Feedforward simple control technique for on-chip all-digital three-phase AC/DC power-MOSFET converter with least components

A novel simple control technique for on-chip all-digital three-phase alternating current to direct current (AC/DC) power-metal oxide semiconductor field-effect transistors (MOSFET) converter with least components, which is employed to obtain small current and DC output voltage ripples as well as excellent performance, and using a feedforward simple control method for DC output voltage regulation is proposed. The proposed all-digital feedforward controller has the features of low cost, simple control, fast response, independence of load parameters and the switching frequency, it has no need for compensation, and high stability characteristics; moreover, the proposed controller consists of three operation amplifiers and few digital logic gates that are directly applied to the three-phase converter. The power-MOSFETs are also known as power switches, whose control signals are derived from the proposed all-digital feedforward controller. Instead of thyristors or diodes, the application of power-MOSFETs can reduce the loss of AC/DC converter that is proper to the power supply system. The input stage of an AC/DC converter functions as a rectifier and the output stage is a low pass inductor capacitor (LC) filter. The input AC sources may originate from miniature three-phase AC generator or low-power three-phase DC/AC inverter. The maximum output loading current is 0.8 A and the maximum DC output ripple is less than 200 mV. The prototype of the proposed AC/DC converter has been fabricated with Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 mum 2P4M complementary MOS (CMOS) processes. The total chip area is 2.333 1.960 mm². The proposed AC/DC converter is suitable for the following three power systems with the low power, DC/DC converter, low-dropout linear regulator and switch capacitor. Finally, the theoretical analysis is verified to be correct by simulations and experiments.     

Advanced control for PWM converter and variable-speed induction generator

The paper describes a simple control structure for a vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Deadbeat current control is developed for a voltage source PWM converter and the three-phase variable speed squirrel-cage IG to regulate DC-link and generator voltages with newly designed phase-locked-loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to build up the voltage of the IG without the need for a battery and to reduce the rating of the PWM converter with the need for only three sensors. This proposed scheme can be used efficiently for variable speed wind or hydro energy conversion systems. The measurements of the IG system at various speeds and loads are given and show that this proposed system is capable of good AC and DC voltages regulation     

Zero-voltage-switching DC/AC inverter

A novel zero-voltage-switching (ZVS) DC/AC inverter is proposed. The proposed inverter can not only provide output voltage that is higher or lower than DC input voltage but can also use the pulse-width modulation (PWM) control technique. Furthermore, in the proposed inverter, besides operating at constant frequency, all semiconductor devices operate at soft-switching without additional voltage stress and current stress. A design example of 1000 W ZVS-PWM buck-boost inverter is examined to assess the inverter performance     

High-efficient three-phase on-line UPS by using T-source inverter with third harmonic injected maximum constant boost PWM control

This paper presents the analysis of three-phase on-line uninterruptible power supply (UPS) by employing T-source inverter (TSI) with third harmonic injected maximum constant boost PWM control and the results are compared with traditional UPS. Traditional UPS consists of step-up transformer or DC–DC booster along with voltage source inverter which decreases the efficiency and increases energy conversion cost. The proposed three-phase UPS using TSI has high-voltage boost capability through shoot-through zero state which is not present in traditional voltage source inverter (VSI) and current source inverter. This proposed UPS with TSI increases the efficiency with fewer components, reduces the harmonics, increases the voltage gain, and reduces the voltage stress. The performance of three-phase on-line UPS based on TSI is analyzed and evaluated in MATLAB/SIMULINK software and the results are compared with Z-source inverter-fed UPS and VSI-fed UPS. Experimental results are presented for the validation of the simulation and theoretical analysis.     

交流变频调速系统仿真建模及谐波特性分析

随着电力电子技术的发展,交流变频调速系统以其强大的优势逐渐取代传统的直流调速传动,其在给人们生产生活带来方便和效率的同时,也造成了电力系统谐波污染加重的问题。因此,设计了一种开环正弦脉宽调制（sinusoidal pulse width modulation,SPWM）控制的交流变频调速系统并搭建仿真模型,实现了对系统中变频器输出电压频率和幅值及电机转速的灵活控制。对系统网侧电压和电流进行了谐波特性分析,结果表明：网侧电压的波形比较理想、畸变很小,而电流波形畸变严重;且随着变频器输出频率的增加,电压波形畸变程度有所加剧,电流畸变程度有所减轻。     

