However, the hysteresis controllers used in the conventional DTC gives two major drawbacks which are variable switchingfrequency and high torque ripple. Theoretically, a reduction of torque ripple can be accomplished by reducing the bandwidth of torque hysteresis comparator such that the torque ripple is restricted to be regulated within its band. In such a way, a high speed processor must be utilized in which normally requires an expensive controller board (i.e. a powerful controller board DSPACE1104) and high-cost design in developing Verilog or VHDL code (i.e. in the case of using FPGA). Although, the use of high speed processor in implementing discrete hysteresis controllers still does not guarantee to perform the DTC at a constant switchingfrequency. This is because the slope of torque may vary on operating conditions (i.e. speed, load torque, flux linkages and etc.), which in turns causes the switching in the torque hysteresis controller that is directly affected the inverter switchingfrequency is unpredictable.
Unlike FOC, the DTC scheme as shown in Fig. 1, offers a simple control structure wherein the torque and flux can be separately controlled using three-level and two-level hysteresis comparators, respectively. The output of the comparators and the stator flux angle are used to index a lookup table of optimum voltage vector as proposed in , to determine the appropriate voltage vectors to control both torque and flux. However, the hysteresis torque controller utilized in the basic DTC structure results in two major disadvantages, namely variable inverter switchingfrequency and high torque ripple. Several methods have been proposed to overcome these problems. For example, the problems were minimized by the use of variable hysteresis band , , dithering technique , controlled duty ra- tio cycle technique , , space-vector modulation (DTC- SVM) , –, and most recently the use of predictive control –.
The most popular variation of DTC of induction motor drives is the one that is based on space vector modulation (SVM), which is normally referred to as DTC-SVM –. The major difference between hysteresis-based DTC and DTC-SVM is the way the stator voltage is generated. In hysteresis-based DTC, the applied stator voltage depends on voltage vectors, which are selected from a lookup table. The selections are based on the requirement of the torque and flux demands obtained from the hysteresis comparators. On the other hand, in DTC-SVM, a stator voltage reference is calculated or generated within a sampling period, which is then synthesized using the space vec- tor modulator. The stator voltage reference vector is calculated based on the requirement of torque and flux demands. Due to the regular sampling in SVM, the DTC-SVM produces constant switchingfrequency (CSF) as opposed to the variable switchingfrequency in hysteresis-based DTC however, at the expense of more complex implementation. Various methods to estimate the voltage reference vector had been reported; these include the use of proportional–integral (PI) current controllers , stator flux vector errors , PI torque and flux controllers , and predictive and dead-beat controllers , , .
This paper presents single phase Power Factor Correction (PFC) with proposed variable switchingfrequency (VSF) control technique. The increasing of non linear loads such as thyristor rectifiers, switching-mode power supplies, adjustable speed drives, and generate harmonic currents causing various problems to the other equipment connected to the point of common coupling. There are several disadvantages in the existing PFC control implementation based on conventional PWM control. This system considered uses a unified overcomes such a drawback by converting a voltage source into a fast- acting current source, which is reduce the harmonics in the line current, increases the efficiency and capacity of power system. The capacitor and inductor with voltage and current ripple with minimum ripple values was designed to absorb sinusoidal input current and to reduce total harmonic distortion (THD) in the input current with output voltage regulation. The principal of operation, theoretical analysis, simulation results on a single phase boost converter are presented.
Abstract. Direct Torque Control (DTC) has gained popularity for development of advanced motor control due to its simplicity and offers fast instantaneous torque and flux controls. However, the conventional DTC which is based on hysteresis controller has major drawbacks, namely high torque ripple and variable inverter switchingfrequency. This paper presents an improved switching strategy for reducing flux and torque ripples in DTC of PMSM drives; wherein the torque hysteresis controller and the look-up table used in the conventional DTC are replaced with a constant frequency torque controller (CFTC) and an optimized look-up table, respectively. It can be shown that a constant switchingfrequency is established due to the use of the CFTC while the reduction of torque and flux ripples is achieved mainly because of the selection of optimized voltage vector (i.e. with an optimized look-up table). This paper also will explain the construction of DTC schemes implemented using MATLAB-Simulink blocks. Simulation results were shown that a significant reduction of flux and torque ripples which is about 90% can be achieved through the proposed DTC scheme.
The direct torque control (DTC) of induction motor drives has gained popularity in advanced motor drive applications since it offers fast instantaneous torque and flux control with simple implementation. This scheme is well known for its robustness in control as it is less dependent on machine parameters, does not require a complex field orientation block, a speed encoder and an inner current regulation loop. However, this scheme, which is based on hysteresis comparators , has major drawbacks namely a variable switchingfrequency, a large torque ripple and high sampling requirements for digital implementation.
 Li YH, Gerling D, Liu WG. A Simplified Voltage Vector Selection Strategy for the Permanent Magnet Synchronous Motor Direct Torque Control Drive with Low Torque Ripple and Fixed SwitchingFrequency. The 13rd International Conference on Electrical Machines and Systems. Brasov. 2010: 674-679.
