Abstract:
ABSTRACT
Input switched SEPIC topology based output voltage regulated 3-phase 3-switch modular rectifier circuit is proposed and developed in this thesis. Fully controlled three phase converters consisting of six controlled switches are ideal methods for bidirectional AC-DC conversion. Complexity of control, requirement of protection against devices failure and costs limit their applications. In large rectifiers, harmonic current injection technique is used for PFC, THD and efficiency improvement but this technique requires separate dc sources for generating harmonic current to be injected.
Three phase AC-DC converters may use uncontrolled bridge rectifiers followed by DC-DC converters. These provide input current shaping with low THD. Large filters at their inputs degrade the conversion efficiency. Modular three phase rectifiers are composed of three single phase PFC rectifiers, where, input current waveforms are controlled by three switches and the output is taken from a DC rail. They are capable of being controlled like single phase boost PFC rectifiers. In this work, amodular three-phase power factor corrected (PFC) single ended primary inductor converter (SEPIC) rectifier is investigated. The advantage of the circuit is its ability to rectify individual voltage of three phases separately and superimpose them at the load. Per phase rectification allows sinusoidal input current shaping in the circuit by standard feedback control. Alsoboost topology at the input stage with series inductor allows easy reduction of input current total harmonic distortion (THD) and improvement of input power factor.
The proposed rectifier is a high performance controlled rectifier compared to traditional ones in terms of power factor, input current THD and conversion efficiency. The SEPIC topology retains benefits of buck/boost gain facility and provides capacitor isolated output. The performance results have been compared for the open and closed loop voltage regulations. In open loop system, the output voltage of the rectifier has been controlled by standard duty cycle control technique. To ensure high performance feedback control circuits have been employed with current and voltage controller loops. The performance of the proposed circuit has been found to be satisfactory in simulation and experimental results. Typical dynamic responses of the circuit are included to demonstrate its effectiveness to
regulate output voltage during load changes with the performance remaining almost the same.
