• The KSFM Journal of Fluid Machinery
• /
• v.13 no.2
• /
• pp.36-40
• /
• 2010

Tidal current power system is the energy converter which converts the kinetic energy of tidal stream into electric energy. The performance of the rotor which initially converts the energy is determined by various design factors and it should be optimized by the ocean environment of the field. Flow direction changes due to rise and fall of the tides, but horizontal axis turbine is very sensitive to direction of flow. To investigate the rotor performance considering the interaction problems with incidence angle of flow, series of experiments have been conducted. The results and findings are summarized in the paper.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.17 no.5
• /
• pp.131-136
• /
• 2018

Research on space development and satellites is being actively pursued. An interesting field is the study of reliable low-cost space launch vehicles. Since chemical fuel-based launching systems are expensive and take a lot of time and cost to maintain, the EML system, which is an electromagnetic force launching apparatus, is attracting attention. The EML system converts electrical energy stored in a capacitor into magnetic energy, and converts magnetic energy into mechanical kinetic energy, thereby accelerating the projectile. Although studies are actively conducted in the field, it is difficult to solve the equation because the impedance and speedance change with time and the nonlinearity is strong. Many researchers have solved this equation in a variety of methods. In this paper, the velocity analysis of the projectile was carried out by FEM (finite element method) using the commercial electromagnetic analysis program MAXWELL.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.273-277
• /
• 1999

A cold cathode flourescent lamp for the backlight in the notebook computer requires high input voltage about 1300(V) when it turns on. But once a discharge starts, the input voltage can be dropped by about one-third for continued output. The equivalent impedance also varies from open to several dozens of kilo-ohms. The piezoelectric transformer converts electrical energy into mechanical energy and then converts it back to electrical energy at a high voltage. Its high output voltage, high efficiency and small size are suitable for driving the LCD backlight in the notebook computer. The piezoelectric transformer operates near the resonance frequency and the output waveform is close to sine wave with very little noise. This paper suggests an inverter for LCD backlight of notebook computer using piezoelectric transformer that includes voltage to frequency converter for gate signal which is useful for tracking of variable resonance frequency depending on load impedance.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.22 no.9
• /
• pp.845-852
• /
• 2012

Recently, wireless power transfer technology is ready to be commercialized in consumer electronics. It draws attention from not only experts but also public because of its convenience and huge market. However, previous technologies such as magnetic resonance and induction coupling have limited applications because of its short transfer distance compared to device size and magnetic intensity limitation on the safety of body exposure. As an alternative, ultrasonic wireless power transfer technology is proposed. The ultrasonic wireless power transfer system is composed of transmitter which converts electrical energy to ultrasonic energy and receiver which converts the ultrasonic energy to the electrical energy again. This paper is focused on the development of high energy conversion efficiency of ultrasonic transmitter. Optimal transfer frequency is calculated based on the acoustic radiation and damping effect. The transmitter is designed through numerical analysis, and is manufactured to match the optimal transfer frequency with the size of 100 mm diameter, 12.2 mm thickness plate. The energy conversion efficiency of about 13.6 % at 2 m distance is obtained, experimentally. This result is quite high considered with the device size and the power transfering distance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.771-776
• /
• 2012

Recently, wireless power transfer technology is ready to be commercialized in consumer electronics. It draws attention of not only experts but also public because of its convenience and huge market. However, previous technologies such as magnetic resonance and induction coupling have limited applications because of its short transfer distance compared to device size and magnetic intensity limitation for the safety of body exposure. As an alternative, ultrasonic wireless power transfer technology is proposed. The ultrasonic wireless power transfer system is composed of transmitter which converts electrical energy to ultrasonic energy and receiver which converts the ultrasonic energy to the electrical energy again. This paper is focused on the development of high energy conversion efficiency of ultrasonic transmitter. Optimal transfer frequency is calculated based on the acoustic radiation and damping effect. The transmitter is designed through numerical analysis, and is manufactured to match the optimal transfer frequency with the size of 100mm diameter, 12.2 mm thickness plate. The energy conversion efficiency of about 13.6% at 2m distance is obtained, experimentally. This result is quite high considered with the device size and the power transfer distance.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.3131-3135
• /
• 2008