敏感用户高品质交-直流级联供电方案研究

工业过程中大量使用的变频器(variable frequency drive,VFD)在采用传统交流供电时易受到电压暂降影响,传统治理方式存在检测延时、控制复杂等问题。为此,该文从敏感负荷变频器在电网扰动工况下的供电需求量化出发,围绕供电拓扑设计、DC/DC变换器的控制策略及储能单元容量配置等方面,构建一种实用化工业用交-直流级联供电方案。该文利用电压暂降过程中直流供电回路与敏感负荷间的压差自感应控制,实现交-直流供电回路无扰动切换,提高电压暂降治理响应的快速性;采用两相交错并联DC/DC变换器接入集中式储能,减少储能系统纹波系数,并给出两相均流控制方法。最后,通过Matlab/Simulink中的建模仿真与样机的实验测试,验证所提方案能够在交流系统发生不同严重程度电压暂降过程中为各类敏感负荷提供稳定的连续供电,为解决工业敏感用户高品质供电问题提供可实用的新思路。     

Negative sequence compensation within fundamental positive sequence reference frame for a stiff micro-grid generation in a wind power system using slip ring induction machine

An isolated wind power generation scheme using slip ring induction machine (SRIM) is proposed. The proposed scheme maintains constant load voltage and frequency irrespective of the wind speed or load variation. The power circuit consists of two back-to-back connected inverters with a common dc link, where one inverter is directly connected to the rotor side of SRIM and the other inverter is connected to the stator side of the SRIM through LC filter. Developing a negative sequence compensation method to ensure that, even under the presence of unbalanced load, the generator experiences almost balanced three-phase current and most of the unbalanced current is directed through the stator side converter is the focus here. The SRIM controller varies the speed of the generator with variation in the wind speed to extract maximum power. The difference of the generated power and the load power is either stored in or extracted from a battery bank, which is interfaced to the common dc link through a multiphase bidirectional fly-back dc-dc converter. The SRIM control scheme, maximum power point extraction algorithm and the fly-back converter topology are incorporated from available literature. The proposed scheme is both simulated and experimentally verified.     

Dynamics on a ZCZVT soft-switching DC/DC boost converter

The non-floating switches, zero-current–zero-voltage-transition (ZCZVT) soft-switching DC/DC boost power converter is proposed in this article. The AC small-signal mathematical model for the ZCZVT boost converter is then derived. It shows that the ZCZVT boost converter exhibits better dynamical behavior than the conventional PWM boost converter. The accuracy of theoretical results is verified by experiments and simulations. In addition, a classical and a modified integral variable structure controllers are designed to achieve output voltage regulation. They are used to eliminate the effect of the variations of input voltage and load on the output voltage. The performances of the proposed converter with these controllers are also validated by experimental results.     

Five-leg inverter PWM technique for reduced switch count two-motor constant power applications

Industrial applications often require a number of variable speed electric drives. In the majority of cases, these multi-motor drive systems require independent control of individual motors. Over the past decade, research efforts have been made to reduce the number of power electronic devices required in multi-motor drive systems in order to reduce the overall complexity and hence cost of the drive. It has been shown recently that it is possible to independently control two three-phase induction machines using a five-leg voltage source inverter (VSI) as the supply, with one inverter leg being common to both machines. The existing pulse-width modulation (PWM) methods for this supply topology either limit the amount of DC bus voltage available to each machine or lead to uneven and increased switching frequency across five legs of the VSI. A new PWM method that effectively utilises the standard three-phase modulators in conjunction with appropriate modifications to generate modulation signals for all five legs of the VSI is presented. It enables an arbitrary distribution of the available DC bus voltage between the two machines. The considered supply topology, when utilised in conjunction with the developed PWM technique, is well suited to constant power applications such as centre-driven winders. Verification of the developed modulation method and its applicability to winder systems are demonstrated by experimental testing that includes both steady state and transient operation.     

A grid-tie PV inverter with the ability to improve power quality under unbalanced and distorted source voltage conditions

ABSTRACT

This paper proposes a grid-tie PV inverter that is able to improve power quality under conditions of both distorted and unbalanced source voltage. The presented strategy is based on the instantaneous power theory and uses a second-order generalized integrator-quadrature signal generator (SOGI-QSG). The presented control strategy is aimed at compensating reactive power, eliminating current harmonics, load balancing, and enabling the PV to inject maximum power to the grid. The advantages of the control system are the use of SOGI-QSG adaptive filter and frequency-locked loop (FLL), and removing the low-pass filter and phase-locked loop (PLL). DC–DC and DC–AC converters are utilized for connecting the PV to the grid. The DC–DC and DC–AC converters are responsible for maximum PV power tracking and achieving the control aims, respectively. Using 4-leg converter structure for grid-tie inverter enables achieving the control objectives in 3-phase 4-wire distribution network without any transformer. The presented control strategy is applied to a 3-phase 4-wire distribution network and is simulated in MATLAB/SIMULINK environment. The results of this simulation are then compared with the conventional instantaneous power method in areas including load balancing, reactive power compensation and the elimination of current harmonics, under unbalanced and distorted source voltage conditions.     

