Rymd-, geo- och miljövetenskap (SEE) // Space, Earth and Environment (SEE)
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Studying at the Department of Space, Earth and Environment at Chalmers
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Browsar Rymd-, geo- och miljövetenskap (SEE) // Space, Earth and Environment (SEE) efter Program "Electric power engineering (MPEPO), MSc"
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- PostAccuracy Evaluation of Power System State Estimation - An evaluative study of the accuracy of state estimation with application to parameter estimation(2016) Hagmar, Hannes; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe following report examines the impact that parameter and model errors have on the result of the power system state estimation. Furthermore, the feasibility of increasing the accuracy of the state estimation is examined by introducing parameter estimation within the ordinary estimation model. Model errors due to unbalanced grid conditions are found to have a large impact on the phase values, but an almost negligible impact on the averaged values that are commonly used as input to the state estimation model. Parameter errors affect the accuracy of the state estimation in various extents, and errors in the line susceptance are found to generally cause the largest errors. The level of measurement redundancy is significant to the result, and reduced measurement redundancy will in general increase the estimation errors due to parameter errors. Furthermore, undesirable combinations of parameter errors within a larger network are also found to increase the estimation errors significantly. In order to estimate the magnitude of estimation errors caused by parameter errors, each grid configuration and power flow state would have to be examined individually. Parameter estimation was found to be highly accurate in estimating the line susceptance for most levels of reasonable measurement errors. However, the line conductance and shunt susceptance were found to be significantly harder to estimate and even small measurement errors resulted in poor estimations. Using parameter estimation for the line susceptance under conditions of relatively low levels of measurement errors was found to significantly decrease the errors in the state estimation. Finally, an alternative method of estimating the line conductance was examined. This estimation was found to be more resilient to errors in the voltage measurement, but was still sensitive to errors in the power flow measurement devices.
- PostActive Fuse System, Improvements in the fuse system in commercial vehicles(2008) Sjöberg, Adam; Steen, David; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn this master thesis work the possibilities with an active fuse system has been investigated, with the background in the increased number of electric loads in commercial vehicles. Different design possibilities have be considered together with implementation alternatives. A prototype was built for testing turn-o_ times of an analogue switch circuit design. Experiments were also carried out on a power distribution unit, constructed by Volvo 3P in 2003 hereinafter referred to as the PDU, which utilizes a digital switch circuit design. The results shows that a analogue switch design is to prefer for best protection, with turn-o_ times down to 0,5_s. The digital switch design was slower in all tests. The power losses for a traditional blow out fuse were compared to the prototype showing an equal power loss up to 10A and a greater power loss in the prototype afterward. A mix of an analogue and digital circuitry design was thought as the best alternative. This design will have rapid response times and flexible fuse levels together with diagnostic features. The implementation of the active fuse system in a commercial vehicle has to be evaluated with respect to case specific needs.
- PostActive Power Filters for Nonlinear Load Applications(2015) Bajra, Mernis; Tell, Victor; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis report is about the development of an active power filter used for filtering nonlinear current. The source of the nonlinear current is a fan system consisting of two parallel connected BLDC motors. A bi-directional power converter is designed analytically which is verified by simulations and a practical prototype. The outcome of the report is a simulation that is used to verify the performance of the active power filter and a cost and size analysis to compare a conventional passive filter used today with the active filter designed for this application. The final result was an active power filter that was 6:8 times more expensive in material cost and the same size as the conventional passive filter.
- PostAn alternative Volt/VAR management scheme for Active Distribution Grids(2014) Benito, Jesus Garcia; Arija, Rocio Hoya; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentLarger penetration of distributed generation and active loads is expected in the near fu- ture. These new loads have brought up new challenges to the electrical networks as well as new possible opportunities. The possibility of using these new elements to regulate and control the voltage is considered as the future scenario. Therefore this thesis, develops a coordination between the most common elements in the networks (capacitor banks, STATCOMs, OLTCs/VRs and DGs), in order to study their interaction and how they together could manage the voltage level. In addition, EV charging station integration has been also evaluated. Considering this scenario, several simulations varying different parameters such as time delay or bandwidth are carried out. Also the concept line compensation is taken into consideration in the networks analysed. Through all the simulations accomplished it is proved that a coordination is necessary between all the elements. Later on, a discussion about how each configuration affects the network complete this thesis. Besides, the simulated scenarios show that DGs and EVs can contribute to voltage regulation in an efficient way.
