Induction Motor Drive

Transcription

1 Induction Motor Drive 1. Brief review of IM theory.. IM drive characteritic with: Variable input voltage Variable rotor reitance Variable rotor power Variable voltage and variable frequency, VVVF drive (VSI V/f inverter drive) Variable current and variable frequency, VCVF drive (CSI I/f inverter drive) 1

2 Introduction Induction machine are very widely ued in indutry becaue of it ruggedne, low maintenance. and alo it i cheaper than mot other electric motor. Traditionally, ued a contant peed drive (without an inverter) variable peed drive (with low dynamic) Recent development in control technique and power electronic ha made it poible for the Induction Motor (IM) to be ued in application requiring fat dynamic repone and decoupled control of torque and flux, like the bruhed DC motor.

3 Phyical Structure of the Induction Motor 3

4 Stator and Rotor 3-phae Sinuoidally Ditributed Stator winding Cage rotor Wound rotor 4

5 Working Principle 3-phae balance current of a certain frequency in three-phae tator winding lead to Rotating Magnetic Field Speed of the rotating magnetic field i the ynchronou peed, f f1 1 1 N rev/ec; yn mech rad/ec yn p p p Becaue of thi rotating field, voltage i induced in the rotor winding (or aluminum bar). The conequent 3-phae current flow in the rotor etablihe a rotor field. Interaction between rotor and tator field will produce the neceary torque to rotate the rotor and load with peed n rot. Nrot f /p rev/ec; f rot mech rad/ec p p 5

6 IM working principle continued 6

7 Slip and lip frequency Slip, N Slip frequency, yn rot yn1 rot N yn N yn fr f1 f1 f = 1 when the rotor i at tandtill. = 0 when the motor run at ynchronou peed , normally. The lip frequency, f 1,ithe frequency of the voltage and current induced in the rotor. Rotor induced voltage/phae: E 444N. ˆ f 444N. ˆ f r r r r r 1 Rotor voltage and current are at the lip frequency f 1. 7

8 The Rotor Circuit I X I X I R X E R (a) At lip frequency R a R ; X E a X tan dtill R E (b) (c) At tator frequency I I a A X R R 1 Mechanical load 1 E ae E I I a Rotor circuit Referred to tator E ae E 1 A R 1 8

9 The approximate equivalent circuit I 1 R 1 X 1 I I a A R X V 1 I c R c I m X m E ae E 1 R 1 A Total Rotor Power: Developed Output Power: R 3R E1 R + 1L P = 3I = R Po P I R I P W W 9

10 Developed power and torque Slip Power: l o P P P P 3I R Developed torque = Developed output power/mech peed in rad/ec: Po 3I R1 / Tdev Nm N N rot 3I R 1 / yn N 1 rot 3p I R 3pI R f f f 1 1 Rotor Power Slip Power Syn Speed Slip Speed Nm Nm W 10

11 I 1 R Th X Th A I R X V Th A R 1 V Th X V m 1 R X X 1 1 m jx R jx Z R jx m 1 1 Th Th Th R1 j X1 Xm Note that for X m >> (R 1 and X 1 ); R Th R 1 ; X Th X 1 ;and V Th V 1. 11

12 Rotor current and torque I V Th R Th Th R X X A T 3p Th dev 1 R RTh XTh X V R Nm 1

13 IM torque peed characteritic with variable voltage, rad/ec yn1 V 1 = 1 pu V 1 = 0.7 pu V 1 = 0.5 pu Re-generating 0 V 1 = 0.5 pu V 1 = 0.7 pu V 1 = 1 pu Fwd Motoring Torque, Nm < 0 = 0 = 1 P T Rev Motoring yn1 Plugging >1 = 13

14 Braking of an IM drive with plugging Two way: By adjuting input frequency below haft frequency. By plugging. Note: Operation with high lip caue high power lo; may lead to high rotor temperature a a conequence. 14

15 T max and lip mt for T max For mall lip, T dev 3p V Th 1 R Nm R For maximum torque, R X X mt Th Th Slip for maximum torque, mt R R X X Th Th Maximum torque, T max 3p 1 V Th R R X X Th Th Th Nm Note that T max i independent of R 15

