21-09-2008, 09:46 AM
A new control scheme for a single ? phase diode clamped rectifier is proposed to achieve a unity power factor, balanced neutral point voltage and constant DC-bus voltage. Four power switches are used in the rectifier to generate a three-level PWM wave form on the rectifier terminal voltage.
The line current command is derived from a DC-link voltage regulator and an output power estimator. The hysteresis current Controller is used to track the line current command. To balance the neutral-point voltage, a capacitor voltage compensator is employed. The main advantages of using a three-level instead of a two-level PWM scheme are that the blocking voltage of each power switch is clamped to half the DC-bus voltage (if the off ?state resistance of power switches is equal),and the voltage harmonic on the AC side of rectifier is reduced.
A novel single phase neutral point diode clamped rectifier has been proposed to achieve high power factor, low current distortion, low peak factor, and stable capacitor voltages. The proposed rectifier can be controlled to operate in two- or-three ? level PWM.
Based on the model analysis, the switching signals of the power switches can be derived from the measured line current error and the mains voltage. Experimental results show a good line current waveform with almost unity power factor and low current harmonics to meet the requirements of IEC 1000-3-2 class A. The transient response due to load change is about one cycle and voltage drop is about 5V. According to measured results the proposed rectifier has the properties of high power factor, low current distortion and fast dynamic response, based on the proposed control algorithm.