- PostAnalys av högfrekvensstörningar och elnätskommunikation i distributionsnät(2009) Påhlsson, Henrik; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe use of Power Line Communication, PLC, as a communication solution for Automated Meter Reading, AMR, is popular by utilities in Sweden and other parts of the world due to demands of accurate and fast meter reading. However the use of the electrical grid as a communication medium is complex and sometimes problematic. This report handles some of the issues and problems that are important to understand when using the grid as a communications medium. Focus is mainly on investigating high frequency distortion in the Kristianstad power grid own by C4energi caused by a frequency converter. Measurements on site are done to investigate signal damping in the grid, different configurations for the frequency converter and signal strength of the PLC-system. The PLC-system that is used is an Echelon-system communicating on 75 kHz and 86 kHz. The results in this report can be applied to other systems communicating different frequencies in the CENELEC A-band. The results from the measurements show that the communication fails due to the frequency converter and that the noise level is too high. Tests done during the measurements show how some of the high frequency noise can be avoided by changing settings in the converter but this is not enough. An important result was that the problem can be to solved by changing the position for the PLC-concentrator further away from the converter another solution can be to add a filter to the frequency converter. COMSOL Simulations on connection cables are also done to analyze resistance due to skin effect at high frequency. The simulations are done to understand why stranded cables often works better then single stranded cables. The results from the simulations show clearly that it is better to use stranded cables then single stranded cables. The report is written in Swedish.
- PostAnalysis and Design of Multioutput Flyback Converter - A study For A Lab Upgrade on the Flyback converter assignment at Chalmers Elteknik(2016) Ahmed, Abdi; Kosar, Abdullahi; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis work is done in order to improve the existing lab in Chalmers for the study of Power Electronics. Assignments for the practical lab and computer simulation sessions of a yback converter have been reviewed and analysed. The analyses of the existing assignments shows that the circuit board used in the lab today is a multi purpose circuit and it is difficult to relate a equivalent circuit diagram of a yback converter. Furthermore, there is no relationship between the circuit and the simulation model. A simulation was done using PSpice and a prototype PCB board built with the aim of showing some of these interesting concepts in the course. The main suggestions are related to the simplification of the circuits so that immediate correlation can be made between the circuits being shown in the class and the PCB used in the lab. The simulation model can be used in the simulation session of the course. The new simulation model and the circuit board can demonstrate the role of the inductor in the yback transformer by varying its value. Another area of improvement would be on demonstrating of magnetics theory. There is no simulation or practical assignments about magnetics in the course today. Understanding the relation between the current ripple and magnetic ux is in the scope of the courses. It is also important to understand how high frequency affects the losses and the size of the core. Two transformers are designed in order to investigate these relationships. The result of the transformer design shows that a new assignment that can demonstrate how magnetic core behaves can be introduced.
