High wind energy curtailment during winter and early spring in north China has drawn widespread concern in recent years, which, at source, results from the incongruous planning between wind power development and other generation expansion. However, the scenarios obtained by traditional planning method without considering the seasonal heat supply constraints are far from the actual operation stage. More difficulty lies in the lack of sequential data of wind power and load demand in planning stage. A nonsequential probabilistic production simulation model is proposed to evaluate the wind energy curtailment during the heat supply period, which only needs the input data of the cumulative probability function (CDF) and/or probability density function (PDF) of heat demand, electricity demand, and wind power. Then an algorithm based on the equivalent joint energy function and minimal power-heat ratio method is applied to solve the model. The simulations have been performed based on the actual data of a large wind power zone in north China. Comparing with the previous sequential simulation method, the precision of the proposed method is satisfactory and the calculation time is dramatically reduced.

The uncertainty of wind/photovoltaics (PV) power generation and load fluctuations highlight the urgent need for flexible yet stable power resources. With the increasing in the share of renewable energy, the fluctuation presents a trend toward the longer periods, larger amplitudes, and more drastic changes. Therefore, research on the long duration flexible resource planning for the scenarios of the ultra high share of renewable power system (UHRPS) has become the focus. In this work, the main structural and operating characteristics of UHRPS are introduced and analyzed, which is followed by the flexibility requirements and flexibility planning challenges of UHRPS scenarios. Then, the current research trends in flexibility planning schemes of renewable energy power systems are reviewed. Finally, the key problems and solutions for research on the long duration flexibility resource planning of UHRPS are proposed.

With the increasing penetration of renewable resources and the DC nature loads, voltage source converter (VSC) based DC distribution systems take an important position in the future smart grid architecture due to many distinguishing features. However, DC distribution systems face frequent power disturbances and multi-mode swithcing problem, how to achieve better DC voltage control and reasonable power sharing performance under various disturbances is still a challenge. After analyzing the control structure and master-slave (M-S) method, an equal loading rate based M-S method is proposed based on the power sharing capability of the VSC station. Moreover, error analysis of the proposed M-S method is conducted and a correction method for the proposed M-S method is developed. The proposed M-S method not only preserves the advantage of M-S method, but also changes the power instructions accordingly based on the operation state of the whole DC distribution system. Moreover, the proposed M-S method is simple and easy to implement. Lastly, simulations of a three-terminal VSC based DC distribution system are conducted in PSCAD/EMTDC to validate the effectiveness of the proposed M-S method.

The joint bidiagonalization (JBD) method has been used to compute some extreme generalized singular values and vectors of a large regular matrix pair [Formula: see text]. We make a numerical analysis of the underlying JBD process and establish relationships between it and two mathematically equivalent Lanczos bidiagonalizations in finite precision. Based on the results of numerical analysis, we investigate the convergence of the approximate generalized singular values and vectors of [Formula: see text]. The results show that, under some mild conditions, the semiorthogonality of Lanczos-type vectors suffices to deliver approximate generalized singular values with the same accuracy as the full orthogonality does, meaning that it is only necessary to seek for efficient semiorthogonalization strategies for the JBD process. We establish a sharp bound for the residual norm of an approximate generalized singular value and corresponding approximate right generalized singular vectors, which can reliably estimate the residual norm without explicitly computing the approximate right generalized singular vectors before the convergence occurs.

The joint bidiagonalization (JBD) process is a useful algorithm for the computation of the generalized singular value decomposition (GSVD) of a matrix pair. However, it always suffers from rounding errors, which causes the Lanczos vectors to lose their mutual orthogonality. In order to maintain some level of orthogonality, we present a semiorthogonalization strategy. Our rounding error analysis shows that the JBD process with the semiorthogonalization strategy can ensure that the convergence of the computed quantities is not affected by rounding errors and the final accuracy is high enough. Based on the semiorthogonalization strategy, we develop the joint bidiagonalization process with partial reorthogonalization (JBDPRO). In the JBDPRO algorithm, reorthogonalizations occur only when necessary, which saves a big amount of reorthogonalization work, compared with the full reorthogonalization strategy. Numerical experiments illustrate our theory and algorithm.

Voltage transient disturbance is one of the key voltage quality disturbances, which can be classified into oscillatory transient and impulsive transient. Currently, there is no simple, accurate and general method to detect, extract, and characterize the voltage transient disturbance. This paper proposes a time-domain voltage transient disturbance detection method based on the RMS (root mean square) values of segmented differential waveforms. Firstly, the abnormal voltage waveforms are detected and extracted, which will be used for further analysis. Secondly, the extracted abnormal voltage waveform data are pre-processed, and then each power frequency cycle are processed in segment. Thirdly, by considering the influence of the system frequency variation, the differential waveform can be obtained by calculating the difference between two consecutive cycles. Finally, the voltage transient disturbance is detected by calculating and comparing the segmented RMS values of differential waveforms and steady-state waveforms. The transient component is extracted as well. Four indicators, i.e., dominant frequency, polarity, magnitude and duration, are used to characterize the voltage transient disturbance. In order to verify the accuracy and feasibility of the proposed method, both simulated data from an improved IEEE-13 node test system and actual voltage transient signal from a laboratory experiment are used.