Hyoung-Suk Kim

Single-Magnetic Cell-to-Cell Charge Equalization Converter With Reduced Number of Transformer Windings

In this paper, a new cell-to-cell charge equalization converter using a multiwinding transformer is proposed. The proposed scheme achieves the direct cell-to-cell charge transportation by buck-boost and flyback operation. In this operation, the adjacent two cells share either a current path or a tap of multiwinding transformer. Therefore, the number of windings ia cut in half in comparison to the number of batteries, resulting in a small circuit size. To verify the operation of the proposed charge equalization converter, an experiment with a lithium-ion battery stack is performed.

Novel soft switching PWM converter using a new parallel resonant DC-link

A novel soft switching pulsewidth modulated (PWM) converter for high-frequency AC/DC and/or DC/AC power conversion is presented by using a parallel resonant DC-link (PRDCL) and by adopting single-phase soft switching (SPSS) technique. The PRDCL provides variable link pulse position as well as variable link pulse width, which is a quite different feature from the other resonant DC-links, and thus the PWM capability can be increased. The SPSS technique is adopted for further enhancement of PWM capability. Moderate combination of two soft switching operations enables the conventional space vector PWM technique to be used. Due to distinctive advantages, including true PWM capability, minimum device voltage stresses, and reasonable additional device count, the proposed converter can be operated in a wide power range (20-200 kW). Operational principles, analyses, and the realization of a space vector PWM of the proposed converter are presented. Simulation results are shown to verify the operational principle.<<ETX>>

Integrated boost-sepic converter for high step-up applications

A general boost converter has limited voltage step-up ratio because of its parasitic resistances. Thus, it is not applicable for high step-up applications. As a solution, combining a boost converter with a series output module can be considered to supplement the insufficient step-up ratio. By applying this concept, a new integrated boost-sepic (IBS) converter, which provides additional step-up ratio with the help of an isolated sepic converter, is proposed in this paper. Since the boost converter and the sepic converter share a boost inductor and a switch, its structure is simple. Moreover, the proposed IBS converter needs no current- snubber for the diodes, since the transformer leakage inductor alleviates the reverse recovery. The operational principle and characteristics of proposed converter are presented, and verified experimentally with a 200-W, 42-Vdc input, 400-Vdc output converter prototype.

High Step-Up DC-DC Converters Using Zero-Voltage Switching Boost Integration Technique and Light-Load Frequency Modulation Control

This paper describes nonisolated high step-up DC-DC converters using zero voltage switching (ZVS) boost integration technique (BIT) and their light-load frequency modulation (LLFM) control. The proposed ZVS BIT integrates a bidirectional boost converter with a series output module as a parallel-input and series-output (PISO) configuration. It provides many advantages such as high device utilization, high step-up capability, power and thermal stress distribution, switch voltage stress clamping, and soft switching capability. As an example of ZVS BIT, a flyback converter with a voltage-doubler rectifier (VDR) as a series output module is presented and analyzed in detail. In addition, to overcome the efficiency degradation at a light load due to the load-dependent soft switching capability of the proposed ZVS BIT, a control method using a frequency modulation (FM) proportional to the load current is proposed. By means of ZVS BIT and LLFM control, the overall conversion efficiency is significantly improved. The experimental results are presented to clarify the proposed schemes.

On/Off Control of Boost PFC Converters to Improve Light-Load Efficiency in Paralleled Power Supply Units for Servers

This paper proposes an on/off control of boost power factor correction (PFC) converters to improve the light-load efficiency in paralleled power supply units (PSUs) for servers. The proposed scheme operates the PFC stages of two paralleled PSUs alternately during one cycle of a 60-Hz ac input only at light loads. This improves the light-load efficiency without deteriorating the heavy-load efficiency by reducing load-independent losses such as capacitive turn-on and core losses. In addition, the proposed scheme alleviates the harmonic distortion by reducing the discontinuous conduction mode region. Experimental results from 1.6-kW PFC boost converters are shown to verify the proposed work.

Zero-voltage switching flyback-boost converter with voltage-doubler rectifier for high step-up applications

A zero-voltage switching (ZVS) flyback-boost (FB) converter with a voltage-doubler rectifier (VDR) has been proposed. By combining the common part between a flyback converter and a boost converter as a parallel-input/series-output (PISO) configuration, this proposed circuit can increase a step-up ratio and clamp the surge voltage of switches. The secondary VDR provides a further extended step-up ratio as well as its voltage stress to be clamped. An auxiliary switch instead of a boost diode enables all switches to be turned on under ZVS conditions. The zero-current turn-off of the secondary VDR alleviates its reverse-recovery losses. The operation principles, the theoretical analysis, and the design consideration are investigated. The experimental results from a 250W and 42V-to-400V prototype are shown to verify the proposed scheme.

Simple switch open fault detection method of voltage source inverter

Recently, permanent magnet synchronous motors are applied to various applications such as electric vehicle, aerospace, medical service, and military applications due to several outstanding characteristics. Because of the importance of high reliable operation in these areas, many researches which are related to the fault detection and diagnosis of inverter systems are conducted. In this paper, a new simple fault detection method of voltage source inverter for permanent magnet synchronous motor is proposed. The feasibility of the proposed method is proved by simulation and experiment. By the simulation and experiments, rapid detection characteristic of the proposed method has been proved without any additional voltage sensor.

Cell-to-cell charge equalization converter using multi-winding transformer with reduced number of windings

In this paper, a charge equalization converter using a multi-winding transformer is proposed. The proposed scheme achieves the cell-to-cell charge transportation by buck-boost and flyback operation. In this operation, adjacent two cells share a current path or secondary tap of multi-winding transformer. Therefore, the number of windings cuts in half in comparison to conventional multi-winding charge equalization converter, resulting small circuit size. To verify the operation of the proposed charge equalization converter, experiment for lithium-ion battery stack is performed.

Start-Up Control to Prevent Overcurrent During Hot Swap in Paralleled DC–DC Converters

Paralleled power systems require a hot swap which indicates the replacement of a converter module without shutting down the whole system for easy maintenance, repair, and upgrade. A practical issue for the hot swap is an overcurrent toward a newly activating module due to inevitable nonuniformity among the paralleled modules, which causes the excessive current and thermal stresses and even leads to a device failure. In this paper, by analyzing the start-up operation of a converter module during the hot swap, the reason for the overcurrent is demonstrated. Then, based on this analysis, a method increasing the voltage reference exponentially is presented, which can contribute to reduce the overcurrent. However, the overcurrent still remains and causes a problem as the number of paralleled modules or difference in output voltage set points increases. Therefore, a control scheme adjusting the output voltage reference during the start-up is proposed to eliminate the overcurrent effectively. Experimental results from 1-kW paralleled phase-shifted full-bridge converters are shown to verify the proposed works.

A new two-switch flyback battery equalizer with low voltage stress on the switches

In this paper, a new battery equalizer applying two-switch flyback topologies is proposed. Since the proposed circuit is based on two-switch flyback structure, voltage stress on the switches can be clamped at the battery stack voltage level. Furthermore, the number of active devices is minimized by using a common switch and a common clamping diode. The operational principle, theoretical analysis, design consideration, and implementation method are presented. In addition, to confirm the performance of the proposed battery equalizer, experimental results from four 3.9 V and 2600 mAh lithium-ion batteries are presented.