- PostAnalysis of Force and Torque Harmonic Spectrum in an Induction Machine for Automotive NVH Purposes(2016) Garcia De Madinabeita, Inigo; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentCurrently, hybrid and fully electric vehicles are being developed in a great variety regarding topology, power and range. This requires a new methodology for NVH (Noise Vibration and Harshness) evaluation of potential problems early in the design phase. This methodology requires reliable simulation approaches for hybrid and electric drivetrains, concerning the whole automobile, and not limited to the electric machine. One of the main NVH sources is the electric drive, as the excitations in the electric motor, caused by the electromagnetic forces, excite its housing and that of the drivetrain, causing a structure-borne vibration. Torque ripple generates excitations in the shaft and gearbox, which are then transmitted to the whole drivetrain housing. It is seen that a low-torque-ripple design aim might not be enough for reducing the NVH issues, and specially radiated noise, in a fully electric or hybrid drivetrain, since Maxwell forces experienced by the stator can be present in frequencies where there is no torque harmonic. Since analytic models cannot represent accurately the non-linearity of the magnetic field and the detailed design of the stator and rotor geometries, the FEM (Finite Element Method) simulations are unavoidable to study the electrical motors in detail. A FEM tool is used in this project to design and assess the performance of an induction machine, focusing on the effect that driving profile and control unit cause on the electric drive, magnetic field and forces in the system for different driving conditions. The produced forces are evaluated to assess the noise and vibration in the system. It is seen that FEM results correlate with what theory predicts, as force harmonic orders are 0, 2 and n ± 1, where n is any magnetic flux density harmonic. The center tooth point only experiences radial forces, whereas the corner points have tangential stress as well, due to saturation. An example of 15μm dynamic eccentricity illustrates alterations force and torque harmonic magnitudes due to shaft assembly eccentricity or shaft bending caused by bearing clearance and/or stiffer gear contact vibration.
- PostAnalysis of the Output Impedance from Switched DC/DC Converters(2014) Hansson, Gustav; uussalu, marcus; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe PuLS is a product used at Ericsson AB for performance testing of switched DC/DC converters by applying pulse shaped current waveforms. In this thesis, the PuLS is redesigned to be able to measure output impedance of switched DC/DC converters by drawing a sinusoidally shaped current while measuring the output voltage ripple. Existing measurement methods are investigated, the theoretical output impedance of a buck converter is calculated and simulations of two buck converters are implemented. Output impedance measurements of two buck converters are done using the redesigned PuLS. The results are compared with an existing impedance measurement method as well as simulations of the buck converters. It is shown that the PuLS is able to measure the output impedance of switched DC/DC converters at frequencies up to 80 kHz with results close to both the simulation and the previously made measurements. At frequencies greater than 80 kHz, the PuLS measurements shows a greater impedance compared to the simulation and the previously made measurements. When measuring passive components it is shown that the PuLS can measure impedance in the frequency range of 0.5-500 kHz.
- PostAncillary Service for Frequency Support - Design of a Battery Storage Based Ancillary Service for Frequency Support in the Nordic Power System(2017) Juárez Moreno, Omar; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn recent years, the frequency in the Nordic power system has been experiencing an increasing number of minutes outside the normal frequency band of ±100mHz determined by ENTSO-E. It could be argued, that this trend is expected to continue, specially with the current tendency to replace conventional generation with intermittent, renewable energy sources that are decoupled from the grid. This in turn, has given rise to new opportunities in the Ancillary Service (AS) market, that can take advantage of network connected devices such as Energy Storage Systems (ESS), to increase the grid’s flexibility. This thesis deals with the design and implementation of a Battery Energy Storage System (BESS) that aims to provide the grid with frequency support in the frame of the Nordic reserve product Frequency Containment Reserve for Disturbance operation (FCR-D). The proposed Ancillary Service (AS) consists of a dynamic battery model that is controlled with an energy-curtailment strategy dependant on its State of Charge (SOC). The control system for the Voltage Source Converter (VSC) that interfaces the battery with the grid is conformed of a two-degree-of-freedom current controller implemented in the synchronous reference frame that receives the active and reactive power references from the outer frequency and voltage controllers, respectively. The proposed AS was implemented using the simulation tool DIgSILENT Power- Factory. The models were tested in CIGRÉ’s Nordic32A bus system with three different study cases: the loss of a generating unit that caused the frequency to drop below 49 Hz, where it was proven that a 50MW, 300MWh BESS could reduce the Nadir enough to avoid the activation of more drastic frequency-controlled actions. The second scenario explored the effect of converter rating versus battery capacity when the BESS is providing FCR-D, where it was concluded that the BESS capacity is not the limiting factor for providing the service but rather the converter’s rating. Finally, the impact of the BESS was studied in a weaker grid where conventional generation was replaced with static generation. Here, it was shown that the proposed AS effect was more noticeable in the weaker grid, where the same BESS was able to reduce the Nadir by an additional 8.11% for the same frequency event, compared to the base case where no conventional generation was phased-out.
