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EPE-PEMC th 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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EPE-PEMC Outline Introduction. The PMSM. DTC. Duty-ratio Control Algorithm. Simulation Results. Conclusions.

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EPE-PEMC 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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EPE-PEMC 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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EPE-PEMC 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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EPE-PEMC DTC

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EPE-PEMC 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 (δ = ton / Ts) to minimise the torque ripple for every sampling period. How can it be done? Analytical methods (Kang 1999). Fuzzy-logic (Bird 97). active null Ts ton

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EPE-PEMC 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 , September/October The duty cycle (δ) is a function of: The torque error. The torque slope produced by the active vector. The torque slope produce by the null vector. ? active null Ts ton

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EPE-PEMC Duty-ratio Control Algorithm Surface-Mounted PMSM (Lsd=Lsq)

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EPE-PEMC Duty-ratio Control Algorithm Active vector Null vector Requires coordinate transformation. Requires rotor speed and angle. Fixed average switching frequency Fs=1/(3Ts) active null Ts ton

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EPE-PEMC Duty-ratio Control Algorithm

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EPE-PEMC Results DTC 100μs DTC 50μs DTC 25μs DTC-DR 100μs

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EPE-PEMC 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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EPE-PEMC Thanks for your attention

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