Katsuaki Murata

Balanced charging of series connected battery cells

Novel method of charging and discharging the battery cells serially connected is presented. The principle is the control of charge stored in respective cells by using electronic switches so that the voltages of respective cells may be balanced automatically. The circuit to realize this principle is essentially the same as that of the ringing choke converter for the DC-to-DC power converter which is the simplest of minimum number of components. The cell voltage being low from 1.2 V to 3.6 V, the trench type MOSFET for the synchronous rectifier is used as a switching element.

Surge analysis of induction heating power supply with PLL

Surges are undesirable with respect to both the reliability and the efficiency of power devices. In this paper, the surge mechanism of an induction heating power supply is studied. First, a modified phase locked loop (PLL) controller is proposed such that the changing resonant frequency of the heated load can be tracked correctly and the zero voltage switching (ZVS) can be reliably maintained simultaneously. Then, a very simple and practical surge model is proposed. Surge analyses for both ZVS and non-ZVS modes are made in sequence. It is found that the extra energy built up in the line inductance during the reverse recovery process of the diodes plays a very important role in generating huge voltages. Finally, some simulation and measured results are provided to verify the validity of the proposed surge model.

Controlled resonant converters with switching frequency fixed

This paper presents a method to regulate the output voltage of resonant DC-DC converter without changing switching frequency. It is based on the concept of changing resonant frequency by using either a variable inductance circuit or a variable capacitance, which is controlled auxiliary switches. The switching loss of the auxiliary switch is minimized due to no intersection between the voltage and the current. A 1-MHz, 50W breadboard regulator of Class-E converter has been built which shows high efficiency of 93.7%.

Self turn-on loss of MOSFET as synchronous rectifier in DC/DC buck converter - in case of a low driving impedance -

In this paper we present a kind of losses on MOSFET as a synchronous rectifier which is very difficult to remove in compare with the other losses. For high performance, downsizing and lightweight of digital equipment as a personal computer, digital ICs are developed with high speed and densely integrated. The supply voltage for these ICs becomes lower and the supply current becomes higher. A buck converter is widely used as a DC/DC converter for this purpose. In the buck converter, a synchronous rectifier of MOSFET with ultra low on-resistance is widely used as a low-side switch for higher conversion efficiency instead of a Schottky barrier diode as a free wheel diode. When the high-side switch is turned on as the low-side switch is off, the drain-source voltage of the low-side switch rises rapidly and the gate-source voltage rises simultaneously through the drain-gate capacity. As a result, the gate-source voltage becomes up to the gate threshold voltage and the low-side switch becomes active state and the drain current flows. We named this phenomenon dasiaself turn-onpsila where the loss occurs in the low-side switch.(Murata et al., 2003) in this paper a precise analysis of the self turn-on phenomenon is presented and the experiments for verification are also presented.

An active power filter with saturable cores

We present a method to realize pulse width modulated wave for power applications by using cores as a control unit. This core unit is made of η cores with four windings. Each core is fed a different amount of magneto motive force to decide the order of flux varying operation. Power transistors are switched by PWM voltage made of the core unit mentioned above. This switching action eliminates the harmonics lower than n-th from supplied squarewave source. This output is followed by a simple lowpass filter and becomes sinusoidal wave. In temperature stability, reliability and power consumption, this method is superior to the conventional PWM method by comparing sinusoidal wave to triangular wave or using a digital circuit, because the number of constructing elements is less than that in conventional method.

Sinusoidal Voltage Converter Controlled by Amorphous Cores

A simple and reliable PWM inverter to generate sinusoidal wave of constant voltage and variable frequency is presented. In the control circuit of this inverter, amorphous cores are used to produce PWM wave. These cores have three kinds of windings, that is, the common windings, the bias winding and the output windings. The bias winding gives each core a different amount of ac mmf to decide the order of a flux varying. The values of the switching angles are decided by the number of layers of amorphous tape and the supply voltage to the common windings wound on all cores. Output voltage is regulated by the feedback. The frequency change is compensated by an integrator with a signal made of induced voltages of the core unit.

An investigation of method to reduce harmonic components in large-scale self-commutated inverter

The authors have devised a novel PWM control scheme capable of controlling a designated order harmonic while other low harmonic components are eliminated, based on the conventional low harmonic component elimination PWM control scheme. And it experimentally proved that the harmonic voltage in power systems could be suppressed, by means of controlling a self-commutated rectifier as a shunt active filter based on voltage detection.

A cascade connection of switching converters for new energy control

For the renewable energy control, a cascade connection of the boost and the buck converter is proposed. Phase difference between converters in the first and the second stage plays a key role for determining conversion efficiency. The output resistance is discussed for evaluating efficiency.