- PostBalancing Asymmetrical Load Using a Static Var Compensator(2014) Alsulami, Amar; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn practical power systems, it is normally impossible to maintain perfect balance or symmetry in phase voltages and currents. The diversity of the load, such as single phase, arc furnaces and railway, enhances the amount of unbalance or negative sequence components. Alongside asymmetrical load, further increase in negative sequence components is introduced due to the network inherent asymmetry i.e. untransposed transmission. Thus, they are usually excessive and exceeds standards at weak nodes in the network. Utilities and customers have to comply certain code agreements to limit the degree of negative sequence components in the network. This is because that negative sequence components cause deterioration to the network equipments. For instance, higher loss, torque oscillation, speed reduction and excessive rotor heat are undesirable obstacles to rotating machines. Asymmetrical load compensator can be based on passive elements, i.e. inductors and capacitors such as a Static Var Compensator (SVC), or a Voltage Source Converter (VSC) such as a Static Synchronous Compensator (STATCOM). The utilization of the negative sequence controller, an SVC or a STATCOM provides, gains a significant interest to most utilities around the globe. The compensators basically inject a different capacitive or inductive negative sequence current that has an opposite phase of the load negative sequence current. As a result, the network see symmetrical load and phase voltages and currents are balanced without exchanging active power between the network and the compensator. The thesis investigates the benefits of the SVC negative sequence controller to a network with a detailed description about the SVC characteristics and control components. The thesis also presents unbalance assessment methods implemented in practical networks during the planning stage. Moreover, drawbacks of negative sequence components to network apparatus i.e. rotating machines and transmission lines are summarized. The analysis is carried out using PSCAD for a simple network representation and IEEE 14 bus system. The result illustrates that the SVC allows utilities to balance asymmetrical loads to mitigate negative sequence components. The SVC response to balance asymmetrical load depends on load type, network strength and sources of unbalance. The SVC exhibits a very fast response to reduce the negative sequence components in extreme cases of unbalance such as asymmetrical short circuit. The SVC in general can mitigate negative sequence components caused by a sources connected in the same bus which means that the SVC provides local balancing only. Besides the negative sequence controller, the SVC enable a power factor correction by compensating for the reactive components of the load positive sequence current.
- PostCable Concept Selection for 600V Hybrid Heavy Duty Vehicle from an EMC Perspective(2007) Sundin, Michaela; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIt is important to minimize the emissions of electromagnetic fields to assure that the electrical equipment work properly. This thesis examines how to minimize electromagnetic fields with different cable types and placing of the cables. The cables are intended to be used in a hybrid heavy duty vehicle, for 600 V DC. Three different cable types was examined, one unshielded type, one shielded type and one type with two conductors with a common shield. The emissions of electric field from the cables were measured separately from the magnetic field emissions. The results of the measurements show that the electric field emissions are minimized by a shielded cable. The unshielded cables have a difference of 8 dBμV to the shielded cables at 0.15 MHz, and at 0.60 MHz is the difference increased to 18 dBμV. The magnetic field emissions are not affected by the cable type it is only affected by the placing of the cables. At 10 A is the magnetic field 28 μT when the cables are placed with 5 cm between them. When the cables have no distance between them the magnetic field is cancelled. Both the electric field and the magnetic field are minimized by a placing of the cables with no distance between them. If the cables are placed next to a grounded girder the electric field emissions is lowered with about 5 dBμV. If the girder is made of a material which conducts magnetic flux the magnetic field emissions is increased. The girder prevents the electromagnetic field to spread in four directions; it limits the emissions to three dimensions.
