Enhanced Linear State Observer–Based PLL-Less Vector-Oriented Control Method for a Three-Phase PWM Rectifier

Abstract

In practical three-phase PWM rectifiers, external disturbances, such as changes in load and grid voltage, and internal disturbances, such as DC capacitor uncertainty, have caused major problems, including DC-link voltage fluctuations, harmonic distortion, and power factor degradation. They can also cause problems with power balance, stability, system dynamics, reduced efficiency, and increased stress. This paper proposes an enhanced linear state observer (ELSO) with a PLL-less voltage-oriented control (PLL-less VOC) method for a three-phase PWM rectifier in the synchronous coordinate frame (dq coordinate), aiming to simultaneously improve the DC-link voltage dynamics, disturbance rejection ability, and the grid current control loop’s transient response. The ELSO is suggested instead of the load current sensor not only to estimate the disturbance but also to estimate the overall switching losses of the PWM rectifier, resulting in good DC-link voltage disturbance rejection and transient fluctuation suppression, high robustness against DC capacitance change, low size and cost, and high reliability. Furthermore, contrary to the traditional VOC method, where the PLL and Park transforms are important parts for controlling the rectifier in the dq coordinate, the PLL-less VOC method can control the grid currents directly in the dq coordinate without needing PLL and Park transforms, which can offer a fast transient response and low computational burden. The frequency domain analysis of the ELSO is used to identify its gains and enhance its stability and disturbance rejection capability. Finally, hardware-in-the-loop (HIL) simulation using the OPAL-RT 4510 real-time simulator is also given to confirm the superiority and efficacy of the suggested control method.