• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• v.4B no.2
• /
• pp.80-85
• /
• 2004

This paper reports the performance of a CB (Circuit Breaker) and converter for the battery operated Wind-PV (Photovoltaic) system. For this purpose, a fluctuating reduction controller for an electric generation hybrid (wind+PV) system is suggested. The method operates a wind turbine, PV, CB, converter and battery. Integration of wind and PV sources, which are generally complementary, usually reduce the capacity of the battery. Also, CB controls the overvoltage of the generation system. The objective is to control the operation of the converter and the CB and reduce power fluctuation. This paper includes discussion on system performance, power quality, fluctuation and effect of the randomness of the wind.

• Computational Structural Engineering
• /
• v.3 no.4
• /
• pp.133-141
• /
• 1990

The nature of fluctuating air pressure inside building was studied by testing a building model in a wind tunnel. The model has a single room and a window opening. Various opening conditions were tested in both laminar uniform wind and turbulent boundary-layer wind. The RMS and the spectra of the fluctuating internal pressure were measured. The test results support a recent theory which predicts the behavior of internal pressure under high wind based on aerodynamic analysis.

• The KSFM Journal of Fluid Machinery
• /
• v.18 no.4
• /
• pp.13-21
• /
• 2015

The system design of the Organic Rankine Cycle(ORC) is greatly influenced by the thermal properties such as the temperature or the thermal capacity of heat source. Typically waste heat, solar energy, geothermal energy, and so on are used as the heat source for the ORC. However, thermal energy supplying from these kinds of heat sources cannot be provided constantly. Hence, an experimental study was conducted to utilize fluctuating thermal energy efficiently. For this experiment, an impulse turbine and supersonic nozzles were applied and the supersonic nozzle was used to increase the velocity at the nozzle exit. In addition, these nozzles were used to adjust the mass flowrate depending on the amount of the supplied thermal energy. The experiment was conducted with maximum three nozzles due to the capacity of thermal energy. The experimented results were compared with the predicted results. The experiment showed that the useful output power could be producted from low-grade thermal energy as well as fluctuating thermal energy.

• Proceedings of the KIPE Conference
• /
• 2011.11a
• /
• pp.285-286
• /
• 2011

Maximum Power Point Tracker (MPPT) is the big issue in generating power based on Wind Energy Conversion System. In case of unknown turbine characteristic, it is useful to implement MPPT based on fuzzy logic control. This kind of control is able to find the value of duty cycle to meet maximum power point at particular wind speed. There are many methods to develop MPPT based fuzzy logic controls. In this paper, two of the methods are compared both at low and high fluctuating wind speed.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2006.11a
• /
• pp.465-468
• /
• 2006

The wave power absorbing performance of a bottom-mounted oscillating water column (OWC) chamber structure is studied. The potential problem inside the chamber is solved by making use of the Green integral equation associated with the Rankine Green function while the outer problem with the Kelvin Green function taking account of fluctuating air pressure in the air chamber. The absorbed wave power, wave elevation inside the chamber, reflection coefficient and wave loads are calculated for various values of a parameter related to the fluctuating air pressure. The present methods can also be used for the design of a OWC breakwater which can absorb and reflect the incoming wave energy at the same time.

• Wind and Structures
• /
• v.26 no.4
• /
• pp.191-204
• /
• 2018

This article presents a study of the largest-ever (height = 220 m) cooling tower using the large eddy simulation (LES) method. Information about fluid fields around the tower and 3D aerodynamic time history in full construction process were obtained, and the wind pressure distribution along the entire tower predicted by the developed model was compared with standard curves and measured curves to validate the effectiveness of the simulating method. Based on that, average wind pressure distribution and characteristics of fluid fields in the construction process of ultra-large cooling tower were investigated. The characteristics of fluid fields in full construction process and their working principles were investigated based on wind speeds and vorticities under different construction conditions. Then, time domain characteristics of ultra-large cooling towers in full construction process, including fluctuating wind loads, extreme wind loads, lift and drag coefficients, and relationship of measuring points, were studied and fitting formula of extreme wind load as a function of height was developed based on the nonlinear least square method. Additionally, the frequency domain characteristics of wind loads on the constructing tower, including wind pressure power spectrum at typical measuring points, lift and drag power spectrum, circumferential correlations between typical measuring points, and vertical correlations of lift coefficient and drag coefficient, were analyzed. The results revealed that the random characteristics of fluctuating wind loads, as well as corresponding extreme wind pressure and power spectra curves, varied significantly and in real time with the height of the constructing tower. This study provides references for design of wind loads during construction period of ultra-large cooling towers.

• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.1022-1024
• /
• 2015

An auxiliary switching power supply is designed for the control circuit of a machine integrated with frequency variation based on TOP249Y in this paper. And experiments have been conducted to verify that this power supply can function well even with fluctuating inputs, indicating the validity of this switching power supply and it can be applied to supply some other electrical equipments.

• Journal of Power Electronics
• /
• v.15 no.3
• /
• pp.670-684
• /
• 2015

The hybrid cascaded multilevel inverter (HCMLI) is a popular converter topology that is being increasingly used in high power medium voltage drives. The intricacy of the control technique for a HCMLI increases with the number of levels and due to fluctuating dc voltages. This paper presents a novel offline quadrant search based space vector modulation technique to synthesize a sinusoidal output from a dispersed pattern of voltage vectors due to different voltages in the auxiliary unit. Such an investigation has never been reported in the literature and it is being attempted for the first time. The method suggested distributes the voltage vectors for a reduced total harmonic distortion at minimal computation. In addition, the proposed algorithm determines the maximum modulation index in the linear modulation range in order to synthesize a sinusoidal output for both normal and abnormal vector patterns. It is better suited for a wide range of practical applications. It is particularly well suited for renewable source fed inverters which utilize large capacitor banks to maintain the dc link, which are prone to such slow fluctuations. The proposed quadrant search space vector modulation technique is simulated using MATLAB/SIMULINK and implemented using a Nexys-2 Spartan-3E FPGA for a developed prototype.

• Wind and Structures
• /
• v.24 no.2
• /
• pp.145-169
• /
• 2017

The auxiliary structures of a high-rise building, such as balconies, ribs, and grids, are usually much smaller than the whole building; therefore, it is difficult to simulate them on a scaled model during wind tunnel tests, and they are often ignored. However, they may have notable effects on the local or overall wind loads of the building. In the present study, a series of wind pressure wind tunnel tests and high-frequency force balance (HFFB) wind tunnel tests were conducted on rigid models of an actual super high-rise building with vertical ribs protruding from its facades. The effects of the depth and spacing of vertical ribs on the mean values, fluctuating values and the most unfavorable values of the local wind pressure coefficients were investigated by analyzing the distribution of wind pressure coefficients on the facades and the variations of the wind pressure coefficients at the cross section at 2/3 of the building height versus wind direction angle. In addition, the effects of the depth and spacing of vertical ribs on the mean values, fluctuating values and power spectra of the overall aerodynamic force coefficients were studied by analyzing the aerodynamic base moment coefficients. The results show that vertical ribs significantly decrease the most unfavorable suction coefficients in the corner recession regions and edge regions of facades and increase the mean and fluctuating along-wind overall aerodynamic forces.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.67 no.6
• /
• pp.695-701
• /
• 2018

For a power grid that has a high wind penetration level, when wind speeds are continuously fluctuating, the maximum power point tracking (MPPT) operation of a variable-speed wind turbine (VSWT) causes the significant output power fluctuation of a VSWT, thereby significantly fluctuating the system frequency. In this paper, an improved power-smoothing scheme of a VSWT is presented that significantly mitigates the frequency fluctuation caused by varying wind speeds. The proposed scheme employs an additional control loop based on the frequency deviation that operates in combination with the MPPT control loop. To improve the power-smoothing capability of a VSWT in the over-frequency section (OFS), the control gain of the additional loop, which is set to be inversely proportional to the rotor speed, is proposed. In contrast, the control gain in the under-frequency section is set to be proportional to the rotor speed to improve the power-smoothing capability while avoiding over-deceleration of the rotor speed of a VSWT. The proposed scheme significantly improves the performance of the power-smoothing capability in the OFS, thereby smoothing the frequency fluctuation. The results clearly demonstrate that the proposed scheme significantly mitigates the frequency fluctuation by employing the different control gain for the OFS under various wind penetration scenarios.