In diesem Beitrag wird gezeigt, welche Auswirkung die Rotorform einer Reluktanzmaschine und die Ansteuerung mittels Umrichter auf den Verlusthaushalt der Maschine hat. Darüber hinaus werden die Möglichkeiten zur Verluststeuerung, welche sich durch den Betrieb von Reluktanzmaschinen ergeben, vorgestellt. / This paper shows the effect of the rotor shape of a reluctance machine and the converter control on the losses of the machine. In addition, it will be shown which possibilities for loss control will result from the operation of reluctance machines.

Connecting more non-dispatchable renewable energy sources (RESs) will result in a higher power variability and a lower system inertia when the synchronous generators are replaced by inverter-connected RES. Inverter control can be divided in three categories: grid-following, grid-forming (GFM) and grid-supporting. A literature review of inverter control strategies identifies the GFM control as having an important role in maintaining system stability assuming near 100 % inverter-connected RES. Critical aspects of the inverter control are also identified; the control need to function autonomously, be able to remain connected during transient events and be insensitive to grid topology. Combining various RES is also shown to improve system stability. The combination of RES that has been investigated in most studies is wind, solar and wave power. Wave power is still a young technology compared to solar and wind power. It generates higher power fluctuations over short time periods with a significant difference between average and maximum power. Additionally, wave power parks (WPPs) are often connected via long cables which contribute reactive power to the grid. These challenges has to be considered to maintain system stability and power quality when connecting a WPP to the grid. In a Power Hardware-In-the-Loop study of how a WPP affects the power quality at the point of common coupling (PCC), it is found that the impact is highest for WPPs with fewer generators as the variability is reduced when several generators are excited at different times. Energy storage is also shown to have a significant impact on the power quality at the PCC with reduced flicker, total harmonic distortion and power and voltage variability. A simulation study also shows the positive impact of energy storage on power variability and the role of inverter control in reactive power compensation.

An electrical distribution network supplies power to many households at a time. Each house has various types of electrical appliances which consume different levels of power depending on its function and the load it supplies. An ideal case would be when no appliances cause power disturbances, however, in reality, many electrical appliances (e.g. refrigerators, computers, heat pumps, etc.), due to their inherent characteristics. The distribution network is now fed back with non-sinusoidal power, called harmonics, causing inefficiencies and potential failure in other appliances connected to the same network. Harmonics are the additional frequency components to the fundamental sinusoidal voltage or current (e.g. 50Hz fundamental frequency in Europe). To avoid the malfunction of the network, each electrical appliance in any household has to comply with the standard IEC 61000-3-2 (current rating $<$16A) defined by the International Electrotechnical Commission (IEC). According to these standards, current harmonics have been observed up to 40th harmonics. If the fundamental frequency is 50 Hz, then harmonic currents up to 2000 Hz have to be considered. Usually, the harmonics are quantified by the measurement when the appliance has been constructed at which point changes are costly and time-consuming.  This thesis investigates the possibility to model these appliances at an early stage of development enabling cost-effective and quick improvements. The model is achieved by reducing a heat pump into a set of chokes, an EMI filter, a rectifier, and a load represented by a variable current source to simulate the compressor which draws the majority of power the system uses. The state-of-the-art, referred to as white box modeling, uses schematics to model these components while this thesis presents a methodology to model without schematics, referred to as black box modeling.  For the black box model, impedance of the components is measured and equivalent circuits are modeled accordingly in Simulink to simulate the harmonics. The validity of a black box simulation model from the equivalent circuit extracted by the impedance measurements is investigated in this thesis. The black box modeling is compared with the white box modeling and measurements for the purpose of verification.   The result is good but more work is needed. The black box model is verified using two different systems which are similarly accurate. Simulating harmonics at a higher power level yields better results. The black box model is more accurate than the white box model, mainly due to the inclusion of parasitics in the EMI filter. Possible additional harmonics generation in unmodeled components is investigated and found to be insignificant.

