Dissertations / Theses on the topic 'Bi-directional Power Converters'

The objective of the research is to develop a cost-effective high-power bi-directional dc/dc converter with low total-device ratings, reduced system parasitic effects, and a wide input/output range. Additional objectives of the research are to develop a small-signal model and control methods, and to present performance characterizations. Device stresses in the proposed topology are controlled to maintain minimal levels by varying the duty ratio and phase-shift angle between the primary and the secondary bridges, which results in a low total-device rating, when compared to conventional bi-directional dc/dc topologies. In the proposed topology, soft switching, which reduces power loss, can be realized under specific operating conditions. When the condition that causes minimal device stress is satisfied, zero-voltage switching (ZVS) can be obtained. In the research, ZVS capability is explored for a wide range of voltage conditions as well as for the minimal device-stress condition. The performance characterization includes verifying the soft-switching regions and power-loss estimation. Another part of the thesis is the controller design of the converter. Small-signal models and feedback controllers are developed, and the controllers are experimentally validated. Because in the isolated high-frequency converters, transformer saturation is an important issue, a method to prevent transformer saturation is proposed and experimentally validated.

This dissertation covers several issues related to the ac-dc bus-interface bi-directional converters in renewable energy systems. The dissertation explores a dc-electronic distribution system for residential and commercial applications with a focus on the design of an ac-dc bi-directional converter for such application. This converter is named as the â Energy Control Centerâ due to its unique role in the system. First, the impact of the unbalanced power from the ac grid, especially the single-phase grid, on the dc system operation is analyzed. Then, a simple ac-dc two-stage topology and an advanced digital control system is proposed with a detailed design procedure. The proposed converter system significantly reduces the dc-link capacitor volume and achieves a dynamics-decoupling operation between the interfaced systems. The total volume of the two-stage topology can be reduced by upto three times compared with the typical design of a full-bridge converter. In addition, film capacitors can be used instead of electrolytic capacitors in the system, and thus the whole system reliability is improved. A set of ac passive plus active filter solutions is proposed for the ac-dc bus-interface converter which significantly reduces the total power filter volume but still eliminate the total leakage current and the common-mode conducted EMI noises by more than 90%. The dc-side low-frequency CM voltage ripple generated by the unbalanced ac voltages can be eliminated as well. The proposed solution features a high reliability and fits three types of the prevalent low-voltage ac distribution systems. Grid synchronization, a critical interface control in ac-dc bus-interface converters, is discussed in detail. First, a novel single-phase grid synchronization solution is proposed to achieve the rejection of multiple noises as well as the capability to track the ac voltage amplitude. Then, a comprehensive modeling methodology of the grid synchronization for three-phase system is proposed to explain the output frequency behaviors of grid-interface power converters at the weak grid, at the islanded condition, and at the multi-converter condition. The proposed models provide a strong tool to predict the grid synchronization instabilities raised from industries under many operating conditions, which is critical in future more-distributed-generation power systems. Islanding detection issues in ac-dc bus-interface converters are discussed in detail. More than five frequency-based islanding detection algorithms are proposed. These solutions achieve different performances and are suitable for different applications, which are advantageous over existing solutions. More importantly, the detailed modeling, trade-off analysis, and design procedures are given to help completely understand the principles. In the end, the effectiveness of the proposed solutions in a multiple-converter system are analyzed. The results drawn from the discussion can help engineers to evaluate other existing solutions as well.
Ph. D.

The main aim of this thesis is to develop a solar energy system for domestic utilities, using a bi-directional DC-DC boost converter with a battery storage system in it. Topologies of the converters employed in the existing system are not efficient, especially in high power applications because of complicated structures with many power devices. In order to step up the DC voltage of the solar panel to a value suitable for AC power conversion, the DC-DC converter topologies has used either multiple stages of voltage amplification or complicated structures with many power devices as the voltage gain offered by the standard boost converter is not adequate enough. This has led to the use of complicated switching control methods. As a result of such power converters with low power density, the cost of the system is also high with relatively low efficiency. The above-mentioned shortcomings have led researchers to investigate new topologies of converters and efficient control methods. The thesis investigates the existing topologies of DC-DC boost converters pointing out advantages and disadvantages and presents ten new topologies that are superior to existing ones. Detailed analysis of converters is presented, and the mathematical model is developed to determine the voltage gain as a function of duty cycle. The presented converter topologies are also designed, and prototypes fabricated in the laboratory. The fabricated converters are tested experimentally using Arduino micro-controller. Programs are developed to control the converters in different modes of operation and the performance curves are generated. The experimental results support the theoretical model developed and the obtained results are presented in the thesis. A bi-directional DC-AC converter topology is also developed to interface the solar panel to the AC grid. The developed topology makes use of one of the DC-DC converter topologies presented and offers battery backup facility in it. This system can be controlled to store power either from AC grid or from the solar panel and can power the AC load or inject power to the grid. Appropriate control methods are developed for the bi-directional converter system and extensive simulation studies are conducted using MATLAB/Simulink to demonstrate the operation of the system in different modes of operation and simulation results are also presented. The converter system has also been fabricated and tested with solar panels. The test results of different modes of operation are also presented. Finally, the authors’ viewpoint in the development of power electronics in solar application is presented.

