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Renewable energy is an advisable choice to reduce fuel consumption and $\rm CO_{2}$ emission. Therein, wind energy and solar energy are the most promising contributors to reach this goal. Although the hybrid wind/solar system has been widely studied, the real-time current sharing based on their maximum capacities is rarely achieved in terms of seconds. Based on this, this paper proposes an accurate current sharing and voltage regulation approach in hybrid wind/solar systems, which is based on distributed adaptive dynamic programming approach. Firstly, the equivalent wind/solar model is built, which is an indispensable preprocessing to achieve the complementary between wind energy and solar energy. Therein, the wind energy and solar energy can output relative current according to their respective capacity ratio, which ensure the maximum utilization ratio of renewable energy source. Furthermore, current sharing and voltage regulation problem is switched into optimal control problem. Under this effect, each source agent aims to obtain the optimal control variable and achieve accurate current sharing/voltage regulation. Moreover, an adaptive dynamic programming approach based on Bellman principle is proposed. It can achieve accurate current sharing and voltage regulation. Finally, the simulation results are provided to illustrate the performance of the proposed adaptive dynamic programming approach. [ABSTRACT FROM AUTHOR]

In the face of extreme events, e.g., hurricanes, the transmission systems, especially the transmission lines, are affected across time and space. To mitigate these impacts on the day-ahead market from a probabilistic perspective, a resilient unit commitment (UC) problem is formulated as a two-stage distributionally robust and robust optimization (DR&RO) problem. In the first stage, the commitment, energy, and reserves of generators are pre-scheduled to minimize the operational cost, responding to the worst load forecasting and line failure scenario in the operating day. The operating status of transmission lines are depicted by a novel uncertainty set with a distributionally chance constraint considering the repair of failed lines. This chance constraint is reformulated to its deterministic equivalence. Using both load shedding and generation curtailment, recourse problems are formulated in the second stage considering the time-varying operating status of transmission lines. The formulated DR&RO problem is solved using a hybrid Benders decomposition and column-and-constraint generation scheme. Simulations are conducted on the modified IEEE reliability test system (RTS) and two-area IEEE RTS-96 under hurricanes. Results verify the effectiveness of the proposed method, in comparison with prevalent two-stage stochastic and robust optimization methods. [ABSTRACT FROM AUTHOR]

Due to the geographic features and fruitful water resources, the distributed generation of Small Hydropower Generator Stack (SHGS) are vigorously developed in southwest China. As the more concerns about security and stability of power grids with the large amount of SHGS feed into the grid, the accurate models are critical to analyze those potential impacts. With the development of online monitoring technologies in smart grid, PMU based dynamic equivalent modeling for SHGS drawn many attentions. However, field applications reveal that traditional SHGS equivalent model may not be robustness enough to adapt the different disturbances. To overcome this deficiency, method to improve the robustness of SHGS dynamic equivalent modeling is proposed. In the paper, a coherency identification based multi-machine modeling method is introduced to enhance the accuracy of equivalent model. Sensitivity and correlation analysis based key parameters selection scheme is implemented to select the critical parameters, meanwhile avoiding the multiple solutions problem. Moreover, multi-objective optimization algorithm is designed for key parameters identification of the equivalent model. Additionally, hybrid dynamic simulation has adopted into the equivalent process to improve the computational efficiency. The effectiveness of the proposed method has been validated with an actual case from China Southwest grids. [ABSTRACT FROM AUTHOR]

The Newton-Raphson (NR) method is a powerful tool in nonlinear equations. However, a well-known disadvantage of this method is that the initial iteration value must be chosen sufficiently close to a true solution in order to guarantee its convergence. The Kantorovich theorem is virtually the only known sufficiency condition for convergence of NR method, and gives very conservative bounds. This letter analyzes the convergence of the NR method in feasible power-flow for direct-current (DC) network, and an explicit convergence condition is obtained. Comparing with the existing results, the proposed convergence condition is more concise and less conservative. Moreover, according to the proposed condition, one can easily set the initial iteration value to guarantee the convergence of the NR method. Case studies verify the correctness of the presented analysis. [ABSTRACT FROM AUTHOR]

Due to the maturity of wide area measurement technology, phasor measurement unit (PMU)-based dynamic equivalent modeling method (PDM) has been wildly used in large-scale power system modeling. However, traditional “event-based” PDM equivalent model may face serious robustness issues, such as although derived equivalent models show the good ability on reproduction of the system behaviors under recorded events where they derived from, they may not work well for other possible disturbances. In this article, to improve the robustness of equivalent model, a novel method on dynamic equivalent modeling of power system is proposed. Based on the result of coherency identification, generators inside the equivalent system can be aggregated into different coherent subgroups and represented by multimachine equivalent model. Key parameter selection, which can shrink the scale of identified parameters, is designed to avoid multiple solutions of the equivalent model. Moreover, a multiobjective parameter identification algorithm is developed to fully consider the PMU measurements in different system events. In addition, hybrid dynamic simulation is performed so that each equivalent submodel can be identified separately. Finally, the effectiveness of the proposed method is verified in an actual power grids in China. [ABSTRACT FROM AUTHOR]

