基于矢量空间电流θ角优化的电梯节能控制研究

文中提出一种电梯运行矢量空间电流θ角节能控制方案,对电梯曳引电机矢量控制系统取得定子电流最小值的方法进行了证明.该节能控制方案不增加系统硬件成本,根据电动机的负载状态对励磁电流进行调节,使定子电流达到最小值,从而达到节能的目的.针对电梯曳引电机轻载运行时,进行基于矢量空间电流θ角优化的仿真研究,当负载率为14%时,节能率可达9%.仿真结果表明本文控制方案不仅能使电梯轻载运行时节能,还使其电磁转矩振荡减小.     

异相游梁平衡式抽油机节能技术改造

本文分析了游梁式抽油机的节能机理，及拖动抽油机的电动机的负载特性，提出了一种对游梁式抽油机进行节能改造技术和方法，并测试了其实际节能效果。     

游梁式抽油机节能技术改造综述(Ⅰ)

以游梁式抽油机主要结构的节能为出发点,改造抽油机结构,优化设计方案。在现有基础上改造技术,研发新型节能抽油机。双驴头抽油机保持了原有常规抽油机的优点,能耗降低达20%~30%,节能效果显著。而偏轮游梁抽油机改善了游梁抽油机的平衡效果,使各构件受力合理,降低能耗,从而达到降低电机额定功率和节能降耗的目的。     

解决游梁式抽油机大马拉小车问题的两种电动机

为解决游梁式抽油机所配电动机功率配置与供电系统不合理以及电能浪费的问题,提出了两种新型节能电动机的解决方案,并对这两种电动机在油田应用的系统节能效果进行了分析评价.     

游梁式抽油机液力偶合传动的节能控制技术

为解决传统游梁式抽油机以皮带方式驱动需要较大启动和运行电流的问题。分析了油田经常采用的各种配套抽油机节能技术的现状及研究方向,应用将调速电动机、偶合器、齿轮减速箱组合为一个独立的动力单元的抽油机液力偶合传动装置;电动机直接驱动偶合器,再由偶合器驱动一对锥齿轮,改变输出转向,经两级齿轮减速后,达到现场油井生产所需冲次,满足了提质增效的需要。现场6口油井应用表明,降低了抽油机启动电流、节能效果明显、油井系统效率得到提高,并增加了系统的安全性和可靠性。在老油田节能改造中具有极大的推广价值和节能意义。     

弯游梁抽油机与低转差电机的优化匹配仿真对比分析

针对大庆九厂油田的井况特点,以弯游梁式抽油机、永磁系列电机和双速双功率电机为对象,建立相应的有杆抽油系统的数学模型,在此模型基础上,从仿真的角度出发,讨论弯游梁式抽油机与两种节能电机的优化选配问题,为弯游梁抽油机与节能电机的合理选配提供了理论依据和解决方法。     

提高油田机采系统用能效率的措施

胜利油田1616口游梁式抽油机井的机采系统测试表明，游梁式抽油机井平均功率因数为0．461，平均系统效率只有28．59％．泵充满系统小于0．4的抽油机井占测试总井数的33％。分析显示．造成抽油机系统效率低的原因主要是：变压器与异步电动机之间匹配方式不合理，设备容量大，自身损耗大；占油田电机总量31．4％的Y系列电机的平均空载损耗大，为2.86kw：低产液井电机的冲次可调范围有限，受电机最低转度和皮带轮最小包角限制，其最小冲次仅可调到4次／min，但1～1．5次，min的冲次即可满足生产需要，造成能耗浪费。为此，开发应用新型抽油机脱动系统，抽油机电机负载率从15％提高到35％，平均有功节电率和无功节电率分别达到15％和80％；开发应用抽油机平衡度实时在线检测技术，实现节能降耗；开发新型永磁电机，以增大启动力矩，合理调节冲次。     

游梁式抽油机节能技术改造综述(Ⅱ)

游梁式抽油机结构简单、性能可靠、使用方便,但是工作效率低,能耗大。文中以游梁式抽油机主要结构的节能为出发点,改造抽油机结构,优化设计方案,研发新型节能抽油机。摆杆式游梁抽油机适合大负荷、长冲程工况,在类似工况下可节电30%以上。下偏杠铃抽油机适用于中、长冲程抽油机的开发,综合节电率将超过20%。而天平式游梁抽油机可比常规游梁式抽油机节电35%~70%。由现场试验表明,各种抽油机节能效果明显。     

一种新型抽油机电机电压空间矢量PWM控制技术研究

油田采油设备使用大量的游梁式抽油机,其电机一般均使用三相异步感应电机,由于目前较为成熟的抽油机电机节能控制常采用两电平PWM变频控制,其输出电压中除基波外,还包含有大量的谐波分量,造成电压波形的畸变,因而运行效率较低,浪费了大量的电能。文中介绍了采用电压空间矢量PWM控制技术来控制抽油机电机的方法,与传统的PWM方法相比,可以减小转矩脉动和铁损耗,并可提高电源电压的利用率,从而实现较好的节能效果。     

游梁式抽油机飞轮储能系统设计及实验

现役的游梁式抽油机耗电量超过油田生产总用电量的50％,其总效率往往低于30％,抽油机系统的效率低下造成了电能的较大浪费,而游梁式抽油机的工作原理及结构特点有利于采用飞轮储能装置提高其效率.本工作设计了适用于游梁式抽油机的飞轮储能系统,建立了抽油机动力学仿真模型,搭建了相应的实验测试平台,采用仿真分析和实验研究相结合的方...     

