A Constant Switching Frequency Of Direct Torque Control Of Brushless DC Motor

Direct torque control (DTC) for DC motor have extensively used in many applications because it provides the simple control structure, faster torque dynamic control and longer lifespan. However, the used of hysteresis comparator in DTC structure have provides two major drawbacks namely, larger torque ripple and variable switching frequency. These problems occur due to low sampling time which creates delay actions in minimization of torque error with appropriate voltage vectors and inappropriate voltage selection of voltage vectors which leads to larger torque ripple in DTC scheme and cause the torque error cannot restrict within the hysteresis bandwidth. Therefore, this thesis presents the optimal DTC switching strategy to reduce torque ripple and gain the constant switching frequency for BLDC motor. Next, to analyze and compare the switching frequency and torque control performance produced by other strategy schemes such as torque hysteresis control (THC), direct torque control (DTC) and constant switching frequency (CSF). The minor modification is made without changing the original structure of DTC scheme. The hysteresis controller is replaced with torque controller and look-up table is added where the selection of voltage vector is occurred. The most suitable voltage vector for different speed range can be defined as the vector that produces minimum torque slopes. The torque ripple and switching frequency can be reduced when the torque slope is minimized. Next, to obtain the constant switching frequency, PI controller and high injection frequency are proposed. The proper proportional integral (PI) controller are determine by analyzing or insuring that the absolute torque shape does not exceed the absolute carrier slope. The results of improvements are obtained and were verified via simulation and experiment, as well as comparison with the conventional DTC and others schemes. The results obtained clearly show that the torque ripple is reduced and constant switching frequency is achieved

Review and Comparison of Sensorless Techniques to Estimate the Position and Speed of PMSM

Sensorless technique becomes popular nowadays in electrical drive applications specificially for AC motor drive. It is applied to determine and estimate the rotor position especially for PMSM motor. This paper presents the comparison sensorless technique to determine and estimate the position and rotor of PMSM motor. PMSM motor is widely used in industrial and automation due to its high performance motor drive. However, the location of PMSM motor in humidity and harsh environment causing the accuracy of motor is inaccurate due to deterioration of position sensor . Therefore, many sensorless techniques have been proposed by previous researchers in order to solve the problem. This paper presents the review of several categories; Model Based Method, Saliency Based Method and Signal Injection, and Artificial Intelligence Based Estimator. In addition, sensorless techniques on each category have been compared and described in terms of their advantages and disadvantages

Minimization Of Torque Ripple And Switching Frequency Utilizing Optimal DTC Switching Strategy For Dual-Inverter Supplied Drive

This paper presents an optimal switching strategy employed in direct torque control (DTC) of induction machine utilizing dual-inverter supplied drive. In the proposed switching strategy, the utilization of appropriate amplitude of voltage vectors based on machine operating condition can reduce the rate change of torque slope while improving the performance of DTC drive in term of torque ripple reduction and also minimization of switching frequency variation. This is achieved by modifying the torque error status according to the capability of torque regulation which is done by evaluating the switching frequencies of torque and stator flux error status from the hysteresis comparators. By doing that the suitable amplitude of voltage vectors is able to be applied based on machine operation. All the improvements offered in the proposed strategy are verified through simulation results

Direct Torque Control Of Induction Machine Using 3-Level Neutral Point Clamped Inverter

This paper presents a Direct Torque Control (DTC) of induction motor drives utilizing 3-level neutral-point clamped (NPC) multilevel inverter. This research aims to provide a simple strategy to address capacitor voltage balancing problem of NPC inverter as well as produce better performance for DTC of induction motor in term of reducing torque ripple and high switching frequency. The proposed method uses 2-level hysteresis comparator to restrict the error of upper and lower capacitor voltages and then generate a signal which determine either to increase or decrease the particular capacitor voltage. Using that information, the appropriate selection of small voltage vectors is tabulated in look-up table (LUT) to stabilize the mismatched of capacitor voltage. Simulation results are presented to show the effectiveness of the proposed capacitor voltage balancing strategy

Constant Switching Frequency For Direct Torque Control Of Induction Motor

DTC drives utilizing hysteresis comparator is one of the simplest and most popular technique used in induction drives. However, due to its disadvantage of variable switching frequency causes serious problem in DTC especially for electromagnetic torque ripple. This paper proposed a technique of constant switching that could reduce the ripple on both torque and phase current for DTC by using triangular waveform or carrier frequency. Thus, the conventional and proposed DTC will be simulated and demonstrated by using Altera field-programmable gate array (FPGA) and digital signal processor. Simulation results presented in this paper shows the torque and stator current ripple with the proposed DTC algorithm when varying the speed and the carrier frequency

Investigation Of Torque And Flux-Current Producing Components In Indirect Rotor Flux Oriented Control (IRFOC) Of Induction Machines

This paper presents an investigation of torque and flux-current producing components in indirect rotor flux oriented control (IRFOC) of induction machine. Induction machine faced the problems when the motor rotates at the highest speed due to complex mathematical model based on the previous research. Therefore, to prove that there have the coupling effect, the investigation towards the torque and flux current component of IRFOC is done. The method that have been used to detect the problem is by using simulation method on MATLAB software. The algorithm and controller that been used is Field Oriented Control (FOC) because it is the first method in drive system that are been used in order to solve the induction machine problems. Simulation results presented in this paper show the torque, rotor flux, direct and quadrant current component when varying the value of torque and flux

Improve Torque Control Performance Of 3-Phase DTC Constant Switching Method Using Optimal PI Parameter Tuning Strategy

This paper presents the advantage of using optimal PI parameter tuning strategy of constant switching method in the three phase Direct torque control (DTC) scheme. The DTC system is known to offer fast decoupled control of torque and flux via a simple control structure. Nevertheless, DTC system has two major drawbacks, which are the variable inverter switching frequency and high torque output ripple. The major factor that contributes to these problems the usage of hysteresis based comparators to control the output torque. The implementation of PI based constant switching method in DTC able to solve these problems while retaining the simple control structure of conventional DTC. The combination usage of 3-level CHMI in this system can further minimize the output torque ripple by providing greater number of vectors. This paper presents detail explanation and calculation of optimal PI parameter tuning strategy consecutively to enhance the performance of 3-level DTC system. In order to validate the feasibility, the proposed method compared with convention DTC system via simulation and experiment results