High voltage power supply generation with super lift Luo converter for X-ray power generation.
Distributed DC-DC conversion technique has developed in recent years since it is required to reach a high power density, high-voltage transfer gain, and high power efficiency. Double-output DC-DC converters convert the positive input source voltage to positive and negative output voltages. They consist of two conversion paths; one is positive conversion path and the other is a negative conversion path. These mirror symmetrical double-output voltages are especially required in industrial applications and computer periphery circuits such as operational amplifiers, computer periphery power supplies, differential servo motor drives and some symmetrical voltage medical equipment. To regulate the output voltage of DC-DC converters irrespective of load variations and supply disturbances, it is necessary to operate the DC-DC converters as closed loop systems. With pulse-width modulation control, the regulation of output voltage of DC-DC converters is achieved by varying the duty cycle of the electronic switch keeping the frequency of operation constant. These converters, in general, have complex non-linear models with parameter variation problems.
With a significant advance of MOS-gate power semiconductor devices, a variety of DC-DC power converters with a high-frequency transformer link have been widely studied and put into practice so far -. One of these, a certain particular application of a high-voltage DC power supply suited to drive an X-ray tube in an X-ray power generator has recently attracted particular interest in medical power electronics. The X-ray power generator must have the special capability to adjust its DC output voltage across the X-ray tube to assure the best quality image for each specified pattern of the body part to be imaged. Higher output voltages are required so as to diagnose more substantial body parts of all types of bones, and lower output voltages may be used for diagnosing soft tissues of the organs -.
Thus, it is necessary to control the DC output voltage across the X-ray tube over widely-specified voltage setting ranges by using high-power DC-DC converter. However, the practically-specified voltage setting ranges of the DC output voltage (tube voltage) across the X-ray tube and the output current (tube current) flowing through the X-ray tube may range from 20kV to 150kV in the output voltage and from 0.5mA to 1250mA, respectively -.
The excellent dynamic and steady-state responses of DC output voltage desired for this high-voltage X-ray power generator in which this resonant power converter using the IGBT modules cannot be sufficiently obtained by the conventional state feedback control procedures based on the classical and modern linear control theories. The desired dynamic responses in rising time and no overshoot performance in a transient state as well as reduced voltage ripple in steady-state of tube voltage responses provide the best-matched quality of the image and the minimum amount of exposure time for special purpose application as X-ray power generator indispensable for medical use. High precision, as well as fast responses of the DC output voltage of converter or tube voltage, has to be performed by the widely-specified voltage setting ranges and variable current setting conditions for X-ray tube drive. In practice, some gain parameters in converter control system used as X-ray power generator must be adequately adjusted by a variety of specific setting load conditions. At present, the system gain parameter adjustment depends on the experience of the skilled operator over a wide load range of output voltage and output current in the hospital as well as needs considerable laborious works -.
In this paper, the discussion is focused on the design of a power supply for an X-ray application for medical purposes. The area of operation of the load and X-ray tube has been represented in Fig. 1. There, it can be observed that both the output voltage and the output power required have a range of 100 kV.
Proposed System Description For X-Ray Power Generator:
Fig. 1 shows the block diagram of proposed DC-DC converter for X-ray power generator. The figure displays the bridge rectifier, used to convert the AC voltage to DC voltage and fed to the DC-DC converter. Positive output super lift. Triple-lift Luo converter is used as a DC-DC converter, in this proposed system. This Luo converter does not consist any large capacitors and switches, the control and operation of this converter are easy because of its structure is very simple in nature.
[FIGURE 1 OMITTED]
Positive output super-lift triple-lift Luo converter:
Positive output super-lift triple-lift circuit is derived from the re-lift circuit by double adding the parts ([L.sub.2]-[D.sub.3]-[D.sub.4]-[D.sub.5]-[C.sub.3]-[C.sub.4]). Its circuit diagram and equivalent circuits during switch on and off are shown in Fig.2 .
