Stabilization of wind firm integrated Hybrid Power System by using STATCOM

This paper deals with the design and implementation of cascaded H-bridge multilevel voltage source converter-based static synchronous compensator (STATCOM) for simultaneous active and reactive power compensation, voltage stability and damping of power oscillations. The main objective is to provide active power support and maintain the voltage stability by compensating the reactive power in the power system. In this paper, the multi pulse inverter-based STATCOM has been replaced by multilevel inverter-based STATCOM to overcome the drawbacks of the former. Cascaded H-bridge (CHB) MLI for implementation of STATCOM has been used as CHB MLI is considered the best for STATCOM applications due to its modular structure and requirement of lesser number of components. MLI-based STATCOM is used to provide simultaneous reactive power and active power compensation established by using super-capacitor. The super-capacitors are connected with each DC link capacitor of CHB MLI by using the DC-DC buck boost converter. The STATCOM is also used to provide voltage stability during the power quality problems such as voltage sag and voltage swell, it is established by injecting or absorbing reactive power. The STATCOM is also used for damping the power oscillations by controlled injection of reactive power hence enhancing transient stability. Nine-level cascaded H-bridge MLI-based STATCOM is designed for simultaneous reactive power and active power compensation, voltage stability and damping the power oscillations. Exhaustive simulations have been carried out using MATLAB/Simulink and SimPowerSystems software. The simulation results are presented to prove the effectiveness of MLI-based STATCOM for simultaneous active and reactive power compensation, voltage stability and damping of power oscillation.

Abstract— The concept of Var compensation embraces a wide and diverse field of both system and customer problems, especially related with power quality issues, since most power quality problems can be attenuated or solved with an adequate control of reactive power. In general, the problem of reactive power compensation is viewed from two aspects: load compensation and voltage support. Static voltage instability is mainly associated with reactive power imbalance. Thus, the load ability of a bus in a system depends on the reactive power support that the bus can receive from the system. As the system approaches the maximum loading point or voltage collapse point, both real and reactive power losses increase rapidly, therefore the reactive power supports have to be locally adequate. With static voltage stability, slowly developing changes in the power system occur that eventually lead to a shortage of reactive power and declining voltage. The Flexible AC Transmission System (FACTS) technology is a promising technology to achieve complete deregulation of power system based on power electronic devices, used to enhance the existing transmission capabilities in order to make the system flexible and independent in operation then the system will be kept within limits without affecting the stability. Increased transmission demand is met where possible by increasing the existing transmission capacity. When trying to improve the transmission capacity, a key assumption is made that if the overall system reliability is not improved, at least the existing system reliability is maintained. The research work in this work is focused on FACT’S Controllers. Keywords: Flexible AC Transmission System, variable-speed wind turbine, rotor-side converter, grid-side converter, doubly fed induction generator, Static Synchronous Compensator, phase-locked loop.

Power quality (PQ) problems include harmonics, voltage flicker, three-phase imbalance, voltage swell/sag, interruption, switching transient and so on. Identification of accurate location and occurrence time of PQ problem is important for understanding the underlying cause and to prevent future occurrence. This study presents a new method for placement of power quality measurement facilities to identify PQ problems. The power harmonics and capacitor switching transients are used as disturbance sources for illustration. The proposed method first utilises harmonic voltages and wavelet coefficients as PQ features. An enhanced genetic algorithm is proposed for solving the modified K-means clustering to place PQ measurement monitors. Simulation results for an 18-bus system show that the proposed approach is effective in comparison with the existing approaches.

Electrical utilities are subject to voltage sags, poor power factor and even voltage instability as long as it suffers from shortage of its reactive power sources. The only mitigation to this problem is to have proper and fast acting reactive power control on the grid. This in turn will overcome the major concerns of network voltage instability, especially during the transient and sub-transients conditions such as major switching operation, and electrical faults. In many cases, the traditional solutions of switching capacitors is too coarse and slow to stabilize a weak network. The most advanced solution to compensate reactive power is to incorporate a STATCOM (or Static Synchronous Compensator) as a variable source of reactive power. STATCOM is an advanced power electronic system for fast capacitive/inductive reactive power supply providing reactive power compensation and, steady state and transient voltage stability, etc… These systems offer advantages compared to standard reactive power compensation solutions in demanding applications. In order to mitigate utility network power quality problems, ADNOC Gas Processing has recently introduced a STATCOM solution in two running plants. This paper deals with the design process of customized Power Quality solutions involving STATCOM Technology to resolve network quality issue up to full commissioning of the system, elaborate on challenges and difficulties faced, and highlight how it was resolved.

