With the rapid development of power electronics, computer science and control theory, a revolution happened in motor drives. Actually, AC drives are the mainstream of motor drives. Permanent magnet synchronous motors (PMSMs) have been widely used as AC drives over the last two decades due to their high efficiency, high power density and no dc field winding in the rotor. It is well known motion control of PMSM requires accurate position and velocity signals to realize field orientation. In conventional motion control systems, optical encoders or electromagnetic resolvers are used for this purpose. However, these additional sensors increase the costs of the system and decrease the reliability. With this background, sensorless operation is fast becoming a requirement, and the elimination of position and velocity sensors has been an attractive prospect.
As technological processes increase in complexity,and the required peformance
specifications become more severe,analytical design procedures assume great importance. It has become essential for engineers to have an understanding of the nature of the dynamic behaviour of systems,and of the methods available for analyzing and improving dynamic performence.
These requirements are making the use of mathematical modelling techniques an
essential part of design. The nature of the model and the methods employed in obtaining it are dependent on the depth of understanding needed at a particular stage of the design study,and on the use to which the model will be put.
It is desirable first to define what is meant by a system,a word which is frequently used in conversation .Broadly,a system can be thought of as a collection of interacting components , although sometimes interest might lie just in one single component. These components will often be functional parts of such physical components. The system of interest might be a power station , a steam turbine in the power station,or a control valve on the turbine;it might be an aeroplane,its air conditioning,anengine,or part of an engine;a process plant for the production of a chemical , or a large or small part of the plant;a human being,or some part of the body such as the muscle control mechanism for a limb;or it might be economic system of country,or any other from a wide range of fields.
The system would normally be considered conceptually as being that part of the universe in which interest lay.There would be interaction between the system and certain parts of the surroundings known as the environment.The two would be separated by an imaginary boundary.In defining the system and its environment it is necessary to decide where this boundary should be placed;this decision depends both on the physical entities involved and on the purpose of the investigation.
In studying a power station,interest might lie primarily in the relationship between the power station and the community,in which case the system and its environment might be envisaged as in Fig.5-1.There might,however,be a more specific interest in the speed control system of the turbogenerator,in which case the system could be as in Fig.5-2.
In abstracting from the whole the system of interest,it is necessary to consider carefully where the boundary shall be placed,and closely allied is the need to decide what relevant signals cross the system boundary.Inaddition,there will be signals of interest within the system boundary,variables which help to describe and define the detailed system
behaviour.Some of these signals will be measurable,some not or only indirectly;some will be useful from the viewpoint of analysis,andsome not.
The signals which pass to the system from the environment will be termed the system inputs,while those passing out across the boundary will be the system outputs.Often there will be only one system input that is varying and one system output which is affected.The systems to be considered in this chapter will be predominantly single-input-single-output systems,the type which occurs most frequently in practice.
Modern power systems are usually large-scale, geographically distributed, and with hundreds to thousands of generators operating in parallel and synchronously. They may vary in size and structure from one to another, but they all have the same basic characteristics:
（1）Are comprised of three-phase AC systems operating essentially at constant
voltage.Generation and transmission facilities use three-phase equipment .Industrial loads are invariablythree-phase; single-phase residential and commercial loads are distributed equally among the phases so as to effectively form a balanced three-phase system.
（2）Use synchronous machines for generation of electricity. Prime movers convert the primary energy (fossil, nuclear, and hydraulic) to mechanical energy that is, in turn, converted to electrical energy by synchronous generators.
（3）Transmit power over significant distances to consumers spread over a wide area. This requires a transmission system comprising subsystems operating at different voltage levels.
