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     

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     

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     

Using reverse-blocking IGBTs in power converters for adjustable-speed drives

A new semiconductor power device that is urgently needed particularly in power converter topologies, the reverse blocking insulated gate bipolar transistor (RB-IGBT), has been realized by adding minor changes to the structure of a standard IGBT to make it capable of withstanding reverse voltage. However, the switching behavior of the device's intrinsic diode during reverse recovery is not as good as a discrete IGBT and series diode implementation. This paper analyzes the use of this device in three power converter topologies that may benefit from it, namely: 1) the matrix converter, 2) the two-stage direct power converter (DPC), and 3) the three-level voltage source rectifier. A commutation method to override the poor reverse-recovery characteristic of the RB-IGBT intrinsic diode in a two-stage DPC is proposed. A loss analysis shows that by using RB-IGBTs the efficiency of the two-stage DPC becomes similar to a two-level voltage source converter.     

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     

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     

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     

Controlled AC drives with ride-through capability at powerinterruption

General purpose PWM inverter drives are equipped with an undervoltage protection mechanism, causing the system to shut down within a few milliseconds after a power interruption in the mains. This may entail loss or damage of material in such critical applications as the production of textile fibers, paper, or with extruder drives. The proposed solution to this problem is to recover some of the mechanical energy stored in the rotating masses. When a power interruption occurs, a sequence of fast feedforward commands is applied to force an immediate transition into the regeneration mode. During the interrupt interval, the drive system continues to operate at almost zero torque, just regenerating a minor amount of power to cover the electrical losses in the inverter. The method is implemented in an additional software package to be used with general-purpose inverter drives of limited dynamic performance. Experimental results are presented     

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.     

An approach to achieve ride-through of an adjustable-speed drivewith flyback converter modules powered by super capacitors

Adjustable-speed drives under short-term power interruptions can interrupt a critical process. In this paper, an approach to provide ride-through with flyback converter modules powered by super capacitors is explored. The proposed approach is modular and facilitates additional modules to be added to suit higher voltage/power ratings. Both unidirectional and bidirectional flyback DC/DC converter topologies are examined. Simulation and experimental results are presented     

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     

Low-cost compact permanent magnet machine for adjustable-speed pumpapplication

The variable-speed driven pump can result in significant energy conservation where reduced flow rates are required for long periods of time. In regard to adjustable-speed pump drives, one major contribution of this paper is the demonstration that a permanent magnet (PM) motor based on the slotless axial-flux permanent magnet machine (AFPM) topology can be a suitable candidate to advantageously compete with the induction motor for such a low-cost drive application. For the purpose of a cost comparison, the paper discusses design and construction of a prototype machine which has been conceived to replace a 1.2 HP induction motor being used in a standard adjustable-speed pump drive. Results taken from laboratory tests of the prototype machine are reported, together with an assessment of the machine manufacturing cost     

提升直流并网风电故障穿越能力的新方法

提出提升柔性直流并网的风电场系统故障穿越能力的新方法.分析了柔性直流输电的传统电流限幅器的不足,设计了动态改变限值的电流限幅器,该限幅器在电流扰动期间,能限制过电流,并能最大限度地提升输出功率.提出了新的转速储能方法,即利用风电机组自身的转子来实现提速储能,用以短时储存故障期间的过剩能量,以提高并网系统的故障穿越能力.仿真分析验证了所提方法的有效性.     

直驱风力发电故障穿越控制方法综述

首先根据电网故障特征,分析了直驱风力发电机组在故障运行条件下的功率关系,根据分析结果将电网故障情况下机组实现故障穿越所面临的问题总结为由电网电压正序分量有效值下降带来的“有功不平衡”和电网电压负序分量带来的“功率波动”2类问题.在此基础上,对目前直驱风力发电机组的故障穿越方法进行了总结和分类,将“有功不平衡”控制策略分为减小发电机的输出功率来减小换流器的输入功率、在直流母线处消除不平衡功率、增大网侧换流器输出功率能力3种方法;将“功率波动”控制策略分为消除并网电流负序分量和消除直流母线电压纹波2种方法,并分析了不同方法的优缺点.根据现有方法的优缺点对直驱风力发电机组故障穿越控制方法的研究方向进行了展望.     

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.     

不同风电机组的低电压穿越能力分析

应用Matlab 7.0建立了含不同风电机组的风电场动态模型,用于研究包含恒速异步风力发电机和双馈异步风力发电机的风电场对电网的影响,通过仿真分析电网发生严重三相短路故障后不同风电机组的低电压穿越能力,以及加装静止无功补偿器(SVC)后风电机组的低电压穿越能力.比较风电机组转速、有功功率和无功功率变化情况,得出结论:双馈异步风力发电机变速平稳,低电压穿越能力较强,有利于优化电能质量.当电网发生故障时,针对风电场中的不同风电机组应采用不同的策略来提高风电机组的低电压穿越能力,维持电力系统的稳定运行.     

柔直系统适时切换的故障穿越方法

为了实现柔性直流输电系统在网侧不对称故障时的故障穿越,同时保持稳态时的柔直阻抗稳定性,本文详细分析了柔直系统的正负序控制以及采用1/4周期延时的正、负序分解算法对柔直系统不同频率分量阻抗波动的影响,推导并建立了柔直系统的交流侧高频阻抗模型。在此基础上提出一种适时切换的故障穿越算法,利用负序电压的稳态量和突变量进行故障判断,稳态时内环采用全序电流控制,不进行正负序分解,从而降低了柔直系统阻抗的周期性波动,故障暂态时叠加负序电流控制,抑制负序故障电流,实现了故障时系统的持续运行。最后在PSCAD/EMTDC中,搭建柔直系统仿真平台进行仿真研究,验证了本文设计策略的有效性。     

用于光伏逆变器故障穿越的载波交叠调制优化

为了解决三电平光伏逆变器故障穿越时的中点电位平衡问题,在已有的脉宽调制和中点电位平衡方法基础上,提出一种新型的深度载波交叠调制法(deep carrier overlapping PWM, DCO-PWM)。该方法通过尽量增加上下层载波的交叠深度,削弱了中矢量对中点电位的影响,实现了在故障冲击和高无功电流工况下保持中点电位平衡和并网电流可控。针对DCO-PWM增加了功率器件开关次数的问题,开发了一种调制策略的分相切换方法,仅在中点电位差超出设定阈值时,将调制波中间相切换到DCO-PWM,其他状态仍然使用常规的载波同相层叠调制法(carrier phase disposition PWM, CPD-PWM),从而降低了并网电流的谐波含量和器件开关损耗。通过实验验证了上述方法在三电平逆变器低电压故障穿越过程中,可有效增强对并网电流和中点电压的控制,从而保证故障状态的安全可靠穿越。