Soft-switching flyback inverter with enhanced power decoupling for photovoltaic applications

A novel single-phase flyback inverter for photovoltaic applications is proposed to achieve low-frequency ripple current reduction on the DC busbar and to draw sinusoidal current into the AC grid. Based on capacitive idling techniques, the proposed circuit topology is derived from a single-ended primary-inductance converter and two-switch flyback inverter to obtain soft-switching operation for all of the active switches. Compared with a buck-boost inverter and other flyback inverter topologies for AC photovoltaic module systems, no extra active switches are used in the proposed inverter to realise both soft-switching and enhanced power decoupling with only four active switches. Peak-current mode control method is employed in the control schemes to ensure pure sinusoidal current with unity power factor on the AC grid. Laboratory experimental results based on a 500 W prototype are provided to verify the effectiveness of the proposed inverter     

Novel zero voltage switching dual-switch forward converter with ripple current cancellation

A zero voltage switching (ZVS) dual-switch forward converter with ripple current cancellation is presented. In the proposed converter, active clamp circuit is used to clamp the voltage stresses and to realise ZVS of all switching devices. Active clamp boost converter with power factor correction is used in the front stage of the proposed converter to draw a sinusoidal line current from the AC source and to maintain a constant voltage at the DC bus. The second stage of the proposed converter is a dual-switch forward converter with current doubler rectifier to obtain the isolated low output voltage. Active clamp circuit used in the DC/DC converter can recycle the energy stored in the leakage inductor and magnetising inductor so that the voltage stresses on the switches are limited and the ZVS feature is realised. The current doubler rectifier offers the ripple current cancellation at the output capacitor and reduces the current stress of the transformer secondary winding. The circuit configuration and principle of operation are analysed and discussed in detail. Experimental results with a laboratory prototype based on a 90-260 V_rms input and 12 V/30 A output were provided to verify the effectiveness of the proposed converter.     

Control of a converter system for an asymmetrical parameter type two-phase induction motor drive operating in motoring and generating modes

The control of a converter system is presented and discussed for an asymmetrical parameter type two-phase induction machine drive that is operating in motoring and generating modes. The proposed system consists of back-to-back voltage source converters. For a machine side, a three-leg voltage source converter provides both unbalanced and balanced two-phase output voltages with a scalar V/F control based on a carrier space vector pulse width modulation (SVPWM) technique. For a front end, a single-phase AC/DC doubled voltage converter with hysteresis current control is used to keep DC-link voltage constant, thus resulting in a bi-directional power flow operation for the motoring and generating modes. A closed-loop design for the DC-link voltage is fully given and also included is a review of carrier-based SVPWM for two-phase three-leg VSI. The proposed drive system was both simulated using MATLAB/SIMULINK and implemented on digital microcontrollers. The comparative performance evaluation of the whole system between balanced and unbalanced two-phase voltages for the machine is given. The simulation and experimental results show that the unbalanced phase voltage offers better performance for the whole system.     

Design and implementation of PV-based three-phase four-wire series hybrid active power filter for power quality improvement

This paper proposes a Photovoltaic (PV)-based three-phase four-wire Series Hybrid Active Power Filter (SHAPF), it comprises of a Series Active Power Filter (SAPF) and an LC shunt passive filter. The proposed system eliminates both the current and voltage harmonics and compensates reactive power, neutral current and voltage interruption. A SAPF demands a source of energy for compensating the voltage sag/swell. This system found a new topology for SHAPF which utilizes the PV with DC–DC boost converter as a source of DC power for the series active filter. The compensation current reference evaluation is based on the twin formulation of the vectorial theory of electrical power theorem with Fuzzy Logic Controller (FLC). The PV array/battery managed DC–DC boost converter is employed to step up the voltage to meet the DC bus voltage requirement of the three-leg Voltage Source Inverter (VSI). The foremost benefit of the proposed system is that, it will provide uninterrupted compensation for the whole day. This system utilizes the renewable energy; accordingly saves the energy and provides the uninterruptable power supply to critical/sensitive load, through the PV array/battery bank during both day time and night time. An experimental model was established and results were obtained, which indicated the capability of the proposed control scheme.     

A single-stage AC/DC converter based on zero voltage switching LLC resonant topology

A zero voltage switching based on LLC resonant topology is proposed to implement a single-stage AC/DC converter which performs both input-current harmonics reduction and power factor correction (PFC). By integrating a boost-PFC cell and an LLC resonant DC/DC cell into a single power conversion stage, the power losses in the secondary rectifier diodes and the primary switches can be significantly reduced. The proposed architecture exhibits extreme simplicity and lower cost while providing nearly unity power factor and well-regulated output; hence, the proposed converter is very suitable for low power level applications. The operating principles and design procedures for the proposed converter are analysed and discussed. Simulation and experimental results from a 125 W laboratory prototype are provided to verify the feasibility.     