- PostCalculation method for powering a tramway network(2012) Edstrand, Jakob; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and Environment
- PostCell Level Power Electronics for Better Battery Management System(2016) Gorantla Narayana Murthy, Sri Vishnu; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn this master thesis, a comparison between two types of battery packs for Electric Vehicles (EVs) is made. Pack 1 is a conventional cells battery pack where all the cells are connected in series. Pack 2 is an autonomous cells battery pack whose cells are equipped with individual micro DC-DC converters. Pack 1 is compared against Pack 2 for energy output (kWh), charging characteristics and ageing. The comparison is performed for two different driving profiles the New European Drive Cycle (NEDC) and a tested and modelled use case. The DC-DC converter makes Pack 2 the autonomous cells battery pack even though the cells are the same. The DC-DC converter ensures load management on individual cell level. Load balancing leads to several advantages in the energy output, charging characteristics, slower ageing rate and susceptibility to capacity spread of the cells forming the battery pack. The battery pack performances are analysed and compared to show that the performance of Pack 2 is better for both NEDC and use case driving profiles. A final sensitivity analysis comparing the battery pack ageing is performed for various use cases thus, giving the holistic view of the advantages in the technology used.
- PostCharacterisation and Control of a Permanent Magnet Synchronous Machine during Open Circuit Fault(2015) Ahlqvist, Erik; Nilsved, Jonatan; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis describes a complete setup of an electric driveline consisting of a permanent magnet synchronous machine, PMSM, converter and a control system. In order to model the system, the parameters of the selected machine parameters needed to be characterised. Comparison between the simulations and tests confirmed that the parametrisation was accurate and the system could be operated in both motor and generator mode. Moreover, simulations of an open circuit fault was performed and a resonant controller implemented to reduce the torque ripple which occurred due to the fault. Similar tests was performed in the lab-setup, which confirmed that the machine was able to continue to operate during an open circuit fault using only a PI-controller if the wye node current is controlled. The same resonant controller was implemented in the control system in the lab, however, due to high frequency noise in the current measurements, it became unstable. As a replacement, a look-up table using the output from the simulated resonant controller was implemented which lowered the torque ripple significantly. From this it is concluded that the resonant controller shows very good performance in simulations and would theoretically do so in lab implementation. However, a real implementation is very hard to achieve, even though the look-up table version did lower the torque ripple significantly.
- PostCommutation Failure Prevention for HVDC Improvement in algorithm for commutation failure prevention in LCC HVDC(2016) Oketch, Innocent; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentLine commutated HVDC systems are widely used due to their high power ratings. However, one of the disadvantages of such HVDC systems is the high risk of commutation failures when AC disturbances arise. These failures normally develop in the inverter station. When failed commutation occurs, the LCC HVDC system is greatly disturbed resulting in loss of power transmission. Moreover, the rapid increase in the direct current during unsuccessful commutation results in additional stresses on the thyristor valves. In an attempt to reduce the probability of unsuccessful commutation, a commutation failure prevention function is added to the HVDC system controls. When an AC system disturbance is detected, this function is activated with the aim of altering the firing order at the inverter station. Since the angle contribution from the function is independent of the minimum inverter extinction angle, this approach possesses limitations under certain AC faults. In this thesis, a commutation failure prevention function based on voltage-time area contribution was designed and implemented. Simulation results show that both the proposed and existing functions are equally ineffective in mitigating the first commutation failures when three phase faults are applied. However, the proposed function is more effective in mitigating the first commutation failure when single phase faults are applied compared to the existing function. In 17% of the investigated cases, improvements were registered when the proposed function was utilised. Moreover, in 25% of the cases when three phase faults were applied, the proposed function reduced the occurrence of multi-valve commutation failures.
