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With the employment of power electronic converters, renewable energy resources introduce noticeable diversity into different generation units and dramatically change the characteristics of the supply side. Cooperation of different kinds of generation units in steady and dynamic states hence becomes important issues for grid integration. This article studies transient active power circulation caused by parameter difference among different kinds of generation units, such as synchronous generator and voltage-controlled power inverters. Parameter differences brought by power electronic inverters are analyzed, including capacity, inertia, and grid-side inductance. Moreover, a simplified transfer function model is utilized for the detailed analysis, which reveals how the transient active power circulation is influenced by the parameter difference. The theoretical analysis is verified with both simulation and experiment. Consequently, some important conjoint influences of inertia, impedance, and capacity difference are clarified, where the effectiveness and ineffectiveness of inertia and impedance imitation are concluded in transient active power allocation. Inertia and impedance design that attenuates transient active power circulation is proposed in several certain situations for inverter cooperated with other generation units.

Load modeling is critical for power system transient analysis and simulation. In recent studies, ambient signal-based parameter identification is considered as an effective method to obtain time-varying model parameters. However, low fluctuation amplitude of ambient signals may exacerbate the issue of multiple local optimal solutions, which is derived from the nonconvex and nonlinear characteristics of parameter identification problem. In this paper, a multi-start strategy based global optimization method is presented for ambient signal-based load parameter identification. Firstly, the selection of start points is formulated as a maximum diversity problem which can be solved by greedy algorithm. Then, we apply trust region-based local solvers to identify model parameters and obtain global optimum from multiple local solutions. Simulation results in the IEEE-39 bus system have demonstrated the global accuracy and efficiency of the proposed method.

With the rapid changes in the actual power system operation mode, power system wide area real time state estimation based on phasor measurement unit (PMU) plays an increasingly important role in energy management system (EMS). However, complex distribution characteristics of PMU measurement error pose challenges to the accuracy of state estimation. Therefore, a state estimation method combining PMU linear measurement model and linear Bayesian estimation is proposed. Considering the prior information of estimated parameters and the complex probability density function of measurement error, linear Bayesian estimation is applied to power system state estimation based on PMU. The correlation between real measurement error and imaginary measurement error is analyzed, and the prior information of estimated parameters is obtained according to the analysis of system state volatility. Compared with complex number least squares (CLS) method, the applicability and accuracy of this method were verified in IEEE 39 bus system.

Distribution networks with high penetration of distributed generation yield complicated and uncertain power flow, which makes most existing faulted line identification methods not adaptable for industrial applications. Driven by this motivation, a novel single-phase-to-ground (SPTG) faulted line identification method is proposed based on hybrid state estimator (HSE). The first step of the method is to present an HSE for power distribution networks using power flow measurements mixed phasor measurement units. Then, an SPTG fault on a power line is treated as an event that suddenly increases one virtual bus in the monitored network, so as to form the extended bus admittance matrix and augmented HSE based on the specific network topology. In this way, the faulted line identification could be obtained by computing parallel estimated results transversally. Robustness and effectiveness of the proposed HSE and the HSE-based SPTG faulted line identification method are validated by means of a cyber-physical system (a cosimulation platform), where two typical three-phase power distribution networks are considered to simulate with its hybrid measurement system.

A state feedback dynamic surface tracking control algorithm is proposed for parametric linearized manipulator model in this paper. Different from ordinary finite-time control schemes, fixed-time convergence can be achieved in the proposed algorithm via both of high and low-degree terms in the controller such that the settling time can be preestablished by the designed parameters independent of the system initial conditions. Moreover, the problem of the “explosion of complexity” and the singularity can be avoided by constructing an auxiliary controller with a first-order filter. The semi-global fixed-time uniform convergence of all the signals in the closed-loop system can be proved by Lyapunov theorem. In order to avoid the employment of acceleration signals and obtain better tracking performance during the procedure, a kind of observer based on uniform exact differentiators was used to compensate the uncertainties online. Finally the superiority of the proposed method has been verified by simulations based on a 2-DOF robot manipulator.

For traditional parameter estimation schemes of uncertain robot, most of them were proposed to identify unknown parameter with desired precision, but few of them focused on the convergence time. Recently finite-time estimation techniques have been proposed by scholars to achieve estimation in finite time. In this paper, we proposed a novel estimation scheme for uncertain robot systems with fixed time instead of finite time. In order to avoid using acceleration signals during the estimation, a kind of auxiliary filtering technique was employed. Besides, a continuous and recursive update law was employed for the parameter estimation such that the computational burdens of real-time inversion of square matrices could be avoided. Finally the effectiveness of the identification algorithm is verified based on a 2-DOF uncertain robot model.

The state information of district heating network (DHN) is significant to the secure operation and control of the integrated energy system. This paper focuses on the dynamic energy flow calculation method of the hot-water heating network under variable flow rate conditions, i.e. under the quantity regulation mode. First of all, known inputs, desired outputs and mathematical formulation of the energy flow calculation model are clarified. For the partial differential equation describing the temperature dynamics in each pipe, we apply the finite difference method to convert it into a group of algebraic equations for standardized solution. After that, a cross iteration method is proposed to solve the high-dimensional nonlinear model, where the global mass flow rate distribution and the temperatures of return water at each load are alternately updated until both converge to their acceptable precision levels. One nice feature of our method is that the temperatures of return water at each load do not need to be known inputs. Instead, the dynamic response of them can be fully captured, which is crucial for identifying the thermal conditions at each load. Test results of a DHN in the Barry Island demonstrate the validity and effectiveness of our method.

