Harmonic Reduction and Power Transmission Enhancement in a Grid Interface of Wind Power Using Shunt-Connected FACTS Device

Transcription

1 Harmonic Reduction and Power Transmission Enhancement in a Grid Interface of Wind Power Using Shunt-Connected FACTS Device R.Siva Subramanyam, Asst.professor, Dept of EEE, Srikalahasteeswara Institute of Technology(SKIT), Srikalahasti, A.P, India. rssr305@gmail.com Abstract The demand for electricity is increased day to day now a day s. With this increase in demand, the renewable energy sources like wind energy are one of the best alternatives for power generation because of its tremendous environmental social and economical benefits. However, the effect of a wind turbine in the grid system affects the performance of the power system and also it introduces more harmonic distortion in the electric grid system. In this paper STATCOM connected FACTS controller is used to overcome the various power quality problems in a wind connected electric grid system. The STATCOM control scheme for the grid connected wind energy generation system for power quality improvement is simulated using MATLAB/SIMULINK in the power system. both inductive and capacitive regions and hence it supplies capacitive and inductive reactive reactance s to the transmission line so as to transmit optimal power. However with the recent innovations in high power semiconductor switch (IGBT), converter topology and digital control technology, faster STACTCOM with low cost is emerging, which is promising to help integrate wind energy, into the grid to archive a more cost-effective and reliable renewable wind energy [4],[5]. Index Terms Power quality, STATCOM, THD I. INTRODUCTION Energy is the primary and most universal measures of all kinds of work by human beings and nature. Everything that happens in the world is the expression of the flow of energy in one of its forms; energy is an important input in all sectors of a country's economy. From the past decades due to globalization, industrialization, and civilization there is great demand for electrical energy. to satisfy these things we have different sources of energy are available, these are thermal, nuclear, hydro, diesel, solar, wind and fuel cells. The need to integrate the renewable energy like wind energy into power system is to make it possible to minimize the environmental impact on conventional plants [1]. The integration of wind energy into existing power system presents a technical challenge and that requires consideration of voltage realization, stability, power quality problems. The power quality is an essential customer focused measure and is greatly affected by the operation of a distribution and transmission network. The issue of power quality is of great important to the wind turbine [2], [3]. In this paper the STATCOM FACTS device with PWM techniques is used to solve the above said problem, because the STATCOM provide many advantages such as fast response time and better voltage support capability in Fig. 1 Block diagram of the control scheme Power quality can affect machine or equipment reliability and reduce the life of components. However, voltage transients and voltage system sags and swells are all power quality problems and are all interdependent. Conventionally the low cast mechanical switched devices and transformer taps changes are used to address these issues related to stability and power quality. Moreover the fastest switching of MSD and TC to deal with power quality issues may even cause resonance and transient over voltage, add additional stress on wind turbine gearbox and shaft, make themselves and turbines wear out quickly and hence increase the maintenance and replacement cost. Therefore a fast shunt VAR compensator is needed to address these issues more effectively. The STATCOM is considered for these applications because it provides many advantages, in particular, the fast response time and superior voltage support capability with its nature of voltage source. [6], [7]. 1994

