Power Factor Correction Techniques Of Three-Phase Full-Bridge Rectifier

With the development of power electronics, the power quality of AC power supply is increasingly paid attention to. In general, diode uncontrolled rectifier and thyristor phase controlled rectifier are adopted for AC/DC convertion, which inject plentiful harmonic and reactive power into AC mains, and result in serious pollution. So lots of reseaches have been focus on high input power factor and minimum harmonic injection into AC mains. Power Factor Correction (PFC) is an efficient technique for reducing harmonic distortion and increasing the power factor. This thesis mainly covers the flowing aspects:1. Firstly, the operation principle of a near unity power factor three-phase full-bridge rectifier was analyzed in detail. This rectifier is composed of two parts based on its operation principle: a power factor compensation circuit and a conventional rectifier circuit. And this rectifier was modeled with accurate mathematical equations based on the operation principle.2. The input inductor of the near unity power factor three-phase full-bridge rectifier is determined in the nominal operating point. With the load variation, the input power factor will be degraded. A new control method was proposed to overcome these drawbacks. The harmonics injected by conventional rectifier can be compensated by the power factor compensation circuit, thus the input power factor can be increased. The average real power consumed by load is supplied by the source, and the power factor compensation circuit does not provide or consume any average real power. Based on power balance theory, the reference compensational current can be obtained. The conduction period of bidirectional switches is controlled by using the hysteresis current control (HCC). The bidirectional switches operate at high frequency under this control method, the input inductor size will be effectively reduced. The simulation and experimental results show that with the proposed controller, the input line currents are nearly sinusoidal in shape and the input power factor near unity under wide load variation.3. Another novel control method for this rectifier is proposed in order to meet harmonic current distoration limits set by IEEE-519. The desired source currents are output from a current compensator, the compensator gain and the phase delay at each phase for each order harmonic are determined by an optimal control algorithm, where the permissible levels of individual and total harmonic distortion, power factor, as well as active power consumption are taken into account. The desired source currents can drive the bidirectional switches. The simulation and experimental results show that this control strategy is effective in minimizing source current distortion and maximizing load power factor. The proposed converter is suitable for a wide power application.4. The DC link voltage in near unity power factor three-phase full-bridge rectifier is very sensitive to the load variation. To improve the dynamic and static characteristic of this rectifier, the simple adaptive control (SAC) was adopted to control the DC link voltage. A new improved SAC based on quadratic performance index was proposed and adopted to adjust the adaptive parameters. This approach can track the reference model and decrease the control increment. This law includes the increment of the control quantity and the sampling values of state error in k and k+1. A controller was designed by adopting this method for DC link voltage. The simulation and experimental results show that the proposed controller can improve the dynamic stability of the system. They also show that this controller possesses strong robustness.