Real-Time Speed and Flux Adaptive Control of Induction Motors Using Unknown Time-Varying Rotor Resistance and Load Torque

In this paper, an algorithm for direct speed and flux adaptive control of induction motors using unknown time-varying rotor resistance and load torque is described and validated with experimental results. This method is based on the variable structure theories and is potentially useful for adjusting online the induction motor controller unknown parameters (load torque and rotor resistance). The presented nonlinear compensator provides voltage inputs on the basis of rotor speed and stator current measurements, and generates estimates for both the unknown parameters and the nonmeasurable state variables (rotor flux and derivatives of the stator current and voltage) that converge to the corresponding true values. Experiments show that the proposed method achieved very good tracking performance within a wide range of the operation of the induction motor (with online variation of the rotor resistance: up to (87%). This high tracking performance of the rotor resistance variation demonstrates that the proposed adaptive control is beneficial for motor efficiency. The proposed algorithm also presented high decoupling performance and very interesting robustness properties with respect to the variation of the stator resistance (up to 100%), measurement noise, modeling errors, discretization effects, and parameter uncertainties (e.g., inaccuracies on motor inductance values). The other interesting feature of the proposed method is that it is simple and easily implementable in real time. Comparative results have shown that the proposed adaptive control decouples speed and flux tracking while standard field-oriented control does not.      

Method for in-field evaluation of the stator winding connection of three-phase induction motors to maximize efficiency and power factor

The performance of the oversized three-phase induction motors can be improved, both in terms of efficiency and power factor, with the proper change of the stator winding connection, which can be delta or star, as a function of their load. A practical method is proposed to quickly and easily evaluate which stator winding connection is more appropriate for the actual motor load profile, in order to increase the motor efficiency and power factor. This new method is suitable for in-field evaluation, because it requires only the use of inexpensive equipment and has enough accuracy to allow a proper decision to be made. The automatic change of the stator winding connection, as a function of the motor line current, is also analyzed. When properly applied, these methods can lead to the improvement of the efficiency and power factor of permanently oversized motors, motors with a load variation between low load and near full load during their duty cycle, and/or motors driving high-inertia, low duty cycle loads. The proposed methods are particularly suitable to industrial plants where typically many electric motor systems are oversized and/or can have a wide load variation. In these conditions, the active and reactive electrical energy bill can be significantly reduced.     

Novel Multiflux Level, Three-Phase, Squirrel-Cage Induction Motor for Efficiency and Power Factor Maximization

In the European Union, the average load factor of electric motors in both industrial and tertiary sectors is estimated to be less than 60%. However, in some industrial sectors, the average load factor for some motor power ranges can be as low as 25%. Most oversized three-phase induction motors operate with low efficiency and power factor, which is, by far, the most important cause for poor power factor in industrial installations. In the low-load operating periods, motor performance can be improved both in terms of efficiency and power factor if the magnetizing flux is properly regulated. In this paper, a multiflux level, three-phase, squirrel-cage induction motor is proposed, in which the efficiency and power factor can be both maximized as a function of load. This novel motor can be a surplus value in industry due to its flexibility, particularly, for variable load applications in which significant energy savings can be obtained, and can also be used as new or rewound general purpose spare motor (with several levels of voltage, magnetizing flux and/or power). The proposed motor has a stator winding with two sets of turns, sharing the same positions in the stator slots (which can be connected either in series or in parallel). Among all the possible stator winding connections, six modes were selected and analyzed (two of which are new). The basic principles for proper connection mode change are discussed. An electronic device and a contactor concept for automatic connection mode change are proposed. As far as the authors know, this concept is described and analyzed for the first time.     

Voltage and frequency control of self-excited slip-ring induction generators

By varying the effective rotor resistance of a self-excited slip-ring induction generator (SESRIG), the magnitude and frequency of the output voltage can be controlled over a wide speed range. A steady-state analysis based on a normalized equivalent circuit enables the control characteristics to be deduced. For a given stator load impedance, both the frequency and the voltage can be maintained constant as the speed is varied, without changing the excitation capacitance. When the stator load is variable, simultaneous voltage and frequency control requires the excitation capacitance to be changed as the rotor resistance is varied. Experiments performed on a 1.8-kW laboratory machine confirm the feasibility of the method of control. Practical implementation of a closed-loop control scheme for an SESRIG using chopper-controlled rotor resistance is also discussed. With a properly tuned proportional-plus-integral (PI) controller, satisfactory dynamic performance of the SESRIG is obtained. The proposed scheme may be used in a low-cost variable-speed wind energy system for providing good-quality electric power to remote regions.     