16 IM torque characteritic with R Load T- characteritic 1 R increae T rated T max T dev 16

17 Induction Motor drive 17

18 IM drive with variable upply voltage Variable AC voltage at the main upply frequency can be obtained from tap-changing tranformer, from back-back phae-controlled thyritor converter or from an inverter. V 1 V 1 in max 18

19 T- characteritic with variable voltage V 1 = 0.5 pu 1 V 1 = 0.7 pu V 1 = 1 pu Load T=K 0 Torque, Nm Variable voltage operation at the utility upply (bae) frequency offer very limited peed range. Pump type load are uitable; however, high lip and very loy operation i inevitable with reduced upply voltage. 19

20 Example 1: Voltage control for a fan or compreor load Fan or compreor type load: o m 3 P T K 1 1 K 1 P 1 o P K 1 l P I R P K 1 K R I 1 For maximum P l : =

21 Example : contant load Contant torque type load: P T K 1 o m P P o 1 K l P I R P K I K R Example 1 & how that, the rotor current or rotor power lo increae le lowly with lip (or load) for a fan or compreor type load than for a contant torque type load. 1

22 WRIM drive with variable rotor power AC Main AC Main Wound Rotor IM Slip Ring Variable Reitor Bank Wound Rotor IM Slip Ring 3-f Diode Bridge Rectifier Variable Reitor AC Main V 1 E I d E V d T Wound Rotor IM Slip Ring 3-f Diode Bridge Rectifier Duty Cycle D Variable Reitor

23 T ω characteritic with variable rotor reitance Load T- characteritic 1 R increae T dev T rated T max Figure T characteritic with variable rotor reitance. 3

24 IM drive with variable rotor power (lip power control tatic Scherbiu ytem) I d V 1 1:n V 1 V V d V di 4

25 T - I d characteritic with control of DC link current 3I R 3I R 1 l o P P P 3I R P 3Emax The rectifier output DC voltage, V Equating the AC and DC power, P P V I l d d 3E I max d d P 3E max If the lip power i mall compared to the total rotor (or air-gap) power, i.e., for mall lip, 3E P Tn Tn P I 3Emax 3pE T Id I d n f max o 1 d T KI d 1 1 I d 5

26 Speed control with lip power recovery P Po Pl Pret P 1 P o P l P P ret By neglecting the voltage drop acro tator impedance, E V a 1 The DC output voltage of rectifier, 3 V 3 V n 1 Vdi co co From V d =V di V a co ; n d 3E 3 V a max 1 for > 90 Normally, n a. Why? 6

27 Speed control with lip power recovery Figure d 7

28 A C M A I N S DC R eactor I d T ref SC + _ + _ C C e c FCC 9 Augut 017 8

29 IM drive with 3 phae VSI VVVf inverter V d VAn,1 m 0.354mVd where m i the depth of modulation 9

30 Performance with VVVF upply We aume that the AC upply voltage to the motor i inuoidal, but of arbitrarily variable amplitude (RMS value V 1 ) and frequency f 1. f f 1 o 0 1 for operation from zero to bae peed. i higher than 1 for operation above bae peed. I 1 R 1 X 1 I R X V 1 E 1 I m X m R 1 Figure

31 VVVF (or V/f) drive with contant air gap flux V R I j LI E RI j LI K ˆ f ag 1 For operation near bae peed, the tator voltage drop: can be neglected, compared to V 1. ˆ V V1 Kag f1 K ˆ 1 ag f 1 R I j L I Thu, for operation near bae peed, contant V/f upply implie operation with contant air gap flux. 31

32 T-ω characteritic with contant V/f drive With negligible tator impedance drop, E1 V1 V1 I = R R R j f 1 L +j1l +j1l Vo f1 ˆ f f o 1Kag I R f L R f L 1 1 ˆ 3p R Kag f1 dev 1 R + 1L T = Thu, of f 1. I = 3p 1 f R K ˆ ag 1 R + f L Nm and T dev value remain the ame for a given f 1,regardle 3

33 IM drive with contant V/f ratio I T dev f 1 Slip freq, f 1 Slip freq, f 1 n o n 1 f o n o n 1 f o f 1 f 1 n n 3 f n f 4 n 3 f f 3 I 33

