Introduction - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 22

V DC /2
−V DC /2

0

π /2 π 3 π /2 2 π

ωt/rad

(a) v aN

V DC /2
−V DC /2

0

π/2 π 3π/2 2π

ω t/rad

(b) v bN

v ab v o

V DC

−V DC

0

π/2 π 3π/2 2π

ωt/rad

(c) v ab and v o

Figure 1.21 Bipolar operation of a single-phase inverter

and 1.2.3 and, hence, will not be discussed any further. The direct AC-AC conversion often
involves bidirectional switches, e.g. triacs and thyristors connected in anti-parallel. One way
to implement direct AC-AC conversion is to use matrix converters to generate AC outputs
with arbitrary amplitude and frequency; see e.g. (Rodriguez et al . 2012; Wheeler et al . 2002).
Here, the circuit shown in Figure 1.23(a) is illustrated with two major control methods: on-off
control and phase control.

1.2.4.1 On-off Control

Figure 1.23(a) shows a single-phase AC-AC converter. Two thyristors are connected in anti-
parallel so when they are triggered, both half cycles of the supply can be passed to the load.
When it is under the on-off control, triggering pulses are provided to turn on the thyristors so
that the supply is passed to the load. The thyristors are turned off when the supply is not passed
to the load. Assume that the ratio of the number of ON-cycles to the number of total cycles
in an operational perio d is k and the RMS value of the s up ply is V , then the RMS value of

the output voltage is √ kV and the input power factor is √ k . For the input voltage sketched in