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Design Methodology for Medium-Frequency Transformer for Solid-State Transformer-Based DC Charging StationsAbdelhamid Younis, Eslam January 2023 (has links)
The global shift towards Electric Vehicles (EVs) is driven by their energy efficiency, lower emissions, and reduced dependence on fossil fuels. As the demand for EVs continues to rise, the need for EV ultra-fast chargers becomes paramount to enable faster charging times and facilitate long-distance travel without compromising convenience. In this context, solid-state transformers (SSTs) have emerged as a promising technology to replace traditional line-frequency transformers (LFTs) in various applications, including EV charging stations. SSTs offer improved system controllability, power factor correction capabilities, and reduced size and weight through the utilization of medium-frequency transformers (MFTs). This thesis focuses on enhancing the efficiency and power density of the MFT used in SSTs.
A 1.2 MVA SST for EV ultra-fast charging stations is designed and simulated. The SST incorporates average controllers responsible for regulating the output voltage and the input power factor, as well as, voltage and power balancing controllers to ensure stable operation among its cells. Furthermore, a design methodology for optimizing the MFT used in DC-to-DC converters for SST-based ultra-fast chargers is introduced. The methodology is optimizing the efficiency and power density of the transformer based on the transformer parameters input by the designer. A software tool is developed to streamline the design process and enable the optimization of various parameters, such as core material, size, and winding configurations. The tool facilitates the development of high-performance MFTs for SST applications.
The developed MFT optimization methodology is utilized to design a 100 kW, 20 kHz MFT, resulting in a remarkable 22.7% improvement in power density compared to conventional design methods. The transformer showed superior efficiency and power density compared to MFT designs in literature. Additionally, two scaled-down transformers are designed and tested at 5 kW, employing both conventional and optimization methods. The results demonstrate a significant 57.8% improvement in specific power. / Thesis / Master of Applied Science (MASc)
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Dual Active Bridge Converter with PWM Control In Solid State Transformer ApplicationJanuary 2012 (has links)
abstract: For the solid-state transformer (SST) application, a three-stage configuration consisting of a PWM rectifier based AC/DC stage, a dual active bridge (DAB) converter based DC/DC stage and a PWM inverter based DC/AC stage offers several advantages. For single-phase SST, the instantaneous input and load power seen by the DC/DC stage varies from zero to twice the load average power at double the line frequency. Traditionally, with phase-shift control, large DAB DC link capacitors are used to handle the instantaneous power variation of the load, with the DAB converter processing only the load average power resulting in better soft-switching range and consequently high efficiency. However, the large electrolytic capacitors required adversely affect the power density and the reliability of SST. In this thesis, a PWM control is used for the DAB converter in SST, which extends the ZVS range of DAB and allows the DAB converter to handle the pulsating power while maintaining/improving efficiency. The impact of the output capacitance of switches with PWM control is discussed for practical implementation. A 40kHz, 500W DAB converter is designed and built, and the experimental results proves that the DAB converter with PWM control in SST can achieve comparable efficiency while the DC link capacitors of SST can be reduced to a value that electrolytic capacitors are not required. / Dissertation/Thesis / M.S. Electrical Engineering 2012
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Modeling of Solid State Transformer for the FREEDM System DemonstrationJanuary 2014 (has links)
abstract: The Solid State Transformer (SST) is an essential component in the FREEDM system. This research focuses on the modeling of the SST and the controller hardware in the loop (CHIL) implementation of the SST for the support of the FREEDM system demonstration. The energy based control strategy for a three-stage SST is analyzed and applied. A simplified average model of the three-stage SST that is suitable for simulation in real time digital simulator (RTDS) has been developed in this study. The model is also useful for general time-domain power system analysis and simulation. The proposed simplified av-erage model has been validated in MATLAB and PLECS. The accuracy of the model has been verified through comparison with the cycle-by-cycle average (CCA) model and de-tailed switching model. These models are also implemented in PSCAD, and a special strategy to implement the phase shift modulation has been proposed to enable the switching model simulation in PSCAD. The implementation of the CHIL test environment of the SST in RTDS is described in this report. The parameter setup of the model has been discussed in detail. One of the dif-ficulties is the choice of the damping factor, which is revealed in this paper. Also the grounding of the system has large impact on the RTDS simulation. Another problem is that the performance of the system is highly dependent on the switch parameters such as voltage and current ratings. Finally, the functionalities of the SST have been realized on the platform. The distributed energy storage interface power injection and reverse power flow have been validated. Some limitations are noticed and discussed through the simulation on RTDS. / Dissertation/Thesis / M.S. Electrical Engineering 2014
