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Hongbin Sun

Publications and source records attributed to Hongbin Sun.

At least 127 records · Page 7Linked to original sources
arXiv2018

NonLERFness of arithmetic hyperbolic manifold groups and mixed 3-manifold groups

We will show that, for any noncompact arithmetic hyperbolic $m$-manifold with $m> 3$, and any compact arithmetic hyperbolic $m$-manifold with $m> 4$ that is not a $7$-dimensional arithmetic hyperbolic manifold defined by octonions, its fundamental group is not LERF. The main ingredient in the proof is a study on abelian amalgamations of hyperbolic $3$-manifold groups. We will also show that a compact orientable irreducible $3$-manifold with empty or tori boundary supports a geometric structure if and only if its fundamental group is LERF.

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arXiv2018

A characterization on separable subgroups of 3-manifold groups

In this paper, we give a complete characterization on which finitely generated subgroups of finitely generated $3$-manifold groups are separable. Our characterization generalizes Liu's spirality character on $π_1$-injective immersed surface subgroups of closed $3$-manifold groups. A consequence of our characterization is that, for any compact, orientable, irreducible and $\partial$-irreducible $3$-manifold $M$ with nontrivial torus decomposition, $π_1(M)$ is LERF if and only if for any two adjacent pieces in the torus decomposition of $M$, at least one of them has a boundary component with genus at least $2$.

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arXiv2018

Robust Estimation of Reactive Power for an Active Distribution System

Increasing distributed energy resources (DERs) may result in reactive power imbalance in a transmission power system (TPS). An active distribution power system (DPS) having DERs reportedly can work as a reactive power prosumer to help balance the reactive power in the TPS. The reactive power potential (RPP) of a DPS, which is the range between the maximal inductive and capacitive reactive power the DPS can reliably provide, should be accurately estimated. However, an accurate estimation is difficult because of the network constraints, mixed discrete and continuous variables, and the nonnegligible uncertainty in the DPS. To solve this problem, this paper proposes a robust RPP estimation method based on two-stage robust optimization, where the uncertainty in DERs and the boundary-bus voltage is considered. In this two-stage robust model, the RPP is pre-estimated in the first stage and its robust feasibility for any possible instance of the uncertainty is checked via a tractable problem in the second stage. The column-and-constraint generation algorithm is adopted, which solves this model in finite iterations. Case studies show that this robust method excels in yielding a completely reliable RPP, and also that a DPS, even under the uncertainty, is still an effective reactive power prosumer for the TPS.

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arXiv2018

Generalized Master-Slave-Splitting Method and Application to Transmission-Distribution Coordinated Energy Management

Transmission-Distribution coordinated energy management (TDCEM) is recognized as a promising solution to the challenge of high DER penetration, but there is a lack of a distributed computation method that universally and effectively works for the TDCEM. To bridge this gap, a generalized mas-ter-slave-splitting (G-MSS) method is presented in this paper. This method is based on a general-purpose transmis-sion-distribution coordination model called G-TDCM, which thus enables the G-MSS to be applicable to most of the central functions of the TDCEM. In this G-MSS method, a basic heter-ogenous decomposition (HGD) algorithm is first derived from the HGD of the coupling constraints in the optimality conditions of the G-TDCM. Its optimality and convergence properties are then proved. Further, inspired by the conditions for conver-gence, a modified HGD algorithm that utilizes the subsystem's response function is developed and thus converges faster. The distributed G-MSS method is then demonstrated to successfully solve a series of central functions, e.g. power flow, contingency analysis, voltage stability assessment, economic dispatch and optimal power flow, of the TDCEM. The severe issues of over-voltage and erroneous assessment of the system security that are caused by DERs are thus resolved by the G-MSS method with modest computation cost.

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arXiv2017

A Response-Function-Based Coordination Method for Transmission-Distribution-Coupled AC OPF

With distributed generation highly integrated into the grid, the transmission-distribution-coupled AC OPF (TDOPF) becomes increasingly important. This paper proposes a response-function-based coordination method to solve the TDOPF. Different from typical decomposition methods, this method employs approximate response functions of the power injections with respect to the bus voltage magnitude in the transmission-distribution (T-D) interface to reflect the "reaction" of the distribution to the transmission system control. By using the response functions, only one or two iterations between the transmission system operator (TSO) and the distribution system operator(s) (DSO(s)) are required to attain a nearly optimal TDOPF solution. Numerical tests confirm that, relative to a typical decomposition method, the proposed method does not only enjoy a cheaper computational cost but is workable even when the objectives of the TSO and the DSO(s) are in distinct scales.

