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Open Access Full Length Article Issue
Integral precession calibration method of PIGA on linear vibration table
Chinese Journal of Aeronautics 2024, 37(3): 219-236
Published: 21 October 2023
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Linear vibration table can provide harmonic accelerations to excite the nonlinear error terms of Pendulous Integrating Gyro Accelerometer (PIGA). Integral precession calibration method is proposed to calibrate PIGA on a linear vibration table in this paper. Based on the precise expressions of PIGA’s inputs, the error calibration model of PIGA is established. Precession angular velocity errors of PIGA are suppressed by integer periodic precession and the errors caused by non-integer periods vibrating are compensated. The complete calibration process, including planning, preparation, PIGA testing, and coefficient identification, is designed to optimize the test operations and evaluate the calibration results. The effect of the main errors on calibration uncertainty is analyzed and the relative sensitivity function is proposed to further optimize the test positions. Experimental and simulation results verify that the proposed 10-position calibration method can improve calibration uncertainties after compensating for the related errors. The order of calibration uncertainties of the second- and third-order coefficients are decreased to 10−8 (rad·s−1)/g2 and 10−8 (rad·s−1)/g3, respectively. Compared with the other two classical calibration methods, the calibration uncertainties of PIGA’s nonlinear error coefficients can be effectively reduced and the proportional residual errors are decreased less than 3 × 10−6 (rad·s−1)/g by using the proposed calibration method.

Issue
Collaborative optimization strategy of information and energy for distributed data centers
Journal of Tsinghua University (Science and Technology) 2022, 62(12): 1864-1874
Published: 15 December 2022
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Downloads:5

With the continuous expansion of data centers, the problem of large energy consumption has become increasingly prominent. Distributed data centers can enable power transfer through the distribution of computing tasks among multiple data centers and realize the balance between power consumption and computing delay through the power control of a single data center. Scheduling of computing tasks and power control of data center interact with each other, and their control effects are affected by multiple uncertainties. Therefore, a fast and reliable control method is required for realizing the collaborative optimization of the information and energy layers of the data center. First, a distributed data center collaborative optimization architecture is constructed. Then, the dynamic characteristics of multiple data center computing task allocation and single data center power optimization are analyzed based on the dynamic differential equation, and a unified adjustment model of the coupling optimization problem is constructed. Given the system operating cost and computing delay in constructing the objective function, the optimal control theory is introduced to solve the problem and realize the second-level collaborative optimal control of the information energy of the data center. Simulation results show that the high-frequency control based on the proposed algorithm can better track the fluctuation of renewable energy output and calculation tasks than the minute-level control and effectively improve the economic benefits of the system and the local consumption rate of renewable energy.

Open Access Regular Paper Issue
Consensus-based Optimal Control Strategy for Multi-microgrid Systems with Battery Degradation Consideration
CSEE Journal of Power and Energy Systems 2024, 10(5): 1911-1924
Published: 18 August 2022
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Downloads:5

Consensus has been widely used in distributed control, where distributed individuals need to share their states with their neighbors through communication links to achieve a common goal. However, the objectives of existing consensus-based control strategies for energy systems seldom address battery degradation cost, which is an important performance indicator to assess the performance and sustainability of battery energy storage (BES) systems. In this paper, we propose a consensus-based optimal control strategy for multi-microgrid systems, aiming at multiple control objectives including minimizing battery degradation cost. Distributed consensus is used to synchronize the ratio of BES output power to BES state-of-charge (SoC) among all microgrids while each microgrid is trying to reach its individual optimality. In order to reduce the pressure of communication links and prevent excessive exposure of local information, this ratio is the only state variable shared between microgrids. Since our complex nonlinear problem might be difficult to solve by traditional methods, we design a compressive sensing-based gradient descent (CSGD) method to solve the control problem. Numerical simulation results show that our control strategy results in a 74.24% reduction in battery degradation cost on average compared to the control method without considering battery degradation. In addition, the compressive sensing method causes an 89.12% reduction in computation time cost compared to the traditional Monte Carlo (MC) method in solving the control problem.

Open Access Issue
Improved Approximate Minimum Degree Ordering Method and Its Application for Electrical Power Network Analysis and Computation
Tsinghua Science and Technology 2021, 26(4): 464-474
Published: 04 January 2021
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Downloads:65

Electrical power network analysis and computation play an important role in the planning and operation of the power grid, and they are modeled mathematically as differential equations and network algebraic equations. The direct method based on Gaussian elimination theory can obtain analytical results. Two factors affect computing efficiency: the number of nonzero element fillings and the length of elimination tree. This article constructs mapping correspondence between eliminated tree nodes and quotient graph nodes through graph and quotient graph theories. The Approximate Minimum Degree (AMD) of quotient graph nodes and the length of the elimination tree nodes are composed to build an Approximate Minimum Degree and Minimum Length (AMDML) model. The quotient graph node with the minimum degree, which is also the minimum length of elimination tree node, is selected as the next ordering vector. Compared with AMD ordering method and other common methods, the proposed method further reduces the length of elimination tree without increasing the number of nonzero fillings; the length was decreased by about 10% compared with the AMD method. A testbed for experiment was built. The efficiency of the proposed method was evaluated based on different sizes of coefficient matrices of power flow cases.

