Showing papers by "Seung-Ki Sul published in 2008"

System Integration and Power-Flow Management for a Series Hybrid Electric Vehicle Using Supercapacitors and Batteries

Abstract: In this paper, system integration and power-flow management algorithms for a four-wheel-driven series hybrid electric vehicle (HEV) having multiple power sources composed of a diesel-engine-based generator, lead acid battery bank, and supercapacitor bank are presented The super-capacitor is utilized as a short-term energy storage device to meet the dynamic performance of the vehicle, while the battery is utilized as a mid-term energy storage for the electric vehicle (EV) mode operation due to its higher energy density The generator based on an interior permanent magnet machine (IPMM), run by a diesel engine, provides the average power for the normal operation of the vehicle Thanks to the proposed power-flow management algorithm, each of the energy sources is controlled appropriately and also the dynamic performance of the vehicle has been improved The proposed power-flow management algorithm has been experimentally verified with a full-scale prototype vehicle

A Carrier-Based PWM Method With Optimal Switching Sequence for a Multilevel Four-Leg Voltage-Source Inverter

Abstract: In a three-phase four-wire utility system, three-phase unbalanced loads and many single-phase nonlinear loads result in a neutral line current that is zero-sequence current. To deal with unbalanced and nonlinear loads in a high power system, this paper suggests a multilevel four-leg pulsewidth modulation (PWM) voltage-source inverter (VSI) as a topology for the high power applications where a function is required to control the zero-sequence component as well as dq components. This paper proposes a carrier-based PWM method for a multilevel four-leg PWM VSI along with introducing a novel offset voltage. The proposed offset voltage makes it possible for the switching sequence of all the legs to be optimized for minimizing the harmonic distortion of the output voltage irrespective of the number of inverter levels. The proposed PWM method based on digital signal processors is implemented and tested by using a prototype three-level four-leg VSI. The feasibility of the proposed PWM method is verified by the spectral analysis, simulation, and experimental results.

Design of Speed Control Loop of A Variable Speed Diesel Engine Generator by Electric Governor

Abstract: Electric governors are widely used in diesel engine applications. And a proportional, integral and derivative(PED) controllers runs the electric governor in order to control the engine speed. However, it is difficult to analyze the system stability due to the non-linear characteristics of the diesel engine, and as a result, the PID controller should be tuned by trial-and-error approach. In this paper, a locally linearized diesel engine model is proposed based on the experimentally obtained engine torque map, and the proposed model is verified by simulations and experiments. Through the simulations and experiments it is concluded that the proposed model can be used in the system analysis and so to determine the PID controller gains.

Variable Speed Engine Generator with Super-Capacitor; Isolated Power Generation System and Fuel Efficiency

Abstract: A variable speed engine generator set for an isolated power system is investigated to reduce fuel consumption and emission than conventional fixed speed engine generator. However, the power quality of the variable speed engine generator set would be degraded to the sudden load power surge, and the power required by the load would not be available because of the lowered operating speed condition and the sluggish dynamics of the engine in this variable speed engine generator system. A super-capacitor bank incorporated with the variable speed engine generator set can improve dynamic characteristics under such a sudden load change, and power quality, fuel consumption, and emission of pollutants can be improved remarkably. And the superiority of three phase four leg inverter to an unbalanced load is verified by the computer simulation and experimental results In this paper, the feasibility of the system has been verified based on a 26 kw commercial diesel engine generator system.

Power Control Algorithm for Hybrid Excavator with Super Capacitor

Abstract: This paper shows several structures of the hybrid excavator with the super capacitor and compares with each other at the view point of the fuel economy, the additional cost due to the hybridization, and the expected payback time. According to the comparison result, it can be concluded that a compound type hybrid structure is better solution than others because of its short expected payback time and higher reliability. And also, the power control algorithm of the engine and the super capacitor is proposed. To verify the proposed algorithm, the computer simulation is performed and the results are presented. The simulation results show that by hybridization, the fuel consumption can be reduced by about 24% compared to the conventional hydraulic excavator. The hardware implementation is now in progress for a 22 ton class excavator.

