Constant switching frequency control of switch mode rectifiers

Abstract

The boost converter is commonly used as a power-factor-correction pre-regulator. For medium to high power applications, the continuous mode of operation is preferred. This paper attempts to give a detailed analysis, not reported previously in the literature, of the limitations of the continuous-mode boost converters as power-factor-correction pre-regulators, in terms of the attainable power factor and harmonic distortions. Results are presented to highlight the relationships between various practical parameters and the attainable performance.

A novel control scheme for single-phase switch-mode rectifiers is presented in this letter. By utilizing the constant-switching-frequency pulse width modulation scheme, the duty ratios of the switches in each switching cycle are determined based on accurate control strategy. No current sensors are required. The simulations and experiments show satisfactory results.

Due to tougher regulations on the input current harmonics, studies on the single-phase boost-type switch-mode rectifiers (SMRs) with unity power factors have been presented in recent years. Among various continuous current control schemes, some of them require high-accuracy current sensors which add to the overall circuit cost, and some adopt varying switching frequencies which make the filtering and the electromagnetic interference (EMI) reduction difficult. In this letter, the authors will present a novel fixed-frequency control method without current sensors for boost-type SMRs. It is known that, in the SMR control, the input current is shaped to follow a sinusoidal command in phase with the ac source voltage. The waveform of the input current is determined by the charging and the discharging voltages of the boost inductor and the duty ratios of the switches. Instead of sensing the input current, slopes of the input currents are observed to determine the duty ratio in a fixed-frequency switching cycle. The well-developed triangle pulse width modulation (PWM) scheme can be employed. In the following sections, the control principles will be explained. Also, simulations and experiments are conducted to demonstrate the feasibility of the presented scheme.