A new Nonlinear Dynamic Inverse (NDI) method is proposed to minimise the ripple torque in an induction motor. This method is based on field oriented with space vector pulse width modulation (SVPWM). The nonlinear dynamic inverse controller cancelled a non-desirable response of the induction motor and enhancing the performance. This cancellation attempts by careful nonlinear algebraic equations. First, a mathematical model of induction motor and decoupling between two inputs have achieved. Then the desired new dynamic is derived from implementing the proposed nonlinear dynamic inverse controller (NDIC) technique that reserves some benefits such as fast torque control, minimum ripple torque, and fast speed response. Also, the proposed method significantly reduced the torque ripple which is the major concerns of the classical hysteresis-based in direct torque control (DTC) and feedback linearization control (FLC) scheme and have an effect on the stator current distortion. Finally, the simulation results with MATLAB/Simulink achieved for a 2-hp induction motor (IM) drive. The results are verification proved that the proposed (NDI-SVPWM) system achieves smaller torque ripple about 0.4% and faster torque response than the conventional SVM-based on proportional integral (PI-DTC) method.
In this paper, the challenge of harmonic injection mitigation becomes critical with the massive use of inverters in electrical distribution systems that has been discussed and analyzed. Currently, between the inverter and the grid, L, LC or LCL filters is often used to mitigate the current harmonic. Further, filter connection in both delta-to-star or star-to-delta transformer for state space model of LC filter couplings with impedance is obtained in this paper and it also talked about the different passive damping techniques that been used to suppress the resonance effect on the filter. The effect of series and parallel damping resistor techniques that impact filtering and stability are also been analyzed and discussed. At the end, the simulation results show that LCL filter with parallel damping resistor achieves best performance compared on those for L, LC, or LCL with series damping resistor while at the same time enhancing the smoothness of the signal output while at the same time reducing the percentage of total harmonic distortion between inverter-grid connection.
This paper presents the chaotic pulse train (CPT) waveforms of the vertical electric field generated by lightning observed in Malaysia. Focusing on the position where these electric field changes occur in a number of cloud to ground (CG) flashes, these CPTs were detected in different ways of occurrences, durations, intensities and amplitudes. Seventy-six chaotic pulse trains were found in this study from a sum of 172 CG flash records from three thunderstorm days. The fast field antenna was employed to do the field measurements. As opposed to the typical occurrence of chaotic pulse trains prior to subsequent strokes as reported in the literature, this study has found chaotic pulse trains occurring in different places along the CG electric field waveforms.
Magnetic actuator driven switchgear is a new medium voltage switchgear technology. In this switchgear, the conventional spring mechanism which is used to operate the circuit breaker is replaced with a magnetic actuator mechanism. The suitability of this technology in the Malaysian utility network specifically in highly loaded areas with frequent switching was assessed via a field evaluation. Preliminary results indicated that magnetic actuator driven switchgear perform commendably on the safety aspect, on-site performance monitoring and online diagnostic test results. However, there are several concerns that need to be addressed such as the ease of installation, substation system requirements, high life cycle cost and reliability of components, before this technology can be used widely.
In recent years, vegetable oil such as Palm Oil (PO) has been identified as a potential alternative dielectric insulating fluid for transformers. It is biodegradable, non-toxic and has high flash and fire points. In this paper, a study on the positive lightning impulse breakdown voltages of PO under non-uniform field is carried out. The testing was carried out using needle-plane electrodes configuration at gap distances of 25 mm and 50 mm. Rising voltage, 1 and 3 shots per step testing methods were used and 3 types of Refined Bleach and Deodorized Palm Oil (RBDPO) and Mineral Oil (MO) were examined. It was found there is no significant effect on the breakdown voltages of all samples. The breakdown voltages of all RBDPO at 50% probability are comparable with MO. At 1% probability and gap distance of 50 mm, the breakdown voltages of all RBDPO are lower than MO.