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On Enhancing Microgrid Control and the Optimal Design of a Modular Solid-State Transformer with Grid-Forming InverterJanuary 2019 (has links)
abstract: This dissertation covers three primary topics and relates them in context. High frequency transformer design, microgrid modeling and control, and converter design as it pertains to the other topics are each investigated, establishing a summary of the state-of-the-art at the intersection of the three as a baseline. The culminating work produced by the confluence of these topics is a novel modular solid-state transformer (SST) design, featuring an array of dual active bridge (DAB) converters, each of which contains an optimized high-frequency transformer, and an array of grid-forming inverters (GFI) suitable for centralized control in a microgrid environment. While no hardware was produced for this design, detailed modeling and simulation has been completed, and results are contextualized by rigorous analysis and comparison with results from published literature. The main contributions to each topic are best presented by topic area. For transformers, contributions include collation and presentation of the best-known methods of minimum loss high-frequency transformer design and analysis, descriptions of the implementation of these methods into a unified design script as well as access to an example of such a script, and the derivation and presentation of novel tools for analysis of multi-winding and multi-frequency transformers. For microgrid modeling and control, contributions include the modeling and simulation validation of the GFI and SST designs via state space modeling in a multi-scale simulation framework, as well as demonstration of stable and effective participation of these models in a centralized control scheme under phase imbalance. For converters, the SST design, analysis, and simulation are the primary contributions, though several novel derivations and analysis tools are also presented for the asymmetric half bridge and DAB. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019
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High-frequency Power Conversion for Medium Voltage Power Electronics InterfacesLi, Zheqing 10 June 2024 (has links)
ith the rapid advancements in modern technology and the increasing demand for efficient energy conversion, the field of medium voltage power conversion has experienced significant progress in recent years. This progress is driven by its high efficiency and improved scalability. Medium voltage power conversion finds applications in various areas such as data centers, electric vehicle fast charging, and smart grids. It enables the reduction of power delivery stages and minimizes the required physical space. The scalability and modularity of this technology offer the flexibility to expand the power level as needed. According to the International Energy Agency, data centers and electric vehicle charging are projected to consume over 10% of the world's total electricity consumption by 2040. To power this amount, approximately 800 nuclear power reactors with a capacity of 1 GW each would be required. Therefore, even small savings in power consumption can have a substantial impact.
The solid-state transformer (SST) is a promising technique for medium voltage conversion that offers high-frequency operation, resulting in reduced volume and excellent insulation capabilities. Currently, the medium voltage transformer poses a challenge for SST systems due to the requirements for high insulation levels, efficient thermal management, improved efficiency, and higher power density. Unlike conventional line-frequency transformers, the solid-state transformer operates at relatively high frequencies, typically in the range of tens of kilohertz. This higher frequency enables a reduction in the cross-sectional area of the magnetic components, leading to a smaller and lighter design.
However, the high-frequency transformer used in the solid-state transformer does face certain limitations. Balancing insulation capability with the goal of achieving high power density presents a dilemma. To ensure medium voltage insulation, a thick insulation layer is required for the transformer. However, the high-frequency Litz wire and compact size of the transformer make it challenging to achieve partial discharge-free operation, unlike traditional line-frequency transformers. To address these challenges and achieve both medium voltage insulation capability and high power density, improvements in the insulation structure have been made. The dissertation firstly proposes the application of a shielding layer and related stress grading layer in the insulation structure. This helps confine the electric field within the primary side winding encapsulation rather than in the air. As a result, there is minimal electric field present in the air, allowing for further reduction in the transformer volume as there is no longer a need for insulation margin. With the enhanced insulation structure, the transformer can operate at even higher frequencies. However, it is important to note that the reduction in size is not directly proportional to the increase in frequency due to the impact of the insulation layer. To address this, a straightforward and comprehensive optimization method is proposed for the first time. This method considers the trade-off between loss and volume, taking into account multiple design objectives and parameters. An optimized 800/400 V, 200 kHz, 15 kW CLLC converter is demonstrated. The peak efficiency of this optimized converter reaches 98.8%, and the power density is 3.7 kW/L. The transformer also exhibits good insulation capability, with a partial discharge-free level reaching 7.7 kV.
