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EEE 2014 Projects

Category Archives

DYNAMIC CHARACTERIZATION OF POWER ELECTRONIC  INTERFACES

ABSTRACT:

                Voltage-type sources such as storage battery, AC  grid and constant-output-voltage-regulated converters have  dominated as input sources for power electronic interfaces for a long time, leading to development of different power stages dedicated to voltage-type input sources. Recent penetration of renewable energy sources has initiated the use of current-type sources as well as input-voltage-regulated converters as input sources for power electronic interfaces. While the power electronic converter topology remains unchanged in both cases, steady-state and dynamic properties of the coupled source-converter system are quite different. Moreover, the voltage/current nature of the load contributes to the complex dynamics as well. The paper investigates the factors determining the dynamic properties of a power electronic converter in a specific arrangement. The findings show that the open-loop converter (without any internal or external feedbacks) automatically adapts its dynamic properties to the properties stipulated by source and load if certain terminal constraints are satisfied. If internal or external feedback is activated, the dynamic properties of the converter may be varied as desired; however, the control design process is substantially different for each source/load arrangement. The findings presented in this project have not been presented in the literature by far.

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HIERARCHICAL CONTROL OF PARALLEL AC-DC CONVERTER INTERFACES FOR HYBRID MICROGRIDS

ABSTRACT:

In this project, a hierarchical control system for parallel power electronics interfaces between ac bus and dc bus in a hybrid microgrid is presented. Both standalone and grid-connected operation modes in the dc side of the microgrid are analyzed. Concretely, a three-level hierarchical control system is implemented. In the primary control level, the decentralized control is realized by using the droop method. Local ac current proportional-resonant controller and dc voltage proportional-in-tegral controller are employed. When the local load is connected to the dc bus, dc droop control is applied to obtain equal or proportional dc load current sharing. The common secondary control level is designed to eliminate the dc bus voltage deviation produced by the droop control, with dc bus voltage in the hybrid microgrid boosted to an acceptable range. After guaranteeing the performance of the dc side standalone operation by means of the primary and secondary control levels, the tertiary control level is thereafter employed to perform the connection to an external dc system.

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MANAGEMENT OF BATTERY-SUPER CAPACITOR HYBRID ENERGY STORAGE AND SYNCHRONOUS CONDENSER FOR ISOLATED OPERATION OF PMSG BASED VARIABLE-SPEED WIND TURBINE GENERATING SYSTEMS

ABSTRACT:

          Standalone operation of a wind turbine generating system under fluctuating wind and variable load conditions is a difficult task. Moreover, high reactive power demand makes it more challenging due to the limitation of reactive capability of the wind generating system. A Remote Area Power Supply (RAPS) system consisting of a PermanentMagnet Synchronous Generator (PMSG), a hybrid energy storage, a dump load and a mains load is considered in this project.

The hybrid energy storage consists of a battery storage and a supercapacitor where both are connected to the DC bus of the RAPS system. An energymanagement algorithm (EMA) is proposed for the hybrid energy storage with a view to improve the performance of the battery storage. A synchronous condenser is employed to provide reactive power and inertial support to the RAPS system. A coordinated control approach is developed to manage the active and reactive power flows among the RAPS components. In this regard, individual controllers for each RAPS component have been developed for effective management of the RAPS components.

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IMPLEMENTATION OF A HIGH-EFfiCIENCY, HIGH-LIFETIME, AND LOW-COST CONVERTER FOR AN AUTONOMOUS PHOTOVOLTAIC WATER PUMPING SYSTEM

ABSTRACT:

          This project proposes a new converter for photovoltaic (PV) water pumping or treatment systems without the use of chemical storage elements, such as batteries. The converter is designed to drive a three-phase induction motor directly from PV energy. The use of a three-phase induction motor presents a better solution to the commercial dc motor water pumping system.

The development is oriented to achieve a more efficient, reliable,maintenance-free, and cheaper solution than the standard ones that use dc motors or low-voltage synchronous motors. The developed system is based on a current-fed multiresonant converter also known as resonant two-inductor boost converter (TIBC) and a full-bridge three-phase voltage source inverter (VSI). The classic topology of the TIBC has features like high voltage gain and low input current ripple. In this paper, it is further improved with the use of a nonisolated recovery snubber along with a hysteresis controller and the use of a constant duty cycle control to improve its efficiency.

