Search

High temperature superconducting (HTS) cable, with significant low dissipation and massive current carrying capability, is a promising solution for the shortage of transmission capacity in mega-cities. China Southern Grid launched a HTS cable project in 2017 to develop a medium voltage concentric HTS cable system for installation in the distribution grid at urban area in Shenzhen City. It is the first time that concentric HTS cable system is developed and will be the first HTS cable installed in urban grid in China. The cable core mainly consists of three concentric phases winded by YBCO tapes and cold dielectric insulations in between phase-to-phase, phase-to-former, and phase-to-screen. The cable has a rated voltage of 10 kV and a rated current of 2.5 kArms. The critical current ( $I_{c}$ ) is at least 6 kA per phase. The outline diameter of the cable core is 76 mm and the cryogenic pipe is 175 mm. As a middle step, we designed and manufactured a 30 m long prototype cable system and it was tested generally according to IEC 63075. For improvement of the manufacture processes, several short cable core samples were made, tested, and dismantled. The ultimate goal of the 30 m prototype is to verify the design and accumulate experience for the installation of the 400 m fully functional cable system in the grid. The test results of the 30 m cable prototype are presented and discussed. The 400 m class HTS concentric cable demonstration project has already started and it is expected to energize in grid in late September, 2021.

A two-mode resonant DC-DC converter is proposed in this paper. Through controlling the on/off state of the auxiliary switch, it can be flexibly converted between LLC mode and LLCC mode. In particular, the proposed converter works in LLC mode near the rated point. As the input voltage rises, it operates as an LLCC converter to acquire wide voltage gain range and over-current protection. The detailed characteristic comparisons are discussed, thus the optimal switching point is determined. Finally, experimental results demonstrate the rationality of the theoretical analysis.

It is benefit to connect different substations from the low voltage side by high temperature superconducting (HTS) cable to make full use of the remaining capacity of the transformer. Meanwhile, if necessary, the HTS cable can form an electromagnetic ring network with the original tie line to improve the power supply reliability. However, the short circuit fault at adjacent components of the HTS cable during closed loop operation may also cause the quench of the HTS cable, which brings difficulties to the protection of the HTS cable. Based on the actual project of HTS cable in Shenzhen Power Grid, this paper calculates the fault current flowing through the HTS cable in different operation modes. The parameter requirements of the resistance superconducting fault current limiter (RSFCL) are analyzed, and the design of the RSFCL is completed. The system with HTS cable and RSFCL was modeled in detail in Matlab software, and the effectiveness of the RSFCL design is verified.

The use of high temperature superconducting (HTS) cable as tie line between stations can effectively improve the reliability of distribution network. The access of HTS cable will inevitably affect the power flow of the system, thus the power system may not operate safely and economically. In an actual distribution network with HTS cable, this paper establishes distribution network model around the access point of HTS cable. The power flow under various operating modes of the distribution network is calculated. With the network loss and voltage deviation as the objective function, the discrete particle swarm optimization (DPSO) is used to optimize the power flow. Optimization is well implemented in the distribution network.

In this paper, based on a variable-structure multi-resonant DC-DC converter, a novel transient smooth control method is proposed. Through the introduction of the gradual control idea, a drive signal gradual adjustment method is discussed. Consequently, smooth switching between different modes is realized and the voltage fluctuation is suppressed effectively.

The paper summarizes the development and operation of the technical supporting systems in control centers and substations of China Southern Power Grid (CSG). Smart applications can be, based on functional integration and data sharing, developed for the operation of complicated power grids. A brand new conceptual model of next generation smart system, named Operation Smart System (OS2), is proposed. OS2 consists of the systems in all levels of control centers and substations of CSG, and the systems are linked with open and standardized service buses, called Operation Service Bus (OSB). The definition, principles, technical architecture, modules, and development of OS2 are discussed in detail.

Wide area protection based on phasor measurements have become more and more important research issue. A method is proposed for fast and accurate real time detection of transient instability based on the wide area measurements. Trajectory characteristic and transient energy are synthesized to improve the detection accuracy for complex power system. The relationship between trajectory characteristic and transient energy is deduced. Trajectory characteristic method is developed by utilization of curve fitting of angular velocity and reevaluation on dual-cluster identification. That avoids certain wrong identifications. The calculation of transient energy is introduced to analyze energy transformation, and a sub-criterion is presented. Simulations are carried out on the IEEE 39 bus system and China Southern Power Grid. The results indicate that the proposed method is effective and reliable in determining the loss of synchronism.

