Unbalanced Power Systems

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Implementation of 3 Phase Electric Springs in Unbalanced Power Systems using Instantaneous Power Theory

Implementation of 3 Phase Electric Springs in Unbalanced Power Systems using Instantaneous Power Theory

The ES are serially-connected to a non-critical load as a smart load. The proposed system is works on both AC and DC and associate with NCL and CL loads. Electric springs(DC-ES) for bus voltage stabilization and power balancing in DC grids is reported. The proposed control strategy is to change voltage control to direct current control, which needs a controlled current source.PID control scheme is implemented for both load and source demand side management. The proposed control strategy is to change voltage control to direct current control, which needs a controlled current source. The ES with CSI in proposed which can be regarded as a current controlled current source (CCCS). The current control where the ES is substituted by a CCCS designated and the branch with line impedance is replaced by a current source designated. ES has to generate an ac current to compensate the fluctuations in the input current to achieve a stable CL voltage. In order to ensure that the power inverter acts as a purely reactive power controller, the vector of the current through the electric spring and the vector of the voltage across the electric spring should be ideally perpendicular to each other. A power transformer supplies electricity to many houses in a residential area, the mains voltage nearest the transformer may be 230 V (which is the nominal voltage) and that farthest from the transformer would be lower than 230 V (e.g., 210 V), because of the voltage drop along the distribution feeder. But it maintains 230v ac constant voltage.
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Implementation of 3 Phase Electric Springs in Unbalanced Power Systems using Instantaneous Power Theory

Implementation of 3 Phase Electric Springs in Unbalanced Power Systems using Instantaneous Power Theory

line conditioners. The term "power conditioning" used in this book has much broader meaning than the term harmonic filtering." In other words, the power conditioning is not confined to harmonic filtering, but contains harmonic damping, harmonic isolation, harmonic termination, reactive-power control for power factor correction, power flow control, and voltage regulation, load balancing, voltage-flicker Suction, and/or their combinations. Active power line conditioners are based on leading-edge power electronics technology that includes power conversion circuits, power semiconductor devices, analog/digital signal processing, voltage/current sensors, and control theory. Concepts and evolution of electric power theory are briefly described below. Then, the need for a consistent set of power definitions is emphasized to deal with electric systems under non-sinusoidal conditions. Problems with harmonic pollution in alternating current systems (ac systems) are classified, including a list of the principal harmonic-producing loads. Basic principles of harmonic compensation are introduced. Finally, this chapter describes the fundaments of power flow control. All these topics are the subjects of scope, and will be discussed deeply in the following chapters of the book. The instantaneous power theory, or ―the p-q theory,‖ makes clear the physical meaning of what instantaneous real and imaginary power is in a three-phase circuit. Moreover, it provides insight into how energy flows from a source to a load, or circulates between phases, in a three- phase circuit. This theory can be used in the design and understanding of FACTS (Flexible AC Transmission System) compensators. The book introduces many concepts in the field of active filtering that are unique to this edition. It provides a study tool for final year undergraduate students, graduate students and engineers dealing i-th harmonic pollution problems, reactive power compensation or power quality in general. 2 EXISTING SYSTEM
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Frequency Estimation of Unbalanced Three-Phase Power System using a New LMS Algorithm

Frequency Estimation of Unbalanced Three-Phase Power System using a New LMS Algorithm

Among various algorithms for frequency estimation, some exploit the frequency from single phase (e.g. refer to [4, 7, 8, 11, 16, 18, 24, 25]), while others extract the frequency from all three phases because of more robustness (e.g. refer to [12, 15, 17, 20, 22]). Since using all phases, it provides a more robust algorithm especially when phases undergo some abnormal conditions. Usually, the Clark's transformation is used to convert the three phase signals to a single complex signal. Moreover, recently, unbalanced power systems have gained more attention [15, 21, 23, 26, 27]. This paper proposes a simple and easy-implementable adaptive LMS algorithm for power system frequency estimation based on all three phases in unbalanced condition where the three phases are not exactly the same and especially their amplitudes are different. In this case, the complex signal derived from Clark's transformation has a recursion different to what an LMS technique is based on. According to this recursion, an LMS algorithm is suggested which uses two consecutive samples of the complex signal instead of a single value. Fortunately, the coefficients of this recursion is real and so the proposed overall LMS algorithm is a real adaptive filter and is computationally efficient specially for applying on DSP's.
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Demonstration of sustained and useful converter responses during balanced and unbalanced faults in microgrids

