153 research outputs found
Predictive control of a direct series resonant converter with active output voltage compensation
Modern high power supplies are based on resonant converters in order to use high frequency reactive elements (for reduced size) without sacrificing converter efficiency. In an effort to achieve compact high power supplies, direct power converter topologies have been considered, since these are mainly characterised by their high power density. A direct resonant converter topology combines matrix converters with conventional resonant converters.
This work focused on achieving high quality input/output power and high efficiency. Thus, this thesis presents the research on the control of a direct series resonant converter. Since the resonant converter allows a sinusoidal high frequency output current to be generated, zero current switching (ZCS) was considered to reduce the power losses. Hence, since the converter is switched at every zero crossing of the output current (fixed period), model predictive control was considered.
Different predictive approaches for controlling the input and output currents were developed and analysed, however, owing to the characteristics of the topology, these strategies resulted in a suboptimal control. Therefore, in order to improve the input and output qualities (reduce distortion), an output voltage compensation strategy was proposed. This compensation approach is based on adding an H-bridge converter in series between the matrix converter and the resonant tank. This converter improves the voltage applied to the resonant tank, thus, reducing the distortion at the output and, as a consequence, also the distortion at the input. The H-bridge converter utilises only a small capacitor on the dc side in comparison with conventional resonant converters and operates at a low voltage.
Simulations were carried out using MATLAB/Simulink and an experimental prototype was built to validate the strategies proposed, achieving a reduction of the input current THD from 4.4% to 2.7%, a reduction of the output current distortion of approximately 40% and an analytically derived efficiency of 89.5%
Optimal PWM switching strategy for single-phase AC-DC converters
The thesis describes an optimal selective harmonic elimination strategy suitable for singlephase
AC-DC converter-fed traction drives. The objective is to eliminate low-order supply
current harmonics, including those injected into the supply due to load-side current ripple.
Other advantages that the switching strategy has to offer over phase-control include
improved supply power factor, reduced VA consumption for a given demand speed and
load, reduced torque and speed ripple and smaller armature circuit smoothing inductance.
The effect of field current boost on the dynamic response of the drive is also described.
It is shown that field boost helps to reduce the speed rise-time by increasing the
electromagnetic torque available during acceleration periods.
Closed-loop control of a 4-quadrant DC drive is described and a comparison made between
the performance of PID-control and pseudo-derivative feedback control. It is shown that
pseudo-derivative feedback control has several advantages to offer, amongst which are ease
of tuning of the controller gains and a superior performance following load torque
disturbances.
A laboratory size drive system was designed and built, and used to validate simulation
predictions for both the switching strategy and pseudo-derivative feedback control. A
microcontroller based hardware implementation of both the switching strategy and a digital
pseudo-derivative feedback controller was adopted, with the switching strategy being
implemented using an off-line approach of precalculating the switching angles and storing
these in look-up tables.
The armature voltage controller comprises a dual-converter employing IGBTs as switching
devices. The use of IGBTs allows higher switching frequencies at significant power levels
than would be possible if GTOs were used. It also simplifies the gate drive circuit design
and minimises the need to use snubber circuits
Predictive control of a direct series resonant converter with active output voltage compensation
Modern high power supplies are based on resonant converters in order to use high frequency reactive elements (for reduced size) without sacrificing converter efficiency. In an effort to achieve compact high power supplies, direct power converter topologies have been considered, since these are mainly characterised by their high power density. A direct resonant converter topology combines matrix converters with conventional resonant converters.
This work focused on achieving high quality input/output power and high efficiency. Thus, this thesis presents the research on the control of a direct series resonant converter. Since the resonant converter allows a sinusoidal high frequency output current to be generated, zero current switching (ZCS) was considered to reduce the power losses. Hence, since the converter is switched at every zero crossing of the output current (fixed period), model predictive control was considered.
Different predictive approaches for controlling the input and output currents were developed and analysed, however, owing to the characteristics of the topology, these strategies resulted in a suboptimal control. Therefore, in order to improve the input and output qualities (reduce distortion), an output voltage compensation strategy was proposed. This compensation approach is based on adding an H-bridge converter in series between the matrix converter and the resonant tank. This converter improves the voltage applied to the resonant tank, thus, reducing the distortion at the output and, as a consequence, also the distortion at the input. The H-bridge converter utilises only a small capacitor on the dc side in comparison with conventional resonant converters and operates at a low voltage.
Simulations were carried out using MATLAB/Simulink and an experimental prototype was built to validate the strategies proposed, achieving a reduction of the input current THD from 4.4% to 2.7%, a reduction of the output current distortion of approximately 40% and an analytically derived efficiency of 89.5%
Real-time model-based loss minimisation control for electric vehicle drives
PhD ThesisEnvironmental concern and the opportunity for commercial gain are two
factors driving the expansion of the electric vehicle (EV) market. Due to
the limitations of current battery technology, the efficiency of the traction
drive, which includes the electric motor and power electronic converter,
is of prime importance. Whilst electric machines utilising permanent
magnets (PMs) are popular due to their high energy density, industry
concerns about the security of supply have led to interest in magnet-free
solutions. Induction machines (IMs) offer such an option.