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DC MICROGRID FOR WIND AND SOLAR POWER INTEGRATION

ABSTRACT:

          Operational controls are designed to support the integration of wind and solar power within microgrids. An aggregated model of renewable wind and solar power generation forecast is proposed to support the quantification of the operational reserve for day-ahead and real-time scheduling. Then, a droop control for power electronic converters connected to battery storage is developed and tested. Compared with the existing droop controls, it is distinguished in that the droop curves are set as a function of the storage state-of-charge (SOC) and can become asymmetric. The adaptation of the slopes ensures that the power output supports the terminal voltage while at the same keeping the SOC within a target range of desired operational reserve. This is shown to maintain the equilibrium of the microgrid’s real-time supply and demand. The controls are implemented for the special case of a dc microgrid that is vertically integrated within a high-rise host building of an urban area. Previously untapped wind and solar power are harvested on the roof and sides of a tower, thereby supporting delivery to electric vehicles on the ground. The microgrid vertically integrates with the host building without creating a large footprint.

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CHARACTERIZING THE DYNAMICS OF THE PEAK-CURRENT-MODE-CONTROLLED BUCK POWER-STAGE CONVERTER IN PHOTOVOLTAIC APPLICATIONS

ABSTRACT:

This project investigates the dynamical properties and operational constraints of a PCM-controlled buck-power-stage converter in the photovoltaic (PV) applications. It has been already earlier noticed that the application of PCM control can make the converter unstable in the PV applications. The investigations reveal that the inductor-current feedback forces the open-loop converter to adopt the dynamic properties of a voltage-fed converter, and consequently, the stable operation is limited to the constant-voltage region of the PV generator. The developed small-signal models reveal that a right-half-plane pole appears in the converter dynamics, when the operation point enters into the constant-current region leading to instability. The stability can be restored by heavily compensating the inductor-current loop, which seriously removes the desired properties materialized in the conventional buck converter.

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AN ISOLATED MULTIPORT DC–DC CONVERTER FOR SIMULTANEOUS POWER MANAGEMENT OF MULTIPLE DIFFERENT RENEWABLE ENERGY SOURCES

ABSTRACT:

This project proposes a new isolated multiport dc–dc converter for simultaneous power management of multiple renewable energy sources, which can be of different types and capacities. The proposed dc–dc converter only uses one controllable switch in each port to which a source is connected. Therefore, it has the advantages of simple topology and minimum number of power switches. A general topology of the proposed converter is first introduced. Its principle and operation are then analyzed. The proposed converter is applied for simultaneous maximum power point tracking (MPPT) control of a wind/solar hybrid generation system consisting of one wind turbine generator (WTG) and two different photovoltaic (PV) panels.

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AN EFFICIENT UPF RECTIFIER FOR A STAND-ALONE WIND ENERGY CONVERSION SYSTEM

 

 ABSTRACT:

         In this project, a near-unity-power-factor front-end rectifier employing two current control methods, namely, average current control and hysteresis current control, is considered.This rectifier is interfaced with a fixed-pitch wind turbine driving a permanent-magnet synchronous generator. A traditional diode-bridge rectifier without any current control is used to compare the performance with the proposed converter. Two constant wind speed conditions and a varying wind speed profile are used to study the performance of this converter for a rated stand-alone load. The parameters under study are the input power factor and total harmonic distortion of the input currents to the converter.The wind turbine generator–power electronic converter is modeled in PSIM, and the simulation results verify the efficacy of the system in delivering satisfactory performance for the conditions discussed.

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AN EFFECTIVE CONTROL METHOD FOR QUASI-Z-SOURCE CASCADE MULTILEVEL INVERTER-BASED GRID-TIE SINGLE-PHASE PHOTOVOLTAIC POWER SYSTEM  

 

ABSTRACT:

         An effective control method, including system-level control and pulsewidth modulation for quasi-Z-source cascade multilevel inverter (qZS-CMI) based grid-tie photovoltaic (PV) power system is proposed. The system-level control achieves the grid-tie current injection, independent maximum power point tracking (MPPT) for separate PV panels, and dc-link voltage balance for all quasi-Z-source H-bridge inverter (qZS-HBI) modules. The complete design process is disclosed. A multilevel space vector modulation (SVM) for the single-phase qZS-CMI is proposed to fulfill the synthetization of the step-like voltage waveforms.

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A NOVEL SOFT-SWITCHING MULTIPORT BIDIRECTIONAL DC–DC CONVERTER FOR HYBRID ENERGY STORAGE SYSTEM

ABSTRACT:

          A novel multiport isolated bidirectional dc–dc converter for hybrid battery and supercapacitor applications is presented, which can achieve zero voltage switching for all switches in the whole load range. The bidirectional power flow between any two of the ports is free, and the circulating power is low for the well matching of the transformer voltages of all time regardless of the voltage variations of the battery and supercapacitor.Moreover,the current ripples are greatly decreased by interleaved control, which is good for battery and supercapacitor. The converter topology and the operation principle are introduced. Detailed analysis on soft-switching of all switches is given. On the basis of theoretical analysis, the principle and method for parameter designing are provided. A hybrid energy management strategy combining bus voltage control and energy management of the energy storage devices is proposed and the control scheme is presented.

