1. DC-AC converters [Inverters]
EE 442 POWER ELECTRONICS I
DC-AC converters
[Inverters]
Dr. Said A. Deraz
Assistant Professor
Electrical Engineering Department
Faculty of Engineering, King Abdulaziz University

2. Introduction
The function of an inverter is to convert a DC input voltage to a symmetrical AC output voltage of desired magnitude and frequency.
Inverters can be classified into two types:
single-phase inverters,
three-phase inverters.
An inverter is called:
a) A voltage source inverter (VSI) if the input voltage remains constant.
b) A current source inverter (CSI) if the input current is maintained constant.
c) A variable DC linked inverter if the input voltage is controllable.

3. Single-phase half-bridge inverter

4. The rms value of the output voltage
𝑉 𝑜 = 𝑉 𝑠 2 =0.5 𝑉 𝑠
The rms value of the fundamental component of the output voltage
𝑉 1 = 𝑉 𝑠 𝜋 =0.45 𝑉 𝑠
Total harmonic distortion THD
𝑇𝐻𝐷= 𝑉 𝑜 2 − 𝑉 𝑉 1

5. Single-phase bridge inverter

6. The rms value of the output voltage
𝑉 𝑜 = 𝑉 𝑠
The rms value of the fundamental component of the output voltage
𝑉 1 = 𝑉 𝑠 𝜋 =0.9 𝑉 𝑠
Total harmonic distortion THD
𝑇𝐻𝐷= 𝑉 𝑜 2 − 𝑉 𝑉 1

7. Three-phase inverter *note Q4 is labeled wrong in the circuit.
The transistors are numbered in the sequence of gating pulses. This means: (123, 234, 345, 456, 561, 612) and so on. It is clear that each transistor operate 1800.

8. Types of three-phase load
There are six modes of operations of the inverter. The following are three modes only for a half cycle for Y-connected R load.
In each mode, you should able to determine the load voltages van, vbn, vcn and the load currents ian, ibn, icn. If u determine the voltages, u easily divide it by the resistance R to get the currents.

10. The rms value of line to line output voltage [line voltage]
𝑉 𝐿 = 𝑉 𝑠
The rms value of the fundamental component of the output line voltage
𝑉 𝐿1 = 𝑉 𝑠 𝜋 cos 30 𝑜 = 𝑉 𝑠
The rms value of line to ground output voltage [phase voltage]
𝑉 𝑝ℎ = 𝑉 𝐿 = 𝑉 𝑠
The rms value of the fundamental component of the output phase voltage
𝑉 𝑝ℎ1 = 𝑉 𝐿1 3