Voltage Source Inverter

Voltage Source Inverter

 Voltage source Inverter is a device that converts power from a DC constant voltage source into AC form by switching behavior. The output voltage has a switching waveform and the output current has AC form. It is classified into two inverters: square wave inverter and PWM inverter.

Fig 2. Voltage Source Inverter 2

Fig 1. Voltage Source Inverter 1

It consists of 3 pairs of 2 switching components. Depending on the switching condition, input and output voltage are determined. In order to prevent short circuit accident, switching component works in a commensurate way.

1. 3 Phase 2-Level Inverter

Fig 3. General Circuit of 3 phase 2-level inverter

Fig 3 is a common circuit of an 3 phase 2-level inverter. Line voltage has 3 level form which is +Vdc, 0, and -Vdc, The detail about this inverter is explained in one of my past posts titled as "Inverter: Single Phase Inverter and 3 Phase Inverter" 

2. 3 Phase 3-Level Inverter

 When the inverter transmits a wave, it contains harmonic components which interfere with actual power. For preventing this, we use 3 phase 3-level inverter. It contains fewer harmonics than a 2-level inverter.
 It works as 3 levels: P, O, N. During P switching, 1, 2 switches are on, so the output voltage is Vdc/2. During O switching, 2, 3 switches are on, so the output voltage is 0. During P switching, 3, 4 switches are on, so the output voltage is -Vdc/2.
 There are 2 types of 3 level inverter: T-type and NPC type

2.1 T-type

Fig 4. T-type 

Fig 6. Negative direction

Fig 5. Positive direction

  2.2. NPC type

Fig. 7. NPC type

Fig 9. Negative direction

Fig 8. Positive direction