【導(dǎo)讀】分關(guān)心的問題,但在設(shè)計(jì)過程中無法進(jìn)行相關(guān)的試驗(yàn)。本論文中建立他勵(lì)直流電。SIMULINK工具，對(duì)系統(tǒng)進(jìn)行仿真，并得出實(shí)驗(yàn)結(jié)果。從而更清楚的了解了其。動(dòng)態(tài)過程,為設(shè)計(jì)人員提供了可靠的參考數(shù)據(jù)。為以后的虛擬實(shí)驗(yàn)的建立發(fā)展積。累了許多寶貴的經(jīng)驗(yàn)。直流電動(dòng)機(jī)是將電能轉(zhuǎn)換為機(jī)械能的裝置。電機(jī)分為直流電動(dòng)機(jī)和交流電。因此，在對(duì)電動(dòng)機(jī)的調(diào)速性能和起動(dòng)性能要求較高的生產(chǎn)機(jī)械上，大都使用直流電動(dòng)機(jī)進(jìn)行拖動(dòng)。但是，直流電動(dòng)機(jī)的制造工藝復(fù)雜，生產(chǎn)成本。機(jī)與交流電動(dòng)機(jī)“各得其所”。定子是直流電動(dòng)機(jī)的靜止部分。它包括主磁極、換向磁極、機(jī)座、端蓋和。電刷裝置等部件。1．主磁極在一般的大中型直流電機(jī)中，主磁極是一種電磁鐵。

　　

【正文】 so that the rotor never stops (like a pass needle does) but rather keeps rotating indefinitely (as long as power is applied and is sufficient for the motor 安徽建筑大學(xué)畢業(yè)設(shè)計(jì)（論文） 30 to overe the shaft torque load and internal losses due to friction, etc.) Many of the limitations of the classic mutator DC motor are due to the need for brushes to press against the mutator. This creates friction. Sparks are created by the brushes making and breaking circuits through the rotor coils as the brushes cross the insulating gaps between mutator sections. Depending on the mutator design, this may include the brushes shorting together adjacent sections— and hence coil ends— momentarily while crossing the gaps. Furthermore, the inductance of the rotor coils causes the voltage across each to rise when its circuit is opened, increasing the sparking of the brushes. This sparking limits the maximum speed of the machine, as toorapid sparking will overheat, erode, or even melt the mutator. The current density per unit area of the brushes, in bination with their resistivity, limits the output of the motor. The making and breaking of electric contact also causes electrical noise , and the sparks additionally cause RFI. Brushes eventually wear out and require replacement, and the mutator itself is subject to wear and maintenance (on larger motors) or replacement (on small motors). The mutator assembly on a large machine is a costly element, requiring precision assembly of many parts. On small motors, the mutator is usually permanently integrated into the rotor, so replacing it usually requires replacing the whole rotor. Large brushes are desired for a larger brush contact area to maximize motor output, but small brushes are desired for low mass to maximize the speed at which the motor can run without the brushes excessively bouncing and sparking (parable to the problem of valve float in internal bustion engines).Small brushes are also desirable for lower cost. Stiffer brush springs can also be used to make brushes of a given mass work at a higher speed, but at the cost of greater friction losses (lower efficiency) and accelerated brush and mutator wear. Therefore, DC motor brush design entails a tradeoff between output power, speed, and efficiency/wear. Brushless DC motors Some of the problems of the brushed DC motor are eliminated in the brushless design. In this motor, the mechanical rotating switch or mutator/brush gear 安徽建筑大學(xué)畢業(yè)設(shè)計(jì)（論文） 31 assembly is replaced by an external electronic switch synchronised to the rotor39。s position. Brushless motors are typically 8590% efficient or more, whereas DC motors with brush gear are typically 7580% efficient. Midway between ordinary DC motors and stepper motors lies the realm of the brushless DC motor. Built in a fashion very similar to stepper motors, these often use a permanent mag external rotor, three phases of driving coils, one or more Hall effect sensors to sense the position of the rotor, and the associated drive electronics. The coils are activated, one phase after the other, by the drive electronics as cued by the signals from either Hall effect sensors or from the back EMF ( electromotive force ) of the undriven coils. In effect, they act as threephase synchronous motors containing their own variablefrequency drive electronics. A specialized class of brushless DC motor controllers utilize EMF feedback through the main phase connections instead of Hall effect sensors to determine position and velocity. These motors are used extensively in electric radiocontrolled vehicles. When configured with the mags on the outside, these are referred to by modellers as out runner motors. Brushless DC motors are monly used where precise speed control is necessary, as in puter disk drives or in video cassette recorders, the spindles within CD, CDROM (etc.) drives, and mechanisms within office products such as fans, laser printers and photocopiers. They have several advantages over conventional motors: Compared to AC fans using shadedpole motors, they are very efficient, running much cooler than the equivalent AC motors. This cool operation leads to muchimproved life of the fan39。s bearings. Without a mutator to wear out, the life of a DC brushless motor can be significantly longer pared to a DC motor using brushes and a mutator. Commutation also tends to cause a great deal of electrical and RF noise。 without a mutator or brushes, a brushless motor may be used in electrically sensitive devices like audio equipment or puters. The same Hall effect sensors that provide the mutation can also provide a convenient tachometer signal for closedloop control (servocontrolled) applications. 安徽建筑大學(xué)畢業(yè)設(shè)計(jì)（論文） 32 In fans, the tachometer signal can be used to derive a fan OK signal. The motor can be easily synchronized to an internal or external clock, leading to precise speed control. Brushless motors have no chance of sparking, unlike brushed motors, making them better suited to environments with volatile chemicals and fuels. Also, sparking generates ozone which can accumulate in poorly ventilated buildings risking harm to occupants39。 health. Brushless motors are usually used in small equipment such as puters and are generally used to get rid of unwanted heat. They are also very quiet motors which is an advantage if being used in equipment that is affected by vibrations. Modern DC brushless motors range in power from a fraction of a watt to many kilowatts. Larger brushless motors up to about 100 kW rating are used in electric vehicles. They also find significant use in highperformance electric model aircraft. Coreless or