Tài liệu tiếng anh Điện tử công suất mạch MERS Power supply for pulsed magnets with magnetic energy recovery current switch

Luận văn, Điện tử công suất, đề tài tốt nghiệp, đồ án, thực tập tốt nghiệp, đề tài

Power Supply for Pulsed Magnets With Magnetic

Energy Recovery Current Switch Taku Takaku, Takanori Isobe, Jun Narushima, and Ryuichi Shimada

Abstract—In this paper, we propose a power supply with

magnetic energy recovery current switch for pulsed magnets,

such as the synchrotron accelerator bending magnets, magnetizer.

The switch which consists of four MOSFET elements and one

capacitor, generates a fast pulsed current with low voltage, and

it improves the power factor The switch absorbs the magnetic

energy stored in the inductance of the load into the capacitor And

in next time on, it regenerates the energy to the load In addition,

this switch operates in zero-voltage switching and zero-current

switching, and the switching loss is very small In order to turn on

the load current at high speed in the circuit with an inductance,

high voltage of several times higher than the voltage which

main-tains steady current Therefore, by adopting this switch in the

power source for pulsed power supply, high-speed pulsed current

is efficiently generated by recovering the magnetic energy which

has been stored in the inductance to the load in the next time on.

As an application of DC circuit, a semiconductor Marx-generator

which generates the high voltage pulse composed of a multistage

magnetic energy recovery is described.

Index Terms—Magnetic energy, power supply, pulsed current.

I INTRODUCTION

IN A circuit containing the inductance , in order to raise

cur-rent faster than time constant , it is necessary to apply

high voltage of several times higher than resistance voltage

which keeps steady current Therefore, power supply for pulsed

magnets requires high voltage higher than and large current,

and the power factor is bad In addition, efficiency is poor when

the magnetic energy which has been stored in the inductance is

dissipated by resistance

We have already proposed a bi-directional magnetic energy

recovery switch [1], [2] This switch absorbs magnetic energy

which has been stored in the inductance of the circuit and

re-covers it to the load The switch generates itself the high voltage

which compensates inductance voltage By adopting this switch

in the power sources for pulsed power supply, a high-speed

pulsed current is efficiently generated Thereby, high speed and

high repetition pulsed currents are realizable only with a low

voltage power source to a load with inductance The function of

this switch is equal to a serial capacitor for power factor

correc-tion The advantage of this switch is that the power factor

cor-rection of power source is possible regardless of the frequency

even in DC Recently, it is expected that a power MOSFET of

SiC semiconductor becomes available It realize high-speed and

low loss power converters It is expected that it is applied not

Manuscript received October 21, 2003.

The authors are with the Research Laboratory for Nuclear Reactors, Tokyo

Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

(e-mail: ttakaku@nr.titech.ac.jp).

Digital Object Identifier 10.1109/TASC.2004.831107

Fig 1 Circuit diagram of bi-directional magnetic energy recovery current switch The switch is inserted in series between power source and load.

only to a matrix converter but to a high-speed and high-repeti-tion pulse power supply, the drive of a high frequency electric motor, induction heating, and an electric power system field as applicable fields with this new current switch

The basic configuration of this switch is shown in Fig 1 Four MOSFETs are connected in two parallel arms Each arm con-sists of two MOSFETs connected in series Four MOSFETs are connected in reverse direction each other both in series and par-allel connection The middle points of series are connected to a capacitor Although it is the same composition as a single phase full bridge, it is a new point that the usage differs

II CIRCUITCONFIGURATION

A Operation Principle

Fig 2 shows a case when the electric current flows from A to

B In this case, on/off control only of S1 and S3 is done, S2 and S4 are kept turned off When S1 and S3 are turned on, current flows in parallel Next, when S1 and S3 are turned off, the mag-netic energy of the load is absorbed by the capacitor through diodes, and the capacitor voltage is increases gradually When the capacitor is completely charged, the switch is blocked After this time, S1 and S3 are turned on, the capacitor discharges the electrostatic energy to the load, and the capacitor voltage grad-ually decreases When the capacitor voltage becomes zero, cur-rent flows in parallel again The magnetic energy is recovered from the electrostatic energy

Also, in the case that a current flows from B to A, the switch

is controlled by turning on or off S2 and S4 The polarization

of the capacitor remains the same regardless of the direction of current

1051-8223/04$20.00 © 2004 IEEE

Fig 2 Operation of the bi-directional magnetic energy recovery current

switch (a) Current flowing in parallel (b) Load energy is absorbed by the

capacitor (c) Off condition (d) Capacitor energy goes to load.

The current raised after the switch is turned on is equivalent to

the current which was flowing just before turned off In steady

state, the current is determined by the resistance and the voltage

of the circuit

The voltage charged in the capacitor is given by

(1) where is the current which was flowing just before turned

off

B Soft Switching

Ideal semiconductor valve devices, such as MOSFETs

or IGBTs, the switching operation is done in a moment, so

the switching loss is zero There is transition time in actual

semiconductor devices, and the switching loss is generated

However, this magnetic energy recovery switch achieves

zero voltage switching and zero current switching so that the

switching loss is reduced

In order to confirm this, switching loss of a magnetic recovery

switch and hard switching was compared Fig 3 shows turn-off

waveforms of one MOSFET element in this switch Switching

frequency is 1 kHz The rise time of current is delayed compared

with hard switching which does not use a switch, because the

circuit becomes equivalent to a series circuit The switch

is turned on with zero current switching

Also Fig 4 shows turn-off waveforms The magnetic energy

stored in inductance is absorbed into the capacitor, the voltage

applied to a MOSFET element does not rise so rapidly The

switch is turned off with zero voltage switching

Turn-on and turn-off switching losses calculated from Figs 3

and 4 is shown in Table I, from which, it is confirmed that

switching losses of the magnetic energy recovery switch were

drastically reduced

Fig 3 Turn-on waveforms of experimental results.