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A HIGH-FREQUENCY LINK MULTILEVEL CASCADED MEDIUM-VOLTAGE CONVERTER FOR DIRECT GRID INTEGRATION OF RENEWABLE ENERGY SYSTEMS

 ABSTRACT:

          Recent advances in solid-state semiconductors have led to the development of medium-voltage power converters (e.g.,6–36 kV) which could obviate the need for the step-up transformers of renewable power generation systems. The modular multi-level cascaded converters have been deemed as strong contenders for the development of medium-voltage converters, but the converters require multiple isolated and balanced dc supplies. In this paper, a high-frequency link multilevel cascaded medium-voltage converter is proposed. The common high-frequency link generates multiple isolated and balanced dc supplies for the converter, which inherently minimizes the voltage imbalance and common mode issues. An 50v system is designed and analyzed taking into account the specified system performance, control complexity, cost, and market availability of the power semiconductors.

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Use of Synchronous Modulation to Recover Energy Gained From Matching Long Cable in Inverter-Fed Motor Drives

Abstract:

As inverter-fed motor drives generate fast- voltage pulses, the transmission-line effects on long motor cable and motor stator windings lead to overvoltage on the cable and motor terminals, as well as inside motor stator windings, and also an increase in the common-mode current. Such phenomenon would cause premature failure of the motor and cable insulation. A general protective measure is the use of a passive filter, such as RC and RLC   filter, to reduce the voltage surges by matching the cable impedance and/or altering the rise time of the voltage pulses. However, passive filter are bulky and lossy. This paper presents an active motor terminal filter with an energy recovery function that can achieve the same functions as the passive filter, but consumes much less power. The proposed filter recovers energy gained from suppressing motor terminal voltage surges and regenerating the recovered energy back to the whole system. An experimental filter has been built and evaluated on a 1-HP three-phase motor drive system. A comparative study into the performance among commonly used RC filter and RLC filter and the proposed filter will be given.

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Sensor less Control of BLDC Motor Drive for an Automotive Fuel Pump Using a Hysteresis Comparator

Abstract:

This paper develops the brushless dc (BLDC) Motor sensor less control system for an automotive fuel pump. The sensor less techniques that are based on a hysteresis comparator and a potential start up method with a high starting torque are suggested. The hysteresis comparator is used to compensate for the phase delay of the back EMFs due to a low pass filter (LPF) and also prevent multiple output transitions from noise or ripple in the terminal voltages. The rotor position is aligned at standstill for maximum starting torque without an additional sensor and any information of motor parameters. Also, the stator current can be easily adjusted by modulating the pulse width of the switching device during alignment. Some experiments are implemented on a single chip DSP controller to demonstrate the feasibility of the suggested sensorless and start up techniques.

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Integrated Inverter/Converter Circuit and Control Technique of Motor Drives With Dual-Mode Control for EV/HEV Applications

Abstract:

A new integrated circuit for motor drives with dualmode control for EV/HEV applications is proposed. The proposed integrated circuit allows the permanent magnet synchronous motor to operate in motor mode or acts as boost inductors of the boost converter, and thereby boosting the output torque coupled to the same transmission system or DC-link voltage of the inverter connected to the output of the integrated circuit. In motor mode, the proposed integrated circuit acts as an inverter and it becomes a boost-type boost converter, while using the motor windings as the boost inductors to boost the converter output voltage. Moreover, a new control technique for the proposed integrated circuit under boost converter mode is proposed to increase the efficiency. The proposed control technique is to use interleaved control to significantly reduce the current ripple and thereby reducing the losses and thermal stress under heavy-load condition. In contrast, single- phase control is used for not invoking additional switching and conduction losses under light-load condition.

Experimental results derived from digital-controlled 3-kW inverter/converter using digital  signal  processing  show  the  voltage  boost  ratio  can  go  up  to 600 W to 3 kW. And the efficiency is 93.83% under full-load condition while keeping the motor temperature at the atmosphere level. These results fully confirm the claimed merits for the proposed integrated circuit.

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Improved Angular Displacement Estimation Based on Hall-Effect Sensors for Driving a Brushless Permanent-Magnet Motor

Abstract:

We  propose  an  improved  method  for  angular  displacement  estimation  based  on  Hall-effect  sensors  for  driving  a brushless  permanent-magnet  (PM)  motor.  The control current              with an angle that leads to the backelectromotive force is then determined to extend the speed range of the motor. Traditionally,  Hall-effect  signals  are  measured  by  both  the  capture  interrupt        and  periodic  timer  interrupt  functions  before  the  angular  displacement  is  precisely  estimated  with  a  digital  signal  processor.     Unfortunately, the capture interrupt function is highly sensitive to external noise. The proposed method retains the periodic timer interrupt function and simplifies the estimation operation, so the controller is robust to external disturbances.  We used the improved method to adjust the phase lead angle for driving both a surface mounted PM motor and an interior PM synchronous motor.   Experimental results show that the improved    angular    displacement estimation effectively rejects noise and is 2.9 times faster than the traditional approach.

