Introduction - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 24

T 1

i s i o

T 2

~

v o

v s

Load

0

π 2π 3π 4π 5π 6π 7π 8π

ω t/rad

( a T p o l g y ( b ) I n p u t v l e

0 π 2 π 3 π 4 π 5 π 6 π 7 π 8 π 0 π 2 π 3 π 4 π 5 π 6 π 7 π 8 π

ωt/rad ωt/rad

(c) Output voltage under on-off control (d) Output voltage under phase control

Figure 1.23 Single-phase AC-AC converter

Figure 1.23(b), the output voltage is sketched in Figure 1.23(c) when the number of off-cycles
is one. Note that the thyristors are triggered when the input voltage crosses 0.

1.2.4.2 Phase Control

For the same circuit shown in Figure 1.23(a), it is possible to control the phase when both half
cycles are turned on by triggering the thyristors at the right time. There is not much difference
from the case with thyristor rectifiers, apart from the fact that both half cycles can be passed
to the load. For the input voltage sketched in Figure 1.23(b), the output voltage is sketched in
Figure 1.23(d) for a firing angle of 6 rad. It can be seen that there are harmonics in the output
voltage and the switches are not triggered when the voltage crosses 0.

1.3 Hardware Issues
A power inverter mainly consists of power stages, an electronic controller and the necessary
auxiliary circuits for isolation, output filtering, voltage and current sensing, signal conditioning
and protection, etc. The functional block diagram of an inverter is shown in Figure 1.24. In
this section, some general guidelines are provided and the readers are suggested to refer
to handbooks about hardware design (FUJI 2004; Kimmel and Gerke 1995; Rashid 2010;
Skvarenina 2002; TI 2011).