Single-stage unity power factor based electronic ballast

This paper deals with the design, modeling, analysis and implementation of unity power factor (UPF) based electronic ballast for a fluorescent lamp (FL). The proposed electronic ballast uses a boost AC–DC converter as a power factor corrector (PFC) to improve the power quality at the input ac mains. In this single-stage UPF based electronic ballast, boost PFC converter and a half bridge series resonant inverter (HBSRI) share a common power switch. Thus one power switch is reduced as compared to the conventional two-stage approach. The design, modeling, analysis and implementation of this topology were carried out in MATLAB-Simulink environment for a T8 36 W, 220 V, 50 Hz fluorescent lamp. The switching frequency was kept more than the resonant frequency of the inverter, to ensure the zero voltage switching (ZVS) operation of both power switches. This resulted in reduction of high frequency switching losses. The power quality parameters such as displacement power factor (DPF), distortion factor (DF), power factor (PF), crest factor (CF) and total harmonic distortion of ac mains current (THD_i) were evaluated to analyze the performance of proposed electronic ballast. Test results on a developed prototype of PFC electronic ballast were included to validate the design and simulated results.     

Analytical closed-form investigation of pwm inverter induction motor drive performance under dc bus voltage pulsation

The voltage unbalance conditions at the input rectifier stage of the AC?DC?AC rectifier-inverter fed induction motor drive is analysed. This unbalance can cause significant voltage harmonic of twice the line frequency 2f1 in the DC bus. This voltage ripple can have a degrading effect on the induction-machine performance characteristics. The authors present an analytical closed-form mathematical model and analysis of the impact of DC bus ripple voltage of the three-phase voltage source inverter with the space-vector PWM on the induction machine phase voltages, currents and torque pulsations. The analytical expressions for the voltage and current space vectors as a function of the DC bus voltage pulsation are derived. Using superposition, the separate parts of the motor currents can be determined. From the current space vectors, the torque behaviour is estimated, again as a function of DC link voltage pulsation. Next, it is shown that the DC link voltage ripple components may cause large torque pulsation. The proposed analytical method is based on the mixed p?z approach, enabling presentation of the results in lucid and closed form. To verify the effectiveness of the proposed analytical model, experimental results based on laboratory setup were obtained.     

Analysis and design of a single-phase AC/DC step-down converter for universal input voltage

This work presents a single-phase AC/DC step-down converter, which is composed of two power stages, buck-boost converter and buck converter. The front stage is used for a power-factor-correction (PFC) circuit and is operated in discontinuous conduction mode (DCM) by using the pulse-width modulation (PWM) technique to achieve almost unity power factor and low total harmonic distortion of input current (THD_i). The rear stage is also operated in DCM to achieve voltage step-down and low DC-link voltage. The proposed converter can be applied for universal input voltage (85-265 V) and wide output power range. Also, the steady-state analysis of voltage gain and boundary operating condition are presented. Moreover, the selections of inductors, capacitors and input filter are depicted. Finally, a hardware circuit with simple control logic is implemented to illustrate the theoretical analysis.     

三端背靠背柔性直流输电的虚拟同步发电机控制策略及其在配电网中的应用

探讨了一种在10 kV配电网中引入三端背靠背（back-to-back,BTB）柔性直流输电（voltage source converter based HVDC,VSC-HVDC）系统的接线方案,通过VSC-HVDC的控制实现提高供电可靠性和抑制环流的目的。VSC-HVDC系统中换流站在传统控制模式下几乎没有转动惯量,难以有效地参与电网调节。为了提高电网受端系统频率的稳定性,改善系统发生故障后的运行特性,在中压（10 kV）交流配电网的背景下,提出了虚拟同步发电机（virtual synchronous generator,VSG）控制策略在三端BTB VSC-HVDC系统中的应用。首先在10 kV系统中加入三端BTB VSC-HVDC互联装置建立交直流混合配电网,建立换流站在传统控制和VSG控制下的数学模型,然后通过PSCAD/EMTDC平台进行仿真,在2种控制方式下得到系统在受到扰动和发生故障时的运行特性。结果表明,三端BTB VSC-HVDC系统受端换流器使用VSG控制能有效地参与电网调节,增加系统惯性,改善系统的暂态特性,提高电网运行的可靠性。     

Vector control of three-phase AC/DC front-end converter

A vector control scheme is presented for a three-phase AC/DC converter with bi-directional power flow capability. A design procedure for selection of control parameters is discussed. A simple algorithm for unit-vector generation is presented. Starting current transients are studied with particular emphasis on high-power applications, where the line-side inductance is low. A starting procedure is presented to limit the transients. Simulation and experimental results are also presented.