Grid Connection of Wind-Solar Hybrid Renewable Energy System, with Active Power Filter Functionality

Abstract

The incorporation of the abundantly available wind and solar energy to the grid using power electronic converter based interfaces makes a reliable hybrid renewable energy system. Assigning harmonic mitigation property to the grid interfacing inverter to mitigate the current harmonics created by the non-linear loads at the load centres, is a cost-effective solution. The inverter controller consists of an outer DC-link voltage control loop and an inner current harmonic mitigation loop. The limitations of existing DC-link voltage controllers are poor stability margin, steady-state error and chattering problem. The widely used pq theory based inner loop controller offers poor performance under non-ideal grid voltage conditions. The conventional low pass filter based fundamental component extraction methods used in pq theory possess some limitations such as additional time delays and low-frequency oscillations. The main focus of this research is the design, simulation, implementation and analysis of a grid-tied wind-solar hybrid renewable energy system with shunt and series active filtering functionalities, under different system conditions. A Backstepping controller based outer loop, with enhanced DC-link loss compensation capability is proposed for the shunt active filter to overcome the limitations of the existing DC-link voltage controllers. The limitations of conventional low pass filter based fundamental component extraction methods are overcome by employing a self-tuning filter in the inner loop of the shunt active filter. An additional self-tuning filter is incorporated to improve the effectiveness of pq theory under non-ideal grid conditions. A self-tuning filter and a Fuzzy logic-based voltage controller are employed to control the series active filter effectively. A laboratory prototype of the shunt active power filter is implemented. The control algorithm is realised in Xilinx Basys-3 FPGA. From the simulation and hardware test results under steady-state and dynamic conditions, it is found that the proposed controller offers better stability, robustness and speed compared to other existing control methods.