Special Power Electronics Converters and Machine Drives with Wide Band-Gap Devices

Power electronic converters play a key role in power generation, storage, and consumption. The major portion of power losses in the converters is dissipated in the semiconductor switching devices. In recent years, new power semiconductors based on wide band-gap (WBG) devices have been increasingly developed and employed in terms of promising merits including the lower on-state resistance, lower turn-on/off energy, higher capable switching frequency, higher temperature tolerance than conventional Si devices. However, WBG devices also brought new challenges including lower fault tolerance, higher system cost, gate driver challenges, and high dv/dt and resulting increased bearing current in electric machines. This work first proposed a hybrid Si IGBTs + SiC MOSFETs five-level transistor clamped H-bridge (TCHB) inverter which required significantly fewer number of semiconductor switches and fewer isolated DC sources than the conventional cascaded H-bridge inverter. As a result, system cost was largely reduced considering the high price of WBG devices in the present market. The semiconductor switches operated at carrier frequency were configured as Silicon Carbide (SiC) devices to improve the inverter efficiency, while the switches operated at fundamental output frequency (i.e., grid frequency) were constituted by Silicon (Si) IGBT devices. Different modulation strategies and control methods were developed and compared. In other words, this proposed SiC+Si hybrid TCHB inverter provided a solution to ride through a load short-circuit fault. Another special power electronic, multiport converter, was designed for EV charging station integrated with PV power generation and battery energy storage system. The control scheme for different charging modes was carefully developed to improve stabilization including power gap balancing, peak shaving, and valley filling, and voltage sag compensation. As a result, the influence on the power grid was reduced due to the matching between daily charging demand and adequate daytime PV generation. For special machine drives, such as slotless and coreless machines with low inductance, low core losses, typical drive implementations using conventional silicon-based devices are performance limited and also produce large current and torque ripples. In this research, WBG devices were employed to increase inverter switching frequency, reduce current ripple, reduce filter size, and as a result reduce drive system cost. Two inverter drive configurations were proposed and implemented with WBG devices in order to mitigate such issues for 2-phase very low inductance machines. Two inverter topologies, i.e., a dual H-bridge inverter with maximum redundancy and survivability and a 3-leg inverter for reduced cost, were considered. Simulation and experimental results validated the drive configurations in this dissertation. An integrated AC/AC converter was developed for 2-phase motor drives. Additionally, the proposed integrated AC/AC converter was systematically compared with commonly used topologies including AC/DC/AC converter and matrix converters, in terms of the output voltage/current capability, total harmonics distortion (THD), and system cost. Furthermore, closed-loop speed controllers were developed for the three topologies, and the maximum operating range and output phase currents were investigated. The proposed integrated AC/AC converter with a single-phase input and a 2-phase output reduced the switch count to six and resulting in minimized system cost and size for low power applications. In contrast, AC/DC/AC pulse width modulation (PWM) converters contained twelve active power semiconductor switches and a common DC link. Furthermore, a modulation scheme and filters for the proposed converter were developed and modeled in detail. For the significantly increased bearing current caused by the transition from Si devices to WBG devices, advanced modeling and analysis approach was proposed by using coupled field-circuit electromagnetic finite element analysis (FEA) to model bearing voltage and current in electric machines, which took into account the influence of distributed winding conductors and frequency-dependent winding RL parameters. Possible bearing current issues in axial-flux machines, and possibilities of computation time reduction, were also discussed. Two experimental validation approaches were proposed: the time-domain analysis approach to accurately capture the time transient, the stationary testing approach to measure bearing capacitance without complex control development or loading condition limitations. In addition, two types of motors were employed for experimental validation: an inside-out N-type PMSM was used for rotating testing and stationary testing, and an N-type BLDC was used for stationary testing. Possible solutions for the increased CMV and bearing currents caused by the implementation of WGB devices were discussed and developed in simulation validation, including multi-carrier SPWM modulation and H-8 converter topology

Aktiivinen magneettilaakeri vaihtoreluktanssimoottorina

The goal of this work was to research the similarities between active magnetic bearings and switched reluctance motor and particularly research the chances for converting magnetic bearing into switched reluctance motor. In addition, ways to cope with the widely reported problems the motor type has were studied. The test environment consisted of test rig, previously used for testing control methods for magnetic bearing. In addition to this, MATLAB Simulink simulation models were built to help the designing of the test setup. The test setup had two alternative controllers, an original magnetic bearing controller, modified to work as a motor controller and a new CompactRIO-based controller that was used for comparing different speed control and commutation methods. New rotor designs were engineered to work with the prototype motor that used unmodified magnetic bearing stator. This setup was tested for obtaining the output torque and maximum speed of the motor together with the accuracy to follow set values. Test results of simulations and test setup were inside the error margins, showing the use of simulations beneficial in design process of this type of a motor. The tests revealed differences between the control methods, suggesting using the advanced angle controller and adjustable commutation angles.Työn tavoitteena oli tutkia yhteneväisyyksiä aktiivimagneettilaakerien ja vaihtoreluktanssimoottorin välillä. Tutkimus keskittyi erityisesti arvioimaan mahdollisuuksia muuntaa magneettilaakeri vaihtoreluktanssimoottoriksi. Lisäksi tutkittiin keinoja ratkaista ongelmia, joita tämän tyyppisessä sähkömoottorissa on raportoitu olevan. Testiympäristö koostui roottorikoelaitteesta, jota on aikaisemmin käytetty magneettilaakerin säätöjärjestelmän tutkimuksessa. Lisäksi rakennettiin MATLAB Simulink simulointimalli, jota käytettiin moottorin säätöjärjestelmän suunnittelun apuna. Testilaitteessa oli kaksi vaihtoehtoista säätöjärjestelmää; alkuperäinen magneettilaakerin ohjain muokattuna toimimaan moottorin ohjaimena sekä uusi CompactRIO -järjestelmään perustuva säätöjärjestelmä. Jälkimmäistä käytettiin erilaisten nopeus- ja kommutointitapojen vertailuun keskenään. Prototyyppimoottorin staattori oli sama, jota käytettiin magneettilaakerin kanssa. Roottori suunniteltiin sopimaan juuri tähän käyttötarkoitukseen. Tätä koelaitetta testattiin vääntömomentin ja maksiminopeuden selvittämiseksi. Lisäksi suoritettiin testejä, joissa tutkittiin kykyä seurata nopeuden asetusarvoa. Simuloimalla saadut tulokset olivat hyvin lähellä koelaitteella saatuja tuloksia osoittaen simuloinnin käytön olevan hyödyllistä tämän tyyppisen moottorin suunnittelussa. Säätömenetelmät suoriutuivat vaihtelevalla menestyksellä testeistä. Suositeltava säätömenetelmä oli edistyskulman säädin, joka käytti hyväkseen säädettäviä kommutointikulmia

