Mill motors for adjustable-speed AC drives

The use of AC adjustable-speed drives for rolling mill applications is addressed. AC motor characteristics and how they relate to adjustable-speed mill drives are described. A review of AC motor theory highlighting distinctions between induction and synchronous machines along with comparisons to DC motor performance is included. Constant power speed range performance and limitations, damper winding requirements, and the selection of motor variables such as terminal voltage and frequency are discussed     

Assessment of ride-through alternatives for adjustable-speed drives

Adjustable-speed drive (ASD) ride-through issues have caused increased concerns due to the susceptibility of ASDs to power disturbances, and the costly results of process disruptions. These losses can be avoided for critical production processes by using ASDs with ride-through capabilities. This paper assesses industrial ride-through requirements through power quality surveys and the results of an ASD ride-through questionnaire conducted by the authors. ASD ride-through alternatives are evaluated based on design, implementation and cost considerations, in order to determine the most suitable solutions for various kilovoltampere ratings and time duration requirements     

Utility capacitor switching and adjustable-speed drives

The authors consider the effect of capacitor switching on adjustable-speed drives. Surges of less than 200% magnitude caused by utility capacitor bank switching can disrupt operation of adjustable-speed drives. Pulse width modulated (PWM) drives are more sensitive to surges because the drive transistors have lower overvoltage tolerance than silicon controlled rectifier (SCR) drives. The authors use the results of a case study to analyze the circumstances of drives tripped by utility capacitor switching. It is shown that low loss utility capacitors increase the surge magnitude by decreasing system damping. Surge magnification is possible at buses remote from the capacitor, and the three conditions for magnification are described. It is also shown that drive sensitivity to the surge depends on whether the drive filter inductor is saturated by the surge     

Voltage sag ride-through for adjustable-speed drives with activerectifiers

Adjustable-speed drives (ASDs) trip due to voltage sags, interfering with production and resulting in financial losses. In this paper, a methodology for incorporating voltage sag ride-through in the design of ASDs with active rectifiers is presented. The magnitude of the voltage sag for which ride-through can be provided is determined by the current rating of the active rectifier and load condition of the ASD, but a sag of any duration can be compensated for     

A novel ride-through system for adjustable-speed drives usingcommon-mode voltage

This paper proposes a new ride-through system for adjustable-speed drives (ASDs) using common-mode voltage. In the proposed ride-through system, the common-mode voltage inherent in a pulsewidth-modulation boost rectifier-inverter system is used for charging the energy storage device at normal conditions of the source power. That is, controlling the common-mode voltage with a small reactor while driving motors can regulate charging current. Using simple additional circuits and the existing rectifier, at the whole range of voltage disturbances from balanced or unbalanced shallow voltage sag to full outage, ride-through is successively available with the proposed system. Various energy storage devices can be selected according to the applications and two kinds of charging topology-using inverter-side or rectifier-side common-mode voltage-are also available in the proposed system     

Current harmonics and acoustic noise in AC adjustable-speed drives

AC adjustable-speed drives (ASDs) are finding increased opportunities for applications in which acoustic noise is a major consideration for acceptability. The major source of noise in an ASD is the excitation of the motor by nonsinusoidal currents. For load characteristics that simulate the performance required for fans and compressors, ASDs based on induction motors, permanent-magnet motors, and switched reluctance motors have been examined for correlation between current and acoustic noise. The effects that the specific types of noise produced by drives have on human subjects is examined with regard to temporary and permanent hearing-threshold shifts     

Applying adjustable-speed drives to three-phase induction NEMAframe motors

This paper addresses why a three-phase induction motor overheats on adjustable-speed drives, under some conditions. It further addresses how the motor may derate when used on a drive and how to determine the amount of derating required     

Multilevel converters for large electric drives

This paper presents transformerless multilevel power converters as an application for high-power and/or high-voltage electric motor drives. Multilevel converters: (1) can generate near-sinusoidal voltages with only fundamental frequency switching; (2) have almost no electromagnetic interference or common-mode voltage; and (3) are suitable for large voltampere-rated motor drives and high voltages. The cascade inverter is a natural fit for large automotive all-electric drives because it uses several levels of DC voltage sources, which would be available from batteries or fuel cells. The back-to-back diode-clamped converter is ideal where a source of AC voltage is available, such as in a hybrid electric vehicle. Simulation and experimental results show the superiority of these two converters over two-level pulsewidth-modulation-based drives     

High-voltage autotransformer frequency converters for electric drives

The application of autotransformers in high-voltage ac electric drives with transistor frequency converters is considered. Circuit designs based on independent inverters of lower voltage, which are intended for increasing the power of electric drives, are demonstrated.     