Open Access Issue
On the Mathematical Nature of Wireless Broadcast Trees
Tsinghua Science and Technology 2018, 23(3): 223-232
Published: 02 July 2018
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Downloads:36

Trees are arguably one of the most important data structures widely used in information theory and computing science. Different numbers of intermediate nodes in wireless broadcast trees may exert great impacts on the energy consumption of individual nodes, which are typically equipped with a limited power supply in a wireless sensor network; this limitation may eventually determine how long the given wireless sensor network can last. Thus, obtaining a deep understanding of the mathematical nature of wireless broadcast trees is of great importance. In this paper, we give new proof of Cayley’s well-known theorem for counting labeled trees. A distinct feature of this proof is that we purely use combinatorial structures instead of constructing a bijection between two kinds of labeled trees, which is in contrast to all existing proofs. Another contribution of this work is the presentation of a new theorem on trees based on the number of intermediate nodes in the tree. To the best of our knowledge, this work is the first to present a tree enumeration theorem based on the number of intermediate nodes in the tree.

Open Access Issue
Distributed Energy Sharing in Energy Internet Through Distributed Averaging
Tsinghua Science and Technology 2018, 23(3): 233-242
Published: 02 July 2018
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Downloads:17

This paper proposes a distributed averaging iteration algorithm for energy sharing in microgrids of Energy Internet based on common gossip algorithms. This algorithm is completely distributed and only requires communi-cations between neighbors. Through this algorithm, the Energy Internet not only allocates the energy effectively based on the load condition of grids, but also reasonably schedules the energy transmitted between neighboring grids. This study applies theoretical analysis to discuss the condition in which this algorithm can finally reach supply-and-demand balance. Subsequently, the related simulation validates the performance of the algorithm under various conditions.

Open Access Issue
COMBAT: A New Bitmap Index Coding Algorithm for Big Data
Tsinghua Science and Technology 2016, 21(2): 136-145
Published: 31 March 2016
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Downloads:21

Bitmap indexing has been widely used in various applications due to its speed in bitwise operations. However, it can consume large amounts of memory. To solve this problem, various bitmap coding algorithms have been proposed. In this paper, we present COMbining Binary And Ternary encoding (COMBAT), a new bitmap index coding algorithm. Typical algorithms derived from Word Aligned Hybrid (WAH) are COMPressed Adaptive indeX (COMPAX) and Compressed “n” Composable Integer Set (CONCISE), which can combine either two or three continuous words after WAH encoding. COMBAT combines both mechanisms and results in more compact bitmap indexes. Moreover, querying time of COMBAT can be faster than that of COMPAX and CONCISE, since bitmap indexes are smaller and it would take less time to load them into memory. To prove the advantages of COMBAT, we extend a theoretical analysis model proposed by our group, which is composed of the analysis of various possible bitmap indexes. Some experimental results based on real data are also provided, which show COMBAT’s storage and speed superiority. Our results demonstrate the advantages of COMBAT and codeword statistics are provided to solidify the proof.

Open Access Issue
An Integrated Cyber-Physical Simulation Environment for Smart Grid Applications
Tsinghua Science and Technology 2014, 19(2): 133-143
Published: 15 April 2014
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Downloads:16

The concept of Cyber-Physical Systems (CPSs), which combine computation, networking, and physical processes, is considered to be beneficial to smart grid applications. This study presents an integrated simulation environment to provide a unified platform for the investigation of smart grid applications involving power grid monitoring, communication, and control. In contrast to the existing approaches, this environment allows the network simulator to operate independently, importing its results to the power system simulation. This resolves conflicts between discrete event simulation and continuous simulation. In addition, several data compensation methods are proposed and investigated under different network delay conditions. A case study of wide-area monitoring and control is provided, and the efficiency of the proposed simulation framework has been evaluated based on the experimental results.

Open Access Issue
Electricity Services Based Dependability Model of Power Grid Communication Networking
Tsinghua Science and Technology 2014, 19(2): 121-132
Published: 15 April 2014
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Downloads:22

The technology of Ultra-High Voltage (UHV) transmission requires higher dependability for electric power grid. Power Grid Communication Networking (PGCN), the fundamental information infrastructure, severs data transmission including control signal, protection signal, and common data services. Dependability is the necessary requirement to ensure services timely and accurately. Dependability analysis aims to predicate operation status and provide suitable strategies getting rid of the potential dangers. Due to the dependability of PGCN may be affected by external environment, devices quality, implementation strategies, and so on, the scale explosion and the structure complexity make the PGCN’s dependability much challenging. In this paper, with the observation of interdependency between power grid and PGCN, we propose an electricity services based dependability analysis model of PGCN. The model includes methods of analyzing its dependability and procedures of designing the dependable strategies. We respectively discuss the deterministic analysis method based on matrix analysis and stochastic analysis model based on stochastic Petri nets.

Open Access Issue
Collaborative Network Security in Multi-Tenant Data Center for Cloud Computing
Tsinghua Science and Technology 2014, 19(1): 82-94
Published: 07 February 2014
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Downloads:79

A data center is an infrastructure that supports Internet service. Cloud computing is rapidly changing the face of the Internet service infrastructure, enabling even small organizations to quickly build Web and mobile applications for millions of users by taking advantage of the scale and flexibility of shared physical infrastructures provided by cloud computing. In this scenario, multiple tenants save their data and applications in shared data centers, blurring the network boundaries between each tenant in the cloud. In addition, different tenants have different security requirements, while different security policies are necessary for different tenants. Network virtualization is used to meet a diverse set of tenant-specific requirements with the underlying physical network, enabling multi-tenant datacenters to automatically address a large and diverse set of tenants requirements. In this paper, we propose the system implementation of vCNSMS, a collaborative network security prototype system used in a multi-tenant data center. We demonstrate vCNSMS with a centralized collaborative scheme and deep packet inspection with an open source UTM system. A security level based protection policy is proposed for simplifying the security rule management for vCNSMS. Different security levels have different packet inspection schemes and are enforced with different security plugins. A smart packet verdict scheme is also integrated into vCNSMS for intelligence flow processing to protect from possible network attacks inside a data center network.

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