Renewable energy source plays an important role in energy co-generation and distribution. A traditional solar-based inverter system has two stages cascaded, which has simpler controller but low efficiency. A new solar-based single-stage grid-connected inverter system can achieve higher efficiency by reducing the power semiconductor switching loss and output stable and synchronizing sinusoid current into the utility grid. In Chapter 1, the characteristic I-V and P-V curve of PV array has been illustrated. Based on prediction of the PV power capacity installed on the grid-connected and off-grid, the trends of grid-tied inverter for DG system have been analyzed. In Chapter 2, the topologies of single-phase grid-connect inverter system have been listed and compared. The key parameters of all these topologies are listed in a table in terms of topology, power decoupling, isolation, bi-directional/uni-directional, power rating, switching frequency, efficiency and input voltage. In Chapter 3, to reduce the capacitance of input filter, an active filter has been proposed, which will eliminate the 120/100Hz low frequency ripple from the PV array's output voltage completely. A feedforward controller is proposed to optimize the step response of PV array output voltage. A sample and hold also is used to provide the 120/100Hz low frequency decoupling between the controller of active filter and inverter stage. In Chapter 4, the single-stage inverter is proposed. Compared with conventional two-stage inverter, which has two high frequency switching stages cascaded, the single-stage inverter system increases the system efficiency by utilizing DC/DC converter to generate rectified sinusoid voltage. A transformer analysis is conducted for the single-stage inverter system, which proves the transformer has no low-frequency magnetic flux bias. To apply peak current mode control on single-stage inverter and get unified loop gain, adaptive slope compensation is also proposed for single-stage inverter. In Chapter 5, a digital controller for single-stage inverter is designed and optimized by the Matlab Control Toolbox. A Psim simulation verified the performance of the digital controller design. In Chapter 6, three bi-directional single-stage inverter topologies are proposed and compared. A conventional single-stage bi-directional inverter has certain shortcoming that cannot be overcome. A modular grid-connect micro-inverter system with dedicated reactive energy processing unit can overcome certain shortcoming and increase the system efficiency and reliability. A unique controller design is also proposed. In Chapter 7, a PFM ZCS flyback inverter system is invented. By using half-wave quasi-resonant ZCS flyback resonant converter and PFM control, this topology completely eliminates switching loss. A detailed mathematical analysis provides all the key parameters for the inverter design. As the inductance of transformer secondary side get smaller, the power stage transfer function of PFM ZCS flyback inverter system demonstrates nonlinearity. An optimized PFM ZCS flyback DC/DC converter design resolves this issue by introducing a MOSFET on the secondary side of transformer. In Chapter 8, experimental results of uni-direcitonal single-stage inverter with grid-connection, bi-directional single-stage inverter and single-stage PFM ZCS flyback inverter have been provided. Conclusions are given in Chapter 9.