With the recent revival of the hybrid vehicle much advancement in power management has been made. The most popular hybrid vehicle, the hybrid electric vehicle, has many topologies developed to realize this hybrid vehicle. From these topologies, as sub set was created to define a particular group of vehicles where the converter discussed in this thesis has the most advantage. This sub set is defined by two electric sources of power coupled together at a common bus. This set up presents many unique operating conditions which can be handled seamlessly by the DC-to-DC converter when designed properly. The DC-to-DC converter discussed in this thesis is operated in Discontinuous Conduction Mode (DCM) of operation because of its unique advantages over the Continuous Conduction Mode (CCM) operated converter. The most relevant being the reduction of size of the magnetic components such as inductor, capacitor and transformers. However, the DC-to-DC converter operated in DCM does not have the inherent capability of bi-directional power flow. This problem can be overcome with a unique digital control technique developed here. The control is developed in a hierarchical fashion to separate the functions required for this sub set of hybrid electric vehicle topologies. This layered approach for the controller allows for the seamless integration of this converter into the vehicle. The first and lowest level of control includes a group of voltage and controller regulators. The average and small signal model of these controllers were developed here to be stable and have a relatively fast recovery time to handle the transient dynamics of the vehicle system. The second level of control commands and organizes the regulators from the first level of control to perform high level task that is more specific to the operation of the vehicle. This level of control is divided into three modes called hybrid boost, hybrid buck and electric vehicle mode. These modes are developed to handle the specific operating conditions found when the vehicle is operated in the specific mode. The third level of control is used to command the second level of control and is left opened via a communication area network (CAN) bus controller. This level of control is intended to come from the vehicle s system controller. Because the DC-to-DC converter is operated in DCM, this introduces added voltage ripple on the output voltage as well as higher current ripple demand from the input voltage. Since this is generally undesirable, the converter is split into three phases and properly interleaved. The interleaving operation is used to counteract the effects of the added voltage and current ripple. Finally, a level of protection is added to protect the converter and surrounding components from harm. All protection is designed and implemented digitally in DSP.
M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE

Modern power distribution systems (PDS) utilize multiple converters, making power flow undergo several conversions between source and the load. Use of high frequency AC (HFAC) in PDSs eliminates a few stages of converters in addition to the smaller sized capacitors and inductors being used; making the converters much lighter in weight offering a variety of solutions for the weight critical applications such as spacecraft, aircraft and electric vehicle onboard PDSs. HFAC converters with resonant filters have been widely used in the past despite of being tuned to a single frequency. Thus, the variable frequency operation as well as parallel connection of multiple converters had been less efficient. This part of the research work focusses on development of a bi-directional AC-AC converter that could work within a range of grid parameters. The proposed two-stage converter constructed with wide bandgap power switches, a high-performance microcontroller, low-pass filters which operates at high switching frequencies provide the desired variable frequency and voltage operation capability. A major drawback in HFAC PDS had been the excessive power loss and voltage drop due to skin effect and proximity effect of conductors. This part of the research work investigates the development of new cable types with hollow core cross-sections. This would minimize skin effect losses by shifting much of the conducting material to the skin depth, keeping the weight increase to a minimal. Feasibility studies performed using PSCAD software showed improved performance of cables upto 100kHz; enabling using such as in wireless power transmission applications.

The DC House project strongly relies on renewable energy sources to provide power to the house for various loads. However, when these sources are unable to provide power at a certain time, a back-up energy source from a battery must be readily available to fulfill the house’s power needs. This thesis proposes a bi-directional flyback power converter to allow a single-stage power path to charge the battery from and to discharge the battery to the DC House 48 V system bus. The design, simulation, and hardware prototype of the proposed flyback bi-directional converter will be conducted to demonstrate its feasibility. Results from a 35W prototype demonstrate the operation of the proposed converter for both charging and discharging purposes.

Wave energy converter (WEC) harnesses energy from the ocean to produce electrical power. The electrical power produced by the WEC is fluctuating and is not maximized as well, due to the varying ocean conditions. As a consequence, without any intermediate power conversion stage, the output power from the WEC can not be fed into the grid. To feed WEC output power into the grid, a two-stage power conversion topology is used, where the WEC output power is first converted into DCpower through rectification, and then a DC-AC converter (inverter) is used to supply AC power into the grid. The main motive of this research is to extract maximum electrical power from the WEC by active rectification and smoothing the power fluctuation of the wave energy converter through a hybrid energy storage system consisting of battery and flywheel. This research also illustrates active and reactive power injection to the grid according to load demand through a voltage source inverter.

The DC House project relies primarily on renewable energy sources to provide DC power to the various loads of the house. However, not all renewable sources are capable of providing power at all times of the day. A back-up energy source in the form of a battery storage system must be available to meet the electrical needs of the house. A bi-directional flyback power converter was initially designed to allow a battery to charge from as well as discharge to the 48V bus line of the DC House. The design provided a 35W prototype to demonstrate the converter’s feasibility. Further improvements to increase power output through changes in design as well as improving the control scheme of the bi-directional converter were conducted. Results allowed an increase of output power to 48W with efficiency at 82% for both charging and discharging. The improvements to the control scheme allowed for better management of charging and discharging cycles of the battery.

