Stator Flux Angle Research Articles

Synchronous DTC for torque sub-harmonic reduction in low switching frequency induction motor drives

A direct torque control (DTC) algorithm with synchronous modulation for high-power induction motors is presented in this paper. While maintaining the dynamic response and robustness of a PI-based DTC operating in the stationary reference frame, the proposed scheme is able to keep an integer PWM modulation ratio, adjusting the stator flux angle and the switching period at each control step so that the synchronicity condition is always satisfied. In this way, it is possible to achieve an improvement of the very low-frequency harmonic spectrum of the torque, in particular by reducing torque sub-harmonics. These represent one of the main problems associated with low-frequency modulation typical of high-power drives and their reduction allows to avoid drawbacks such as resonance and mechanical stresses. The performance of the proposed algorithm is evaluated with experimental tests on a small-scale test bench.

Direct Torque Control (DTC) and three phase induction motor simulation in MATLAB/Simulink

Direct Torque Control (DTC) is considered one of the most effective methods for the decoupled control of electromagnetic torque and speed in an induction motor. In DTC, torque is directly regulated by the torque angle, defined as the difference between the stator flux angle and the rotor flux angle. The advantages of employing DTC include the simplicity of implementation, a reduced number of controllers, excellent torque dynamics, and decreased torque oscillation. Implementing DTC with microcontrollers is easier than with Field-Oriented Control (FOC). This paper discusses the operational principles of DTC and highlights its advantages over the FOC method. The goal is to independently control stator flux linkages, rotor flux linkages, electromagnetic torque, and speed by providing the appropriate switching pulses to the Voltage Source Inverter (VSI). To validate the effectiveness of this control method, we modeled DTC and a 6-kW induction motor using MATLAB/Simulink. The results confirm the efficacy of DTC for decoupled control of torque and speed in the induction motor, demonstrating lower switching losses and excellent torque dynamics. The induction motor was tested under both no-load and a 10 Nm load conditions.

Comparative Analysis of Conventional (CDTC) and Torque Controller Output Manipulated Stator Flux Angle Based Direct Torque Control (TCSF-DTC) of Permanent Magnet Synchronous Motor (PMSM)

Objective: It is recommended to use DTC when a quick response time is required. However, the ripple in torque, as well as flux, is the biggest drawback of DTC. This study presents a comparative analysis of two direct torque control methods CDTC and TCSF-DTC for PMSM’s that operate at a constant speed. Method: Matlab 2021b is used to model both CDTC and TCSF-DTC including all switching signals generation. During the simulation, the switching state is chosen to achieve a fast torque and flux response. Finding: A comparison of the two methods was made based on the results of the simulation. In comparison to CDTC, TCSF-DTC uses double-tracking control to manipulate flux values, which minimizes flux ripples. Although the torque performance is similar in both cases, TCSF-DTC has better flux ripple minimization. In both cases, the torque ripple is 2.857%, whereas the flux ripple is 1.879% and 0.1% for CDTC and TCSF-DTC respectively Furthermore, the simulation result for the supply voltage of the motor illustrates improvements in the harmonic distortion and fundamental component magnitudes. Novelty: Flux and torque are controlled independently in DTC, but a PI controller is added for TCSF-DTC. This study compares the performance of CDTC and TCSF-DTC for flux and torque ripple at a constant speed to recommend the control scheme that is suitable for fine torque and flux ripple control. It has been raised in several works that DTC ripples can be reduced, and researchers have recommended several DTC algorithms, including model-predictive DTC, space vector pulse width modulated DTC, and duty ratio optimization. As a result of adding this feature, computational complexity increases. In particular, duty ratio optimization increases computation complexity for slope estimation. The main advantage of this scheme is that it does not increase the complexity of signal processing but it is effective in minimizing flux ripple. Keywords: Direct torque; flux angle; flux ripple; permanent magnet synchronous motor; torque ripple

