Improve System Stability Research Articles

DC Impedance Modeling and Design-Oriented Harmonic Stability Analysis of MMC-PCCF-Based HVDC System

Modular multilevel converter with passive circulating current filter (MMC-PCCF) is a novel topology that can inherently suppress circulating currents and has a lower modulation index penalty than traditional MMC. However, the harmonic stability issue of MMC-PCCF-based HVDC system is more complex, which has not been well addressed yet. This paper, for the first time, develops accurate dc impedance models of MMC-PCCF in different control modes and compares them with that of the traditional MMC in a wide frequency range mathematically. It is revealed that more resonance points exist in MMC-PCCF leading to higher harmonic instability risks. To comprehensively study the stability of MMC-PCCF-based HVDC system, this paper proposes a design-oriented harmonic stability analysis method based on resistance sensitivity and phase-difference sensitivity and sums up a guideline for the system stability improvement. Furthermore, this paper also presents a more intuitive explanation of the leading cause for system harmonic instability. It is demonstrated that the proportional coefficient of the dc voltage controller behaves as a negative resistance-inductance at the dc side. Based on this new sight, two typical damping control methods are compared in terms of parameter design and dynamic performance. Finally, real-time hardware-in-the-loop results verify the theoretical analysis.

Experimental verification of STATCOM based on quasi impedance source inverter for power quality enhancement in the hybrid distributed generation system

PurposeThis paper aims to introduce the quasi impedance source inverter (qZSI)-based static compensator (STATCOM), which is incorporated into the hybrid distributed power generation system for enhancement of power quality. The distributed power generation system includes the photovoltaic (PV), wind energy conversion system (WECS) and battery energy storage system.Design/methodology/approachThe WECS is used by the self-excited induction generator (SEIG) and the flywheel energy storage system (FESS). To regulate its terminal voltage and frequency, the SEIG requires adjustable volt-ampere reactive (VAR). A combination of a STATCOM and a fixed condenser bank usually serves to satisfy the VAR demand. The maximum correntropy criterion-based adaptive filter technique (AFT) is proposed to control the qZSI-STATCOM and to guarantee that the voltage at the SEIG terminal is harmonic-free while providing non-linear three-phase and single-phase loads.FindingsThe coordinated operation of the suggested voltage control and flywheel control systems ensures that load voltage and frequency are retained in their respective values at very low harmonic distortions regardless of wind speed and load variation. The simulation and experimental studies are carried out under different load conditions to validate the efficiencies of the PV-assisted STATCOM.Originality/valueTo improve system stability and minimize total costs, extra load current sensors can also be avoided. This paper proposes to control the SEIG terminal voltage and harmonic elimination in the standalone WECS systems using maximum correntropy criterion-based AFT with a fuzzy logic controller.

Synchronous Generator Imitation Control and Dynamic Power Sharing for Distributed Power Generation Systems

In this paper, a control method called synchronous generator imitation control (SGIC) as well as a dynamic power sharing for distributed power generation systems (DPGSs) are presented. In order to imitate the behavior of a synchronous generator (SG), the SGIC method for the voltage source converter (VSC) station is proposed. The SGIC includes three loops, namely active power and frequency loop (Pf loop), reactive power and voltage loop (QU loop) as well as inner current loop. The Pf loop is used to emulate the swing equation of the SG. The exciter of the SG is mimicked by the QU loop. The inner current loop is developed for fast current and voltage regulations as well as current limiting. The system stability performances are analyzed through small-signal model, and the effectiveness of the proposed control is validated by PSCAD/EMTDC simulations. The results show that the Pf loop of the VSC emulates the motion equation of the SG rotor very well, which makes the VSC station to have inertia just as a SG; the VSC station can maintain a stable output voltage and regulate the reactive power at the same time; through the dynamic power sharing, precise power control, frequency offset elimination and system stability improvement are achieved; the system has the merits of fault ride-through capability as well as good dynamic performance.

