Investigation On Boost-PFC Peregulators And Their Control Strategies

Nowadays PFC AC/DC converters which are being used in many fields play an important role in the life. It is used in many applications, because of several advantages such as: regulation of input power factor to unity, minimum harmonic distortion of input line currents, near sinusoidal current waveforms, precise regulation of output DC voltage, and bi-directional power flow. This dissertation investigates two digital controlled methods and an improved topology of the Boost-PFC. The main contributions of this dissertation are as follows. (1) An Improved Algorithm for DSP Implementation of Boost PFC ConverterWith the development of the digital technique, more and more control algorithms can be implemented in power electronics by the digital chips. The merits of digital control: no temperature drift, simple hardware, flexible control and easy to realize advanced arithmetic etc, make digital technique to be used in power supply manufacture to let it more credible and easier to realize in batches with lower costs. So in the current it's popular to use digital control in power design.All of the existing control technique cannot take full advantages of the DSP and the switching frequency of the converter is limited by the speed of the DSP. So an improved digital control algorithm is proposed to solve the above mentioned problems in digital controlled PFC.An approach for the design of a digital controller for single-phase boost PFC pre-regulator is presented, which is performed by means of a standard DSP (TMS320LF2407).This thesis proposes an improved digital control algorithm of power factor preregulators (PFP) to reduce the CPU requirement. It avoids the complex calculations for the duty cycles needed in the conventional methods. Based on the improved algorithm, most of the duty ratio calculation was accomplished in main routine cycle. The input voltage and the output voltage also can be sampled only once in several switching periods. So in every switching cycle, it only needs to sample the input current and calculate the duty cycle by the simple equations of Boost topology. How to get the control parameters is analyzed in details. Experimental results on a single-phase 5OOW boost PFP show the effectiveness of the proposed solution, which demonstrate that the proposed strategy for PFC achieves unity input power factor with higher switchingfrequency than commonly used average current mode control. ( 2 ) A 2-switch H-bridge Boost-PFC with ripple free input currentThe 2-switch H-bridge Boost-PFC has lower conduction losses due to the fact that only two semiconductors conduct at the same time during the different stages of operation of the converter.An improved topology of boost converter is proposed in the third chapter, in which extra coupled inductors and a capacitor are added into a 2-switch H-bridge rectifier to reduce the input current ripple. Moreover the special design considerations for applications are proposed detail. Simulation and experimental results for the improved rectifier 3kW laboratory prototype are also presented.(3) Application of simplified space-vector modulation algorithm to three-phase voltage source PWM rectifier.A simplified algorithm is proposed for space-vector modulation of three-phase voltage source PWM rectifier. It avoids the calculation of arc tangent, square root, and polar coordinate calculation. In this algorithm, the working sector is determined by the voltage commands in Cartesian coordinates. Then the duty cycles of space voltage vectors are calculated directly in each sector, so that the PWM control can be more efficient. It avoids the look-up tables of sine and/or arctangent and complex calculations needed in the conventional methods. In addition, transfer function of the proposed rectifier is deduced and it can be used for the control loop design of the system.A prototype of project is completed based on a Digital Control System for Power Electronics "PE-PRO / VC33". The experimental results are given for verification of the validity of the algorithm and the control loop design. The system has the advantages including unity input power factor and greatly reduced harmonic distortion due to nearly sinusoidal input line current attainable with controlled rectifiers.