Extending DC Bus Utilization for Induction Motors with Stator Flux Oriented Direct Torque Control

This paper presents a method to extend the DC bus utilization on an induction motor (IM) by using a combination of Space-Vector Modulated Direct Torque Control (DTC–SVM) and conventional DTC. The scheme proposed in this paper exploits the advantages of both control methods. During the linear region, it allows for a low torque ripple and low current harmonic distortion (THD). During the overmodulation region, it allows for the fastest torque response up to the six-step operation region. In both regions, there is complete independence of the motor parameters. The paper describes a way to provide a smooth transition between the two control schemes. Non-linearities affect the stator flux angle estimation, which leads to the inability to decouple torque and flux. To overcome this problem, a novel PI-based control scheme as well as a simplification on the decoupling terms’ calculation are proposed. Simulation and experimental results are presented to verify the feasibility of the proposed method.

An Optimal Direct Torque Control Strategy for Surface-Mounted Permanent Magnet Synchronous Motor Drives

This article investigates an observer-based optimal direct torque control (DTC) strategy for improving the transient and steady-state performance of surface-mounted permanent magnet synchronous motor (SPMSM) drives. Unlike conventional DTC techniques, the proposed method simultaneously controls speed, torque, and flux variables by employing the optimal control theory in the stationary reference frame. This helps achieving a simple structure along with good low-speed operation as the stator flux angle need not be estimated. Further, the feedforward control terms are designed to compensate for system uncertainties. Additionally, an in-depth stability analysis is presented through the Lyapunov theory. Comparative results via a real-time prototype SPMSM test-bed with TI-TMS320F28335 DSP indicate improved performance of the proposed optimal DTC compared to conventional PI DTC, nonlinear optimal DTC, and adaptive DTC, including less computational burden, less torque and flux ripples, more robustness to parameter uncertainty, and improved transient response under very low speed/load step-changes and speed reversal.

A Simplified Stator Frequency and Power Control Method of DFIG-DC System Without Stator Voltage and Current Sensors

The primary objective of the grid connected DFIG-DC system is to achieve the accurate control of stator frequency and active power. In this letter, a simplified power control method is proposed by just controlling the magnitude of the rotor current vector, which can avoid the stator voltage and current sensors. The stator active power is calculated by the product of dc voltage and dc current. The stator frequency is simply controlled by the rotating speed of the rotor current vector, which is achieved through a given rotating frame. Furthermore, the parameter dependence and dc sampling offset problems can be eliminated because the voltage model or current model, which are usually used for acquiring stator frequency and stator flux angle, can be avoided. Therefore, the robustness and stability of the stator frequency and power control can be improved. Finally, experiments based on a 1 kW DFIG-DC setup are carried out to verify the proposed method.

Predictive Stator Flux and Load Angle Control of Synchronous Reluctance Motor Drives Operating in a Wide Speed Range

This paper presents a new simplified finite-control-set model predictive control strategy for synchronous reluctance motors operating in the entire speed range. It is a predictive control scheme that regulates the stator flux and the load angle of the synchronous reluctance motor, incorporating the ability to operate the drive in the field-weakening region and respecting the motor voltage and current limits as well as the load angle limitation needed to operate this type of motor in the maximum torque per voltage region. The proposed control strategy possesses some attractive features, such as no need for controller calibration, no weighting factors in the cost function, good robustness against parameter mismatch, and smaller computational cost compared to more traditional finite-control-set model predictive control algorithms. Simulation and experimental results obtained using a high-efficiency synchronous reluctance motor demonstrate the effectiveness of the proposed control scheme.

