电机拖动 第二章 直流电机（Motor dragdc motor ）

1、03电机拖动 第二章 直流电机3（Motor drag 2 dc motor 3）Fundamentals of electrical engineering and tractionFundamentals of electrical engineering and tractionSchool of automation, Chongqing UniversityOneFundamentals of electrical engineering and tractionThe second chapter: DC motorTwoprimary coverageFirst, the wor

2、king principle and structure of DC motorFundamentals of electrical engineering and tractionThe operating principle of seventh DC motor calculation section sixth DC motor excitation windings fourth DC motor nameplate data section third section second DC motor DC motor and the fifth magnetic field ind

3、uced electromotive force and the electromagnetic torque of the reversingThreeSixth quarterOneFundamentals of electrical engineering and tractionThe operating principle of DC motorThe basic equation of DC motor motor? In energy conversion, must have its motion equation in the energy conversion, must

4、have its motion equation to describe the internal process of electromagnetic electromagnetic process and type, characterized by its internal electromagnetic process and electromechanical process? (a) electromotive force balance equation (two) torque balance? Equation (three) the power balance equati

5、on?Four(1) electromotive force balance equationTake excitation for exampleFundamentals of electrical engineering and tractionThe direction of each motor is specified: the direction of each motor is specified:The armature electromotive force E and the current I armature electromotive force Ea and the

6、 current Ia direction opposite, the electromagnetic torque T and the speed n direction are same, the electromagnetic torque Te and the speed n direction is same, is the drive torquePositive direction of generator: regulation of positive direction in generator:The armature electromotive force E and t

7、he current I armature electromotive force Ea and the current Ia direction are consistent, the electromagnetic torque T and the speed n direction are opposite, the electromagnetic torque Te and the speed n direction opposite, is the braking torqueFive(1) electromotive force balance equationFor steady

8、-state operation, for motors: steady running, for motors:Fundamentals of electrical engineering and tractionU = U, a = Ea + Ra, I, aU = U, f = (RF + r =) = I, f = R, F, I, fImportant speed formula: important speed formula:U, Ra, I, a, n=, Ce, PhiSteady state operation for generator: steady state ope

9、ration, for generator:Ea = U + Ra, I, aU = Rf, I, fSix(two) torque balance equationFor motors: for motors:Fundamentals of electrical engineering and tractionD = Te = T2 +, T0 +, TJ = T2 +, T0 +, J, DTT2 - load braking torque T0 - no-load loss torque TJ - inertia torqueIn steady state operation, the

10、motor rotates at a constant angular speed, and the motor rotates at a constant angular speed in steady state operation:Te = T2 + T0T2 + T0 Ia = CT PhiCorollary: corollary:? If the total braking diameter unchanged, unchanged, unchanged Ia was stable after? The actual load, Ia = 0For generators: for g

11、enerators:T1 = Te + T0T1 prime mover drag torqueSeven(three) power balance equationFor motors: for motors:Input electric power P1 input electric power PFundamentals of electrical engineering and tractionP = UI = U (I, F + I, a) 1 = UI, F + (I, a, Ra + 2, U, C +, Ea) I, a = pCuf +, pCua +, PC + PeEle

12、ctromagnetic power Pe, electromagnetic power P, no-load loss P0, no-load loss pPe = Ea, I, a = Te = = (T0 + T2) = P0 + P2, P0 = pFe + pmech + P?Output mechanical power P2 P2 = T2 output mechanical power PPower balance type: power balance type:P = P2 +, pCuf +, pCua +, PC +, pFe +, pmech +, P = P2 +

13、sigma, p 1Efficiency: efficiency:P2 P) * 100% = sigma ETA = (1 x 100% P P2 + p 1 sigma?Eight(three) power balance equationFor generators: for generators:Input mechanical power P1 P1 = T1 = = (Te + T0) = Pe + P0 input mechanical power PFundamentals of electrical engineering and traction= Pe + pFe + p

14、mech + P?Electromagnetic power Pe electromagnetic power PPe = Ea, I, a = (U +, I, a, Ra + 2, U, c) I, a2 = UI, a +, I, a, Ra + 2, I, a, U, C = 2 + UI, F + I, a, Ra + 2, I, UI, a, U, C= P2 + pCuf + pCua + PCOutput electric power P2 output electric power PP2 = UIPower balance type: power balance type:

