Hv Capacitor Charger for 150KJ Pulsed Power Applications

DESIGN AND TESTING OF THE HIGH VOLTAGE CAPACITOR CHARGER FOR 150KJ PULSED POWER APPLICATION

S. R. Jang1, H. J. Ryoo2, J. S. Kim2, Y. B. Kim2 1 Dept. of Energy Conversion, University of Science & Technology, KERI Campus

2 Applied Electrophysics Research Center, KERI, Sungjudong 28-1, Changwon, South Korea

Abstract This paper describes detail procedures of testing high voltage capacitor charger for 7kV, 150kJ pulsed power application. The designed high voltage capacitor charger was developed based on current source load resonant converter and its average charging power is 35kJ/s. The various kinds of testing were performed including normal operating condition and the malfunctioning condition of the system. The tests for malfunctioning were performed for the case of open during charging, short during charging and misfiring during charging. The charging time of 150kJ is calculated less than 7 seconds and it was experimentally confirmed that it shows very reliable operation even for the fault operating conditions of the system.

I. INTRODUCTION Various industry applications such as lasers accelerators, plasma source implantations and non-thermal pollution gas treatments need high voltage high repetition pulsed power supplies.

For the pulsed power application, there is capacitor charging power supply is required. To increase charging speed and reduce the volume and the weight, a constant current high voltage capacitor charger based on resonant inverter is proposed. When compare with constant voltage source with current limiting resistor, it has advantages of high efficiency and relatively small size with fast charging speed.

Some results have been reported [1] – [3] so far based on a series resonant converter technology.

In this paper, a resonant inverter based constant current capacitor charger which is used for charging 150kJ elctro thermo chemical (hereafter refered as ETC) gun pulsed power application.

For the reliable fault free operation of the system, it should always show the reliable operation toward not only proper working condition but also unpredictable severe faulty condition such as short, open and unintended shot during charging procedure.

Various kinds of detail tests are performed to verify performance of the capacitor charger for this application and very reliable operation of the developed charger was confirmed.

II. HIGH VOLTAGE CAPACITOR CHARGER

The specification of developed capacitor charger to charge 150kJ energy within 10 seconds is summarized as follows. - Output average power: 35kJ/sec - Output voltage: 24kV, 12kV, 8kV selectable

by rectifying circuit connection - Output current: 5.8A for 12kV charging condition - Input voltage: 3 phase 380Vac - Efficiency: > 90% - Protection: over voltage over current, over temperature - Size: 484mm(H)*450mm(D)*476mm(W) - Weight: 90kg

(a) Hardware block diagram

Figure 1. High voltage capacitor charger based on resonant current source inverter

13769781-4244-4065-8/09/$25.00 ©2009 IEEE

Since for the high voltage charger of ETC gun application, the charging time is requested below level of 10 seconds to insure 5 shots per minute at the charging condition of 7kV voltage with 6.1mF capacitor bank, the rectifier circuit is set to 12kV configuration which has 7.4 seconds of charging time and over 50% voltage margin.

III. ETC SYSTEM The ETC system consists of four modules which are triggered step by step with time delay to make 2msec total pulse width and sum of energy storage capacitance of the system is 6.12mF. Table 1 shows design specification of the pulsed power system for ETC gun. Figure 2 and figure 3 show the simulation model and simulation results of current generation of ETC system which has four modules configuration.

Table 1. design specification of the ETC gun

Lind1

Rcab

C2

Rind3

C3

Ls3

0

Lind2

U2

01

2

Rcr4

Lcr1

U1

01

2

Rs3DbreakDcr1

Lcr1

DbreakDsw2

Ls1

Rind2

Lind3

PI

0

Ls2

U4

01

2

Lcr1

Rcr1 Rcr2

0

Rs1

Lind4

DbreakDcr4

C4

DbreakDsw4

Rs4

DbreakDsw1

DbreakDcr3

U3

01

2

Rind4

DbreakDsw3

Rcr3 Ls4

DbreakDcr2

Rind1

Lcr1

0

Lcab

Rs2

C1

Figure 2. Simulation model of the ETC system

Figure 3. Simulation result of total current generation by adding four module currents.

IV. EXPERIEMNTAL RESULTS Various kinds of charging tests were performed to insure reliable operation of the charger such as normal charging operation, short during charging, open during chargind and triggering main switch during charging A. Normal charging operation Normal charging test was performed with 1.236mF capacitor to charge up 7kV. The charging time is measured as 1.215seconds and the charging time of real case with 6.12mF can be calculated as 6.1 seconds. It was shown at figure 4. B. Short circuit test during charging operation

Short circuit test during charging operation is performed in order to verify that charger is not damaged from short condition during charging procedure. It was tested by close switch 2 in figure 5 (a) during charging operation. Figure 5 (b) shows the test results.

