Phytohormones are of great significance in plant growth, development, immunity, and stress responses. As one of the promising phytohormones, salicylic acid (SA) is a natural phenolic compound synthesized from chorismate through two distinct pathways mediated by isochorismate synthase and phenylalanine ammonia-lyase, respectively. It plays crucial roles in regulating various biological processes related to plant growth and development, as well as in response to diverse biotic and abiotic stresses. Pathogens and herbivores are the most confronting biotic factors that pose severe threats to plant fitness and crop yield. The significance of SA in defense responses against these biotic stresses has been well addressed in the past decades. This review pays attention to the biosynthesis, metabolism, and signaling pathways of SA, and SA-mediated defense responses against pathogens and herbivores, thereby providing theoretical perspectives on the regulatory mechanism of SA-mediated immunity under biotic stress and improving the plant fitness and resistance to diseases caused by biotic factors.

Existing generator parameterization methods, typically developed for large turbine generator units, are difficult to apply to small kW-level diesel generators in microgrid applications. This paper presents a model parameterization method that estimates a complete set of kW-level diesel generator parameters simultaneously using only load-step-change tests with limited measurement points. This method provides a more costefficient and robust approach to achieve high-fidelity modeling of diesel generators for microgrid dynamic simulation. A two-stage hybrid box-constrained Levenberg-Marquardt (H-BCLM) algorithm is developed to search the optimal parameter set given the parameter bounds. A heuristic algorithm, namely Generalized Opposition-based Learning Genetic Algorithm (GOL-GA), is applied to identify proper initial estimates at the first stage, followed by a modified Levenberg-Marquardt algorithm designed to fine tune the solution based on the first-stage result. The proposed method is validated against dynamic simulation of a diesel generator model and field measurements from a 16kW diesel generator unit.

Concepts for control of wind farms (WFs) can be clustered into two distinct concepts, namely, wind power plant control (WPPC) and wind farm flow control (WFFC). WPPC is concerned with the connection to the power system, compliance with grid codes, and provision of power system services. This comprises the traditional way of operating a WF without consideration of aerodynamic turbine interaction. However, flow phenomena like wake effects can have a large impact on the overall performance of the WF. WFFC considers such aerodynamic phenomena in the WF operation. It can be viewed as a new feature that shall be integrated with the existing control functions. The interaction of these different control concepts is discussed in this article, leading to an identification of the challenges whose solutions will contribute to a successful integration of electrical system and aerodynamic aspects of WF control.

With frequency stability being challenged in modern power systems, transmission system operators have been designing new mitigation measures, such as fast frequency response (FFR), to maintain operation security of power systems. To accommodate technical requirements of new frequency control services (FCSs), the corresponding control should be implemented at asset controllers to enable fast responses. However, control counteraction can arise between plant controllers and asset controllers during the provision of FCSs. In this paper, a novel hierarchical frequency control approach is proposed to allow hybrid power plants (HPPs) to provide three types of FCSs, namely FFR, frequency containment response (FCR) and frequency restoration response (FRR). To solve control counteraction issue, an innovative frequency response observer (FROB) is proposed. The FROB at plant controllers and the hybrid power plant controller (HPPC) accurately estimates frequency response initiated by asset controllers, and the obtained estimation is used for control compensation at plant controllers and the HPPC to avoid control counteraction. Design guidelines and robustness analysis of the FROB are then discussed. Case studies are implemented in a power system dynamic model in MATLAB/Simulink, and the results show that the proposed frequency control approach enables coordinated operation of multiple technology power plants, with robust performance achieved when there are system uncertainties in HPPs.

The concept of hybrid wind power plants (HWPPs) that consist of wind, solar and batteries has received a lot of attention, since HWPPs provide a number of advantages thanks to the complementary nature of wind and solar energy and the flexibility of batteries. Nevertheless, converter-based technologies, as interfaces of HWPPs to the utility grid, contribute to the reduction of total system inertia, making the system more volatile and creating additional threats to frequency stability. To address these operational challenges, the capability of supercapacitors (SCs) to provide fast frequency reserve (FFR) is explored in this paper to enhance the frequency response of the HWPP. Two topologies for integrating SCs into the HWPP are proposed: (1) connecting SC to the DC link of wind turbine (WT) via a DC-DC converter interface, (2) directly connecting SC to the DC link of WT without converter interface. Frequency controllers at the asset level are proposed for these two topologies accordingly. The idea of the proposed frequency controller is to provide frequency response by varying SC voltage in proportion to frequency deviation, namely droop-based FFR. A practical SC sizing method for FFR provision is also discussed. The simulation results have shown, that in the case of frequency event, the proposed frequency controllers for SCs in both topologies positively contribute to the frequency of the system by reducing the rate of change of frequency by at least 5% and improving frequency nadir by at least 10%, compared to the case where the SC has no contribution to FFR. However, the capacitor size requirement for directly connected SC is more demanding in order to achieve the same level of improvement. The performance of frequency support has been highly related to total system inertia and control parameters. Therefore, any change to the severity of frequency events or control parameters calls for the reevaluation of the capacitance.