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 sderaz@kau.edu.sa saidderaz@yahoo.com

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.

Single-phase half-bridge inverter

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 = 2 𝑉 𝑠 𝜋 =0.45 𝑉 𝑠 Total harmonic distortion THD 𝑇𝐻𝐷= 𝑉 𝑜 2 − 𝑉 1 2 𝑉 1

Single-phase bridge inverter

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

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.

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.

The rms value of line to line output voltage [line voltage] 𝑉 𝐿 = 2 3 𝑉 𝑠 The rms value of the fundamental component of the output line voltage 𝑉 𝐿1 = 2 2 𝑉 𝑠 𝜋 cos 30 𝑜 =0.7794 𝑉 𝑠 The rms value of line to ground output voltage [phase voltage] 𝑉 𝑝ℎ = 𝑉 𝐿 3 = 2 3 𝑉 𝑠 The rms value of the fundamental component of the output phase voltage 𝑉 𝑝ℎ1 = 𝑉 𝐿1 3