The idea of district heating is to heat up a whole district from a central source through a distribution network. The heat is extracted by heat exchangers and the water is then subsequently returned to the central source. The heat exchange between the district heating network and the building occurs in district heating substations. Heat meters are located in such substations and are divided into two main categories depending on their heat energy estimation frequency modes. Which are either constant or flow rate dependent. The Swedish district heating industry is a business with revenue of approximately 19.8 billion SEK (as of the year 2002). Considering an error of 1% in energy delivered, that is a loss of 198 million SEK, which justifies the current research. The accuracy in heat measurement for billing purposes is then one of the major reasons for conducting this research. Few studies have been done in this area. A Swedish study shows that the major causes of the errors are: flow meters, temperature sensors, integrating units, lightning, control systems, valves, leaks in heat exchangers and the dynamic heat demand imposed on the district heating substation. I have chosen to study the heat measurement errors due to dynamic load imposed on the district heating substation because they are the least investigated and presumably account for a substantial portion of the total error. I have delimited my research area to include single family houses, since the effects of dynamic heat load on heat metering are more important in this kind of dwelling. A major tool in the investigation has been simulations based on a Simulink model, of a district heating substation and a house. For this purpose, the simulation model has been extended to handle new heat measurement strategies. A district heating laboratory was built at Luleå University of Technology to test not only the accuracy of different heat measurement algorithms but also control and diagnosis methods. Based on analysis of the measurement strategies, an adaptive algorithm and a feed-forward method are proposed in this thesis to reduce the heat measurement errors due to the dynamic heat demand imposed on the substation. Simulations conducted show that the adaptive algorithm has a higher measurement accuracy than both kinds of existing heat meters. The feed-forward method has the highest measurement accuracy compared to both kinds of existing heat meters and the adaptive algorithm. / Godkänd; 2006; 20061116 (pafi) / Fjärrvärme

The research presented in this thesis discusses an electromagnetic (EM) analysis tool which is based on the partial element equivalent circuit (PEEC) method and is appropriate for combined EM and circuit simulations especially power electronics applications. EM analysis is important to ensure that a system will not affect the correct operation of other devices nor cause interference between various electrical systems. In power electronic applications, the increased switching speed can cause voltage overshoots, unbalanced current share between semiconductor modules, and unwanted resonances. Therefore, EM analysis should be carried out to perform design optimizations in order to minimize unwanted effects of high frequencies. The solver developed in this work is an appropriate solution to address the needs of EM analysis in general and power electronics in particular. The conducted research consists of performance acceleration and implementation of the solver, and verification of the simulation results by means of measurements. This work was done in two major phases.In the first phase, the solver was accelerated to optimize its performance when quasi-static (R,Lp,C)PEEC as well as full-wave (R,Lp,C,tau)PEEC simulations were carried out. The main optimizations were based on exploiting parallelism and high performance computing to solve very large problems and non-uniform mesh, which was helpful in simulating skin- and proximity effects while keeping the problem size to a minimum. The presented results and comparisons with the measurements confirmed that non-uniform mesh helped in accurately simulating large bus bar models and correctly predicting system resonances when the size of the problem was minimized. On-the-fly calculation was also developed to reduce memory usage, while increasing solution time.The second phase consists of methods to increase the performance of the solver while including some levels of approximations. In this phase sparsification techniques were used to convert a dense PEEC system into a sparse system. The sparsification was done by calculating the reluctance matrix, which can be sparsified by maintaining the accuracy at the desired level, because of the locality and the shielding effect of the reluctance matrix. Efficient algorithms were developed to perform sparse matrix-matrix multiplication and assemble the sparse coefficient matrix in a row-by-row manner to reduce the peak memory usage. The sparse system was then solved using both sparse direct and iterative solvers with proper preconditioning. The acquired results from the sparse direct solution confirmed that the memory consumption and solution time were reduced by orders of magnitude and by a factor 3 to 5. Moreover, the Schur complement was used together with the iterative approach, making it possible to solve large problems within a few iterations by preconditioning the system, and using less memory and lower computational complexity. Bus bars used in two types of power frequency converters manufactured by ABB were modelled and analysed with the developed PEEC-based solver in this research, and the simulations and measurements agreed very well. Results of simulations also led to improvement in the physical design of the bars, which reduced the inductance of the layout.With the accelerated solver, it is now possible to solve very large and complex problems on conventional computer systems, which was not possible before. This provides new possibilities to study real-world problems which are typically large in size and have complex structures. / Godkänd; 2012; 20121114 (dan); DISPUTATION Ämne: Industriell elektronik/Industrial Electronics Opponent: PhD Bruce Archambeault, IBM, Research Triangle Park, North Carolina, USA. Opponenten utför sitt uppdrag via distansöverbryggande teknik Ordförande: Docent Jonas Ekman, Institutionen för system- och rymdteknik, Luleå tekniska universitet Tid: Torsdag den 17 januari 2013, kl 13.30 Plats: A109, Luleå tekniska universitet