15、P = P2 +, pCuf +, pCua +, PC +, pFe +, pmech +, P = P2 + sigma, p 1NinePower diagramFundamentals of electrical engineering and tractionTenTwoWorking characteristics of DC motorWork characteristics: refers to the U=UN, without the armature circuit resistance, external characteristics: refers to the U

16、=U in external armature circuit resistance, electromagnetic torque and speed n T efficiency If=IfN, n speed, electromagnetic torque Te and efficiency of three and the relationship between the transmission power of P. The relation between output power and P2. Namely: machineFundamentals of learning a

17、nd draggingN = f (P2, Te) = f (P2), ETA = f (P2)In actual operation, Ia can be directly measured, and the increase of Ia with P2 and the actual operation, can be directly measured, both increased, the increasing trend is similar, both increased, the increasing trend is not much, so often work charac

18、teristics expressed as: characteristics expressed as:N = f (I, a) Te = f (I, a) = f (I a).Eleven(1) shunt (separately excited) motor speed characteristic and shunt (separately excited)U=UN, R, =0, If=IfN, n= (Ia), =0, n=f (I) relationship curve for speed characteristics, speed characteristics. The r

19、elation curve is speed characteristic.Fundamentals of electrical engineering and tractionAccording to the formula of speed: according to the formula of speed: the formula of speedU, N, Ra, I, a, Ra, n= = N0, Ia, Ce, Ce, phi, PhiUN, N0 = ideal no-load speed ideal, no-load speed Ce PhiIf the armature

20、reaction is not decreased, if the armature reaction is not considered, if the armature reaction is taken into account, the armature reaction may be increased if the armature reaction is considered,Twelve(two) shunt (separately excited) torque characteristic of motor and shunt (separately excited)Whe

21、n U=UN and If=IfN, the relation curve of Te=f (Ia) is torque characteristic. Torque characteristic. (Is relationship curve is torque characteristicFundamentals of electrical engineering and tractionAccording to the torque formula: according to the torque formula: torque formulaTe = CT phi I aIf the

22、armature reaction is not considered, the line is close to the straight line. If the armature reaction is not considered, if the armature reaction is considered, the decrease is not enough, if the armature reaction is taken into account,Thirteen(three) the efficiency characteristic of shunt (separate

23、ly excited) motor and shunt (separately excited)U=UN, If=IfN, =f (Ia) curve for efficiency characteristics. Efficiency characteristics. (Is relation curve is efficiency characteristicFundamentals of electrical engineering and tractionP2 P) * 100% = sigma ETA = 1 x 100% (P = 11? P (1?2 pCuf + pFe + p

24、mech + P + + I a Ra + 2 I a U C?U N (Ia + I, f)* 100%Among them, among them,PCuf + pFe + pmech + P is invariant to loss2, pCua = I, a, Ra, PC = 2, I, a, U, CVariable lossFourteenThere are two times the relationship between ETA and Ia, one of the most efficiency curve exists between the two, there ar

25、e two large value negligible excitation current; electric? Due to IfNIN, negligible excitation current; and P and PC can estimate the machine can be made available to D ETA = 0:Fundamentals of learning and dragging迪一2 pcuf +生活+ PMech =我一个RA结论：当电动机在某负载下不变损耗等于可变损结论：耗时，此时效率最高。耗时，此时效率最高。？推论：1）额定运行时总损耗推论

26、：2，P = 2 i n RA2）可从额定数据来估算电枢回路总电阻？上述结论和推论具有普遍性1美元？pn =？2 2十五（四）串励直流电动机的工作特性基本方程式：基本方程式：电机学及拖动基础电动势平衡方程式U = CeN+1个（RA + RFC）电动势公式转矩平衡方程式转矩公式转速公E a c eN = C NTE = T2 + T0TE = CT我=我Au？我A（RA）u 1 N = =？RACECA我Ca为串励绕组电阻，（RFC为串励绕组电阻，RA= RA + R FC CA= Ce K F CT = CT K F）十六结论：结论：转速特性：1）随负载增大迅速转速特性：电降低；空载时有飞速