34 Starting with maximum torque, V/f drive For maximum developed power and torque in the rotor circuit R X When T max i developed, 1 f1 R f f f f 1 o X for 1 1 X f f f Note: maximum torque occur at the ame lip frequency for all f 1. For maximum torque to occur at zero peed, f fr o R 1 X L From and 5..7, T max ˆ ag 3p K 4 X f o Nm 34

35 IM drive with contant V/f ratio Rated V 1 Kˆ gap V 1 f o f 1 35

36 Contant max torque and power characteritic Speed, Rad/ec Rated V 1 & f o T dev Nm T max Figure T- characteritic under VVVF drive with f 1 below and above f o. 36

37 T characteritic with VSI V/f drive, rad/ec Bae peed with rated V 1 and bae f 1 Q Q 1 Sequence: a-b-c T rated T max T, Nm Sequence: a-c-b Q 3 Q 4 37

38 V/f drive at low peed V R I j L I E R I j L I K ˆ f ag 1 R I j L I At low peed, the tator impedance drop: may not remain negligible compared to V 1 or E 1. It implie reduction of the air-gap flux ˆ ag,, and conequent reduction of T dev 3p R K ˆ f ag 1 dev 1 R + 1L T = 38

39 V/f drive at low peed Bae Speed Speed, Rad/ec 1 increae with negligible tator impedance with tator impedance T dev Nm Figure Drooping T- characteritic at low peed with VVVF drive 39

40 V/f drive with low frequency voltage boot Rated V 1 low-frequency voltage boot V bo f 1 f o Figure Voltage boot of VVVF drive at low peed The zero-frequency boot i V R I bo 1 1rated 40

41 VSI V/f drive controller open loop Speed reference 1 1 T f V 1 Reference f 1 Reference Open loop V/f controller 41

42 Speed control with an inner lip loop E V K ˆ f I = R R R f L 1 1 ag 1 +j1l +j1l 1 V 1 * l + + f 1 Fig Cloed loop peed controller with inner lip control 4

43 CSI drive tructure for IM Vdc A B C Motor * i a P W M * i b P W M * i c P W M 43

44 IM drive with variable I-f upply I 1 A I j X I m I 1 jx m E 1 R A Figure Per-phae equivalent circuit with current ource input 44

45 IM drive with variable I-f upply T dev 3pI R f 1 Torque i inverely proportional to lip frequency 45

46 IM drive with variable I-f upply Maximum rotor power and hence developed torque occur when R X m X 1 f1 R f f f f 1 o X m X When T max i developed mt X R m X fr o 1 1 Xm X f f f Normally, X m >> X. S mt for CSI drive i much maller than for VSI. For tarting from tandtill with T max For maximum torque to occur at tart f X R m X fr o R 1 Xm X Lm L 46

47 IM drive with variable I-f upply contd. T dev 3pI R f f 1 For a given I 1, the rotor current I i given by (uing current diviion) I j X I m 1 R j Xm X Uing the lip condition for maximum torque, mt X R m X T max XmI1 m o 3p 4 X X f Nm 47

48 I-f drive with contant air-gap flux I I m 1 R R j X m j X X I R f1l I m 1 R f1 Lm L 48

49 I 1 for contant air gap flux operation I 1 Q Q 1 No load I 1 -f 1 0 +f 1 Q 3 Q 4 I 1 in revere equence 49

50 I 1 at no-load E1 X ˆ mim Kag f E V 1 1rated 1 K ˆ ag f f E X I 1 m m 1rated m m ag f1 f1 fo fo K ˆ I m I 1,no load V 1rated X m V X I 1 o 50

51 Speed-control ytem block diagram ref + + l f 1 I 1 I-Ref Gen I N V M + Figure Variable current, variable frequency inverter drive cheme. 51

52 CSI I/f drive for large IM machine Rectifier L I d Inverter T1 C T3 C T5 AC Main C C C T4 T6 C T * I d FCCR e c1 e c e c3 FCCI T1 T6 M T 5

53 Quai-quare phae current waveform i a T 1 T 1 +I d T 4 T 4 -I d T 1 i b T 6 T 3 T 3 T 6 T 6 i c T T 5 T T 5 Figure Motor current waveform and thyritor witching tate for a current ource drive. 53