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The energy transition is aimed to take advantage of the operational flexibility of hydropower to extend the integration of intermittent renewable sources. Consequently, the hydrogenerators will have to operate in regimes far away from their designed best-point operation. In order to accurately assess the impact, this paper presents a useful approach to determine the overall operating efficiency of synchronous generators under intermittent operation. An accumulated average efficiency (AAE) model is proposed and compared against an alternative approach; the weighted average efficiency (WAE) model. It is found that the WAE approach produces unrealistic low efficiencies when the generator operates in synchronous condenser mode (SCM) for long periods. In general, the AAE supersedes the WAE for all the different load distributions that were investigated. This was further illustrated by a worked example and by constructing more complex load distributions. A load distribution dominated by SCM yields a difference as high as $33.18 \,\%$ , while an even distribution deviates $1.43 \,\%$ in their respective efficiencies. Finally, a yearly on-site measurement of our studied $103 \,\mathrm{MVA}$ generator’s concentrated load distribution revealed a discrepancy of $0.67 \,\%$ , which is a significant deviation considering what the operating regime would mean in terms of economic implications. [ABSTRACT FROM AUTHOR]

Unified power flow controller (UPFC) gains growing application in power systems due to its power flow regulation ability. However, there is still a dilemma in the incorporation of UPFC into security-constrained economic dispatch (SCED). The modeling of UPFC involves nonlinear and nonconvex operational constraints, which is difficult to solve efficiently and accurately. Conventional methods adopted Taylor expansion or sensitivity analysis to realize the convexification of UPFC models, which leads to a loop structure and is subject to initial point choice. In this paper, a novel three-terminal injected UPFC model is proposed. In the proposed model, the voltage source variables are eliminated completely. Instead, only power injection variables are introduced to equivalently describe physical characteristics and constraints of UPFC. The nonlinear and nonconvex operational constraints of UPFC are transformed into mixed integer second-order cone form. Moreover, compared with conventional UPFC models, the control characteristic of UPFC is considered in a more accurate and practical manner in the proposed SCED, which helps to prevent potential risks of power flow over-limit under N-1 contingencies. Simulation results show the effectiveness and efficiency of the established solution. [ABSTRACT FROM AUTHOR]

This paper focuses on the issue of network connectedness (NC) in security-constrained optimal transmission switching problems, which is complicated by branch contingencies and corrective line switching. Two criteria are firstly proposed with the principle of preserving NC as much as possible within reasonable limits. By extending the electrical flow based NC constraints, a proposition is derived to associate different cases of NC with the optimum of a linear program, yielding the mathematical formulation of the NC criteria. By Karush-Kuhn-Tucker conditions, this formulation is further transformed into a tractable version which can be incorporated with existing SCOTS models without affecting the applicability of original solution approaches. Finally, case studies on various networks and SCOTS models demonstrate the efficacy of the proposed approach. [ABSTRACT FROM AUTHOR]

The reduced inertia levels in low-carbon power grids necessitate explicit constraints to limit frequency’s nadir and rate of change during scheduling. This can result in significant curtailment of renewable energy due to the minimum generation of thermal plants that are needed to provide frequency response (FR) and inertia. Additional consideration of fast FR, a dynamically reduced largest loss and under frequency load shedding (UFLS) allows frequency security to be achieved more cost effectively. This paper derives a novel constraint from the swing equation to contain the frequency nadir using all of these services. The expected cost of UFLS is found probabilistically to facilitate its comparison to the other frequency services. We demonstrate that this constraint can be accurately and conservatively approximated for moderate UFLS levels with a second order cone (SOC), resulting in highly tractable convex problems. Case studies performed on a Great Britain 2030 system demonstrate that UFLS as an option to contain single plant outages can reduce annual operational costs by up to $\pounds $ 559 m, 52% of frequency security costs. The sensitivity of this value to wind penetration, abundance of alternative frequency services, UFLS amount and cost is explored. [ABSTRACT FROM AUTHOR]