Additionally, achieving a suitable insulation level for the DC-DC module poses challenges due to thermal limitations. Insulation materials are not efficient thermal conductors, and as insulation levels increase, the thickness of the insulation layer must also increase, resulting in a significant rise in thermal resistance. To address this issue for applications requiring a 13.2 kV grid, an alternative insulation material called FR4 is considered in this dissertation. FR4, which can be implemented as the insulation layer for a PCB winding, offers the advantage of being fabricated together with the winding during the PCB manufacturing process. This process takes place in a vacuum environment, reducing the presence of air cavities that could lead to partial discharge within the insulation structure. Thus, the entire insulation fabrication process can be simplified. To enhance the insulation capability further, the dissertation proposes the incorporation of an arc section within the PCB winding. This design reduces the electric field crowding in the corner area. However, winding losses in the PCB winding remain a concern. To mitigate these losses, an ER core structure is introduced to balance the magnetic flux within the transformer core. This balanced distribution of the magnetic field helps reduce leakage flux into the air, subsequently reducing winding losses. The dissertation also suggests a sandwich winding structure to decrease the magnetomotive force in the winding, in comparison to a completely separate winding structure. Another optimization process for the PCB winding is performed to strike a better balance between size and loss in the transformer. In line with these improvements, another 800/400 V, 200 kHz CLLC transformer is designed utilizing the PCB winding approach. Compared to the Litz wire-based transformer, the efficiency performance is similar, but the power density is doubled due to the low-profile design enabled by the PCB winding. In terms of insulation capability, the FR4 insulation, with its high dielectric strength, allows the transformer to be partial discharge-free even with the same insulation thickness as the epoxy used in the Litz wire transformer for the 13.2 kV applications.
Thirdly, considering the power limitation mainly because of the thermal issue in the primary side PCB winding, the PCB Litz wire concept is proposed to further improve the winding loss. To further improve the power level of the PCB winding transformer, the winding should be designed wider to reduce the DC winding resistance. However, the current distributes in a bad manner due to the proximity effect in the winding. That makes winding width increment insignificant to the loss reduce. The Litz wire is widely used in the high-frequency power conversion applications. A similar concept has been proposed in this dissertation in the PCB winding. Using two layers constructing one turns, the interwoven strategy can be implemented in the PCB winding to achieve the flux cancellation effect. That helps to make the current distribute uniformly inside the PCB winding. The PCB Litz construction method and connection method is introduced in this chapter to reduce the design burden with such a complicated winding pattern. Some design considerations are also proposed to optimize the PCB Litz concept.
This dissertation solves the challenges in magnetic design in high-frequency DC/DC converters in the solid-state transformer with medium voltage insulation. This includes the Litz wire transformer and the PCB winding based transformer. With the academic contribution in this dissertation, the insulation performance is better for both Litz wire transformer and PCB winding based transformer. The straightforward and comprehensive optimization method is benefit for both academic and industry for transformer design in this application. The proposed PCB winding transformer makes the insulation fabrication much easier compared to the conventional fabrication method. And the PCB Litz concept helps to further reduce the winding loss, which makes it possible to further lift the power level in the PCB winding based transformer. / Doctor of Philosophy / With the rapid advancements in modern technology and the increasing demand for efficient energy conversion, the field of medium voltage power conversion has experienced significant progress in recent years. This progress is driven by its high efficiency and improved scalability. Medium voltage power conversion finds applications in various areas such as data centers, electric vehicle fast charging, and smart grids. It enables the reduction of power delivery stages and minimizes the required physical space. The scalability and modularity of this technology offer the flexibility to expand the power level as needed. According to the International Energy Agency, data centers and electric vehicle charging are projected to consume over 10% of the world's total electricity consumption by 2040. To power this amount, approximately 800 nuclear power reactors with a capacity of 1 GW each would be required. Therefore, even small savings in power consumption can have a substantial impact.