Multirotor Design Optimization: The Mechatronic Approach

Doktorgradsavhandling ved Fakultet for teknologi og realfag, Universitetet i Agder, 2015Multirotors such as the more famous quadcopter have been a favoured research object the last years. It is widely used as a flying platform for the hobby enthusiasts, but recently also used more and more by the industry. The multirotor has complex dynamics and requires sensors and a control system in order to fly. To get the desired flight characteristics batteries, motor and the propeller have to be chosen wisely as different combinations create different properties. The usual design approach is to test different combinations of motors and propellers, and based on experience select components that will be closest to the desired flight properties. This thesis presents an optimization method that calculates what hardware to use in order to get closest to the demanded properties. The method will only select from a given database, hence not returning a diameter and pitch of a propeller that are not available. A wide range of criteria can be optimized, examples are dynamics of the motor/propeller, flight dynamics, flight time, payload etc. The optimization routine will also calculate if the better choice is a quadcopter with four propellers, a hexacopter with six or an octocopter with eight propellers. The optimization is not trivial due to the non-linear characteristics of the propeller. A lot of experimental work was done to test the response of the propeller, both for acceleration and deceleration. Theory and experimental work show that the thrust response of the propeller can be more or less equal if the electronic speed controller controls the motor in a special mode. This mode also makes the response of the motor faster than normal. The new design is tested with a new approach for attitude estimation, and a controller operating directly with the result of the estimator. Most of the multirotors use a microcontroller with limited resources as the control system, hence the attitude and controller were designed specifically without time consuming trigonometric functions such as the sine and cosine. Overall, the methods and results presented in this thesis will aid the engineer when designing a multirotor system consisting of control system, mechanical frame, battery, actuators and propellers

Development of Double-Sided Interior Permanent Magnet Flat Linear Brushless Motor and Its Control Using Linear Optical Potentiometer

A new 6/4 double-sided interior permanent-magnet (IPM) flat linear brushless motor (IPM-FLBM) and novel optical potentiometer mechanism for a linear motion-control system are presented in this dissertation. For this purpose, new detent-force-minimization methodologies for the IPMFLBM are studied on the basis of the superposition principle. The end-effect force is reduced by a new two-dimensional optimization using the step-shaped end frames. The cogging force is minimized through a destructive interference using the slot-phase shift between the upper and lower stators. A base model prototype with the detent force of only 1.5% of the maximum thrust force is developed using the electrical solid steel. Analytic modeling techniques of the base model prototype with slot-phase shift and alternate teeth windings are investigated. A variable winding function is newly developed to evaluate the inductances of the salient motor with the alternate teeth windings. The steady-state thrust force is modeled for this linear brushless AC (BLAC) motor. Their validities are demonstrated experimentally. The electromagnetic and steady-state performance analyses of a new prototype using a soft magnetic composite (SMC) material are also studied using a simplified nonlinear magnetic equivalent circuit (MEC) analysis. Its iron and copper losses are investigated in terms of the thermal limitation. The feasibility of the IPM-FLBM using the SMC material is demonstrated through the comparisons of the average steady-state thrust and ripple forces for these two prototype linear motors. A novel low-cost high-precision absolute displacement-sensing mechanism using optoelectronic components is developed. The working principle that is based on the change of the optical power that is reflected off the monotone-colored pattern track from a light emitting diode (LED) to a red-green-blue (RGB) photo diode (PD) is presented. The performance of the proposed optical potentiometer (OP) mechanism is verified by the bandwidth (BW) of 4.42 kHz and nonlinearity of 2.8% are achieved. A novel low-ripple 12-step current control scheme using a single current sensing resistor is developed using the six Hall-effect sensors for the force control of the IPMFLBM. Its performances are experimentally verified and compared with a conventional field-oriented control (FOC) scheme. In the end, the position-control loop, which includes the 12-step current control loop, double-sided IPM-FLBM, and linear optical potentiometer (LOP), is designed using a proportional controller with a lead compensator. The performances of the linear motion-control system are demonstrated through the various experiments in the time and frequency domains