Direct torque control (DTC) is known to be a promising candidate for interior permanent magnet synchronous motor (IPMSM) drives. It provides fast dynamic response and good immunity to parameter variations. However, except for its merits, DTC also suffers from two major problems of variable switching frequency and large torque ripples. Research proposals have been published to solve these problems. Nonetheless, most of the proposals present very complex control algorithms. This paper proposes a constant switching frequency based DTC algorithm for IPMSM drives. It is consisted of only one PI regulator and one triangular-wave carrier. The proposed algorithm reduces the torque ripples to a noticeable extent. In-depth analysis and design guidelines of the proposed controller are given. Simulation and experiment results are provided to verify the effectiveness of the proposed method.
- Interior permanent magnet synchronous motor
- Direct torque control
- Constant switching frequency
- Torques ripple
- Carrier Controller stability.
Fig. 1 Block diagram of the proposed constant switching frequency control algorithm.
EXPECTED SIMULATION RESULTS
Fig. 2 Response of torque reversal from -4Nm to 4Nm. (a) Classical DTC : reference torque (red), real torque (blue); (b) Proposed constant switching frequency DTC : reference torque (red), real torque (blue).
Fig. 3 Response of speed reversal from -375r/min to 375r/min. (a) Classical DTC : subplot 1: rotor electrical speed, subplot 2: reference torque (red), real torque (blue); (b) Proposed constant switching frequency DTC : subplot 1: rotor electrical speed, subplot 2: reference torque (red), real torque (blue).
Fig. 4 FFT analysis of line current at 375 r/min (a) Classical DTC : subplot 1: line current, subplot 2: Frequency Spectrum of line current; (b) Proposed constant switching frequency DTC : subplot 1 : line current, subplot 2: Frequency Spectrum of line current.
This paper presents a simple but effective constant switching frequency based direct torque control method. It significantly reduces the torque ripples and maintains nearly all the merits of the classical DTC. The proposed torque regulator is consisted of one PI controller and one fixed frequency triangular-wave carrier. This benefits the real-time implementation by reducing the computational burden. In-depth modeling and small-signal analysis of the proposed regulator are provided. The design of stable torque regulator by using conventional bode plots is discussed. Both simulation and experimental results are given to verify the performance of the proposed control method.
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