Chapter 14. Reluctance Drives: Stepper-Motor and Switched- Reluctance Drives

Transcription

1 Chapter 14 Reluctance Drives: tepper-motor and witched- Reluctance Drives

2 Reluctance Drives 14-1 tepper Motor and witched Reluctance Drives q Reluctance Drives tepper Motor drives - ccurate position control without feedback - Electrical pulse input gives discrete angle change - Types: Variable Reluctance Permanent Magnet Hybrid witched Reluctance drives - Variable-reluctance stepper-motor designed to go into saturation - Feedback necessary

3 14-2 tepper-motor Positioning q m step anglel 0 t Electrical pulse input 0 t q Each pulse moves motor a discrete angle step angle q Counting pulses tells how far motor has turned without actually measuring (no feedback)

4 Reluctance Motors Operating 14-3 Principles l it () + q fixed l 2 R T Dl 2 et () l 1 atq +Dq atq 1-0 i 1 i q alient rotor aligns to salient stator

5 14-4 tepper - Motors q Variable reluctance motors - relies on rotor saliency q Permanent magnet motors - relies on rotor magnets q Hybrid motors - relies on both saliency and rotor magnets

6 Variable Reluctance tepper 14-5 Motors q = 1 3 rotor q = 0 tooth pitch i a z i b z q = 2 3 rotor tooth pitch i a q =1 rotor tooth pitch z z i c

7 Variable - Reluctance tepper 14-6 Motors (cont ) q Rotor and stator saliency q Unequal number of poles q tator current effectively pulls rotor pole in line with stator pole 360 step-angle = q r 0 q = number of phases = number of rotor poles r

8 Permanent Magnet tepper Motor z B B B B q =135 o z q =90 o z B B B B q = 45 o z q =0 o q =180 o z q Permanent magnets replace salient poles of variablereluctance motor 14-7

9 Hybrid tepper Motor 14-8 L R stator windings shaft end cap end cap stator air gap outer casing L' R' q Uses both rotor saliency and permanent magnets on rotor q aliency on ends of rotor ends not lined up q Permanent magnet makes one of the rotor ends a south pole and the other a north pole

10 Hybrid tepper Motor (cont ) rotor 4 pitch tooth

11 14-10 tepper-motor Equivalent Circuit i ph + R ph v ph L ph e ph

12 Half tepping and Micro-tepping i a i b q Possible to move rotor by half steps by exciting two stator windings equally q Finer steps possible by exciting two windings unequally

13 PPU for Variable-Reluctance tepper-motor + + v ph - T 1 i ph L ph e ph + - D 1 V d Phase winding T 2 D 2 - R sense i ph I ref T 1 on T 1 off T 2 on T 1 on t T1, T2off

14 14-13 PPU for Variable-Reluctance tepper-motor (cont ) q Currents do not need to reverse q Circuit uses incomplete switch poles that can pass current only one direction through the motor phase

15 14-14 PPU for PM and Hybrid tepper- Motor + T 1 D 1 Phase winding T 3 D 3 V d T 4 D 4 + v ph - T 2 D 2 - q Phase currents must be reversible q Complete switch poles used

16 witched-reluctance Motor Drives i a q =-30 o q =0 o i a l a q =0 o q =-30 o i a q Variable-reluctance stepper-motor q Closed-loop, uses feedback q Motor goes into saturation q Rugged, inexpensive

17 14-16 ummary/review q What are the three broad categories of reluctance drives? q How is the principle on which reluctance drives operate different than that seen earlier with other drives? q Write down the reluctance torque expression. What does the direction of torque depend on? q Describe the operating principle of a variable-reluctance stepper-motor. q Describe the operating principle of a permanent-magnet steppermotor. q Describe the operating principle of a hybrid stepper-motor. q What is the equivalent-circuit representation of a stepper-motor? q How is half-stepping and micro-stepping achieved in steppermotors?

18 14-17 ummary/review q What is the nature of power-processing units in stepper-motor drives? q Describe the operating principles of switched-reluctance drives. q What are the application areas of switched-reluctance drives?