The solid-state transformer (SST) is a promising technique for medium voltage conversion that offers high-frequency operation, resulting in reduced volume and excellent insulation capabilities. Currently, the medium voltage transformer poses a challenge for SST systems due to the requirements for high insulation levels, efficient thermal management, improved efficiency, and higher power density. Unlike conventional line-frequency transformers, the solid-state transformer operates at the range of tens of kilohertz. This higher frequency enables a reduction in the cross-sectional area of the magnetic components, leading to a smaller and lighter design.
Balancing insulation capability with the goal of achieving high power density presents a dilemma. To ensure medium voltage insulation, a thick insulation layer is required for the transformer. However, the high-frequency Litz wire and compact size of the transformer make it challenging to achieve partial discharge-free, unlike traditional line-frequency transformers. To address these challenges and achieve both medium voltage insulation capability and high power density, improvements in the insulation structure have been made. A straightforward and comprehensive optimization method is proposed for the first time. This method considers the trade-off between loss and volume, taking into account multiple design objectives and parameters. An optimized 800/400 V, 200 kHz, 15 kW CLLC converter is demonstrated. The peak efficiency of this optimized converter reaches 98.8%, and the power density is 3.7 kW/L. The transformer also exhibits good insulation capability, with a partial discharge-free level reaching 7.7 kV.
Additionally, insulation materials are not efficient thermal conductors, and as insulation levels increase, the thickness of the insulation layer must also increase, resulting in a significant rise in thermal resistance. An alternative insulation material called FR4 is considered in this dissertation. FR4, which can be implemented as the insulation layer for a PCB winding, offers the advantage of being fabricated with the winding during the PCB manufacturing process. To enhance the insulation capability further, the dissertation proposes an arc section within the PCB winding. This design reduces the electric field crowding in the corner area. The dissertation also suggests a sandwich winding structure to decrease the magnetomotive force in the winding, in comparison to a completely separate winding structure. Another optimization process for the PCB winding is performed to strike a better balance between size and loss in the transformer. In line with these improvements, another 200 kHz CLLC transformer is designed utilizing the PCB winding approach with doubled converter power density. In terms of insulation capability, the FR4 insulation, allows the transformer to be partial discharge-free for the 13.2 kV applications.
Thirdly, considering the power limitation mainly because of the thermal issue in the primary side PCB winding, the PCB Litz wire concept is proposed to further improve the winding loss. The current distributes in a bad manner due to the proximity effect in the PCB winding. That makes winding width increment insignificant to the loss reduce. The Litz wire is widely used in the high-frequency power conversion applications. A similar concept has been proposed in this dissertation in the PCB winding. Using two layers constructing one turns, the interwoven strategy can be implemented in the PCB winding to achieve the flux cancellation effect. That helps to make the current distribute uniformly inside the PCB winding. The PCB Litz construction method and connection method is introduced in this chapter to reduce the design burden with such a complicated winding pattern. Some design considerations are also proposed to optimize the PCB Litz concept.
This dissertation solves the challenges in magnetic design in high-frequency DC/DC converters in the solid-state transformer with medium voltage insulation. This includes the Litz wire transformer and the PCB winding based transformer. With the academic contribution in this dissertation, the insulation performance is better for both Litz wire transformer and PCB winding based transformer. The straightforward and comprehensive optimization method is benefit for both academic and industry for transformer design in this application. The proposed PCB winding transformer makes the insulation fabrication much easier compared to the conventional fabrication method. And the PCB Litz concept helps to further reduce the winding loss, which makes it possible to further lift the power level in the PCB winding based transformer.
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Predictive control of a series-input, parallel-output, back-to-back, flying-capacitor multilevel converterDu Toit, Daniel Josias 12 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis investigates the viability of constructing a solid-state transformer (SST) with
a series-input, parallel-output connection of full-bridge, three-level
ying-capacitor converters.