Demonstration of sustained and useful converter responses during balanced and unbalanced faults in microgrids

Abstract-In large power grids where converter penetration is presently low and the network impedance is predominantly reactive, the required response from converters during faults is presently specified by phrases such as “maximum reactive output”. However, in marine and aero power systems most faults are unbalanced, the network impedance is resistive, and converter penetration may be high. Therefore a balanced reactive fault current response to an unbalanced fault may lead to over-voltages or over/under frequency events. Instead, this paper presents a method of controlling the converter as a balanced voltage source behind a reactance, thereby emulating the fault response of a synchronous generator (SG) as closely as possible. In this mode there is a risk of converter destruction due to overcurrent. A new way of preventing destruction but still providing fault performance as close to a SG as possible is presented. Demonstrations are presented of simulations and laboratory testing at the 10kVA 400V scale, with balanced and unbalanced faults. Currents can be limited to about 1.5pu while still providing appropriate unbalanced fault response within a resistive network.
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THE IMPACT OF LOCATION BASED ATTACKS ON GEOGRAPHICAL ROUTING PROTOCOLS

THE IMPACT OF LOCATION BASED ATTACKS ON GEOGRAPHICAL ROUTING PROTOCOLS

The nature and the type of faults that the system need to overcome decides the size of the STATCOM. Although the final rating of the STATCOM is determined based on system economics, the rating chosen must be atleast adequate for the system to be stable after a fault or temporary system disturbances. The STATCOM ratings are based on many parameters which are mostly governed by the amount of reactive power the system needs to recover and ride through system faults on the power system and to reduce the interaction of other system causing disturbances. This causes out of synchronism with the grid. The nature and the type of faults that the system need to overcome decides the size of the STATCOM. For example, a three phase fault of low impedance requires a very high rating STATCOM.A high impedance short circuit fault needs a lower rating device[5]. This support is needed to stabilize the system after a disturbance. The capability of the STATCOM is also decided based on the converter current ratings and the size of the capacitor. The devices in a voltage source converter are clamped against over-voltages across the DC link capacitor bank to minimize losses and not have to withstand large spikes in reverse over- voltage [5].
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Transient analysis of dynamic systems under unbalanced operations.

Transient analysis of dynamic systems under unbalanced operations.

Performance equations describing completely the physical facts involved in a synchronous machine have been derived in the preceding sections. Under any unbalanced operation conditions, having substituted equation (17) into equation (11) it is possible to solve equations (11) for the four unknown currents (i^, ig, i^, i^). Then by using equations

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Abstract: Wind energy is utilizing the air flow through wind turbines to generate the electrical power and energy. In this paper, we proposed a new method for controlling the stator active or reactive power ripple components under unbalanced grid voltage for wind power generation using doubly-fed induction generators (DFIG) by employing the PWM controller. Direct control strategy is utilized for the stator active and reactive power by selecting appropriate voltage vectors on the rotor side. Simulation results on a 9 MW DFIG system are provided to illustrate the proposed control strategy effectiveness during variations of reactive and active power, converter dc link voltage and rotor speed. The system is simulated by using MATLAB software and the results showed that the achieved strategy make a good control performances of the system.
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ELIMINATION OF HARMONICS AND SHORT CIRCUIT BY USING DVR WITH REPETITIVE CONTROL

