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The widespread integration of renewable energy sources (RESs) into the grid through inertia-less power converters is reducing the overall system inertia leading to large frequency variations. To mitigate this issue, grid-forming (GFM) control strategies in bidirectional battery chargers have emerged as a promising solution, since the inertial response of synchronous generators (SGs) can be emulated by power converters. However, unlike SGs, which can withstand currents above their rated values, the output current of a power converter is limited to its nominal design value. Therefore, the estimation of the power delivered by the GFM power converter during frequency events, called Virtual Inertia (VI) support, is essential to prevent exceeding the rated current. This article analyzes the VI response of GFM power converters, classifying the dynamic behavior as underdamped, critically damped, or overdamped according to the selected inertia constant and damping coefficient, parameters of the GFM control strategy. Subsequently, the transient power response under step-shaped and ramp-shaped frequency deviations is quantified. The proposed analysis is validated using a 1.2 KW single-phase power converter. The simulation and experimental results confirm that the overdamped response under a ramp-shaped frequency event shows higher fidelity to the theorical model.

Frequency instability, voltage instability or a combination of both have been the cause of several power system breakdowns throughout the world in the recent decades. Occurrence of a super-component contingency (SCC) that refers to multiple and simultaneous outages of grid facilities like a power plant or substation may lead to blackout if no remedial action schemes (RAS) are implemented. This study proposes a new event-based RAS to overcome the frequency and voltage instabilities caused by SCCs through optimal load shedding. To do this, a new multi-objective framework is presented simultaneously optimising the competing objective functions of long-term voltage stability margin, steady-state frequency deviation, maximum transient frequency deviation and load shed amount. A modified system frequency response model is also proposed for frequency stability assessment. Multi-objective decision making (MODM) is performed using a combination of analytical hierarchy process, modified augmented ε-constraint method and technique for order preference by similarity to ideal solution. The effectiveness of both the proposed model and MODM solution approach is extensively illustrated on a simulated model of Iran's power system in 2012.

Wind energy high penetration levels in power systems require robust and practical operation algorithms to maintain and improve the present conventional systems performance. Thus, several studies consider the impact of wind farms installation on grid frequency, especially during frequency drops. The proposed algorithm makes the wind turbine provide promising support during frequency deviations through two operation modes, namely, normal and support. Normal mode controls wind turbine output by adjusting rotational speed and pitch angle according to the incident wind speed category. Novel normal operation secures wind turbine positive contribution in frequency deviations curtailment regardless of poor accompanying wind speed conditions. The innovative concept of merging pitch de-loading and rotational speed overproduction deceleration is implemented to avoid continuous de-loading; hence wasted wind energy is reduced. Wind turbine generator is overloaded when frequency drop occurs during high wind speed. Major algorithm parameters are tuned based on wind turbine specifications and dominant wind speed conditions at wind turbine location. The amount of supportive excess energy during frequency deviation clearance is estimated at different wind speed circumstances, including serious wind speed drop events. An islanded medium capacity hypothetical benchmark system is implemented to examine the proposed algorithm through MATLAB and Simulink simulation environments.

This paper deals with an adaptive technique-based design of load frequency controller for hybrid distributed generation systems. The hybrid system model is consisting of multiple power generating units and energy storage units. The proposed adaptive technique is the modified cuckoo search algorithm and support vector machine (SVM), which is utilized for obtaining the optimal solutions. In this paper, the proposed adaptive technique is utilized for optimized load frequency control (LFC) of a hybrid distributed generation systems model. The studied hybrid distributed generation systems consist of renewable/nonrenewable energy-based generating units such as wind turbine generator, solar photovoltaic, solar thermal power generator, diesel engine generator, fuel cell with aqua-electrolyzer, while energy storage units consist of battery energy storage system, flywheel energy storage system and ultra-capacitor. Here, fractional-order proportional–integral derivative (FOPID) controller is utilized to mitigate any frequency deviation owing to sudden generation/load change. The gain of the FOPID controller is optimized using the proposed adaptive technique. The proposed adaptive method-based LFC is implemented in the MATLAB/Simulink platform and analyzed their results. In order to analyze the effectiveness of the proposed adaptive technique, this is compared with that of other well-established techniques such as FOPID controller, GA with ANN-FOPID and SVM-FOPID controller. Moreover, the proposed tuned frequency controllers improve the overall dynamic response in terms of settling time, overshoot and undershoot in the profile of frequency deviation and power deviation of the interconnected hybrid power system.

Standalone microgrids, which are mainly constructed on island areas have low system inertia, may result large frequency deviations even for small load change. Moreover, increasing penetration level of renewable energy sources (RESs) into standalone microgrids makes the frequency stability problem even worse. To overcome this problem, this paper proposes an active power sharing method with zero frequency deviations. To this end, a battery energy storage system (BESS) is operated as constant frequency (CF) control mode, whereas the other distributed generations (DGs) are operated as an active and reactive power (PQ) control mode. As a result, a state of charge (SOC) of the BESS is changed as the system load varies. Based on the SOC deviation, DGs share the load change. The SOC data is assumed to be sent via communication system, hence the communication time delay is considered. To enhance reliability, controllers of DGs are designed to take account of the failure of communication system. The simulation results show that active power can be shared among DGs according to desired ratio without frequency deviations even for large variation of output power of RESs.

