Combined vector control and direct torque control method for high performance induction motor drives

A new control method is proposed for three phase high performance induction motor drives. The control system enjoys the advantages of vector control and direct torque control and avoids some of the implementation difficulties of either of the two control methods. In particular, the proposed control system includes a current vector control in connection with a switching table. An extensive comparative performance evaluation of a motor under the proposed control method confirms the effectiveness of the method and its partial superiority over either vector control or direct torque control despite its relative structural simplicity.     

Transient performance of an isolated induction generator underunbalanced excitation capacitors

This paper presents transient performance of a stand-alone self-excited induction generator (SEIG) under unbalanced excitation capacitors. An approach based on a three-phase induction machine model is employed to derive dynamic equations of an isolated SEIG under unbalanced conditions. The neutral points of both a Y-connected excitation capacitor bank and Y-connected stator windings of the SEIG is connected together through a neutral line. Experimental results obtained from a laboratory 1.1 kW induction machine driven by a DC motor are also performed to confirm the feasibility and effectiveness of the proposed method     

Stability of doubly-fed induction generator under stator voltage orientated vector control

The stability of a doubly-fed induction generator (DFIG) under vector control in stator voltage orientation (SVO) is investigated. Prior art has tended to assume that the inner current loop dynamics can be neglected when an SVO is employed. As a result, the poorly damped poles of the DFIG system were considered unaffected by the inner current loop tuning. The state-space model of the machine including the inner current closed loop dynamics is developed for schemes where different feed-forward compensation terms are used. The interaction between inner current loop dynamics and damping of the critical poles of the system is illustrated through analysis and simulation. The main outcome of the analysis is that the stability of the machine system in an SVO depends solely on the parameters of the proportional-integral controllers. Erroneous tuning can lead to instability, irrespective of the particular feed-forward compensation scheme, which could cause the disconnection of the machine as a result of rotor current oscillations of unacceptable magnitude in an actual case. The main contribution is to provide the necessary methodology in order to ensure the stable operation of a DFIG under SVO vector control.     

Effects of unbalanced voltage on the operation performance of athree-phase induction motor

This paper uses a real load test to investigate the effects of an unbalanced voltage supply on an induction motor's performance. Based upon various experiments, including: (1) cases with the same unbalance voltage factor but different unbalanced voltages; (2) cases with only one unbalanced voltage but different degrees of unbalance; and (3) cases with the same positive-sequence voltage but different negative-sequence voltages, the importance of the positive-sequence voltage in the motor's apparent performance and of the negative-sequence voltage in the hidden damage are pointed out. Finally, it is strongly suggested that the related regulations, and a motor's derating factor and temperature rise curves should be based on not only a voltage unbalance factor, but also the magnitude of the positive-sequence voltage     

Effects of nonsinusoidal voltage on the operation performance of athree-phase induction motor

This paper uses a real load test to investigate the effects of each order of harmonic from 2 to 13 under various voltage distortion factors (VDF) on the performance of a three-phase induction motor. The investigation includes input current, power factor, efficiency, temperature rise and their impacts on the consumers and utility companies. Since the life span of the motors is dramatically affected by the temperature rise, a new derating factor is proposed in this paper. Besides, the impacts of harmonics on electricity energy, consumers and the life span of a motor are also discussed, respectively. Finally, it is strongly suggested that even order harmonics and harmonics having an order below 5 should be considered in related regulations of harmonics control and limits     

一种改进的双馈感应发电机低电压穿越控制策略

为提高双馈感应发电机的低电压穿越能力,对转子侧换流器考虑了电网故障时定子磁链变化对有功、无功解耦的影响,并将反映电流耦合及定子磁链变化的附加量作为前馈分量加入电流指令值,对传统矢量控制策略进行了改进。对网侧换流器,提出一种考虑直流环节两侧功率不平衡及电网电压突变的改进控制策略。仿真验证了改进方案对转子过电压、过电流及直流母线电压波动均有很好的抑制作用,有效提高了双馈机的低电压穿越能力。     

电网电压不对称故障时双馈风电机组多目标优化控制

文章首先对电网不对称故障对双馈风电机组造成的影响进行分析,采用转子侧和网侧变换器的比例积分谐振控制器(PIR)来简化传统低压穿越控制结构;通过引入两个可调参数,从而对前馈量进行调节来得到不对称故障期间双馈电机的多目标优化控制策略;在仔细研究模型的基础上,通过对电网电压不对称故障时双馈风电机组的多目标优化控制的PSCAD模型进行仿真试验,仿真结果表明,该方案对于电网电压不对称故障时的LVRT有一定的可行性。     

