A new approach for design and control on bridgeless power factor correction circuit

Undesired voltage and current harmonics in an electricity system have become inevitable because of the new circuits and control techniques appeared with the technological growth. The power factor correction (PFC) circuits have been developed to reduce current harmonics in utility systems produced by nonlinear loads. Poor power factor generated by nonlinear loads disrupts the ac line voltage and effects the other equipments connected to the same source. In conventional PFC circuits, the switch of the converter is controlled such that the input current tracks the input ac line voltage. Since the input voltage is not always a sinusoidal wave and includes different harmonic components, the input current will not be a sinusoidal wave and will be distorted including the same harmonic components of the input voltage. This is an important disadvantage of conventional PFC converters especially when they are fed by a distorted ac line voltage. In the proposed control approach, the input voltage is not directly used as reference as in the conventional methods. This is due the fact that, the input ac mains voltage is not always a sinusoidal wave. In this method, an ideal sine wave is generated by a DSP microprocessor based on detected zero crossing points of the input voltage. Thus, a reference signal is generated with the same phase and frequency of the ac mains voltage. In this manner, the injection of the input current harmonics as the result of the distorted input voltage to the ac mains is prevented. Using bridge rectifier and semiconductor components in these converters increases the conduction losses. The topology used in this study, is a bridgeless PFC converter. An important advantage of this topology over the similar PFC converters is that the conduction losses of the semiconductor switches are lower. This is due to minimum possible number of semiconductor switches in the current path at any instant of operation, which is two. This topology is composed of two single-phase boost converters without input rectifier as used in other PFC circuits. The system satisfies the conditions of IEC 61000?3?2 current harmonics standards successfully. The design, control and switching techniques of the circuit have been carried out using Simulink blocks in MATLAB program. The proposed method and the theoretical analysis are verified by the results of experiments carried out in the laboratory.