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DC/DC Buck Power Converter as a Smooth Starter for a DC Motor based on a Hierarchical Control

Abstract:

In  this  paper  a  smooth  starter,  based  on  a  DC/DC Buck power converter, for the angular velocity trajectory tracking task of a DC permanent magnet motor is presented. To this end, a hierarchical controller is designed, which is integrated with a  control  associated    with  the   DC   motor    based   on  differential flatness at the high level, and a control related to the DC/DCBuck  converter  based  on  a  cascade  control  scheme  at  the  low level. The control ofhigher level allows the DC motor angular velocity to track a desired trajectory and also provides the desired voltage profile that must be tracked by the   output voltage of the DC/DC Buck power converter. In order to assure the latter, a  cascade   control   at  the  low   level  is designed,    considering    asliding  mode    control   (SMC)     for  the   inner  current    loop a  proportional-integral  (PI)  control  for  the  outer  voltage  loop.

The hierarchical controller is tested through experiments Matlab, Simulink and   the DS1104    board   from space. The obtained results show that the desired angular velocity is well tracked under abrupt variations in the system parameters  and  that  the  controller  is  robust  in  such  operation  conditions,  confirming the  validity of the proposed controller.

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An Adjustable Speed PFC Bridgeless Buck Boost Converter Fed BLDC Motor Drive

Abstract:

This paper presents a power factor corrected (PFC) bridgeless (BL) buck boost fed brushless direct current (BLDC) motor drive as a cost effective solution for low power applications. An approach of speed control of the BLDC motor by controlling the DC link voltage of the voltage source inverter (VSI) is used with a single voltage sensor. This facilitates the operation of VSI at fundamental frequency switching by using the electronic commutation of the BLDC motor which offers reduced switching losses. A BL configuration of the buck boost converter is proposed which offers the elimination of the diode bridge rectifier, thus reducing the conduction losses associated with it. A PFC BL buck boost converter is designed to operate in a discontinuous inductor current mode (DICM) to provide an inherent PFC at AC mains. The performance of the proposed drive is evaluated over a wide range of speed control and varying supply voltages (universal AC mains at 90-265V) with improved power quality at AC mains.

The obtained power quality indices are within the acceptable limits of international power quality standards such as the IEC 61000.3.2. The performance of the proposed drive is simulated in the MATLAB / Simulink environment, and the obtained results are validated experimentally on a prototype of the drive.

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A Six-Phase Current Reconstruction Scheme for Dual Traction Inverters in Hybrid Electric Vehicles with a Single DC-Link Current Sensor

Abstract:

This paper presents a six-phase current reconstruction   scheme   for   dual   traction   inverters   in   hybrid electric vehicles with a single DC-link current sensor. During the     phase current reconstruction, one of the inverters is proposed to operate using active vectors while the other inverter operates using non-active vectors. An advanced phase shift scheme for all PWM signals based on the sequence of duty cycles is implemented. PWM signals are considered in three types of large, medium, andsmall duty cycles.  Then, the minimum phase shift scheme  is   applied  for  each  type  of  PWM  signals  to  ensure  the  minimum duration  of  the  active  vector  for  stable  current  reconstruction With this proposed phase shift scheme, the  maximum  allowable  modulation index and a DC-link voltage utilization is improved.

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A Novel Speed Measurement Method for a High-Speed BLDC Motor Based on the Signals From the Rotor Position Sensor

Abstract:

The paper presents a digital algorithm of a speed control block for a brushless motor and a method for measuring the motor’s rotational speed based on the signals from the rotor position sensor. The proposed method allows an increase in the measurement frequency (six measurements per rotation for a four pole motor) and the measurement results are not affected by the misalignment mounting of the sensor. The paper describes a conceptual structure of a series PI controller.

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A Four-Level Inversion Scheme for a 6n-Pole Open-End Winding Induction Motor Drive for an Improved DC-Link Utilization

ABSTRACT:

In this paper, a new power-circuit configuration for four-level inversion with an open-end winding induction motor is proposed.  This  configuration  is  suitable  for  an  induction  motor with 6n  (n = 1, 2, . . .) Number of poles. Two isolated DC power supplies, each rated for one third of the total DC-link voltage, are sufficient to realize this four-level inverter scheme.  It is shown that it is possible to produce a voltage vector of 1-p.u. Magnitude with a total deck-line voltage of 0.66 p.u., indicating that the DC-link utilization is enhanced by a factor of 33% with this power-circuit configuration.  In the proposed power circuit, the zero-sequence current is arrested as the motor phase windings of the open-end winding induction motor are segmented into two separate groups in the ratio of 2: 1, with one end of each group forming an isolated neutral point. Each phase group is then powered by two individual  two-level  inverters  with  two  separate  DC-power  supplies  with  a common  negative  rail.