Five-level double converters for induction motor drives

In this article, a PWM control strategy for a three-phase, five-level double converter system is proposed. The proposed method is able to correct the five-level DC potentials, maintain the input power factor at near unity, and achieve adjustable-speed drive. Simulation and experimental results verified the validity of the control strategy. However, large voltage ripples were observed in the experimental results. Further study is needed to develop a control method that can reduce voltage ripples at the DC link capacitors as well as the harmonic distortions of the input and output waveforms     

Designing harmonic filters for adjustable-speed drives to complywith IEEE-519 harmonic limits

This paper discusses the application of the revised IEEE 519 harmonics standard to typical industrial facilities employing adjustable-speed drives (ASDs). The harmonic generation characteristics of ASDs are described. Requirements for control of the harmonic currents are developed as a function of the ASD characteristics, overall plant loading level, power system characteristics, and power-factor-correction requirements. Filter design procedures are presented for controlling the harmonic currents injected into the power system     

Effects of balanced and unbalanced voltage sags on DC adjustable-speed drives

This paper analyzes the sensitivity of DC adjustable-speed drives to balanced and unbalanced voltage sags. The influence of sag type, depth, duration and phase-angle jump on DC drives is studied. The control of the DC drive has been taken into account to understand drive behavior in the presence of voltage sags. Two working modes of the DC motor are considered in the study: as a consumer load and as a regenerative load. When the DC motor works as a consumer load, the study shows that sag type and depth have a significant influence on drive behavior. However, the voltage sag can be ridden through if the rectifier firing angle is set correctly by the control. When the DC motor works as a regenerative load, the study shows the consequences of the three-phase rectifier commutation failure due to the voltage sag.     

Effect of adjustable-speed drives on the operation of low-voltageground-fault indicators

The petroleum and chemical industry has found increasing favor with 60 Hz low-voltage (⩽600 Vac) power systems that utilize a high-resistance grounded (HRG) neutral philosophy. Historically, the older generation of adjustable-speed drives (ASDs) had little or no effect on the normal operation of ground-fault indicators (GFIs) used with the installed HRG systems. This paper focuses on nuisance GFI alarms that may occur when present-generation ASDs are retrofitted into the existing plant. The paper first reviews possible neutral grounding systems, with emphasis on the types of HRG systems possible and GFI alarm philosophy. The paper then discusses how ASDs may generate zero-sequence high-frequency noise currents in the HRG neutral circuit, which may cause nuisance ground-fault alarms and potentially mask a legitimate ground fault. GFI noise current magnitude is defined for both present and older ASD technologies. The effect this transient zero-sequence noise current magnitude has on GFI operation is described. Mitigation methods used at the drive to reduce ASD noise current magnitude to acceptable nonalarm levels is investigated. Filter solutions located at the HRG/GFI meter that reduce nuisance alarms are also investigated. The pros and cons of at the drive or at the meter filter solutions are supported with laboratory and field test data. Application guidelines are given to help avoid nuisance problems with a plant ground-fault protection scheme, which needs to successfully operate in the presence of multiple ASDs     

Specific features of the application of frequency converters in power electric drives of circulation pumps

Specific features of the selection and use of high-voltage frequency converters for asynchronous electric drives of circulation pumps of atomic power plants are studied.     

