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ECT 459

ECT 459. Lecture 5 AC Motors. Common Input Power. DC 110 230 460 600 VAC or other 0.75 – 500 Hp Output Power. Control Inputs. Torque vs Speed Speed Presets 2 wire (FWD REV) 3 wire (START STOP FWD/REV) 0-10 VDC 4-20 mA Remote Potentiometer Digital Communications Interface.

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ECT 459

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  1. ECT 459 Lecture 5 AC Motors

  2. Common Input Power DC 110 230 460 600 VAC or other 0.75 – 500 Hp Output Power

  3. Control Inputs Torque vs Speed Speed Presets 2 wire (FWD REV) 3 wire (START STOP FWD/REV) 0-10 VDC 4-20 mA Remote Potentiometer Digital Communications Interface

  4. Internal Wiring

  5. Control Methods

  6. Motor S Curve

  7. Input Rectifier

  8. Output Transistors

  9. AC Motor Formulas F = NP/120 N = 120 * F/P Where: F = Frequency in Hz N = RPM P = # of poles

  10. Other Terminology Soft Starting Zero Speed Control Plugging DC Injection Braking Hunting Prevention Slip Compensation Stall Prevention

  11. A Step-Sine Motor Controller for Electric Vehicle Applications

  12. Storage of Energy • DC Batteries • Fuels

  13. DC vs. AC Motors • Energy is stored as DC • AC is more efficient

  14. AC Advantages • Increased power density • Easier to control • High torque • High speed • Small and Light

  15. Figure 1: Sine to Square comparison Figure 2: Sine to Pulse Width Modulation comparison Common Control Methods Square Wave Pulse Width Modulation

  16. Single Phase Step-Sine Waveform

  17. Figure 9: Actual 3-phase output of motor controller 3 Phase Step-Sine Waveform

  18. Example Implementation One way to generate a stair-step approximation is to connect several equal voltage battery section in series and attach them to a motor winding with a pair of multiplexer switch as illustrated in Figure 1. During the positive half cycle, switch B is connected to the bottom of the battery stack as Switch A is moved through the five steps {0-4}. During the negative half cycle, the roles of the two switches may be reversed.

  19. Another Implementation

  20. Advantages and Disadvantages Advantages: Less heat per IGBT Lower harmonic content Potentially more efficient power transfer Disadvantages: More IGBT’s More Expensive Heavier Battery current misbalance

  21. Harmonic Analysis Step-Sine Inverter Pulse-Width Inverter

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