A new high-power-factor three-phase AC-DC converter: analysis,design, and experimentation

This paper proposes a new high-power factor three-phase AC-DC power converter, which is composed of a line interphase transformer (LIT) and two three-phase diode rectifiers, followed by a pulsewidth modulation (PWM) DC-DC boost power converter. The active switch of the boost converter is gated at a constant frequency such that the AC input current is discontinuous. This procedure provides an input current shaping without the third, fifth and seventh harmonics. The currents that flow through the LIT and boost inductors have such a high-switching frequency that ferrite cores with a small size can be utilized. In addition, the output voltage is regulated by PWM to compensate for line voltage variations and load change. Theoretical analysis, design procedure and example, along with experimental results taken from a 6 kW laboratory prototype are given     

Self-Driven Synchronous Rectification System With Input Voltage Tracking for Converters With a Symmetrically Driven Transformer

Synchronous rectification (SR) is mandatory to achieve good efficiencies with low output voltages. If a transformer is driven asymmetrically without dead times, the self-driven SR (SDSR) is a very interesting solution. However, if the transformer is driven symmetrically, the synchronous rectifiers are off during the dead times, and as a consequence, the efficiency is lowered. This paper deals with the optimization of an SDSR system that keeps the rectifiers on even during the dead times. The input voltage is tracked, and the information is used to adapt the gate to the source voltage of the synchronous rectifiers and improve the efficiency. The system has been implemented in a prototype, and the results have been compared with the ones obtained in the same prototype without SDSR.     

Effects of firing angle imbalance on 12-pulse rectifiers withinterphase transformers

Firing angle or source imbalances between 6-pulse bridges comprising a 12-pulse rectifier lead to current imbalance, due to the finite magnetizing inductance of the interphase transformer. The magnitude of the imbalance is limited by the negative feedback produced by load regulation of the 6-pulse groups. This paper uses both an averaged model and a piecewise-linear simulation to obtain a quantitative understanding of this effect. The averaged model is used to predict steady-state current shifts and transient behavior. The piecewise-linear model of the system is then used to verify and extend the results via computer simulation. It is shown that the current imbalance can be accurately predicted by the averaged model, making the model suitable for both feedback control and interphase transformer design     

A comparison of piezoelectric transformer AC/DC converters with current doubler and voltage doubler rectifiers

The objective of this study was to develop recommendations for an optimal design of piezoelectric transformer (PT) AC/DC converters. The paper presents a comprehensive comparison of the two commonly used rectifier topologies in a PT based power converters: current doubler and voltage doubler rectifiers. The advantages and disadvantages of the two rectifiers were investigated and the range of their applications with respect to output current, voltage, power capability, load resistance etc.-was delineated. Generic parameters are proposed and used to derive normalized and closed form equations that can help choosing a PT for a given set of requirements. Simulation and experimental results were found to be in a good agreement with the derivation of the theoretical analysis.     

Sequential connection and phase control of a high-current rectifieroptimized for copper electrowinning applications

This paper proposes an optimized sequential control technique for copper electrowinning high-current rectifiers. The converter comprises two series-connected six-pulse double-wye rectifiers, a step-down transformer, and a tuned input filter. The six-pulse rectifiers are fed from delta and polygon primary windings with different turns ratio and phase shifted by 5°. Under the proposed control scheme, one rectifier is kept at nominal output voltage, and the other one is phase controlled to control the load's current. The proposed strategy greatly improves the rectifier's performance, reducing its reactive power maximum demand by 62% compared to conventional rectifiers and, therefore, reduces the input filters power rating also by 62%. This is accomplished while keeping the input power factor above 0.95 throughout the whole operating range. Further, the converter's reactive power consumption presents a low varying characteristic, allowing it to use a fixed filter, even when operating from a power system not capable of withstanding large reactive power variations. Finally, it presents a harmonic current distortion comparable to conventional 12-pulse high-current rectifiers. This paper presents the design and optimization procedure of the rectifying system. A 2.5 kVA laboratory prototype was used to validate the converter model, later employed in evaluating the converter operating in a 10.5 MVA copper electrowinning facility. The results obtained confirm the advantages of the proposed converter and its control strategy     