This paper introduces a novel automatic hybrid classifier to detect and classify the Power Quality(PQ) problems in power systems using Wavelet Packet Transform (WPT) and Artificial Neural Networks (ANN). Various PQ events like Normal, Sag, Swell and Interruptions are obtained by modeling three phase distribution system using MATLAB simulink. For classification, the selection of suitable features from the disturbance signal is extremely important. Recent literature survey deals with various signal processing techniques like Fast Fourier Transform (FFT), Discrete Wavelet Transform (DWT) and Wavelet Packet Transform (WPT) were used for feature extraction. From the above techniques, the main issues addressed are selection of optimal feature subset and the design of ANN architecture model. To build a competent and robust classifier, it is essential to extract the utilizable feature vectors from the disturbance signal that can optimize data size as well as incorporate the main characteristics of the signal. This paper addresses these issues, and the distinctive feature vectors are obtained with reduced number of coefficients by using Energy Entropy based WPT. From these, the best discriminative feature vectors with reduced number of coefficients are obtained and are used as input to ANN, so that the burden over classification can be reduced. The classification performance is compared with FFT based ANN. The simulation results obtained have significant improvement over existing methods. Thus the proposed hybrid classifier provides the most excellent detection among PQ problems that arises in real time by improving classification accuracy in terms of both computation time and means square error.

Electric railway power systems (ERPS) as one of the most critical and high-power end-user loads of utility grids are characterized by outlandish power quality (PQ) problems all over the world. The extension and evolution of different supply topologies for these systems has resulted in significant and various forms of distortions in network voltage and current in all ERPS, the connected power system, and adjacent consumers. During the last years, numerous studies have been offered to investigate various aspects of PQs in a specific supplying topology. Variation in the supply structure of the ERPS and different types of locomotives has propelled the observation of different PQ phenomena. This versatility and development have led to confront considerable types of two-way interactive interfaces as well as reliability and PQ problems in ERPS. In addition, the lack of standards explicitly dedicated to ERPS has added to the ambiguity and complexity of this issue. In this paper, an extensive review of PQ distortions and phenomena in different configurations of ERPS is proposed and a systematic classification is presented. More than 140 scientific papers and publications are studied and categorized which can provide a fast review and a perfect perspective on the status of PQ indexes for researchers and experts.

Having an inter-tie between low/medium voltage grid and distributed generation (DG), both exposes to power quality (PQ) problems created by each other. This paper addresses various PQ problems arise due to integration of DG with grid. The major PQ problems are due to unbalanced and non-linear load connected at DG, unbalanced voltage variations on transmission line and unbalanced grid voltages which severely affect the performance of the system. To mitigate the above mentioned PQ problems, a novel integrated control of distribution static shunt compensator (DSTATCOM) is presented in this paper. DSTATCOM control helps in reducing the unbalance factor of PCC voltage. It also eliminates harmonics from line currents and makes them balanced. Moreover, DSTATCOM supplies the reactive power required by the load locally and hence, grid need not to supply the reactive power. To show the efficacy of the proposed controller, several operating conditions are considered and verified through simulation using MATLAB/SIMULINK.

Voltage stability assessment of isolated hybrid dish-stirling solar thermal-diesel microgrid with STATCOM using mine blast algorithm

In this paper, the power quality problems of a DC arc furnace load are investigated. An 18-pulse converter is used to provide the DC currents to the furnace. The power quality problems concerned are the harmonics and voltage flicker (voltage fluctuation). Field measurement is used to reveal the harmonic distributions of the rectifiers under balanced and unbalanced conditions. The effect of passive harmonic filters is also investigated. Although the DC arc furnace is operated in constant current mode, there is still an obvious reactive power variation to cause voltage flicker. Statistics is used to reveal the load fluctuation. Finally, a feasible reactive power compensation scheme with instantaneous values is studied to mitigate the voltage flicker problem.

Multilevel inverters are currently the subject of extensive investigation and are used primarily for medium and high voltage distribution systems. The work presented in this paper provides a cost-effective and realistic solution to mitigate power quality (PQ) problems. A Cascaded H-Bridge multilevel inverter (CHB-MLI) has been configured as a shunt active power filter (SAPF). It is well reported that large-scale use of power electronics-based devices leads to several PQ problems such as poor power factor, unregulated dc voltage, harmonics, voltage regulation etc. In this paper, an improved immune feedback control algorithm is proposed and developed to mitigate PQ issues by predicting the weighted active component of load current and to generate reference current for the grid. Extensive MATLAB simulation and experimental work have been reported for validation on a single-phase system. A low prototype model is developed in the laboratory to study and compare the steady-state and dynamic results of the proposed controller with conventional Least Mean Square (LMS) and Immune algorithm.

