By: B. Fahimi. Department of Electrical & Computer Engineering University of Missouri-Rolla Tel: (573) Fax: (573) EML:

Transcription

1 By: B. Fahimi Department of Electrical & Computer Engineering University of Missouri-Rolla Tel: (573) Fax: (573) EML:

2 Basic Magnetic Configuration of SRM Drives

3 T = 1 2 i 2 dl? dθ Magnetic Behavior of SRM

4 Local and Bul Saturation in SRM Drives

5 = = = = i e i di i const i W T di i W 0 0 ), (. ), ( θ λ θ θ θ λ CLOSED LOOP DIGITAL CONTROL OF TORQUE, SPEED AND POSITION

6 Basic Principles of Operation W 1 2 dl Te =! i θ 2 dθ 2 W L E =! iω θ I θ

7 Low speed High speed

8 4-Q Operation of SRM Torque Reverse Motoring A-D-C-B Forward Motoring A-B-C-D Speed Reverse Generating A-D-C-B Forward Generating A-B-BC-D

9 Classic Power Inverter for SRM Drive

10 REGION EQUATION 1 Region I Region II Region III Region IV Region V dl di V = Ri+ ( L * + i ) di dt dl di V = Ri+( L( θ) + i ) di dt dl dl di V = ( R+ ω ) i+ ( L( θ) + i ) dθ di dt dl di V = ( R+ω ) i+ L( θ) dθ dt dl di dij V = ω i+ L(θ ) + M j dθ dt dt * Variations of the phase voltage equation in various operational region

11 Torque r dl r +ω d θ dl( θ ) L( θ ) + i di dl r +ω d θ dl r +ω d θ L(θ ) + di - M j j dt dl( θ ) L( θ ) + i di L(θ ) r Speed L * + dl i di * Dynamics of SRM drive over the entire Speed Range

12 Torque Speed

13 Advantages: Rugged construction allows high speed operation possible Control principle is simple With appropriate excitation, the drive is as efficient as other drives Disadvantages: Sensors Low power factor Torque ripple, acoustic noise New Technology safe and reliable operation Low cost manufacturing Extended constant power region

14 IM BLDC SRM SM IPM Robustness + + Motor Cost + + Efficiency + + Open-loop Control + + Closed-loop Simplicity + + Torque Ripple Wide Speed Range + ++ No Position Sensor Acoustic Noise - Comparison of SRM with Other Adjustable Speed Candidates

15 Structural Robustness Automotive Industry Fault Tolerance Aerospace Industry High Speed Capability Mining Industry Safety Low Cost Manufacturing Office Products Application Areas Sensorless Control Home Appliances

16 θ estimated / sensed General Bloc Diagram of the SRM drive

17 Correspondence between mode of control & quadrants of operation

18 Computation of commutation instants/sequence of excitation Commutation instants are to be selected such that maximum torque/ampere is achieved. That is to position the current pulse in the area with positive (motoring) or negative (generating) slope of inductance. In the single pulse mode of operation (high speeds), proper phase advancing is necessary to build up maximum current in the phase when the positive slope starts. The sequence of excitation is ey in determining the direction of rotation. SRM rotates Opposite to the direction of phase excitation on the stator.

19 TMS320F240 Processor A (15-0) D (15-0) Program ROM/ Flash Data RAM 544w x 16 16Kw x 16 C25LP CORE 16-bit T-register 16-bit Barrel 16 x 16 Multiply Shifter (L) 32-bit P-register ShiftL (0,1,4,-6) 32-bit ALU 32-bit Accumulator ShiftL (0-7) 8 Auxiliary Regs 8 Level H/W Stac 2 Status Registers Repeat Count PA (64K-0) (A 15-0, D 15-0) Three 8-bit I/O Ports 3 Timers & 1 Watchdog 9 PWM outputs 4 Input Capt/ 12 Compare outputs Quadrature Pulse control SCI& SPI 2 10-bit ADCs 16 input ch.

20 Basic Drive Electronics for a three phase drive

21 Optimization of commutation angle by online search Phase current and gating pulse without optimization: Motor terminal voltage = 50 V; Load = 120 W, Reference current = 5.5 A; Speed = 1200 RPM; Conduction angle = 30 Phase current and gating pulse with optimization: Motor terminal voltage = 50 V; Load = 120W; Reference current = 4.7 A; Speed 1200 RPM; Conduction angle = 27.25

22 Dynamics of SRM at High Speed: di dl V = ri + L( θ ) +ω i dt dθ Torque Inductance Current The main objective in control is to tune t0 and t3 such that maximum current and maximum torque match while Avoiding excessive negative torque. θ = θ d = L π N u r I V max bus ω θ (min( α d s, α r ) + α s 2 α r ) t0 t1 t2 t3 t4

23 Current pulse during generation = + = = + θ θ ω θ θ τ θ π θ ω θ θ ω π θ τ θ τ d dl L e d N dl V t i e d dl V t i N r t r Bus g t Bus m ) ( ) ( ) ( 1 ) ( ) ( ) )(1 ) ( ( ) ( ) ( ) (