ELIMINATION OF HARMONICS AND SHORT CIRCUIT BY USING DVR WITH REPETITIVE CONTROL

This paper implemented the dynamic voltage restorer with the repetitive controller system arrangement to mitigate the important power quality issues such as voltage sags, distortions, unbalanced voltages and single and three phase faults. In this proposed system consisting of one feed forward parameter to control and maintained the zero error in the steady state and it improves the transient response of the system. In this paper additionally controls the grounding faults total harmonic distortions and harmonics and line-line faults, line- ground faults in the power system are compensated by the repetitive controller in the DVR. The implemented models are designed in the MATLAB/ SIMULINK is discussed. The usage of repetitive controller the problems in the system is compensated then correspondingly the performance is enhanced.
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Novel Load Flow Algorithm for Multi-Phase Balanced/ Unbalanced Radial Distribution Systems

Novel Load Flow Algorithm for Multi-Phase Balanced/ Unbalanced Radial Distribution Systems

ABSTRACT: In this work, distribution system load flow analysis is formulated and tested for fundamental steady-state and harmonics power flow. For the steady-state analysis, a novel power flow formulation method for the general multiphase balanced and/or unbalanced radial distribution systems is presented. The special topology of the power distribution system has been fully exploited to facilitate obtaining a direct solution using the graph theory. Only one developed matrix used in conjunction with simple standard formulation is enough to obtain the power flow solution. This matrix is the branch-path incident matrix. A feature of using this method is that it significantly reduces the number of power flow equations, as compared to conventional methods, hence very low computation time and memory storage. The presence of nonlinear loads in the power system causes the circulation of harmonics currents in the system, leading to harmonics voltage drops. The harmonics flow analysis in this paper, uses the network techniques in conjunction with graph theory resulting in a powerful algorithm for nonlinear load flow analysis. Six pulse converters model were used to represent the nonlinear load. Two MATLAB programs have been built and used to solve for the load flow solution of standard test systems in both steady-state and harmonics cases. The results of the distribution system cases studies are presented and shows a very good resemblance with a standard results.
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DSTATCOM Performance for Voltage Sag, Swell Mitigation

DSTATCOM Performance for Voltage Sag, Swell Mitigation

ABSTRACT: The performance of a DSTATCOM in mitigating voltage sag/ swell is demonstrated with the help of MATLAB. The modeling and simulation results of a DSTATCOM are presented. D-STATCOM is promising device which is used for voltage sag, swell mitigation at distribution side. In this work only the Vrms value is required to measure. DSTATCOM compensator is a flexible device which can operate in current control mode for compensating voltage variation, unbalance and reactive power and in voltage control mode as a voltage stabilizer. The latter feature enables its application for compensation of dips coming from the supplying network. In addition, the regulated VRMS voltage showed a reasonably smooth profile. It was observed that the load voltage is very close to the reference value, i.e., 1pu and the voltage sags are completely minimized. The hardware results showed clearly the performance of the Dstatcom in mitigating voltage sag as well as swell. This thesis explained the two level VSC based DSTATCOM and can be extended to multilevel inverter based DSTATCOM to reduce the harmonic content in current. The DSTATCOM can be designed using a current source inverter. An integrated DSTATCOM controller can be design for voltage regulation, reactive power compensation, power factor improvement and unbalanced load compensation.
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A Study on the Impact of Ethical Behaviour of Firms on Global Competitiveness Ranking

A Study on the Impact of Ethical Behaviour of Firms on Global Competitiveness Ranking