[FIGURE 2 OMITTED]
The voltage across capacitor [C.sub.1] is charged to Vin. As described before the voltage [V.sub.1] across capacitor [C.sub.2] is [V.sub.1] =(2 - k/1 - k)[V.sub.in] (1)
Moreover, voltage [v.sub.2] across the capacitor [c.sub.4] is
[V.sub.2] = [(2 - k/1 - k).sup.2] [V.sub.in] (2)
The voltage across capacitor [C.sub.5] is charged to [V.sub.2]. The current flowing through inductor [L.sub.3] increases with voltage [V.sub.2] during switch-on period [k.sub.T] and decreases with voltage--([V.sub.o] - 2[V.sub.2]) during switch- off (1 - k) T. Therefore,
The ripple of the inductor current [i.sub.L2] is
[DELTA][i.sub.L3] = [V.sub.2]/[L.sub.3] kT = [V.sub.o] - 2[V.sub.2]/[L.sub.3] (1 - k)T (3)
[V.sub.o] = 2 - k/1 - k [V.sub.2] = [(2 - k)/1 - k).sup.2] [V.sub.1] = [(2 - k)/(1 - k).sup.3] [V.sub.in] (4)
The Voltage Transfer Gain is
G = [V.sub.o]/[V.sub.in] [(2 - k/1 - k).sup.3] (5)
[DELTA][i.sub.L1] = [V.sub.in]/[L.sub.1] kT [I.sub.L1] = [I.sub.in]/2 - k
[DELTA][i.sub.L2] = [V.sub.1]/[L.sub.2] kT [I.sub.L2] = 2 - k/[(1 - k).sup.2] [I.sub.o]
[DELTA][i.sub.L3] = [V.sub.2]/[L.sub.3] kT [I.sub.L3] = [I.sub.o]/1 - k
Therefore, the variation ratio of current [i.sub.L1] through inductor [L.sub.1] is
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (6)
The variation ratio of current [i.sub.L2] through inductor [L.sub.2] is
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (7)
The variation ratio of current [i.sub.L3] through inductor [L.sub.3] is
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (8)
Moreover, the variation ratio of output voltage [v.sub.o] is
[epsilon] = [DELTA][v.sub.o]/[V.sub.o] = 1 - k/2Rf[C.sub.6] (9)
RESULTS AND DISCUSSION
The Simulink representation of high voltage generation involving positive output super-lift Luo converter in shown in Fig.3. The figure displays the bridge rectifier, used to convert the AC voltage to DC voltage and fed to the DC-DC converter. Positive output super lift. Triple-lift Luo converter is used as a DC-DC converter, in this proposed system. This Luo converter does not consist any large capacitors and switches, the control and operation of this converter are easy because of its structure is very simple in nature. The duty of the Luo converter is varied, simultaneously the output voltage of the converter is also improved. The duty cycle is varied from 0.1 to 0.9. The output voltage of the proposed Luo converter 108 KV, 109 KV, 110 KV, 140 KV, 165 KV voltages is obtained for the corresponding duty variation of 0.1, 0.3, 0.5, 0.7 and 0.9 respectively.
our objective is to produce a high voltage without the use of a transformer for medical use X-ray power generation. Short circuit protection, coolant, installing space, weight and core loss are the main factors that affect the X-ray power generation system due to the presence of transformer. To eliminate the transformer, to compensate those additional burdens of the X-ray power generator a novel circuit has been implemented to produce high voltage generation. Fig. 4 shows the output voltage generated by the Luo converter for various duty variation. Fig.5 displays the input voltage fed to the Luo converter. The output voltage waveform of the Luo converter for the proposed X-ray power generation is shown in Fig 6. The proposed X-ray power generation system need an 110 KV, So, the duty is fixed at 0.5.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
In this paper, the positive output super-lift triple-lift Luo converter is presented for the medical use X-ray power generator from a practical viewpoint. It has been discussed how to take disadvantages of the harmful parasitic energy storage circuit elements of the high-voltage high-frequency transformer. The dynamic circuit modeling of proposed Luo converter was introduced. The proposed DC-DC converter system is effective for the medical- use X-ray power generator from a practical point of view According to the MATLAB/Simulink simulation results, the desired output X-ray tube voltage with a fast rise-time within 0.035ms and without producing overshoot. The settling time of the converter response is 0.12ms. The transformer is eliminated with the use of this proposed converter control.
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(1) M. Ramasubramaniyan and (2) S. Somasundaram
(1) Research Scholar, Department of EIE, Annamalai University, Annamalai Nagar, Tamil Nadu, India.
(2) Assistant Professor, Department of EIE, Annamalai University, Annamalai Nagar, Tamil Nadu, India.
Received 15 May 2016; Accepted 7 July 2016; Available 22 July 2016
Address For Correspondence:
Ramasubramaniyan M, Annamalai University, Department of EIE, Annamalai Nagar, Tamil Nadu, India.
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|Author:||Ramasubramaniyan, M.; Somasundaram, S.|
|Publication:||Advances in Natural and Applied Sciences|
|Article Type:||Technical report|
|Date:||Jul 1, 2016|
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