Direct Flux-Vector Oriented Control for Interior Permanent Magnet Synchronous Motor

Because traditional direct torque control (DTC) has unfixed switching frequency and ripple of torque and flux, deadbeat direct torque and flux control (DB-DTFC) of interior permanent magnet synchronous motor (IPMSM) is studied. At first, DB-DTFC based on IPMSM mathematical model is deduced. The calculated proper voltage vector can make reference torque and stator flux during one sampling period. But, parameters of IPMSM such as inductance of stator windings vary with its operation and affect on torque and flux performance. Secondly, parameter identification based on recursive least squares with forgetting factor is analyzed, which can identify IPMSM parameters online and eliminate their affects on performance of torque and stator flux. Finally, simulations are carried out and validate the proposed DB-DTFC which has both excellent dynamic and steady performance.

Direct torque control (DTC) has become a widely acceptable alternative to field-oriented control in permanent magnet synchronous motor (PMSM) drives. Deadbeat direct torque and flux control (DB-DTFC) is a significant improvement over the classical DTC. However, there are some aspects that can be improved, such as insufficiently small electromagnetic torque ripple, unsmooth dynamic response, heavy computation burden, and relatively weak robustness to motor parameters variation. To improve the operation performance, an advanced DB-DTFC strategy is proposed in this article. First, the algorithm model based on stator flux oriented coordinate system is deduced. On this basis, the basic principle of proposed DB-DTFC is presented. Second, a novel graphical analysis method is proposed to help illustrate the proposed strategy. Third, a general solution method is proposed to solve the reference stator voltage, which is a key variable for the DB-DTFC. Finally, the stability of system is analyzed. Theoretical and experimental comparisons between the proposed DB-DTFC and the conventional DB-DTFC are done. The results show that the performance in the aspects of electromagnetic torque and stator current ripples reduction, dynamic response, computation burden, and robustness to motor parameters variation are all improved in the proposed DB-DTFC.

This study is focused on very low speed performance comparison between two sensorless control systems based on the novel `active flux` concept, that is, the current/voltage vector control versus direct torque and flux control (DTFC) for interior permanent magnet synchronous motor (IPMSM) drives with space vector modulation (SVM), without signal injection. The active flux, defined as the flux that multiplies iq current in the dq -model torque expression of all ac machines, is easily obtained from the stator-flux vector and has the rotor position orientation. Therefore notable simplification in the rotor position and speed estimation is obtained. For IPMSM, a stator-flux observer is employed based on combined current and voltage models, with speed-dependent smooth transition between them using a PI compensator of flux error. Comparative experimental results using both sensorless control systems are presented to verify the principles and to demonstrate the effectiveness of the active flux observer at very low speeds from 20 to 2 rpm (1 0.1 Hz).

This paper presents the latest advancements in direct torque and flux control (DTFC) schemes of interior permanent magnet synchronous motor (IPMSM) drives. A novel eighteen-sector based DTFC scheme incorporating a model based loss minimization algorithm is proposed to mitigate the torque ripples and achieve high efficiency as compared to the conventional six-sector based DTFC scheme. Finally, in order to have direct and better control of reducing the torque/flux ripples further, a nonlinear control incorporating motor electromagnetic developed torque and stator air-gap flux linkage as virtual control variables is developed. In conventional nonlinear controller d-q axis currents (i d , i q ) are considered as virtual control variables that indirectly controls the torque/flux which may not be suitable for high performance drives. Thus, the proposed work overcomes the major drawback (i.e., torque ripple) of the conventional DTFC based IPMSM drive. Feasibility of the developed DTFC schemes is verified through both simulation and experimental results.

This paper proposes a new framework for the deadbeat predictive direct torque control for interior permanent magnet synchronous machine (IPMSM) utilizing active flux. Unlike the existing deadbeat predictive direct torque and stator flux control, it is relatively simple and does not require to neglect any physical quantities such as stator resistance votlage drop and cross-coupling. In addition, a sliding-mode-disturbance-observer (SMDO) is combined to track the system disturbances caused by parameter mismatch in real time. The effectiveness of the proposed composite control is verified by simulation and experiment results.

In this paper, a dead-beat direct torque and flux control with a novel sliding-mode stator flux observer is proposed for electric vehicle (EV) drives. Compared to the direct torque control, the proposed scheme exhibits both static and dynamic performances. Since the system parameters have impact on the control effect of the permanent magnet synchronous motor (PMSM) deadbeat-direct torque control (DB-DTC) system, an observer combining the flux current model and voltage model is proposed. The simulation results verify that the proposed scheme can improve both observation performance and robustness.