2 The grid connected system shown in above fig 1. Consist of wind energy generation system and shunt connected STACTCOM FACTS device in the grid system. The STATCOM output is varied according to the controlled strategy so as to maintain the power quality norms in the grid system. In this proposed system wind generations are based on constant speed topologies with pitch control turbine and the induction generator is used in the proposed scheme because of its simplicity it does not require a separate field circuit, it can accept constant and variable loads and has natural protection against shunt circuit. The STATCOM come in a 3-phase voltage source inverter having the capacitance on its Dc link and connected at the point of common coupling. The STATCOM injects a compensating current of variable magnitude and frequency component at the bus of common coupling. II. ENERGY RESOURCES Energy is used for heating, cooking, transportation and manufacturing. Energy can be generally classified as Non-renewable energy resources Renewable energy resources A. Non-renewable energy resources Over 85% of the energy used in the world is from non-renewable supplies. Most developed nations are dependent on non-renewable energy sources such as fossil fuels (coal and oil) and nuclear power. B. Disadvantages of non-renewable energy sources They are not- renewable and fast depleting. They leave behind harmful by-products upon combustion, thereby causing a lot of pollution. Mining of such fuels leads to irreversible damage to the adjoining environment. Fossil fuel pollution the environment. It will eventually run out. It cannot be recycled. C. Renewable energy resources Renewable energy is generally defined as an energy that comes from resources which are naturally replenished on a human timescale such as sunlight, the wind, rain, tides, waves and geothermal heat. Renewable energy replaces conventional fuels in four distinct areas: electricity generation, hot water/space heating, motor fuels, and rural (off-grid) energy services. About 16% of global final energy consumption presently comes from renewable resources, with 10% of all energy from traditional biomass, mainly used for heating, and 3.4% from hydroelectricity. New renewable (small hydro, modern biomass, wind, solar, geothermal, and biofuels) account for another 3% and are growing rapidly. At the national level, at least 30 nations around the world already have renewable energy contributing more than 20% of energy supply. National renewable energy markets are projected to continue to grow strongly in the coming decade and beyond. Wind power, for example, is growing at the rate of 30% annually [8]. D. Wind turbine These are clean and green (pollution free) and non-conventional sources are up to end of the living beings. Airflows can be used to run wind turbines. Modern utility-scale wind turbines range from around 600 kw to 5 MW of rated power, although turbines with rated output of MW have become the most common for commercial use; the power available from the wind is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically up to the maximum output for the particular turbine [9]. III. POWER QUALITY AND ITS IMPORTANCE Power quality is defined as the fitness of electrical power supplied to the consumers. A. Cost of poor power quality Unexpected power supply failures Equipment overheating Damage to sensitive equipment Electronic communication interferences. The Increase of system losses. Penalties imposed by utilities because the site pollutes the supply network too much. Connection refusal of new sites because the site would B. Effect of Low Voltage poor Power Quality Reactive power, as it loads up the supply system unnecessary, Harmonic pollution, as it causes extra stress on the networks and makes installations run less efficiently, Load imbalance, especially in office Fast voltage variations leading to the flicker. All this phenomena potentially lead to the inefficient running of installations, system downtime and reduced equipment life and consequently high installation running costs. If due to poor Power Quality the production is stopped, major costs are incurred [10]. C. POWER QUALITY IMPROVEMENT METHODS Power factor correction(active and Reactive power management through FACTS) Harmonic filtering (reduction of THD) 1995

3 Transient voltage surge suppression. Proper earthling systems. IV. PRINCIPLE OPERATION OF STATCOM FACTS DEVICE Flexible AC Transmission Systems, called FACTS, got in the recent years a well-known term for higher controllability in power systems by means of power electronic devices. Several FACTS devices have been introduced for various applications worldwide. The most used FACTS-device is the SVC or the version with Voltage Source Converter called STATCOM. Almost half of the SVC and more than half of the STATCOMs are used for industrial applications. STATCOM has a characteristic similar to the synchronous condenser, but as an electronic device it has no inertia and is superior to the synchronous condenser in several ways, such as better dynamics, a lower investment cost and lower operating and maintenance costs. An STATCOM is built with Thyristors with turn-off capability like GTO or today IGBT or with more and more IGBTs. The advantage of an STATCOM is that the reactive power provision is independent of the actual voltage on the connection point. This can be seen in the Fig.2 for the maximum currents being independent of the voltage in comparison to the SVC. This means, that even during most severe contingencies, the STATCOM keeps its full capability. Several different control techniques can be used for the firing control of the STATCOM, Pulse Width Modulated (PWM) techniques, which turn on and off the GTO or IGBT switch more than once per cycle, can be used. STATCOM can also behave as a shunt active filter, to eliminate unbalance or distortions in the source current or the supply voltage. Theoretically, the power converter employed in the STATCOM can be either a VSC or a current-source converter (CSC).In practice; however, the VSC is preferred because of the bi-directional voltage-blocking capability. Fig. 2 STATCOM structure and voltage / current characteristics A. STATCOM block diagram An STATCOM is a controlled reactive source, which includes a Voltage Source Converter (VSC) and a DC link capacitor connected in shunt, capable of generating and/or absorbing reactive power. The AC terminals of the VSC are connected to the Point of Common Coupling (PCC) through an inductance, which could be a filter inductance or the leakage inductance of the coupling transformer, as shown in Fig. 3. Fig.3 Block diagram of STATCOM The DC side of the converter is connected to a DC capacitor, which carries the input ripple current of the converter and is the main reactive energy storage element. This capacitor could be charged by a battery source, or could be recharged by the converter itself. In this proposed scheme, A STATCOM is built with Thyristors with turn-off capability device called IGBT used.[4] B. Features of IGBT Today IGBT or with more used because of high voltage, high current, and low switching frequencies favor IGBTs.An IGBT features a significantly lower forward voltage drop compared to a conventional MOSFET in higher blocking voltage rated devices. As the blocking voltage rating of both MOSFET and IGBT devices increases, the depth of the drift region must increase and the doping must decrease, resulting in roughly square relationship decrease in forward conduction vs. blocking voltage capability of the device. V. SIMULATION RESULTS In this paper the proposed system is simulated in the MATLAB/SIMULINK in power system environment and it is observed that the source current on the grid is affected due to the effects of wind generator, the purity of waveforms may be lost in respect of active power, reactive power, voltage, and current. The harmonic pollution is often characterized by the Total Harmonic Distortion or THD which is by definition equal to the ratio of the RMS harmonic content to the fundamental. Also, it is found that the total harmonic distortion (THD) without STATCOM is And with the introduction of STATCOM the performance of the system is improved also the THD level has been reduced to