- PostComparison of control approaches for permanent magnet motors(2013) Klintberg, Emil; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis deals with comparing control techniques for two existing permanent magnet motors with harmonics in their back emfs. To do so, ideal models of a Brushless DC (BLDC) motor and a Permanent Magnet Synchronous Motor (PMSM) have been modified to describe the behavior of two existing permanent magnet motors. Comparisons of the motor constant and the relative torque ripple are performed when the motors are controlled with Field Oriented Control (FOC) as well as with traditional BLDC control. A novel control scheme aiming at controlling the currents to have the same shape as the back emfs are presented. Simulations are performed to show how this method affects the motor constant and relative torque ripple. Torque ripple due to phase commutation in BLDC motors is discussed and a version of lead angle adjustment is implemented to reduce this problem. Even though an ideal BLDC motor has a higher motor constant than an ideal PMSM, simulations showed that a higher motor constant (almost 5% and about 2% for the two motors respectively) can be obtained by utilizing FOC compared to traditional BLDC control. A lower relative torque ripple (almost 86% and almost 44% for the two motors respectively) was also obtained for FOC compared to traditional BLDC control. A higher average torque per peak current was, however, obtained with traditional BLDC control. These results are valid for both motors. Simulations showed that it is possible to achieve a higher motor constant, compared to FOC and traditional BLDC control, by controlling the currents to have the same shape as the back emfs. The relative torque ripple was however increased by using this method. It is also shown, by an example, that the motor constant can be increased by implementing lead angle adjustment.
- PostComparison of Methods for Evaluating Stability Performance of Power System Stabilizers(2017) Hiramsson, Joakim; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentTwo methods are commonly used by transmission system operators to evaluate the stability performance of a power system stabilizer (PSS). However, cases have been encountered where the two evaluation methods do not agree. This is problematic since it may affect the stability of the power system. In this study it is investigated and suggested which of two evaluation methods that is better to use when evaluating the stability performance of a PSS. This study is based on dynamic simulations of the Nordic32-system where PSS2Bs are placed at different synchronous machines that are located at different buses in the power system; then, the impact of tuning the PSS2Bs according to the two evaluation methods is analyzed by the traditional method of eigenvalue analysis. The eigenvalue analysis shows that tuning of the PSS2Bs according to the evaluation method used by Statnett results in higher increases in the damping ratios of the complex eigenvalues with imaginary parts in the range of 0.6 - 6.3 rad/s compared with tuning of the PSS2Bs according to the evaluation method used by National Grid. Therefore, for the specific cases simulated, it is suggested that the evaluation method used by Statnett is better to use for purposes of evaluating the stability performance of a PSS.
- PostConstruction of a low-ripple inverter with accurate phase control for calibration of measurement equipment(2014) Einarsson, Adam; Vand, Ali Asgari; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentFor the design of an electric power system, knowledge of the parameters of all the components is essential. Especially the transformers are an important part of this. It is therefore important that the measurement equipment for determining these values is accurate. In no-load operation, the transformer mainly consumes reactive power. A small error in the measurement of the power angle therefore gives a large error in the active power calculation. The Technical Research Institute of Sweden, SP, performs calibrations of these measurement systems. Calibrations are done by measuring a reference voltage and generating a current in a secondary circuit with a controllable phase shift. The voltage and current make up a virtual power and are measured by the reference instrument and by the equipment to be calibrated. This thesis describes the work of constructing a single-phase full-bridge converter for inverter operation with accurate phase control of the current in the secondary circuit relative to the sinusoidal reference voltage. A CompactRIO™ system from National Instruments is used to control the converter through pulse-width modulation (PWM). An analogueto- digital converter (ADC) module is used to sample the reference signal and a digital I/O module outputs the PWM signals. A phase-locked loop (PLL) algorithm estimates the phase of the sampled reference voltage