This paper presents an improved direct torque and flux control of a sensorless control system with Interior Permanent Magnet Synchronous Motor (IPMSM). The estimation of torque and flux is enhanced by the real-time update of machine parameters including stator resistances, d- and q- axis inductance, permanent magnet flux linkage. The estimation of rotor speed and position is based on the measurement of current slopes at one zero- and two active-voltage vectors during every PWM cycle. The d- and q- axis inductances are estimated at PWM frequency based on those current derivatives and the DC bus voltage. The stator resistance and permanent magnet flux linkage which vary slowly due to temperature and aging factors are estimated based on the use of recursive least square technique. The numerical simulation and experimental study of the proposed methods show the effectiveness of the proposed parameter identification method and the improvement of estimated torque and flux of the sensorless control system.

The paper describes Model Reference Adaptive System (MRAS) observers for the speed estimation of an induction motor with direct torque and flux control. The first estimator is a reference frame MRAS (RF-MRAS) and the second estimator is a current based MRAS (CB-MRAS). At first, direct torque controlled induction motor drive with two estimators are implemented on Matlab-Simulink environment. Then, comparison of two observers is done by evaluation of the rotor speed difference. The simulation results confirm that both MRAS estimators are simple to simulate and experiment. By comparison of both observers, the CB-MRAS observer gives higher accuracy of the rotor speed estimation.

A model based predictive torque and flux control (PTFC) is proposed in this paper for doubly fed induction generator (DFIG) applied in wind energy applications. Different from the conventional switching-table-based direct torque control (DTC), which selects the output vector from a switching table, the developed PTFC selects the most suitable vector minimizing the errors of rotor flux and torque based on predictions of their evolutions versus time. Compared to DTC with the same sampling frequency, there are significant reductions in both torque and flux ripples for PTFC with lower switching frequency, while their dynamic performances are similar. Furthermore, by incorporating the frequency reduction in PTFC, the average switching frequency can be reduced up to 38.76% without affecting its performance. The results of PTFC operating at a very low switching frequency of below 550 Hz are presented, validating the capability of PTFC to satisfy the low switching frequency requirement of high power wind energy applications. Simulation results are presented to validate the effectiveness of the proposed PTFC.

This paper reports results of investigation of the Direct Torque Control (DTC) technique to an fractional-slot Interior Permanent Magnet Synchronous Machine (IPMSM) with concentrated windings (CW). Application of concentrated winding to IPM machine is gaining attention from research community because of its advantages such as high-power density, high efficiency, short end-turns, wider flux-weakening capability, fault tolerance, robust rotor, and presence of additional reluctance torque component, and, the major disadvantage is of non-sinusoidal magnetomotive force (MMF). However, using appropriate combination of slot and pole, sinusoidal EMF and low cogging torque can be achieved despite presence of MMF harmonics. A 14-pole, 18-slot, double layer concentrated winding IPM had been designed and constructed at the University of the New South Wales. The DTC was applied to the prototype machine. In DTC scheme, the requirement of the continuous rotor position sensor and coordinate transformation between stationary and rotating (dq) reference frame is eliminated since all of the calculation is done in stator reference frame. The speed is estimated from the stator flux linkage vectors and the torque angle. The performances of the DTC control scheme is evaluated in terms of torque and current ripple, transient response to step variations of the speed command and load disturbances at maximum torque per ampere and field weakening regions. The experiment results presented clearly demonstrate effectiveness of DTC in IPMSM with CW.

Direct Torque and Flux Control of PV Connected Permanent Magnet Synchronous Machine

This paper investigates a sensorless direct torque and flux control scheme for interior permanent magnet synchronous motor drives at low speeds, including standstill. Closed-loop control of both torque and stator flux linkage are achieved by using two proportional-integral controllers. The reference voltage vectors are generated by a space vector modulation unit. A high-frequency signal injection technique is adopted at low speeds to obtain the rotor position information. A hybrid current-voltage model flux observer with a smooth handover algorithm estimates the stator flux linkage over the whole speed range. Experimental results confirm the effectiveness of the proposed method.

This paper presents switched-inductor quasi-z-source inverter (qZSI)-based cascaded multilevel inverter for induction motor application using direct torque and flux control (DTFC) technique. The proposed control scheme accomplishes soft-start capability and improves the reliability of the system. Converted photovoltaic output is fed to SL-qZSI-based cascaded multilevel inverter and has been implemented with increased voltage level, reduced switch count and reduced cost of system than conventional. Additionally, the cascaded multilevel inverter ensures improved voltage gain, and regulates the DC-link voltage. Moreover, increase in the settling time of motor speed and reduction of the stator inrush current have been achieved by using direct torque and flux control. Design of cascaded multilevel inverter with less number of switches fed induction motor has been implemented using MATLAB/Simulink.

Novel deadbeat direct torque and flux control for interior permanent magnet synchronous motor

This paper presents a sliding mode controller for an interior permanent magnet (IPM) synchronous motor, in which direct torque control (DTC) concept, variable structure control and space vector modulation (SVM) are integrated to achieve high performance. In comparison with conventional DTC, the inverter switching frequency is constant and controllable by using SVM, the torque and flux ripple are significantly reduced. The fast response and robustness merits of DTC are preserved. Position and angular speed of the rotor are obtained through an extended Kalman filter (EKF).