MATLAB SIMULATION OF

SPWM Inverter Using

Bipolar and Unipolar Switching Strategy

Aditya ParmarB.Tech Electrical Engineering

Charotar University Of Science & TechnologyChanga - Anand

OBJECTIVE: To analyze the output voltage of a SPWM inverter using FFT.

■ In most of the inverter applications, the magnitude of the output AC voltage and the input DC voltage varies continuously.

■ This requires continous variation of the control pulse width inorder to achieve the desired output voltage waveform.

■ In this method a reference signal is compared with a high frequency triangular wave to generate PWM signal.

■ If the reference signal is a sine wave, the modulation is called Sine wave pulse width modulation(SPWM).

■ The SPWM is realized by comparing a sine wave reference signal(Vr) with a high frequency triangular or sawtooth wave carrier signal(Vc).

■ The ratio Vr/Vc is called the modulation index and it determines the harmonic content in the inverter output voltage wave form.

■ The frequency of the reference signal determines the inverter output frequency and its peak magnitude determines the modulation index which inturn determines the RMS output voltage.

■ When the reference signal is compared with the carrier signal, their intersection determines the switching instants of the inverter switches.

CIRCUIT DIAGRAM OF BIPOLAR SWITCHING

OUTPUT WAVEFORMS

FFT Analysis

CIRCUIT DIAGRAM OF BIPOLAR SWITCHING

OUTPUT WAVEFORM

FFT Analysis

CONCLUSION

■ A SPWM inverter was simulated and FFT analysis was made in Matlab for the 2 different switching strategies. It was found that unipolar inverter with a filter circuit will give better sinusoidal output waveform compared to bipolar inverter.

THANK YOUFor Matlab Simulation FileDownload Following Files:

http://downloads.ziddu.com/download/25104164/unipolar_SPWM_Copy.pdf.htmlhttp://downloads.ziddu.com/download/25104163/Bipolar_SPWM_Copy.pdf.html

http://downloads.ziddu.com/download/25104161/Instruction.txt.html