A simple method to reduce torque ripple in direct torque-controlled permanent-magnet synchronous motor by using vectors with variable amplitude and angle

In this paper, a modified direct torque control (DTC) for permanent-magnet synchronous machines, which enables important torque- and flux-ripple reduction by using voltage vectors with variable amplitude and angle, is proposed. In the proposed DTC, the amplitudes of torque and flux errors are differentiated and employed to regulate the amplitude and angle of the output voltage vectors online, which are finally synthesized by space-vector modulation (SVM). Two simple formulas are developed to derive the amplitude and angle of the commanding voltage vectors from the errors of torque and flux only. The conventional switching table and hysteresis controllers are eliminated, and a fixed switching frequency is obtained with the help of SVM. Stator flux is estimated from an improved voltage model, which is based on a low-pass filter with compensations of the amplitude and phase. The proposed DTC is comparatively investigated with the existing SVM-DTC from the aspects of theory analysis, computer simulation, and experimental validation. The simulation and experimental results prove that the proposed DTC is very simple and provides excellent steady-state response, quick dynamic performance, and strong robustness against external disturbance and control-parameter variations. © 2006 IEEE

Torque Control

This book is the result of inspirations and contributions from many researchers, a collection of 9 works, which are, in majority, focalised around the Direct Torque Control and may be comprised of three sections: different techniques for the control of asynchronous motors and double feed or double star induction machines, oriented approach of recent developments relating to the control of the Permanent Magnet Synchronous Motors, and special controller design and torque control of switched reluctance machine

Implementation and Analysis of Direct Torque Control for Permanent Magnet Synchronous Motor Using Gallium Nitride based Inverter

Permanent magnet synchronous machines (PMSMs) attract considerable attention in various industrial applications, such as electric and hybrid electric vehicles, due to their high efficiency and high-power density. In this thesis, the mathematical model of PMSM and two popular control strategies, field-oriented control (FOC) and direct torque control (DTC), are analyzed and compared. The results demonstrated that the DTC has better dynamic response in comparison to FOC. Moreover, DTC can eliminate the use of position sensor, which will save the cost of the PMSM drive system. Therefore, this thesis focuses on the design and implementation of high-performance DTC for PMSMs with a Gallium Nitride (GaN) based high switching frequency motor drive. First, the characteristics and operation principles of a PMSM are introduced. Then, the mathematical models of a PMSM under different coordinate systems are investigated. Consequently, a PMSM model is developed based on the dq rotating reference frame and implemented in the MATLAB/Simulink for validation. Two advanced PMSM control strategies, FOC and DTC, are investigated and compared in terms of control performance through comprehensive simulation studies and the results demonstrate that DTC has better dynamic performance. Conventional DTC contributes to higher torque ripple in the PMSM due to the limited switching frequency in a conventional semiconductor-based motor drive, which inevitably deteriorates the drive performance. Therefore, this thesis aims to reduce the torque ripple in the DTC based PMSM drive by using the new generation wide bandgap switching devices. More specifically, DTC is improved by using the optimized space vector pulse width modulation strategy and a higher switching frequency contributed by the GaN based motor drive. Finally, the proposed DTC-SVM based PMSM control strategy is implemented on the digital signal processor (DSP) and evaluated on the laboratory GaN based PMSM drive. Both the simulation and experimental results show that the proposed improvement in the DTC can further improve the PMSM drive performance

Advances in Rotating Electric Machines

It is difficult to imagine a modern society without rotating electric machines. Their use has been increasing not only in the traditional fields of application but also in more contemporary fields, including renewable energy conversion systems, electric aircraft, aerospace, electric vehicles, unmanned propulsion systems, robotics, etc. This has contributed to advances in the materials, design methodologies, modeling tools, and manufacturing processes of current electric machines, which are characterized by high compactness, low weight, high power density, high torque density, and high reliability. On the other hand, the growing use of electric machines and drives in more critical applications has pushed forward the research in the area of condition monitoring and fault tolerance, leading to the development of more reliable diagnostic techniques and more fault-tolerant machines. This book presents and disseminates the most recent advances related to the theory, design, modeling, application, control, and condition monitoring of all types of rotating electric machines

Direct Torque Control for Silicon Carbide Motor Drives

Direct torque control (DTC) is an extensively used control method for motor drives due to its unique advantages, e.g., the fast dynamic response and the robustness against motor parameters variations, uncertainties, and external disturbances. Using higher switching frequency is generally required by DTC to reduce the torque ripples and decrease stator current total harmonic distortion (THD), which however can lower the drive efficiency. Through the use of the emerging silicon carbide (SiC) devices, which have lower switching losses compared to their silicon counterparts, it is feasible to achieve high efficiency and low torque ripple simultaneously for DTC drives. To overcome the above challenges, a SiC T-type neutral point clamped (NPC) inverter is studied in this work to significantly reduce the torque and flux ripples which also effectively reduce the stator current ripples, while retaining the fast-dynamic response as the conventional DTC. The unbalanced DC-link is an intrinsic issue of the T-type inverter, which may also lead to higher torque ripple. To address this issue, a novel DTC algorithm, which only utilizes the real voltage space vectors and the virtual space vectors (VSVs) that do not contribute to the neutral point current, is proposed to achieve inherent dc-link capacitor voltage balancing without using any DC-link voltage controls or additional DC-link capacitor voltages and/or neutral point current sensors. Both dynamic performance and efficiency are critical for the interior permanent-magnet (IPM) motor drives for transportation applications. It is critical to determine the optimal reference stator flux linkage to improve the efficiency further of DTC drives and maintain the stability of the drive system, which usually obtained by tuning offline and storing in a look-up table or calculated online using machine models and parameters. In this work, the relationship between the stator flux linkage and the magnitude of stator current is analyzed mathematically. Then, based on this relationship, a perturb and observe (P&O) method is proposed to determine the optimal flux for the motor which does not need any prior knowledge of the machine parameters and offline tuning. However, due to the fixed amplitude of the injected signal the P&O algorithm suffers from large oscillations at the steady state conditions. To mitigate the drawback of the P&O method, an adaptive high frequency signal injection based extremum seeking control (ESC) algorithm is proposed to determine the optimal reference flux in real-time, leading to a maximum torque per ampere (MTPA) like approach for DTC drives. The stability analysis and key parameters selection for the proposed ESC algorithm are studied. The proposed method can effectively reduce the motor copper loss and at the same time eliminate the time consuming offline tuning effort. Furthermore, since the ESC is a model-free approach, it is robust against motor parameters variations, which is desirable for IPM motors

