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DC-DC CONVERTERS VIA MATLAB/SIMULINK


MOHAMED ASSAF, D. SESHSACHALAM, D. CHANDRA, R. K. TRIPATHI

Electrical Engineering Department

Motilal Nehru National Institute of Technology

Allahabad, Utter Pradesh- 211004

INDIA





Abstract— the design of power electronic converter circuit with the use of closed loop scheme needs modeling and then simulating theconverter using the modeled equations. This can easily be done with the help of state equations and MATLAB/SIMULINK as a tool for simulation of those state equations. An attempt has been made in this paper to simulate all basic non-isolated power converters. So that these models can be readily used for any close loop design (say using PI, fuzzy, or sliding mode control etc.).


Index Terms—Switchingconverters, MATLAB/SIMULINK, system modeling, cascade control, subsystems


I.
II. 1 Introduction


Controller design for any system needs knowledge about system behavior. Usually this involves a mathematical description of the relation among inputs to the process, state variables, and output. This description in the form of mathematical equations which describe behavior of thesystem (process) is called model of the system. This paper describes an efficient method to learn, analyze and simulation of power electronic converters, using system level nonlinear, and switched state- space models. The MATLAB/SIMULINK software package can be advantageously used to simulate power converters. This study aims at development of the models for all basic converters and studying itsopen loop response, so these models can be used in case of design of any close loop scheme. Also as a complete exercise a closed scheme case has been studied using cascaded control for a boost converter.


2 Simulink Model Construction of DC-DC Switching Converter

System modeling is probably the most important phase in any form of system control design work. The choice of a circuit modeldepends upon the objectives of the simulation. If the goal is to predict the behavior of a circuit before it is built. A good system model provides a designer with valuable information about the system dynamics. Due to the difficulty involved in solving general nonlinear equations, all the governing equations will be put together in block diagram form and then simulated using Matlab’s Simulinkprogram. Simulink will solve these nonlinear equations numerically, and provide a simulated response of the system dynamics.



A. Modeling Procedure

To obtain a nonlinear model for power electronic circuits, one needs to apply Kirchhoff's circuit laws. To avoid the use of complex mathematics, the electrical and semiconductor devices must be represented as ideal components (zero ON voltages, zeroOFF currents, zero switching times). Therefore, auxiliary binary variables can be used to determine the state of the switches. It must be ensure that the equations obtained by the use of Kirchhoff's laws should include all the permissible states due to power semiconductor devices being ON or OFF.

The steps to obtain a system-level modeling and simulation of power electronic converters arelisted below.

1) Determine the state variables of the power circuit in order to write its switched state-space model, e.g., inductor current and capacitor voltage.

2) Assign integer variables to the power semiconductor (or to each switching cell) ON and OFF states.
3) Determine the conditions governing the states of the power semiconductors or the switching cell.
4) Assume themain operating modes of the converter (continuous or discontinuous conduction or both) or the modes needed to describe all the possible circuit operational modes. Then, apply Kirchhoff's laws and combine all the required stages into a switched state-space model, which is the desired system-level model.
5) Write this model in the integral form, or transform the differential form to include the...