Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Converter control design for Battery Energy Storage Systems applied in autonomous wind/diesel systems by Magni Þ. Pálsson 1. operating hours and the number of start/stop cycles of the diesel engine. Initiation I graduated from the University of Iceland, Reykjavík, Department of Electrical Engineering, in June 1990. The BESS consists of battery bank connected to a forced commutated converter. In September 1994 I started my studies towards a dr. ing. degree here at NTNU. My main field of research is design of converter controllers for Battery Energy Storage Systems (BESS) for use in autonomous wind/diesel systems. The main purpose of using a BESS in such applications, is to enhance power quality and increase the efficiency of the system, by reducing the number of operating hours of the diesel engine. 3. Modelling The configuration of the wind/diesel model is based on the second generation wind/diesel system on Frøya, pictured below [1]. Wind turbine AG Customer loads Diesel generator set This work was suggested by my supervisor professor dr. ing. Hans H. Faanes and originated from a project that EFI (The Norwegian Electric Power Research Institute) has had going for several years on the island of Frøya off the coast of Sør-Trøndelag. My scientific advisor is dr. ing. Kjetil Uhlen, researcher at EFI. DE SG Converter and control unit Battery storage Converter Dumpload DC AC CONTROL SYSTEM I completed the obligatory courses in the spring 1996 and since then I have been working on the research part on a full time basis 2. Fig. 1: The Frøya wind-diesel system [1] The computer program PSCAD/EMTDCTM[2] has been used for the modelling and simulation. I have also developed reduced-order models in SIMULINK[5]. The EMTDC model is more detailed than the SIMULINK model, which enables me to study more closely the switching phenomena of the converter. In the SIMULINK model I use a static model of the converter, but in PSCAD/EMTDC I am able to control each transistor. The SIMULINK model has been used as a basis for deriving linear models. The purpose, in this work, of linearising is to be able to use eigenvalue analysis to study the behaviour Description Using wind energy to produce electricity exposes power systems to special problems. The fluctuating nature of the wind power induces fluctuations in the system voltage and frequency of an autonomous wind/diesel system. The voltage fluctuations may cause annoying flicker in incandescent light bulbs. The need for reducing the fluctuations is therefore present. Effective use of a BESS also increases the efficiency of the wind/diesel system, by reducing the number of 41 of the two converter control techniques developed and try and reveal any differences. The linearised models are also an ideal starting point for further control design. BESS ”lifts” the voltage level. This may be achieved by other means, e.g. by installing a capacitor bank. This solution though might cause problems when shifting between low load and high load conditions. 4. The models have also been validated against measurements on the Frøya wind/diesel system. The simulated and measured results proved to correspond quite well. Status of the work I have developed two control strategies for the converter. The first one uses a sinusoidal pulse width modulation technique (sinusoidal PWM)[3] and is based on controlling the amplitude and phase of the converter output voltage. The latter method is a hysteresis type current control method[3], based on controlling the converter output current. 5. I have now written my thesis and will defend it this spring. Both control techniques show good simulation results both in wind/diesel applications and in a simulated weak power grid (e.g. distribution grid). Although this latter application has not been a central part of this work, the simulation results are very promising and should encourage to further studies. Fig. 2 shows the system voltage when wind power is integrated into a weak power grid. The three trajectories in the figure are (from top to bottom): using BESS with current controlled converter; using BESS with voltage controlled converter and using no BESS. 6. [1] [2] [3] System voltage with wind integration into a weak power grid 230 [4] BESS w/CCC BESS w/VCC 226 222 V 218 [5] 214 No BESS 210 0 1 2 3 4 Further work 5 sec Fig. 2: System voltage in a weak grid with wind power integration. Using a BESS obviously enhances the voltage quality in this case. The most significant difference is how the BESS is able to damp the voltage fluctuations almost completely. Another clear difference is the voltage level, i.e. how the 42 References Uhlen, K.: Modelling and robust control of autonomous hybrid power systems. Division of Engineering Cybernetics NTH, 1994. PSCAD/EMTDCTM: Manitoba HVDC Research Centre, 400-1619 Pembina Hwy., Winnipeg, Manitoba, Canada. Mohan, N.; Undeland, T. M.; Robbins, W. P.: 1995, Power electronics. Converters, applications and design, John Wiley & Sons, Inc., USA. Pálsson, M.; Uhlen, K.; Toftevaag, T: 1997, Modelling and simulation of an autonomous wind/diesel system equipped with forced commutated converter, Proceedings of the 7th European Conference on Power Electronics and Applications (EPE’97), Trondheim, Norway. SIMULINKTM: The MathWorks, Inc., Cochituate Place, 24 Prime Park Way, Natick, Massachusetts 01760, USA.