In the district heating industry, heat meters, consisting among other things of a flow meter, are used for billing purpose. The district heating industry desires accurate and low cost flow measurements. There are mainly two reasons. An under estimation of the flow rate leads to a loss of income for the district heating industry. Further, the total cost for measuring, including the cost for the heat meter, the reading and the maintenance, represents a relatively large part of the total energy cost. Therefore a project concerning measurement quality assurance in district heating systems is in progress at Luleå University of Technology. As a part of this project the possibility of self diagnostic techniques for flow meters is investigated. It is well known that installation effects greatly impair the flow measurement involved in heat metering. Thus this thesis focus on self diagnostics of different installation effects. The basic assumption is that the flow meter noise level is correlated to turbulence intensity. Since the turbulence intensity is effected by installation effects, the noise level can be used to detect conditions for which the flow meter shows erroneous results. In district heating applications the use of ultrasonic flow meters are becoming more and more frequent. The self diagnostic approach has therefore been investigated for a small size prototype ultrasonic flow meter. Single and double elbow pipe bends and pipe diameter reductions mounted in front of the meter and pulsating flow give rise to small but reproducible errors. The magnitude of the maximum errors were in the range of 2 to 4% of flow rate. At low flow rates with pulsating flow the errors were larger. Also small commercial ultrasonic flow meters were investigated. These commercial meters are commonly used in heat meters in small district heating subscriber stations. The results demonstrate that both temperature changes and installation effects introduce errors in the flow measurements. By studying the noise level of the signal from the prototype ultrasonic flow meter it is clear that all installation effects tested caused a clear increase in the flow signal noise level. It is clear that no tested disturbance causing measurement errors, larger than 1% of the flow rate, will pass undetected. Neither will normal conditions with a varying flow rate or single measurement outliers cause false alarms. It is anticipated that this increase in the future can be detected on-line by the flow meter itself giving it a self diagnostic capability. / <p>Godkänd; 2001; 20061115 (haneit)</p>

Flow metering plays a major role in modern life. In the process industry, flow metering is critical in industries ranging from food processing to cosmetics. It is also essential in custody transfer or billing, as flow meters are present in gas pumps and district heating substations. In the district heating industry, the ultrasonic flow meter has become the desired meter in many of its applications because it has a low cost while being accurate. This accuracy is however sensitive to installation effects and other sources of errors. This thesis stems from research that addresses the recognition of these installation effects, informs when they are unacceptable and considers reducing the measurement errors. To present these concepts, the thesis details the estimation of the mean flow velocity, the calibration of the meter and the measurement noise properties. Once installed, any kind of meter provides larger errors than in the facility where it has been calibrated and compensated. It is particularly true for ultrasonic flow meters as they are very sensitive to installation effects. Installation effects can either be static or dynamic. Special attention is paid to errors generated by temperature and velocity profile variations. Velocity profile variations can be due to pipe bends or flow pulsations. Such disturbances often induce a bias error and change the properties of the measurement noise. It is therefore with help of the change in noise that velocity profile disturbances can be detected. The detection of such abnormal behaviour of the measurement process constitutes a diagnosis. A diagnosis of the sensitivity of the meter to installations effects would allow for compensations for the errors. Signal analysis allows detection of specific noise properties, characteristic of installation effects. An example of self-diagnosis showing the detection of real pulsations in a flow is described in details. The detection of the flow pulsations and the estimation of their frequency allow to reduce the error of estimation on the flow rate. This technique is confirmed by the simulations of a pulsating flow. To empower one with the decision whether a flowmeter performance is normal or abnormal, a study of the relative error as a function of flow rate and temperature has been conducted. / <p>Godkänd; 2004; 20080708 (evan)</p>

