In this paper a new scheme based on direct torque control strategy is presented. The new controller is used to control an induction motor fed with a three-level inverter. The new control scheme avoids the use of the classical hysteresis block and the look-up table. Instead, the torque and stator flux errors are used together with the motor speed to generate a reference voltage that can be synthesized using different techniques afterwards. Experimental results show some improvement regarding the reduction of torque ripple, stationary mean torque error, THD in stator currents and switching frequency when compared to the classical DTC scheme.

In this paper a novel controller based on direct torque control is presented. This controller has been designed to be applied in the control of induction motors fed with a three-level voltage source inverter (VSI). This type of inverter has several advantages over the standard two-level VSI, such as a greater number of levels in the output voltage waveforms, less harmonic distortion and lower switching frequencies. In the new controller the hysteresis regulators and look-up table are not used, and instead, the torque and stator flux errors are used together with the motor speed to generate a reference voltage vector that can be synthesized using different techniques afterwards. Experimental results of the novel system are presented and compared with those obtained for classical DTC system when employing two-level VSI. The new controller is shown to reduce the ripple in the torque and flux responses. Lower current distortion and switching frequency of the semiconductor devices are also obtained in the new presented system

Inthis papera novel controller based on Direct Torque Control ispresented. Thiscontroller hasbeen designed tobeapplied inthecontrol ofinduction motorsfedwithathree-level Voltage Source Inverter (VSI). Thistypeofinverter hasseveral advantages overthestandard two-level VSI,suchas a greater numberoflevels intheoutputvoltage waveforms, lessharmonic distortion andlowerswitching frequencies. Inthe new controller thehysteresis regulators andlook-up table arenotused, andinstead, the torque andstator flux errorsareusedtogether withthemotorspeed togenerate areference voltage vector that canbesynthesized using different techniques afterwards. Experimental results ofthenovel system are presented andcompared withthose obtained forClassical DTC systemwhenemploying two-level VSI. Thenew controller isshown toreduce theripple inthetorque andflux responses.Lowercurrent distortion andswitching frequency ofthesemiconductor devices arealso obtained inthe new systempresented.

Multilevel inverters, such as three-level inverters, are an emerging technology and are commonly applied to high power motion drives instead of the standard two-level voltage source inverters (VSI). In three-level inverters the blocking voltage of each switch is half of the DC bus voltage, lower dV/dt is generated and the output voltage and current have lower harmonic distortion. In this paper the application of the Direct Torque Control (DTC) strategy is studied for this particular topology. In the three-level inverter the voltage selection possibilities are enhanced since more inverter states are available. Two different control methods have been designed. The first is based on the conventional DTC scheme adapted for a three level inverter. The second is based on the application of a Fuzzy Logic Controller to the DTC scheme to select the appropriate switching state, instead of applying the conventional DTC table. In the simulation results, the novel system based on Fuzzy Logic shows reduction in torque ripple and harmonic distortion in the stator currents and voltages. Both features are important for applications in motion control where smooth movement and high efficiency are necessary.

Accurate values of convection heat transfer coefficients are required for the simulation of the thermal characteristics of printed circuit boards. This paper presents the results of experiments carried out using a Schlieren apparatus to examine the natural convection plumes from a horizontally positioned partially heated printed circuit board plate. It has been demonstrated that for a board with a centrally positioned resistor, the convection coefficients may be approximated to two values, one over the heated resistor area and another over the rest of the plate. These observations were then used in an optimization process to estimate the convection coefficients from such surfaces. Values of 4 W/m2K and 13.5 W/M2K were obtained for the resistor and the adjoining unheated sections, respectively. It is concluded that it is not generally satisfactory to assume a uniform value for convection coefficients during thermal simulation of electronic structures. However, a simplifying assumption of two values for convection coefficient appears to be acceptable; the lower value applying in the region of convection plumes and the higher value elsewhere.

Accurate values of heat transfer coefficient are needed for simulation of the thermal characteristics of a thick film resistor. In this paper, the results of an investigation are presented where an optical technique is used to study the convection plumes from a horizontally positioned hybrid resistor package. The observations have shown that simplifying approximations to the convection coefficients may be made in thermal analysis of such devices. Using these approximations and an optimization technique, values have been estimated for the coefficients.

Accurate values of thermal conductivity are required for the simulation of temperature phenomena in electronic circuits. This paper presents the results of measurements carried out to determine the thermal conductivity along and normal to the plane of fibre glass laminates used in the manufacture of printed circuit boards. It has been found that the reinforced fibre-glass substrates used in PCBs are strongly anisotropic with the conductivity normal to the boards being much smaller than tangential to it. The test samples were type FR4 epoxy/glass laminates. An experiment has been designed which determines the thermal conductivity in-the-plane of the laminates by matching the measured temperature distribution along a heated specimen with a finite difference solution. An electrically heated Lees’ disc apparatus is also used to measure the thermal conductivity of these boards in a direction normal to their plane. The samples tested yielded values of 0.343 W/mK and 1.059 W/mK for thermal conductivity through and along the plane of the boards, respectively.

It has been demonstrated that the simulation of the electrical and thermal aspects of circuit behaviour can be combined via the ASTEC3 software system. The finer the cell mesh the more accurate the results obtained, at the expense of extending the computation. The use of mixed coarse/fine cells reduces this problem and a semi-automatic method of generating the mesh file has been developed. The results obtained from the simulations have been shown to correspond to theoretical predictions and, with some reservations, to the experimental situation. However, further work needs to be done on the effects of convection before the method is fully developed. The advantage of the combined simulation is seen to be a more realistic estimation of the thermal effects as a result of being able to take account of the phasing of the heat generation processes

AbstractThis paper describes the application of ASTEC3, a general purpose analogue electronic circuit simulation package, to the analysis of thermal properties of given structures. The modelling of each system is considered for both conduction and convection mechanisms, radiation being assumed to play a very minor role in heat dissipation from most electrical circuits. A procedure is given for the modelling of one‐, two‐ and three‐dimensional thermal problems which is then used for the simulation of relatively simple examples. The results obtained with ASTEC3 are compared with results determined by using more traditional and independent techniques.

Astec 3 is a general-purpose analogue electronic circuit simulation package developed in France and available on IBM and DEC VAX computers. Designed for DC, AC and transient analysis, the system stands as a rival to the widely used SPICE. This article, the first of two on the system, outlines the general features of the Astec 3 simulation language.

Student progression and retention has always been a focus of attention at Glamorgan for many reasons. Not the least of these is the University's mission towards widening access to disadvantaged groups. The School of Electronics suffered a particularly difficult year for retention in 1999-2000, with the result that a programme of intensive action was initiated in the 2000-2001 session. This appears to have been successful. The programme involved close monitoring and counseling of students. In addition adjustments to the initial curriculum were implemented. As a result withdrawal has been halved and information on reasons for withdrawal has been enhanced. In addition to this tactical response a longer-term strategic programme has been started with the intention of addressing those factors which the School perceives to be the underlying causes of withdrawal. In this paper we look at some research carried out by others, regarding the underlying causes of withdrawal, offer some additional opinions on further causes, examine the 2000 - 2001 session tactical response and its outcome and offer, for discussion, the philosophy underlying the future strategic attack on the problem.