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S6: Static converters
73 EEE8044: Fundamentals
Section 6Static Converters
Introduction
The percentage of the electrical load controlled by power electronics in the UK, Europeand North America is increasing very rapidly. In the 1970s, only a small proportion of thetotal load was controlled in this way. By 1990, the proportion was 20% and it is nowestimated to be in 代写essay excess of 50%. Power electronic equipment, and particularly convertercircuits, is the major source of harmonics on the distribution network and the implicationsin terms of the related quality of supply issues are very significant.The main function of a converter circuit is to convert ac power to dc, which is defined asrectification, or dc power to ac, which is known as inversion. In this section we willexamine single-phase and three-phase bridge converter circuits and analyse their
performance. The main points of interest are:
a) Voltage and current waveforms on the ac and dc sides
b) Mean and rms voltage and current values
At the end of this section we will also examine, very briefly, the use of static power
electronics converters and devices to help control the flow of reactive power and reduce
harmonic distortion in the network.
Unless otherwise stated, all the converter circuits discussed in this section utilise the ac
supply voltages to transfer current from one device to the next and do not need any extra
circuits to effect this current commutation between devices. This is why they are referred
to as naturally-commutated or phase-controlled converters.
In all of the following analysis, the ac line voltages are assumed to be balanced and purely
sinusoidal. Unless otherwise stated, voltage drops in the semiconductor devices are
ignored.
S6: Static converters
74 EEE8044: Fundamentals
Learning Outcomes
At the end of this section you will be able to:
􀂃 Draw the power circuit and construct voltage and current waveforms for single-phase
and three-phase converter bridge circuits for operation in the rectification and inversion
modes.
􀂃 Calculate dc mean voltage and rms line current values for single-phase and three-phase
converter bridge circuits.
􀂃 Specify the harmonic content of the ac current waveforms of both single-phase and
three-phase bridge converter circuits.
􀂃 Describe four of the effects of supply inductance on the operation of static converter
circuits.
􀂃 Use the dc equivalent circuit to perform converter circuit calculations.
􀂃 Describe the use of converter circuits in high voltage dc (HVDC) transmission systems.
􀂃 Describe the operation of sinusoidal current converters.
Time
You will need about 4 hours for this section
Resources
Calculator and scrap paper
S6: Static converters
75 EEE8044: Fundamentals
6.1 Single-Phase Bridge Converters
Before we begin our examination of the more common three-phase converter circuits, we
will spend some time looking at the simpler, less complicated single-phase circuits, starting
with the single-phase diode bridge rectifier.
6.1.1 Single-phase diode bridge rectifier: voltage & current waveforms
Fig. 6.1 shows a single-phase diode-bridge rectifier. The ac input is connected to a singlephase
ac supply with rms line voltage VL. The dc output is connected to a highly inductive
load, which may be a simple R-L load or may be an