonant converter that is integrated into a single-stage topology. To increase the conduction angle of the bridge-rectifier diodes current and to decrease the current harmonics that are injected in the utility line, the ZCDS Class-E rectifier is placed between the bridge-rectifier and a dc-link capacitor. The ZCDS Class-E rectifieris driven by a high-frequency current source, which is obtained from a square-wave output voltage of the ZVS Class-D LLC resonant converter using a matching network. Additionally, the proposed converter has a soft-switching characteristic that reduces switching losses and switching noise. A prototype for a 150-W LED street light has been developed and tested to evaluate the performance of the proposed approach. The proposed LED driver had a high efficiency (>91%), a high PF (>0.99), and a low total harmonic distortion (THD i <; 8%) under variation of the utility-line input voltage from 180 to 250 V rms . These experimental results demonstrate the feasibility of the proposed LED scheme

Optimization And Design Of Photovoltaic Micro-inverter

To relieve energy shortage and environmental pollution issues, renewable energy, especially PV energy has developed rapidly in the last decade. The micro-inverter systems, with advantages in dedicated PV power harvest, flexible system size, simple installation, and enhanced safety characteristics are the future development trend of the PV power generation systems. The double-stage structure which can realize high efficiency with nice regulated sinusoidal waveforms is the mainstream for the micro-inverter. This thesis studied a double stage micro-inverter system. Considering the intermittent nature of PV power, a PFC was analyzed to provide additional electrical power to the system. When the solar power is less than the load required, PFC can drag power from the utility grid. In the double stage micro-inverter, the DC/DC stage was realized by a LLC converter, which could realize soft switching automatically under frequency modulation. However it has a complicated relationship between voltage gain and load. Thus conventional variable step P&O MPPT techniques for PWM converter were no longer suitable for the LLC converter. To solve this problem, a novel MPPT was proposed to track MPP efficiently. Simulation and experimental results verified the effectiveness of the proposed MPPT. The DC/AC stage of the micro-inverter was realized by a BCM inverter. With duty cycle and frequency modulation, ZVS was achieved through controlling the inductor current bi-directional in every switching cycle. This technique required no additional resonant components and could be employed for low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes were derived from the basic theory of the proposed technique. They were referred to as Boundary Current Mode (BCM), Variable Hysteresis Current Mode (VHCM), and Constant Hysteresis Current Mode (CHCM) individually in this paper with their advantages and disadvantages analyzed in detail. Simulation and experimental iv results demonstrated the feasibilities of the proposed soft-switching technique with the digital control schemes. The PFC converter was applied by a single stage Biflyback topology, which combined the advantages of single stage PFC and flyback topology together, with further advantages in low intermediate bus voltage and current stresses. A digital controller without current sampling requirement was proposed based on the specific topology. To reduce the voltage spike caused by the leakage inductor, a novel snubber cell combining soft switching technique with snubber technique together was proposed. Simulation and experimental waveforms illustrated the same as characteristics as the theoretical analysis. In summary, the dissertation analyzed each power stage of photovoltaic micro-inverter system from efficiency and effectiveness optimization perspectives. Moreover their advantages were compared carefully with existed topologies and control techniques. Simulation and experiment results were provided to support the theoretical analysis

A New Single-Phase Single-Stage AC-DC Stacked Flyback Converter With Active Clamp ZVS

Single-stage AC-DC converters integrate an AC-DC front-end converter with a DC-DC back-end converter. Compared with conventional two-stage AC-DC converters, single-stage AC-DC converters use less components and only one controller, which is used to regulate the output voltage. As a result, the cost, size and complexity of AC-DC converters can be reduced, but single-stage converters do not perform as well as two-stage converters, and most have drawbacks that are related to the fact that the DC bus voltage is not controlled an can become excessive. A new single-phase single-stage AC-DC converter that uses stacked flyback converters is proposed in this thesis. The proposed converter consists of two low power flyback converters stacked on top of each other and an active clamp that helps the main switches operate with ZVS. The stacked structure helps reduce the voltage stresses typical fund in many single-stage converters. In the thesis, the operation of the converter is explained, the steady-state characteristics of the converter are determined and its design is discussed. The feasibility of the new converter is confirmed with experimental results obtained from a 100VAC~220VAC worldwide input, 48V output, 100kHz switching frequency and 200 W output power prototype converter