A continuous power flow (CPF) calculation method for the islanded microgrids with droop control is proposed in this paper. The starting point of CPF is solved by the modified factored load flow algorithm. The algorithm ensures the robustness of the starting point calculation with a two-step solution. The tangent prediction method and the Newton-Raphson method are used to determine the prediction and correction steps. Further, this paper proposes an adaptive step size control method based on frequency variation, which avoids the comparison among different nodal voltage magnitudes. In addition, node type switching is considered for handling the limit violations of PV nodes and droop nodes. The case analysis shows that the proposed CPF method has high efficiency and strong robustness.

Compared with the synchronous generator controllable rectification system, the synchronous generator uncontrolled rectification system has a simpler structure and control method which makes it more widely used. In the synchronous generator rectification system, the establishment of the mathematical model of the rectifier is the focus of analysis. Due to the existence of the rectifier, the system has strong nonlinearity and is difficult to model precisely. Meanwhile, the proportion of constant power load is getting larger and larger, and its negative impedance characteristic has adversely affected the stability of the power systems. Considering that the design of the system controller and the dynamic simulation process both rely on real-time numerical calculations, the amount of calculations will become larger and larger as the scale of the system increases. This makes real-time calculations even impossible. Based on the idea of model reduction, the authors firstly proposed a reduction model of three-phase uncontrolled rectifier generator through strictly mathematical theory. The reduction model retains main dynamic performance of the system. Then the authors combined the proposed model with engineering practice, and reduced the order of power systems with light load and heavy load respectively. The simulation results demonstrated the correctness and effectiveness of the raised model.

In recent years, Virtual Synchronizer Generator (VSG), which simulates the inertia and damping of the synchronous generator, has been gradually applied in microgrid. This paper studies the microgrid inverter using the VSG control strategy. Due to the existence of virtual inertia and damping coefficient in the VSG, the frequency and output active power of the microgrid inverter will oscillate when the active power scheduling command is abrupt, and the inverter will break down in severe cases due to over-current protection. Aiming at this problem, based on the root trajectory analysis of active power closed-loop transfer function, the influence of damping coefficient on VSG stability and dynamic performance is studied, combined with the physical meaning of the power angle curve and damping coefficient of VSG, the fuzzy algorithm is proposed to configure virtual damping coefficient. The VSG adaptive control algorithm of the coefficient is given, and the membership function and fuzzy rule table are given. Finally, the correctness and effectiveness of the control strategy are verified by constructing the simulink simulation model.

Voltage quality is an important aspect of power quality and a stable voltage amplitude is significant for network security and operational economy. Reactive voltage compensation is mostly paid attention on the transmission grid side, while the reactive voltage on the distribution grid side is rarely noticed. Compensating the reactive voltage of each node is uneconomical, so using a small amount of treatment equipment to meet the voltage requirements of each node of the distribution network is quite necessary. In this paper, a genetic algorithm-based method is developed for positioning of reactive voltage compensator. The effectiveness of the algorithm is verified by a 4-node system. The results indicate that the proposed genetic algorithm-based method can effectively calculate the position of the compensator.

Numerical methods can provide sufficient information for thermal dynamics of district heating (DH) network. However, high computation burden restricts its application, especially for large-scale DH networks. This dilemma can be overcome by establishing fast numerical calculation procedure and properly selecting the calculation steps without reduction of numerical accuracy. The first-order implicit upwind method is an iteration-free numerical approach for fast simulation of DH pipeline thermal dynamics, while the first-order precision restricts its numerical performance. To further improve the simulation performance, two iteration-free numerical methods with high-order precision, the second-order implicit upwind method and third-order semi-implicit QUICK method are developed. Validations of the three numerical methods are conducted with the measured data of a real DH pipeline. Preferred calculation steps of the three methods are studied via comprehensive numerical experiments. Based on the preferred step size, simulation comparisons of the numerical methods are performed. Results show that the outlet temperature fluctuations of DH pipeline can be feasibly predicted by these methods with satisfying accuracy. The second-order implicit upwind method perform best considering least computation burden (0.003 s) within acceptable error. With the application of the second-order implicit upwind method, simulation analyses on DH pipeline under varying flow velocities are performed.

Centralized control using system-wide data has been suggested to enhance the dynamic performance of large interconnected power system. However, the impact of time delays in acquisition and transmission of key signals cannot be ignored. A novel direct method (DM) based on cluster treatment of characteristic roots (CTCR) is introduced in this paper to analyze the stability of a power system considering the feedback transmission delay. The complete stability view of a time delayed single-machine infinite-bus (SMIB) system is obtained through the direct method in time delay space. The validity of this method is verified by time domain simulation results.

WAMS will play a vital role in the monitoring, analysis, modeling and control of interconnected power system. However, the impact of time delays introduced by WAMS canpsilat be ignored. A novel framework called the cluster treatment of characteristic roots (CTCR) is introduced to analyze the stability of a power system considering the feedback transmission delays. The ldquobuilding blockrdquo concept yields a very practical and efficient procedure for the stability assessment of multiple time delayed systems. This novel perspective serves very well for the preparatory steps of the CTCR method. The complete stability picture of a multiple time delayed single-machine infinite bus (SMIB) system is obtained through the combination of ldquobuilding blockrdquo concept and the CTCR method in time delay space. The validity of this method is verified by time domain simulation results.

This paper presents a novel fuzzy modeling strategy using the hybrid algorithm EPPSO based on the combination of Evolutionary Programming (EP) and Particle Swarm Optimization (PSO) for control of nonlinear dynamical systems. The EPPSO is used to automatically design fuzzy controllers for nonlinear dynamical systems. In the simulation part, one multi-input multi-output (MIMO) plant control problem is performed. The performance of the suggested method is compared to that of EP, PSO and HGAPSO in the fuzzy controllers design. Simulation results demonstrate the superiority of the proposed method.