The increasing complexity of modern AC/DC power systems poses a significant challenge to a fast solution of large-scale transient stability simulation problems. This paper proposes the hybrid parallel-in-time-and-space (PiT+PiS) transient simulation on the CPU-GPU platform to thoroughly exploit the parallelism from time and spatial perspectives, thereby fully utilizing parallel processing hardware. The respective electromechanical and electromagnetic aspects of the AC and DC grids demand a combination of transient stability (TS) simulation and electromagnetic transient (EMT) simulation to reflect both system-level and equipment-level transients. The TS simulation is performed on GPUs in the co-simulation, while the Parareal parallel-in-time (PiT) scheduling and EMT simulation are conducted on CPUs. Therefore, the heterogeneous CPU-GPU scheme can utilize asynchronous computing features to offset the data transfer latency between different processors. Higher scalability and extensibility than GPU-only dynamic parallelism design is achieved by utilizing concurrent GPU streams for coarse-grid and fine-grid computation. A synthetic AC/DC grid based on IEEE-118 Bus and CIGRÉ DCS2 systems showed a good accuracy compared to commercial TSAT software, and a speedup of 165 is achieved with 48 IEEE-118 Bus systems and 192 201-Level detail-modeled MMCs. Furthermore, the proposed method is also applicable to multi-GPU implementation where it demonstrates decent efficacy. [ABSTRACT FROM AUTHOR]

Despite cascading failures being the central cause of blackouts in power transmission systems, existing operational and planning decisions are made largely by ignoring their underlying cascade potential. This paper posits a reliability-aware AC Optimal Power Flow formulation that seeks to design a dispatch point which has a low operator-specified likelihood of triggering a cascade starting from any single component outage. By exploiting a recently developed analytical model of the probability of component failure, our Failure Probability-constrained ACOPF (FP-ACOPF) utilizes the system’s expected first failure time as a smoothly tunable and interpretable signature of cascade risk. We use techniques from bilevel optimization and numerical linear algebra to efficiently formulate and solve the FP-ACOPF using off-the-shelf solvers. Extensive simulations on the IEEE 118-bus case show that, when compared to the unconstrained and N-1 security-constrained ACOPF, our probability-constrained dispatch points can significantly lower the probabilities of long severe cascades and of large demand losses, while incurring only minor increases in total generation costs. [ABSTRACT FROM AUTHOR]

Simultaneous vibration control and energy harvesting of vehicle suspensions have attracted significant research attention over the past decades. However, existing energy harvesting shock absorbers (EHSAs) compromise suspension performance for high-efficiency energy harvesting and being only responsive to narrow-bandwidth vibrations. In this paper, we propose a new ball-screw-based EHSA design – inerter pendulum vibration absorber (IPVA) – that integrates an electromagnetic rotary EHSA with a nonlinear pendulum vibration absorber.We show that this design simultaneously improves ride comfort and energy harvesting efficiency by exploiting the nonlinear effects of pendulum inertia. To further improve the performance, we develop a novel stochastic linearization model predictive control (SL-MPC) approach in which we employ stochastic linearization to approximate the nonlinear dynamics of EHSA that has superior accuracy compared to standard linearization. In particular, we develop a new stochastic linearization method with guaranteed stabilizability, which is a prerequisite for control designs. This leads to an MPC problem that is much more computationally efficient than the nonlinear MPC counterpart with no major performance degradation. Also, the effect of different road preview configurations on control performance is investigated, which is shown to have a significant impact on the control performance. Extensive simulations are performed to show the superiority of the proposed new nonlinear EHSA and to demonstrate the efficacy of the proposed SL-MPC. [ABSTRACT FROM AUTHOR]

In the power control process of the range extender, both the engine and the generator are at risk of reaching the torque output limit. The limitation not only comes from the restriction of their own torque output capacity, but also comes from the additional constraints that are established to avoid power reverse undershoot. In order to improve the system performance under time-varying torque constraints, a real-time model predictive controller (MPC) that manipulates the torque commands of the engine and the generator to track the reference power is designed. Different from the traditional penalty function method, the quadratic function is taken as the penalty function in this paper, which greatly improves the efficiency of solving the optimal solution. Meanwhile, the steady-state torque command in the feasible region is taken as the extreme point of the quadratic penalty function, which avoids the penalty coefficient tending to infinity. By adjusting the penalty coefficients of different constraints, the overall optimal solution approaches the boundary of the active inequality constraints. And according to the Karush-Kuhn-Tucker (KKT) condition, it is proved that the optimal solution of the original problem can be obtained through iteration. The effectiveness and practicability of the proposed strategy are evaluated through numerical simulations on Simulink and experiments on a range extender. [ABSTRACT FROM AUTHOR]