This paper presents a voltage flicker estimation based on a pair of inter-harmonics analysis method. The proposed algorithm is able to estimate flicker frequency and amplitude changes of a voltage waveform. The correlation of the pair of inter-harmonics, flicker frequency, and amplitude changes are presented and their formulas highlighted. .Experimental results indicate the amplitude of pair of inter-harmonics can detect the voltage flicker. Furthermore, the experimental results are compared with the measurement results obtained by using the Fluke power analyzer (Pst).
Lightning is a natural phenomenon that generates a high electric field during thunderstorm. It has been
reported that lightning strikes amid storms can occur around 100 times per second. The atmospheric
electric field is an imperative parameter during a thunderstorm. Therefore, monitoring the electric field
and its parameters is the best way for local lightning forecast. The electric field monitoring data can
validate the accuracy of weather prediction in a local area from meteorology department or by using
equipment specially designed to measure this electric field that exists when the phenomenon of lightning occurs. In this paper, the relationship between lightning, air humidity and temperature is discussed to understand the post lightning effect on these electric parameters. Additionally, the characteristics of the parameters are observed and analysed.
This paper presents a modified design of low power recovery circuit in micro-system implanted device to stimulate the human nerve and muscle. The amplitude shift keying ASK was used to modulate data by using operating frequency 6.78MHz ISM industrial scientific medical band to be less invasive to tissue. The proposed system consists of an external part which has ASK modulator and class-E power amplifier with 94.5% efficiency. The internal part has half wave rectifier and voltage regulator to generate very stable 1.8VDC using 0.35um CMOS technology. The Orcad pspice 16.6 and MULTISIM 11 software were used to simulate the design of power recovery and class-E power amplifier respectively. The regulated voltage utilised to power the sub-electronic device implanted inside human body with very stable voltage even change implanted load resistance. The proposed system has 12.5%modulation index and low power consumption.
One of the concerns in power system preventive control and security assessment is to find the point where the voltage and frequency collapse and when the system forces a severe disturbance. Identifying the weakest bus in a power system is an essential aspect of planning, optimising and post-event analysing procedures. This paper proposes an approach to identify the weakest bus from the frequency security viewpoint. The transient frequency deviation index for the individual buses is used as the weakest bus identification as well as a frequency security indicator. This approach will help to determine the bus with the worst deviation, which helps to analyse the system disturbance, takes proper control action to prevent frequency failure, and most importantly, observes consumer frequency. The approach is applied to the WSCC 9 bus test system to show the feasibility of the method.
This paper presents an auto grasping algorithm of a proposed robotic gripper. The purpose is to enhance the grasping mechanism of the gripper. Earlier studies have introduced various methods to enhance the grasping mechanism, but most of the works have not looked at the weight measurement method. Thus, with this algorithm, the weight of the object is calculated based on modified Wheatstone Bridge Circuit (WBC) which is controlled by programmable interface controller (PIC) method. Having this approach introduces and improves the grasping mechanism through an auto grasping algorithm. Experimental results show that an auto grasping algorithm based on pressure sensor measurements leads to a more precise grasping measurement and consequently enhance the sensitivity measurement as well as accurate movement calibration. Furthermore, several different grasping objects based on the proposed method are examined to demonstrate the performance and robustness of our approach.
A programmable CMOS delay line circuit with microsecond delay range and adjustable duty cycle is proposed. Through circuit simulation, approximately 2μs delay range can be achieved using 10-bit counter operating at a clock frequency of 500MHz. Utilising synchronous counters instead of synchronous latches has significantly reduced the large occupied active silicon area as well as the huge power consumption. The generated coarse time delay has shown excellent linearity and immunity to PVT variations. The proposed CMOS delay line is designed using a standard 0.13μm Silterra CMOS technology. The active layout area is (101 x 142) μm2, and the total power consumption is only 0.1 μW.
