Structures of transformerless step-up and step-down controlled rectifiers

New single-switch structures of single- and three-phase transformerless controlled rectifiers are proposed and analysed. These structures consist of a common rectifier, an input inductor filter, a high-frequency operated switch and a diode-capacitor ladder network. The latter, in its known application as a multiplier, is used for increasing the input voltage. A new scheme of a diode-capacitor network, which can be used as a divider to reduce the input voltage, is also proposed. The detailed analysis of the steady-state mode is performed and simple formulas for the calculation of step-up and step-down rates of the voltage are derived. Transient analysis of the proposed circuits, by solving the recurrent equations and by using the z-transform, is also performed. Since the proposed schemes do not consist of any transformers and/or any inverters, their operation is very efficient; no high harmonics and/or a DC component are produced, and so the input current and voltage waveform are close to the sinusoid. The power factor of such structures reaches unity and their weight is low, compared with those having a transformer. A laboratory model of one of the proposed structures has been built and tested. The experimental results confirm the converter's efficiency and the correctness of the theoretical analysis.