4 Fig. 4 Simulation block diagram Fig.5 Voltage and Current waveforms for without STATCOM model Fig.6 Active and Reactive power waveforms for without STATCOM model 1997

5 Fig.7 Voltage and Current waveforms for with STATCOM model Instrum. Meas., vol. 58, no. 2, pp , Feb [4] N.Nirmala and V.suresh kumar, A STATCOM-Control Scheme for Wind Energy System to Improve Power Quality, IETCG [5] M. N. Eskander, M.A.Saleh, Maged N.F.Nashed and S. Amer, Superiority of LVRT of Grid Connected Wind Energy Conversion System Using Unified Power Quality Controller, International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.6, pp ,Jun [6] K. S. Hook, Y. Liu, and S.Atcitty, Mitigation of the wind generation integration related power quality issues by energy storage, EPQU J.vol. XII, no. 2, [7] C. Han, A. Q. Huang, M. Baran, S. Bhattacharya, and W.Litzenberger, STATCOM impact study on the integration of a large wind farm into a weak loop power system, IEEE Trans. Energy Conv., vol. 23, no. 1, pp , Mar [8] J.Manel, Power electronic system for grid integration of renewable energy source: A survey, IEEE Trans. Ind. Electron., vol. 53, no. 4, pp , [9] M. Tsili and S. Papathanassiou, A review of grid code technology requirements for wind turbine, Proc. IET Renew. Power gen., vol.3, pp , [10] Narain G. Hingoranl, Laszlo Gyugyi, Understanding FACTS Concepts and Technology of Flexible AC Transmission Systems IEEE Power Engineering Society. Fig.8 Active and reactive power waveforms for with STATCOM model I. CONCLUSION AND FUTURE SCOPE This paper mainly focused on power quality improvement in a grid connected wind energy system by using shunt connected FACTS devices such as STACTCOM using MATLAB/SIMULINK environment and also absorbed that THD level after STATCOM is very much reduced, which intern enhance the power transmission in the line using STACTCOM FACTS device. In future with the use of combined FACTS devices the performance of the grid is more enhanced by connecting more and more renewable energy system sources. REFERENCES [1] R.Billinton and Y.Gao, Energy conversion system models for adequacy assessment of generating systems incorporating wind energy, IEEE Trans. on E. Conv., vol. 23, no. 1, pp , [2] D. L. Yao, S. S. Choi, K. J. Tseng, and T. T. Lie, A statistical approach to the design of a dispatchable wind power Battery energy storage system, IEEE Trans. Energy Conv., vol. 24, no. 4, Dec [3] J. J. Gutierrez, J. Ruiz, L. Leturiondo, and A. Lazkano, Flicker Measurement system for wind turbine Certification, IEEE Trans. 1998