A novel dynamics model of a trailer bogie brake system and its application in stability analysis

The dynamic performance of the trailer bogie brake system is essential for the safe operation of a high-speed train during the braking process. In this work, we developed a novel ten-degree-of-freedom (ten-DOF) dynamics model of a trailer bogie brake system based on dynamic and tribological theories. The non-linear factors including disc-pad non-linear friction and wheel-rail non-linear interactions were considered. The field test results demonstrated that more intense vibrations occur at low vehicle speeds, which is also supported by numerical simulations based on the novel dynamics model. The abnormal vibration is caused by the limit cycle oscillation of the brake unit, and it leads to the instability of the whole system. To further understand the instability of the trailer bogie brake system, the equilibrium points and the linear stability of the system under different braking conditions and suspension parameters were investigated based on the Lyapunov theory. Then, the non-linear vibration response and stability of the trailer bogie brake system affected by the suspension parameters were further calculated by numerical integration methods. The results demonstrated that the mounting stiffness of the brake unit approached 3.4×107N/m and the primary suspension stiffness approached 6.0×105N/m or remained within the range of 10×105-14×105N/m, causing more violent vibrations and increased system instability. A primary suspension damping exceeding 2.4×104N·s/m was conducive to improving system stability.

Centralized bidding mechanism of demand response based on blockchain

In future power systems with the characteristics of high-elastic, demand response (DR) is considered to be an essential way for improving system stability and awakening demand-side resources. However, all the DR programs in China are implemented in a centralized model, which is easier for supervision, but hard to deal with the challenges of data credibility, privacy protection, transaction efficiency, and so on. Therefore, a novel blockchain-based framework for the DR program is proposed to deal with the problems. On this basis, the bidding transaction process based on the repeated verification mechanism is designed, and the effectiveness of blockchain in DR is analyzed. Then, the smart contract functions involved in DR bidding transactions and subsidy settlement are customized. The feasibility of the DR bidding mechanism is illustrated by the simulation results on the platform of Remix IDE.

Techno-Economic and Environmental Impact Analysis of Large-Scale Wind Farms Integration in Weak Transmission Grid from Mid-Career Repowering Perspective

Repowering a wind farm enhances its ability to generate electricity, allowing it to better utilize areas with high mean wind speeds. Pakistan’s present energy dilemma is a serious impediment to its economic development. The usage of a diesel generator as a dependable backup power source raises the cost of energy per kWh and increases environmental emissions. To minimize environmental emissions, grid-connected wind farms enhance the percentage of wind energy in the electricity system. These wind generators’ effects, on the other hand, are augmented by the absorption of greater quantities of reactive electricity from the grid. According to respective grid codes, integration of commercial onshore Large-Scale Wind Farms (LSWF) into a national grid is fraught with technical problems and inter-farm wake effects, which primarily ensure power quality while degrading overall system operation and limiting the optimal use of attainable wind resources. The goal of this study is to examine and estimate the techno-economic influence of large-scale wind farms linked to poor transmission systems in Pakistan, contemplating the inter-farm wake effect and reactive power diminution and compensating using a range of voltage-ampere reactive (VAR) devices. This study presents a partial repowering technique to address active power deficits produced by the wake effect by raising hub height by 20 m, which contributed to recovering the active power deficit to 48% and so reduced the effects of upstream wind farms. Simulations were conducted for several scenarios on an actual test system modeled in MATLAB for comparative study using capacitor banks and different flexible alternating current transmission system (FACTS) devices. Using the SAM (System Advisor Model) and RETscreen, a complete technical, economic, and environmental study was done based on energy fed into the grid, payback time, net present value (NPV), and greenhouse gases (GHG) emission reduction. The studies suggest that the unified power flow controller (UPFC) is the optimum compensating device via comparison analysis as it improved the power handling capabilities of the power system. Our best-case scenario includes UPFC with hub height augmentation, demonstrating that it is technically, fiscally, and environmentally viable. Over the course of its lifespan, the planned system has the potential to save 1,011,957 tCO2, resulting in a greener environment. When the energy generated annually by a current wake-affected system is compared to our best-recommended scenario, a recovered shortfall of 4.851% is seen, with improved system stability. This modest investment in repowering boosts energy production due to wake effects, resulting in increased NPV, revenue, and fewer CO2 footprints.

A Comprehensive Virtual Synchronous Generator Control Strategy for Harmonic and Imbalance Voltage Suppression of Multi-Inverter Parallel Microgrid

To reduce the impact of the imbalance of mixed non-linear loads on an inverter voltage output in the microgrid, we improve the disadvantage of the lack of damping and inertia for traditional droop control. This paper proposes a comprehensive virtual synchronous generator (VSG) control strategy for harmonic suppression and imbalance suppression of a multi-inverter parallel microgrid. On one hand, an improved VSG control strategy is proposed to increase the damping and inertia of distributed generations (DGs) in the microgrid, and secondary control is introduced to improve system stability. On the other hand, the frequency division suppression control strategy is used to eliminate the influence of harmonics, and the negative sequence component is compensated to eliminate the influence of imbalance. Then small-signal analysis is used for analysis of the stability of the strategy. Finally, we verify the comprehensive control strategy proposed in this paper through experiments. The experimental results suggest a significant improvement on the voltage, frequency, power optimization, handling of non-linear load and capacity distribution precision, as well as providing inertia support for the system.