A novel thermal infrared pedestrian segmentation algorithm based on conditional generative adversarial network (IPS-cGAN) is proposed for intelligent vehicular applications. The convolution backbone architecture of the generator is based on the improved U-Net with residual blocks for well utilizing regional semantic information. Moreover, cross entropy loss for segmentation is introduced as the condition for the generator. SandwichNet, a novel convolutional network with symmetrical input, is proposed as the discriminator for real–fake segmented images. Based on the c-GAN framework, good segmentation performance could be achieved for thermal infrared pedestrians. Compared to some supervised and unsupervised segmentation algorithms, the proposed algorithm achieves higher accuracy with better robustness, especially for complex scenes. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) generators have continuously increased in recent years, whose power is usually controlled through the perturbation and observation (P&O) method. In essence, the P&O method is nonlinear and discontinuous. Hence, the conventional small-signal stability analysis is not suitable anymore when the influence of the P&O-based power control is considered. Focusing on this problem, this paper adopts the nonlinear describing function (DF) method to conduct the accurate stability analysis of PV generators with consideration of P&O-based power control. The detailed procedures about the DF method are introduced, and then the related influence factors like perturbation size, filters, and so on are analyzed quantitatively. Furthermore, the comparison with the conventional stability analysis methods is made, which suggests that the DF method can effectively enhance the accuracy of the stability analysis. All the conclusions are verified by the real-time hardware-in-loop tests. [ABSTRACT FROM AUTHOR]

Dealing with electrical rotating machines fed by voltage converters, understanding the effect of impulsive voltage parameters on partial discharge features is of great importance to select appropriate impulsive voltage to perform partial discharge inception voltage measurements. Similarly, the dependence of insulation endurance on voltage parameters might help to develop qualification tests providing more accurate evaluation of insulation performance. The effect of voltage duty cycle on partial discharge characteristics and endurance of inverter-fed motor insulation were investigated through a large number of tests performed on single-contact crossed enameled wires under bipolar repetitive impulse wave voltages. The partial discharge pattern, magnitude, repetition rate show that short impulsive voltage duration (i.e. small duty cycles), can induce asymmetric PD patterns and reduce the probability of PD inception at the falling flanks of impulsive voltages. Moreover, the endurance tests indicate that the duty cycle of the repetitive square wave voltage can affect the insulation endurance significantly. Repetitive square wave voltages with small duty cycles tend to overestimate endurance. Accordingly, when performing partial discharge inception voltage and endurance tests on insulation of inverter-fed motors, the influence of duty cycle should be carefully considered. [ABSTRACT FROM AUTHOR]

To ensure insulation system reliability of rotating machines driven by power electronics, accelerated tests under repetitive impulsive voltages should be performed on turn-to-turn insulation according to the standards provided by the International Electrotechnical Commission. The parameters of repetitive impulsive voltage can significantly influence insulation lifetime, and thus, voltage parameters should be carefully controlled during the accelerated tests. To increase endurance test efficiency when testing many insulation specimens in parallel, the rise time of impulsive voltage should be controlled at certain constant values after the breakdown of one or more specimens to obtain objective endurance test results. This study provides a description of a novel square wave voltage generator used for the insulation evaluation of rotating machines driven by power electronics. A single-channel generator with variable rise times used for one specimen and a multi-channel generator with a constant rise time used to test five specimens in parallel are presented based on a push-pull solid-state switch. In the multi-channel generator, the RC parameter of the high-voltage circuit can be adjusted automatically by resorting to controlling units and a circuit structure after the breakdown of one or more samples when performing endurance tests on parallel specimens to keep the rise time of impulsive voltage at constant values. The multi-channel generator can significantly increase the endurance evaluation efficiency of the insulation systems of rotating machines fed by power electronics. [ABSTRACT FROM AUTHOR]

With high renewable power penetration, uncertainty and intermittence of renewable sources become major concerns of power system planning and operation. Large and fast wind speed change may cause great variation of active power generation, which may lead to system stability and reliability problems. The response speeds of the committed conventional generators (CGs) for frequency regulations are critical for system reliable and stable operation. The slow response of the committed CGs may result in power shortage or surplus, which may affect system frequency. This paper proposes a technique to evaluate operational reliability and efficiency problems of power systems with high wind power penetration from frequency aspect. Energy unnecessarily consumed and less supplied during system frequency control processes are modeled in detail. The reliability and economic indexes are formulated with considering system dynamic frequency control processes. The IEEE-RTS79 is used to verify the proposed models and method. [ABSTRACT FROM AUTHOR]

This paper presents two linear power sharing schemes for distributed generators (DGs). The purpose is to reduce the total generation cost (TGC) of the considered autonomous microgrid. The saving in cost is realized by tuning the DG droop gradients in accordance to their respective maximum or mean generation costs. Compared with the existing nonlinear cost-based schemes, the proposed schemes use linear droop functions, which are easier to tune and implement in practice for a greater reduction in TGC. The proposed schemes have been tested experimentally with an example microgrid powered first by dispatchable DGs only, and then by a combination of dispatchable and nondispatchable DGs. Experimental results obtained have demonstrated the anticipated outcomes under different operating conditions. [ABSTRACT FROM AUTHOR]