Figure 4. Charging test of normal operation

Item Designed specification

Type of energy storage Capacitor bank (6.12mF)

Load Plasma ignited ammunition

Maximum charging energy 150kJ

Maximum charging voltage Over 7kV

Peak power 150~250MW

Peak current 200kA

Pulse width 0~2msec

Energy density Over 300kJ/ m3

Efficiency Over 80%

Charging frequency 4~5 times per minute

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(a) Test procedure

(b) Test waveform

Figure 5. Short circuit test during charging procedure.

Switch 2 closed at charging voltage of 6.2kV and constant current was keep going to supply after short condition without any damage of the charger. C. Open circuit test during charging operation

Open circuit test during charging operation is most difficult operating condition in case of constant current type of capacitor charger.

It was tested by opening switch 1 at figure 6 (a) during charging procedure. But due to higher charging currents, even mechanical switch was disclosed, charging current was kept flowing by way of corona arc path and there is no interruption of charging sequence. After charging procedure was completed, charging current is stopped by switch 1 open condition and there is also no damage at the capacitor charger.

Figure 7 shows charging test waveforms with open condition of charger output terminal. The reference charging voltage was set as 7.5kV considering voltage loss of resistor R1 to ensure exceeding 7kV of real capacitor voltage and the tests were performed 10 times.

The maximum voltage was rise up to 10.5kV because it doesn’t have any big output capacitor and due to sensing & control time delay, but no fault was occurred at capacitor charger. From two kinds of test results, our developed capacitor

charger was showing very reliable operation even it was designed based on current source inverter.

(a) Test procedure

(b) Test waveform

Figure 6. Open circuit test during charging procedure.

Figure 7. Charging test with open condition of charger output terminal. D. SCR triggering during charging operation The last test was performed by SCR triggering during charging procedure. If main triggering SCR is fired during charging procedure, the capacitor can be charged negative polarity voltage up to maximum 30% of the positive charging voltage. Because the output side of capacitor charger is ended with series stacking of rectifying diodes, this negative voltage can damage the internal diodes of charger by excessive freewheeling currents.

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For fault free operation, ballast resistor R1 of 40 ohm is connected at the output side of capacitor charger. After set as reference charging voltage of 8kV, main SCR was triggered at the charging voltage of 7kV during capacitor charging. All the capacitor energy was dumped into load and negative voltage charging was started in capacitor due to inductance. As a result, maximum output current is reached up to 27A but no damage was found at output diodes due to ballast resistor. It was shown at figure 8.

(a) Test procedure

(b) Test waveform

(b) Magnified current watveform(5A/div.) Figure 8. SCR triggering test during charging procedure.

Figure 9. Experimental waveforms of ETC.

Figure 9 is experimental waveforms of ETC system with developed capacitor charger. It was charged up 7kV at each module capacitor shown at figure 2 and SCR of each module are triggered step by step to form 2 msec pulse width. As output load, 50mΩ resistor was used to simulate ETC gun.

V. CONCLUSIONS In this paper, a novel high voltage capacitor charger design and reliability test procedures were introduced. To ensure reliable operation of capacitor charger and total ETC gun system, various kinds of tests were performed.

From all the experimental results, the developed capacitor charger shows very stable and reliable operation and it was confirmed that designed capacitor charger can be good candidate for this application.

The developed system will be tested with real ETC gun make more trouble shooting for reliable fault free operation.

VI. REFERENCES [1] A. C. Lippincott, R. M. Nelms, M. Garbi and E. Strickland, “A series resonant converter with constant on-time control for capacitor charging applications”, Proc. of the 5th Annual IEEE Applied Power Electronics Conf., 1990, pp. 147-154 [2] B. E. Strikland, M. Garbi, F. Cathell, S. Eckhouse and M. Nelms, “2 kJ /sec 25-kV high-frequency capacitor-charging power supply using MOSFET switches”, Proc. of the 1990 19th Power Modulator Symp., 1990, pp. 531-534 [3] A. C. Lippincott and R. M. Nelms, “A capacitor-charging power supply using a series-resonant topology, constant on-time/variable frequency control, and zero-current switching”, IEEE Trans. on Industrial Electronics, Vol. 38, No. 6, 1991, pp.438-447

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