European Association for the Development of Renewable Energies, Environment and Power Quality (EA4EPQ) International Conference on Renewable Energies and Power Quality (ICREPQ’10) Granada (Spain), 23rd to 25th March, 2010 Single-Phase Single-Stage AC-DC Converter with Reduced Line-Current Harmonics Nader Anani, John Williamson and Prasad Ponnapalli Department of Engineering and Technology Manchester Metropolitan University Chester Street, Manchester M1 5GD United Kingdom Tel: +0044 161 2471649 E-mail: n.anani@mmu.ac.uk Abstract. The circuit topology for a single-phase single stage ac-dc converter with the aim of minimising the converter’s line current harmonics is presented. The circuit is based on the half- controlled ac-dc converter topology and employs active switching devices to achieve its objective. These devices are used to provide alternative paths for the line current during periods when the smoothing capacitor is supplying the load current, thus reducing the line current harmonics. Extensive simulation studies have been carried out on the circuit and results are presented and compared with the results obtained from a standard ac-dc uncontrolled converter operating under similar conditions. The results indicate that the line current harmonics are reduced to levels compliant with those set out by the relevant European Union’s Directive, IEC61000-3-2, on harmonics injection into the supply mains directed at equipment that draws current 16 A ≤ . Key words AC-DC converter, minimisation of line current harmonics, IEC-61000-3-2. 1. Introduction The number of small electrical and electronic equipment which requires low dc power for their operation, such as desktop computers, has been increasing at an enormous rate especially in the last decade. This dc power is typically obtained by the process of rectification of the ac mains and for small power ranges less than about 2 kW, the single-phase diode bridge ac-dc converter of Figure 1 remains the most attractive choice. This is because of its simplicity, reliability, and its low cost and low losses. The output voltage is a unidirectional pulsating waveform whose dc value is only about 63% of its peak value and thus the waveform contains large ripple voltage [1]. To reduce this ripple voltage a large smoothing capacitor is connected across the output terminals of the diode bridge. The value of the smoothing capacitor must be chosen so that the ripple voltage is reduced to, typically, 5 to 10% of the required dc voltage and it depends on the frequency of the mains, typically 50 Hz, and on the value of the load current. The smoothing process whilst increasing the dc value of the output voltage waveform has an adverse affect on the supply current drawn by the converter. The smoothing capacitor causes the line current to flow only for short intervals of time as shown in figure 1(b). For the remaining time the capacitor supplies the load current. That is the supply current consists of short narrow pulses. This means that the input current is rich in harmonics. The generated harmonics will be injected into the supply mains and may be harmful to other equipment connected to the mains. Further, if there is a Fig. 1 Diode bridge (a) and input current , input voltage and output voltage (b). (b) (a) (t) (t) https://doi.org/10.24084/repqj08.707 1510 RE&PQJ, Vol.1, No.8, April 2010