S6: Static converters
73 EEE8044: Fundamentals
Section 6
Static Converters
Introduction
The percentage of the electrical load controlled by power electronics in the UK, Europe and North America is increasing very rapidly. In the 1970s, only a small 英國dissertation網(wǎng)proportion of thetotal load was controlled in this way. By 1990, the proportion was 20% and it is nowestimated to be in 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 powerelectronics converters and devices to help control the flow of reactive power and reduceharmonic 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 extracircuits to effect this current commutation between devices. This is why they are referredto 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 areignored.
S6: Static converters
74 EEE8044: Fundamentals
Learning Outcomes
At the end of this section you will be able to: