Jun-Hyuk Choi

Robust DC-link voltage control scheme for photovoltaic power generation system PCS

A power conversion system (PCS) for photovoltaic power generation system is composed of the DC/DC converter and the DC/AC inverter. To maximize power generation, DC/DC converter operated with MPPT (Maximum Power Point Tracking) algorithm and the PCS has been developed by the method of transformer tab change. DC/AC inverter controls DC-link voltage and grid current. But, single phase grid has 120Hz (Grid voltage frequency is 60Hz.) power ripple which arise DC-link voltage ripple. This paper presents a robust DC-link voltage control scheme. The control scheme utilizes a widow averaged DC-link voltage as a feedback signal. Experiment performed with 3kW PCS and the results support the validity of the control scheme.

Indirect Adaptive Regulator Design Based on TSK Fuzzy Models

In this paper, we have proposed a new adaptive fuzzy control algorithm based on Takagi-Sugeno fuzzy model. The regulation problem for the uncertain SISO nonlinear system is solved by the proposed algorithm. Using the advanced stability theory, the stability of the state, the control gain and the parameter approximation error is proved. Unlike the existing feedback linearization based methods, the proposed algorithm can guarantee the global stability in the presence of the singularity in the inverse dynamics of the plant. The performance of the proposed algorithm is demonstrated through the problem of balancing and swing-up of an inverted pendulum on a cart.

Development and control of BLDC Motor using fuzzy models

This paper presents the design and control of a small brushless DC (BLDC) motor. In order to control the developed BLDC motor, an adaptive fuzzy control (AFC) scheme via parallel distributed compensation (PDC) is developed for the multi- input/multi-output plant model represented by the Takagi-Sugeno (TS) model. The alternative AFC scheme is proposed to provide asymptotic tracking of a reference signal for systems with uncertain or slowly time-varying parameters. The developed control law and adaptive law guarantee the boundedness of all signals in the closed-loop system. In addition, the plant state tracks the state of the reference model asymptotically with time for any bounded reference input signal. The suggested design technique is applied to velocity control of a developed small BLDC motor.

A study on design and manufacturing of a micro brushless DC motor

The reduction of size and weight is very often one of the most important requirements in product design. Many applications in robotics, automation, medicine systems etc require powerful micro motor and actuator. In this paper, a design and fabrication result of an ultra-small brushless DC motor is presented. The outer diameter of the designed motor is 2 mm. This motor is designed to 3-phase slotless winding type, and operated with both a synchronous type driver and a sensorless type one. The experimental results for back EMF value and speed characteristics are presented and discussed.

A design of PWM converter inverter system for building air conditioner compressor

Many countries are making strong harmonic current regulations for high power consuming equipments to reduce power loss and voltage distortion in power distribution. To comply with the regulation, the PWM converter is receiving more interest due to the low harmonic current generation compared with diode rectifier and unity power factor. This paper introduces a design of PWM converter inverter system for building air-conditioner compressor. For cost reduction, control algorithm is developed on one integer microprocessor and eliminated input voltage sensor, position sensor. And for overall system efficiency, converter operation is limited for the high power or high voltage demand. Experimental results show the validity of the PWM converter inverter system.

Optimal design of piezoelectric transformer for high efficiency and high power density

The characteristics of piezoelectric transformer, such as resonance frequency, matching impedance, electromechanical coupling coefficient and efficiency, were analyzed using the finite element analysis along with the equivalent circuit. The validity of the proposed numerical methods was conformed experimentally. Through all of the verified results, the optimal design for a high efficiency and high power density was determined using the multi-modal optimization algorithm based on an evolution strategy.

A study on BLDC motor for blower system considering vibration

A brushless DC (BLDC) motor for air management system of fuel cell modules is presented. Using magnetic equivalent circuit model a basic design of the motor is determined, and specific configurations are inspected thanks to finite element analysis. In order to reduce an unbalanced magnetic force in an axial direction, induced forces between a stator core and a permanent magnet are calculated with respect to the relative positions of them. Also vibration mode and eccentricity of a rotor are considered at the rated and maximum rotational speed. Finally, air blower system combined with the motor and an impeller is manufactured and output properties, such as an air pressure and an amount of flowing air, are measured. Through the experimental results, a validity of the simulated one is confirmed.

A Initial Current Control Method for PWM Converter Against Low DC-Link Voltage

When a PWM converter starts operation with non - zero load, the initial DC-link voltage could not be high enough to generate converter output voltage vector for current regulation. This lack of converter voltage vector could cause unregulated over-current at converter operation start. In this paper, a new current control scheme is proposed for a PWM converter against low DC-link voltage. To avoid unregulated over-current, the proposed control scheme regulates only one phase current and generates the current command considering the uncontrolled current magnitude information calculated in advance. Simulation is performed with resistive load, and the results support the validity of the proposed scheme.

Design of brushless DC motor for air management system of fuel cell modules

This study presents a brushless DC (BLDC) motor for air management system of fuel cell modules. Magnetic equivalent circuit model and finite element analysis are used to design the motor, and an improved structure is considered to reduce a mechanical loss induced from bearing units. Finally, air blower system combined with the motor and an impeller is manufactured and output properties, such as an air pressure and an amount of flowing air, are measured. Through the experimental results, a validity of the simulated one is confirmed.

Rough Set Based Fuzzy Modeling by Occupancy Degree and Optimal Partition of Projection

The rough set theory suggested by Pawlak has a property that it can represent the degree of consistency between condition and decision attributes of data pairs which don’t have linguistic information. In this paper, by using this ability of rough set theory, we define a measure called occupancy degree which can represent a consistency degree of premise and consequent variables in fuzzy rules describing experimental data pairs. We also propose a method by which we partition the projected data on input space and find an optimal fuzzy rule table and membership functions of input and output variables from data without preliminary linguistic information.