Controlled humidity environment is of significance in many scientific researches and experiments. In most laboratory-scale atmospheric chambers, an electrical temperature-based control system is used to adjust humidity. Since these chambers are not affordable in every laboratory, other low cost chambers using nitrogen gas or silica gel are used to adjust humidity. In this paper, a mechanism was developed to control the relative humidity in closed lab-scale chambers. Humidification is done by spraying water through a blower fan while de-humidification is by pumping air through silica gel as well as nitrogen gas injection. A Mamdani type fuzzy controller was designed to control the components and relative humidity. The results show the proposed system and controller can adjust and maintain relative humidity from 41% to 100% with maximum overshoot of 1% and the maximum range of error of steady state of 1.2 %.
Transformer failures lead to interruption of power supply. Therefore, asset management is important to monitor the efficient functioning of transformers. An important approach in asset management is condition assessment whereby the health status of the transformer is assessed via a health index. There are many methods in determining the final value of a health index. This paper examines how different assessment methods can be used in order to come up with the final health index and output of final health index. The output trend shapes are almost the same for Assessment Model A, B and C except for Assessment Model D. There is no strong correlation between the health index and age of the transformer. Generally, the value of health index of the transformer is reflected by its operation and loading history .This paper hence examines the assessment steps and results that will guide the development of a new approach to determine health index value.
Top-Oil Temperature (TOT) is one of the basic components to estimate the Hot-Spot temperature (HST) of the transformers. This paper presents an alternative TOT model based on the heat transfer theory that utilises Nonlinear Thermal Resistance (NTR) and Lumped Capacitance (LC) approaches. It is applied in a thermal-electrical analogy and the heat transfer equivalent equation is determined. This model is tested on a measured TOT of 250 MVA ONAF and 400 MVA ONAF transformers obtained from IEC 60076-7 and previous research. A comparison of TOT is carried out with the existing models IEC 60076-7 exponential and IEEE Loading Guide clause 7 methods. It is found that the thermal model based on the NTR and LC approach could determine the measured TOT closer than the existing methods available in the standards.
Soil plays an important role in ground designing. Engineers normally consider only soil resistivity under normal or steady state condition when designing the grounding system. Under certain circumstances such as lightning, electrical response of the soil will change accordingly and thus, the performance of the grounding system will be affected. The purpose of this study is to investigate the effect of moisture content on the electrical behaviour of sand and clay under high impulse voltage condition. Both soil samples are dried in the oven at 110 ± 5°C to remove the water content until became 0%. The samples are subjected to 30 shots of standard (1.2/50μs) lightning impulse voltage for both positive and negative impulse polarities. This is followed by moistening the samples with 5% amount of water over the volume of the samples. The corresponding V50% for both sand and clay was calculated and the value obtained was converted to standard atmospheric condition. The voltage at breakdown and time to breakdown for each soil sample was analysed a statistical analysis conducted for these two parameters to determine if type of soil and moisture content have an effect on the breakdown voltage. In general, it was found that clay is more efficient in neutralising high impulse voltage than sand likely due to the former’s low resistivity and porosity.
Shunt active power filter (SAPF) is the most effective solution for current harmonics. In its controller, DC-link capacitor voltage regulation algorithm with either proportional-integral (PI) or fuzzy logic control (FLC) technique has played a significant role in maintaining a constant DC voltage across all the DC-link capacitors. However, PI technique performs poorly with high overshoot and significant time delay under dynamic state conditions, as its parameters are difficult to be tuned without requiring complete knowledge of the designated system. Although FLC technique has been developed to overcome limitations of PI technique, it is mostly developed with high complexity thereby increases computational burden of the designed controller. This paper presents a fuzzy-based DC-link capacitor voltage regulation algorithm with reduced computational efforts to enhance performance of three-phase three-level neutralpoint diode clamped (NPC) inverter-based SAPF in overall DC-link voltage regulation. The proposed method is called effort-reduction FLC technique. The proposed algorithm is developed and evaluated in MATLAB-Simulink. Moreover, conventional algorithm with PI technique is tested for comparison purposes. Simulation results have confirmed improvement achieved by the proposed algorithm in comparison to the conventional algorithm.