A topology survey of single-stage power factor corrector with aboost type input-current-shaper

A topological review of the single stage power factor corrected (PFC) rectifiers is presented in this paper. Most reported single-stage PFC rectifiers cascade a boost-type converter with a forward or a flyback DC-DC converter so that input current shaping, isolation, and fast output voltage regulation are performed in one single stage. The cost and performance of single-stage PFC converters depend greatly on how its input current shaper (ICS) and the DC-DC converter are integrated together. For the cascade connected single-stage PFC rectifiers, the energy storage capacitor is found in either series or parallel path of energy flow. The second group appears to represent the main stream. Therefore, the focus of this paper is on the second group. It is found that many of these topologies can be implemented by combining a two-terminal or three-terminal boost ICS cell with DC-DC converter along with an energy storage capacitor in between. A general rule is observed that translates a three-terminal ICS cell to a two-terminal ICS cell using an additional winding from the transformer and vice verse. According to the translation rule, many of the reported single-stage PFC topologies can be viewed as electrically equivalent to one another. Several new PFC converters were derived from some existing topologies using the translation rule     

多脉波整流器的变压器联接方式

文中对多脉波整流器几种移相变压器的结构和绕组联接方式进行了分析、研究。自藕变压器的伏安容量大大小于变压器输出功率，减小了变压器的体积和价格。实验证明了多边形自藕变压器和24脉波整流自藕变压器的有效性。     

Three-Phase Rectifier With Near Sinusoidal Input Currents and Capacitors Connected on the AC Side

An analysis of a three-phase low-harmonic diode rectifier equipped with inductors, capacitors connected on the ac side, and diodes is presented. Inductors and capacitors are used in conjunction with the three-phase diode bridge rectifier to improve the waveform of the currents drawn from the utility grid. The operation of the proposed converter is analyzed, and on this basis, design considerations are commented. The converter characteristics are determined as a function of the load current. Comparisons between the studied converter and other rectifiers (classical rectifiers with passive or active filters, three-phase rectifiers with near sinusoidal input currents and capacitors connected on the dc side, and three-phase low-harmonic rectifiers applying the third harmonic current injection) are also presented. Several possible applications of the two variants of the three-phase rectifiers with near sinusoidal input currents (with capacitors connected on the dc side or on the ac side) are mentioned. Analytically derived results are experimentally verified     

Zero-voltage-switching half-bridge DC-DC converter with modified PWM control method

Asymmetric control scheme is an approach to achieve zero-voltage switching (ZVS) for half-bridge isolated dc-dc converters. However, it is not suited for wide range of input voltage due to the uneven voltage and current components stresses. This paper presents a novel "duty-cycle-shifted pulse-width modulated" (DCS PWM) control scheme for half-bridge isolated dc-dc converters to achieve ZVS operation for one of the two switches without causing the asymmetric penalties in the asymmetric control and without adding additional components. Based on the DCS PWM control scheme, an active-clamp branch comprising an auxiliary switch and a diode is added across the isolation transformer primary winding in the half-bridge converter to achieve ZVS for the other main switch by utilizing energy stored in the transformer leakage inductance. Moreover, the auxiliary switch also operates at ZVS and zero-current switching (ZCS) conditions. Furthermore, during the off-time period, the ringing resulted from the oscillation between the transformer leakage inductance and the junction capacitance of two switches is eliminated owing to the active-clamp branch and DCS PWM control scheme. Hence, switching losses and leakage-inductance-related losses are significantly reduced, which provides the converter with the potential to operate at higher efficiencies and higher switching frequencies. The principle of operation and key features of the proposed DCS PWM control scheme and two ZVS half-bridge topologies are illustrated and experimentally verified.     