To address the reliability of rotating machine insulation, the International Electrotechnical Commission implemented new standards and technical specifications that are relevant to low-voltage and medium-voltage inverter-fed motors. Insulation evaluation under such power supply relies upon partial discharge (PD) measurements and accelerated life tests, which should be conducted (at least for the turn-to-turn insulation) under impulsive voltage waveform. The effect of impulsive voltage parameters on PD inception voltage and, in particular, endurance tests must be investigated to design test procedures that can indicate insulation quality and its behavior in service. This paper examines the effect of repetitive impulsive voltage waveform parameters on PD and the endurance (life) of organic insulation for rotating machine wires based on experiments performed on single-contact crossed pairs. Results show that the features of repetitive voltage impulse affect PD time and frequency characteristics, PD phase distribution, and endurance. Consequently, evaluation of insulation subjected to power electronics waveforms should take into account the appropriate choice of impulsive voltage parameter to fit to the type of PD phenomenology occurring in service conditions. [ABSTRACT FROM PUBLISHER]

Droop schemes have traditionally been applied to the control of parallel synchronous generators in power systems. It has subsequently been brought over to the control of distributed generators (DGs) in microgrids with the same retained objective of proportional power sharing based on ratings. This objective might, however, not suit microgrids well since DGs are usually of different types, unlike synchronous generators. Other factors like cost, efficiency, and emission penalty of each DG at different loading must be considered since they contribute directly to the total generation cost (TGC) of the microgrid. To reduce this TGC without relying on fast communication links, an autonomous droop scheme is proposed here, whose resulting power sharing is decided by the individual DG generation costs. Comparing it with the traditional scheme, the proposed scheme retains its simplicity and it is hence more likely to be accepted by the industry. The reduction in TGC has been verified by experiment. [ABSTRACT FROM PUBLISHER]

The deregulation of power systems allows customers to participate in power market operation. In deregulated power systems, nodal price and nodal reliability are adopted to represent locational operation cost and reliability performance. Since contingency reserve (CR) plays an important role in reliable operation, the CR commitment should be considered in operational reliability analysis. In this paper, a CR model based on customer reliability requirements has been formulated and integrated into power market settlement. A two-step market clearing process has been proposed to determine generation and CR allocation. Customers' nodal unit commitment risk and nodal energy interruption have been evaluated through contingency analysis. Customers' reliability cost including reserve service cost and energy interruption cost have also been evaluated. [ABSTRACT FROM PUBLISHER]

With high wind-power penetration, power-system operators require accurate wind-power output from wind farms for system operation. A more accurate four-dimension wind speed model is proposed in this paper to simulate the effects of terrain and time delay of wind speed. Two coordinate transformation matrices are proposed to easily incorporate wind direction in wind-speed simulation. The effects of random failures and wake of wind turbine generators on wind-speed distribution in a wind farm are also considered in the proposed model. A sequential Monte Carlo simulation technique is developed to evaluate adequacy of power systems with wind farms using the proposed model. The modified IEEE RTS is analyzed to illustrate the models and technique. The simulation results show that those factors have significant impact on power output of a wind farm and system reliability. [ABSTRACT FROM PUBLISHER]

This paper focuses on the influence of repetitive square wave voltage rise time on partial discharge pulse characteristics in the ultra-high frequency range. Paerial Discharge (PD) tests on single-point contact crossed pairs were carried out using repetitive square wave voltages with a wide range of rise times, from 200 ns to 400 μs, including also 50 Hz sinusoidal voltage waveforms. Experimental results show that rise time has a significant influence on magnitude and frequency spectrum of PD pulses. Voltages of shorter rise times generate larger PD pulses with a predominance of high frequency components in the energy spectrum. Interpretations are presented for this phenomenon. [ABSTRACT FROM AUTHOR]

Reactive power plays a significant role in power system operation. However, in reliability evaluation, attention has seldom been paid to reactive power. In conventional power system reliability evaluations, the fixed maximum and minimum values are applied as the reactive power limits of generators. Failures of reactive power sources are rarely considered. The detailed causes of network violations for a contingency are also seldom studied. Real power load shedding is usually used to alleviate network violations without considering the role of reactive power. There are no corresponding reliability indices defined to represent the reactive power shortage in the existing techniques. Reactive power shortage and the associated voltage violations due to the failures of reactive power sources are considered in this paper. New reliability indices are proposed to represent the effect of reactive power shortage on system reliability. The reliability indices due to reactive power shortages have been defined and are separated with those due to real power shortages. Reactive power limits determined by real power output of a generator using P-Q curve have been studied. A reactive power injection technique is proposed to determine possible reactive power shortage and location. The IEEE 30-bus system has been modified and analyzed to illustrate the proposed technique. The results provide system planners and operators very important information for real and reactive power management. [ABSTRACT FROM AUTHOR]