Chung-Neng Huang

Feature analysis of power flows based on the allocations of phase-shifting transformers

This paper proposes a novel approach for identifying the deviations of power flows that are controlled by multiple phase shifting transformers (PSTs). In order to control the power flows of each loop independently, at first the minimum need of PST sets is determined as the number of co-tree to the entire network. Because co-tree patterns are not unique, many PST allocations exist and can be found as the co-tree patterns. Features of the controllable area of power flows corresponding to all PSTs allocation candidates can be extracted by the eigenanalysis of the matrix. Finally, judging from the power flow profiles, the optimal allocation to the specific control target can be found. The optimal PST allocation for power flow control can be found by the flexible power flow control in an open-access network. The effectiveness of the proposed method is confirmed by the simulation studies of two model systems.

The optimal allocation pattern of phase shifting transformers for unwinding parallel flows

This paper proposes a new method to determine the optimal allocation pattern of multiple phase shifting transformers (PSTs) for unwinding parallel flows. In the proposed method, the concept of co-tree in graph theory is used to determine the minimum number of PSTs required for the independent modulation of individual loop flows. Moreover, eigenanalysis is applied to find out the correlation between each allocation patterns of PSTs and corresponding power flow profiles. Consequently, the sensitivity of flow alteration vector to the input angle vector of PSTs can be characterized into a matrix. Whereas, by the sensitive matrix, the required control angles of each PST for unwinding parallel flows can be found precisely. As a result of the proposal, the optimal allocation pattern of PSTs is determined as which can unwind the specific parallel flows by minimum control angles against other patterns. The validity of the proposed method is confirmed through the simulation studies.

Preventive flow control for transient stability by phase shifting transformers

Interconnections make economic use of the power generated and generally improve overall reliability, but the complexity exists in the power system. Synchronous generators thousands of kilometers apart must operate stably in synchronism even the power transfer conditions such as equipment outages or power disturbance are occurring. If one group of generators accelerates another group, instability and loss of synchronism will be caused. In order to ensure and improve the transmission reliability and capacity against these unexpected accidents, this paper proposes a concept to improve the transmission capacity of the network by phase shifting transformers (PSTs). The concept is, in advance, shifting power flow of the line where an accident is considered to occur to other lines by PSTs. Consequently, the influence of the contingency on the generators can be relieved a lot and operate more stably to prevent from the cascading of failures and the area affected. The effectiveness of the proposal is confirmed through the simulation studies in a three-unit six-bus model system.

Autonomous control of energy storage devices for enhancing power system stability

In recent years, due to petroleum price going-up and the increasing interest of wholesale wheeling alternatives open to third-party generations as wind power etc., the problems about power system instability grow into a serious matter. For making better use of those green powers but without system instability, an autonomous control basing on multiple energy-storage devices (ESDs) is proposed. Where, each ESD only respects to a simple rule as well as its individual controller to determine charging or discharging. Through such an autonomous control to ESDs, the change of total injection power of an area can be minimized. That is, system stability can be enhanced. In addition to extend the ESD control to interconnected systems where are with multiple machines and tie lines, the considerations about area control error (ACE) and automatic generation control (AGC) are also combined into this control. Since the proposal for ESD control is particular useful in solving the problems involving with multi-machine and multi-tieline systems, a three-machine seven-bus two-loop testing system is given to confirm the effectiveness and show the function of it.

Introduction of perturbing power filter to vehicle generation system for stabilizing electric power supply

In order to stabilize the electric power delivery from the alternator of a vehicle system, a conception of introducing the perturbing power filter (PPF) to vehicle generation system is proposed in this paper. Make use of PPF, the driven velocity of alternator transmitted from engine can be smoothened in constant. Consequently, the supply voltage of electric power can be maintained in stability. The effectiveness and validity of this proposal are confirmed by a simulation study.

Determining optimal allocation of flow controllers based on system stability and controllability

A hierarchical screened method for determining the optimal allocation of flow controllers are proposed in this paper. Since the allocation patterns are found basing on the concept of tree/co-tree in graph theory, all line flows of the system are controllable only by the minimum number of flow controllers. In order to prevent from system instability resulting from flow control, the eigen analysis of the sensitive matrices characterized the corresponding allocations are taken. It is helpful to screen out the invalid allocations where flow controllers may cause instability in the system. Finally, by comparison with the flow controllability of each allocation, the optimal one hit the target of flow control can be found. A three-machine four-bus two-loop model system is given as an example to confirm the effectiveness of the proposed method.

Feature analysis of power flows based on the allocations of phase shifting transformers

Summary form only given. This paper proposes a novel approach to identify the deviations of power flows, which are controlled by multiple phase shifting transformers (PSTs). In order to control the power flows of each loop independently, at the first, the minimum need of PST sets is determined as the number of co-tree to the entire network. For the reason of the co-tree patterns are not unique, there are many PSTs allocations existing and can be found as the co-tree patterns. Continuously, characterizing the sensitivity of power flow deviations to PSTs control angles into a matrix. By which, the features of the controllable area of power flows corresponding to all PSTs allocation candidates can be extracted by the eigenanalysis of the matrix. Finally, judging from the power flow profiles, the optimal allocation to the specific control target can be found. From the viewpoint of the flexible power flow control in an open access network, it is contributed to find out the optimal PSTs allocation for power flow control. The effectiveness of the proposed method is confirmed by the simulation studies of two model systems.