power electronics

POWER ELECTRONICS

Instructor: Eng. Jalal Al Roumy

The Islamic University of GazaFaculty of EngineeringElectrical Engineering Department

الرحمن الله بسمالرحيم

EELE 5450 — Summer 2012

Lecture 22

Three switches conducting

The conducting sequence is as follows (each device conducts for a 180o period):

Three conducting devices- line voltage and current

Values of line voltage and line (also phase) current for 60o intervals are shown, from which the waveforms are constructed. The other two lines have identical values, displaced mutually by 120o

Three conducting devices- line voltage and current

Values of line voltage and line (also phase) current for 60o intervals are shown, from which the waveforms are constructed. The other two lines have identical values, displaced mutually by 120o

Comparing rms line currents

Comparing rms line currents

Two switches conducting

INVERTER HARMONICS

INVERTER HARMONICS

INVERTER HARMONICS

SINUSOIDAL PULSE-WIDTH MODULATION

One of the methods used to reduce the low frequency harmonics in the inverter waveform is sinusoidal pulse-width modulation. In this method, a reference copy of the desired sinusoidal waveform, the modulating wave, is compared to a much higher frequency triangular waveform, called the carrier wave The resulting drive signals cause multiple turn-on of the inverter switches in each half-cycle with variable pulse width to produce a quasi-sine wave of load voltage. The pulse width increases from a very narrow width at the start of each cycle to a maximum width in the middle of each cycle. Then the pulse width reduces again after maximum until its minimum width at the end of the half-cycle period.

SINUSOIDAL PULSE-WIDTH MODULATION

Typically in the comparator when the sine wave voltage exceeds the triangular wave voltage, the load voltage is +Vdc, and when the triangular wave voltage exceeds the sine wave voltage, the load voltage is -Vdc.

SINUSOIDAL PULSE-WIDTH MODULATION

End of Lecture