Application of a disturbance observer for a relative position control system

Abstract: In a relative position control system, where feedfoword control can not be applied and the position control performance is restricted only by the bandwidth of the position controller, a disturbance observer are used actively to enhance the control performance. The position reference is considered as a disturbance by the proposed method. Therefore, the relative position control is performed by the disturbance observer as well as by the position controller. As a result, the position control performance is enhanced up to about 33 [%] compared to that of the conventional method with the disturbance observer. The feasibility of the proposed method has been verified by the experimental results using a high precision linear motion control system as well as by the analysis based on Bode plot.

FPGA-based motion controller with a high bandwidth current regulator

Abstract: In this paper, a motion controller based on a Field Programmable Gate Array (FPGA) with a high performance current regulator is presented. This system contains a processor and a high bandwidth current regulator as a peripheral, and all of these are implemented on a single-chip FPGA. The execution time of the current regulator is less than 200 ns at 100 MHz clock frequency. Thanks to this fast execution, the inevitable digital delay, which is 1.5 times the sampling period in a PWM inverter has been reduced to a half of the sampling period. As the result, the control bandwidth of the current regulator has been extended up to about 3 kHz at 10 kHz PWM switching frequency. By exploiting the performance of the current regulator, the speed regulation bandwidth also enhanced up to 700 Hz. The experimental results are presented to demonstrate the validity of the proposed system and the performance of the regulator.

Design of Flux Observer Robust to Parameter Variation of Interior Permanent Magnet Synchronous Motor

Abstract: This paper presents a modified flux observer which is robust to the parameter variation. In this paper, the mathematical modeling of an interior permanent magnet synchronous motor (IPMSM) is shown and the proportional and integral (PI) current regulator with decoupling strategy is analyzed. The flux error terms from the current regulator are used to compensate the parameter variation. The proposed flux observer shows satisfactory performance not only in maximum torque per ampere (MTPA) region, but also in flux weakening region. The experimental results reveal the effectiveness of the proposed observer.

Novel speed and rotor position estimation strategy using a dual observer for low resolution position sensors

Abstract: Recently, high performance AC motor drive technologies including a field oriented control (FOC) are widely used in home appliance products such as a direct- drive drum washing machine. In home appliance, speed or position sensors with high resolution are prohibitive due to the cost problems. Usually, a low resolution sensor is installed to calculate the speed and rotor position. In the FOC, however, accurate rotor angle information is essential for high performance torque control. On top of the low resolution of the sensor, the accuracy of the sensor is poor due to mechanical errors of sensor itself and installation. The inaccurate and delayed position information degrades the performance of current regulation and also increases torque ripples, which is the source of vibration and acoustic noise. In order to overcome the hardware problems, this paper proposes a software technique using a novel dual observer and position sensor offset compensation strategy. The dual observer can estimate the rotor speed and position without any time delay and bumps with the compensation algorithm for the position sensor offset by adjusting the misaligned synchronous reference frame d and q-axis. Experimental results verify the effectiveness of the proposed method.

Analysis of the effect of the parameter variation on the flux weakening controller for improving torque capability

Abstract: This paper analyzes the effect of the parameter variation on the flux weakening controller which utilizes the difference between the outputs of the current regulator and the PWM block. To perform this analysis, the parameter variation is modeled as a disturbance, and a Bode plot and a time domain response is presented. From the result, it can be known that the flux weakening algorithm itself is robust, but the current controller is subject to the parameter variation. A method to overcome this problem is presented, and the results are verified by computer simulation and experimental results.

Implementation of Super High-speed Permanent Magnet Synchronous Machine Drive

Abstract: Recently, super high-speed motor drives have been available due to the development of power electronics technology And they are used in various fields of industry because of their advantages. This paper describes the control algorithm for a permanent magnet synchronous motor(PMSM) drive at the speed of 118,000r/min using DSP and IGBT inverter. Hall sensors are implemented to measure the rotor position and speed, and a speed observer is used to reduce the performance deterioration caused by the low resolution of hall sensors. To enhance the output power capacity in the high-speed operating region, a flux weakening controller which also can work as an anti-wind up controller is used. Computer simulations and experiments are peformed to validate the proposed method.

Guest Editorial on the Special Section on Control Issues on Electric Power System

Abstract: Until now, Electric Power System has played an important role for various industrial applications. In these days, energy crisis issue along with environmental problem becomes the major concern, so that the paradigm of the conventional electric power system has expanded and covers renewable energy sources, such as photovoltaic, wind power, fuel cell, and so on. Many countries intensively put their financial and human resources to develop an advanced electric power system.