Bundling conservation agriculture with drought-tolerant crops improves system productivity and stability in Zimbabwean smallholder systems

PurposeIn order to research the law of the low‐frequency power oscillation which often exists in the synchronous generator rectification system, the purpose of this paper is to study theoretical analysis and numerical calculation on the static stability of the system.Design/methodology/approachDifferent from the common three‐phase synchronous generator operating in large power networks, the stability of synchronous generator rectification systems is much more difficult to analyze because of its nonlinear loads. Some papers have analyzed the stability of the synchronous generator rectification system and presented different parameter conditions of system stability, but since factors that influence the system stability are complex, the essence of this kind of oscillation is not completely known yet. By considering rectification systems as an equivalent to DC circuits, the correct circuit model which is necessary to analyze the rectification systemic stability is set up, the changing law and relationship of various parameters under mini‐disturbances is analyzed, a linear differential equation about the DC‐side average current is derived, the stability of the synchronous generator rectification system is analyzed and deduced by using Hull criterion, all parameters influencing system stability are calculated and analyzed, and their ranges for a stable rectification system are given. Also, the reason why and how the parameters affect system stability is explained.FindingsThe operational stability of synchronous generator rectification systems is completely and correctly recognized.Practical implicationsThe paper has a reference value for the design and safe operation of synchronous generator rectification systems.Originality/valueThe paper puts forward system stability criterion and gives a rational physical explanation about system stability.

The integration of renewable energy into existing power grids presents significant challenges due to the intermittent nature and rapid dynamics of renewables. These characteristics can lead to power system oscillations, notably inter-area oscillations, which may result in power generation loss, reduced transmission capacity, and potential blackouts. Additionally, local power plant-level oscillations further minimise equipment wear and efficiency. This paper presents a Kundur two-area power system model to address these issues, offering a straightforward framework for analysing system stability. The model focuses on local and inter-area oscillations and their mitigation, which are crucial for maintaining system stability. Two mitigation techniques are modelled and analysed. The first uses phase-compensated power system stabilisers within the Kundur two-area network modelled in PSSE, emphasising their impact on system stability. The second replaces conventional hydropower plants with renewable energy sources, eliminating traditional damping equipment. In this scenario, a solar farm in hybrid mode manages both active and reactive power without stabilisers, as modelled in PSCAD. This approach effectively dampens inter-area and local oscillations. A three-phase bus fault is used to induce disturbances for system testing. RMS and EMT dynamic simulations are conducted within PSSE and PSCAD software, respectively, demonstrating the effectiveness of both techniques in mitigating power system oscillations, thereby enhancing system stability. Notably, the solar farm in hybrid mode presents a promising solution for integrating renewables while maintaining stability without traditional damping equipment.

Power system stability is the ability of an electric power system unit, for giving operating conditions beginning to recover operating state of equilibrium after being subjected to a physical interference. Power system stability has been recognized as an important problem for safe operation of system unit. Stability of power system is similar to the stability of any dynamic system, and has basic mathematical. Concepts from the mathematics and theoretical stability control are first revised to provide background information related to stability of dynamic system generally and establish a connection theoretical. This paper presents to improve of dynamic power system stability using frequency response as tuning of system stabilizer. It is started by electrical power systems mathematic modeling in state variable equation then set the expertise function of frequency response as tuning of system stabilizer. The plant controlled by function of frequency response is tuned to left half plane (LHP) as system stabilizer which their input from the rotor speed. When the system occur fault, the rotor speed should be synchronized, for this case one electrical controller is needed to make sure the system is stable.

Parallel running operation of 100 kVA superconducting generator (SCG) with high response excitation and 0.4 MJ SMES (superconducting magnet energy storage) was carried out. The exciter capacity of the high response excitation is rather large compared with that of conventional generators. The exciter controller, that is, AVR (automatic voltage regulator) and PSS (power system stabilizer) are designed taking the exciter power change at the excitation into account to improve the system stability. The SMES can also improve the power system stability. The SMES can give the small active power modulation of sinusoidal wave to the system. The system responses due to the SMES power modulation were observed and analyzed in order to evaluate the designed control functions of AVR, PSS and SMES. Frequency characteristics of the designed control functions were obtained from on-line data of the system. The system stability of parallel running of the SCG and the SMES was evaluated by use of SMES power control.

