three phase inverter

THREE PHASE INVERTERAIMTo simulate Three phase inverter using MATLAB Simulink modelSOFTWARE USEDMATLAB 2010SIMULINK LIBRARY BROWSERItemPathIcon

Opening Simulink

1. Click on the Simulink icon on Matlab taskbar2. Type Simulink on Matlab Command Window

Selecting New FileFile -> New -> Model

Selecting DC SourceLibraries ->SimpowerSystems-> electrical sources

Selecting IGBTLibraries ->SimPowerSystems ->PowerElectronics ->Thyristor

Selecting Series RLC branchLibraries ->SimpowerSystems-> Elements

Selecting Pulse Generater(Triggering)Libraries -> Sources

Mux Libraries -> Simulink ->Commonly used blocks

Voltage MeasurementLibraries ->SimpowerSystems-> Measurement

ScopeLibraries -> Sink

THEORY Device that converts dc input voltage to ac output voltage of desired magnitude and frequency is called an inverter.Inverters can be classified into single phase inverters and three phase inverters . Switching devices used in inverters uses PWM control signals for producing an ac output voltage. If the input voltage remains constant the inverter is called a Voltage source inverter and if the input current remains constant it is known as a Current source inverter. Three phase inverters are normally used for high power applications. A Three phase inverter can be obtained from a configuration of six transistors and six diodes as shown. Two types control signals can be applied to the transistors 180 conduction or 120 conduction.180 conduction conduction has better utilisation of switches and is preferredmethod. In 180conduction mode each transistor conducts for 180 and in 120conduction mode each transistor conducts for 120CIRCUIT

180o CONDUCTIONIn 1800 conduction scheme,each device conducts for 1800. They are turned ON at regular interval of 600 in the sequence Q1,Q2,Q3,Q4,Q5,Q6.The output terminals A B and C of this bridge are connected to the terminals of a 3-phase star or delta connected load.For a star connected balanced load, the operation is explained below.During the period 00 to 600, s1 s5 and s6 are conducting. Load terminals A and C are connected to positive terminal of the source and load terminal B is connected to negative terminal of the source. Equivalent circuit is shown below. Resistance between positive terminal and neutral is R/2 and between negative terminal and neutral is R. Hence, load voltages areVAN=V/3,VBN=-2V/3,VCN=V/3Line volages areVAB=VAN-VBN=V,VBC=VBN-VCN=-V ,VCA=VCN-VAN=0Similarly other equivalent circuits and voltages can be found.0-600 : T1,T5,T6VAB=VAN-VBN=V,VBC=VBN-VCN=-V ,VCA=VCN-VAN=0

VAN=V/3, VBN=-2V/3, VCN=V/3

600-1200: T1,T2,T6VAB=VAN-VBN=V,VBC=VBN-VCN=0 ,VCA=VCN-VAN= -V

VAN=2V/3, VBN= -V/3, VCN= -V/3

1200-1800: T1,T2,T3VAB=VAN-VBN=0,VBC=VBN-VCN=V ,VCA=VCN-VAN= -V

VAN=V/3, VBN= V/3, VCN= -2V/3

1800-2400: T2,T3,T4

VAB=VAN-VBN=-V,VBC=VBN-VCN=V ,VCA=VCN-VAN= 0

VAN= -V/3, VBN=2 V/3, VCN= -V/3

2400-3000: T3,T4,T5

VAB=VAN-VBN=-V,VBC=VBN-VCN=0 ,VCA=VCN-VAN= V

VAN= -2V/3, VBN= V/3, VCN= V/3

3000-3600: T4,T5,T6

VAB=VAN-VBN=0,VBC=VBN-VCN=-V ,VCA=VCN-VAN= V

VAN= -V/3, VBN=- V/3, VCN= 2V/3

Wave forms for 180conduction mode

1200 CONDUCTION In 1200 conduction scheme each device conducts for 1200.It is preferable for a delta connected load because it provides a six step waveform across any phase.As each device conducts for 1200 , only two devices are in conduction state at any instant.During the period 00 to 600 , Q1 to Q6 are conducting. Load terminals A is connected to positive terminal and load terminal B is connected to negative terminal of the source. Load terminal C is in floating state.Phase Voltages=Line VoltagesVAB= VVBC= -V/2 Vca= -V/2 Waveform for 120conduction

SETTING PULSE DELAY FOR IGBT

1. The Pulse Generator block generates square wave pulses at regular intervals. This square wave pulses are applied to IGBT for triggering. The block's waveform parameters, Amplitude, Pulse Width, Period, and Phase Delay, determine the shape of the output waveform. Pulse typeThe pulse type for this block: time-based or sample-based. The default is time-based.TimeSpecifies whether to use simulation time or an external signal as the source of values for the output pulse's time variable. If you specify an external source, the block displays an input port for connecting the source. The output pulse differs as follows:If you select Use simulation time, the block generates an output pulse where the time variable equals the simulation time.If you select Use external signal, the block generates an output pulse where the time variable equals the value from the input port, which can differ from the simulation time.So set pulse type and time as shown in the figure.2. AmplitudeThe pulse amplitude. The default is 1.

3. PeriodThe pulse period specified in seconds if the pulse type is time-based or as number of sample times if the pulse type is sample-based. The default is 10 seconds.

Here the period to be set =20 millisecond because the time period of the ac wave to be generated = =1/frequency of ac wave =1/50=20ms , 4.Pulse widthThe duty cycle specified as the percentage of the pulse period that the signal is on if time-based or as number of sample times if sample-based. The default is 5 percentHere time delay is set as 33.33 % 5. Phase delayThe delay before the pulse is generated specified in seconds if the pulse type is time-based or as number of sample times if the pulse type is sample-based. The default is 0 seconds.

Values for phase delay can be obtained as follows

20ms=360010=20/360600=(20/360)*60

In the figure shown above the specifications given are for pulse generator 4

PULSE GENERATORDELAY IN DEGREEDELAY IN MILLISECONDS

Pulse generator 100

Pulse generator 2603.33ms


Pulse generator 418010ms



6. Sample timeThe length of the sample time for this block in seconds. This parameter appears only if the block's pulse type is sample-based. 7. Interpret vector parameters as 1-DIf you select this check box and the other parameters are one-row or one-column matrices, after scalar expansion, the block outputs a 1-D signal (vector). Otherwise the output dimensionality is the same as that of the other parameters. RESULT: The simulation of 3-phase ac inverter was done using matlab and obtained the output waveforms .

three phase inverter

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