This paper presents an energy harvester using piezoelectric elements that is a kind of generator which converts the mechanical power to the electric one using windmill system with many PZT actuators. In this study, low frequency characteristics of the cantilever-type piezoelectric actuator are experimentally investigated. Advantages of the cantilever use are to take a very large displacement and to improve the endurance of the PZT element. The material of cantilever is an aluminum and three kinds of cantilever of which size is $150[mm]{\times}20[mm]{\times}1.5[mm]$, $170[mm]{\times}20[mm]{\times}1.5[mm]$ and $190[mm]{\times}20[mm]{\times}1.5[mm]$ were experimented, respectively. The cantilever was fixed on the vibrator. The characteristics of frequency and mass variation of cantilever end part such as 0[g], 5[g], 10[g] are investigated. Maximum voltage was outputted at the condition of $150[mm]{\times}20[mm]{\times}1.5[mm]$ and 10[g] of mass. It was confirmed that the lower natural frequency at the larger length of cantilever and at the bigger of mass is gotten.

• Proceedings of the KIEE Conference
• /
• 2006.07b
• /
• pp.1181-1182
• /
• 2006

The solar power system comprises a solar battery that directly converts light energy to electrical energy with a photovoltaic effect and a power converter system, that is, inverter that converts direct current power, which is generated from solar battery to common alternating current. In this paper, database was constituted through remote monitoring supervision measurement for the long-time positive operation of 3kW solar power system installed within the solar energy positive research complex of Chosun University. As a result of analyzing the reduction of the efficiency of solar battery and inverter that are compositional components of PV system through an analysis on the acquired data, the PV output was proven over 65% of the total output when insolation intensity exceeded 600W/m2 in 2005, and the array conversion efficiency dropped much more than rating; meanwhile, insolation intensity dropped below 600W/m2. Therefore, it has been demonstrated that approximately 35% of the entire amount of PV output operated under the condition that the inverter efficiency rate dropped rapidly by 60 to 70%.

• Journal of Drive and Control
• /
• v.14 no.1
• /
• pp.23-28
• /
• 2017

A wind power heat generation system that converts wind power directly to heat instead of electric power is considered in this study. The system consists of a wind turbine part and a heat generation part. The heat generation part is materialized by a hydraulic system including a hydraulic pump, a flow control valve, a hydraulic oil tank, etc. The flow control valve primarily converts hydraulic energy generated in the pump to heat energy. It should have a function of overspeed protection under excessive wind speeds. In this study, a novel flow control valve design is proposed for excellent flow control characteristics under excessive pump driving torque (excessive wind speed). The performance of the suggested valve is analyzed using numerical simulation.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.54 no.12
• /
• pp.609-615
• /
• 2005

A 30kW electrical power conversion system is developed for a variable speed wind turbine. In the wind energy conversion system(WECS) a synchronous generator with field current excitation converts the mechanical energy into electrical energy. As the voltage and the frequency of the generator output vary according to the wind speed, a 6-bridge diode rectifier and a PWM boost chopper is utilized as an ac-dc converter maintaining the constant dc-link voltage with only single switch control. An input current control algorithm for maximum power generation during the variable speed operation is proposed without any usage of speed sensor. Grid connection type PWM inverter converts dc input power to ac output currents into the grid. The active power to the grid is controlled by q-axis current and the reactive power is controlled by d-axis current with appropriate decoupling. The phase angle of utility voltage is detected using software PLL(Phased Locked Loop) in d-q synchronous reference frame. Experimental results from the test of 30kW prototype wind turbine system show that the generator power can be controlled effectively during the variable speed operation without any speed sensor.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2009.10a
• /
• pp.407-410
• /
• 2009

A piezoelectric device which converts mechanical vibration energy into electrical energy is able to harvest energy and the usable energy is mW ${\sim}$ W, hence a converter is necessary to acquire the energy efficiently. Various limited conditions should be considered for the design of AC/DC converter for energy harvesting of a piezoelectric device supplying small amount of energy. In addition to simple structure, compact size, light weight and high efficiency, the energy harvesting AC!DC converter should adopt the technique of self operating, in which only the harvested energy from the piezoelectric device is available. This paper proposes new AC/DC resonant boost converter to harvest efficiently electrical energy from mechanical vibration energy, analyzes the operating characteristics of the converter and proves its feasibility for energy harvester with PSPICE simulation and experiment.