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Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011

Simulation of Three-level Inverter SangammaV. Gubbewad 1

Mahadevi Biradar2

Dept. of Electrical and Electronics, PDA college of Engineering , Gulbarga Email: Sangamma_spatil@yahoo.in 1 mahadevibiradar@yahoo.co.in 2 simulation of three level PWM inverter and shown output line voltage. In this present work, simulation of three phase inverter will be developed and studied about the three waveforms of three phases, IGBT is used as switching devices.

Abstract- The need for energy savings and introduction of new high power devices like IGBTs accelerate the broad use of medium and high voltage adjustable speed drives (ASD) in industrial and traction applications. To design a three-level converter-based ASD, a simulation system is developed using MATLAB package for the purpose of validating the practical power electronic circuits and offering suggestion for controller design. The various aspect of the proposed simulation system are discussed, including the Simulink modeling of the power electronic circuit, control mechanism of the simulation and the friendly graphic user interface (GUI) Some key in improving simulation efficiency are also highlighted.

III METHOD OF STUDY The power electronic circuit of the adjustable speed AC motor drive system is shown in figure1 which consists of the following parts. The input isolation transformer, which is connected to the AC transmission through the main breaker. A conventional diode rectifier in a 24-pulse series arrangement, Electronic switches (SD1 and SD2), each consisting of two protection IGBTs in series connection. They are used to disconnect the rectifier from the DC link immediately in case of inverter failures. The common mode circuit to protect the motor against common mode voltages DC-Link with the di/dt choke

I. INTRODUCTION Nowadays, energy savings have become a significant issue, which attracts a lot of interest from academic and industries. In India, especially with its power industry moving to the market mechanism, power Generation Corporation has become more and more concerned about reducing plant loads thus elevating generation efficiency, which in turn determines their competitiveness in the power market. Since the majority of plant loads are pumps and fans operated with fixed speed drive, one of the most effective method to save energy is to replace them with adjustable speed drive (ASD). The multilevel inverters have drawn tremendous interest in the power industry they present a new set of features that are well suited for use in reactive power compensation it may be easier to produce a high power, high voltage invented with the multilevel structure because of the way structure increasing the no. of voltage levels in the inverter without requiring higher ratings on individual devices can increase the power rating so the unique structure of multilevel voltage source inverters allows them to reach the voltages with low harmonics as the no. of voltage level increases the harmonic content of the output voltage waveform decreases. It is widely acknowledged that computer simulation plays a very important role in Research and Development of power electronic devices because of its high ability to speed up system implementation, and low cost. The objective of present work is to address the problem is to simulate the three phase inverter which is capable of generating sine wave output whivh can drive the three phase induction motor

Fig 1. Circuit of a three level inverter

The voltage-sourced inverter, which is based on the threelevel also as Neutral-Point Clamped (NPC) configuration. A total of 24 IGBTs are employed to build up the inverter. With short time over-voltage considered, the value may be even higher. The output LC filter, for the purpose of the supplying the motor with sinusoidal voltage.

II. LITERATURE

A. Simulation system This paper presents developed simulation system is based on the well-known MATLAB which is selected as the under lying environment because of its various unique advantages. High programming efficiency, strong numerical algorithm support convenient simulink CAD environment power

Trigg and Nayar(1) simulated single phase voltage controlled voltage source inverter and shown output waveforms using MOSFET. Shabon(2) studied and explained in detail about designing of power electronic circuits and studied simulation for single phase system. Sie et al (3) studied ÂŠ 2011 ACEEE DOI: 02.CEMC.2011.01. 537

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Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011 system block set (PSB) offering models of many power electronic devices elegant graphical user interface and most of all its open Architecture making it possible to customize, expand and integrate complicated system model and control scheme to meet special requirement. The hierarchical structure of the simulation system is illustrated in figure-2 the base modulate is the “simulink model” of the ASD system upon that is “simulation control block” which comprises two parallel components the “Control Data” which serves as the container of various data in the simulation and the “Control Program” which is a set of routine implementing the simulation predefined by the “Control Data” that top layer is the Graphic user interface (GUI) with which the user can fulfill the whole processes of simulation including creating or editing control data, starting or stopping simulation and viewing or print simulation results.

Fig.2 Hierarchical structure of the simulation system

B. Simulink Model: This model developed in simulink CAD environment is represented as “mdl” file which can be loaded by other programs or even from the MATLAB command window it contains five sub system (See fig-3) DC link with Auxiliary circuits three level inverter, LC output filter the induction motor as the load and the controller. MATLAB PSB does not provide the model of IGBT considering the fact that IGBT is an improved version of GTO so, the three level inverter is designed by Using IGBTs with appropriate adjustment of model parameters. In the developed simulation system the controller is actually an application program written with matlab language based on input signals including measurements and the simulation time from the clock model the controller exports two groups of control signals Con1 and Con2 Con1 is applied to the DC link to turn on or off the main breaker and protection IGBTs Con2 is to electronically switch the gates of IGBT of the three level inverter to make the inverter produce voltage of required frequency and amplitude.

Fig.3 Simulink Model of the ASD System

IV RESULTS AND DISCUSSION With the switching high frequency of 2 kHz simulation results produces smooth sinusoidal waveform with minimum ripple. Using IGBT switches will give merits such as, utilization factor, direct torque control, ASD, and ripple free pulses than GTO’s The switch ratings are 600V,30A and 1200V,15A for the IGBT, controlled turn off ability is minimum ie 1µs but in GTO controlled turn off ability is high ie 2.5µs. so IGBT’S are quite efficient for switching hence the frequency where the additional supply and conduction losses are lower than other MOSPET and GTO switches.

C. Simulation Control block: MATLAB/Simulink offer general simulation environment it has various draw back for instance the complicated manipulation. Lack of a unified interface to handle simulation parameters and results. With the simulation going on, the volume of stored data steadily increases, which in turn decelerates the simulation. If the simulation time is so long that the computers memory will be exhausted and too frequent hard-disk handling could even make further simulation infeasible. To overcome these problems, the designed the simulation control block, which consists of two parallel parts: “Control Data” and Control Program.

Fig. 4 Gate pulses applied for three phases

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Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011

Prototype demonstration kit was introduced so that output load is three phase induction motor will runs smoothly and also added overload protection of the motor. Three phase inverter can be used in DC power source utilization, UPS, induction heating and industrial application. REFERENCES

Fig.5 Three waveforms of three phases

V CONCLUSION “MAT-LAB Based simulation of Three Level Inverter” was successfully designed and tested in power electronics laboratory. Simulation of Inverter was verified with the switching frequency of 2 KHz and DC voltage of 600v. Simulation results produce smooth sinusoidal waveform.

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[1] MATLAB Simulink Modelling of a single-phase Voltage Controlled Voltage Source Inverter by M.C..Trigg and C.V.Nayar [2] A MATLAB/ Simulink Based Tool for power Electronic circuits by Abdulatif A.M.Shaban [3] MATLAB-based Simulation of Three-level PWM Inverter-fed Motor speed control system by Xiaorong Sie, Qiang Song, Gangui Yan, Wenhua Liu. [4] Control of a hybrid Asymmetric multilevel inverter by Martin Veenstra and Prof. Alfred Refer. [5] Modeling Simulation and test of three level voltage source inverter by a Sapin member, IEEE and PK Steimer [6] Power Electronics by Mohd. H.Rashid. [7] Multilevel inverter Based on Multi stage connection of Three level converters by JUAN Dixon and LUIS Moran, [8] Digital Simulation of Power Systems uing MATLAB by Gilbert Sybille