**7. References**

106 Power Quality Harmonics Analysis and Real Measurements Data

**9**

**kHz**

**10**

**2**

**kHz**

**Hz**


Phase shift [Degrees]

Fig. 20. Normalized VT voltage ratio vs. phase shift angle for frequency band up to 9 kHz

Modelling of VT voltage transfer characteristic in wide frequency range is rather challenging. Main problems with accurate modelling using circuit models are related to windings' parasitic capacitances and especially identification of its unequal distribution along windings. To model the influence of parasitic capacitive couplings existing in a typical VT several simplifications should be considered. The method of VT parasitic capacitances analysis based on the lumped representation is often used and particularly rational, nevertheless limits the frequency range within which acceptable accuracy can be obtained. Its parameters can be determined based only on wideband measurement of leakage and magnetizing impedances, unfortunately it can be successfully used only in the limited frequency range. For typical VT used in MV grids the flatten fragment of transfer characteristic can be obtained usually only up to few kHz. Above this frequency VT usually exhibit a number of resonances which change evidently its transfer characteristic and cannot be reflected adequately by simplified circuit models. Wideband performance of VT in a particular application is also noticeably related to its load level and character (inductive or capacitive). For typical VT it is possible to improve slightly its wideband performance by lowering its load level or by changing its character into inductive, but it usually requires laborious experimental verification. Despite of recognized restrictions and limited accuracy of the developed circuit model it can be successfully used for approximate assessment of VT

0.0

**6. Conclusions** 

pass band.

0.5

1.0

1.5

Modulus of normalized voltage transfer ratio [-]

2.0

2.5


**Part 2** 

**Converters** 

Yao Xiao; Jun Fu; Bin Hu; Xiaoping Li; Chunnian Deng; Problems of voltage transducer in harmonic measurement., IEEE Transactions on Power Delivery, Volume 19, Issue 3, July 2004 Page(s):1483 – 1487

**Part 2** 

**Converters** 

108 Power Quality Harmonics Analysis and Real Measurements Data

Yao Xiao; Jun Fu; Bin Hu; Xiaoping Li; Chunnian Deng; Problems of voltage transducer in

July 2004 Page(s):1483 – 1487

harmonic measurement., IEEE Transactions on Power Delivery, Volume 19, Issue 3,

**4** 

*Bulgaria* 

**Study of LCC Resonant Transistor DC / DC** 

The transistor LCC resonant DC/DC converters of electrical energy, working at frequencies higher than the resonant one, have found application in building powerful energy supplying equipment for various electrical technologies (Cheron et al., 1985; Malesani et al., 1995; Jyothi & Jaison, 2009). To a great extent, this is due to their remarkable power and mass-dimension parameters, as well as, to their high operating reliability. Besides, in a very wide-working field, the LCC resonant converters behave like current sources with big internal impedance. These converters are entirely fit for work in the whole range from no-load to short circuit while

There is a multitude of publications, dedicated to the theoretical investigation of the LCC resonant converters working at a frequency higher than their resonant one (Malesani et al., 1995; Ivensky et al. 1999). In their studies most often the first harmonic analysis is used, which is practically precise enough only in the field of high loads of the converter. With the decrease in the load the mistakes related to using the method of the first harmonic could

During the analysis, the influence of the auxiliary (snubber) capacitors on the controllable switches is usually neglected, and in case of availability of a matching transformer, only its transformation ratio is taken into account. Thus, a very precise description of the converter operation in a wide range of load changes is achieved. However, when the load resistance has a considerable value, the models created following the method mentioned above are not correct. They cannot be used to explain what the permissible limitations of load change depend on in case of retaining the conditions for soft commutation at zero voltage of the

The aim of the present work is the study of a transistor LCC resonant DC/DC converter of electrical energy, working at frequencies higher than the resonant one. The possible operation modes of the converter with accounting the influence of the damping capacitors and the parameters of the matching transformer are of interest as well. Building the output characteristics based on the results from a state plane analysis and suggesting a methodology for designing, the converter is to be done. Drawing the boundary curves between the different operating modes of the converter in the plane of the output characteristics, as well as outlining the area of natural commutation of the controllable switches are also among the aims of this work. Last but not least, the work aims at designing and experimental investigating a

retaining the conditions for soft commutation of the controllable switches.

laboratory prototype of the LCC resonant converter under consideration.

**1. Introduction** 

obtain fairly considerable values.

controllable switches – zero voltage switching (ZVS).

**Converter with Capacitive Output Filter** 

Nikolay Bankov, Aleksandar Vuchev and Georgi Terziyski

*University of Food Technologies – Plovdiv* 
