A New Generalized Step-Down Single-Stage AC/AC Power Converter

Abstract

Most traditional AC/AC power converters suffer from power quality problems and multi-stage power conversion losses. The rectifier and inverter-based AC/AC converter topology not only increases multi-stage power conversion losses, but also increases the volume, weight, and cost, and decreases the longevity of the converter due to the DC-link capacitor, line filter and electromagnetic interference (EMI) filter. High-frequency (about 10 kHz) switching advanced pulse width modulation techniques are generally used in order to compensate the power quality problems, which increase the switching losses and introduce the EMI problems. In this paper, a new generalized step-down single-stage line-frequency switching AC/AC power converter topology is proposed. The proposed converter uses line-frequency switching, and does not require any pulse width modulation techniques. The proposed topology offers promising performances in terms of lower order harmonics, total harmonic distortion, the elimination of DC-link capacitors and EMI filters, and switching losses. The circuit was designed and simulated in a MATLAB/Simulink environment. A scaled-down laboratory prototype of the proposed topology was developed in order to validate the feasibility. The experimental and simulation results reveal the feasibility of the proposed generalized step-down single-stage converter topology, and its excellent features.

A Transformerless AC-AC Converter with Improved Power Quality Employed to Step-Down Power Frequency at Output

“…The conduction of the developed circuit is less than the topologies in [23,26] and slightly greater than the circuit in [25].…”

“…The application of the low-frequency transformer is the main source of power losses and low conversion efficiency. Although the converter reported in [25] has the ability to achieve the required output with the conduction of one diode and one thyristor during any instant of its operation, but its voltage control capability requires a multiple windings transformer operated at line frequency. The voltage of these windings is connected to the load through the number of diodes and thyristors.…”

“…The instantaneous values of the voltage and current may regard constant as their variation can be ignored at high switching frequencies. The value of switching losses for the existing circuits of [23,25,26] and the proposed topology in Equations ( 41)-( 44) respectively may be realized with the procedure as detailed in [28,29].…”

“…The main source of the conversion losses consists of conduction losses (especially for diode and thyristors) and line frequency input transformer. The conduction losses in the topologies reported in [23,25,26] and the developed circuit are calculated from Equations ( 45)-( 48) respectively by following the procedure adopted in [29]. In these equations, the notation V f is used to represent the value of the forward voltage of a diode or a thyristor.…”

“…The total harmonic distortion (THD) of such output voltage waveforms becomes more worsen than a square waveform of the output voltage that is approximately 48%. A new approach is developed in [25] shown in Figure 1 to address and tackle such issues. This circuit facilitates to attain the output pulses with the peak of ±V m /2 and ±V m but this solution requires the use of a line frequency multi-winding transformer to change the instantaneous values of the selected output pulses.…”