Optimal Placement of FACTS Devices Using Filter Feeding Allogenic Engineering Algorithm

Flexible Alternating Current Transmission System (FACTS) are a useful tool for power system stability improvement and control. This research developed a new algorithm for optimal placement of FACTS devices named the Filter Feeding Allogenic Engineering (FFAE) algorithm inspired by the filter feeding and the motile behaviour of Allogenic Engineers.Kenya’s 87-Bus, 25-Generator, 132 kV and 220 kV transmission network was used as the test case in Matlab’s environment. The said algorithm was used to solve the twin objectives on minimization of active power loss and voltage deviations. One meta-heuristic technique-the whale optimization algorithm (WOA)-and one sensitivity based method-the fast voltage stability index (FVSI)—were used to test the accuracy of the proposed method. The computation time was 0.283 s and 0.308 s for FFAE and the whale optimization algorithm respectively mainly because of the use of Kalman filtration to achieve targeted iterations and using a more robust algorithm. The FFAE algorithm summed the total active power losses to 99.911% whereas the whale optimization algorithm gave a total of 99.770% indicating superior computational ability of the new method.

Robust longitudinal motion control of underground mining electric vehicles based on fuzzy parameter tuning sliding mode controller

The desire to reduce costs and increase productivity is driving mining industries to deploy underground mining electric vehicles (UMEVs). Due to the complex, working environments in underground mines, safer and more stable control strategies of UMEVs are required than the conventional control approaches used for electric vehicles (EVs). In this paper, first a UMEV model with bounded system uncertainties is derived. Next, a fuzzy parameter tuning (FPT) technique is used to adjust parameters in the sliding mode controller (SMC) against unexpected external disturbances and unbounded system uncertainties, which significantly improves system stability and robustness. Simulation and experimental results demonstrate that the proposed fuzzy parameter tuning sliding mode controller (FPTSMC) achieves better performance than SMCs with parametric uncertainties.

Multiharmonic Interaction and Stability Analysis of Two-Stage Double-Input Buck Inverter

Due to stronger nonlinear interaction and coupling effect, multi-input inverters can exhibit a variety of complex oscillations with multiple harmonics. This article develops a multiharmonic modal analysis method to uncover the occurrence reasons of various harmonics in the two-stage double-input Buck inverter. First, a frequency-selective approach is proposed to eliminate the time variance of the nonlinear averaged equations from both line frequency and second harmonic. Second, the nonlinear modal representation of the model obtained here is derived to capture various harmonic interactions and coupling effect from the viewpoint of both fundamental and second-order harmonic characteristics. Third, fundamental harmonic modal analysis is performed with the help of the trajectories of the fundamental modes, and significantly, the occurrence cause of two new harmonic components is explained in detail. And then, second-order harmonic modal analysis is used to discover a series of new nonlinear interacted harmonics, and the influence of these harmonics on different variables is evaluated by the second-order interaction indices. Furthermore, the coupling harmonic analysis is carried out to explore some coupling harmonics. In addition, the stability boundaries for different key parameters and load models are given to improve system stability. Finally, some experimental results are provided to validate the above analysis ones.

Optimal Penalty Factor for the MOV-FxLMS Algorithm in Active Noise Control System

The minimum output variance filtered reference least mean square (MOV-FxLMS) algorithm is a effective algorithm that utilizes the penalty mechanism to help the active noise control (ANC) system achieve noise cancellation with constrained output variance or power. As it can constrain output power, the MOV-FxLMS algorithm can freely determine the ANC system’s control effort, avoiding output saturation, and improving system stability. However, its performance is determined by a penalty factor, which is normally chosen by trial and error. Hence, this work proposes an optimal penalty factor and its feasible estimation that does not require any assumptions of Gaussian reference signal or input independence. This factor assists the MOV-FxLMS in achieving the optimal solution under the target output-variance constraint. Numerical simulations on measured paths demonstrate its effectiveness for various types of noise.