The techniques employed for power quality improvements in exiting systems facing power quality problems are classified in a different manner from those used in newly designed and developed equipment. These mitigation techniques are further sub classified for the electrical loads and supply systems, since both of them have somewhat different kinds of power quality problems. In existing nonlinear loads, having the power quality problems of poor power factor, harmonic currents, unbalanced currents, and an excessive neutral current, a series of power filters of various types such as passive, active, and hybrid in shunt, series, or a combination of both configurations are used externally depending upon the nature of loads such as voltage-fed loads, current-fed loads, or a combination of both to mitigate these problems. However, in many situations, the power quality problems may be other than those of harmonics such as in distribution systems, and the custom power devices such as distribution static compensators (DSTATCOMs), dynamic voltage restorers (DVRs), and unified power quality conditioners (UPQCs) are used for mitigating the current, voltage, or both types of power quality problems. Power quality improvement techniques used in newly designed and developed systems are based on the modification of the input stage of these systems with power factor corrected (PFC) converters, also known as improved power quality AC–DC converters (IPQCs), multi pulse AC–DC converters, matrix converters for AC–DC or AC–AC conversion, and so on, which inherently mitigate
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A Cascaded H-Bridge Inverter For Three Phase Connected Photo Voltaic System

A Cascaded H-Bridge Inverter For Three Phase Connected Photo Voltaic System

Abstract — This Project Presents Distributed MPPT Based Modular Cascaded H-Bridge Multilevel Inverter. The Modular Cascaded Multilevel Topology Helps To Improve The Efficiency And Flexibility Of PV Systems. The SPWM technique based PWM inverter is help full in making the switching pulse with better output. A new modulation method called trapezoidal triangular multi carrier (TTMC) SPWM is implemented and compared with other methods. This new modulation method gives advantages in multilevel inverter to minimize the percentage of total harmonic distortion (THD) and to increase the output voltage. To realize better utilization of PV modules and maximize the solar energy extraction, a Distributed Maximum Power Point Tracking control scheme is applied to the three phase multilevel inverters. The power generated by the inverter is delivered to power network, so the utility grid. The proposed system is simulated using MATLAB.
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Power Quality Enhancement using Grid Interfaced Dual Voltage Source Inverter

Power Quality Enhancement using Grid Interfaced Dual Voltage Source Inverter

The proposed DVSI scheme has the advantage to exchange power generated from the DER and also to compensate unbalanced and nonlinear load components. The control algorithm for the reference current generation is developed by using ISCT theory. As compared to a single level inverter, five-level inverter has less THD value for both load current and load voltage. By using sinusoidal pulse width modulation technique (SPWM), the output of the five-level inverter is more balanced and sinusoidal. Hence, there is no need of filter at the main inverter side. The DVSI method has advantages like increase in reliability, decrease in filter size and utilization of full capacity of five-level inverter to transfer real power from DER to load.
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ADMITTANCE BASED CONTROL OF A STANDALONE SOLAR PHOTO-VOLTAIC HYBRID SYSTEM

ADMITTANCE BASED CONTROL OF A STANDALONE SOLAR PHOTO-VOLTAIC HYBRID SYSTEM

The control algorithm extracts fundamental component of the load using admittance control technique. Further Active and Reactive power components of load power are determined. In order to compensate for any voltage changes at PCC along with Reactive power ( ) Proportional Integral Control Loop is used. The Susceptance ( ) is obtained by the reference reactive power ( ), computed using reactive power Output of PI controller ( ) and the reactive power component () generated using reference load currents. The reference conductance ( ) is generated using reference load active power (Pr). Pr is limited to operate DG set at 80 to 100% of its full load capacity and VSC– BESS allows load
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Field-test of wind turbine by voltage source converter

Field-test of wind turbine by voltage source converter

Moreover, grid codes specify the steady-state frequency and voltage operation range within which the wind turbine should operate continuously. For voltages, normal condition is considered to be at 1.0 pu, with a frequency of 50 or 60 Hz. A deviation of approximately ± 0.1 pu from the rated volt- age and ± 0.5 Hz from the rated frequency is also considered a normal condition. Any steady-state grid condition outside these boundaries is defined by a minimum operational time. In some cases, a control action on the active power set point of the wind farm can be requested by the TSOs: e.g. the Dan- ish (ENERGINET, 2010), Irish (EirGrid, 2015) and German (E.ON, 2006, 2008) TSOs. When active power curtailment is requested in case of frequency deviations, the generation unit must vary its active power output in order to contribute to the overall regulation of the system frequency. In severe cases where the system frequency is outside the frequency opera- tion band, the generating plant is allowed to disconnect.
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Distributed Mppt Based Moduler Cascaded H-Bridge Multilevel Inverter