The air-cooled turbo-generator often works in the more frequent start-up and shut-down operation. Either the misoperation or the failure of synchronizing controllers can cause the out of phase synchronization fault. The fault can disturb the power angle and cause a strong impact electromagnetic force for the generator. With the traditional numerical calculation method, it is difficult to calculate the variations of key physical parameters and the electromagnetic field in the end region of the generator under complex working conditions, especially the out of phase synchronization fault. In order to solve the problem, a calculation method of the nonlinear transient electromagnetic field with multi-domain field-circuit-grid coupled is proposed. The correctness of the model and method is validated by comparing the calculated and test values of the magnetic density flux at the key points of the generator under the no-load condition. Based on this method, the power angle variation, the magnetic flux leakage distribution in the end region, and the electromagnetic force on the end winding in the transient process of the fault are calculated and analyzed. [ABSTRACT FROM AUTHOR]

Health monitoring of current complex systems significantly impacts the total cost of the system. Centralized fault diagnosis architectures are sometimes prohibitive for large-scale interconnected systems, such as distribution systems, telecommunication networks, water distribution networks, or fluid power systems. Confidentiality constraints are also an issue. This article presents a decentralized fault diagnosis method that only requires the knowledge of local models and limited knowledge of their neighboring subsystems. The method, implemented in the decentralized diagnoser design ($D^{3}$) algorithm, is based on structural analysis and can advantageously be applied to high-dimensional systems, linear or nonlinear. Using the concept of isolation on request, a hierarchy is built according to diagnostic objectives. The resulting diagnoser is based on analytical redundancy relations (ARRs) generated along the hierarchy. Their number is optimized via binary integer linear programming (BILP) while still guaranteeing maximal diagnosability at each level. $D^{3}$ proves of lower time complexity than its centralized equivalent. It is successfully applied to a nonlinear combined cycle gas-turbine power plant. [ABSTRACT FROM AUTHOR]

In this article, a sliding mode control (SMC) is applied to regulate the delivered power of a symmetrical six-phase induction generator. For this, the SMC strategy associated to the field-oriented control strategy is used in order to adjust the inner current loops of a squirrel cage six-phase induction generator (SC6PIG). In this way, the control algorithm switches between positive and negative feedback according to the position of the operating point in the phase plane. This technique guarantees the robustness of the SC6PIG in case of the loss of one to three stator phases or machine converter legs. The switching line slope and the initial operating point have been set so that the system starts with a negative feedback, then it continuously switches back and forth to positive feedback in order to maintain the desired trajectory of the system. The simulation and experimental results demonstrate the effectiveness and the robustness of this technique since the delivered power of the SC6PIG presents the same dynamics in healthy or faulty modes with one to two phase losses. [ABSTRACT FROM AUTHOR]

A linear and convex model has been recently presented for the operation of battery energy storage units that does not explicitly prevent their simultaneous charge and discharge in the problem formulation. This letter claims that the model in such a literature contribution is capable of ensuring the physical realizability of the battery dispatch only when nondiscrete decisions are considered in the optimization problem. This claim is demonstrated through the solution of two instances of a simple unit-commitment-based example comprising two generating units, one battery energy storage unit, and two time periods. [ABSTRACT FROM AUTHOR]

Convex hull pricing is a well-documented method for coping with the non-existence of uniform clearing prices in electricity markets with non-convex costs and constraints. We revisit primal and dual methods for computing convex hull prices, and discuss the positioning of existing approximation methods in this taxonomy. We propose a dual decomposition algorithm known as the Level Method and we adapt the basic algorithm to the specificities of convex hull pricing. We benchmark its performance against a column generation algorithm that has recently been proposed in the literature. We provide empirical evidence about the favorable performance of our algorithm on large test instances based on PJM and Central Europe. [ABSTRACT FROM AUTHOR]

of this work proposed a mathematical model and three types of solutions for conductive electrical tree growth in dielectrics. In this section, experiments are presented using a cone-plane electrode and nanosecond voltage pulses to investigate the electrical tree growth in polymethyl methacrylate (PMMA) samples. The results show that the tree length ${l}$ is proportional to the tangent of the pulse number ${N}$ under high-voltage pulses but ${l}$ approaches a limiting length under relatively low voltage pulses. These results agree with those predicted from the model. Therefore, the mathematical model for conductive electrical tree growth in dielectrics is verified. [ABSTRACT FROM AUTHOR]