The  existence  of  this  common  negative rail  is  the  principal  cause  of  an  increased  DC-bus  utilization simple decoupled space-vector pulse width modulation is adequate to control both of these inverters, which further demonstrates the simplicity of the drive control.

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SHE-PWM CASCADED MULTILEVEL INVERTER WITH ADJUSTABLE DC VOLTAGE LEVELS CONTROL FOR STATCOM APPLICATIONS

ABSTRACT:

This project presents a new multilevel selective harmonic elimination pulse width modulation (MSHE-PWM)  technique  based transformer less Static Synchronous Compensator (STATCOM) system employing cascaded H-bridge inverter (CHI) configuration. The proposed MSHE-PWM method optimizes both the DC voltage levels and the switching angles, enabling more harmonics to be eliminated without affecting the structure of the inverter circuit.

The method provides constant switching angles and linear pattern of DC voltage levels over the modulation index range. This in turns eliminates the tedious steps required for manipulating the off-line calculated switching angles and therefore, easing the implementation of the MSHE-PWM for dynamic systems. Although the method relies on the availability of the variable DC voltage levels which can be obtained by various topologies, however, the rapid growth and development in the field of power semiconductor devices led to produce high efficiency DC-DC converters with a relatively high voltage capacity and for simplicity, a buck DC-DC converter is considered in this project.

Current and voltage closed loop controllers are implemented for both the STATCOM and the buck converter to meet the reactive power demand at different loading conditions. The technique is further compared with an equivalent conventional carrier-based pulse width modulation (CB-PWM) to illustrate its enhanced characteristics.

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MEDIUM-VOLTAGE 12-PULSE CONVERTER OUTPUT VOLTAGE HARMONIC COMPENSATION USING A SERIES APF

ABSTRACT:

     In this project, compensation of the dc-side voltage harmonics of a medium-voltage (MV) 12-pulse ac/dc converter is achieved using a series active power filter (APF). The output voltage harmonics are dependent on the converter firing delay angles and, consequently, on the specific power locus followed by the ac/dc converter. This power locus ensures minimum fifth and seventh harmonics (total rms) in the input current which provides minimum input current total harmonic distortion when the reactive power is less than 0.5 p.u.

The series APF is connected between the load and the converter output via a magnetic amplifier to eliminate the dc current from the APF inverter, thus reducing inverter losses. Voltage harmonic compensation using a series APF,with and without a magnetic amplifier, is examined with both resistive and inductive loads.

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Multi-Objective Planning For Reactive Power Compensation Of Radial Distribution Networks With Unfied Power Quality Conditioner Allocation Using Particle Swarm Optimization

ABSTRACT:

          This project presents a particle swarm optimization (PSO)-based multi-objective planning algorithm for reactive power compensation of radial distribution networks with unified power quality conditioner (UPQC) allocation. A UPQC consists of a series and a shunt inverter. The UPQC model based on phase angle control (UPQC-PAC) is used. In UPQC-PAC, the series inverter injects a voltage with controllable phase angle in such a way that the voltage magnitude at load end remains unchanged. Due to the phase angle shift, the series inverter participates in load reactive power compensation along with the shunt inverter during healthy operating condition. In the proposed approach, the optimal location, the optimal reactive power compensation required at the location, and the optimal design parameters of UPQC are determined by minimizing three objective functions:

1) the rating of UPQC, 2) network power loss, and 3) percentage of nodes with under voltage problem. These objectives are simultaneously minimized to obtain a set of non-dominated solutions using multi-objective PSO (MOPSO). The performances of two MOPSO variants are compared and the better one is used in all subsequent studies. A load flow algorithm including the UPQC-PAC model is devised.

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Impact of midpoint STATCOM on generator Loss of excitation protection

 ABSTRACT:

This project explores the impact of a transmission-line midpoint STATCOM on the performance of the generator loss-of-excitation (LOE) protection. In this context, investigations are conducted on a two-hydro generator power station for two LOE contingencies, namely, a complete LOE due to a field-winding short circuit and a partial LOE due to a sudden drop in the excitation voltage at different generator loadings. The results of these investigations show that the midpoint STATCOM has adverse impacts on the LOE distance relay in the form of delay time and/or under-reach phenomenon. These adverse impacts vary with the generator loading and the LOE mode.