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arXiv2017

A Water Mass Method and Its Application to Integrated Heat and Electricity Dispatch Considering Thermal Dynamics

Currently, most district heating networks are running in a heat-setting mode, limiting the adjustment of the electrical power of combined heat and power (CHP) units. By considering the electrical power system (EPS) and district heating system (DHS) together, the peak regulatory capability of CHP units can be improved and renewable energy accommodation can be promoted. In this paper, a tractable integrated heat and electricity dispatch (IHED) model is described that addresses the thermal dynamic characteristics of pipelines and buildings to increase flexibility. To deal with the complexity of the optimization model, a water mass method (WMM) for pipeline thermal dynamics is proposed. Benefiting from the WMM, the proposed IHED model is an ordinary, non-linear model. An iterative algorithm based on the generalized Benders decomposition, and a sequential approach combined with the iterative algorithm and IPOPT, are proposed to solve the IHED model. Compared with a steady state model without thermal dynamics, considering the thermal dynamic characteristics in the DHS can further expand the peak regulatory capabilities of CHP units. The WMM is tested in the thermal dynamic simulations compared to an existing node method and a commercial simulation software. And the proposed solution strategy is verified in a small-scale system and a practical system. The simulation results of case studies are discussed to demonstrate the feasibility and economy of the dispatch model proposed here.

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arXiv2017

A Distributed Power Routing Method between Regional Markets based on Bellman-Ford Algorithm

With the deregulation of power industry, large power users can buy electricity directly from power producers. For trades between different regional markets, it is necessary to research on the method to find the cheapest route for power exchanging. Moreover, as there exists no coordinator above regional markets, the power routing problem must be solved in a distributed way. Most previous research are based on power electronic transformers. Some research proposed EMS of sub-networks as energy routers, but failed to consider the power flow constraints or did not converge in some specific cases. Our method is based on the EMS of multiple markets, which saves cost by eliminating expensive electronic transformers and has high efficiency in systems with numerous nodes by considering the regional markets as generalized nodes. We take transmission costs and congestion costs into consideration, and uses Bellman-Ford algorithm to determine the cheapest route for power transmission between different regional markets and make convergence analysis about our algorithm. This method proves effective and convergent when there is no loop among the markets. A four-market loop-free case was used to illustrate the efficiency of the method.

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arXiv2017

Geometrically finite amalgamations of hyperbolic 3-manifold groups are not LERF

We prove that, for any two finite volume hyperbolic $3$-manifolds, the amalgamation of their fundamental groups along any nontrivial geometrically finite subgroup is not LERF. This generalizes the author's previous work on nonLERFness of amalgamations of hyperbolic $3$-manifold groups along abelian subgroups. A consequence of this result is that closed arithmetic hyperbolic $4$-manifolds have nonLERF fundamental groups. Along with the author's previous work, we get that, for any arithmetic hyperbolic manifold with dimension at least $4$, with possible exceptions in $7$-dimensional manifolds defined by the octonion, its fundamental group is not LERF.

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arXiv2017

Volume of representations and mapping degree

Given a connected real Lie group and a contractible homogeneous proper $G$--space $X$ furnished with a $G$--invariant volume form, a real valued volume can be assigned to any representation $ρ\colon π_1(M)\to G$ for any oriented closed smooth manifold $M$ of the same dimension as $X$. Suppose that $G$ contains a closed and cocompact semisimple subgroup, it is shown in this paper that the set of volumes is finite for any given $M$. From a perspective of model geometries, examples are investigated and applications with mapping degrees are discussed.

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arXiv2016

Clearing and Pricing for Coordinated Gas and Electricity Day-ahead Markets Considering Wind Power Uncertainty

The natural gas and electricity systems are now becoming more and more strongly coupled. While gas-fired units (GFUs) are replacing the retired coal plants, the power systems are also increasingly dependent on the flexibilities provided by GFUs to accommodate intermittent renewable energies. The GFUs' capability of power generation relies on the availability of gas resources, which is determined jointly by the capacity of gas suppliers and their associated pipeline networks. However, the gas and electricity markets are operated separately. As a con-sequence, the GFUs actually have to "represent" the whole power system to bid on the gas market: they need to make forecasts on future gas consumption, and bear the risk of improper contracts or being unable to meet the generation schedules due to insufficient gas supply. When facing larger shares of renewable energies and more-frequent gas network congestion, the current market framework is especially unreliable and inefficient, and also economically unfriendly to the investors of the GFU assets. In this paper, we try to develop a framework which can combine the two markets. By properly pricing the scarce resources, e.g., gas transmission capacity, the joint market can help allocate them more efficiently while satisfying the demands. And by considering the uncertainty brought by renewable energies, a more forward-looking day-ahead market clearing framework is presented. The formulation, algorithm of the pro-posed joint market model will be presented, as well as some case studies.