The weakly damped low frequency oscillation deteriorates the stability of some interconnected power systems. In order to suppress the swings more efficiently, the global dynamics of different areas are required, and then the synchrophasor measurement techniques are becoming necessary for real time and continuous control. In this paper, the design, implementation and commission of a coordinated wide-area adaptive damping control (WADC) system through the modulations of multiple HVDC links in China Southern Power Grid (CSG) are presented. Based on the calculations of observability and controllability, six phasor measurement units (PMU) and three HVDC links were chosen to be included in this system. The controllers were coordinated to damp two dominant inter-area oscillation modes. Another key issue for the wide-area control system is the random time delay and a solution using low-pass filter was proposed. Based on the improved online Prony identification, the controller parameters can be adapted according to the changes of the oscillation frequency. The above WADC were implemented and tested in the CSG real time digital simulations (RTDS) platform, which is composed of more than 10 racks of RTDS, real HVDC control and protection cubicles. After field debugging and trial operations, the WADC system was further validated in the practical CSG through artificial block and de-block of three different HVDC links and tripping a 500kV AC tie-line in the years of 2008 and 2009. The field test results show that the commission of WADC system can increase the damping ratio of the dominant modes more than 10%.

With the wide use of phasor measurement unit (PMU) and Wide Area Measurement System (WAMS), the transient instability real time prediction has been one of hot issues in power systems. The perturbed rotor angle trajectory prediction is a key step for transient instability prediction. The curve fitting based perturbed trajectory extrapolation methods had been paid widely attention since they do not need the knowledge of the network topology, model and parameters of power system and do not need network equivalence. Only a few post-fault measurements are required. The existed methods, such as the polynomial model, the trigonometric function model, the auto-regressive model and the angular velocity prediction & integration based method, are overviewed in this paper respectively. The experimental simulations on both IEEE 39-bus system and China Southern Power Grid are done to test the effectiveness of these models. An analysis and comparison is presented in terms of the fault condition, the sampling period, the number of the required measurements and the forecasting accuracy. The numerical results show that the polynomial model based prediction method has best effects for perturbed rotor angle trajectory prediction in terms of stability, rapidity and accuracy.

A novel curve fitting method based on the grey Verhulst model for perturbed trajectory prediction of post-fault rotor angle is presented in this paper. For avoiding self-error in the model, the unbiased grey model is realized. An error correction scheme is proposed for improving the prediction precision by using two new coming phasor measurements to predict the error. Compared with the trigonometric function and the auto regression model, the proposed method has better prediction effects. Numerical simulations are conducted in IEEE 39-bus system and the China Southern Power Grid to test the effectiveness of the proposed method. The results show that the modified grey Verhulst model works better than the original grey Verhulst model both for the stable and unstable cases.

With the wide application of PMU in power system, the real time prediction and emergency control of power system transient instability using the wide-area measurements has brought wide attention. There are two sub-problems: the postfault rotor-angle trajectory prediction and the real time transient instability detection. There are three categories for the former sub-problem. They are the network reduction based rotor-angle trajectory super-real time simulation, the curve-fitting based trajectory extrapolation and the angle speed prediction and integration methods. The curve-fitting based trajectory extrapolation includes the polynomial function, the auto regression model and the trigonometric function model. There are three types of criteria for the transient instability detection. They are the threshold-type criteria, the differentiation-type criteria and the integration-type criteria. The threshold-type criteria include the rotor angle threshold and the angle speed threshold and the post-fault voltage trajectory based criteria. The differentiation-type criteria include the trajectory concave and convex characteristics based criterion and the instability criterion based on the variation rate of energy function. The integration-type criterion mainly is the EEAC theory based instability criterion. A comprehensive comparison, analysis and reviews of the fundamental properties of these methods are presented in this paper.

Comprehensive urban passenger transportation hub is the place that passenger flows distribute and transfer. Shanghai south railway station is an important point in Shanghai. In this paper, related to the knowledge of a complex network, making the station as the object of study, the station will be built into the two kinds of networks and their complex characteristicwould be analyzed, and test the network survivability. The results show that t degree distribution of the station network is in line with power-lawdistribution. Then, making the average shortest path and clustering coefficient both for the evaluation criteria, through the network changes its properties by the chosen and randomly attack tomake the corresponding discussion of a complex network of fault-tolerance and anti-aggressive, and conclude relationship of the anti-aggressive with the network parameters change.

Comprehensive urban passenger transportation hub, be the key link of urban passenger transport system, and the intersection of the transport networks made up with different modes of transport, is the place that passenger flows distribute and transfer. Comprehensive urban passenger transportation hub can be abstracted as transfer passageways and hubs for the physical nodes in a network. In this paper, related to the knowledge of a complex network, making the city's comprehensive passenger transport hub as the object of study, according to the original law and the dual method, an integrated passenger transport hub will be built into the two kinds of networks and their complex characteristic would be analyzed. The results show that t degree distribution of the city's comprehensive passenger transport network is in line with power-law distribution. Thus we can tell that the network in the internal of the city’s comprehensive passenger transport hub is a scale-free complex network.

