Analysis and Demonstration of Control Scheme for Multiple Operating Modes of Energy Storage Converters to Enhance Power Factor

Abstract

Rectifiers are required by the devices connected to the distribution end of the electrical power networks for AC/DC conversion. The line current becomes non-sinusoidal when a capacitor with a significant value is used to mitigate the output voltage ripple. This type of converter emulates a non-resistive impedance to the grid, due to which a bend occurs in the shape of the line current, which results in high total harmonic distortion and a low power factor. For perceiving sinusoidal current, power factor correction techniques are required. A digital controller for parallel-connected buck-boost power factor correctors is presented in this article to maintain a constant output voltage and to deal with circulating currents amongst parallel-connected converters. The proposed digital supervisory controller also regulates the input and line currents to keep them sinusoidal according to the input supply voltage to maintain the high power factor of the system. In this paper, using the differential equations of a buck-boost converter, the duty cycle calculations are performed for both Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM), which are responsible for providing a unity power factor. A supervisory controller encompasses a feed-forward control algorithm for tuning model parameters for eliminating the harmonics from the line current. The proposed scheme helps calculate duty cycles which provides a unity power factor and minimizes the circulating currents. The proposed method was simulated in MATLAB/Simulink and their digital-hardware validation testing was also performed using C2000 MCU Launchpad.