双馈风电机组的高电压穿越控制策略

分析了广义电网电压骤升(含对称、不对称骤升)故障下双馈风电机组电磁暂态过渡过程,评估了影响机组高电压穿越运行的关键因素,并梳理了电压骤升、骤降故障诱发双馈机组脱网机理的异同。提出了一种基于瞬态灭磁控制和无功电流支持的双馈机组高电压穿越控制方案。仿真和实验结果表明,所述方案能够显著加快故障电网条件下双馈感应电机定子磁链中直流、负序分量的衰减,进而快速抑制机组电磁转矩和母线电压的波动;同时能够满足并网规范对机组无功电流输出的要求,实现机组的故障穿越运行。     

Analysis and improvement of high temperature floating charge performance for high voltage lithium ion batteries

为研究高电压体系锂离子电池浮充性能的影响因素,对浮充失效电池的产气成分、正负极材料的结构变化、金属溶出情况、隔膜形貌及Gurley值变化等进行了深入分析研究,结果表明：电池在长时间高温浮充过程中,正极材料发生相变,金属元素溶出,同时释放O₂造成电解液的氧化分解;高温高电压状态下负极SEI膜也会破坏,并发生不断的重整及修复反应,这些反应产物沉积到负极表面及隔膜孔隙内,导致靠近负极侧的隔膜孔隙堵塞甚至贯穿,即引起正负极微短路,释放出大量气体。通过提高正极材料的结构稳定性、优化电解液形成稳定的CEI和SEI,改善增加隔膜的穿刺强度都能明显改善电池的高温浮充性能。     

Influence of unbalanced voltage on the steady-state performance of a three-phase squirrel-cage induction motor

The negative effects of a particular unbalanced voltage on the performance of an induction motor are studied in this paper. The paper suggests that the available definitions of unbalanced voltages are not comprehensive and complete. Therefore, the results of these analyses on motor performance are not very reliable. To prove this claim, a three-phase 25-hp squirrel-cage induction motor is analyzed under different unbalanced conditions. It is shown that it is necessary to define a more precise unbalanced factor for more accurate results. Experimental results verify the theoretical analysis.     

电压不平衡下笼型机风电场STATCOM控制策略的研究

公共连接点(PCC)电压不平衡情况下,负序电压引起笼型风力发电机组电磁转矩以2倍电网频率脉动,从而降低传动装置的使用寿命。文章设计了笼型机风电场静止同步补偿器(STATCOM)的正、负序双环叠加控制策略,正序电压控制策略控制公共连接点电压和STATCOM直流侧电容电压为给定值,负序电压控制策略控制公共连接点负序电压分量为零,从而消除笼型发电机电磁转矩的脉动。最后,在PSCAD/EMTDC环境下建立包括风电场、STATCOM和电网的仿真模型。仿真结果表明,所提出的控制策略有效地改善了PCC电压不平衡度,消除风力发电机组电磁转矩的脉动,从而验证了所提出的正、负序双环叠加控制策略的正确性和有效性。     

Wind-driven self-excited induction generator with voltage and frequency regulated by a reduced-rating voltage source inverter

This paper discusses the regulation of the voltage and frequency of a stand-alone fixed-pitch wind energy conversion system (WECS) based on a self-excited squirrel-cage induction machine. A shunt connected voltage source inverter (VSI) and a controllable dump load are used for regulation purposes. A battery bank is included in the dc side of the VSI so that it can absorb and inject active power thus increasing the efficiency and availability of the system. A control scheme for the VSI with independent control of active and reactive power allows the state of charge of the batteries to be kept in a safe range while maximizing the voltage regulating capabilities of the VSI. The characteristics of the wind turbine, self-excited generator, and the ratings of the VSI are considered in order to determine the load range for which voltage and frequency can be regulated for a given wind speed range. The feasibility of the proposed system is verified by simulations.     

非对称横槽管高效换热元件传热性能研究

基于k-ε模型,针对一种非对称横槽管换热元件,对高温高压工况下管内氦气的流动与传热进行了数值模拟研究。比较了非对称横槽管与对称横槽管的综合传热性能。同时,应用"中心复合设计"(CCD)方法对非对称横槽管的三个基本结构参数(槽间距a、槽宽b、槽深e)进行了优化设计,考察了不同结构对非对称横槽管传热性能的影响,并对其内部机理进行了初步的探讨。结果表明,非对称横槽管传热性能优于传统的对称型横槽管,最优结构参数为a12-b8-e0.6。     

Real time implementation of backstepping-multiscalar control to induction motor fed by voltage source inverter

A novel version of nonlinear induction motors (IM) control algorithm based on the backstepping approach has been proposed in this work. For that, the conventional mathematical model of IM is replaced by the multiscalar one, which is more suitable for application of the backstepping design. By using such combination, the system has fast dynamic response, better load disturbance rejection capability, less parameters sensitivity and better tracking performance of rotor speed and rotor flux magnitude. The effectiveness of the proposed control structure is validated by simulation as well by experiment under critical disturbance conditions.     