A prototype of three-fingered robot hand was very rigid in its motion, and prone to damages when dealing with hard surfaces or when subjected to external environmental forces. The robot hand could damage fragile objects during grasping tasks if a position control alone is used. Therefore, this study proposes application of force control to the robot hand to improve its current grasping capabilities. Impedance control that considers the dynamic of the robot to produce the softness like human hand was implemented in this study. The dynamical behaviour of the robot hand strongly depends on the impedance parameters known as virtual mass, damping and stiffness. Therefore, the optimal values of impedance parameters need to be investigated to develop a position-based impedance control for the robot finger. Hence, the objective of this study is to determine the optimal value of impedance parameters to impose desired dynamics to the robot system. A constant force weighing 100 g was used by implementing varying impedance parameters to the tip-end’s position. Three experiments were conducted: first to decide the order of parameters to be adjusted, then to determine the optimal value of impedance parameters, and finally to test the optimal values with random force applied to the robot finger. The determined optimal values are: stiffness=1000, damping=10 and mass=1. Thus, the combined parameters have proven that the modified position is capable of responding according to the exerted contact force.
This paper looks at electrical power generation from solar concentrator using thermoelectric generator. An experiment was conducted on a concentrator thermoelectric generator (CTEG) utilising solar thermal energy. The CTEG used a parabolic dish as concentrator with thermoelectric device installed at the focal point to convert thermal energy to generate electricity. The investigation covered the cooling effect of the cold side of the thermoelectric generator using natural and forced convection cooling for optimum output. Forced convection cooling with a fan provided 69% more power output from the CTEG system as the temperature difference across the TEG was greater than the system cooled by natural convection. The outcome of this project showed maximum power output was obtained for the CTEG system cooled by forced convection cooling.
In this paper, a micropropagation protocol of sugar palm (Arenga pinnata Wurmb Merr) through callogenesis and somatic embryogenesis was examined. Callus induction frequency and somatic embryogenesis response were dependent on plant growth regulators (PGRs) and genotype. Semi-compact and compact embryogenic calluses were induced from excised immature zygotic embryo (IZE) cultured on semi-solid MS (Murashige & Skoog, 1962) medium supplemented with various concentration and combination of 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyl aminopurine acid (BAP). MS medium supplemented with 0.4 mg/L 2,4-D and 0.5 mg/L BAP was found optimum to induce 100% rate of embryogenic calluses and maximum degree of callus formation after 8 and 12 weeks of culture. The incorporation of increased sucrose concentration (60.0 g/L) and 2.0 g/L casein hydrolysate (CH) to the culture medium with similar PGRs composition enhanced the induction of globular somatic embryos (SEs), while addition of silver nitrate (AgNO3) produced SEs of different stages. SEs maturated in MS medium containing 1.0 mg/L BAP and 1.0 mg/L naphthalene-acetic acid (NAA) formed cotyledon-stage embryos. Clonal roots regeneration was obtained on half-strength MS devoid of PGRs after 4 months of culture. Frequent subcultures increased embryogenesis rate favourably.
A new smart grid system is widely used for energy supply system because it is simple, available, low cost, high efficiency and environmentally friendly. Conventionally, inverter techniques are utilised to convert input DC into output AC with the same frequency and phase. This process suffers the same problem which is a higher harmonic distortion, phase synchronisation, lower quality of waveform and long distance, among others. In this paper, three phase synchronous inverters (PSI) were used to direct synchronous PWM control, LCL filter, three phase RLC load, three phase Yg-Delta transformer, 5 km feeder with 2 MW load. PWM was used to generate the pulse signal for synchronisation. However, LCL filters were used to remove the noise in inverter output and transformer output side of the design. A balanced three phase load (10 kVAR) and also the input DC voltage 500 V were considered in this design. Three phase transformer (100kVA/260V/25kV) was used to increase the inverter output voltage and current with the fundamental frequency (50 Hz). The system conversion efficiency was 99.96% and phase synchronous error for each phase was approximately 4.5 degrees.