Control of IMs is a mature but complex field. Many techniques for optimising
the efficiency of the drive system have been proposed. The vast
majority of these methods involve an analytical study of the system to
reveal relationships between the controlled variable and efficiency, allowing
the latter to be optimised. This inevitably involves simplifications
of the problem to arrive at a practically-implementable control scheme.
What has not been investigated is real-time calculation of the system
losses in order to optimise the efficiency, and the work presented in this
thesis attempts to achieve this.
The conventional control scheme is examined and a new structure implemented
where a model of the system loss is able to directly influence
the switching action of the inverter, thus reducing loss. The need to
maintain performance alongside loss minimisation is recognised and a
cost function-based solution proposed. The validation of this structure
is performed both in simulation and on a practical test platform.
A model of the principle losses in the drive system is derived, taking
into account the processing power typically available for this application,
and implemented in the structure outlined. The effect of the new
control scheme on efficiency is investigated and results show gains of up
to 3%-points are achievable under certain conditions
Wide-bandgap semiconductor based power converters for renewable energy systems
The demand for low carbon economy and limited fossil resources for energy generation drives the research on renewable energy sources and the key technology for utilisation of renewable energy sources: power electronics. Innovative inverter topologies and emerging WBG semiconductor based devices at 600 V blocking class are the enabling technologies for more efficient, reliable and accessible photovoltaic based electricity generation.
This thesis is concerned with the impact of WBG semiconductor based power devices on residential scale PV inverter topologies in terms of efficiency, volume reduction and reliability. The static and dynamic characterisation of the Si and WBG based devices are carried out, gate drive requirements are assessed and experimental performance comparison in a single phase inverter is discussed under wide range of operating conditions. The optimisation of GaN HEMT based single phase inverter is conducted in terms of converter efficiency, switching frequency and converter volume. The long term mission-profile based analysis of GaN and Si based devices is conducted and impact of WBG devices under low and high switching frequency conditions in terms of power loss and thermal loading are presented. Finally, a novel five-level hybrid inverter topology based on WBG devices is proposed, simulated and experimentally verified for higher power applications
A PWM Strategy for the Minimisation of Losses in a 3-level T-type Voltage Source Inverter
This paper discusses the approach for the witching loss minimisation in a 3-level inverter. It utilises a model predictive method which is used for evaluation of both the switching loss and voltage unbalance. The method is based on the cost functions implemented to provide simultaneous minimisation of loss and DC link voltage balance control. The simulation results shown that the total loss is reduced in 15% compared to a standard PWM strategy for a 3-level inverter operating at PWM frequency of 16 kHz
Study and analysis of state-of-the-art FCS-MPC strategies for thermal regulation of power converters
La degradación en los convertidores de potencia basados en silicio, enmarcados en sistemas de tracción
eléctrica y fuentes de energías renovables, es un tema de estudio de especial interés para aquellas
aplicaciones donde los fallos amenazan la seguridad de personas o donde el mantenimiento es particularmente
costoso. Motivado por la influencia de los fallos en IGBTs sobre los fallos habituales en los convertidores
de potencia comunes, este trabajo utiliza la herramienta software PLECS como marco de trabajo para
la simulación de algoritmos de control predictivo basado en modelo con conjunto finito de acciones de
control (FCS-MPC) que pretenden -simultáneamente a conseguir el seguimiento eléctrico- extender directa o
indirectamente la vida útil de los IGBTs.
El trabajo se enfoca principalmente a la simulación en ordenador de los algoritmos controlando un inversor
de dos niveles conectado a una carga RL. Además, pretende también introducir la implementación de
éstos sobre un microcontrolador para su estudio controlando el inversor simulado en la plataforma PLECS
RT Box 1, con el fin último de poder desarrollar validaciones de los controladores basadas en técnicas
Hardware-In-the-Loop.Degradation of silicon-based power electronics converters in traction and renewable energy systems is
a topic of interest particularly where module failure supposes a safety threat or where maintenance
becomes especially expensive. Motivated by the influence of IGBT aging in usual power converters, this work
uses the software tool PLECS as framework to simulate Finite Control Set Model Predictive Control (FCSMPC) algorithms that, simultaneously to achieving a certain current tracking, aim to directly or indirectly
extend IGBTs’ lifetime.
Whilst the work focuses on offline simulation of the algorithms on PLECS, it also targets to pave the way
to implement algorithms in a micro-controller and to study how they control a two-level inverter connected
to a RL load simulated on a PLECS RT Box 1 platform. The ultimate goal is to develop validations based on
Hardware-In-the-Loop techniques of the control algorithms.Universidad de Sevilla. Máster Universitario en Ingeniería Electrónica, Robótica y Automátic
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