Model Predictive Torque Control with low Torque Ripple for Interior PM Motor Variable Speed Drives
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This paper proposes a discrete Model Predictive Torque Control (MPTC) methodology, utilizing low torque ripple for Interior Permanent Magnet Motor (IPMM). The proposed controller utilizes a non-linear accurate discrete IPMM model, as well as a convenient cost function, in order to achieve optimal tracking control over wide speed range. More specifically, Maximum Torque per Ampere (MTPA) and Field Weakening (FW) operating principles are imposed via particular terms in the cost function. Typically, the switching principle of MPC in voltage-source inverter causes significant torque ripple. The designed MPTC forces the produced electromagnetic torque to remain within certain tolerance bands, through a specific constraint. The developed IPMM control technique is evaluated and compared with relevant MPTC approach without torque ripple limitation, under both steady state and dynamic operating conditions. The obtained results verify the superiority of MPTC in terms of robustness and dynamic behavior, as well as its effectiveness in reducing the IPMM torque ripple.Keywords:
Torque ripple
Stall torque
Damping torque
Model Predictive Control
Robustness
For the large torque ripple of inductance motor based on direct torque control, especially at a low speed, this paper proposes a new control strategy. On the basis of improving conventional switch table of direct torque control system, a two-hysterics control switch table is established in the strategy in order to decrease torque ripple. The simulation shows that it can get good torque performance.
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Torque motor
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This paper examines the torque response based on direct torque control (DTC) for an interior permanent magnet synchronous motor. DTC with a PI controller for torque control is used in this paper. The relationship between the gains of the PI controller and the torque response is derived based on the transfer function of the torque control loop. In addition, this paper discusses the influence of the nonlinearity of the torque control loop on the torque response. It also proposes a linearization method for the torque control loop based on gain scheduling, and improvement of torque response is achieved. The effectiveness of the proposed method is verified by both simulation and experimental results.
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Damping torque
Torque motor
Torque limiter
Feedback linearization
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This paper examines the torque response based on direct torque control (DTC) for an interior permanent magnet synchronous motor. DTC with a PI controller for torque control is used in this paper. The relationship between the gains of the PI controller and the torque response is derived based on the transfer function of the torque control loop. In addition, this paper discusses the influence of the nonlinearity of the torque control loop on the torque response. It also proposes a linearization method for the torque control loop based on gain scheduling, and improvement of torque response is achieved. The effectiveness of the proposed method is verified by both simulation and experimental results.
Stall torque
Damping torque
Torque limiter
Torque motor
Feedback linearization
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To solve torque ripple in the direct torque control(DTC),based on the equation of torque of induction motor,the effect of different voltage vectors on torque is analyzed,the reason of unreasonable torque ripple is given,and the method to solve the problem is proposed.
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In this paper, a proportional-plus-integral (PI) torque controller with variable proportion for direct torque control (DTC) of permanent magnet synchronous motor (PMSM) drive based on the torque angle control is proposed. By analyzing the torque control of PMSM, the optimum design of proportion in the PI torque controller is presented in order to reduce the torque error in dynamic state resulted from the nonlinear relationship between the torque and torque angle, and ensure exact and quick control of torque in dynamic state. In order to eliminate the steady-state error of torque and guarantee the stability of system, the design of the integral part of PI torque controller is deduced by using the small signal model of system. The experimental results verify the feasibility and effectiveness of the proposed PI torque controller.
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To reduce the low speed torque ripple of induction motor based on direct torque control(DTC),a new control strategy-torque predict is proposed.The experiment shows that it can reduce the torque ripple,improve the waveform of stator flux and current.
