Electric power conversion systems – Current conversion – Having plural converters for single conversion
Patent
1987-02-27
1989-02-21
Salce, Patrick R.
Electric power conversion systems
Current conversion
Having plural converters for single conversion
363126, 336180, H02M 710
Patent
active
048071056
DESCRIPTION:
BRIEF SUMMARY
In order to be able to reduce radiation stress on a patient, present-day X-ray technique requires that the tube voltage exhibit, in the stationary condition, a low standing wave ratio while the pulse rise time and pulse decay time of the tube voltage are to be brief as compared with the exposure time. At the same time, there is the requirement of small dimensions and low weight (single-tank design, movable X-ray machines); also desirable are a relatively low uptake of supply current from the mains, storage-battery operation, and low acoustic noise. The aforementioned requirements can be satisfied in the majority of cases by means of correspondingly controlled medium frequency converters. However, the use of medium frequency brings numerous, heretofore unknown problems. The problems inherent in constructing the system of high voltage transformer and rectifier are of extreme importance among the problems to be solved. With an increasing frequency, the charging currents are increased which are determined by the capacitances of the secondary winding system. This increase leads to overload of the drive generator, of the high voltage transformer; local hot spots can be observed in connection with the transformer. New problems are likewise encountered in solving the insulating tasks since the behavior of the insulating materials in the medium frequency force field as well as the creeping distances along the interface have not as yet been entirely explained.
As a consequence of the aforementioned effects, the posed problem cannot be solved satisfactorily either with regard to technology or economy with the use of the conventional transformer and rectifier arrangements; thus, the advantages of medium frequency techniques cannot be exploited as effectively as desired.
At present, X-ray generators are built primarily for operation with mains frequency. One design with higher frequency is represented, for example, by the X-ray generator type EDX 100 (manufacturer: Medicor), but this generator operates at a frequency of 400 Hz; therefore, the advantages enumerated in the foregoing, as inherent in the medium frequency (low standing wave ratio, low weight, small dimensions, etc.), are not as yet realized.
Medium frequency solutions are likewise known. Worth mentioning are the products of the company SIEMENS, such as, for example, the X-ray generators "Polyhos 30 M", "Polydoros 50", "Mobilett". The frequency employed (about 5 kHz), the power-oriented electrical solution, the pulse group control, and the power range selected make it possible to include the transformer and rectifier of the X-ray generator in a structural arrangement that can still be considered as conventional. In general, the secondary high-voltage winding is subdivided into two parts, and a design with two transformers is also frequently used, and the two AC voltages are individually rectified. The two rectified voltages are connected in series, and the positive and negative rectifier output forming the center is grounded.
In classical X-ray technique, this arrangement is, on the one hand, based on reasons of insulating technique; on the other hand, measurement of the tube current is made possible subsequent to this point. The static (standing wave) and dynamic characteristics of the wave form of the tube voltage in this apparatus fall significantly behind the similar characteristics in X-ray generators realizable with the present-day transistor technology. This is so because, using the present power transistors, the X-ray generator operating in a range of between 10 and 20 kHz can be realized in a relatively economical fashion; the tube voltage wave form of this generator exhibits even in the single-tank design 12 pulses; at the same time, the rise times and decay times of the tube voltage pulses are brief. This frequency range requires, however, a novel construction of the high voltage transformer and rectifier. The essential aspect of the solution according to this invention is based on the following realizations:
By designing the secondary winding sys
REFERENCES:
patent: 4099510 (1978-07-01), Perrier et al.
patent: 4227143 (1980-10-01), Elders et al.
patent: 4323781 (1982-04-01), Baumann et al.
patent: 4394722 (1983-07-01), Nero
Southworth et al., "Modular Power Supply", IBM Technical Disclosure Bulletin, Dec. 1978, pp. 2622-2623.
Areldt Gyorgy
Gajasz Zoltan
Varjasi Istvan
Budapesti Muszaki Egyetem
Peckman Kristine
Salce Patrick R.
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