Today a number of different optical techniques capable of measuring range, velocity or both exist. With recent advancements in laser diode manufacturing, small tunable sources have become available. By modulating current supplied to the laser the optical output frequency can be modulated. If the outgoing modulated light is divided into two parts, a transmitted and a local oscillator part, and a photodiode is used as detector, the frequency difference between the two parts can be obtained directly from the photodiode current. This frequency difference is often referred to as the beat frequency. If triangular frequency modulation is used, both range and radial velocity can be determined from the measured beat frequency. The common name for this technique, which was first implemented using regular radar, is frequency modulated continuous wave (FMCW). The thesis consists of an introduction and five papers. Paper one is a theoretical investigation where contributions from different noise sources are discussed. We have investigated how the signal to noise ratio for the photodiode is affected by how the optical power is divided between the transmitted part and the local oscillator part. Paper number two introduces a new modulation scheme that avoids ambiguity problems resulting from a Doppler shift larger than the frequency shift associated with the range. As a result of this new modulation scheme other benefits are also gained. The modulation scheme was tested and verified in our lab system built with a tunable laser diode and a fiber optic coupler. Paper number three presents a single stage OP-amp solution suited for an FMCW system. Our circuit combines a high gain in the desired frequency region with minimal gain at dc, without using any inductors. The risk of saturation or clipping due to the local oscillator can thereby greatly be reduced. Inserting a high pass filter between the photodiode and the first amplifier stage, to remove the dc level, is often not practical when using a regular current to voltage converter. A cascade of two stages, with a high pass filter between the two, is therefore commonly used. Our solution has similar performance as the cascade solution, but since it uses only one OP-amp, it is less sensitive to external disturbances. Paper number four and five deal with a common problem in an FMCW systems where the optical frequency is used as the carrier wave, and the modulation is obtained by modulating a current to the laser. For optimum performance, the frequency sweep should be as linear as possible, but due to thermal effects, a linear current ramping seldom results in a linear frequency ramping. At lower modulation frequencies, below 1 MHz, the temperature behaviour of the laser has a large influence on the frequency behaviour. To model the frequency behaviour we hence started by investigating the thermal behaviour. This work is presented in paper four. The goal is to obtain a model for the frequency behaviour with respect to changes in the laser drive current. In paper five, this model has been tweaked a bit and is used to obtain modulation currents that gives a linear frequency ramping. / <p>Godkänd; 2004; 20061025 (haneit)</p>

This thesis concerns localization and control of mobile robots using range measurements from optronic sensors, in particular scanning time-of-flight lasers. The thesis covers the localization algorithms, on-line sensor calibration and tele-operation for semi-autonomous control of mobile robots. A real-world application of an autonomous mobile robot equipped with an arm for surface finishing operations is also developed. The Range Weighted Hough/Radon transform is introduced for robust detection of walls and extraction of geometric parameters. Thus a robot can automatically create a map of its environment and update it using an extended Kalman filter. The required association of observations with the map features uses a Bayesian classifier. New walls are added to the map as they are observed and classified as new. Navigation is performed with typical fluctuations of 1 cm and 1 degree (standard deviation) at speeds of 0.5 m/s. The navigation is robust even in cluttered environments and with several persons moving around. Sheet-of-light range cameras have also been tested for mobile robot navigation. A calibration algorithm for simultaneous calibration and localization integrates the calibration into the localization system. The only absolute reference needed by the calibration algorithm is the relative motion of the robot. The resulting system performs calibration during normal operation without lowering the localization performance. The algorithms above were applied to two applications: - A mobile robot capable of autonomously spray-plastering the walls and ceiling of a room. The prototype was successfully tested at construction sites. - A semi-autonomous robot tele-operated using tele-commands. The tele- commands include navigation along corridors, through open doors, following walking persons and automatic map generation of the remote site. / <p>Godkänd; 1998; 20061122 (haneit)</p>

This thesis presents contributions to work for better methodologies for addressing Electromagnetic Compatibility (EMC) issues. In particular measurement methods are reviewed and devised for acquiring data on barriers used for EMC. Such data is used for characterization, modeling and model verification of barriers. The concept of EMC barriers is introduced as a general view of filter components, separation of conductors (crosstalk problems), electromagnetic shielding etc. The aim is to find methodologies to help engineers to identify EMC problems and to include the management of EMC in the design of a electrical circuit in a practical and effective manner. Methodologies for generation of EMC barrier modeling techniques have been developed. This work have resulted in design tools for electronic design engineers to include EMC considerations at an early design stage of a new product. Problems with existing barrier characterizing measurement methods have been identified. By comparison of far field and near field shielding effectiveness measurement methods, data for shielding thermoplastic materials was acquired. Considering the purpose of studied shielding materials in an application the usefulness of the far field shielding effectiveness measurement method is questioned. EMC barrier measurement methodologies of interest in this thesis includes shielding effectiveness measurements, transfer impedance measurements, scattering parameter measurements, measurements of material permittivity and permeability and near field scanning techniques for analysis of current distributions. / <p>Godkänd; 2004; 20061029 (ysko)</p>