Techniques for minimizing the input current distortion ofcurrent-controlled single-phase boost rectifiers

Techniques for minimizing the input current distortion of current-controlled single-phase boost rectifiers are described. The switching patterns of several boost rectifiers are examined to identify the nature of their input current waveforms. This analysis is used to examine the low-frequency current distortion levels, and hence the power quality, associated with the rectifiers. A PWM (pulse width modulation) strategy that selectively switches between positive unipolar PWM and negative unipolar PWM, called phase-adjusted unipolar PWM, is shown to produce the lowest current distortion levels. A novel two-switch asymmetrical half-bridge rectifier is presented that draws an input current at a unity fundamental power factor and with the same low distortion as obtained with the four-switch H-bridge rectifier. The operation of the various rectifiers is examined with reference to theoretical predictions, circuit simulations, and experimental results. This analysis is used to compare the performances of the various rectifier switching patterns     

Excellent reverse blocking characteristics of high-voltage 4H-SiCSchottky rectifiers with boron-implanted edge termination

Edge-terminated high-voltage Ti/4H-SiC Schottky rectifiers were successfully fabricated by using highly resistive layers at the periphery of Schottky contacts. The highly resistive layers were formed by B⁺ implantation followed by a heat treatment to improve the crystallinity of implanted layers. Utilizing these layers for the edge termination of 4H-SiC Schottky rectifiers, the reverse blocking characteristics were significantly improved in comparison with the rectifiers without edge termination, and a high-blocking voltage over 1100 V (the maximum: 1750 V) was achieved. The temperature dependence of the reverse-blocking characteristics was investigated, and high temperature operation even at 150°C was demonstrated with a blocking voltage over 1100 V     

An analysis of three-phase rectifiers with near-sinusoidal input currents

An analysis of a three-phase low-harmonic diode rectifier equipped with inductors, capacitors, and diodes is presented. Inductors and capacitors are used in conjunction with the three-phase diode rectifier bridge to improve the waveform of the currents drawn from the utility grid. The operation of the proposed converter is analyzed and, on this basis, design considerations are commented upon. The converter characteristics are determined as a function of the load current. Comparisons between the studied converter and other rectifiers (classical rectifiers, with passive or active filters, and three-phase low-harmonic rectifiers applying the third-harmonic current injection) are also presented. Several possible applications of the three-phase rectifiers with near-sinusoidal input currents are mentioned. Analytically obtained results are experimentally verified.     

Performance evaluation of high-power GaAs Schottky and siliconp-i-n rectifiers in hard- and soft-switching applications

The dynamic switching characteristics of high-power GaAs Schottky and silicon p-i-n rectifiers are studied at various temperatures. Devices were first characterized to measure forward and reverse I-V, C-V, reverse breakdown voltage, and reverse-recovery performance. The same devices were characterized for turn on and turn off in switching circuits designed to study the dynamic switching performances under hard- and soft-switching conditions at different temperatures. Advanced two-dimensional (2-D) mixed device and circuit simulations were used to study the internal plasma dynamics under boundary conditions imposed by the circuit operation. It is shown that for hard-switching applications, GaAs Schottky power rectifiers exhibit significantly reduced switching power losses compared to silicon p-i-n rectifiers. For soft-switching applications, there is not a significant difference in the switching power losses for these two devices. Diode performance at elevated temperatures is measured and simulated, and temperature dependencies of switching and conduction power losses are analyzed     

一种电压互感器油位巡视装置

电压互感器作为变电站电压采集的重要设备,对变电站的安全运行具有重要意义。针对变电站内部分电压互感器油位无法巡视的缺点,为了提高变电站电压互感器油位巡视覆盖率,研制了一种电压互感器油位巡视装置。该装置由相机、相机保护套、角度调节器、伸缩杆和防高压绝缘套组成,通过WiFi与手机通信。利用该装置记录无法巡视的电压互感器油位录像,或者直接与手机进行通信在低处进行安全观察,可切实解决电压互感器油位无法巡视的问题。通过对某地区变电站电压互感器油位无法巡视问题算例的分析,证明了该装置具有较高的实用价值。     