The PhD project aims to develop a smart grid-connected inverter (SGCI) for a micro-grid, which can be applied in a built environment such as a community, and associated power electronic DC/DC converters. The micro-grid generally includes distributed renewable power generators and battery storage. The SGCI is a bi-directional DC/AC inverter for distributed generation with battery storage installed at its DC side. In one aspect, it is expected the DC/AC inverter functions as a controlled inverter that can deliver expected real power to the power grid with quantitative reactive power compensation (RPC). In other words, all the SGCIs in the community microgrid can share the reactive power of the whole community because a SGCI can quantify its active and reactive power output. It is also expected that the inverter can work in both on-grid and off-grid modes. In other words, the DC/AC inverter functions as a controlled rectifier with high quality power factor correction (PFC), which can deliver expected DC power from the AC power grid at unity power factor. With the above features, battery storage on the DC bus of the SGCI can be charged/discharged through a four-phase, interleaved, bi-directional, boost/buck DC/DC converter (IBDBBC) for distributed renewable power system, either wind or solar PV or hybrid wind/solar PV system. The IBDBBC can discharge power from a low voltage battery to a high voltage DC bus as the IBDBBC operates in boost mode, or it can also draw power from the DC bus to charge the battery as the IBDBBC operates in buck mode. Based on MATLAB/Simulink, a mathematical model was developed for the grid-connected bi-directional DC/AC inverter that operates as a rectifier with PFC and as a grid-connected inverter (GCI) with expected real power output and quantitative RPC. In a practical application, the sampling of input signal through AD converter usually has some noise due to common-mode interference; simulation results demonstrate that the second order generalised integrator (SOGI) has great advantages to prevent interference. Therefore, SOGI can be utilised to construct a pair of orthogonal signals in a single-phase system to instantaneously split grid’s active and reactive power to achieve RPC for local community loads. The methodology of the constructed the pair of orthogonal signals was also used to generate the required reference current for the DC/AC inverter when which operated as a single-phase rectifier with PFC. Using three TI C2000 Solar Inverter DSK Boards, a small lab scale distributed power system was developed. In the lab distributed power system, the operating mode of the inverters could be switched between on-grid and off-grid through instruction from the control centre. The lab test outcomes demonstrate that each distributed power system unit worked properly under loss of power grid signal, simulating grid failure.

Indiana University-Purdue University Indianapolis (IUPUI)
This study presents a novel converter configuration that is related to the area DC-DC power converters. To begin with, a brief introduction is given by stating the importance of power electronics. Different types of converters, their operating principles and several new topologies that are being proposed over the years, to suit a particular application with specific advantages are listed in detail. In addition, pro- cedure for performing small signal analysis, which is one among the several averaging techniques is summarized in the first chapter. In the second chapter, small signal modeling is carried out on the single input dual output DC-DC buck converter. This analysis is performed to get a clear un- derstanding on the dynamics of this novel configuration. Routh stability criterion is also applied on this converter topology to determine the limiting conditions for operating the converter in its stability. Third chapter proposes the single input multiple output DC-DC synchronous buck converter. It’s operation, implementation and design are studied in detail. In further, small signal analysis is performed on this topology to determine the transfer function. In the following chapter, results obtained on comparison of a losses between the conventional and traditional topologies are presented in detail. In addition, results achieved during the analysis performed in the previous chapter are displayed. In the end, advantages and its highlights of this novel configuration proposed in this study is summarized. Future course of actions to be done, in bringing this configuration in to practice are discussed as well.

碩士
國立臺灣科技大學
電機工程系
94
This thesis presents the design and implementation of a digital signal processor based bi-directional dc-dc power converter for battery charge and discharge. When power converters operate at boost mode, the low-voltage side battery will discharge and provide power for dc-link; while at buck mode, the high-voltage side dc-link will charge the battery. The output voltage can be steady with voltage and current feedback control. The high-frequency transformer which uses two windings in parallel with power converter, together with the use of interleave control will split input current and raise the efficiency of conversion. In buck mode, the power switches are operated by phase-shifted control with soft switching and thereby reduce switching loss. The 16-bit digital signal processor, TMS320LF2407A, is used to implement the control function of the system. Experiments of 500W power converter are given. The terminal voltage range of battery is 20V~27V, and the dc-link voltage is 300V. The efficiency at full load of boost and buck modes are 88% and 92%, respectively.

碩士
國立臺灣科技大學
電機工程系
92
This paper presents the analysis and implementation of a unity power factor, three-phase, three-level, dual bi-directional power converter for induction motor drives. In order to reduce current harmonic, the neutral-point-clamped power converter and power inverter are adopted to convert three-phase electrical power and to drive induction servo motor, respectively. Based on synchronous rotating-frame on the ac input side, the proposed ac-to-dc power converter is employed to improve power factor to unity and to reduce current harmonic as well. The dc-to-ac power inverter controlled by indirect rotor flux oriented algorithm is used to yield the rotor speed stably. In addition, the three-phase voltage command of power inverter is adjusted by voltage error between upper and lower capacitors at dc-link in order to decrease voltage imbalance between capacitors when rotor speeds up or down. With the instantaneous power balance control, the proposed system can not only convert three-phase electrical power from ac input, but also yield dc-link voltage stably. In order to reduce circuitry complexity, a low-cost, 16-bit digital signal processor (DSP TMS320LF2407A) is used to serve as the core control device to implement a 1.5kW drive system under 2.5kHz switching frequency. Experimental data show that power factor is improved to unity and total current harmonic distortion is around 3.6%, 6.6% at ac input side and induction motor, respectively. The efficiency of whole system reaches 86% and voltage error between upper and lower capacitors is approximate to zero under 2000rpm, 7.1N-m output. Besides, the regenerative power is sent back to the input side of power converter when motor is braking. Finally, simulation and experiment results are given to justify the proposed system performance.