to use in the generation of the PWM signals. Three different PLLs have been implemented with LabVIEW™ code on the FPGA chip of the CompactRIO™ system. The three PLLs are the inverse Park PLL (IP-PLL) based on the synchronous reference frame, the enhanced PLL (E-PLL) based on the gradient descent method and the KF-PLL based on the Kalman filter. Both the E-PLL and the KF-PLL are also based on models for estimating specific signal components. With the basic configurations, the IP-PLL shows superior performance in simulations with dc offset and low-order harmonic in the input signal. This is due to its low-pass filters. While the standard deviation in the phase error of the IP-PLL was 50 rad it was 350 rad for the E-PLL and 570 rad for the KF-PLL with a dc offset at 1.8 % of the fundamental amplitude in the input signal. With a third harmonic at 10 % of the fundamental amplitude, the standard deviations of the phase errors were 50.3 rad, 776 rad and 889 rad for the IP-PLL, the E-PLL and the KF-PLL respectively. By extending the E-PLL and the KF-PLL to include estimation of dc-offset and harmonics, these steady-state errors are completely eliminated. However, especially the KF-PLL but also the E-PLL, is much more complex and harder to tune than the IP-PLL. When implemented on CompactRIO™ the KF-PLL including estimation of dc offset got the best results with a standard deviation in the phase error of 5.1 rad compared to 49.2 rad for the IP-PLL with minimized cut-off frequency iii of the low-pass filters for a dc offset of 0.41 % of the fundamental amplitude in the input signal. It is shown that the phase error of the complete system can be kept below a standard deviation of 600 rad, with a stable reference voltage. The pattern of the phase error however has an oscillatory shape with a frequency of about 0.12 Hz. This is thought to originate from a drift in the clock of the ADC module relative to the clock of the FPGA in the CompactRIO™ system. This must be further investigated. Additionally, the amplitude accuracy of the fundamental frequency is found to have a standard deviation of about 63 ppm, with a dc-source specified to be accurate to 50 ppm.
- PostConstruction of an inductive charging station(2014) Ekman, Christian; Petersson, Carl; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentAn inductive charging station has been designed, constructed and is operational. It is able to transfer roughly 500W to the receiving side with a peak efficiency of approximately 85%. The system was fed with a voltage between 24 to 63V from a Direct Current (dc) supply. Then, it converted the dc voltage to a high frequency Alternating Current (ac) voltage. The ac voltage was fed to the coils which transferred the energy to the receiving side and to the resonance circuit. The conversion from ac to dc was made with the body diodes in the transistors.
- PostControl of a subsea PMSM with a very long feeding cable using a top-side converter – design and performance evaluation(2016) Tang, Junfei; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn oil and gas extraction applications, Permanent Magnet Synchronous Motors (PMSMs) are becoming a more preferred choice to drive Electric Submersible Pumps in order to achieve a higher efficiency than Induction Motors (IMs). In the drive system, a subsea PMSM is fed from a top-side Variable Speed Drive (VSD) through a transmission system including a step-up transformer and a long feeding cable. In this work, both the series impedance and the shunt admittance of the transmission system are taken into consideration. Sensorless control of such a subsea PMSM is implemented and evaluated in this thesis work. The sensorless control is realized by the combination of the Static Compensated Voltage Model (SCVM) method and the High Frequency Injection (HFI) method. An equivalent IM model current controller is developed to deal with the transformer shunt branch and a static estimator is implemented to estimate the PMSM voltage and current. The developed controller can successfully start and accelerate the PMSM up to 6000 rev/min within 5 s and the efficiency during steady state operation achieves 91.65% excluding the iron-core loss of the PMSM. The steady state angle estimation error with perfect parameters is -0.8506° with peak dynamic angle estimation errors at +0.7063° and -4.7335° respectively. A ±10% parameter error is acceptable for a successful PMSM start-up except for a -10% PMSM magnet flux linkage error which generates a too large angle estimation error during the start-up and leads to a start-up failure. In conclusion, the field-oriented sensorless control of a PMSM through a transmission system is possible. A five-level inverter needs to be applied to reduce the harmonic contents to realize a successful start-up of the PMSM. It is also suggested that the accuracy of the PMSM magnet flux linkage and the stator inductance are of essential importance.