It focusses on the active recti er front-end of the SST which is used to control
the input current to be sinusoidal and in-phase with the sinusoidal input voltage. A stack
of two converters are built and tested. The input current, as well as the
ying capacitor
voltages of the two active recti ers in the stack, are actively controlled by a nite-state
model-based predictive (FS-MPC) controller.
The use of multiple
ying-capacitor converters poses a problem when using FS-MPC
because of the large number of possible switching states to include in the prediction
equations. Three FS-MPC control algorithms are proposed to attempt to overcome the
problem associated with the large number of switching states. They are implemented
on an FPGA digital controller. The algorithms are compared on the bases of voltage
and current errors, as well as their responses to disturbances that are introduced into
the system. The simulation and experimental results that are presented shows that by
interleaving the control actions for the two converters, one can obtain fast and robust
responses of the controlled variables. The viability of extending the interleaving control
algorithm beyond two converters is also motivated. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die moontlikheid van volbrug, drievlak vlieënde-kapasitoromsetters
wat gebruik word om 'n serie-intree, parallel-uittree drywingselektroniese transformator
(DET) te bou. Dit fokus op die aktiewe gelykrigter van die DET wat gebruik word om
die intreestroom te beheer om sinusvormig en in fase met die sinusvormige intreespanning
te wees. 'n Stapel van twee omsetters word gebou en getoets. Die intreestroom,
sowel as die vlieënde kapasitorspannings van die twee aktiewe gelykrigters in die stapel,
word aktief beheer met behulp van 'n eindige-toestand, model-gebaseerde voorspellende
beheerder (ET-MVB).
Die gebruik van veelvuldige vlieënde-kapasitoromsetters bemoeilik die implementering van
'n ET-MVB-beheerder as gevolg van die groot aantal skakeltoestande wat in die voorspellende
vergelykings in ag geneem moet word. Drie ET-MVB-algoritmes word voorgestel
om te poog om die probleme, wat met die groot aantal skakeltoestande geassosieer word,
te oorkom. Die algoritmes word in 'n FPGA digitale verwerker geïmplementeer. Die
algoritmes word vergelyk op grond van hul stroom- en spanningsfoute, asook hul reaksie
op steurings wat op die stelsel ingevoer word. Die simulasie en praktiese resultate toon
dat, deur die beheeraksies vir die twee omsetters te laat oorvleuel, die gedrag van die beheerde
veranderlikes vinniger en meer robuust is. Die moontlikheid om die oorvleuelende
beheeraksies uit te brei tot meer as twee omsetters word ook gemotiveer.
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ATM cash management for a South African retail bankDu Toit, Delyno Johannes 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Cash can be seen as a fast moving consumer good. Approaching
cash as inventory within the ATM cash management environment
of a South African retail bank, provided the opportunity to apply
well known industrial engineering techniques to the financial industry.
This led to the application of forecasting, inventory management,
operational research and simulation methods.
A forecasting model is designed to address the multiple seasonalities
and calendar day effects that is prevalent in the demand for cash.
Special days, e.g. paydays, lead to an increase in demand for cash.
The weekday on which the special day falls will also influence the demand.
The multiplicative Holt-Winters method is combined with an
improvised distribution method to determine the demand for cash for
the region and per ATM. Reordering points are calculated and simulated
to form an understanding of the effect this will have on the ATM
network. Direct replenishment and the traveling salesman problem is
applied and simulated to determine the difference in using one or the
other.
Various simulation models are build to test the operational and financial
impact when certain variables are amended. It is evident
that more work is required to determine the optimal combination of
variable values, i.e. forecasting frequency, aggregate forecasting or
individual forecasting, reorder levels, loading levels, lead times, cash
swap or cash add, and the type of transportation method. Each one of
these are a science in itself and cannot be seen (calculated) in isolation
from the other as a change in one can affect the overall operational
efficiency and costs of the ATM network. The thesis proves that significant cost savings is possible, compared to
the current set-up, when applying industrial engineering techniques
to a geographical ATM network within South Africa. / AFRIKAANSE OPSOMMING: Kontant kan gesien word as vinnig bewegende verbruikersgoedere.
