12th International Conference EPE-PEMC 2006 Portoro

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12th International Conference EPE-PEMC 2006
Portorož
Torque Ripple Reduction by Means of a Duty-ratio Controller in a DTC-PMSM Drive
Xavier del Toro García (1), Antoni Arias (2), Luigi Salvatore (3) (1) University of Glamorgan, UK (2) Universitat Politècnica de Catalunya, Spain (3) Politecnico di Bari, Italy


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Outline

• Introduction.
• The PMSM.
• DTC.
• Duty-ratio Control Algorithm.
• Simulation Results.
• Conclusions.

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Introduction

• This work aims to study the application of the
  Direct Torque Control strategy to Permanent
  Magnet Synchronous Motor (PMSM).
• Vector Control concept (early 70s). Field
  Oriented Control (FOC) (Blaschke 1972).
• Direct Torque Control (DTC) (Takahashi 1986).
  Direct Self Control (DSC) was developed
  (Depenbrock 1988).
• These thecniques were first developed and
  applied to Induction Motors (IMs), due to their
  success they were then adopted in PMSM drives
  (Zhong 1996).
• The torque ripple present in DTC systems is one
  of the main drawbacks of this technique. A
  possible method to reduce the amplitude of the
  torque ripple is presented for DTC-PMSM drives.

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The PMSM

• Main advantges of the PMSM
• Absence of brushes and slip rings, lower
  maintenace required.
• Lower inertia and better dynamic performance.
• Higher efficiency, there are no rotor losses.
• Higher power/weight ratio.
• Disadvantages
• Higher cost.
• Variation of PM properties.
• Applications
• High acceleration and precise control required.
• Robotics, machine tools.

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DTC

• High performance and simplicity.
• Decoupled and direct control of flux and torque.
• Indirect control of stator currents and voltages.
• Approximately sinusoidal stator fluxes and stator
  currents.
• Quick torque response.
• Inherent motion-sensorless control method (the
  motor speed is not required to achieve the torque
  control).
• Absence of coordinate transformation (required in
  FOC).
• Absence of voltage modulator, as well as other
  controllers such as PID and current controllers
  (used in FOC).
• Variable inverter switching frequency (depends on
  on the hysteresis bands, the operating point and
  the error level of the variables under control).
• Stator flux and torque estimation is required.
  Only the stator resistance is needed for the
  estimator.
• Low sampling period required.
• High torque and flux ripples (accentuated when
  controlling a PMSM).

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DTC
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Duty-ratio Control Algorithm

• Duty-ratio Control A possible solution to reduce
  the torque ripple amplitude inherent to the DTC
  strategy.
• Requires the calculation of the duty cycle (d
  ton / Ts) to minimise the torque ripple for every
  sampling period. How can it be done?
• Analytical methods (Kang 1999).
• Fuzzy-logic (Bird 97).

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Duty-ratio Control Algorithm

• J. Kang and S. Sul "New Direct Torque Control of
  Induction Motor for Minimum Torque Ripple and
  Constant Switching Frequency." IEEE Trans. on
  Ind. Appl., vol 35, no 5, pp. 1076-1082,
  September/October 1999.
• The duty cycle (d) is a function of
• The torque error.
• The torque slope produced by the active vector.
• The torque slope produce by the null vector.

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Duty-ratio Control Algorithm
Surface-Mounted PMSM (LsdLsq)
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Duty-ratio Control Algorithm
Active vector
Null vector

• Requires coordinate transformation.
• Requires rotor speed and angle.
• Fixed average switching frequency Fs1/(3Ts)

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Duty-ratio Control Algorithm
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Results
DTC 100µs
DTC 50µs
DTC 25µs
DTC-DR 100µs
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Conclusions

• The application of the Direct Torque Control
  strategy to Permanent Magnet Synchronous Motor
  (PMSM) has been investigated.
• Due to the low stator inductance torque and flux
  ripples are very high (when compared to the
  Induction Motor case).
• The duty-ratio control scheme has been
  investigated in order to reduce the torque
  ripple. An analytical approach has been employed
  based on the motor model.
• Torque ripple is considerably reduced.
• Average switching frequency is fixed in
  steady-state to one third of the sampling
  frequency.
• Requires coordinate transformation, rotor speed
  and angle.

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Thanks for your attention