The basic elements of a modern power system in USA are shown in Fig.6-1. Electric power is produced at generating stations (GS) and transmitted to consumers through a complex network of individual components, including transmission lines, transformers, and switching devices. It is common practice to classify the transmission network into the following subsystems: Transmission system; Subtransmission system; Distribution system. Basic elements of a power system The transmission system interconnects all major generating stations and main load centers in the system. It forms the backbone of the integrated power system and operates at the highest voltage levels (typically, 230 kV and above in USA). The generator voltages are usually in the range of 11 to 35 kV. These are stepped up to the transmission voltage level, and power is transmitted to transmission substations where the voltages are stepped down to the subtransmission level (typically, 69 to 138 kV). The generation and transmission subsystems are often referred to as the bulk power system. The subtransmisson system transmits power in small quantities from the transmission substations to the distribution substations. subtransmisson Large industrial
customers are commonly supplied directly from the subtransmission system. In some systems, there is no clear demarcation between subtransmission and transmission circuits. As the system expands and higher voltage levels become necessary for transmission, the older transmission lines are often relegated to subtransmission function.
The distribution system represents the final stage in the transfer of power to the
individual customers. The primary distribution voltage is typically between 4.0 kV and 34.5 kV. Small industrial customers are supplied by primary feeders at this voltage level. The secondary distribution feeders supply residential and commercial customers at 120/240 V.
Small generating plants located near the load are also connected to the subtransmission or distribution system directly. Interconnections to neighboring power systems are usually formed at the transmission system level. The overall system thus consists of multiple
generating sources and several layers of transmission networks. This provides a high degree
of structural redundancy that enables the system to withstand unusual contingencies without service disruption to the customers.
Instability may also be encountered without loss of synchronism. For example, a system consisting of a synchronous generator feeding an induction motor load through a
transmission line can become unstable because of the collapse of load voltage. Maintenance of synchronism is not an issue in this instance; instead, the concern is stability and control of voltage. This form of instability can also occur in loads covering an extensive area supplied by a large system. This kind of stability is referred to \the ability of interconnected synchronous machines of a power system to remain in