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Elimination Of Coupling Transformer Core Saturation In Cascaded Multilevel Converter Based T -Statcom Systems

ABSTRACT:

          This project deals with coupling transformer core saturation problem in cascaded multilevel converter (CMC) based transmission-type static synchronous compensator (T-STATCOM) systems. The effects of nonlinear characteristics of the coupling transformer and CMCs on the core saturation phenomenon are investigated, and the associated mechanisms are described. In order to prevent the transformer core from being saturated, dc current components in the coupling transformer secondary lines are eliminated by modulating one or more than one voltage steps of staircase CMC voltage waveforms via the electronic gating circuitry.

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DESIGN AND IMPLEMENTATION OF AN 11-LEVEL INVERTER WITH FACTS CAPABILITY FOR DISTRIBUTED ENERGY SYSTEMS

ABSTRACT:

          In this project, a new single-phase wind energy inverter (WEI) with flexible AC transmission system (FACTS) capability is presented. The proposed inverter is placed between the wind turbine and the grid, same as a regular WEI, and is able to regulate active and reactive power transferred to the grid. This inverter is equipped with distribution static synchronous compensators option in order to control the power factor (PF) of the local feeder lines. Using the proposed inverter for small-to-medium-size wind applications will eliminate the use of capacitor banks as well as FACTS devices to control the PF of the distribution lines. The goal of this paper is to introduce new ways to increase the penetration of renewable energy systems into the distribution systems. This will encourage the utilities and customers to act not only as a consumer, but also as a supplier of energy. Moreover, using the new types of converters with FACTS capabilities will significantly reduce the total cost of the renewable energy application.

In this project, modular multilevel converter is used as the desired topology to meet all the requirements of a single-phase system such as compatibility with IEEE standards, total harmonic distortion (THD), efficiency, and total cost of the system.    The proposed control strategy regulates the active and reactive power using power angle and modulation index, respectively. The function of the proposed inverter is to transfer active power to the grid as well as keeping the PF of the local power lines constant at a target PF regardless of the incoming active power from the wind turbine.

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CASCADED TWO-LEVEL INVERTER-BASED MULTILEVEL STATCOM FOR HIGH-POWER APPLICATIONS

 ABSTRACT:

          In this project, a simple static var compensating scheme using a cascaded two-level inverter-based multilevel inverter is proposed. The topology consists of two standard two-level inverters connected in cascade through open-end windings of a three-phase transformer. The dc-link voltages of the inverters are regulated at different levels to obtain four-level operation. The simulation study is carried out in MATLAB/SIMULINK to predict the performance of the proposed scheme under balanced and unbalanced supply-voltage conditions.

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AVERAGE POWER BALANCING CONTROL OF A STATCOM BASED ON THE CASCADED H-BRIDGE PWM CONVERTER WITH STAR CONFIGURATION

ABSTRACT:

          This project presents the average power balancing control method for the modular multilevel cascaded converter based on single-star bridge cells in the static synchronous compensator applications.

The proposed control method accomplishes both the reactive power compensation and the dc bus voltages balancing control even under grid voltage sags. The low voltage ride-through capability of the proposed method will become more and more important as more distributed generation resources are integrated into the grid.

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ADAPTIVE PI CONTROL OF STATCOM FOR VOLTAGE REGULATION

ABSTRACT:

STATCOM can provide fast and efficient reactive power support to maintain power system voltage stability. In the literature, various STATCOM control methods have been discussed including many applications of proportional-integral (PI) controllers. However, these previous works obtain the PI gains via a trial-and-error approach or extensive studies with a tradeoff of performance and applicability. Hence, control parameters for the optimal performance at a given operating point may not be effective at a different operating point. This paper proposes a new control model based on adaptive PI control, which can self-adjust the control gains during a disturbance such that the performance always matches a desired response, regardless of the change of operating condition. Since the adjustment is autonomous, this gives the plug-and-play capability for STATCOM operation.

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A COMBINED APPROACH OF USING AN SDBR AND A STATCOM TO ENHANCE THE STABILITY OF A WIND FARM

ABSTRACT:

          This project presents a method to enhance the stability of a grid-connected wind farm composed of a fixed-speed wind turbine generator system (WTGS) using a combination of a small series dynamic braking resistor (SDBR) and static synchronous compensator (STATCOM). The SDBR and STATCOM have active and reactive power control abilities, respectively, and a combination of these units paves the way to stabilize well the fixed-speed wind farm. In this paper, a centralized control scheme of using an SDBR and a STATCOM together is focused, which can be easily integrated with a wind farm. Different types of symmetrical and unsymmetrical faults are considered to evaluate the transient performance of the proposed control scheme, applicable to a grid-connected wind farm. The effect of a multimass drive train of a fixed-speed WTGS in fault analysis, along with its importance in determining the size of the SDBR to augment the transient stability of a wind farm, is investigated. Extensive simulation analyses are performed to determine the approximate sizes of both SDBR and STATCOM units. Dynamic analysis is performed using real wind speed data.