Grid connected converters are widely used as front end rectifiers, interface between renewable energy and grid, and power quality applications. Popular control techniques to generate gating signals for active devices, reported in literature are voltage-oriented control, direct power control and one cycle control. In literature, one cycle control has also been reported as scalar resistive emulation or unified constant frequency integration control. The above-mentioned control techniques has been collectively addressed as conventional one cycle control (C-OCC). Light load instability and steady state dc offset phenomenon are the major concerns with of the conventional one cycle control reported in literature. These issues were addressed in the literature by treating them independently. This thesis proposes a common solution to address the light load instability and steady state dc offset phenomenon of conventional one cycle control. C-OCC employs peak detection comparison method, hence the peak of the current always confines with the grid voltage. Therefore, the average current will differ by the ripple error. This results in the steady state dc offset, which is more severe at light load. Further in C-OCC, since the valley of current is not controlled a localized sub-harmonic instability occurs when slope of the falling current is greater than that of the slope of carrier. This thesis proposes a method to control both peak and valley of current, such that the converter changes its state when the expected value of current has been attained. Valley of current in each carrier cycle is decided such that the current has no steady state dc offset in current. To control peak and valley of current, this comparison is necessitated once more. This results in two comparisons in a carrier cycle, hence the name dual comparison one cycle control (DC-OCC). A generalized approach for controlling average current in a carrier cycle for grid connected converter has been proposed. Stability of the inherent current loop in DC-OCC, using propagation dynamics of small disturbance, showed that the proposed control strategy did not suffer from localized sub-harmonic instability. In a converter controlled by C-OCC and DC-OCC, the current lags the grid voltage. The reason for this has been discovered to be the inductive drop across the boost inductor. A novel method to compensate for the inductive drop is proposed in this thesis. The sensed input current is modified by adding a 90°phase shifted current with appropriate gain and is used for comparison to generate gating signals for active devices. The sensed input current is added with a fictitious current, generated from gating signal of the active devices, to enable bi-directional power ow in converters controlled by DC-OCC. A second order band pass filter (BPF) is used to generate the fictitious current from the gating signal. Effects of BPF corner frequency in quality of current drawn or injected into the grid is used during the design of the filter. The sum of sensed input current and fictitious current, is further modified by adding a 90°phase shifted current with appropriate gain. This modification enabled the converter to draw or inject power at an adjustable displacement power factor. Moreover, this modification also enables the converter to operate as a STATCOM. The gain of the phase shifted current determines the phase of the current drawn or injected. The current loop showed a tendency to become unstable when the gain of the phase shifted current approached 0.5. Small signal model of the converter is used to analyze this instability. Average modeling technique is used to derive the model of the converter controlled by DC- OCC. Further, the non-linear average model is linearized using small signal analysis. The small signal model shows the presence of an inherent current loop with a proportional controller. Gain of the proportional controller is the effective resistance seen by the current loop. As the gain of the phase shifted current loop approaches 0.5, the closed poles of the inherent current loop crosses over to the right half of s-plane, causing an instability in the current loop. Design of voltage loop controller parameters is also presented in this thesis. All of the above modifications are validated in simulations and experiments. Simulation and experimental results are presented in this thesis for converters in the range from 600 W to 2 kW.

碩士
國立高雄應用科技大學
電機工程系博碩士班
103
The frequency of most AC power systems is 50Hz or 60Hz. However, 400Hz power systems are widely used in the aircraft, communications and vessels. If conventional converter input frequency and output frequency are not the same. You must use the AC-DC and DC-AC two-stage power converter to achieve frequency conversion function. If you can use a single-stage power converter and provide two different frequency AC power at the same time, it will improve the flexibility of application for power converter. This thesis develops a bi-directional 60Hz-400Hz medium frequency power converter, its circuit architecture consists of a single-stage power converter as a major converter, a DC port, 60Hz AC port and a 400Hz medium frequency port. The digital signal processor TMS320F28035PN is used to control the system. Finally, a hardware prototype will be developed and tested to verify the performance of the proposed 60Hz-400Hz medium frequency power converter.

博士
中原大學
電機工程研究所
95
In recent years, growing concerns about environmental issues have demanded more clean energy sources such as fuel cells, wind turbines, and photovoltaic arrays. The rapid advances in fuel cell technology and power electronics have enabled the significant developments in fuel cell power system. The fuel cells have numerous advantages such as high density current output ability, clean electricity generation and high efficiency operation. However, the fuel cell characteristics are different from that of the traditional chemical-powered battery. The fuel cell output voltage drops quickly when first connected with a load and gradually decreases as the output current rises. The fuel cell also lacks energy storage capability. Therefore in power supply system applications, an auxiliary energy storage device (i.e. lead-acid battery) is always needed for a cold start and to absorb the regenerated energy fed back by the load. In addition, a bidirectional DC/DC converter is also needed to draw power from the auxiliary battery to boost the high-voltage bus during starting. The regenerated energy can be also fed back and stored in the battery using the DC/DC converter. In this dissertation, a high efficiency bidirectional isolated DC/DC converter for fuel cell power systems is studied. The new converter has the advantages of high efficiency, simple circuit and low cost. The detailed design and operation considerations are analyzed and described. Simulation results from the proposed circuit are given to verify the operation principles. A laboratory prototype is also implemented and tested to show its performance. Keywords: Clean energy source, Fuel cell power system, Bidirectional isolated dc-dc converter, Lead-acid battery

碩士
國立高雄應用科技大學
電機工程系博碩士班
106
The frequency of most AC power systems is 50Hz or 60Hz. However the 400Hz power systems are used in the communications, vessels and aircraft. If there is a frequency converter that can convert 400Hz voltage to 60Hz and 50Hz, or convert 60Hz or 50Hz voltage to 400Hz, it will improve the flexibility of 60Hz and 50Hz general power supplies and the convenience of using special power equipments with 400Hz voltage. This paper proposes a 60Hz-400Hz bi-directional frequency power converter based on decoupling technique. Through the decoupling technology, the function of bi-directional frequency conversion can achieve using only a single-stage power electronic converter. To verify the feasibility of the proposed 60Hz-400Hz bi-directional frequency power converter based on decoupling technique, a 60Hz-400Hz bi-directional frequency converter with the digital signal processor TMS320F28069 as controller was designed for experimental verification. The experimental results prove that the proposed frequency converter can achieve the expected performance.