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arXiv2016

Virtual 1-domination of 3-manifolds

It is shown in this paper that given any closed oriented hyperbolic 3-manifold, every closed oriented 3-manifold is mapped onto by a finite cover of that manifold via a map of degree 1, or in other words, virtually 1-dominated by that manifold. This improves a known result of virtual 2-domination. The proof invokes a recently developed enhanced version of the connection principle in good pants constructions.

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arXiv2016

Positive simplicial volume implies virtually positive Seifert volume for $3$-manifolds

In this paper, it is shown that for any closed orientable $3$-manifold with positive simplicial volume, the growth of the Seifert volume of its finite covers is faster than the linear rate. In particular, each closed orientable $3$-manifold with positive simplicial volume has virtually positive Seifert volume. The result reveals certain fundamental difference between the representation volume of the hyperbolic type and the Seifert type. The proof is based on developments and reactions of recent results on virtual domination and on virtual representation volumes of $3$-manifolds.

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arXiv2016

Coordinated Multi-area Economic Dispatch via Critical Region Projection

A coordinated economic dispatch method for multi-area power systems is proposed. Choosing boundary phase angles as coupling variables, the proposed method exploits the structure of critical regions in local problems defined by active and inactive constraints. For a fixed boundary state given by the coordinator, local operators compute the coefficients of critical regions containing the boundary state and of the optimal cost functions then communicate them to the coordinator who in turn optimizes the boundary state to minimize the overall cost. By iterating between local operators and the coordinator, the proposed algorithm converges to the global optimal solution in finite steps, and it requires limited information sharing.

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arXiv2016

Wind Power Providing Flexible Ramp Product

The deepening penetration of renewables in power systems has contributed to the increasing needs for generation scheduling flexibility. Specifically, for short-term operations, flexibility here indicates that sufficient ramp capacities should be reserved to respond to the expected changes in the load and intermittent generation, also covering a certain amount of their uncertainty. To address the growing requirements for flexible ramp capacity, markets for ramp products have been launched in practice such as the ones in California ISO and Midcontinent ISO. Some-times, to guarantee sufficient ramp capacity, expensive fast start units have to be committed in real-time. Moreover, with higher penetration of renewable generation, the flexibility provided by the conventional units might not be enough. Actually, wind power producers are physically capable of offering flexibility, which is sometimes also economically efficient to the entire system. In this paper, we aim to explore the mechanism and possibility of including wind power producers as ramp providers to increase the supply of flexibility. To conduct the anal-yses, a two-stage stochastic real-time unit commitment model considering ramp capacity adequacy is formulated. Case studies indicate that both the system and the wind power producers can benefit if the wind power is allowed to provide flexible ramp products.

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arXiv2016

A Bilateral Reserve Market for Variable Generation: Concept and Implementation

Substantial changes in the generation portfolio take place due to the fast growth of renewable energy generation, of which the major types such as wind and solar power have significant forecast uncertainty. Reducing the impacts of uncertainty requires the cooperation of system participants, which are supported by proper market rules and incentives. In this paper, we propose a bilateral reserve market for variable generation (VG) producers and capacity resource providers. In this market, VG producers purchase bilateral reserve services (BRSs) to reduce potential imbalance penalties, and BRS providers earn profits on their available capacity for re-dispatch. We show in this paper that by introducing this product, the VG producers' overall imbalance costs are linked to both their forecast quality and the available system capacity, which follows the cost-causation principle. Case studies demonstrate how the proposed BRS mechanism works and its effectiveness.

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arXiv2015

Further Discussions on Sufficient Conditions for Exact Relaxation of Complementarity Constraints for Storage-Concerned Economic Dispatch

Storage-concerned economic dispatch (ED) problems with complementarity constraints are strongly non-convex and hard to solve because traditional Karush-Kuhn-Tucker (KKT) conditions do not hold in this condition. In our recent paper, we proposed a new exact relaxation method which directly removes the complementarity constraints from the model to make it convex and easier to solve. This paper further extends our previous study, with more than one group of sufficient conditions that guarantee the exact relaxation presented, proven and discussed. This paper may contribute to wider application of the exact relaxation in storage-concerned ED problems.

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arXiv2014

A Fully Distributed Reactive Power Optimization and Control Method for Active Distribution Networks

This paper proposes a fully distributed reactive power optimization algorithm that can obtain the global optimum of non-convex problems for distribution networks without a central coordinator. Second-order cone (SOC) relaxation is used to achieve exact convexification. A fully distributed algorithm is then formulated corresponding to the given division of areas based on an alternating direction method of multipliers (ADMM) algorithm, which is greatly simplified by exploiting the structure of active distribution networks (ADNs). The problem is solved for each area with very little interchange of boundary information between neighboring areas. The standard ADMM algorithm is extended using a varying penalty parameter to improve convergence. The validity of the method is demonstrated via numerical simulations on an IEEE 33-node distribution network, a PG&E 69-node distribution system, and an extended 137-node system.

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