The conventional approach to vehicle design is restrictive, limited, andbiased. This often leads to sub-optimal utilisation of vehicle capabilities and allocated resources and ultimately entails the repercussions of designing andlater on an using an inefficient vehicle. To overcome these limitations, it is important to gain a deeper understanding of the interaction effects at component,subsystem, and system level. In this thesis, the research is focused on identifying appropriate methods and developing robust models to facilitate the interaction analysis. To scrutinise and identify appropriate methods, criteria were developed.Initially, the Design Structure Matrix (DSM) and its variations were examined.While DSM proved to be fundamental for capturing interaction effects,it lacked the ability to answer questions about the structure and behaviour ofinteractions and to predict unintended effects. Therefore, network theory wasexplored as a complementary method to DSM which was capable of providing insights into interaction structures and identifying influential variables. Subsequently, two criteria were established to identify subsystems significant to interaction analysis: high connectivity to other subsystems and multidisciplinary composition. The traction motor was observed to satisfyboth criteria as it had higher connectivity with other subsystems and was composed of multiple disciplines. Therefore, a detailed model of an induction motor was developed to enable the interaction analysis. The induction motor model was integrated into a cross-scalar design tool.The tool employed a two-step process: translating operational parametersto motor inputs using Newtonian equations and deriving physical attributes,performance characteristics, and performance attributes of the motor. Comparing the obtained performance characteristics curve against existing studiesvalidated the model’s reliability and capabilities. The design tool demonstrated adaptability to different drive cycles and the ability to modify motor performance without affecting operational parameters. Thus validating the capability of the design tool to capture cross-scalar and intra-subsystem interaction effects. To examine inter-subsystem interaction, a thermal model of an inverter was developed, capturing temperature variations in the power electronics based on motor inputs. The design tool successfully captured interaction effects between motor and inverter designs, highlighting the interplay with operational parameters. Thus, this thesis identifies methods for interaction analysis and develops robust subsystem models. The integrated design tool effectively captures intra-subsystem, inter-subsystem, and cross-scalar interaction effects. The research presented contributes to the overarching project goal of developing methods and models that capture interaction effects and in turn serve as a guiding tool for designers to understand the consequences of their design choices. / Det konventionella tillvägagångssättet för fordonsdesign är restriktiv, begränsat och partiskt. Detta leder ofta till en suboptimal användning av fordonets kapacitet och tilldelade resurser och innebär i slutändan att konsekvenserna blir att använda ett ineffektivt fordon. För att övervinna dessa begränsningar är det viktigt att få en djupare förståelse för interaktionseffekterna på komponent-, delsystem- och systemsnivå. I denna avhandling fokuserar forskningen på att identifiera lämpliga metoder och utveckla robusta modeller för att underlätta interaktionsanalysen. För att granska och identifiera lämpliga metoder utvecklades kriterier. Till att börja med undersöktes Design Structure Matrix (DSM) och dess variationer. Medan DSM visade sig vara grundläggande för att fånga interaktionseffekter, saknade den förmågan att besvara frågor om interaktionsstrukturer och beteende samt förutsäga oavsiktliga effekter. Därför utforskades nätverksteori som en kompletterande metod till DSM, vilket kunde ge insikter i interaktionsstrukturer och identifiera inflytelserika variabler. Därefter etablerades två kriterier för att identifiera delsystem som är betydelsefulla för interaktionsanalysen: hög anslutning till andra delsystem och mångdisciplinär sammansättning. Dragkraftmotorn observerades uppfylla båda kriterierna eftersom den hade högre anslutning till andra delsystem och var sammansatt av flera discipliner. Därför utvecklades en detaljerad modell av en induktionsmotor för att möjliggöra interaktionsanalysen. Induktionsmotormodellen integrerades i ett tvärskaligt designverktyg. Verktyget använde en tvåstegsprocess: att översätta operativa parametrar till motorinsatser med hjälp av Newtons ekvationer och härleda fysiska egenskaper, prestandakaraktäristik och prestandaattribut hos motorn. Jämförelse av den erhållna prestandakaraktäristikkurvan med befintliga studier validerade modellens tillförlitlighet och förmågor. Designverktyget visade anpassningsbarhet till olika körcykler och förmågan att modifiera motorprestanda utan att påverka operativa parametrar. Detta validerade designverktygets förmåga att fånga tvärskaliga och intra-subsystem interaktionseffekter. För att undersöka inter-subsysteminteraktion utvecklades en termisk modell av en inverter, som fångade temperaturvariationer i kraftelektroniken baserat på motorns styrning. Designverktyget fångade framgångsrikt interaktionseffekter mellan motor- och inverterdesign och belyste samspelet med operativa parametrar. Därmed identifierar denna avhandling metoder för interaktionsanalys och utvecklar robusta delsystemmodeller. Det integrerade designverktyget fångar effektivt intra-subsystem-, inter-subsystem- och tvärskaliga interaktionseffekter. Den presenterade forskningen bidrar till det övergripande projektets mål att utveckla metoder och modeller som fångar interaktionseffekter och i sin tur fungerar som ett vägledande verktyg för designers att förstå konsekvenserna av sina designval. / <p>QC 231003</p>

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Battery energy storage system (BESS) is promising to be implemented in residential applications for supporting PV integration, load shifting, and backup power purposes. For this application, 48V second-life battery draws more and more attentions for their cost-effectiveness, safe voltage level, reliability, and potential large market. This thesis proposes the comprehensive control and design of an isolated battery-driven grid interface (IBDGI) with the dual-active-bridge (DAB) converter for residential applications with 48V battery pack. The three-phase DAB converter is a promising candidate as the front-end DC/DC converter in the two-stage IBDGI due to its high efficiency, high power density, and low capacitance requirement. An effective design strategy for the three-phase DAB converter is proposed based on the zero-voltage-switching (ZVS) zone and back-ow power to achieve high efficiency for a wide operating voltage range and different load conditions. Based on the power loss model, an easily-implemented variable switching frequency operating method is proposed to further increase the efficiency at light load conditions. The dead-time effect is observed in the three-phase DAB converter. To avoid the dead-time effect and better understand the phenomena, a comprehensive analysis is proposed. All the cases of the dead-time effect in the three-phase DAB converter are analyzed in terms of the buck, boost, and matching states. The expressions of the transmission power, constraint conditions, and key time of the dead-time effect are derived for each state. The operation waveforms of the dead-time effect are also presented. The hybrid capacitor bank composed by the LC resonant lter with electrolytic capacitor and lm capacitor is utilized for the DC bus of the IBGDI. The electrolytic capacitors work as passive decoupling purpose while the lm capacitor is responsible for high switching harmonic ltering. Moreover, a current sharing method between the hybrid capacitor bank is proposed to extend the electrolytic capacitor's life. The LCL single-phase inverter is applied for the downstream of the IBDGI. A step-by-step design procedure of the LCL lter with passive damping is proposed for the 120V/240V dual grid-tied and standalone modes. The PR controllers are also designed for the LCL inverter for standalone and grid-tied modes. At the system level, a novel second harmonic current (SHC) reduction strategy is proposed for the IBDGI with the three-phase DAB converter by adding a load current feedforward (LCFF) path to the DAB voltage closed-loop controller. This method will suppress the SHC without modi cations of the original controller's bandwidth, which make it easy to be implemented. The small-signal model of the three-phase DAB converter is provided and veri ed by the step response. The parameter sensitivity analysis for the LCFF method is proposed to show that the SHC is well suppressed within ±20% parameter error. The proposed converter and control methods are veri ed by simulation and experimental results. / Thesis / Doctor of Philosophy (PhD)