Deur kontant te benader as voorraad binne die ATM kontant bestuur
omgewing van ’n Suid Afrikaanse kleinhandelsbank, het dit die geleentheid
geskep om bekende bedryfsingenieurstegnieke toe te pas in die
finansiële industrie. Dit het gelei tot die toepassing van vooruitskatting,
voorraadbestuur, operasionele navorsing en simulasie metodes.
’n Vooruitskattingsmodel is ontwerp om die verskeie seisoenaliteite
en kalenderdae effekte wat deel uitmaak van die vraag na kontant
aan te spreek. Spesiale dae, bv. betaaldae, lei tot ’n toename in die
vraag na kontant. Die weeksdag waarop die spesiale dag voorkom
sal ook ’n invloed hê op die vraag. Die multiplikatiewe Holt-Winters
metode is gekombineer met ’n geïmproviseerde verspreidingsmetode
om die vraag na kontant vir die streek en per ATM the bepaal.
Bestellingsvlakke is bereken en gesimuleer om ’n prentjie te skep van
die invloed wat dit op die ATM netwerk sal hê. Direkte hervulling en
die handelsreisigerprobleem is toegepas en gesimuleer om die verskille
te bepaal tussen die gebruik van of die een of die ander.
Veskeie simulasie modelle is gebou om die operasionele en finansiële
impak te toets, wanneer sekere veranderlikes aangepas word. Dit is
duidelik dat meer werk nodig is om die optimale kombinasie van veranderlike
waardes te bepaal, bv. vooruitskatting frekwensie, totale
vooruiskatting of individuele vooruitskatting, bestellingsvlakke, leitye,
kontant omruiling of kontant byvoeging, en die tipe vervoermetode.
Elkeen van hierdie is ’n wetenskap op sy eie en kan nie in isolasie gesien
en bereken word nie, want ’n verandering van een se waarde kan die
hele operasionele doeltreffendheid en kostes van die ATM netwerk
beïnvloed.
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Insulation Coordination of Solid State Devices Connected Directly to the Electric Power Distribution SystemJanuary 2017 (has links)
abstract: With the penetration of distributed renewable energy and the development of
semiconductor technology, power electronic devices could be utilized to interface re-
newable energy generation and the distribution power grid. However, when directly
connected to the power grid, the semiconductors inside the power electronic devices
could be vulnerable to the power system transient, especially to lightning strikes.
The work of this research focuses on the insulation coordination of power elec-
tronic devices connected directly to the power distribution system. The Solid State
Transformer (SST) in Future Renewable Electric Energy Delivery and Management
(FREEDM) system could be a good example for grid connected power electronic
devices. Simulations were conducted in Power Systems Computer Aided Design
(PSCAD) software. A simulation done to the FREEDM SST showed primary re-
sults which were then compare to simulation done to the grid-connected operating
Voltage Source Converter (VSC) to get more objective results.
Based on the simulation results, voltage surges caused by lightning strikes could
result in damage on the grid-connected electronic devices. Placing Metal Oxide Surge
Arresers (MOSA, also known as Metal Oxide Surge Varistor, MOV) at the front lter
could provide eective protection for those devices from power transient. Part of this
research work was published as a conference paper and was presented at CIGRE US
National Conference: Grid of the Future Symposium [1] and North American Power
Symposium [2]. / Dissertation/Thesis / Masters Thesis Engineering 2017
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Robust Control of Wide Bandgap Power Electronics Device Enabled Smart GridJanuary 2017 (has links)
abstract: In recent years, wide bandgap (WBG) devices enable power converters with higher power density and higher efficiency. On the other hand, smart grid technologies are getting mature due to new battery technology and computer technology. In the near future, the two technologies will form the next generation of smart grid enabled by WBG devices. This dissertation deals with two applications: silicon carbide (SiC) device used for medium voltage level interface (7.2 kV to 240 V) and gallium nitride (GaN) device used for low voltage level interface (240 V/120 V). A 20 kW solid state transformer (SST) is designed with 6 kHz switching frequency SiC rectifier. Then three robust control design methods are proposed for each of its smart grid operation modes. In grid connected mode, a new LCL filter design method is proposed considering grid voltage THD, grid current THD and current regulation loop robust stability with respect to the grid impedance