A Class-E-Based Resonant AC-DC Converter With Inherent PFC Capability

This paper investigates the use of the class-E inverter for power factor correction (PFC) applications. Analytical and state-space models are derived showing the class-E inverter’s capability of achieving inherent PFC operation with a constant duty cycle. The inherent PFC operation limits the controller responsibility to the regulation of the output voltage, which is key for resonant converters with challenging control. A converter incorporating a diode bridge, a class-E inverter, and a class-D rectifier is presented for the PFC stage in single-phase offline converters. A prototype is designed to validate the analysis and presented design method. The prototype operates with zero-voltage switching (ZVS) across the load range and achieves up to 211 W of output power at an efficiency of 88%, with an inherent power factor of 0.99 and a total harmonic distortion (THD) of 8.8 %. Frequency modulation is used to achieve lower output power down to 25 W, with a power factor of 0.95, THD of 28 %, and an efficiency of 88 %

Power Factor Correction Using Bridgeless Boost Topology

Power quality is becoming a major concern for many electrical users. The high power non linear loads (such as adjustable speed drives, arc furnace, static power converter etc) and low power loads (such as computer, fax machine etc) produce voltage fluctuations, harmonic currents and an inequality in network system which results into low power factor operation of the power system. The devices commonly used in industrial, commercial and residential applications need to go through rectification for their proper functioning and operation. Due to the increasing demand of these devices, the line current harmonics create a major problem by degrading the power factor of the system thus affecting the performance of the devices. Hence there is a need to reduce the input line current harmonics so as to improve the power factor of the system. This has led to designing of Power Factor Correction circuits. Power Factor Correction (PFC) involves two techniques, Active PFC and Passive PFC. An active power factor circuit using Boost Converter is used for improving the power factor. This thesis work analyzes the procedural approach and benefits of applying Bridgeless Boost Topology for improving the power factor over Boost Converter Topology. A traditional design methodology Boost Converter Topology is initially analyzed and compared with the Bridgeless Boost topology and the overall Power Factor (PF) can be improved to the expectation. Method of re-shaping the input current waveform to be similar pattern as the sinusoidal input voltage is done by the Boost converter and the related controls that act as a Power Factor Correction (PFC) circuit. Higher efficiency can be achieved by using the Bridgeless Boost Topology. In this paper simulation of Boost Converter topology and Bridgeless PFC boost Converter is presented. Performance comparisons between the conventional PFC boost Converter and the Bridgeless PFC Boost Converter is done

Analysis of PFC Buck-Boost Converter Fed PMBLDC Motor Drive Systems

Electric motors influence almost every aspect of modern life. Refrigerators, vacuum cleaners, air conditioners, fans, computer hard drives, automatic vehicle windows, &amp; a number of other household products &amp; devices employ electric motors to convert electrical energy into usable mechanical energy. Electric motors power a wide range of industrial processes in addition to powering residential appliances. Brushless DC (BLDC) motor drives have grown in popularity in recent years due to their suitability for a wide range of low and medium power applications such as household appliances, medical equipment, position actuators, Heating, Ventilation, and Air Conditioning (HVAC), motion control, and transportation. These drives have great efficiency, dependability, durability, and outstanding performance across a wide range of speed control. The BLDC motor cannot be connected directly to the supply and must be driven by a drive consisting of VSI controlled by an electronic commutation system. Harmonics are introduced into the main power supply and power factor issue by the electronic commutation system and rectification procedure. Power Factor Correction (PFC) converters are used to improve the power quality and power factor of the alternating current mains