Power consumption is an important design constraint for circuits used in portable devices. In this thesis an analytic approach to minimize the power dissipation of Binary Decision Diagram (BDD) mapped digital circuits is presented. Our synthesis approach combines logic minimization, low power optimization and mapping to a Pass Transistor Logic (PTL) multiplexor circuit. The low power optimization procedure utilizes statistical properties for the input signals to reduce the estimated power dissipation. For BDD mapped circuits, the variable order of the underlying BDD heavily affects both the number of nodes (size) and the switching activity for each node. In turn, static power dissipation increases with circuit size, while dynamic power dissipation increases with switching activity and capacitive load. The capacitive load for a mapped node is modeled as the number of incoming edges. The cost model based on a PTL mapping is applied in a heuristic optimization procedure iteratively improving the overall cost by local variable exchanges. Three novel BDD based approximative methods for switching activity estimation are introduced. The first method assumes no temporal signal correlation. The second method assumes temporal correlation on the input signals only. Both of these simplifications allows the low power optimization to be carried out exclusively by local BDD operations. The third method accounts also for temporal correlation of internal signals in the circuit. The latter approach is refined at the cost of computation complexity, whereas the optimization is no longer local. The mapped circuits have in simulation (using a commercially available process model) shown reduced power dissipation characteristic. Furthermore a technique for extracting signal properties from synchronous Finite State Machine (FSM) implementations is described. All computations are performed using decision diagram techniques. As an application of this method, the extracted information is utilized in the presented low power synthesis procedure. Experimental results on MCNC (combinational) and ISCAS89 (sequential) benchmarks show significant reductions of the estimated power dissipation. The ISCAS89 results how an average reduction of 40 percent and up-to 90 percent on individual benchmarks. / <p>Godkänd; 2001; 20070313 (ysko)</p>

This thesis is on mobile robot navigation using range sensors. The two sensors types used are time-of-flight lasers and sheet-of-light range cameras, both giving densely spaced range measurements. Map generation and navi gation are achieved in indoor environments, even when there are lots of disturbing objects giving cluttered range measurements. The walls are observed in the range scans using the Range Weighted Hough Transform, (RWHT) and the estimates of the map and the robot position are maintained during motion using Extended Kalman Filtering (EKF). The calibration of sensor parameters during operation uses the relative motion given by the incremental encoders on the wheels as the absolute calibration reference. Matching of observations to previous estimates are performed using a deci sion directed classifier. The algorithms can be used both to build a map, or during navigation using an existing map. The algorithms have been verified in several experiment with the range sensors onboard actual mobile robots. The size of a large room was estimated with a standard deviation of 1 cm. The robot navigates autonomously through an open door detected by the laser. The accuracy during passage was 1 cm at a speed of 0.5 m/s. The trajectory is perpendicular to the wall within 0.5 degrees. In one experiment the robot created a map of its environment while moving at speeds from 0.5 to 1 m/s. The standard deviation in the esti mated map dimensions for a series of tests were 1 to 2 cm and 1 degree. The navigation system has also been used for an autonomous plastering robot with automatic planning to include doors and windows. The navigation is very robust against both outliers in the measurements and disturbing objects. It is not seriously disturbed even when most of the walls are occluded and there are several persons moving around during operation.

The subject of Electromagnetic Compatibility (EMC) is introduced. A short overview of the regulatory EMC requirements in Europe and in the United States is presented. An explanation is given why it is important for people in the electronics business to understand the need for EMC regulations. Electromagnetic shielding is a often used as an electromagnetic barrier for attenuation of disturbances from radiating sources. An orientation over the concept of electromagnetic barriers is presented. Ways to characterize barriers are presented and measurement methods are reviewed. Results from transfer impedance measurements show that conductive gaskets made of tin coated stainless steel, can give as good shielding performance as gaskets made of beryllium copper in the entire frequency interval of the investigation. The results show that the difference in shielding performance with gaskets made of tin coated stainless steel and of beryllium copper can be insignificant compared to the influence of a very small change in contact pressure. The difference between gaskets with and without tin coating is small with beryllium copper as base material. With stainless steel as base material the difference is about 10dB at 2MHz and less at higher frequencies. A method to describe electromagnetic barriers such as filters, shielded cables and connectors etc. with circuits consisting of linear discrete components is presented. By comparing a barrier with a multi-conductor transmission line a lumped circuit can be constructed where component values are designated by the per-unit length transmission line parameters. For barriers that cannot be viewed as transmission lines a method for determining equivalent circuits outgoing from measured S-parameters has been developed. Different measurement fixtures were constructed in order to obtain accurate S-parameter values. Derived models have been used in SPICE simulations and validated by comparison with measurements. The current distributions on the surface of a printed log periodic dipole antenna (LPDA) have been investigated. A position scanned magnetic field probe was used to obtain values of the magnitude and phase of the magnetic field at each point of the scan. From the measurements the time variant instantaneous values of the magnetic field and the instantaneous currents on the LPDA were derived. The wave nature of the current distribution can be readily observed and problems with the design such as standing waves on the feeder lines are highlighted. Measured current distributions are compared with predicted distributions obtained from Method of Moments (MOM) analysis of the LPDA structure. Measured and predicted far field radiation patterns are also compared. / <p>Godkänd; 2000; 20070318 (ysko)</p>