Fig 4 Turn-off waveforms of experimental results.

TABLE I

T URN -O N AND T URN -O FF S WITCHING L OSSES

III HIGHREPETITIONPULSEDPOWERSUPPLY

A Pulsed Current in High Repetition

This switch can be applied to a power supply which sup-plies high-speed and high-repetition pulsed current to induc-tance load By absorbing and recovering the magnetic energy for the load using resonance, the inductance of the load

is equivalently zero, and the fast current pulse can be realized When S1 and S3 are turned off, the magnetic energy is absorbed

to the capacitor By choosing suitable capacitor from (1), high voltage can be generated to the capacitor The high voltage is applied on the load when S1 and S3 are turned on again, and the current, which is determined by the resistance and the voltage,

is turned on and off faster than the time constant of the circuit inductance and resistance

On the circuit of Fig 1, a simulation and an experiment which switches S1 and S3 simultaneously were carried out Current

Fig 5 Simulation waveforms of current pulses generation Power source

voltage

Fig 6 Experimental waveforms of current pulses generation V = 10 V,

and capacitor voltage waveforms is shown in Fig 5

Mea-sured capacitor voltage is shown in Fig 6 gradually rises

with the switch repeated turn on and off, and it reached 70 V

which was 7 times the source voltage The maximum voltage of

is given by

(2) where is determined by

(3) where is power source voltage Measured value is lower than

the theoretical value given by (2), presumably because the

cur-rent decreases by on-resistance of MOSFET and switching loss

B Current Waveform Control

It is required to control the current in time for operation of a

synchrotron accelerator or a plasma control system By

control-ling S1 and S3 using PWM, the current waveform can be freely

Fig 7 Experimental waveforms of voltage and current controlled by PWM.

Fig 8 Magnetic energy recovery type Marx-generator.

controlled Fig 7 is experiment waveforms with a model circuit When S1 and S3 are turned on simultaneously, load current in-creases by the capacitor discharge When S3 is turned off, the capacitor does not discharge and the current is kept constant be-cause the switch acts as freewheel diode When both S1 and S3 are turned off, the energy which was stored in the inductor is charged in the capacitor and current decreases

IV MAGNETICENERGYRECOVERYTYPEMARX-GENERATOR

A Magnetic Energy Recovery Type Marx-Generator

A magnetic energy recovery type Marx-generator is multi-staged magnetic energy recovery switches as shown in Fig 8 Like the conventional Marx-generator, capacitors are used in parallel in charging and in series in discharging

First, all MOSFETs are turned on with enough time, the flowing current is given by (3) and magnetic energy is stored in the inductor When all switches are turned off, the

TABLE II

P ARAMETERS OF M AGNETIC E NERGY R ECOVERY T YPE M ARX -G ENERATOR

magnetic energy stored in the inductor charges capacitors in

parallel The time required for charging is given by

(4) where is the number of stage The voltage charged in one

capacitor is

(5)

Next, if switches are turned on, capacitors are discharged in

se-ries and the voltage of capacitors become zero The time

required for discharging is

(6) The voltage applied to the load is given by

(7)

and the current is raised to In steady state, is

deter-mined by the resistance and the voltage source as

Exploiting the advantage of Marx circuit that capacitors

charges in parallel and discharges in series, this magnetic

energy recovery type Marx-generator is more advantageous to

obtain high voltage of several times higher than that of one

stage magnetic energy recovery switch And, it can be said that

it is effective for the high repetition pulsed power supply by

adding features of magnetic energy recovery current switch to

a conventional Marx circuit

B Experimental Results

Using previously presented circuit, four-stage magnetic

en-ergy recovering switch was made The circuit parameters are

given in Table II

Fig 9 shows experimental waveforms of current and voltage

of the load The repetition rate is 2 kHz Since the capacitors are

charged with a DC power source, the voltage is 24 V right after

Fig 9 Experimental waveforms of current and voltage of the load When the switch is turned on, the capacitor discharges stored energy and current increases quickly Next the switch is turned off, current decreases and the capacitor is charged.

the switching started And the discharge voltage rises gradually

by repeated switching

In steady state after time passed enough, high-voltage pulse

of 1250 V was applied to the load The load current rapidly increased by the discharge of the capacitor, and it reached 2

A in about 70 When all MOSFETs are turned off, cur-rent rapidly decreased, and the capacitor was charged at 300 V Moreover, the charge time of a capacitor is about 4 times longer than the discharge time From these results, it is confirmed that the proposing circuit is effective for fast pulsed current source

V SUMMARY The application of a magnetic recovery switch to the pulsed power supply was proposed This switch can flow pulsed cur-rent in high repetition, without being concerned with induc-tance of load By absorbing and recovering the magnetic energy stored in inductance of load, the power factor of power source is improved The magnetic energy recovery type Marx-generator which consists of semiconductor elements was proposed It was shown that a high voltage and large current pulse can be easily generated only with a low voltage power source

REFERENCES

[1] R Shimada et al., “Development of magnetic energy recovery current switch,” in 2003 National Convention Record IEE Japan, 2003, no 4,

pp 102–103.

[2] K Shimada et al., “Bi-directional current switch with snubber regen-eration using P-MOSFETs,” in Proc International Power Electronics

Conference, Apr 2000, no 3, pp 1519–1524.