In order to obtain a better output current waveform, a pulse width modulation (PWM) technique is applied, instead of a staircase waveform operation. Staircase waveform can easily be obtained at the fundamental switchingfrequency, so switching losses can be negligibly low. However more distortion of the output waveform is generated and a larger filter is needed. In this paper, a level-shifted multi-carrier based sinusoidal PWM technique is employed to generate the gate signals for the CSI power switches to obtain the PWM current waveforms as shown in Figure 7, and Figure 8 in more detail. All carrier waveforms (C 1 , C 2 , C 3 and C 4 ) are in phase with the identical frequency. The frequency of the reference sinusoidal waveform determines the fundamental frequency of the output current waveform, while the frequency of triangular carrier waves gives the switchingfrequency of the power switches. An M-level output current waveform using this modulation requires (M-1) triangular carriers with the same frequency -.
Low voltage electrical arcflash caused occurs when a short circuit and triggering a fire case. The phenomenon of short circuit occurs when protective equipment can not detect the disturbance, although nominal currents during a short circuit is very high but the duration during a short circuit is so fast that safety equipment such conventional fuse and miniature circuit breaker (MCB) can not detect the disturbance. It is which cause a fire case due to short circuit. In this final project will be carried out low voltage arcing detection by observing the characteristics of the arc that increased significantly at specific time duration. The incoming current signal is transformed using a wavelet. Experiments performed by comparing three conditions ,it is normal conditions, switching and arcing condition. There are two threshold that used as a parameter detection. The first threshold is the peak of the high frequency curret, the value is 2A and the second is the number of disturbance points, the value is 7. Based on the result of detection, normal indicator will be “ ON ” during the first and the second threshold is not exceeded, switching indcator is “ ON ” when the first threshold is exceeded but not the second threshold, and then arcing indcators “ ON ” when both of threshold is exceeded.
“ I hereby declare that I have read through this report entitle “ SWEEP FREQUENCY RESPONSE ANALYSIS (SFRA) USING TIME FREQUENCY DISTRIBUTION (TFD) ” and found that it has comply the partial fulfillment for awarding the degree of Bachelor of Electrical Engineering (Control, Instrumentation and Automation) ”
This study deals with error in oral production made by English department students of Muhammadiyah University of Surakarta. The aims of this study are (1) to classify the type of errors, (2) to analyze the frequency of error utterances in oral production, (3) to analyze the dominant type of error, and (4) to describe the sources of error in speaking showed up by English department students of UMS. The type of this research is descriptive qualitative research. The data source of this research is error utterances that made by English department students in psycholinguistic presentation class. The data collection technique is documentation. The technique of data analysis is descriptive. The writer uses the theories from Clark and Clark, James and Selinker to analyze the type of error. The result of this study shows that (1) the writer found four types of error namely: speech error, pronunciation error, grammatical error, and code switching; (2) The frequency of each type of error are 139 utterances of speech errror (74,33%), 33 utterances of pronunciation error (17,67%), 8 utterances of grammatical error (4,27%), 7 utterances containing code switching (3,74%); (3) the dominant types of error is speech error especially filled pause; there are 53 utterances filled pause or about 28,34%; (4) the sources of error are cognitive reason, psychological reason, socials reason, the interlingual transfer and intralingual transfer. In interlingual transfer there are four categories, namely language interference, transfer in grammar, pronunciation interference, transfer in vocabulary. In itralingual transfer, there are two categories, namely false analogy and incomplete rule application.
Based on the analysis, the researcher discovered that the single-word code- switching type had the biggest number of frequency in the feature article of Pulsa tabloid edition 163. McCormick (1994:581) stated, compared to the other types of code-switching, the frequency of switching for the single-word type is high. To support the theory suggested by McCormick (1994), the researcher used the verification of one of the writers of Pulsa tabloid and then compared it. The writer of Pulsa tabloid said that most of the English words used in the feature article of Pulsa tabloid edition 163 were familiar to the readers. The researcher discovered that there were 581 cases for the single-word code-switching type. It was the highest frequency compared to the other types of code-switching in the feature article of Pulsa tabloid edition 163. Based on the analysis, the researcher concluded that there was an identical idea between the theory from McCormick (1994) and the verification of the writer. In conclusion, it was true that the writers of Pulsa tabloid used the single-word code-switching type most of the time. This was indicated by the finding which showed that the single-word code-switching type had the biggest frequency compared to the other frequencies of types of code-switching in the feature article of Pulsa tabloid edition 163.
The problem statement of this project is when different customer is using the same sector of cells at the same geographic distance and time, there are interference in the system and this results in the degradation of quality of communications. Over the past decades, the number of users has expanded and the source is limited. In order to overcome this problem, frequency reuse is used in OFDMA network.
The data of this study were analyzed in several stages, i.e. identifying code-switching occurrences, classifying the types and the functions of code- switching, quantifying every type and function of code-switching, interpreting and discussing the results of data analysis, and drew conslusions and proposed suggestions for future studies.