ПОВЫШЕНИЕ ТОЧНОСТЬ РАБОТЫ РОБОТА ЗА СЧЕТ ПРИМЕНЕНИЯ НЕЙРОННЫХ СЕТИ (НЕЙРОННЫХ КОМПЕНСАТОРОВ И НЕЛИНЕЙНОЙ ДИНАМИКИ)

The subject of this article is a programmable control system for a robotic arm. The complex nonlinear dynamics associated with the practical application of systems and manipulators is considered. The traditional control method is replaced by the developed Elma system and the adaptive radial neural network core function, which improves system stability and response speed. With the help of software associated with MATLAB, the corresponding controllers and compensators are developed. The results of training a neural network controller for programming robot trajectories are presented. Dynamic errors of various types of neural network controllers and two control methods are analyzed.

Control of PV Systems for Multimachine Power System Stability Improvement

The goal of achieving decarbonized operation of power systems in response to climate change has led to an increase in the number of sources connected to electrical grids through inverters, of which photovoltaic systems are an example. The operating characteristics of these systems in steady-state or transient operation are different from those of synchronous machines, giving rise to issues related to power system stability. The vast majority of grid codes stipulate that fault ride-through operating requirements should be enabled during severe contingencies in the transmission network, prioritizing delivery of reactive power to the power system to support voltage stability. However, this control action may contribute to rapid collapse of the system voltage under adverse operating conditions, such as when the critical voltage in the power vs. voltage curve is near the reliable voltage operating bound. Supporting power system stability under these circumstances represents a new challenge for inverter control schemes. This paper adapts a recently published fault ride-through control scheme for PV inverters for use in a multimachine power system and shows that the scheme can successfully maintain transient and voltage stability even under adverse voltage operating conditions.

Optimal Placement of Fault Passage Indicators in Distribution Networks using Genetic Algorithms

Fault Passage Indicators (FPIs); also named Faulted Circuit Indicators (FCIs), have been under development for the last 70 years including new capabilities to satisfy the needs of the distribution network operators. In order to improve system stability, these devices can be deployed along the feeder to reduce, or even eliminate, the uncertainty about the fault location. The number and location of FPIs affects the network reliability that can lead to extra charge on the distribution companies as well as the consumers. In this work, the optimal number and location of fault passage indicators in Power Distribution Networks (PDN) are determined. The problem is cast as an optimization task with a special economical combined objective function and solved using the genetic algorithms. The work has been tested on the two case studies, IEEE 9 bus and IEEE 33 bus systems.

Predictive maintenance scheduling for multiple power equipment based on data-driven fault prediction

In view of the maintenance of multiple power equipment operating in abnormal conditions in large-scale power plants, based on the prediction of fault state, a predictive maintenance scheduling method is proposed to schedule the maintenance activities. Firstly, based on the actual operating data, combined with the influencing factors of fault state deterioration by Pareto analysis, a time-variant function is improved to predict the deterioration state of potential fault in future maintenance interval. Then, maintenance priority is divided based on the fault state, considering the constraints of maintenance resources and equipment downtime, with the objective of minimizing the total maintenance cost, a scheduling model is built for the maintenance of multiple equipment. Finally, aiming at the continuity of maintenance time, a two-stage algorithm is proposed, which divides the maintenance time-window to transform the complex continuous time optimization problem into a combinatorial optimization problem of time periods, and then develops the optimal maintenance scheme. Taking the maintenance of multiple power transformers as an example, combined with the data resources provided by Yunnan power grid of China, the effectiveness of the improved prediction function of fault state is proved. In addition, by comparing with the traditional maintenance strategy based on the principle of first-fault-first-repair, the superiority of the proposed maintenance scheduling method is verified in reducing cost and improving system stability.

Power Transfer Control Strategy Based on True Bipolar MMC-MTDC System

The true bipolar modular multilevel converter-based multi-terminal direct current (MMC-MTDC) DC transmission line is prone to single-pole grounding fault, which may cause overload and overcurrent of the non-fault DC line with fault poles, resulting in system protection misoperation and system collapse. Therefore, the power transfer control strategy should be adopted to improve system stability. In addition, considering that the commutator stations of true bipolar MMC-MTDC system may have unipolar faults, it is necessary to adopt the control strategy of inter-pole power transfer or inter-station power transfer to improve the transmission capacity of the system under fault conditions. In this paper, a power transfer control strategy is proposed, which is widely applicable to MMC-MTDC system. In the case of line fault, the power transfer takes into account the line power margin and the power margin of converter station. The inter-pole power transfer is better than the inter-station power transfer under the converter station fault condition, and the inter-station power transfer takes into account the priority of the power margin of the converter station. At the same time, based on the Zhangbei four-terminal flexible direct current transmission project, the Zhangbei four-terminal flexible direct current transmission system is built by using PSCAD/EMTDC, and the flexibility and effectiveness of the proposed strategy are verified by simulation.