Lithium-ion based battery energy storage system has become one of the most popular forms of energy storage system for its high charge and discharge efficiency and high energy density. This dissertation proposes a high-efficiency grid-tie lithium-ion battery based energy storage system, which consists of a LiFePO4 battery based energy storage and associated battery management system (BMS), a high-efficiency bidirectional ac-dc converter and the central control unit which controls the operation mode and grid interface of the energy storage system. The BMS estimates the state of charge (SOC) and state of health (SOH) of each battery cell in the pack and applies active charge equalization to balance the charge of all the cells in the pack. The bidirectional ac-dc converter works as the interface between the battery pack and the ac grid, which needs to meet the requirements of bidirectional power flow capability and to ensure high power factor and low THD as well as to regulate the dc side power regulation. A highly efficient dual-buck converter based bidirectional ac-dc converter is proposed. The implemented converter efficiency peaks at 97.8% at 50-kHz switching frequency for both rectifier and inverter modes. To better utilize the dc bus voltage and eliminate the two dc bus bulk capacitors in the conventional dual-buck converter, a novel bidirectional ac-dc converter is proposed by replacing the capacitor leg of the dual-buck converter based single-phase bidirectional ac-dc converter with a half-bridge switch leg. Based on the single-phase bidirectional ac-dc converter topology, three novel three-phase bidirectional ac-dc converter topologies are proposed. In order to control the bidirectional power flow and at the same time stabilize the system in mode transition, an admittance compensator along with a quasi-proportional-resonant (QPR) controller is adopted to allow smooth startup and elimination of the steady-state error over the entire load range. The proposed QPR controller is designed and implemented with a digital controller. The entire system has been simulated in both PSIM and Simulink and verified with hardware experiments. Small transient currents are observed with the power transferred from rectifier mode to inverter mode at peak current point and also from inverter mode to rectifier mode at peak current point. The designed BMS monitors and reports all battery cells parameters in the pack and estimates the SOC of each battery cell by using the Coulomb counting plus an accurate open-circuit voltage model. The SOC information is then used to control the isolated bidirectional dc-dc converter based active cell balancing circuits to mitigate the mismatch among the series connected cells. Using the proposed SOC balancing technique, the entire battery storage system has demonstrated more capacity than the system without SOC balancing. / Ph. D.

This dissertation aims to present a detailed analysis of the grid voltage disturbance in frequency domain for the current control design in the grid-tie inverter applications and to propose current control techniques in order to minimize its impact and maximize feasibility of the power conditioning system in distributed generations. Because the grid voltage is constantly changing, the inverter must be able to response to it. If the inverter is unable to respond properly, then the grid voltage power comes back to the system and damages the fuel cell power conditioning systems. A closed-loop dynamic model for the current control loop of the grid-tie inverter has been developed. The model explains the structure of the inverter admittance terms. The disturbance of the grid voltages has been analyzed in frequency domain. The admittance compensator has been proposed to prevent the grid voltage effect. The proposed lead-lag current control with admittance compensator transfers current properly without system failure. In order to get rid of the steady-state error of the feedback current, a proportional-resonant controller (PR) has been adopted. A PR control with admittance compensation provides great performance from zero power to full power operation. In addition, active and reactive power flow controller has been proposed based on the PR controller with admittance compensation. The proposed active and reactive power flow control scheme shows a wide range power flow control from pure leading power to pure lagging power. Finally, the proposed controller scheme has been verified its feasibility in three phase grid-tie inverter applications. First of all, a half-bridge grid-tie inverter has been designed with PR controller and admittance compensation. Then three individual grid-tie inverters has been combined and produced three phase current to the three phase grid in either balanced condition or unbalanced condition. The proposed control scheme can be applied not only single phase grid-tie inverter application, but also three phase grid-tie inverter application. This research can be applicable to the photovoltaic PCS as well. This technology makes renewable energy source more plausible for distributed generations. / Ph. D.