Voltage dip is a power quality problem that occurs the most frequently in the Provincial Electricity Authority (PEA) power system and impacts the industry's sensitive load. This paper presents a photovoltaic (PV) farm converter control as a static synchronous compensator (STATCOM), supplying dynamic reactive power for voltage dip mitigation and the industry's failure load reduction near the PV farm. The PV farm's power system and the industry connect with the 22 kV distribution system of Bang Phra khru substation (BPH) in Phra Nakhon Si Ayutthaya Province. A case study simulated on the DIgSILENT PowerFactory software and converter control as STATCOM operated in two modes: full STATCOM mode and partial STATCOM mode is presented. The distribution system data has been collected from the Geographic Information System (GIS). The voltage dip event data, caused by a single line to ground fault on other feeder and affected sensitive load, received from disturbance analyzer. The results of both STATCOM modes demonstrated an increased voltage value in the standard range of PEA. The partial STATCOM mode showed the voltage value better than the full STATCOM mode. As a result, PEA should improve the grid code determined the PV farm installed near the industry's sensitive load had to support dynamic power.

With the wind power generation in power system increase gradually,the problem of power quality which caused by grid-connection is becoming more and more serious. Power quality indexes of 100 MW wind farm including voltage deviation, harmonic.Three-phase unbalance and voltage flicker were made real-time monitoring in Inner Mongolia. Data analysis displays that the wind farm can satisfy the standard of power quality. Researches show that power quality's testing of the wind farm can improve the reliability of the power system stabilization. Moreover,it is beneficial to the wind turbine's security,stability and preventive maintenance.

To improve the efficiency of existing transmission lines, Smart Power Flow controlled (SPFC) is presented based on Flexible AC transmission (FACTS). By Injecting controllable voltage in series to transmission lines, reactive and active power can be controlled. SPFC helps the transmission lines to obtain their maximum power capacity by avoiding the redundant reactive power which overloads the transmission line. This paper investigates three different modes of SPFC using a 48-pulse controller i.e., static synchronous series compensator (SSSC), unified power flow controller (UPFC), and static synchronous compensator (STATCOM). STATCOM, SSSC, and UPFC are designed to stabilize voltage and provide compensation to reactive power of the power grid system, by using a 48-pulse converter. Using 48-pulse STATCOM reduces harmonics and gives the maximum power at 90 degrees of injected voltage in SSSC. The overall SPFC has been investigated and simulated in MATLAB/SIMULINK environment.

The unified power quality conditioner (UPQC) is a power conditioning device, which is a integration of back to back connected shunt active power filter (APF) and series APF to a common DC link voltage. For improvement of power quality (PQ) problems in a three-phase four-wire distribution system, two topologies are proposed in this paper. A comparative analysis of these topologies along with the most common four-leg voltage source inverter (VSI) based topology of four-wire UPQC is discussed in this work. The performance of each topology of UPQC is evaluated for different PQ problems like power-factor correction, load balancing, current harmonic mitigation, voltage harmonic mitigation and source neutral current mitigation. The synchronous reference frame (SRF) theory is used as a control strategy of series and shunt APFs. The simulation results using MATLAB/Simulink enviournment are obtained, which support the effectiveness of these topologies of UPQC for power quality improvement.

Reactive power compensation is essential in hybrid grid-connected systems because power electronic inverters utilized for supplying DC energy into the grid causes a reduction in the overall power factor of the power systems. Due to the ability to provide a reliable and efficient power supply to remote and off-grid areas, hybrid power systems are growing in popularity. It can provide greater opportunities for operational growth by combining economic and technology advancement. To meet the demand for electrical energy in both regular and critical situations, operators must be in charge of the power systems reliable and secure operation. The primary objective of the work is to control the reactive power flow in a grid-connected hybrid renewable energy system (PV-wind-battery). The power quality problems that these systems frequently experience include voltage sags, harmonics, and flicker. A FACTS device Unified Power Quality controller (UPQC) with a Genetic Algorithm based PI controller is suggested to handle these power quality issues. In order to improve the performance of the power system, the proposed optimization approaches are used to tune the UPQC in a multiline transmission system. The model was developed with the help of the MATLAB/Simulink work framework.