Control Strategy of Photovoltaic Grid Connected System Based on PI and QPR Double Closed Loop Control

The traditional proportional integral (PI) controller in photovoltaic three-phase inverter system has the problems of no static error tracking and poor resonance suppression effect. In order to improve the resonance suppression effect and current control effect of photovoltaic three-phase inverter system, a control strategy of photovoltaic three-phase inverter system based on PI and quasi proportional resonance (QPR) double closed-loop control is proposed. The control strategy and control block diagram based on PI and QPR double closed-loop control are designed to realize no static error tracking of incoming current, which has better waveform of incoming current and resonance suppression effect, and improves system stability. Finally, the effectiveness of the control strategy are verified by simulation.

Novel properties of heterogeneous delay in inverter-based cyber–physical microgrids under fully distributed control

Inverter-based microgrids will be vital components of future energy systems with large-scale integration of renewable energy resources. To cope with the low inertia problem induced by inverters, fully distributed control has been shown to effectively improve system stability owing to its fast response capability. Investigating the property of multiple delays in distributed control architecture is critical to guide its practical implementation in cyber–physical systems. Compared with power systems equipped with decentralized or centralized controllers, inverter-based cyber–physical microgrids under fully distributed control have a more complicated and heterogeneous delay environment. Existing, proven delay properties in centralized systems, such as the delay merge property that measurement and control delays of decentralized power system stabilizers can be merged for small-signal stability analysis, are not applicable to distributed systems To investigate the novel delay properties in distributed systems, we first propose a block-matrix-based cyber–physical model considering heterogeneous delays for inverter-based microgrids under fully distributed control. Then, we derive and prove the novel properties of heterogeneous delay in such systems. Finally, we perform numerical tests based on a real-world 7-bus islanded microgrid and a modified PG&E 69-bus microgrid under fully distributed frequency control. Our findings show that the impacts of measurement delay and control delay of one distributed controller on system stability are equivalent only if all distributed controllers are identical. Moreover, as the diversity of distributed controllers increases, the heterogeneous delay property becomes more significant.

High-Stability PGC Demodulation Algorithm Based On a Reference Fiber-Optic Interferometer With Insensitivity to Phase Modulation Depth

An ameliorated phase generated carrier demodulation algorithm based on a reference interferometer is proposed. It is theoretically analyzed, numerically simulated, and experimentally verified in this paper. The method of matching the amplitude of the quadrature signal in the reference interferometer algorithm eliminates the harmonic distortion caused by modulation depth fluctuations, suppresses system noise, and improves system stability. In experiments, where the sensed signal amplitude is 0.68 rad, the frequency is 1 kHz, and the modulation depth ranges from 1.5 to 3.5 rad, the ameliorated algorithm has SINAD that reaches 24.5 dB, which is an average improvement of 7.9 dB over the PGC-DCM algorithm based on a reference interferometer and an average improvement of 3 dB over the PGC-Arctan algorithm based on a reference interferometer. The ameliorated algorithm achieves a THD of 0.451%, which consistently maintains the best level of the traditional PGC algorithm based on a reference interferometer. The method provides an effective reference for signal processing in practical applications of fiber-optic sensors.

Modelling of Electric Grid to Enhance Generated Power Evacuation

The study of evacuation of power from the power plants in Rivers State Nigeria, connecting to the 330kV transmission network of the Transmission Company of Nigeria (TCN). The Power World Simulator Educational version was used in the modelling and simulation of the electric power grid. The study of load flow analysis, short circuit, transient and N-1 contingency analysis and their effect on the 330 kV/132kV transmission bus connected to the existing power plants in Rivers State Nigeria namely; Rivers IPP (180MW), Afam III (265.6MW), Afam IV & V (351.00 MW) and Afam VI G. S (650.00 MW) was carried out. From the short circuit study, it is observed that when a bus is faulted with a 3-phase fault, the three-phase voltages of the system drastically become zero in all the phases. The other buses of the network experience an increase in voltage and all the buses fed have the same effect as the bus under fault, though the effect is felt more on the buses. However, with the introduction of substation splitting at Afam III and ongoing Afam IV substations, the short circuit level will be reduced by 15%; leading to improvement in the overall system stability.