Sachio Kubota

Novel power supply for induction heating with power factor control using phase shift

An induction heating is used in various fields because it has many merits. Especially ferromagnetic metals are efficiently heated. However, when these metals are heated more than Curie temperature, they are transmuted into paramagnetic ones. Simultaneously, an induction heating load is changed suddenly. If an operation of power supply is not controlled securely, power supply is broken down. Though highly precise resonant frequency tracking control is applied generally to prevent a power supply failure, the heating piece is also changed by changing the penetration depth. Therefore, the new heating control method is proposed for the purpose of heating a ferromagnetic metal efficiently. In this method, a power factor is controlled at constant frequency by phase shift control instead of PFM (Pulse Frequency Modulation) to maintain a soft switching. In this paper, it is proved that the proposed control method is useful to heat a ferromagnetic metal.

Quasi variable capacitor applied to soft switching inverter for induction heating

In this paper, a quasi-variable capacitor applied to soft switching inverter for induction heating and its novel operation control scheme are presented. The proposed quasi variable capacitor has many advantages, such as wide output power regulation range and outputting at double or triple frequency. Moreover, a stable operation is achieved because all switches are always maintaining a soft switching even if different metal, such as stainless steel, aluminum, ferromagnetic metal and paramagnetic metal are heated respectively. Through the experimental results, the usefulness of the proposed quasi variable capacitor has been proved.

Soft switching PWM inverter for induction heating applied to heating of ferromagnetic metal

In this paper, a soft switching PWM(pulse width modulation) inverter for heating up to high temperature ferromagnetic metals is proposed as a power supply to apply to the diesel emission control system. And an optimal circuit design and an operating method about this inverter to solve several problems caused by heating up to high temperature it are described in detail. The validity of the proposed method is verified through both the simulated results and the experimental results.

The design method of the inverter for heating both a ferromagnetic metal and a paramagnetic metal

In case that a ferromagnetic metal is heated up more than Curie temperature, the metallic characteristics change from ferromagnetism to paramagnetism. In this paper, the design method of inverter which always performs a stable operation even if a ferromagnetic metal is transformed to paramagnetic metal is described. And the circuit characteristics of the proposed inverter are analyzed in detail and verified by simulation and experiment.

Characteristics of quasi variable capacitors for induction heating

In this study, the diesel emission control system using induction heating is proposed as a method of reducing toxic substances included in exhaust gas. When the trapping filter of that system is heated by induction heating, ferromagnetic metals are suitable for that filter. However, they are transmuted to paramagnetic metals at high temperature more than Curie temperature. Therefore, automatic resonance tracking control is required to prevent breakdown of power supply because the equivalent circuit parameters of induction heating are rapidly changed at this temperature. Generally, although resonant frequency is tracked by PFM (Pulse Frequency Modulation), it is desirable to operate at constant frequency because the heating piece is changed in accordance with an operating frequency. Accordingly, we have proposed the quasi variable capacitor to maintain a resonance. This paper presents a comparison of the behavior of the proposed quasi variable capacitors. An analytical study of the proposed quasi variable capacitor is performed, and the main results are shown. The results derived from this analysis and the feasibility are verified through experimental prototype.

Soft switching inverter for induction heating with power factor control function using quasi variable capacitor

Recently, reduction of toxic substances included in exhaust gas, and conversion to a low carbon society are demanded for the purpose of environment protection. To prevent global warming, it is important to progress energy-saving technologies and environment protection technologies. IH (Induction heating) technology is useful for energy-saving because it is an efficient heat source. In this study, induction heating is utilized for purifying the toxic substances included in exhaust gas from marine diesel engine. Ferromagnetic metals are suitable for metallic filter within this system. However, because ferromagnetic metals have Curie temperature, equivalent circuit parameters of induction heating are rapidly changed at Curie temperature. For this reason, automatic resonance tracking control is applied to prevent breakdown of power supply. In general, although resonant frequency is tracked by PFM (Pulse Frequency Modulation), the heating piece is changed because a penetration depth is changed in accordance with controlling frequency. Consequently, it is desirable that the power supply for IH is operated at constant frequency. In this paper, to heat the metals at constant frequency, quasi variable capacitor is proposed and is applied to power supply for IH as resonance tracking control. The proposed quasi variable capacitor performs the same function as a variable capacitor. As a result, the proposed inverter can control a power factor. This is an advantage that resonant frequency is tracked and that metallic filter is also heated efficiently. Moreover an output power is controlled, without changing frequency.

PWM Parallel Resonant Inverter Designed for Marine Diesel Emission Control system

From a viewpoint of environmental protection, it is important to reduce PM (particulate matters) causing an air pollution. In order to reduce PM, it is necessary to heat at high temperature the exhaust gas from marine diesel engine. We have proposed the after-treatment system utilizing an induction heating for reducing PM in exhaust gas as a diesel emission control system. In the case of an induction heating, although a metallic filter is efficiently heated by using a ferromagnetic material, metallic characteristics change from ferromagnetism to paramagnetism and the circuit parameters are also changed rapidly, if a temperature of metallic filter reaches Curie temperature. Therefore PWM parallel resonant inverter is proposed as power supply for heating corresponding to changing circuit parameters. In this paper, easy control method of the proposed inverter and heating method of filter are explained, and the circuit characteristics are analyzed by numerical analysis

ZCS high frequency inverter for electromagnetic propulsion system

In this paper, the electromagnetic propulsion system using high frequency AC is proposed to solve several problems which are caused by electrolysis of sea water. And ZCS (Zero Current Switching) high frequency inverter is proposed as a high frequency power supply applied for this system. Moreover the operating method of the proposed power supply is presented as a method of controlling speed of an electromagnetic propulsion system. Especially, it is proved that electrolysis of sea water is suppressed and that poisonous gas is not generated, through the experiment.

PWM high frequency inverter with soft switching for an emission control system in diesel engine

This paper presents PWM high frequency inverter with soft switching, which is applied for a diesel emission control system. It is indicated that output power in the proposed inverter can be controlled according to change of the generating power of an engine, and it can be used to equip a diesel engine with the diesel emission control system. In this paper, it is shown that the proposed inverter realizes a PWM (pulse width modulation) control with soft switching at all switches.