Power Transformers Model used for Inverters
Simulation
A. Taut, O. Pop, and S. Lungu
Applied Electronics Department, Technical University of Cluj-Napoca,
26-28 G.Baritiu street, Cluj-Napoca, Romania
adrian.taut@ael.utcluj.ro
Summary: This paper intends to present a model of power transformers used in simulation of
power inverters. For modeling of power transformers, we implemented a Matlab software, based
on mathematical equations who describe the functionality of transformers. Also we compare the
Matlab results with a Pspice simulations results. Matlab program that we've implemented
enables the modification of input parameters of the transformer and the choice of a circuit to be
analyzed. Also the Matlab model permits to view the waveforms of circuits in transient or steady
state regime.
Keywords: Transformer, Inverter, Matlab, Pspice.
Motivation
Transformers find wide and important applications in RF circuits. Historically,
transformers were used in power systems for voltage step-up and step-down [1]. We chose this
method of implementing a transformer, because it wants find a transformer parameters to be used
in the simulation of power inverters used in induction heating.
In induction heating systems, the heating coil and the load be represented by an equivalent
series inductance Leq and resistance Req. The quantity of heat generated in load will be
determinate by the resistivity (ρ) and permeability (µ) of the conductive object also the distance
and the position were the load is placed in electromagnetic field [2]. The equivalent circuit for
heating systems can be modeled like a transformer with a single turn. The model can be
simplified by an equivalent inductance and resistance like we see in equation system 1 [3].
Fig. 1: The load equivalent circuit
Req  r   122  RL
(1)
X eq  X L1   122  X L 2
For L2  R L   12 
Fig. 2: The result circuit from system equation 1
Xm
L2
(2)
Results
Started from the study of power transformers, the Matlab program developed allows the
analysis of electrical circuits who using these transformers. A separate study it is rectifiers with
and without capacitive filter, also presented in this paper. The results obtained solving these
equations are graphical represented.
In order to prove the results given by this simulator, commercial software like SPICE was
also used. The results were compared and demonstrate the accuracy of the simulator.
Fig. 3: Matlab results at 50 Hz
Fig. 4: Matlab results at 100 kHz
This platform allows to introducing the transformer parameters like inductance and
resistance in the primary and secondary terminals, voltage and frequency of primary, the model
of power transformers like in phase or anti-phase, number of the displayed periods, etc. Also we
can visualize the waveforms in transient or steady-state regime. The advantage of using this
software is also an educational one, offering the possibility to show to the students the equations
which describe the functioning of the power transformers or power rectifiers.
References
[1]
[2]
[3]
[4]
Ali M Niknejad, Electromagnetics for High-Speed Analog and digital Comunications Circuits,
Cambridge University Press 2007, ISBN 978-0-521-85350-7
R Y.S. Kwon, S.B. Yoo, D.S.Hyun, "Half-bridge series resonant inverter for induction heating
applications with load-adaptive PFM control strategy", Applied Power Electronics Conference and
Exposition, 1999. APEC apos;99. Fourteenth Annual Volume 1, Issue, 14-18 Mar 1999
Page(s):575 - 581
Dawson, F.P. Jain, P, "Systems for induction heating and melting applications: a comparison of
load commutated inverter", Power Electronics Specialists Conference, 1990. PESC '90 Record,
21st Annual IEEE
R Sheffer, Fundamentals of Power Electronics with Matlab, ISBN 1-58450-852-3