24 General structure of the Torque Estimator in SRM

25 5 Torque[N-m] T ave 12 π i m 0 ( L ( i) L ) comm min idi time[sec] M 2 L comm [ mh] = 2 i i i i i 45 M Torque[N-m] time[sec] Estimated and Measured Torque Signals

26 Torque Control during motoring and generating

27 f ω[. rpm..] N = r 60 Estimation of Speed in SRM drive

28 time[sec] Speed regulation in SRM Drive

29 Start Send voltage pulse with a fixed and short enough duration to all phases Compare the magnitude of resulting currents to the region in which rotor position is located Also select the equation which should be solved. Select the phase which should be used for first excitation. Also compute the initial position of the rotor. Excite the proper phase and switch over to sensorless technique at near zero speeds. SENSORLESS AT STANDSTILL

30 Ia T B D F Ib T A C E T 0 0 { L, L } { L(7.5 ), L(15 )} I B A ( L B Ic I II III IV V VI = SENSORLESS AT STANDSTILL π LA) θ = VBUS T 24 B

31 L Sensorless Start-up routine Select the Phase/s in ON state Estimation of Position Chec for the region 2 Chec on State of Switches and Calculate Switching Function S Sensorless Routine at High Speeds Compute the following Quantities V eq, R eq, = S V = R Coil Bus + (1 S ) V + (1 + S ) R D Mosfet Perform the Digital Filtering on the Current Data ~ I ~ = αi + βi 1 Chec for the region 1 Y H Perform the following scaling: ˆ A ( ), ˆ f V = Veq, L = L( R R eq, s eq, ) Perform the search for commutation/hystersis current control and update the phase status(on/off) ~ ~ ~ Vˆ I = Lˆ ( I I ) 1 SENSORLESS AT LOW SPEEDS

32 H Estimation of Position Select the Phase/s in ON state Chec for the region 1 Chec on State of Switches and Calculate Switching Function S Sensorless Routine at Low Speeds Compute the following Quantities V eq, R eq, = S V = R Coil Bus + (1 S ) V + (1 + S ) R D Mosfet Perform the following scaling: ˆ A ˆ 2 f V = Veq, ( ), L = L( R R eq, s eq, ) Chec for the region 2 Y L Perform the search for commutation/hystersis current control and update the phase status(on/off) V ˆ I ) + ( Vˆ I ) = Lˆ ( I ) ( j j j 1 j 1 SENSORLESS AT HIGH SPEEDS

33 i R Î Estimation of Position V I d L v T 1 T 2 E Equivalent circuit of an idle phase T T 1 2 LIˆ V E LIˆ V + E T T 1 2 = V V + E E

34 Apply a voltage pulse with a fixed duration of T1 Estimation of Position Measure the time it taes for current to be completely removed after the switches are turned off. T 2 Y System Is Operating in High Speed Region? N T1 T 2 N T1 T2 T + T 1 2 α HM N L T1 T 2 Y T1 T2 T + T 1 2 α LM Y L Y Y N N T2 T1 T + T 1 2 α HM N L H T2 T1 T + T 1 2 α LM Y L H Y H Detection Methodology for operational region N H

35 Current at Phase_A Current at Phase_B Current[A] Time[msec] Current[A] Time[msec] Diagnostic pulses for detection of position at stand still PHASE AT ALIGNED ACTUAL POSITION IN DETECTED POSITION IN ERROR(%) POSITION NUMBER OF PULSES NUMBER OF PULSES Phase_A 900[ ] 882[ ] 2% Phase_B 1500[ ] 1465[ ] 2.3% Phase_C 300[7.5 0 ] 288[7.2 0 ] 4% 0 Sample results for sensorless at standstill ( Overall E 1 Mech )

36 Actual Position 60 Position[mech. degree] EXPERIMENTAL RESULTS Time[msec] Estimated position Operation in High Speed Regime (n=1500 r.p.m.) 60 Position[Mech. Degree] time[msec]

37 Sensorless Startup Position[Mech. Degree] Time[msec] EXPERIMENTAL RESULTS Two example operation under sensorless Control 0 Overall E 1.5 Position[Mech. Degree] Sensorless Operation from standstill Time[msec]

38 Experimental testbed for position control

39 Web-enabled SRM Control system

40 Accomplishments:! Closed loop control of SRM drives is essential in successful application of this emerging Technology. E ( Mech)! Optimal torque control of SRM in the presence of parameter variation and system disturbances have been solved and is presented as a technology ready for applications.! Estimation of ey quantities such as torque, speed, and position will reduce the cost, dimension and unreliability of closed loop control systems.! Cost effective processors and motor controllers are ey elements in development of high grade and robust SRM drives.! Wor is underway to complete the position control of SRM drives in a closed loop format.!similar wor is being pursued for power control of SR Generators.