TELKOMNIKA Indonesian Journal of Electrical Engineering Vol.12, No.2, February 2014, pp. 976 ~ 983 DOI: http://dx.doi.org/10.11591/telkomnika.v12i2.4210
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A New Transformer for High Voltage Charging Power Supply Jianming Liu， Meng Wang， Fucai Liu College of Electrical Engineering, Yanshan University, Qinhuangdao, China Corresponding author, e-mail:
[email protected]
Abstract In this paper, the authers present a new high-frequency transformer for high-voltage capacitor charging power supply. They also establish a new topology structure and the charging control strategy for the charging power supply. The effects of leakage inductance and distributed capacitance by using the soft switching in the transformer were then analyzed. Finally, the different leakage inductances in the two transformers were tested. The results of the above study provide a theoratical basis for the application of the new high frequency transformer in pulsed power supply. Keywords: charging power supply, distributed capacitancet, transformer, leakage inductance Copyright © 2014 Institute of Advanced Engineering and Science. All rights reserved.
1. Introduction In recent years, the pulse forming network (PFN) of capacitor energy storage type is widely used in intense particle beam, X ray fields and electromagnetic launch [1]. The highvoltage capacitor charging power is an important part of PFN [2]. With the development of pulse conversion technology [3], the high-frequency charging technology has been rapidly applied [4]. The series resonant constant-current source plays an important role in the high-frequency charging technology. It gives the charging system higher efficiency, more precision and more miniaturization [5]. Now, the majority capacitor charging power supply is charged by the LC series resonance constant-current source. The capacitor power supply developed by the United States National Ignition Facility (NIF) is charged with a soft switching charging mode. Its maximum charge voltage is 24kV, charging rate is 25KW. The main circuit of the 70KW/24KV capacitor charging power supply developed by Germany is single inverter series resonant type [6]. The high frequency transformer of large power is the core component of capacitor constantcurrent charging power supply. How to select the distributed capacitance, the turns ratio of the transformer, magnetic flux density and winding process are important in the design of the highfrequency transformer [7-10].
2. The Simulation and Control Strategy The main circuit structure of the capacitor charging power supply by using the series resonant is shown in Figure 1.
Figure 1. The circuit structure of CCPS
Received July 25, 2013; Revised September 2, 2013; Accepted September 27, 2013
TELKOMNIKA n is the ratio.
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Ts is switching cycle. The resonance period Tr 2 Lr * Cr . f s is
switching frequency. The resonant frequency f r 1/(2 Lr Cr ) , When
ISSN: 2302-4046
Vin is the rectified voltage.
f s f r /2, the circuit is discontinuous. The conduction time of IGBT is within Tr T
Tr / 2 . When n 2 C 0 >> C r , the charging current average value of the secondary side is: I0
8Vin f s C r n
When
(1)
Vin =500V, f s =10KHz and f r =22KHz, the outputs of the current from the
resonance and the rectifier are shown in Figure 2. The capacitor voltage and the envelope of the charging current are shown in Figure 3.
Figure 2. The Waveforms of the Current
Figure 3. Resonant Current and Inverter Voltage
When f r /2< f s < f r , the resonant current and the charging current are continuously switched at the zero current point (ZCP). The two switch tubes in the same bridge arm are forced to be converted when the switch is turn-on. There are switching losses and noise here. When f s > f r , the main circuit is continuous. There are more switching losses and larger noise here. Due to the presence of inductance circuit, the switching device is often damaged by the higher peak voltage. The outputs of the current are shown in Figure 4.
Figure 4. The Current with Width-modulated
3. The Influence of Distributing Parameters 3.1. The Transformer Model The permeability of the transformer core actually is not infinite, the core reluctance
Rm L S is not zero. The equivalent circuit of transformer is shown in Figure 5. A New Transformer for High Voltage Charging Power Supply (Jianming Liu)
978
ISSN: 2302-4046
n2 i2 n1
Figure 5. Equivalent Circuit of Transformer
u1 and u 2 are voltages. n1 and n2 are numbers of turns. i1 , i 2 and im are currents.
Rm n1i1 n2i2 , u1 n1
u1
(2)
d d u2 n2 dt dt
(3)
di n1 d (n1i1 n2 i2 ) n d (n1i1 n2 i2 ) n2 di Lm m Lm m 2 Rm dt Rm dt n1 dt dt
(4)
n12 n . im i1 2 i2 . 1 is leaking magnetic flux of i1 . 2 is leaking magnetic flux Rm n1 of i2 . L1 n1 d1 / di1 , L2 n2 d 2 / di2 . The voltages of windings are: Lm
u 1 n1
d di d d ( 1 ) di d n1 n1 1 1 n1 L1 1 di1 dt dt dt dt dt
(5)
u 2 n2
di d d di d d ( 2 ) L2 2 n2 n2 2 2 n2 dt dt dt di2 dt dt
(6)
By Equation (3) and (4), u1 and u 2 are:
d n di (i1 2 i2 ) L1 1 dt n1 dt
(7)
n2 d n di Lm (i1 2 i2 ) L2 2 n1 dt n1 dt
(8)
u1 Lm u2
The primary leaking inductance is:
1 1 u0 H 2 dv L1i12 2 2
0
is the permeability of vacuum.
(9)
H is the intensity of the permeability in the leaking
magnetic field. dv is the volume of the distributing element in the leaking magnetic field.
TELKOMNIKA Vol. 12, No. 2, February 2014: 976 – 983
TELKOMNIKA
ISSN: 2302-4046
3.2. The Model of Distributed Capacitance The distributed capacitances in the primary winding are C1 , C 2 and
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C12 .The model of
the transformer with the distributed capacitance is shown in Figure 6.
Figure 6. The Model of Transformer Including Leakage Inductance
4. The New High Frequency High Voltage Transformer 4.1. The Selection of Magnetic Core The new transformer is made of microcrystalline, Fe-Ni amorphous, Po-Mo alloy, Mn-Zn ferrite and so on. Microcrystalline alloy has the advantages of lower price, higher saturation magnetization, lower coercivity and good thermal stability. Its parameters are shown in Table 1. Table 1. Core Parameters Saturation magnetic flux density 1.25T Coercivity 1.60A/m
Residual magnetic flux density Permeability