Distributed Mppt Based Moduler Cascaded H-Bridge Multilevel Inverter

The modular cascaded H-bridge multilevel inverter, which requires an isolated dc source for each H-bridge, is one dc/ac cascaded inverter topology. The separate dc links in the multilevel inverter make independent voltage control possible. As a result, individual MPPT control in each PV module can be achieved, and the energy harvested from PV panels can be maximized. Meanwhile, the modularity and low cost of multilevel converters would position them as a prime candidate for the next generation of efficient, robust, and reliable grid-connected solar power electronics.
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Distributed MPPT Based Modular Cascaded H-Bridge Multilevel Inverter Multistring Topology for Large Scale Photo Voltaic Systems

Distributed MPPT Based Modular Cascaded H-Bridge Multilevel Inverter Multistring Topology for Large Scale Photo Voltaic Systems

As mentioned earlier, a PV mis match may cause more problems to a three -phase modular cascaded H-bridge multi-level inverter. With the individual MPPT control in each H-bridge module, the input solar power of each phase would be different, which introduces unbalanced current to the grid. To solve the issue, a zero sequence voltage can be imposed upon the phase legs in order to affect the current flowing into each phase. If the updated inverter output phase voltage is proportional to the unbalanced power, the current will be balanced.
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Robust Power Control of Microgrid based on Hybrid Renewable Power Generation Systems

Robust Power Control of Microgrid based on Hybrid Renewable Power Generation Systems

According to the Eq. (31), in order to regulate the dc link voltage it is necessary to keep the power balance in dc link. In this equation, the change in grid power is considered as disturbance during the load power variations. Moreover, to meet the power balance in DC link it is important to consider the dynamic limitations of fuel cell power. In this case, the fuel cell power could not change rapidly and the fuel cell controller with DC- DC converter should regulate the operating point of fuel cell. The details of fuel cell and DC-DC converter control strategy are presented in next part. But the amount of power that should be absorbed by battery energy storage to balance the power in DC link is very important and it depends on the DC link energy. The DC link energy measurement is carried out by means of the following calculation:
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Power Controllability of A Three-Phase Converter With An Unbalanced Ac

Power Controllability of A Three-Phase Converter With An Unbalanced Ac

Abstract: Three-phase dc–ac power converters suffer from power oscillation and over current problems in case of the unbalanced ac source voltage that can be caused by grid/generator faults. Existing solutions to handle these problems are properly selecting and controlling the positive- and negative-sequence currents. In this paper, a new series of control strategies which utilize the zero sequence components are proposed to enhance the power control ability under this adverse condition. It is concluded that by introducing proper zero-sequence current controls and corresponding circuit configurations, the power converter can enable more flexible control targets, achieving better performances in the delivered power and the load current when suffering from the unbalanced ac voltage.
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POWER QUALITY IMPROVEMENT OF UNBALANCED DISTRIBUTION SYSTEM USING LMBNN BASED D-STATCOM

POWER QUALITY IMPROVEMENT OF UNBALANCED DISTRIBUTION SYSTEM USING LMBNN BASED D-STATCOM

In this paper to address well known power quality issues such as voltage swell, voltage sag of unbalanced distribution system, a Levenberg-Marquardt Back propagation(LMBNN) based D-STATCOM is proposed. The performance of proposed an ANN based D-STATCOM is tested on 13-bus IEEE test feeder, a D-STATCOM is placed at bus no-632.The performance of proposed ANN based D-STATCOM is compared to D- STATCOM with PI control mechanism using MATLAB-simulink.

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