Bo H. Cho

The State and Parameter Estimation of an Li-Ion Battery Using a New OCV-SOC Concept

The open circuit voltage (OCV) is widely used to estimate the state of charge (SOC) in many SOC estimation algorithms. But the relationship between the OCV and SOC can not be exactly same for all batteries. Because the conventional OCV-SOC differs between batteries, there is a problem in that the OCV-SOC data should be measured to accurately estimate the SOC in different batteries. Therefore, the conventional OCV- SOC should be modified. In this paper, a new OCV-SOC that is independent of the battery conditions is proposed. Thus, problems resulting from the defects of the EKF can be avoided by preventing the OCV-SOC data from varying. In this paper, the SOC and battery capacity are estimated using the dual EKF with the proposed OCV-SOC.

Current Control Design for a Grid Connected Photovoltaic/Fuel Cell DC-AC Inverter

In this paper, a current controller design method for a DC-AC inverter in a grid-connected photovoltaic or fuel cell power conditioning system (PCS) is proposed. A state feedback current controller using a sine reference function tracking algorithm and I-P(Integral-Proportional) outer DC-link voltage controller using a 120Hz notch filter are proposed to control the output current to be in-phase with the grid voltage and to regulate the input DC-link voltage. Since the analysis and design are performed in the time domain using the state equations, the current loop controller can be systematically designed for the required system specification using the pole placement technique. Also, the 120Hz notch filter for DC-link voltage regulation can enhance the dynamic performance by increasing the voltage loop bandwidth. The design guideline of each controller is provided using the stability analysis. For a design example, the prototype two-stage PCS hardware with a TMS320F2812 DSP and a real 200W solar array has been experimented to validate the proposed digital control scheme.

Empirical small-signal modeling of switching converters using Pspice

The objective of this paper is to present a new technique for generating small-signal transfer functions of switching converters. The technique requires generation of the input-output data from a switching converter using any simulation software packages, such as Pspice, and applies a simple algorithm on the recorded data to identify an autoregressive moving average (ARMA) model for the switching converter. A small-signal transfer function can be obtained from the ARMA model thereby.<<ETX>>

Zero-current-switching (ZCS) power factor pre-regulator (PFP) with reduced conduction losses

This paper proposes a new boost power factor pre-regulator (PFP) featuring zero-current-switching (ZCS). By employing an improved ZCS pulse-width-modulation (PWM) switch cell, ZCS of all the active switches is achieved without additional current stress of the main switch. The additional conduction losses are minimized, since the circulating current for the soft switching flows only through the auxiliary circuit and a minimum number of switching devices are involved in the circulating current path. The diodes commutate softly and reverse recovery problems are alleviated. Design guidelines with a design example are described and verified by experimental results from the 1.2 kW prototype boost PFP.

Modeling and control of automotive HID lamp ballast

This paper presents design and analysis of an HID lamp ballast for fast turn on characteristics and stable operation. It produces a high open circuit voltage for the ignition and it is controlled to effectively supply the power required to shorten the warm-up period after the breakdown. The lamp modeling by empirical data is presented. It is very effective in the design of the control loop in the steady-state operating region. A stable operation of the lamp power regulation in the steady state is achieved, which is crucial for the long life time and constant light output. Stability analysis of the system is performed and the results are verified through various simulation results and the hardware experiments.

Modeling, analysis and design of 10 kW parallel module zero-voltage zero-current switched full bridge PWM converter

In this paper, the modeling and the design of the 10 kW parallel module converter are presented. Due to the high input voltage and power level, IGBTs are selected for the switching devices. The ZVZCS techniques enable the ZVZCS FB-PWM topology to operate at the switching frequency of 40 kHz, while maintaining an efficiency of over 94% at full load. The parallel scheme featuring power sharing and interleaving offers reduction of the overall system size and improvement of dynamics and EMI characteristics. A complete small-signal model for the ZVZCS FB-PWM converter employing the charge control is developed. The design equations and model predictions are verified by experimental results.

Review of current mode control schemes and introduction of a new digital current mode control method for the parallel module DC-DC converters

Ever increasing demands for the development of compact, lightweight power supplies with more power density, higher efficiency and fast dynamics, often require power conversion through parallel connected converter. In order to realize the parallel module DC-DC converters, a current mode control scheme is essential for current sharing control among the modules. The general analog current mode control schemes, such as peak current mode control (PCM), charge current mode control (CC) and average current mode control (ACM), are reviewed and compared of their characteristics, in this paper. With recvent advances in digital systems, digital control has becmoe increeasingly visible even for high-frequency, low-to-medium power switching converters. However, digital current mode control for the parallel module converter is not easy because the switch or inductor current is a fast-changing waveform and the switching frequency is high. This paper introduces one of possible solutions for a digital current mode control employing nonlinear resistive current mode control as well.

Analysis and design considerations of zero-voltage and zero-current-switching (ZVZCS) full-bridge PWM converters

In this paper, a detailed analysis of the zero-voltage and zero-current-switching (ZVZCS) full-bridge PWM converters is performed. The differences of the zero-voltage-switching (ZVS) operation between the conventional ZVS full-bridge PWM converters and the ZVZCS full-bridge PWM converters are analyzed in depth. Circuit parameters that affect the soft-switching conditions are examined and the critical parameters are identified. Based on the analysis, practical design considerations are presented. The analysis and design considerations are verified by experimental results from a 630 V/4 kW converter operating at 80 kHz.

A frequency controlled bidirectional synchronous rectifier converter for HEV using super-capacitor

In this paper, a control method of a bidirectional zero-voltage-switching (ZVS) DC-DC converter for HEV power system is presented. By controlling the minimum and maximum values of the inductor current, the ZVS condition is achieved. Also employing the variable frequency control with respect to the variation of the DC-link current and the super-capacitor voltage, the circulating energy loss at the light load condition is minimized. A 1.25 kW experimental hardware prototype module is built to verity the efficiency improvement, especially at the light load condition. It shows about 34% efficiency improvement compared to the fixed frequency control at the light load condition.

Modeling of CCFL using lamp delay and stability analysis of backlight inverter for large size LCD TV

Cold cathode fluorescent lamps (CCFL) for LCD TVs have a special v-i characteristic, which can make the backlight inverter system unstable. In this paper, modeling of both the cold cathode fluorescent lamp and the backlight inverter is performed in terms of incremental impedance in the frequency domain. The stability analysis of the backlight inverter and the CCFL is presented using the derived models. It is concluded that the time delay, after which the lamp voltage responds to the lamp current change, contributes to the incremental impedance of the CCFL at the high frequency region, which may cause instability of the backlight inverter. The time delay is considered as a lamp characteristic. The effect of the inverter design parameters on the stability is also investigated. The lamp model and the stability analysis results are verified from experiments with a backlight inverter for 32-inch LCD TVs.