In this applet there is one sinusoidal voltage source and a PWM voltage interconnected by an inductor. The PWM source is switched at high frequency and produces a sinusoidal low frequency voltage and high frequency switching voltages. It is assumed that the PWM voltage source always produces a fundamental component that has the same magnitude as the sinusoidal source. The inductor value is assumed to be small so that there is virtually no voltage drop across it at the fundamental frequency. The current in the inductor consists of a high frequency ripple component. This applet allows us to visualise the generation of the ripple current.

To generate a sinusoidal voltage using PWM, three voltage vectors are applied during each switching period, Tp. The switch state (or voltage polarity) of each phase during the switching period can be viewed. In space vector modulation there are always two active vectors applied and a zero vector. The zero vector is a result of all the three phase voltages being positive (111) or all being negative (000). In this case, symmetrical SVM is used where the pattern starts and ends with the (000) zero vector and at half the switching period the (111) zero vector is used. This switching strategy results in only one switching device changing state at any one time. As the red line is shifted on this plot the voltage vector at that time is highlighted in black on the vector diagram. The on-times for each switching voltage vector changes as the required sinusoidal voltage changes as can be seen if the red timeline on the fundamental voltage plot or the red arrowhead is moved.

The ripple current is created by the instantaneous voltage that is applied to the inductor and is shown by the green voltage vector. The ripple current vector is shown on the current vector diagram. The magnitude of the current ripple is dependent on relative times that each voltage vector is applied for. The largest current ripple occurs when the two active vectors are applied for equal times.

• Change the red timeline of the fundamental time plot to view how the different switching vectors are selected.
• For any sector, move the red timeline in the switching period plot to view how each vector is applied and the resulting inductor voltage vector and current vector.
• Adjust the inductor value and observe the change in the current ripple.