The use of high power converters has increased tremendously. Increased demand for transportation, housing and industrial needs means that more number of power converters interact with the utility power grid. These converters are non-linear and they draw harmonic currents, significantly affecting power quality. To reduce harmonics, filters, power factor correction circuits and capacitor banks are required. And the development of hybrid technologies and renewable energy power stations trigger a demand for power converters with bi-directional capabilities. The objective of this thesis is to develop a high power quality, bi-directional AC-DC power converter that is a solution to the aforementioned problems. This thesis studies an existing topology for a high power AC-DC power conversion with transformer isolation. The topology consists of an uncontrolled rectifier followed by a DC-DC converter to produce a set voltage output. A design example of the topology is simulated using the PSIM software package (version 6). Critical performance characteristics such as power factor and total harmonic distortion are analyzed. Following that study a new topology is proposed, which is an improvement over the older design, with reduced power conversion stages. The new topology has a fully controlled current source Pulse Width Modulation (PWM) rectifier at the front end to replace the uncontrolled rectifier and DC-DC combination. This topology has multiquadrant operational capabilities and the controller employs Selective Harmonic Elimination techniques to produce the programmed PWM switching functions for the rectifier. A design example of the converter and the digital controller are simulated in PSIM environment. The converter input current THD (Total Harmonic Distortion) and input power factor are within IEEE 519 and DoE standards. The converter is simulated in both first and fourth quadrant operations. A side-by-side comparison of the two topologies is done with respect to design and performance features such as power factor, THD, filter size, etc. The new topology converter provides performance superior to that of the older topology. Finally the thesis explores possible applications for the converter in power supplies, renewable energy and hybrid technologies.

碩士
國立臺南大學
電機工程學系碩士班
101
Nowadays electric utilizes globally are heavily investing to upgrade their antiquated delivery, pricing, and service networks including investments in the advanced metering infrastructure which usually includes direct control and monitoring of devices and appliances inside customer premises. Therefore this thesis is aimed to develop a smart charger of electric vehicle with power converters and super-capacitor enhancement, hence anticipating reaching the rapid battery-charging speed and the bidirectional line interactive for further smart grid. The method proposed in this thesis is examined under various scenarios. The results will help consolidate the feasibility and practicability of the approach for the applications considered.

碩士
國立臺灣科技大學
電子工程系
104
In this thesis, an isolated high-power bi-directional DC-DC converter is studied and implemented. The prototype circuit consists of two stages of bidirectional DC-DC converters. The stage attached to the battery-side is an interleaved buck/boost converter, and the stage of the grid-side is a three-phase series resonant converter. The battery-side stage consists of two buck / boost converters, so the load current can be shared by these two circuits. Consequently, it can reduce the stress of the switch elements. Besides, the switching control signals of the two converters have a phase-shifted of 180° each other, so it can effectively reduce the output current ripple. The grid-side stage mainly consists of three half-bridge legs i.e. there are six switches. There are three isolated transformers and three resonant tanks, the control signal for each leg has a phase-shift of 120° with each other. This converter stage is operated as a series resonant converter. The three isolated transformers are Y-connected on both the primary and secondary sides. Compared with conventional single-transformer full-bridge configuration, the developed scheme can share the output power with three transformers, and the size and cost of each transformer are thus reduced. In this thesis, a prototype circuit with 20 kW rated power has been built and tested. A digital-signal processor chip TMS320F28035 is used to realize the controller of this converter. The measured efficiencies are all higher than 90 % within the full range of load conditions.

碩士
國立臺灣科技大學
電子工程系
105
In this thesis, a high power bi-directional DC-DC converter module for electric ships is studied and implemented, to be used for energy conversion between battery and DC bus. The module consists of two-stage circuits: a bi-directional buck/boost converter at battery side and a full-bridge series resonant converter at DC bus side. The developed bi-directional DC-DC converter module can be applied to the electric ship power system for charging/ discharging between battery and DC bus and adjusting bidirectional power transfer. In addition to establish a bi-directional DC-DC converter module and to discuss the bi-directional buck/boost converter and the full-bridge series resonant converter, the design criterions have been found. A 15 kW prototype module with circuit specifications of 400 V to 750 V input and output voltages was implemented and tested. A digital signal processor TMS320F28035 is used to realize the digital controller. According to the experimental results, the overall conversion efficiency can be up to 93%.

碩士
國立臺北科技大學
電機工程系
106
This paper is aimed to design and implement a CLLC resonant DC-DC converter with bi-directional power flow control, which is installed in front end of energy storage system (ESS) to act as energy buffer for load. The CLLC will provide extra power from ESS to load side when the load needed transient power. In contrast, the CLLC will store the regenerated energy from load side to ESS. Therefore, the pulsating energy yielded by transient load can be reduced through CLLC. Hence, not only the current stress of the front-end AC-DC converter or rectifier but also the risk of grid’s overload are effectively decreased. Due to the need of suppling transient power, the CLLC should provide the capability of fast current control. In addition, the CLLC can reach ZCS to enhance efficiency of the constructed ESS with adequate design under charging mode. Finally, a DSP (TMS320F28075)-based controller is used to constructed an 1kW/400V/48V bi-directional power flow converter as test platform to verify the effectiveness of proposed system.