27、危险，降低；2）空载时有飞速危险，机学不允许在空载或负载很小情况及下运行。下运行。拖动基础并励电动机转矩特性：以高于电流一次方转矩特性：的比例增加，的比例增加，保证在同样大小的起动电流下得到比并励电动机更大的起动转矩。机更大的起动转矩。？效率特性：与并励相似效率特性：与并励相似。串励电动机十七（五）复励直流电动机的工作特性结论：结论：工作特性介于并励与串励的特性之间；？工作特性介于并励与串励的特性之间；？若并励磁动势为主，则接近并励特性；若并励磁动势为主，则接近并励特性；？若串励磁动势为主，则接近串励特性；若串励磁动势为主，则接近串励特性；？由于有并励磁动势存在，空载时没有飞速由于有并励磁动势

28、存在，的危险。的危险。1并励电动机并励电动机2积复励电动机积复励电动机3串励电动机串励电动机十八电机学及拖动基础一台他励直流电动机的额定数据为：例2-1】一台他励直流电动机的额定数据为：PN = 1325kw U n = 750v我n = 1930a NN = 200r/min电机电枢绕组的电阻Ra0.0161？电刷接触压降学2？u2伏及拖动基础设电动机原来在额定转速和额定负载下运行，在负设电动机原来在额定转速和额定负载下运行，载的总制动转矩（包括损耗转矩）载的总制动转矩（包括损耗转矩）保持不变的情况下，试求（1）在电枢回路中突然串入电阻= 0.0743，求串）在电枢回路中突然串入电阻R入电阻

29、最初瞬间和达到稳定时的电枢电流和转速分别是多少？别是多少？十九（2）减少电动机的励磁电流，使磁通减少）减少电动机的励磁电流，使磁通减少10%，当达到稳定时的电枢电流和转速分别是多少到稳定时的电枢电流和转速分别是多少？当达到稳定时的电枢电流和转速分别是多少电解EA = u？我是RA？2？=（750？19300。0161? 2) V = 717V (1) in the armature circuit resistance into the first moment) on suddenly suddenly in the armature circuit resistance R and Ea

30、on I = 717V a = U? Ea? U 2? C = 750? 717? 2 A = 343A Ra + 0.0161 R + 0.0743 I steady drag a = 1930A Ea = U I? A (Ra + R)? 2? U C. = 750? 1930 x (0.0161 + 0.0743) 2 V = 574V?N = n Ea 574 = (200 *) R / min = 160r / min Ea 717TwentyElectric I a = (1930 / 0.9) A = 2145A reduced to 0.9 of the original (2

31、) flux reduced to the original machine ) Ea = U? I a Ra? 2? U (C = 750 x 0.0161? 2145? 2) V = 713V and Ea Phi 7131 n = n = 200 * r / min = 221r / min drag Ea Phi 7170.9 basicTwenty-oneTwo?Characteristics of a direct current generatorFour basic physical quantities of DC generator: four basic physical

32、 quantities U, I, If, n DC generator: DC generator by motor drive, usually n=n DC generator by motor drive, usually n=nN remained unchanged as the power supply, the primary concern is the characteristics of the terminal voltage as the power supply, the primary problem attention is the common charact

33、eristics of DC generator voltage: DC generator excited, excited, commonly used: shunt and shuntFundamentals of electrical engineering and tractionTwenty-two(1) no-load operation - no-load characteristics, no-load operation, no-load characteristicsNo-load characteristic: when load I=0, the no-load te

34、rminal voltage U0 and the excitation current no-load characteristic: the load I=0, the time and space load voltage U I=0 relations curve U (I If0 relations curve U0=f (If0) electric)Fundamentals of mechanics and dragU 0 = E0 Ce = nN U f = Phi 0? 0 (I f 0) / Phi 0 = f (I f 0)The no-load characteristi

35、c is the magnetization curve, which shows the nature of the magnetic circuit of the motor, shows the nature of the magnetic circuit of the motor, and the shunt and compound excitation generator are measured separately. Excitation mode measurement. MeasuringTwenty-three(two) - self excitation voltage

