To generate a sinusoidal voltage using PWM with a 6-switch inverter it is common to use a technique called Space Vector Modulation (SVM). In SVM three voltage vectors are applied during each switching period, Tp. Two of these vectors are active vectors while the third is a zero vector. The zero vector is generated when all the three phase voltages are positive (111) or all are negative (000). Each vector has to be applied for a certain time so that the average voltage over one switching cycle is equal to the required output voltage. The sum of all of the vector’s duty cycle must be one. On the vector diagram the duty cycle for each vector is given numerically. As the uSIN vector rotates the new values of duty cycle are calculated.

In this applet symmetrical SVM is used where the switching 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 and the current flow in the 6-switch inverter is visualised. 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.

• Move the red timeline on the voltage and current plot and observe the rotation of the uSIN voltage vector and the selection of the different space vectors.
• Drag the red arrowhead on the uSIN vector to change the magnitude and angle.
• Move the red timeline on the switching period plot and observe the relationship between the switch states and the selected vector.