A salient feature of this work is that the effectiveness of the proposed system to minimize  the  blade – shaft  torsional  oscillation  of  a  fixed – speed WTGS is also analyzed.

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UNIVERSAL DIGITAL CONTROLLER FOR BOOST CCM POWER FACTOR CORRECTION STAGES BASED ON CURRENT REBUILDING CONCEPT

ABSTRACT:

          Continuous conductionmode power factor correction (PFC) without input current measurement is a step forward with respect to previously proposed PFC digital controllers. Inductor volt-second (vsL) measurement in each switching period enables digital estimation of the input current; however, an accurate compensation of the small errors in the measured vsL is required for the estimation to match the actual current. Otherwise, they are accumulated every switching period over the half-line cycle, leading to an appreciable current distortion. A vsL estimation method is proposed, measuring the input (vg ) and output voltage (vo). Discontinuous conduction mode (DCM) occurs near input line zero crossings and is detected by measuring the drain-to-source MOSFET voltage vds . Parasitic elements cause a small difference between the estimated voltage across the inductor based on input and output voltage measurements and the actual one, which must be taken into account to estimate the input current in the proposed sensorless PFC digital controller.

This paper analyzes the current estimation error caused by errors in the ON-time estimation, voltage measurements, and the parasitic elements. A new digital feedback control with high resolution is also proposed.

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SYMMETRIC AND ASYMMETRIC DESIGN AND IMPLEMENTATION OF NEW CASCADED MULTILEVEL INVERTER TOPOLOGY

ABSTRACT:

          Nowadays, use of multilevel inverters in high power applications clearly can be seen. High quality and lower distortion of the output voltage and low blocking voltage of semiconductor switches are being presented as the major privileges of the multilevel inverter compared to the traditional voltage source inverter.

In this project, a new topology of multilevel inverter is proposed as fundamental block. The proposed topology is generalized using series connection of the fundamental blocks. The proposed multilevel inverter has been analyzed in both symmetric and asymmetric operation modes. A great perfection in voltage levels number with minimum switching devices has been obtained in both symmetric and asymmetric modes.

Thereafter a detailed study of losses and Peak Inverse Voltage (PIV) of proposed multilevel inverter is given. Also in continue a comparison between proposed topology and the traditional one and a recently developed topology is carried out.

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SURVEY ON FAULT-TOLERANT TECHNIQUES FOR POWER ELECTRONIC CONVERTERS

ABSTRACT:

           With  wide-spread application of power electronic converters in high power systems, there has been a growing interest in system reliability analysis and fault-tolerant capabilities.

This project presents a comprehensive review of conventional fault-tolerant techniques regarding power electronic converters in case of power semiconductor device failures. These techniques can be classified into  four  categories based on the type of hardware redundancy unit: switch-level, leg-level, module-level  and system-level. Also,  various fault-tolerant methods are assessed according to cost, complexity, performance, etc. The intent of this review is to provide a detailed picture regarding the current landscape of research in power electronic fault-handling mechanisms.

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ROBUST TIME-DELAY CONTROL FOR THE DC–DC BOOST CONVERTER

ABSTRACT:

          This project studies a robust control for regulating a boost converter capacitor output voltage. The boost converter is inherently a highly nonlinear system that displays interconnected state variables and system parameter variations due to load change with input disturbances. Therefore, a robust control scheme is required to cope with these characteristics. The main objective of controlling the capacitor output voltage is to keep the output voltage constant under input voltage variations with fast response, and little overshoot and ripples. To satisfy this objective, a robust control with time-delay concept is introduced. The control utilizes time-delayed switching input to the converter, as well as output current and voltage variables, to replace the unknown dynamics and disturbance. To prove the effectiveness of the algorithm, two operating point variations are considered: variations in source voltage, and changes in output load.

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OPERATION MODES ANALYSIS AND LIMITATION FOR DIODE-ASSISTED BUCK–BOOST VOLTAGE SOURCE INVERTER WITH SMALL VOLTAGE VECTOR

ABSTRACT:

          Diode-assisted buck–boost voltage source inverter (VSI) boosts the dc source voltage by introducing diode-assisted capacitor network. With parallel capacitive charging and series capacitive discharging, the new topology extends voltage regulation range and avoids extreme duty ratio of switching devices in the front boost circuit.

As for the unique structure, various novel pulse-widthmodulation strategies are provided to obtain the linear voltage gain with regard to the chopped intermediate dc-link voltage of the inverter bridge in one switching time period. It provides a competitive solution for high voltage gain applications.