36、 of no-load no-load voltage of self establishmentHe needs no self excitation, and excitation and excitation is self excited without self excitation, the operation of the generator? We need to establish the voltage at no-load, for the operation of the generator need to establish voltage in no-load to

37、 the excitation current, this process is called self excitation to the excitation current, this process is called self excitation stable point volt ampere characteristics of excitation circuit and load characteristic curve intersection point? Self stable voltammetric characteristics of excitation ci

38、rcuit and load characteristic curveSelf excitation voltage establishing condition: self excited voltage building condition: motor must have remanence; 1. motor must have polarity remanence; 2. excitation winding parallel to the armature must be correct, must be correct, should make the direction of

39、the magnetic field generated by the excitation current and the remanence direction; 3. resistor excitation circuit should be less than the speed of the critical resistance. Critical resistance at high speed.Twenty-fourFundamentals of electrical engineering and traction1 - no-load characteristic 2 -

40、excitation resistance line no-load characteristic excitation resistance line 3 - critical resistance line critical resistance line(three) load operation - external characteristics, load operation, external characteristicsExternal characteristics: the characteristic curve of generator terminal voltag

41、e varies with load: U=f (I) U= (I) power. Conclusion: under normal circumstances, the terminal voltage decreases with the increase of load. Conclusion: under normal circumstances,Fundamentals of mechanics and dragU = Ea, I, a, Ra = Ce, N, phi, I, a, Ra?1 - product complex excitation, 2 - he - excite

42、d 3 - shunt product, compound excitation, he - excited shuntWith the increase of load and the increase of load, the demagnetizing property of armature reaction leads to the decrease of magnetic flux and the decrease of magnetic flux,The induced electromotive force EMF decreases; decline; the resista

43、nce drop and brush contact drop armature circuit are increased; and the brush contact pressure drop increase; the shunt generator, the shunt generator terminal voltage drop when the excitation current is reduced, reducing excitation current decreases, causing further reduce the flux and induced elec

44、tromotive force the. Step reduction.Twenty-fiveSeventh quarterCommutation of direct current motorThe DC motor depends on the brush and commutator to change the internal alternating current into an external direct current. Direct current of the department.Fundamentals of electrical engineering and tr

45、actionDC motor, through each branch current direction is not DC motor work, change, change, the current direction is opposite to the adjacent branch winding closed loop, is on the contrary, the winding element continuously from a branch out into the adjacent branch road, and into the adjacent branch

46、, process to the current element, it is necessary to change the one side of the element in the current direction of change, the process of changing the direction of the current element, is called reverse. Commutation. The commutation will cause sparks between the brush and the commutator. When the f

47、ire reversing is bad, sparks are generated between the brush and the commutator. To a certain extent, it may damage the brush and commutator surface, and to a certain extent, it may damage the brush and commutator surface, so that the motor can not work properly. The motor is not working properly.Tw

48、enty-sixOneCommutation of electromagnetic phenomenaFundamentals of electrical engineering and tractionThe electromotive force induced by self inductance and mutual inductance in the reactance ex electromotive force E 1. reactance electromotive force. Electromotive force. Armature reaction electric p

49、otential E 2. armature reaction electric potential EA because the commutator brush placed on the pole axis, the commutator brush is placed on the pole axis, in neutral line, although the main magnetic flux density is zero, the neutral line, although the main magnetic flux density is zero, but the ar

50、mature magnetic field the magnetic flux density is not zero, therefore, reversing cutting element of armature magnetic field, the magnetic flux density is not zero, therefore, reversing cutting element of armature magnetic field, will produce an induction electromotive force. An electromotive force

51、is induced by induction. The current commutation is blocked and the current commutation delay is shown. Both the ex and the EA block current commutation and show reversal of current commutation. When the commutation element which is short circuited by the brush is cut off instantaneously, the additi

52、onal current is not zero when the reversing element which is short circuited by the brush is cut off at once. IK is not zero.Twenty-sevenTwoMethod for improving commutationPrinciple: improving commutation is to reduce or eliminate the additional current IK principle: to improve commutation is to reduce or even eliminate additional current I start. To start。 electricFundamentals of mechanics and dragMethods: general method: installation of commutating pole - reversing magnetic neutral line located at the geometric 1) with commutating pole set commutation pole placed in neutral line can