Micro turbine (MT) is the best choice for CCHP (Combined cooling, heating and power) system. As a kind of clean and high efficiency technology, it has a broad application prospect in China. Combining the dual mode MT with the important load as a MicroGrid can realize high-efficiency utilization of energy, exert the potential of MT as distributed generation, and enhance power supply reliability of important load. Aimed at the national 863 goal-oriented project “The key technology and demonstration project of grid-connecting issue for a MW level CCP distributed energy MicroGrid”, this paper detailed introduces the design experience of the CCP (Combined cooling and power) MicroGrid in the aspect of grid-connecting voltage, MT type choosing, MT capacity and grid-connecting mode.

Wide-area measurement system (WAMS) provides a platform for more efficient control, and some discontinuous types of wide-area control projects have been reported in commission in the recent years. In this paper, a continuous type of wide-area damping control system (WADCS) is introduced, which is used to suppress the inter-area oscillations in a complicated real power grid by modulating multiple HVDC links. The background of WADCS project is described. The design fundamentals and the implementation framework of WADCS are briefly summarized. The details of the field experiment items and some important test results are presented, which show that some new problems in wide-are control are successfully solved and WADCS can operate correctly in different conditions.

Adaptive damping controller is a challenging issue in the area of power system stability and control because of the difficulties in identification and design in real system. In this paper, a heuristic adaptive HVDC supplementary damping controller (AHDC) is designed based on online Prony analysis. Parameters of the controller are tuned according to the damping ratios of the weak-damped inter-area oscillation estimated by an improved Prony algorithm. The adaptive controller can achieve a desired damping effect without model-identification when the operating condition is changed. Numerical simulations of a real bulk power system and experimental results using real time digital simulator (RTDS) are presented to show its effectiveness. In the physical experiments, the adaptive controller is implemented by hardware, and phasor measurement unit (PMU) is also applied to acquire the selected feedback signal for a primary research of wide area damping control.

Low frequency oscillation is becoming a serious bottleneck limiting power system stability enhancement, especially in the conditions of interconnections of regional networks. Because of the global properties, most of the units are involved in this problem. The controllers of these devices must be designed coordinately. In this paper, an optimal controller design approach is proposed for the applications in large scale power system. A special injection signal is used to excite the dynamics in certain frequency range, and then prediction error method (PEM) is employed to identify the reduced order system based on multiple inputs and outputs. Traditional optimal control techniques are improved to include the lead-lag blocks, so the popular supplementary damping controllers are compatible. Finally, this approach is applied in the design of two HVDC modulation controllers in China Southern Grid, and the results demonstrate the advantages.

Many applications use classification models on streaming data to detect actionable alerts. Due to concept drifts in the underlying data, how to maintain a model's up-to-dateness has become one of the most challenging tasks in mining data streams. State of the art approaches, including both the incrementally updated classifiers and the ensemble classifiers, have proved that model update is a very costly process. In this paper, we introduce the concept of model granularity. We show that reducing model granularity will reduce model update cost. Indeed, models of fine granularity enable us to efficiently pinpoint local components in the model that are affected by the concept drift. It also enables us to derive new components that can easily integrate with the model to reflect the current data distribution, thus avoiding expensive updates on a global scale. Experiments on real and synthetic data show that our approach is able to maintain good prediction accuracy at a fraction of model updating cost of state of the art approaches.

This paper is concerned with large scale, interconnected, AC/DC transmission network of a power system. As the system grid becomes larger and power demand becomes higher, low frequency oscillation has become the primary concern of power system stability. High voltage direct current (HVDC) modulation control is a traditional means of damping the low frequency swing. However, for multi-infeed system, the interactions and correlations among multiple HVDC links have made the stabilizing controller design more challenging. The current approach to controller design, which only takes into consideration of a single transmission link, is not sufficient to cope with the complex network topology, and the stringent stabilization requirement of a system operating close to its limit. In this paper, a coordinated control framework using an approximate dynamic programming (ADP) technique is proposed based on wide-area measurement system (WAMS). Since real-time system responses are available through WAMS, the parameters of different controllers can be adjusted online to optimize one common objective function that reflects the system stability as a whole instead of just one single transmission link. The paper will include a design procedure on how ADP can be applied. The performance of this coordinated control approach using the proposed ADP is validated in a real system, namely the China Southern Grid