A simple method to reduce torque ripple and mechanical vibration in direct torque controlled permanent magnet synchronous motor

The Direct Torque Control (DTC) technique of Permanent Magnet Synchronous Motor (PMSM) receives increasing attention due to its simplicity and robust dynamic response compared with other control techniques. The classical switching table based DTC presents large flux, torque ripples and more mechanical vibrations in the motor. Several studies have been reported in the literature on classical DTC. However, only limited studies that actually discuss or evaluate the classical DTC. This paper proposes a simple DTC method / Switching table for PMSM, to reduce flux and torque ripples as well as mechanical vibrations. In this paper two DTC schemes are proposed. The six sector and twelve sector methodology is considered in DTC scheme I and DTC scheme II, respectively. In both DTC schemes a simple modification is made in the classical DTC structure that is by eliminating two level inverter available in the classical DTC is replaced by three level Neutral Point Clamped (NPC) inverter. To further improve the performance of the proposed DTC scheme I, the available 27 voltage vectors are allowed to form different groups of voltage vectors such as Large - Zero (LZ), Medium - Zero (MZ) and Small - Zero (SZ), where as in DTC scheme II, all the voltage vectors are considered to form a switching table. Based on these groups, new switching table is proposed. The proposed DTC schemes are comparatively investigated with the classical DTC and existing literatures from the aspects of theory analysis and computer simulations. It can be observed that the proposed techniques can significantly reduce the flux, torque ripples, mechanical vibrations and improves the quality of current waveform compared with traditional and existing methods

TECHNIQUE OF CONTROL PMSM POWERED BY PV PANEL USING PREDICTIVE CONTROLLER OF DTC-SVM

The present paper is a part of the study of Direct Torque Control based (DTC) on space vector modulation using predictive controller (Predictive SVM) of a permanent magnet synchronous motor (PMSM) powered by a photovoltaic (PV) source. In the conventional direct torque control (DTC) of a permanent magnet synchronous motor (PMSM), hysteresis controllers are used to choose the proper voltage vector resulting in large torque ripples. The direct torque control can accelerate the torque responses but increases the torque ripple at same time. Nowadays, exist some other alternative approaches to reduce the torque ripples based on (Predictive SVM) technique. This method is based on the replacement of hysteresis comparators (used in conventional DTC) by Proportional Integral (PI) regulators and the selection table by space vector modulation (SVM). The simulation results confirm that this proposed method where the control of the switching frequency is well controlled, allows us to reduce the oscillations of the electromagnetic torque and flux by 20 % and 30%, respectively with a good dynamic response compared with conventional DTC

Performance enhancement of direct torque-controlled permanent magnet synchronous motor with a flexible switching table

In this paper, a flexible switching table (FST) for direct torque control (DTC) of permanent magnet synchronous motors (PMSMs) was proposed to enhance the steady-state and dynamic performances of the drive system. First, the influence of each converter output voltage vectors on the torque and stator flux deviation rates was analyzed to assess the voltage selection strategies of the conventional STs and their impact on the DTC system’s performance. Then, a new flexible ST was proposed which uses a simple algorithm to adaptively select the appropriate voltage vector for two of its states according to the system operating condition. The effectiveness and feasibility of the proposed FST were verified through a comparative evaluation with the conventional STs using experimental results obtained from a 0.75 kW PMSM drive system

Direct Torque Control of Permanent Magnet Synchronous Motor

Permanent Magnet Synchronous Motors (PMSM’s) are used in places that require fast torque response and high-performance operation of the machine. The Direct Torque Control (DTC) technique is different from methods which use current controllers in an proper reference frame to control the motor torque and fluxe values. The DTC technique does not any current controllers. DTC controls the Voltage source Inverter states on the basis of difference between the required and obtained torque and flux values. This is done by selecting one out of the six voltage vectors obtained by the Inverter (VSI) to have torque and flux fluctuations in between the limits of 2 hysteresis bands. This thesis obtains the modelling of the Direct Torque Control (DTC) system of PMSM using MATLAB/Simulink®. Speed control of PMSM using Field Oriented Control technique and Direct Torque Space Vector Pulse Width Modulation technique is also analysed and compared with traditional DTC. Simulation results are presented to help analyse the system performance and PI controller parameters influence on the system performance. The analysis is also done with fuzzy logic controller