New protection issues of a matrix converter: design considerationsfor adjustable-speed drives

Induction motors are traditionally controlled by standard pulsewidth modulation voltage-source inverters. An alternative is the matrix converter, which consists of nine bidirectional switches. This converter has benefits compared to a standard inverter, like sinusoidal input current and bidirectional power flow. The main disadvantage is the lack of a bidirectional switch, because such a switch may be done by two transistors and two diodes. An important topic is protection of the matrix converter, and this paper proposes two new protection circuits for matrix converters with a reduced number of components. The number of protection diodes is reduced by six. Design expressions of the protection circuit are calculated and validated by simulation. The standard protection circuit and the new circuits are demonstrated by simulation to have the same performance. Experimental results on an 8 kVA matrix converter show the design expressions are correct. It is concluded that it is possible to reduce the necessary power components in a matrix converter     

Immittance converters suitable for power electronics

An immittance converter has fine performance in many power electronics applications. Its function is to convert voltage sources into current sources and current sources into voltage sources. The immittance converter has an input impedance that is proportional to the admittance of loads connected across output terminals. Therefore, in this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently, it converts a constant voltage source into a constant current source and a constant current source into a constant voltage source. When an immittance converter operates at a resonant frequency and is inserted to high-frequency link systems, voltage source outputs turn into current source outputs and current source outputs turn into voltage source outputs. Some power electronics applications of this converter are photovoltaic inverters and dc-dc converters with constant current outputs. It is well known that a quarter-wavelength transmission line shows immittance conversion characteristics. However, it has a very long line length for its switching frequency (e.g., 20 kHz), and is not suitable for power electronics applications. Therefore we propose five immittance converters that consist of lumped L and C elements and show the immittance conversion characteristics at a resonant frequency. These immittance converters are much smaller and lighter than the transmission line. Their principles, basic circuits, and basic characteristics are described in this paper. We also evaluate their application to high-frequency link systems of power electronics. © 1998 Scripta Technica, Electr Eng Jpn, 124(2): 53–62, 1998     

A comparison of three-level converters versus two-level converters for low-voltage drives, traction, and utility applications

This paper evaluates three-level topologies as alternatives to two-level topologies in converters for low-voltage applications. Topologies, semiconductor losses, filter aspects, part count, initial cost, and life-cycle cost are compared for a grid interface, a conventional drive application, and a high-speed drive application.     

Transient analysis of converter-fed adjustable-speed generator-motor for the pumped storage power plant

A converter-fed adjustable-speed generator-motor for a pumped storage power plant has been developed in order to contribute to the automatic frequency control on an electric power system during pumping operations, as well as to improve the efficiency of turbines during generating operations together with stability. This system consists of a reversible pump turbine, a generator motor, cycloconverter and control units. The rotor of the generator motor, which is coupled directly with the turbine runner, normally is operated at a rotating speed which is equal to the difference between the frequency of the electric power system and that of the rotor current. In the state that a fault has occurred in the primary circuit of the generator motor, the adjustable-speed generator-motor fault current differs from that of a conventional synchronous generator motor. This paper describes the fault current analysis results for the condition when a sudden short-circuit is made on the primary side of the generator motor, and collates the results with the field test and EMTP simulation results.     

功率驱动用三相开关电源设计与实现

针对传统稳压稳压电源体积大、不符合工业用三相电源输入电压范围要求等问题,开发出一种功率驱动用三相开关电源,设计出可大为减小电源体积的硬件电路和反激式高频变压器,有效解决了系统需外接两相电源的问题.通过对所设计的电源性能进行相关测试,验证了设计方法及电源的稳定性与可靠性.     

用于风电的模块化多电平变流器IGBT的定制化设计

模块化多电平换流器(MMC)已广泛应用于风力发电系统中,其中绝缘栅双极型晶体管(IGBT)模块的设计直接影响着系统的各项性能。而IGBT模块的设计选型缺乏理论指导,存在IGBT模块裕量选取过大造成的成本浪费现象,因此文中提出一种基于双目标优化的IGBT的定制化设计方法。首先以损耗和芯片成本作为IGBT定制化设计的指标,结合风力发电的年运行工况,根据风速的概率分布来评估IGBT损耗,通过双目标粒子群算法求得Pareto前沿。最后,分别采用IGBT模块和分立元件2种方法进行定制化设计,结果表明所提设计方法在降低器件成本的同时可以兼顾变流器的损耗和可靠性。