Study on speed sensorless system of permanent magnet synchronous motor based on improved direct torque control

The traditional direct torque control system of permanent magnet synchronous motor has many problems, such as large torque ripple and variable switching frequency. In order to improve the dynamic and static performance of the control system, a new torque control idea and speed sensorless control scheme are proposed in this paper. First, by deriving the equation of torque change rate, an improved torque controller is designed to replace the torque hysteresis controller of the traditional direct torque control. The improved direct torque control strategy can significantly reduce the torque ripple and keep the switching frequency constant. Then, based on the improved direct torque control and considering the sensitivity of the stator resistance to temperature change, a speed estimator based on the model reference adaptive method is designed. This method realizes the stator resistance on-line identification and further improves the control precision of the system. The performance of the traditional direct torque control and the improved direct torque control are compared by simulation and experiment under different operating conditions. The simulation and experimental results are presented to support the validity and effectiveness of the proposed method.

An investigation of flux characteristic in direct torque control using sector rotation strategy

Stator flux fails to regulate at low operating speed condition is a common drawback for the conventional DTC. It is due to the inevitable of voltage drop across the stator resistance that interrupts the controlling of stator flux in DTC. Hence, a fixed sector rotation strategy is one of the solutions to rectify the raised issue. The strategy is based on the decreasing stator flux droop, which is an easy technique to change the sector of flux locus at a specific angle. However, this strategy only focuses at low operating speed. Thus, the stator flux droop effect at the various speed needs to be analysed. In this paper, an investigation is conducted by using simulation (MATLAB/Simulink) and experimental setup (dSPACE board) where a good agreement has been achieved between the predicted and measured results. The analysis taking into account between the conventional method (without strategy) and the proposed method (with strategy). In conclusion, the influence of stator flux droop is inversely proportional to the operating speed.

Sensorless nonlinear sliding mode control of the induction machine at very low speed using FM-MRAS observer

<span lang="EN-US">The induction motor is complex because its dynamic is nonlinear, multivariable and highly coupled. In addition, the induction motor (IM) controller design can be degraded due to wide ranges operating speed specially in low and near-zero speeds and also to variation of interval parameters such as the stator resistance change because of stator heating during operation. Our contribution is the use of a nonlinear sliding mode control using a fuzzy mutual reference adaptive system observer based on two fuzzy adaptation mechanisms to estimate both rotor speed and stator resistance. The proposed work was verified and compared by simulation and tested in various ranges of speed with motor and regenerating regions of operation. The results show that the proposed approach has proved good effectiveness in tracking and observation.</span>

Comparative Analysis of Two Speed-Estimation Methods for Dual Three-Phase Induction Motor with Stator Resistance Online Identification

The dual three-phase induction motor (DTPIM) has gained wide attention in special applications, such as vessel propulsion, because of its advantages of less torque ripple and higher reliability. However, speed sensors are greatly affected and easily become faulty when used in harsh environments for a long time. In this paper, two model reference adaptive system (MRAS) speed-estimation methods are proposed, based on the double (α, β) coordinate system (DCS) and vector space decomposition method (VSD) of the two groups of the three-phase armature vectors, respectively. Both methods can be used for the speed sensorless control system of the DTPIM to improve reliability. The changing of the stator resistance value, caused by temperature variation, affects the accuracy of the speed-estimation. Two online resistance-identification algorithms, combining the DCS method and the VSD method, were proposed to reduce the effect of changes in stator resistance. Simulation results show that the dynamic speed-estimation error of the VSD method decreased greatly compared with the DCS method, which verifies the effectiveness of the theoretical analysis.

Off-line Parameter Identification of Permanent Magnet Synchronous Motor

This paper first explains the necessity of off-line parameter identification of permanent magnet synchronous motors, and then introduces the identification methods and principles of the stator resistance, stator d/q axis inductance and back-EMF coefficient of permanent magnet synchronous motors. An identification method of stator d/q axis inductance injected with high frequency voltage is proposed. Finally, based on the MBD development model, the proposed identification method is modeled by Matlab/Simulink and the code is generated for experiments. The results verified the accuracy and feasibility of the proposed method well.

Stator flux in direct torque control using a speed and torque variation-based sector rotation approach

A typical problem of traditional DTCs is that the stator flux fails to regulate at low running speeds. The regulation of stator flux in DTC is disrupted because of the unavoidable voltage drop across the stator resistance. As a result, one of the solutions to the problem is to use a fixed sector rotation technique. The concept is based on decreasing stator flux droop, a simple technique for changing the flux locus sector at a certain angle. This method, however, is only effective at low working speeds at one value of torque. As a result, the stator flux droop effect at various speeds as well as torque must be studied. The study is carried out in this paper using simulation (MATLAB/Simulink) and a practical setup (dSPACE board) where both have performed similar outcomes. The comparison is done between the conventional method (without a strategy) and the proposed method (with strategy). In summary, the effect of stator flux droop has been found to have an inverse linear relationship to the speed and torque variation.

DRNN Robust DTC for Induction Motor Drive Systems Using FSTPI

In this paper, a self-tuning PI speed controller based on diagonal recurrent neural network is (DRNN) investigated and simulated to increase the robustness of the direct torque control (DTC) scheme for three-phase low-power IM drive system using a Four Switch Three-Phase Inverter (FSTPI). The drive is subjected to different system inputs and disturbances, step changes in speed under different load conditions, abrupt loading at high speed and speed reversal. Furthermore, the robustness of the controller is evaluated by varying motor parameter, stator resistance and moment of inertia. A comparison of classical and self-tuning PI speed controllers was presented to determine the effectiveness of the proposed controller. It is concluded based on simulation results using Matlab/Simulink. that the self-tuning PI speed controller provides the best performance by reacting rapidly and adaptively.