博士
國立臺灣科技大學
電子工程系
102
This dissertation presents a isolated bi-directional DC-DC converter can be applied in power generation system and battery array testing system. The topology of this converter is a three-phase full-bridge type, that is mainly consists of three half-bridge switch legs (six switches), three isolated transformers, three half-bridge synchronous rectification switch legs and inductor. The three isolated transformers are configured in Y-Δ connection with series high-voltage side and parallel low-voltage side, it can reduce the turns of Y side and the winding current stress of Δ side by current sharing, besides, Y-Δ connection has high voltage transfer ratio. Comparing with the general single-transformer full-bridge type (four switches), it can share output power by three transformers, the size and cost of each transformer are thus reduced. Asymmetrical control scheme is used for driving the power switches, so that the zero-voltage-switching can be achieved. In this dissertation, a laboratory prototype with 11-kW rated power has been built and tested. The voltage of low-voltage side is 45 V and current is 240 A. A digital-signal processor chip TMS320F28035 is used to realize the controller of this converter. The measured efficiencies are above 90% form 20% to 100% load conditions.

碩士
國立清華大學
電機工程學系
103
This thesis presents a high power bi-directional three-phase four-wire half bridge converter for charger/discharger systems, including grid-connection mode, rectification mode and dc-bus voltage regulation mode. In grid-connection mode, power is transferred from DC to AC and injected into the utility grid. In rectification mode, the utility power is transformed to DC with power factor correction. In dc-bus voltage regulation mode, the converter can inject power into the utility grid or supply DC loads when the bus voltage is higher than the setpoint. On the contrary, it will regulate the voltage by operating at rectification mode. A single-chip microcontroller Renesas RX62T is adopted to realize the control algorithm. In the thesis, component selection, including IGBT modules and design of inductors is first presented. Next, control law and operation principle of the converter with division-summation (D- ) digital control are addressed. Additionally, the converter in grid-connection mode and rectification mode with the D- digital control is simulated. Due to the DC bus constructed with capacitors in series, capacitor voltage balancing algorithm is also proposed. Finally, the converter has been implemented and tested so as simulated and measured results can verify the control scheme and feasibility. The major contributions of this research can be summarized as follows: First, the derived control law can accommodate grid voltage and inductance variations. The microcontroller RX62T is adopted to calculate the duty ratio exactly which can avoid output current distortion when inductance varies over a wide range. Secondly, the proposed operation does not yield high frequency common mode voltage so as it can be applied to PV inverter system. Thirdly, the converter has a property of multi-functions which can not only reduce production cost and volume, but can execute different operation modes according to load demands.

碩士
國立高雄第一科技大學
電子工程系碩士在職專班
103
The aim of this thesis is to present a converter, which can achieve high voltage gain, reduce cost, and promote efficiency. It has the intrinsic features of leakage energy recycling and zero-voltage switching. The presented converter consists of a boost converter, a buck-boost converter, and a high frequency transformer. As compared to traditional bi-directional DC-DC converters, fewer power active components, lower cost, easier control design are its advantages. Under the same conditions of turns ratio and duty ratio, higher voltage gain can be accomplished. To improve conversion efficiency, the energy stored in the leakage inductance of the transformer can be totally recycled. In the thesis, theoretical analysis, detailed derivation, and operation principle are conducted. The feasibility of the presented converter has been verified through hardware implementation.

碩士
國立中山大學
電機工程學系研究所
102
With the development of smart grids, more and more Distributed Generation Systems (DGSs) and Renewable Energy Generation Systems (REGSs) will be interconnected to power grids in the foreseeing future. Most of DGSs and REGSs are DC power sources; therefore, power inverters are used to convert DC power of DGSs and REGSs to AC powers and to interconnect to power grids. In addition, most of REGSs are unstable power sources; they require Energy Storage Systems (ESSs) to stabilize output power. The ESSs can be charged by the REGSs and by power grids if necessary, so the design and development of a bi-directional AC/DC converter is necessary. This thesis develops and implements a single-phase bi-directional AC/DC converter with power factor correction and phase-locked loop. A fully digital controller for the implemented 1kW bi-directional AC/DC converter is designed by Microchip dsPIC33FJj16GS504. Experimental results show that the proposed single-phase bi-directional AC/DC converter can not only has rated power of 1kW but also achieve power factor correction and phase-locked loop.

碩士
國立臺北科技大學
電力電子產業研發碩士專班
98
This thesis is aimed to design a bi-directional full-bridge DC-DC converter for high power application, its buck and boost mode are implemented through phase-shift full-bridge and current-fed full-bridge circuit structure. To overcome the power limitation of high-frequency transformer, therefore multiple transformers connected in parallel are carried out to increase output power. A careful components placement and layout of power circuit are proposed to guarantee well current sharing among paralleled transformers and less leakage inductance. The proposed controller consists of voltage and current regulator in cascade to achieve constant-voltage and constant-current control. In order to facilitate the studies performed in this thesis, a DSP-based converter with necessary peripherals is established to provide 400V input and 10kW/310V output. All the control algorithms are implemented by assembly language to shorten the execution time, and hence the carrier frequency can be increased to reduce the converter volume. After establishing the converter, some measured results are provided to show its successful operation and effectiveness.