PSS-control as an ancillary service

This paper discusses the causes of power system instability and the importance of fast fault clearing. The k-constant model is used to explain the relationships among the following: small signal stability, high impedance transmission lines, line loading and high gain, fast acting excitation systems. Various types of power system instability, utilizing both mathematical and practical approaches, are covered. Transient stability is discussed, including synchronizing and damping torques. The power angle curve is used to illustrate how fault clearing time and high initial response excitation systems can affect transient stability. In the past number of years, "power system stability" has become an increasingly popular term used in generation and transmission. The sudden requirement for power system stabilizers for use with new and existing excitation equipment has created much confusion about their applicability, purpose, and benefit to the power system. This paper will discuss the fundamentals of the power system stabilizer and its effectiveness in the system. An explanation will be provided concerning the various types of power system stabilizers and the benefit of some types over others. Lastly, the paper will address regulatory commission guidelines identified by NERC that will impact generation connected to the transmission system.

The modular multilevel converter (MMC) has emerged as a promising solution for large-scale renewable energy integration. However, its inherent internal dynamics pose challenges in ensuring and assessing system stability. This article focuses on addressing the internal-dynamics-driven (IDD) instability in MMC systems. Unlike existing studies that rely on the output impedance compressing the entire dynamics into an all-in-one transfer function with internal dynamics hidden, this article visualizes the MMC internal dynamics as a targeted equivalent impedance, which directly links internal control parameters to system stability and thus facilitates targeted control design. The analysis reveals that the capacitive characteristics shaped by internal dynamics cause instability when coupled with inductive grids. Moreover, circulating current control can broaden this capacitive frequency band and exacerbate the instability risk without targeted design. Based on this insight, an internal-dynamics-originated (IDO) stability region is derived as practical control design guidance. A targeted stabilization control design framework is then established, enabling system stability without precise prior knowledge of the system impedance. Finally, multicondition experiments validate the effectiveness of the framework, providing a generalizable guideline for stability enhancement in MMC-based renewable energy systems and other MMC-interfaced applications.

Adaptive stabilization and tracking control of a nonholonomic mobile robot with input saturation and disturbance

This paper presents the design of a power system stabilizer (PSS) for stability improvement of a droop-controlled inverter-based microgrid systems. For faster power sharing, high droop gains are required, but increasing the droop gains degrades the system stability. Hence, there is a tradeoff between the faster load sharing and system stability. An answer to the given problem is presented in this paper by developing a PSS for inverter-based microgrid. The proposed stabilizer provides sufficient damping to the low-frequency oscillation even at higher value of droop gains which are usually unstable otherwise. The PSS designed in this paper is a generalized one and a step-by-step method to select the PSS parameters is also presented. Time domain simulation, experimental results, and eigenvalue analysis are presented for verification of the proposed controller.

Nowadays electromechanical oscillations of lower frequencies (LFO) have become a quite common phenomenon in modern power systems, posing a major threat to stability and security of the systems. For mitigation of these oscillations to improve system stability, Power System Stabilizers (PSS) are provided in power systems. However, in cases of certain faults and increased loading in a transmission line, equipping power systems with only PSS might not be enough. For better controllability as well as improved stability, Flexible AC Transmission System (FACTS) technologies are predominantly used in power systems. With unified use of FACTS devices along with PSS, there is improvement not only in just control of the power flow and response but also further enhancement in power system stability by damping out oscillations. Thyristor Controlled Series Capacitor (TCSC) is a modern versatile FACTS device extensively used in power systems for its effectiveness in rapid regulation of voltage, maintenance of balance in power flow and hence leading to greater stability limits as compared to other FACTS devices. However the linear control methods might not be effective in design of coordinated parameters. Hence taking nonlinearities in power system into consideration, a robust and unique evolutionary optimization technique termed as ‘Spider Monkey Algorithm’ is used for dynamic tuning of PID specifications of PSS for improvement of system stability to a much greater extent. The SMO based PID controller is designed and compared with conventional PID for justification and validation of the enhancement achieved, in terms of transient stability performance using MATLAB/SIMULINK environment by subjecting it to non linear loading conditions. The results demonstrate greater transient performance and immense potential of dynamically tuned SMO technique based PSS-PID of the two machine system as compared to the conventional PSS based PID controller.

While many promising data-driven power system transient stability assessment (TSA) studies have been recently reported, very few of them further propose efficient data-driven solutions for follow-up control actions, e.g., generator tripping, against potential instability. To address this inadequacy, this work develops an integrated data-driven transient stability monitoring and enhancement (TSMAE) approach that can reliably and efficiently handle various emergency situations in real time. First, by introducing the emerging spatial-temporal synchronous graph convolutional network (STSGCN), wide-area spatial-temporal features w.r.t. system stability are sufficiently learned to reliably implement online TSA. Then, to handle impending instability in a tractable manner, remedial actions are quickly taken based on intelligent critical generator identification (CGI). Specifically, with the help of the STSGCN again, the potential effects of tripping individual generators on system stabilization are efficiently predicted from the spatial-temporal perspective. Based upon that, the most critical generators for tripping are adaptively selected to enhance system stability. Numerical test results on a realistic provincial power grid of China illustrate the efficacy of the proposed TSMAE approach.

