title: Sliding mode control of renewable energy generation systems
Creators: name: Alsumiri, Mohammed
Publisher: name: University of Liverpool Repository
Year: 2015

description: As a result of decades of research and innovation in the renewable energy industry, advanced technologies have been developed for both wind and solar energy conversion systems. However, there are still some aspects of the systems that need to be enhanced to enable maximum and cost effective energy conversion. Wind is emerging as an alternative source for electrical power generation. Small-scale wind power generation system applications are becoming widespread because of rising fuel prices and the demand for reducing carbon emission. For such applications, vertical axis wind turbines (VAWT) appeal due to their ability to capture wind from different directions and their low noise-pollution. Wind energy and its conversion system are studied first. The need for advanced maximum power point tracking (MPPT) controllers is discussed in literature focusing on widely implemented algorithms. Sliding mode control theory has been studied and implemented in controlling wind power generation system (WPGS). The dynamic performance of the WPGS using sliding mode control has shown improved dynamic performance, overshoot errors eliminations and higher energy conversion ratios than the widely used proportional integral (PI) control. A new approach in WPGS control strategy by development of a novel soft control strategy based on the mathematical residue theorem has been introduced. The idea of using the residue theorem is to set a soft dynamic boundary for controlled variables around a reference point, so that controlled variables lie on a point inside this boundary. The stability of the system has been ensured by following the Forward Euler method. The developed control strategy has been implemented in different control techniques of a small-scale permanent magnet synchronous generator (PMSG) based WPGS. The introduction of the new control approach based on residue theorem has further improved the energy conversion ratio by 2:5%. Moreover, a wind speed estimation algorithm is provided and implemented to the proposed controllers to overcome the wind speed measurements issues, i.e. cost and accuracy. Furthermore, an improved back-EMF observer based on residual theorem has been designed to estimate the mechanical rotor speed of the PMSG using the stator current and voltage measurements. The improved back-EMF observer has overcome the well-known limitation of the classical back-EMF at low speed observation. In addition, the wind speed has been estimated using the calculated power obtained from the PMSG voltage and current measurements as well as the estimated rotor speed. Based on the wind and rotor speeds, the tip speed ratio (TSR) is calculated and controlled to its optimal value. A MPPT controller has been developed for photovoltaic power generation systems based on a sliding mode control scheme in stand-alone configuration. The developed controller provides a solution to atmospheric conditions measurement issues and it enhances the efficiency of the PV power system. In addition, the developed controller overcomes the power oscillation around the operating point which appears in most implemented MPPT techniques. The MPPT operation is achieved by regulating the input voltage of the PV system using DC-DC boost converter topology. Moreover, a single-ended primary inductor converter (SEPIC) topology has been employed in PV power systems. The restrictions on the application of SEPIC have been solved based on sliding mode control. The efficiency of the PV system has significantly improved.