As the future electric power grid will be driven by distributed renewable energy sources, the deployment of grid-connected power converters will also grow to enable seamless grid and energy source interaction. To provide the reliable operation of these converters, the estimation of fundamental grid parameters is important. The most common estimation techniques are a phase-locked loops (PLL) and a frequency-locked loops (FLL). However, those techniques encounter challenges in conducting parameter estimation when the input signal is unbalanced due to DC-offset, harmonics, signal sags, and frequency and phase variations. This paper presents an enhanced FLL loop enriched with an additional loop for estimation and rejection of the DC-offset. Active and reactive power calculations in grid-connected microgrids by using the modified FLL loops with DC-offset rejection is a novel application introduced in this paper. Experimental verification has demonstrated that the enhanced FLL loop provides fast and reliable parameter estimation as well as stable and robust power calculations, even in the presence of a DC-offset.

The subject of this paper is design, testing and implementation of voltage control of buck power electronics converter using programmable logic controller (PLC) which is based on Beckhoff technology. The proposed control structure is first modelled in the Matlab/Simulink software environment. The built Simulink model is then integrated and transferred to the TwinCAT 3 software which converts personal computer (PC)/laptop into the real-time PLC. This paper proposes an experimental platform consisting of the following components: laptop computer used as the PLC, Beckhoff input/output (I/O) interface, power electronics converter with gate driver module, and electronic modules for measuring and adjusting the signals between the converter and the Beckhoff PLC. In this paper, the control is implemented on the example of the buck converter. However, the proposed modular experimental platform can be used for any type of the converter. Thanks to the integration of the Matlab/Simulink and TwinCAT 3 software environments and the modularity of the platform, the proposed experimental platform is suitable for rapid prototyping of different control structures of power electronics converters, which is especially useful for educational and research purposes. The given experimental results validate excellent performances of the proposed platform.