高输入功率因数的三相无源AC-DC变换器

对于采用三相不控整流桥作为前级的变换器，自然条件下其输入电流波形系数不高，使得输入功率因数委低，降低了电源的利用率。为此需要采用功率因数提高技术，其中无源PFC是一类重要的功率因数校正技术，在某些场合非常具有应用价值。本文介绍了几种三相无源AC-DC变换器的高功率因数方案，如采用LC滤波器、移相电抗器，谐振电抗器，移相变压器，相间变压器，相间电抗器等，在进行简单的工作原理描述后，给出了部分方案的MATLAB/SIMULINK仿真结果。     

升压变压器低阻抗保护的原理及测试方法

升压变低阻抗保护主要作为发电机—变压器组相间短路的后备保护,逻辑判据中包含相间阻抗、相电流及负序电流三个变量参数,在测试过程中有一定的难度。通过对国电南京自动化股份有限公司生产的GDGT801型数字式发变组保护A柜变压器低阻抗保护的调试和检测,总结出该保护的调试技巧及测试方法,对有类似微机保护装置的发电厂、变电站、电力职业院校及电力培训中心也有一定借鉴意义。     

Performance investigation of a current-controlled voltage-regulatedPWM rectifier in rotating and stationary frames

Active front-end rectifiers with reduced input current harmonics and high input power factor will be required in the near future for utility interfaced applications. In order to meet the new and more stringent regulations with force-commutated switches, the voltage source inverter approach is superior to the conventional current source approach, in terms of number of components and control options. However, the straightforward power angle control of the rectifier is characterized by a slow response and potential stability problems. This paper proposes a current-controlled PWM rectifier as an alternative. It provides near sinusoidal input currents with unity power factor and a low output voltage ripple. Moreover, it produces a well-defined input current harmonic spectrum, exhibits fast transient response to load voltage variations, and is capable of regenerative operation. PWM pattern generation is based on a carrier technique and the current controller is implemented in the: (a) stationary (abc) frame; and (b) rotating (dqo) frame. The design and the performance of the two controller options are investigated and compared     

Dynamic control of a fixed pattern rectifier

A three-phase, sinusoidal, active rectifier is presented, based on the classical inverter topology. The switches are governed by a fixed pulse width modulation (PWM) pattern, and the control strategy is extremely simplified as compared with many active rectifiers. General equations describing the steady-state operation of fixed pattern rectifiers are given. A dynamic model of the simplified control rectifier is presented, based on the nonlinear equations describing the system. Based on the analytical model, the classical PI-controller yields poor dynamic results, especially at low load conditions. However, the dynamic performance of the prototype is much better, due to the effects of commutation dead time of the rectifier switches. It is shown that a small modification to the classical PI-controller yields a remarkable increase in amplitude and phase margin, without slowing down the response. The obtained dynamics show a clear improvement over the classical PI-controller and are adequate for most applications     

变压器相间后备保护现存问题及改善措施

在导致变压器损坏或者故障的外部因素中,变压器相间后备保护方面的问题是最主要的因素之一,其对低压侧相间故障的灵敏程度不够,而且动作的时间限制较长是故障的主要原因。文中介绍了变压器的后备保护,分析了变压器相间后备保护中存在的问题,并且提出了针对性的改善措施。     

Analysis and Design Strategy of UHF Micro-Power CMOS Rectifiers for Micro-Sensor and RFID Applications

Design strategy and efficiency optimization of ultrahigh-frequency (UHF) micro-power rectifiers using diode-connected MOS transistors with very low threshold voltage is presented. The analysis takes into account the conduction angle, leakage current, and body effect in deriving the output voltage. Appropriate approximations allow analytical expressions for the output voltage, power consumption, and efficiency to be derived. A design procedure to maximize efficiency is presented. A superposition method is proposed to optimize the performance of multiple-output rectifiers. Constant-power scaling and area-efficient design are discussed. Using a 0.18-mum CMOS process with zero-threshold transistors, 900-MHz rectifiers with different conversion ratios were designed, and extensive HSPICE simulations show good agreement with the analysis. A 24-stage triple-output rectifier was designed and fabricated, and measurement results verified the validity of the analysis