Optimal efficiency control strategy for interior permanent-magnet synchronous motor drives

In this paper, the problem of efficiency optimization in vector-controlled interior permanent-magnet (PM) synchronous motor drives is investigated. A loss model controller is introduced that determines the optimal d-axis component of the stator current that minimizes power losses. For the implementation of the suggested controller, the knowledge of the loss model is not required since an experimental procedure is followed to determine its parameters. Furthermore, it is shown that the loss model of the interior PM motor can be used as a basis for deriving loss minimization conditions for surface PM synchronous motors and synchronous reluctance motors as well. Experimental results of an interior PM motor are presented to validate the effectiveness of the proposed method and demonstrate the operational improvements.     

Vectorial command of an asynchronous motor fed by a photovoltaic generator

In order to promote renewable energy, Tunisia has developed a large program to exploitate photovoltaïc systems (PV) to provide electric power in rural electrification. These needs increase continually following standard of living improvements, from lighting and media communication (radio, TV) to motors, refrigeration and pumping. The fluctuation of solar energy on one hand, and the necessity to optimise available solar energy on the other, it is useful to develop new efficient and flexible modes to control motors. A vectorial control of an asynchronous motor fed by a photovoltaïc system is proposed. In this case, the control of the circulating current becomes an important objective in the algorithm design. This paper presents an efficient current controller scheme that can achieve high accuracy and a fast dynamic response of induction machine. This scheme uses voltage decoupling and proportional integral controller loops (PI). Furthermore, to operate the PV array at its maximum power point for every instant, the PV system must contain a maximum power point tracking controller (MPPT). Good static and dynamic performances were obtained in simulation of the proposed structure.     

Modeling and simulation of saturated induction motors in phasequantities

This paper proposes a new model for saturated induction motors. The saturation effects are incorporated in the magnetizing inductance and the stator mutual inductances, taking into account the nonuniform distribution of magnetic saturation within the motor core. The proposed model can be used to analyze the manner in which the induction motors interact with the supply network or power source, since it can predict the motor current/voltage harmonics produced by magnetic saturation. Experimental tests show that the proposed model represents with reasonable accuracy (8%) the motor saturation effects at nominal stator voltage as well as for overvoltage operation     

Core loss in buried magnet permanent magnet synchronous motors

The steady-state core-loss characteristics of buried-magnet synchronous motors operating from a sinusoidal constant frequency voltage supply are investigated. Measured and calculated core loss, with constant shaft load, is shown to increase with decreasing terminal voltage due to an increase in armature reaction-induced stator flux-density time harmonics. Finite-element modeling is used to show that the additional loss due to the time-harmonic fields can increase core loss by a factor of six over the loss associated with only the fundamental component field at low motor flux levels. A simple air-gap model of motor flux components shows that this increased loss is due to localized rotor saturation. Thus, stator-core harmonic fields should be expected for all buried-magnet rotor synchronous motors (with or without a cage) operating at low flux levels. This factor becomes increasingly important when the motors are operated in the high-speed low-flux mode in conjunction with a variable-speed drive     

Pattern recognition-a technique for induction machines rotor brokenbar detection

A pattern recognition technique based on Bayes minimum error classifier is developed to detect broken rotor bar faults in induction motors at the steady state. The proposed algorithm uses only stator currents as input without the need for any other variables. Initially, rotor speed is estimated from the stator currents, then appropriate features are extracted. The produced feature vector is normalized and fed to the trained classifier to see if the motor is healthy or has broken bar faults. Only the number of poles and rotor slots are needed as pre-knowledge information. A theoretical approach together with experimental results derived from a 3 hp AC induction motor show the strength of the proposed method. In order to cover many different motor load conditions, data are obtained from 10% to 130% of the rated load for both a healthy induction motor and an induction motor with a rotor having 4 broken bars     

Multiple signature processing-based fault detection schemes for broken rotor bar in induction motors

The existence of broken rotor bars in induction motors can be detected by monitoring any abnormality of the spectrum amplitudes at certain frequencies in the motor current spectrum. It has been shown that these broken rotor bar-specific frequencies are settled around the fundamental stator current frequency and are termed lower and upper sideband components. Broken rotor bar fault detection schemes should depend on multiple signatures in order to overcome or reduce the effect of any misinterpretation of the signatures that are obscured by factors such as measurement noises and different load conditions. Multiple discriminant analysis (MDA) provides an appropriate environment to develop such fault detection schemes because of its multi-input processing capabilities. The focus of this paper is to provide a new fault detection methodology for broken rotor bar fault detection and diagnostics in terms of its multiple signature processing feature and the motor operation partitioning concept to improve the overall detection performance. This paper describes two fault detection schemes within this methodology, and demonstrates that multiple signature processing is more efficient than single signature processing. The first scheme, which will be named the "monolith scheme," is based on a single large-scale MDA unit representing the complete operating load torque region of the motor, while the second scheme, which will be named the "partition scheme," consists of many small-scale MDA units, each unit representing a particular load torque operating region.