碩士
國立臺北科技大學
電機工程系研究所
99
This paper is aimed to design a single-phase DC- AC converter with bi-directional power flow control. The converter is implemented by a full-bridge circuit with bipolar PWM control to act as grid-connected inverter or provide transient current to non-linear load to reduce AC voltage harmonics. A power device with both motoring and generating mode is connected to DC link and controls power flow between power device in DC-side and power grid in AC-side of the proposed DC-AC converter according to DC link voltage. The converter becomes DC-AC converter and sends the energy generated by the power device to electric grid when the DC-link voltage is higher than default voltage command. As the DC link voltage is less than default voltage command, the proposed converter withdraws power from electric grid to the power device. Meanwhile, the converter also provides near unity power factor control for electric grid in the bi-directional power flow control. In order to enhance light-load efficiency of the proposed converter when send the energy to electric grid, an integral-cycles injection of current is developed. When the generated power is less than a preset value, the energy will be stored in the electrolytic capacitance installed in the DC link and all the power switches of full-bridge circuit are turned off. In the need of high dynamic response for AC power supply with line frequency transformer as isolated output, the AC-side of the proposed converter is connected to output of the line-frequency transformer. The converter co-works with the AC power supply and provides extra transient current, which is determined by the difference between AC voltage command and actual voltage of load, for the nonlinear loads to compensate the voltage distortion. Therefore, output voltage harmonics of the AC power supply can be reduced dramatically to meet the requirement of regulations. A single-phase full-bridge DC-AC converter controlled by a DSP-TMS320F28035 with 110V/1 kW is constructed. To realize the digital power control, all the controlling strategies are written by software. Some experimental results are provided to show its efficiency.