In recent years, all-solid-state high-voltage pulse generators have been widely used in irreversible electroporation for tumor ablation technology. However, high voltage may cause the breakdown of loads that leads to short circuits. The short circuit of loads will generate high short-circuit currents that will affect the performance of semiconductor switches. To improve the reliability and lifetime of solid-state pulse generators, a passive synchronous isolated gate drive circuit with short-circuit protection based on decreasing the gate–source voltage is proposed in this article. To verify the overcurrent protection during the breakdown of loads, a solid-state Marx generator prototype using the drive circuit was built and tests were carried out. The experimental results show that the 205-A short-circuit current was clamped with 90 A in less than 500 ns, while the transient voltage can be neglected. Besides, the response time, the maximum transient voltage, and the maximum current amplitude can all be adjusted. [ABSTRACT FROM AUTHOR]

This work aims to improve the combined flow and thermal network (CFTN) accuracy for radially air-cooled generators by investigating the possible error stemming from the flow part. The nonlinear resistance characteristics of the T-junction dividing flow are first time considered for such cooling arrangement, which is achieved by employing the Gardel equations and the blend equation as the governing equations. Compared with the CFD model results as the benchmark, the nonlinear CFTN predicts an accurate flow rate in the radially extended airducts, making only 9% root mean square (rms) error for all the airducts. On the contrary, the linear CFTN fails to obtain a reliable flow distribution, as the rms error is as large as 34%. As a result, the nonlinear CFTN improves the accuracy of the maximum winding temperature by 6.4% over the linear CFTN and gives a more reasonable temperature gradient in the axial direction. Furthermore, the relative difference between the linear and nonlinear CFTNs is found to be even larger in the following conditions: large cooling air flow rate, wide airgap, low slot fill factor, and large airduct number. The proposed nonlinear CFTN modeling approach is also validated against experimental measurements for a prototype. The modeled temperatures match well with the measurements at different axial positions. According to the aforementioned findings, the nonlinear CFTN modeling approach is considered to be a reliable thermal analysis tool for the radial air-cooling arrangement. [ABSTRACT FROM AUTHOR]

In this study, a characteristic simulation method of a megawatt three-blade horizontal axis wind turbine (MW-THAWT) is proposed based on a laboratory kilowatt low-power motor system, which can realize the parameter correspondence and the rotational inertia compensation between the simulation platform and the wind turbine. First, the virtual proportional THAWT model of MW-THAWT is established to make the parameters of the motor and the wind turbine correspond. The control strategies of speed output and torque output are then designed to solve the problem that the conventional method cannot simulate the unstable region. The dynamic simulation strategy combining the shaft torque feedback rotational inertia compensation method and load characteristic simulation is proposed, which can ensure the consistency of the change time and mode between the simulation platform and the wind power system in the dynamic process. Finally, the MW-THAWT simulation experiment platform based on 1.4-KW motor is developed for theoretical verification. The experimental results verify that the proposed method can realize the characteristic simulation of static and dynamic of MW-THAWT in full speed range and is suitable for industrial production and laboratory research of wind turbine. [ABSTRACT FROM AUTHOR]

This letter proposes a data-driven sparse polynomial chaos expansion-based surrogate model for the stochastic economic dispatch problem considering uncertainty from wind power. The proposed method can provide accurate estimations for the statistical information (e.g., mean, variance, probability density function, and cumulative distribution function) for the stochastic economic dispatch solution efficiently without requiring the probability distributions of random inputs. Simulation studies on an integrated electricity and gas system (IEEE 118-bus system integrated with a 20-node gas system) are presented, demonstrating the efficiency and accuracy of the proposed method compared to the Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

This letter develops a mathematical model to distribute the under-frequency load shedding amount across the power system load points. The objective is to preserve the system operating point at post-contingency and after the load shedding as close as possible to that of pre-contingency. To do so, the total absolute change in line flows is sought to be minimized. Hence, the system security constraints satisfied before contingency occurrence are less vulnerable to violation. It is proven that when the number of credible contingencies exceeds load shedding candidates, an even distribution across the load points is optimal. [ABSTRACT FROM AUTHOR]