However,when the inverter supplies inductive or capacitive load with extreme low load power factor, the unidirectional current flow of the diode may limit the application of the converter utilizing small voltage vectors for ac output voltage extension. As a result, diode-assisted buck–boost VSI exhibits new operation mode that has not been discussed before.

This project makes a detailed circuit analysis of the relationship between the undesired operation condition and load power factor. Then, a simple approach to totally eliminate the undesired limitation by replacing the diodes with controlled switching devices is provided.

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NEW EXTENDABLE SINGLE-STAGE MULTI-INPUT DC-DC/AC BOOST CONVERTER

ABSTRACT:

This project presents a new extendable single-stage multi-input DC-DC/AC boost converter. The proposed structure comprises two bidirectional ports in the converter central part to interface output load and battery storage, and several unidirectional input ports to get powers from different input dc sources. In fact, the proposed topology consists of two sets of parallel dc-dc boost converters, which are actively controlled to produce two independent output voltage components. Choosing two pure dc or two dc-biased sinusoidal values as the converter reference voltages, situations of the converter operating in two DC-DC and DC-AC modes are provided, respectively.The proposed converter utilizes minimum number of power switches and is able to step-up the low level input dc voltages into a high level output DC or AC voltage without needing any output filter.The converter control system includes several current regulator loops for input dc sources and two voltage regulator loops for generating the desired output voltage components, resulting in autonomously charging/discharging the battery to balance the power flow.

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MULTIVARIABLE CONTROL OF SINGLE-INDUCTOR DUAL-OUTPUT BUCK CONVERTERS

ABSTRACT:

          Cross regulation is the main technical challenge of a single-inductor multiple-output (SIMO) dc–dc converter.

This project proposes amultivariable digital controller to suppress the cross regulation of a single-inductor dual-output (SIDO) buck converter in continuous conduction mode (CCM) operation. The controller design methodology originates from the open-loop shaping of the multi-inputmulti-output (MIMO) systems. The control design procedure includes: 1) determination of a family of nonparametric models of the SIDO converter at operating points of interest, 2) determination of the class of the controller, and 3) system open-loop shaping by the convexminimization of the summation of the square second norm of the errors between the system open-loop transfer function matrices and a desired open-loop transfer function matrix.

The proposed controller minimizes the coupling between the outputs of the SIDO converter and provides satisfactory dynamic performance in CCM operation.

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MINIMUM TIME CONTROL FOR MULTIPHASE BUCK CONVERTER ANALYSIS AND APPLICATION

ABSTRACT:

The combination of minimum time control and multiphase converter is a favorable option for dc–dc converters in applications where output voltage variation is required, such as RF amplifiers and dynamic voltage scaling in microprocessors, due to their advantage of fast dynamic response. In this paper, an improved minimum time control approach for multiphase buck converter that is based on charge balance technique, aiming at fast output voltage transition is presented. Compared with the traditional method, the proposed control takes into account the phase delay and current ripple in each phase. Therefore, by investigating the behavior of multiphase converter during voltage transition,it resolves the problem of current unbalance after the transient,which can lead to long settling time of the output voltage. The restriction of this control is that the output voltage that the converter can provide is related to the number of the phases, because only the duty cycles at which the multiphase converter has total ripple cancellation are used in this approach. The model of the proposed control is introduced, and the design constraints of the buck converter’s filter for this control are discussed.

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ISOLATED SWITCH-MODE CURRENT REGULATOR WITH INTEGRATED TWO BOOST LED DRIVERS

ABSTRACT:

          A new isolated switch-mode current regulator is proposed for an LED driving system. The two boost LED drivers are integrated with the dc/dc converter, which results in a simple structure and low component count. The primary side provides an ac voltage source to the secondary side in which one boost inductor, two switches, and diodes comprise two boost drivers. Each secondary switch controls each LED current to be balanced. The voltage stresses of the primary switches are clamped to the input voltage, and those of secondary switches and diodes are clamped to the output voltages. Furthermore, all switches can easily achieve zero-voltage switching by using the transformer magnetizing current without additional auxiliary circuits. 

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HYBRID MULTILEVEL CONVERTER WITH CASCADED H-BRIDGE CELLS FOR HVDC APPLICATIONS

ABSTRACT:

           Hybrid multilevel converters are contemplated in an attempt to optimize the performance of voltage source converters in terms of magnitude of semiconductor losses and converter footprint, and to achieve additional features such as dc short circuit proof, which is essential for a high integrity multi-terminal HVDC grid.      Therefore, this project considers an emerging hybrid cascaded converter that offers the dc side short circuit proof feature at reduced loss and footprint compared to the existing multilevel and other hybrid converters.  Its operating principle, modulation and capacitor voltage balancing strategies are described  in  detail. Furthermore, hybrid converter scalability to high voltage applications is investigated.

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