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και τη μοντελοποίηση ενός αιολικού συστήματος παραγωγής ηλεκτρικής ενέργειας βασισμένο σε σύγχρονη γεννήτρια μόνιμου μαγνήτη (PMSG). Ειδικότερα, παρουσιάζονται και αναλύονται όλα τα τμήματα που αποτελούν το αιολικό σύστημα καθώς και οι λογικές ελέγχου που ακολουθήθηκαν για την αποτελεσματική λειτουργία του. Επιπλέον, μελετάται και μοντελοποιείται μια διάταξη αποθήκευσης ενέργειας από την οποία πλαισιώνεται το αιολικό σύστημα κατά την αυτόνομη λειτουργία του. Τέλος, παρουσιάζονται και σχολιάζονται τα αποτελέσματα της προσομοίωσης της λειτουργίας του συστήματος, σε σύνδεση με το δίκτυο και κατά την αυτόνομη λειτουργία του. Για την ανάπτυξη του μοντέλου και την προσομοίωση χρησιμοποιήθηκε το πρόγραμμα Simulink/Matlab. Στο Κεφάλαιο 1 γίνεται αναφορά στο ενεργειακό πρόβλημα και μια γενική εισαγωγή στις ανανεώσιμες πηγές ενέργειας. Επιπλέον, δίνονται διάφορες πληροφορίες γύρω από την αιολική ενέργεια και αναλύονται τα πλεονεκτήματα και μειονεκτήματα της χρήσης ανεμογεννητριών. Επίσης, παρουσιάζεται η δομή μιας ανεμογεννήτριας και παραθέτονται διάφοροι τύποι ανεμογεννητριών, ενώ δίνονται και οι βασικές σχέσεις μετατροπής της αιολικής ενέργειας σε ηλεκτρική. Στο Κεφάλαιο 2 γίνεται ανάλυση κάθε τμήματος της ανεμογεννήτριας (πτερωτή, σύστημα μετάδοσης κίνησης, γεννήτρια) και παρατίθενται οι εξισώσεις που περιγράφουν τη λειτουργία τους. Επιπρόσθετα, παρουσιάζεται ο τρόπος μοντελοποίησης του κάθε τμήματος στο περιβάλλον του Simulink. Ιδιαίτερη έμφαση δόθηκε στη μελέτη της σύγχρονης γεννήτριας μόνιμου μαγνήτη καθώς παρουσιάζεται με λεπτομέρεια η δομή της καθώς και οι αρχές που διέπουν τη λειτουργία της. Τέλος, δίνονται όλα τα χαρακτηριστικά μεγέθη της ανεμογεννήτρια που χρησιμοποιήθηκε στην παρούσα εργασία. Στο Κεφάλαιο 3 αρχικά, γίνεται μια γενική παρουσίαση των στοιχείων που αποτελούν τους μετατροπείς, ενώ στη συνέχεια παρουσιάζονται οι βασικές κατηγορίες μετατροπέων που υπάρχουν και αναφέρονται μερικοί βασικοί τύποι μετατροπέων που βρίσκουν εφαρμογή σε αιολικά συστήματα γενικότερα. Έπειτα, το κεφάλαιο επικεντρώνεται στους μετατροπείς που χρησιμοποιήθηκαν στο αιολικό σύστημα της παρούσας εργασίας καθώς εξηγείται ο τρόπος λειτουργίας τους και παρουσιάζεται ο τρόπος μοντελοποίησης τους στο Simulink. Έμφαση δόθηκε στον dc/dc μετατροπέα ανύψωσης τάσης που χρησιμοποιήθηκε, όπου γίνεται διαστασιολόγηση και παρουσιάζεται μια μικρή προσομοίωση της λειτουργίας του. Τέλος, παρουσιάζεται, επίσης, το φίλτρο που τοποθετείται στην έξοδο του αντιστροφέα. Στο Κεφάλαιο 4 περιγράφονται αναλυτικά η τεχνική διαμόρφωσης εύρους παλμών (PWM) και η τεχνική της ημιτονοειδούς διαμόρφωσης εύρους παλμών (SPWM), οι οποίες και εφαρμόστηκαν για την παλμοδότηση των μετατροπέων. Στη συνέχεια, περιγράφονται αναλυτικά οι μηχανισμοί ελέγχου που εφαρμόστηκαν με τη βοήθεια PI ελεγκτών, τόσο στην πλευρά της μηχανής (dc/dc μετατροπέας ανύψωσης τάσης) όσο και στον αντιστροφέα του αιολικού συστήματος. Στο Κεφάλαιο 5 παρουσιάζονται και σχολιάζονται τα αποτελέσματα της προσομοίωσης του αιολικού συστήματος σε σύνδεση με το δίκτυο. Το σύστημα προσομοιώνεται για δύο περιπτώσεις, σε πρώτη φάση γίνεται προσομοίωση του συστήματος υπό σταθερή ταχύτητα ανέμου ίση με 12 m/s και σε δεύτερη φάση προσομοιώνεται η λειτουργία του συστήματος για βηματικές μεταβολές της ταχύτητας του ανέμου. Στο Κεφάλαιο 6 μελετάται η αυτόνομη λειτουργία του αιολικού συστήματος το οποίο, πλέον, πλαισιώνεται με μια διάταξη αποθήκευσης ενέργειας. Αρχικά, παρουσιάζεται το σύστημα αποθήκευσης ενέργειας που χρησιμοποιήθηκε. Συγκεκριμένα η συστοιχία μπαταριών της οποίας δίνονται τα χαρακτηριστικά μεγέθη, καθώς και το μοντέλο της στο Simulink. Επίσης, παρουσιάζεται και μοντελοποιείται ο dc/dc μετατροπέας δύο κατευθύνσεων ο οποίος συνδέει τη συστοιχία με το υπόλοιπο σύστημα. Στη συνέχεια, περιγράφεται αναλυτικά ο μηχανισμός ελέγχου που εφαρμόζεται στη διάταξη αποθήκευσης ενέργειας για τον έλεγχο της φόρτισης/εκφόρτισης. Στο τέλος του κεφαλαίου παρουσιάζονται τα αποτελέσματα της προσομοίωσης του αυτόνομου αιολικού συστήματος για σταθερή ταχύτητα ανέμου-μεταβαλλόμενο φορτίο και για μεταβαλλόμενο άνεμο-σταθερό φορτίο.
In this thesis, a wind energy conversion system (WECS) based on a permanent magnet synchronous generator (PMSG) was studied and simulated. All parts of the WECS are presented and discussed in detail. Furthermore, control strategies for the generator-side converter and the voltage source inverter are developed. The WECS is simulated both in grid connected and stand-alone mode. In the stand-alone mode, the WECS is supplied with an energy storage system for which a bi-directional buck/boost converter and control strategy was designed. Finally, simulation results are presented and performance of the system in various modes of operation is evaluated. Simulink/Matlab is used for modeling and simulating the WECS. At the beginning of Chapter 1, a discussion of energy crisis and renewable energy sources is held. Furthermore, information about wind energy has been reviewed and its benefits and drawbacks are examined. In addition, the structure of a wind turbine and the principles of converting wind energy into electricity are presented. In Chapter 2 all parts of the wind turbine are studied and its characteristics are specified. Even more, the model of every part in Simulink is presented. Theoretical background, structure and operation principles of PMSG are presented in detail. In Chapter 3, firstly a general presentation of converters components takes place. Then the major existing categories of converter are presented and some basic types of converters, which are generally used in WECS, are mentioned. Moreover, the chapter focuses on the converters that are used in this thesis, explaining the way they operate. After all, their models in Simulink are shown. Emphasis was given to the dc/dc boost converter whose parameters are calculated and its operation is simulated. Finally, there is a presentation of the filter which was placed at the output of the inverter. In Chapter 4, Pulse-width Modulation (PWM) and Sinusoidal Pulse-width Modulation (SPWM) techniques that are used in this thesis are described. Moreover, the control strategy for the generator-side converter with maximum power extraction is presented. The control strategy of the voltage sourced inverter is shown as well. In Chapter 5 simulation results of the grid connected WECS are presented and evaluated. On the first part of the presentation, the WECS is simulated for constant wind speed (12m/s), and in the second part for step-changed wind speed. In Chapter 6 the stand-alone operation of the WECS is studied and supplied with an energy storage system. Initially, there is an analysis of the energy storage system, which was used, and in particular the battery bank, whose characteristics are given. Moreover, a Bi-directional dc/dc Buck-Boost converter which is used to interconnect the battery bank to the dc-link is presented and modeled. Afterwards, there is a detailed description of the control strategy used in order to control charging / discharging of the battery bank. At the end of this chapter, simulation results of two different stand-alone operation modes are presented, one with constant wind speed and variable load and the other one with step-changing wind speed and constant load.

This thesis deals with the design of Hybrid Energy Storage System (HESS) for Light Electric Vehicles (LEV) and EVs. More specifically, a tri-mode high-efficiency non-isolated half-bridge converter is developed for the LEV based HESS applications. A 2 kW, 100 V interleaved two-phase converter prototype was implemented. The peak efficiency of 97.5% and a minimum efficiency of 88% over the full load range are achieved. Furthermore, a power-mix optimizer utilizing the real-time Global Positioning System (GPS) data for the EV based HESS is proposed. For a specific design, it is shown that at the cost of less than 1.5% of the overall energy savings, the proposed scheme reduces the peak battery charge and discharge rates by 76% and 47%, respectively. A 30 kW bi-directional dc-dc converter is also designed and implemented for future deployment of the designed HESS into a prototype EV, known as A2B.