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It is widely known that Direct Torque Control (DTC) has fast dynamic torque response. It originates in the fact that torque and flux is directly controlled by instantaneous space voltage vector unlike Field Oriented Control (FOC). For the reason, Direct Torque Control gradually has been used in the field requiring fast response since its introduction in the mid-1980's. In spite of these merits, Direct Torque Control has several problems. These problems are : (1) the variation of the switching frequency by hysteresis band and speed; (2) the increase of the torque ripple in the low speed region; (3) the short control period (25 /spl mu/s) for the good performances etc. To solve the problems of Direct Torque Control, several studies were carried out. This paper improves one of the drawbacks of Direct Torque Control, torque ripple, with the constant switching frequency. In some papers it was tried to improve the drawback, but some papers are very complicated and didn't show large improvement. Their methods even resulted in losing the merits of Direct Torque Control. In this paper Direct Torque Control method is performed with constant switching frequency. So this scheme is easy to be realized with digital signal processor and also minimizes torque ripple.
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Due to the large torque ripple of inductance motor based on direct torque control, especially at a low speed, this paper proposes a new control strategy. On the basis of conventional direct torque control, a torque ripple minimum controller is introduced in the strategy in order to decrease torque ripple. The simulation shows that it can get good torque performance.
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Damping torque
Torque motor
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This paper presents an improved direct torque and flux control algorithm for induction machines based on the Direct Mean Torque Control. The new algorithm combines the high dynamic performance of a direct torque control method with a precise flux control. Summary Servo drive systems for high dynamic applications need a fast torque and flux control. Several methods to control torque and flux of an induction machine are well known: the field oriented control and the some direct torque control algorithms like the Direct Torque Control (DTC), the Direct Self Control (DSR). Here we use the Direct Mean Torque Control (DMTC). DMTC is a model-based, predictive method, which results in a constant switching frequency and is applicable for all kinds of induction machines, especially for servo drives with a very low leakage inductance. Under some particular conditions, the original DMTC algorithm [1], [2] did not provide the maximum dynamic performance. The maximum dynamic performance is necessary for active damping of mechanical oscillations with high resonance frequencies (up to 1kHz). The original algorithm uses one voltage vector and one zero voltage vector for torque and flux control per sampling cycle. At low speed and torque, the duration of active voltage vectors for torque control is too short to avoid a decay of the flux. Then flux supporting voltage vectors have to be chosen which may influence the torque in an adverse way. In the subsequent cycles the adverse effects of the flux supporting voltage vector concerning torque and speed has to be corrected. At the experimental set-up this leads to the excitation of unwanted torque and speed oscillations. But with the improvements presented in this paper this problems can be solved and it is possible to actively damp mechanical oscillations even with high resonance frequency [3]. 1. Direct Mean Torque Control Hysteresis controllers like the DTC can result in extremely short sampling periods if the control of an induction machine with low leakage inductance is realised by a micro processor [4]. This is especially true at low or high speed. At these operating points, the difference between an active voltage vector applied by the inverter and the EMF is large, consequently the rate of change of the stator currents is high.. To obtain a suitable torque ripple, a sampling period of less than 5 μs would be necessary with DTC at our servo machine. This would end in an unacceptable high computational burden for the controller. A significant improvement is achieved by the original DMTC, which is a model-based, predictive method, resulting in sampling periods of e.g. 125μs. DMTC calculates two switching events per sampling period. The switching events are calculated such that the torque time area under and over the torque set point value has the same size in steady state operation [1], [2]. See fig. 1:
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Direct torque control method is one of the best control strategies which allow a torque control in steady state and transient operation of induction motor. The main aim of direct torque control strategies is to effectively control the torque and flux of induction motor. Direct torque control method made the motor more accurate and fast torque control, high dynamic speed response and simple to control. This paper present the principle of the direct torque control for voltage source inverter fed induction motor drive, and switching table, amplitude selection of the hysterics band of torque and flux. And also this method based on space vector modulation and it's considered as an alternative to field oriented control technique. Direct torque control methods are the first technology to control the 'real' motor control variable of torque and flux. And it has also more advantage such as it not required a feedback device and also not need external excitation. The performance of direct torque control method has been demonstrated by simulation using a simulation package in matlab.
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