Background: Wind-solar hybrid power systems, playing a pivotal role in renewable energy integration and diversification of energy sources, frequently face low-frequency oscillation issues due to inadequate damping under disturbances. These oscillations pose challenges for realizing system stability through coordinated control strategies. Objective: This study aims to utilize intelligent algorithms for optimizing controller parameters, effectively suppress the occurrence of low-frequency oscillations, and thereby significantly improve the overall stability and reliability of wind-solar hybrid power systems. Methods: The power system stabilizer and flexible AC transmission system devices are utilized to enhance the stability of the wind-solar hybrid power system, and an improved snake optimizer algorithm is proposed to optimize the parameters of power system stabilizer and flexible AC transmission system devices, as well as the installation location of flexible AC transmission system devices. Results: Simulations demonstrate that the proposed algorithm shows a notable enhancement in system stability and reliability, with better performance in optimization precision and computation speed when compared to conventional methods. Conclusion: The proposed method effectively mitigates low-frequency oscillations, significantly improving stability and reliability in wind-solar hybrid power systems.

ABSTRACTIn power networks, low‐frequency oscillations—particularly inter‐area oscillations—pose a serious threat to system stability because of disruptions like short‐circuit faults and the increasing use of renewable energy sources like wind farms. To lessen the negative impacts of time delays when sending distant signals, this study presents a novel approach for the creation and optimization of a wide‐area damping controller (WADC). To accomplish smooth integration with the power system stabilizer (PSS), the Salp Swarm Algorithm (SSA) is used to precisely alter the WADC's parameters. The study also looks into how time delays, changes in wind speed, and load variations affect the effectiveness of the controller. A typical six‐machine test system with 200 MW of wind power is used for simulations under various operating conditions and disruptions. The results show that the suggested controller counteracts the detrimental effects of time delays, considerably lowers inter‐area oscillations, and preserves overall system stability. This study emphasizes the significance of wide‐area signal usage and robust control frameworks while providing a workable method for enhancing the dynamic performance of power systems with significant penetration of renewable energy.

SummaryMitigating inter‐area low‐frequency oscillations is a significant concern in multi‐machine power systems due to their adverse effects on system stability. These oscillations are intricately linked with power oscillations. So appropriate power modulation through the Battery Energy Storage System (BESS) can be an effective strategy for preserving system stability. In this paper, the maximal of all minimal residue indices under variations in power system operating conditions is utilized as the index for identifying the location for installation of the BESS, the damping control loop, and the feedback signal. A fixed‐structure scheme‐based wide‐area damping controller (WADC) is proposed for the BESS, providing sufficient damping of inter‐area oscillation modes. A modified IEEE 39‐bus system is simulated using a real‐time digital simulator as a test system in this work. The simulation results confirmed that the proposed WADC could effectively damp various inter‐area oscillation modes. Furthermore, it offers robust damping performance over contingencies associated with the system's various operating scenarios as well as the uncertainty associated with fixed and variable communication delays in the feedback signal of WADC and the integration of solar photovoltaic systems. Moreover, a comparative analysis of the proposed WADC is carried out with a BESS‐based wide‐area power system stabilizer, which is found to be more effective in mitigating system inter‐area oscillations.

ABSTRACTThis research proposes a coordinated approach for power oscillation damping (POD) of wind farms (WFs), power system stabilizer (PSS) of synchronous generators (SGs), and static var compensator (SVC) to enhance transient stability. The study explored the impact of wind speed variation, WF integration, and replacement of SG with WF and severe disturbances on system stability, addressing challenges such as dynamic performance impact and reduced power system inertia, which can lead to stability issues and undamped oscillations in generators. Different control strategies, including POD, PSS, and SVC, are proposed to tackle these challenges and improve transient stability. Conventional controllers face limitations in handling nonlinear characteristics, especially during severe disturbances. Coordination between POD, PSS, and SVC is crucial for achieving desired performance, facilitated by fuzzy logic control (FLC). FLC adapts to system operating conditions, generating optimal signals to adjust controllers based on measured variables. Utilizing FLC, lead‐lag parameters of controllers are finely tuned, demonstrating improved stability performance over conventional approaches. The MATLAB/Simulink using RT‐Lab‐OP4500 experimental platform with the modified IEEE‐9‐bus system confirm the proposed approach's effectiveness in enhancing transient stability under diverse operating conditions. Comparative analysis confirms the proposed approach's robustness and superiority in stabilizing power oscillations, especially during three‐phase faults. Results demonstrate improved stability performance and effective damping of oscillations, establishing the coordinated controller combinations with FLC as a viable solution for system stability enhancement. The proposed approach enhances small signal and transient stability by effectively damping oscillations, demonstrating promising results for practical applications during challenges related to uncertainties and nonlinearities.