change. In grid islanded mode, µ synthesis method combined with variable structure control is used to design a robust controller for grid voltage regulation. For grid emergency mode, multivariable controller designed using H infinity synthesis method is proposed for accurate power sharing. Controller-hardware-in-the-loop (CHIL) testbed considering 7-SST system is setup with Real Time Digital Simulator (RTDS). The real TMS320F28335 DSP and Spartan 6 FPGA control board is used to interface a switching model SST in RTDS. And the proposed control methods are tested. For low voltage level application, a 3.3 kW smart grid hardware is built with 3 GaN inverters. The inverters are designed with the GaN device characterized using the proposed multi-function double pulse tester. The inverter is controlled by onboard TMS320F28379D dual core DSP with 200 kHz sampling frequency. Each inverter is tested to process 2.2 kW power with overall efficiency of 96.5 % at room temperature. The smart grid monitor system and fault interrupt devices (FID) based on Arduino Mega2560 are built and tested. The smart grid cooperates with GaN inverters through CAN bus communication. At last, the three GaN inverters smart grid achieved the function of grid connected to islanded mode smooth transition / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017
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Design and implementation of the main controller of a solid-state transformerSchietekat, Louis Magnus 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The Solid-State Transformer (SST) is presented as an alternative to the traditional Line-Frequency
Transformer (LFT) used for voltage-level transformation in distribution grids. The LFT technology
is highly matured which results in low costs and high efficiency. The SST however, introduces
several advantages compared to the LFT, some of which are input unity power-factor,
near perfect output-voltage regulation, frequency variation as well as harmonic filtering.
The SST consists of three power-electronic converter stages: The input stage, the isolation
stage and the output stage. The input and isolation stages are implemented with a multilevelconverter
topology incorporating a converter-stack for each phase. Each stack consists of N
converter building blocks, called cells. In this thesis the design and implementation of the main
controller is presented. The main controller, together with N cell controllers, is responsible for
the control of the cells within the respective stack. Three main controllers are thus implemented
within the SST.
Each cell consists of an Active Rectifier (AR) and a DC-DC Converter (DC-DC). The SST
control design thus starts with the AR control which is subsequently expanded to Cascaded
Active-Rectifier (CAR) control. Design is completed with the addition of the DC-DC control.
Time domain simulations of the AR- and CAR-control are presented and discussed. Test measurements,
verifying functionality of each control design-phase, are presented and discussed. / AFRIKAANSE OPSOMMING: Die Drywingselektroniese Transformator (DET) word voorgestel as ’n alternatief vir die Lyn
Frekwensie Transformator (LFT) wat gebruik word vir spannings-vlak tranformasie op distribusie
vlak. The LFT tegnologie is ver gevorderd wat ly tot hoë effektiwiteit en lae kostes.
The DET bied wel voordele soos intree eenheids arbeid faktor, na aan perfecte uittree-spannings
regulasie, frequensie variasie sovel as harmoniese filrteering.
Die DET bestaan uit drie drywingselektroniese omsetter stadiums: Die intree-stadium, die
isolasie-stadium en die uittree-stadium. The intree- en isolasie-stadiums word geïmplimenteer
met ’n multivlak-omsetter topologie wat bestaan uit ’n omsetter-stapel vir elke fase. Elke stapel
bestaan uit N omsetter boustene wat selle genoem word. In hierdie tesis word the ontwerp
en implementasie van die hoofbeheerder voorgestel. Die hoofbeheerder, tesame met N selbeheerders,
is verantwoordelik vir die beheer van elke sel in die spesifieke stapel. In die DET
word daar dus drie hoofbeheerders gebruik.
Elke sel bestaan uit ’n Aktiewe Gelykrigter (AG) en ’n GS-GS omsetter (GS-GS). Die DET
beheerontwerp begin dus met die (AG) beheer wat daarna uitgebrei word na Kaskade Aktiewe
Gelykrigter (KAG) beheer. Die beheer ontwerp word voltooi deur die byvoeging van die GSGS
beheer. Tyd-gebied simulasies van die AG- en KAG-beheer word voorgelê en bespreek.
Toetsmetings wat die funksionaliteit van elke beheer ontwepsfase verifeer, word voorgelê.
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