Sensorless Direct Torque Control of Induction Motor Using AI Based Duty Ratio Controllers

This paper presents some improvements in direct torque control of an induction motor using fuzzy logic switching controller along with fuzzy logic and neural network based duty ratio controller. The conventional direct torque control of induction motor suffers from major drawbacks like high torque and flux ripples, current and torque distortion when sector changes and poor transient response. High torque and flux ripples are reduced to some extent by replacing hysteresis controller and switching table with fuzzy logic switching controller (FDTC). However, in FDTC the selected switching vector is applied for the complete switching time period which results in ripples under steady state. The FDTC steady state performance is improved by using duty ratio controller. Using duty ratio controller, the selected switching vector is applied to voltage source inverter only for the time determined by the duty ratio (δ) and for the remaining time, a zero switching vector is applied. As the switching vector is applied for only the time period till torque reaches its reference value, it results in the reduction of torque and flux ripples of induction motor. The selection of duty ratio is a nonlinear function of flux error, flux error and stator flux angle which is effectively implemented in this paper using the following artificial intelligence techniques: fuzzy logic and neural networks. The effectiveness of the proposed methods are evaluated by the simulation with Matlab/Simulink.

Direct Torque Control for VSI–PMSMs Using Four-Dimensional Switching-Table

In this paper, a direct torque control using a four-dimensional switching-table (4D-ST) is proposed for the voltage source inverter–permanent magnet synchronous motor drive system. The proposed strategy takes a number of virtual vectors, of which magnitude and angle can be configured freely, as candidate vectors. By taking advantage of the variety of the virtual vector, the proposed strategy can obtain superior steady-state and dynamic performance. To choose the optimal vector from all of virtual vectors, first quantify the change rule of the torque and stator flux generated by each different virtual vector, and then take the magnitude and angle of the virtual vector, stator flux angle, and the quantificational factor as four dimensions to establish 4D-ST; by analyzing the distributed laws of quantificational factors in 4D-ST, we can compress 4D-ST and propose a quarter selector to choose the optimal vector accurately and rapidly. By taking the step function instead of the hysteresis comparator as the torque and flux controller, the direct torque control using 4D-ST can be realized. Finally, numerical simulations and experiments with prototype are carried out to validate the feasibility and effectiveness of the proposed strategy.

Nonlinear Optimal DTC Design and Stability Analysis for Interior Permanent Magnet Synchronous Motor Drives

This paper presents a nonlinear optimal direct torque control (DTC) scheme of interior permanent magnet synchronous motors (IPMSMs) based on an offline approximation approach for electric vehicle (EV) applications. First, the DTC problem is reformulated in the stationary reference frame in order to avoid estimating the stator flux angle, which the previous DTC schemes in the rotating stator reference frame require. Thus, the proposed DTC method eliminates the Park's transformation, and consequently, it reduces the computational efforts. Particularly, since the estimated stator flux angle is not accurate in low speed range, the proposed method that does not need this information can significantly improve the control performance. Moreover, a nonlinear optimal DTC algorithm is proposed to deal with the nonlinearity of the IPMSM drive system. In this paper, a simple offline θ- D approximation technique is utilized to appropriately determine the controller gains. Via an IPMSM test bed with a TI TMS320F28335 DSP, the experimental results demonstrate the feasibility of the proposed DTC method by accomplishing better control performances (e.g., more stable in low speed region, much smaller speed and torque ripples, and faster dynamic responses) compared to the conventional proportional-integral DTC scheme under various scenarios with the existence of parameter uncertainties.

Hardware Implementation of Direct Load Angle Controlled Induction Motor Drive

In this article, a direct load angle (DLA) control method for induction motor drive is proposed to reduce the torque and flux ripple. It is based on control of incremental change in load angle. The torque control is achieved without losing the benefits of conventional direct torque control (DTC) by reference stator flux angle, which is the sum of load angle and rotor flux angle. In this proposed DTC scheme, coordinate transformation is not required in torque control unit and reference voltage sector number and angle are not required in PWM unit, which reduces the control complexity. Proposed DTC control method is applied to two level voltage source inverter fed induction motor drive and hardware results are presented. From the hardware results, it is found that the proposed DTC control scheme impressively reduces the torque and flux ripples when compared with conventional space vector modulation (SVM) DTC.

