## 1 Introduction  
Solar energy is one of the best renewable energy sources to meet the energy demand in countries with high solar irradiation. Generally, solar energy is a permanent source of energy, and is locally available. There are two main technologies used in solar power plants--namely, photovoltaic technology, and concentrated solar power (CSP) technology. In general, only direct radiation is used in these systems, while the diffuse part of sunlight cannot be concentrated. Direct normal irradiation (DNI) is reflected by means of mirrors and concentrated on the absorbent surface, leading to a rise in the temperature of the absorbent surface [1, 2]. This concentrated solar radiation is then transformed into thermal energy to heat a certain fluid, which can be used directly to generate renewable heat, or can be used for producing electricity. In the case of electricity production, the heated fluid will run a turbine (usually a steam turbine). Thereafter, the mechanical power resulting from the steam turbine will be transformed into electricity by the electrical power generator [3, 4, 5]. Today, CSP technology can be divided into four types--namely, linear Fresnel reflector, central tower, parabolic trough, and parabolic dish technology. Among the CSP technologies, parabolic trough technology is the most mature, as has been commercially proven [6, 7, 8]. The general design of parabolic trough power plants is principally concentrated on the high performance of the process, while the market requirements increasingly aim to improve the operating flexibility due to the current international trends in renewable energies. A dynamic simulation is a useful tool for enhancing the operation of parabolic trough power plants at different operating periods subject to the vagaries of weather, which in turn leads to load fluctuations and several start-up processes. Certain applications can be implemented based on the dynamic simulation, such as the optimisation of control circuits, and stress evaluation for critical components. In the literature review, there are several steady-state models concerning the parabolic trough power plant, while dynamic models are rarely implemented. Among the few dynamic models in the literature, there is no updated work that discusses in detail the description of the advanced controllers used in the solar field (SF) and thermal storage system (TSS) of a parabolic trough power plant. [PERSON] et al. [9] indicated that the simplified solar field design and a competitive thermal storage system are required in order to make better use of the economic potential of direct steam generation (DSG). Several works have been presented with regards to feasibility of integrating various thermal storage options with parabolic trough (PT) or linear Fresnel reflector (LFR) solar fields using DSG technology. [PERSON] et al. [3] implemented and developed the control strategies for generating steam directly under high pressures and temperatures using parabolic trough solar collectors. The controllability of the power plant was achieved using a PI control scheme during clear days, and even with the transient periods of the solar radiation. Classical controllers were implemented due to the knowledge of power plant operators using PI controllers. [PERSON] et al. [10] implemented two different DSG solar fields using advanced process simulation software. These models are used to simulate and to optimise thermal energy storage operations. Regarding the solar fields for both technologies (PT and LFR), only the configuration of the solar collector modules was described. Further simulation results for the stable operations and storage requirements in different cases were discussed. [PERSON] et al. [11] examined and compared a dynamic simulation with several phase change materials (PCMs) using the TRNSYS program. They have demonstrated that materials whose melting point temperature is close to the superheated steam temperature are suitable for a thermal potential energy storage system.