一种适用于微电网黑启动的改进微源电压控制策略

孤岛运行的微电网故障后,系统的重新恢复供电关系到微网能否安全稳定运行。文章根据光储微电网中各微源的特性以及黑启动微源的选取原则,选取合适的黑启动电源。为了让黑启动电源在系统恢复初期更好地为微网交流母线提供电压频率支撑,提出一种适用于微电网黑启动的微源电压控制策略,通过改进微源下垂特性,实现微电源输出电压从零开始上升建立电压的过程,确保配电变压器的零起升压功能。最后,在PSCAD仿真平台上搭建了相应模型进行仿真,结果表明,所提电压控制策略有效支撑了微网孤岛运行的电压频率,提高了微网的安全稳定性。     

A novel stand-alone dual stator-winding induction generator with static excitation regulation

On the basis of the new idea of electric power integration, a novel stand-alone dual stator-winding induction generator (DWIG) system is built. In this generator, there are two sets of windings to be embedded in the stator slots. One, referred to as the 12-phase power winding, supplies power to the dc load via a 12-phase bridge rectifier, and the other, called the 3-phase excitation winding, is connected to a pulsewidth modulation (PWM) voltage source static excitation regulator (SER). A solid iron squirrel cage rotor is suitable for high speed generation. Experiments and simulations show the ac capacitors can reduce the inductance of rectifier loads and help to reduce the capacitance of the SER. A simple control methodology based on stator voltage orientation (SVO) is presented to regulate the output voltage of the 12-phase bridge rectifier in this paper. Moreover, the electric energy quality and the relative influence factors are studied by detailed experiments and analyses. The proposed system is especially suitable for self contained electrical systems, such as those found on electric vehicles, ships, and aircraft, where high performance and compact size are essential.     

High performance speed and position tracking of induction motorsusing multi-layer fuzzy control

An electric drive system is considered high performance when the rotor position or shaft speed can be made to follow a preselected track at all times. The design of tracking controllers for induction motors is difficult due to motor nonlinearities and unknown load dynamics. An extension to fuzzy control, multi-layer fuzzy control (MLFC), is proposed and applied to high performance tracking of induction motors. The MLFC has two layers. The first layer is the execution layer which is made up of small subcontrollers. The second layer is the supervisor layer which fuzzily combines the execution layer subcontrollers to achieve the system objectives. The design and the tuning of the controller is simpler because of the layered topology. The MLFC tracking controllers are tested in the laboratory and their effectiveness in tracking applications is verified. The ease of controller tuning is also demonstrated     

Optimization with constraints for excitation control in synchronous generators

Electric power networks are being modified fast, mainly due to the changes introduced in generation systems and load features. Research studies indicate that this process is going to continue in the near future. In this context, several control strategies and devices are used to increase the stability and performance of the new power systems. An optimization with constraints for the excitation control in synchronous generators is presented in this work, in order to damp oscillations in the grid. Generator states move away from their operating points in presence of disturbances in the electric network such as sudden load variations, transmission line losses and short circuits. Then, the generator states must be brought back to its equilibrium point by the excitation control. As the generator model is nonlinear, the controller tuning in order to perform this function is not easy, being necessary to apply nonlinear techniques to obtain a high performance. Moreover, optimal control schemes are currently required owing to a demanding market which rewards power units that deal with energy in an optimal way and keep the generator stable even under network faults.     

Ridethrough of wind turbines with doubly-fed induction generator during a voltage dip

In this paper, a solution is described that makes it possible for wind turbines using doubly-fed induction generators to stay connected to the grid during grid faults. The key of the solution is to limit the high current in the rotor in order to protect the converter and to provide a bypass for this current via a set of resistors that are connected to the rotor windings. With these resistors, it is possible to ride through grid faults without disconnecting the turbine from the grid. Because the generator and converter stay connected, the synchronism of operation remains established during and after the fault and normal operation can be continued immediately after the fault has been cleared. An additional feature is that reactive power can be supplied to the grid during long dips in order to facilitate voltage restoration. A control strategy has been developed that takes care of the transition back to normal operation. Without special control action, large transients would occur.