High Performance of Space Vector Modulation Direct Torque Control SVM-DTC Based on Amplitude Voltage and Stator Flux Angle

Various aspects related to controlling induction motor are investigated. Direct torque control is an original high performance control strategy in the field of AC drive. In this proposed method, the control system is based on Space Vector Modulation (SVM), amplitude of voltage in direct- quadrature reference frame (d-q reference) and angle of stator flux. Amplitude of stator voltage is controlled by PI torque and PI flux controller. The stator flux angle is adjusted by rotor angular frequency and slip angular frequency. Then, the reference torque and the estimated torque is applied to the input of PI torque controller and the control quadrature axis voltage is determined. The control d-axis voltage is determined from the flux calculator. These q and d axis voltage are converted into amplitude voltage. By applying polar to Cartesian on amplitude voltage and stator flux angle, direct voltage and quadratures voltage are generated. The reference stator voltages in d-q are calculated based on forcing the stator voltage error to zero at next sampling period. By applying inverse park transformation on d-q voltages, the stator voltages in α and β frame are generated and apply to SVM. From the output of SVM, the motor control signal is generated and the speed of the induction motor regulated toward the rated speed. The simulation Results have demonstrated exceptional performance in steady and transient states and shows that decrease of torque and flux ripples is achieved in a complete speed range.

Research on Fuzzy Direct Torque Control System Based on Improved Grey Model Prediction

In order to increase the accuracy and real-time of grey prediction fuzzy direct torque control system, an improved grey prediction fuzzy direct torque control method was advanced. The equal-dimensional new information model was used to construct the new grey prediction model. The position angle of motor stator flux was divided into sectors, by which the simplified fuzzy algorithm was obtained. The simulation results show that the improved method can greatly overcome the shortcomings caused by the original method, such as the overlarge dimensions of original time sequence and the decrease of effective information amount due to the lasting of time. The calculation quantity in prediction process is reduced. The precision of prediction and the real-time of fuzzy control system are increased. The instability of stator flux is lowered and the speed respond of motor is meliorated.

Modelling and Simulation of Direct Torque Controlled Induction Motor Drive using Slip Speed Control

In this paper an effective control strategy to reduce the torque and flux ripple in direct torque control (DTC) of induction motor drive based on a slip speed control of stator flux is presented. This control strategy is applied to three-level inverter configuration using cascaded two two-level inverters for improving the performance of the system. Torque control is achieved by reference stator flux angle which is generated from the sum of incremental change in stator flux angle and actual stator flux angle. Modelling and simulation of proposed DTC is presented and results of the simulation are compared with basic DTC. From the simulation results it is observed that the torque and flux ripple are less with proposed DTC and also an improvement in the steady-state performance of the drive system at high and low speed operation.

Modeling and Simulation of Direct Torque Control Induction Motor Drives via Constant Volt/Hertz Technique

Direct torque control based constant Volt/Hertz technique was the effortless speed control method for the three phase induction motor drives. This method used the stator flux and torque error to generate the stator voltage and frequency reference for controlling the induction motor. The complications of the stator voltage reference calculations were reduced by neglect the stator flux angle and the optimum switching table which were used in the classical direct torque control method. To verify the concept of this control technique, this paper presented its modeling and simulation. The mathematical model which consist of three parts, the three phase induction motor model, the space vector modulation inverter model and the magnitude of the stator flux and torque model, were derived. The overall speed control system was modeled and simulated in MATLAB/Simulink. The simulation results under no load as well as full load identified the obvious validity of the proposed method and its ability could use for three phase induction motor speed control in practice.