This manuscript focuses on the analysis of a critical height of radio altimeters that can help for the development of new types of aeronautical radio altimeters with increased accuracy in measuring low altitudes. Altitude measurement accuracy is connected with a form of processing the difference signal of a radio altimeter, which carries information on the measured altitude. The definition of the altitude measurement accuracy is closely linked to the value of a critical height. Modern radio altimeters with digital processing of a difference signal could shift the limit of accuracy towards better values when the basics of the determination of critical height are thoroughly known. The theory results from the analysis and simulation of dynamic formation and the dissolution of the so-called stable and unstable height pulses, which define the range of the critical height and are presented in the paper. The theory is supported by a new method of derivation of the basic equation of a radio altimeter based on a critical height. The article supports the new theory of radio altimeters with the ultra-wide frequency deviation that lead to the increase the accuracy of a low altitude measurement. Complex mathematical analysis of the dynamic formation of critical height and a computer simulation of its course supported by the new form of the derivation of the basic equation of radio altimeter guarantee the correctness of the new findings of the systematic creation of unstable height pulses and the influence of their number on the altitude measurement accuracy. Application of the presented findings to the aviation practice will contribute to increasing the accuracy of the low altitude measurement from an aircraft during its landing and to increasing air traffic safety.

Nowadays, the use of Microgrids is increasing due to their ample applications and advantages. Microgrids have much smaller financial commitments, and they use renewable resources; hence are more environmentally friendly with lower carbon footprints. Also, microgrids require fewer technical skills to operate, rely more on automation, and are isolated from grid disturbance or outage. Traditionally, microgrids have been employed in remote locations that cannot be connected to the central power grid and serve critical infrastructure. Due to the recent advancements in technology, microgrids have become more accessible and economically feasible. Microgrids can be employed in organizations that intend to lower their energy cost. The paper explains a detailed literature review and the contributions of the authors in Interconnected Microgrids. Also, the data taken from the survey was used in the transfer function blocks in simulation. The simulation of the interconnected microgrids comprising Thermal, solar, and wind turbine systems is formulated on MATLAB. The frequency error and ACE are reduced to zero in a quick time by using a fuzzy PID controller. Also, the paper aims at achieving one of the most important United Nations Sustainability Development Goals (UNSDGs), Affordable and Clean Energy (UNSDG- 7).

Power systems are the most complex systems that have been created by men in history. To operate such systems in a stable mode, several control loops are needed. Voltage frequency plays a vital role in power systems which need to be properly controlled. To this end, primary and secondary frequency control loops are used to control the frequency of the voltage in power systems. Secondary frequency control, which is called Load Frequency Control (LFC), is responsible for maintaining the frequency in a desirable level after a disturbance. Likewise, the power exchanges between different control areas are controlled by LFC approaches. In recent decades, many control approaches have been suggested for LFC in power systems. This paper presents a comprehensive literature survey on the topic of LFC. In this survey, the used LFC models for diverse configurations of power systems are firstly investigated and classified for both conventional and future smart power systems. Furthermore, the proposed control strategies for LFC are studied and categorized into different control groups. The paper concludes with highlighting the research gaps and presenting some new research directions in the field of LFC.

The possibility of expanding working frequency ranges and increasing the precision of State Primary Special Standard of the unit of frequency deviation GET 166–2004 is considered. Methods and means of measuring the frequency deviation that may be incorporated into the improved GET 166–2004 are proposed. Results of studies of the following four independent methods of measuring frequency deviation are presented: method of electronic computer frequency meter; method of direct digital synthesis; method of Bessel function zeros; and method of measuring the extremal values of the period.

The operation of the system’s frequency can be strongly impacted by load change, solar irradiation, wind disturbance, and system parametric uncertainty. In this paper, the application of an adaptive controller based on a hybrid Jaya-Balloon optimizer (JBO) for frequency oscillation mitigation in a single area smart μ G system is studied. The proposed adaptive control approach is applied to control the flexible loads such as HPs and EVs by using the JBO which efficiently controls the system frequency. The suggested technique uses the power balance equation to provide a dynamic output feedback controller. The main target is to regulate the frequency and power of an islanded single area μ G powered by a PV and a diesel generator with integrations of smart bidirectional loads (HPs and EVs) that are controlled by the proposed adaptive controller in presence of electrical random loads. Moreover, the JBO is designed to minimize the effect of the system load disturbance and parameter variations. For a better assessment, the proposed controller using JBO technique is compared with two other methods which are the coefficient diagram method (CDM) and adaptive one using classical the Jaya technique. In the obtained results, the frequency deviation is found as 0.0015 Hz, which is fully acceptable and in the range of the IEEE standards. The MATLAB simulation results reveal that the suggested technique has a substantial advantage over other techniques in terms of frequency stability in the face of concurrent disturbances and parameter uncertainties. The real-time simulation tests are presented using a dSPACE DS1103 connected to another PC via QUARC pid_e data acquisition card and confirmed the MATLAB simulation results.