Teruhiko Kohama

Load-current-sharing control for parallel operation of DC-to-DC converters

The control strategy for parallel operation of multiple converters is investigated. Analysis and design considerations of load-current sharing for the parallel system are presented and the superiority of current-balance control is discussed. The prominent features of the load-current sharing and analytical results are confirmed experimentally for a three-paralleled forward-converter system.<<ETX>>

Dynamic analysis of parallel-module converter system with current balance controllers

Dynamic response and stability analyses of a parallel-module power converter system with current balance controllers are described. The state-space averaging method is used to obtain a small-signal model for the dynamic analysis. The root locus method is used to discuss the stability of the parallel system. As a result, instability of the parallel system is observed in the system composed of modules with different circuit parameters. Influence of module parameters on the stability of the parallel system is discussed. Analytical results are confirmed experimentally for a two-paralleled forward power converter system.<<ETX>>

Characteristics of a parallel-module high power-factor AC-to-DC converter system with current-balancing controllers

Characteristics of a parallel-module high power-factor AC-to-DC power converter system using current-balancing controllers are presented. Problems caused by the parallel connection of power factor correction (PFC) power converter modules are discussed. Two types of current-balancing controllers, i.e. conventional and improved, are applied to the parallel-module PFC system to share the load current between the power converter modules. The effectiveness of the current-balancing controllers for the PFC power converter system is confirmed by experiment. The current-balancing controller improved here has fast transient response to load current sharing under dynamic conditions.

Static and dynamic response of a parallel-module high power-factor converter system with current-balancing controllers

Steady-state and dynamic characteristics of a parallel-module high power-factor converter system are discussed. The current imbalance occurs when using the parallel connection of converter modules. To solve this problem a current-balancing controller is utilized and its effectiveness is confirmed by experiment. Two types of current-balancing controllers, i.e., voltage reference control method and current reference control method, are compared. Stability of the current-balancing control loop in the PFC converter system is investigated by using a small-signal model. As a result, the current reference control method is more stable and has a faster transient response when compared with the voltage reference control method.

Novel control strategy for parallel operation of power supply modules

In order to construct a paralleled DC-to-DC power converter system with good performance of load current sharing and highly reliable configuration, a novel control scheme and three types of connection implementations of current balance controllers (CB controllers) are described. To perform the parallel operation of multiple different-capacity modules, the unification concept of CB controllers is presented. Finally, the prominent features of the load current sharing are confirmed experimentally for a three-parallel forward power converter system.<<ETX>>

Automatic interleaving control for paralleled converter system and its ripple estimation with simplified circuit model

Ripple estimation for paralleled converter system with automatic interleaving control is presented. Current ripple in output capacitor of multi-phase converter is estimated through a simplified circuit model which is available for any paralleled converter system under ideal out-of-phase operation. Relationships between the ripple and circuit parameters such as duty ratio, inductor and number of modules are revealed clearly which lead a simple design guideline for ripple-minimized paralleled converter system.

A Layered 3D Touch Screen Using Capacitance Measurement

In this paper, we develop a layered 3D touch screen using capacitance measurement to detect an object both before and after contact for operation of a 3D image on the display. The proposed 3D touch screen employs layered parallel and plane-type capacitance sensors. The 3D touch screen can detect indentations and the precise position of an object and can identify the material in contact with it. In addition, it can detect the object and its position during noncontact (proximity range). Thus, the proposed 3D touch screen detects objects in the 3D range. In this paper, the proposed 3D touch screen is set on a display and detects objects and their positions before and after contact. The proposed 3D touch screen has the potential to be used as functional and useful interface.

Analysis of abnormal phenomena caused by synchronous rectifiers in a paralleled converter system

Problems of synchronous rectification in a parallel-module DC-DC converter system are described. These include excessive power dissipation due to the bidirectional current flow capability of MOSFETs and abnormal oscillation due to the cross coupling of the MOSFETs used as synchronous rectifiers. The abnormal oscillation, which causes excessive voltage stress, is analyzed; the results of which are subsequently confirmed by experiment.

New switching control for synchronous rectifications in low-voltage paralleled converter system without voltage and current fluctuations

Synchronous rectifiers (SRs) used in paralleled converter system cause several problems such as surge voltage, inhalation current and return current. Normally, to avoid the problems, SR operation is stopped in light load. However, at the same time, voltage fluctuation occurs, which causes serious errors in semiconductor devices such as CPU and LSI operating with very low voltage. Moreover, unstable current fluctuation occurs due to the voltage fluctuation in the paralleled system with current-sharing control. This paper proposes new switching control methods for rectifiers to reduce the voltage and current fluctuations. Experimental results are shown to confirm the effectiveness of the proposed methods.

Operation-mode control of active-clamped bi-directional flyback converter as EDLC charger and discharger

An EDLC (electric double layer capacitor) is attractive as a new energy-storage element, and its application as a substitute of the battery has been proposed. However, as the characteristics of EDLC are different from the battery, it is necessary to control charging and discharging procedures under some conditions matched to the demand and the system scale. This paper proposes to use an active-clamped bidirectional flyback converter as a EDLC charger and discharger. A single-chip microcontroller is used to control the operation mode of the flyback converter. An independent photovoltaic power generation system with EDLC charger/discharger is built as an example and the effectiveness of the bidirectional flyback converter as the charger/discharger is examined.