synchronism. It is most important to power system stability problems. The stability problem involves the study of the electromechanical oscillations inherent in power system. A
fundamental factor in this problem is the manner in which the power outputs of synchronous machines vary as their rotors oscillate.
随着电力电子技术、计算机技术以及自动控制技术的飞速发展，给电气传动领域带来了历史性的革命，交流调速传动逐渐上升为电气传动的主流。永磁同步电动机由于无需励磁电流、运行效率和功率密度都很高，在过去的二十年里已被广泛地应用在交流调速传动中，但它的高性能控制需要精确的转子位置和速度信号去实现磁场定向。在传统的运动控制系统中，通常采用光电编码器或旋转变压器来检测转子的位置和速度。然而，这些机械式的传感器增加了系统的成本，并且降低了系统的可靠性。因此，取消这些装置以提高系统的可靠性并降低成本的研究逐渐热门。
由于科技过程复杂性增加的,需要更加严重,规格技艺水平具有重要意义的分析设计程序承担它已成为基本为工程人员了解自然的动态行为的系统和可行的方法来分析与改进动态性能良好。
这些要求利用数学建模技术设计的重要组成部分大自然的模型和方法的使用,在获得它依赖于需要理解的深度在某一阶段的设计研究,模型的使用将。
首先,这是合乎情理的定义指的是什么系统,一个词经常被使用在谈话.Broadly,一个系统可以被认为是相互作用的部分组成的集合,尽管有时利益或许生存期就一个单一成分这些组件功能部位常常会这样的物理单元系统的兴趣的可能是一个电站、蒸汽涡轮机在电站、或控制阀门靠涡轮,还可能是飞机,它的空调、发动机,或部分引擎;工艺厂生产一种化学,或大或小的部分厂;一个人,或某些部位如肌肉控制机制,一根大树枝或者它可能是经济制度的国家,或任何其他从广泛的领域。
系统将概念上通常被考虑作为是兴趣位置宇宙的那个部分。有周围之间的系统和某些部分的互作用以环境著名。二将由一个虚构的界限分离。在定义系统和它的环境决定是必要的哪里应该安置这个界限; 这个决定取决于介入的物理个体和调查的目的。
在研究一个发电站，可能主要在于利益之间的发电站和社区，在这种情况下，系统及其环境可能设想在图5 - 1的关系。有可能，不过，是在汽轮发电机组调速系统，在这种情况下，该系统可以在图5 - 2更具体的利益。
在从整个系统的抽象的利益，有必要认真考虑在那里的边界应放置，并密切相关的是，必须决定什么相关的信号跨系统边界.此外，将有感兴趣的信号系统内的边界，这有助于变量和定义的详细描述系统的行为。这些信号有些人会是可衡量的，没有或只有一些间接的，有些是从分析的观点，有有的没有用处。
它的信号传递到从环境系统将称为系统的投入，而那些通过跨越边界，将是该系统的输出.通常只会有一个系统的输入是一个系统的输出变，那就是在这一章主要是考虑将单输入单输出系统，类型，多见于实践affected.The系统。
现代电力系统通常规模大，地域分布，并与数百名，并同步在数以千计的发电机并联运行。他们可能会有所不同的规模和结构从一个到另一个，但它们都具有相同的基本特征：
（1）是由三个三相交流电压恒定系统经营本质上。发电和输电设施使用三个阶段的设备。工业负荷总是三相，单相负载的住宅和商业之间平等分配的阶段，从而有效地形成一个平衡的三相系统。
（2）使用电力同步一代机器。牵引车转换的一次能源（化石，核能和水力）为机械能就是反过来，中，转换为电能的同步发电机。
（3）重大的距离发射功率超过的面积分布在一个广大消费者。这就要求传输系统的子系统组成的经营水平在不同的电压。
系统在美国一个现代化强国的基本要素是：1显示在图6 -。电功率）产生于发电厂（GS和传播给消费者通过一个复杂网络的各个组成部分，包括输电线路，变压器和开关设备。
它通常的做法是分类传输网络分为以下子系统：传输系统; Subtransmission制度;分配制度。
电力系统的基本要素1
该传输系统互连所有主要发电厂在系统中心和主要负载。它形成了系统的骨干力量的整合和经营水平在最高电压（通常为230千伏及以上美国）。发电机的电压范围通常在11至35千伏。这是加强宣传，电压等级输电和电力传输到传输）变电站的电压在那里下台的subtransmission水平（通常是69至138千伏。T该系统传输subtransmisson变电站的电力由分布在小批量的输电站通过。大工业用户通常直接供应
subtransmission制度。在一些系统中，没有明确划分输电线路之间subtransmission和。随着系统的扩展和更高电压等级输电成为必需的，旧的输电线路往往沦为subtransmission功能。
分配制度代表了个人客户的最后阶段中的转移权力的。主要分布电压一般为4.0千伏和34.5千伏。小型电压等级的工业客户提供的主要是饲养在此。二次配电馈线供应住宅和五，商业用户在120/240
小型发电厂附近的负载也连接到subtransmission直接或分配制度。系统互连到邻近的权力通常形成于水平的传输系统。整个系统网络由多个从而产生源的传播和若干层。这为一个客户高度结构性过剩，使系统中断承受无异常紧急服务。
三。翻译成中文以下
不稳定性也可能会遇到不同步的损失。例如，一个系统包括一个同步发电机喂养通过传输线的感应电动机负荷的电压不稳定，因为可以成为负载的崩溃。同步维修的问题不是一个实例在此，而是值得关注的是稳定和电压控制。这种不稳定的形式也可以在负载发生大面积覆盖的系统提供了一个大。这种稳定性种被称为“电压稳定”。转子角稳定系统的能力是一个相互关联的权力留在同步电机同步。最重要的是电力系统的稳定性问题。稳定问题涉及到电力系统的研究中固有的机电振荡。阿在这个问题最根本的因素是何种方式的同步机的功率输出为不同的转子振荡。
电气专业文章英汉对比