A Simplfied Voltage Vector Selection Strategy for Direct Torque Control

The direct torque control (DTC) for permanent magnet synchronous motor (PMSM) under the control of switching table suffers from high torque ripple and variable switching frequency. For PMSM DTC system, voltage vector selection strategy as the hysteresis control principle determines the system’s performance. The angle ( a ) between stator flux vector and the applying voltage vector determines effect of the voltage vector on the amplitude of stator flux and torque angle . The effect of the voltage vector on toque is dependent on a , torque angle and parameters of PMSM. A voltage vector selection strategy based on the technology of space vector modulation (SVM) is proposed to control stator flux, torque angle and torque . E xperimental results for a 15-kW interior PMSM show it can decrease stator current and torque ripples and fix the switching frequency.

A Novel Direct Torque Control Permanent Magnet Synchronous Motor Drive used in Electrical Vehicle

In this paper, a modified direct torque control (DTC) scheme for permanent magnet synchronous motor (PMSM) is investigated, which enables low torque ripple by using an improved voltage vector selection strategy instead of switching table used in conventional DTC. Based on the control of stator flux, torque angle and torque, voltage vector selection strategy of PMSM DTC drive is proposed. In the proposed voltage vector selection strategy, the applied voltage vector is determined according to outputs of hysteresis comparators for stator flux and torque, angular position of stator flux and torque angle, which is finally synthesized by space vector modulation (SVM). Modeling and experimental results for an interior PMSM used in Honda Civic 06My Hybrid electrical vehicle are given. Simulation and experimental results show torque ripple is reduced and the total harmonics of stator current is decreased when compared those of conventional DTC. And a fixed switching frequency is obtained with the help of SVM. In addition, the proposed DTC doesn’t need any additional PI controller, which maintains the simplicity in conventional DTC. DOI: http://dx.doi.org/10.11591/ijpeds.v1i2.141 Keywords : direct torque control, permanent magnet synchronous motor, electrical vehicle, torque ripple, switching frequency

New direct torque neuro-fuzzy control based SVM-three level inverter-fed induction motor

In this paper, a novel direct torque neuro-fuzzy control (DTCNF) scheme combining with space voltage modulation (SVM) technique of a three levels inverter is presented. Using neuro-fuzzy technique, the reference space voltage vector can be obtained dynamically in terms of torque error, stator flux error and the angle of stator flux. Compared with conventional direct torque control (C_DTC), in this new technique, the ripples of both torque and flux are reduced remarkable, and switching frequency is maintained constant. Simulation results verify the validity of the proposed method.

Direct Torque Control Strategy (DTC) Based on Fuzzy Logic Controller for a Permanent Magnet Synchronous Machine Drive

This paper introduces the design of a fuzzy logic controller in conjunction with direct torque control strategy for a Permanent Magnet synchronous machine. A stator flux angle mapping technique is proposed to reduce significantly the size of the rule base to a great extent so that the fuzzy reasoning speed increases. Also, a fuzzy resistance estimator is developed to estimate the change in the stator resistance. The change in the steady state value of stator current for a constant torque and flux reference is used to change the value of stator resistance used by the controller to match the machine resistance.

Adaptive Direct Torque Control of Induction Motors

In direct torque control (DTC), many induction motor parameters are needed, especially those that affect the values of current and flux required in the control algorithm. DTC of induction machines presents an acceptable tracking scheme for both electromagnetic torque and stator flux. This control scheme depends only on stator measurements. The measurement of the stator flux is very difficult to achieve and can be estimated by an observer. The electromagnetic torque and the stator flux (magnitude and angle) can be determined despite their direct dependence on the knowledge of the stator resistance. This resistance can change up to 180% of its nominal value. The resistance changes with the operational conditions of the motor, such as temperature and frequency. Under these circumstances, a parameter identifier is developed to account for the resistance variations, hence establishing adaptive DTC (ADTC). Moreover, load torque represents the changing tasks required from the motor. In this article, the load torque variations are coupled with stator resistance changes, and the effectiveness of ADTC is investigated. More stable motor operations of polyphase induction motors are obtained under these uncertainties using ADTC.