Advanced Materials Research Vols. 960-961

Abstract: Large delay is the main characteristics of medium-speed pulverizer system which used in subcritical and supercritical unit. By introducing and analyzing the operating principle and working process, considering energy saving and consumption reducing, and combined with the performance requirement of AGC (Automatic Generation control), recommend solutions were put forward. It can effectively solve AGC control problems of load and pressure control accuracy and ensure frequency stability of the grid, provide a reference for similar units.

Abstract: The uC_OS-II embedded real-time operation system is used to improve the original designed fuel supply system of a Stirling engine which governed by the electronic control system based on a rotating speed control method. Task modules for each level are built and the fail-safe modules are also improved in this paper. The developed fuel supply system is investigated through experiment, and test results show that the new real-time operating system works stably and realizes the fuel supply fast adjustment.

Abstract: In power system, flow transferring can cause non-fault overload. Traditional zone 3 distance relays cannot distinguish overload caused by faults or by transferred power flow and may operate incorrectly, thus cause cascading trips, even blackout. Based on wide area measurement system (WAMS), this paper proposes two criteria to realize flow transferring identification function. First, three-phase voltages and currents are measured and compared with those calculated before fault, which should be applied to the given identification criteria. Then, the logical relationship for flow transferring identification are put forward to prevent distance relays from incorrect behavior caused by non-fault overload and unblock zone 3 distance relays when fault occurs. Through the simulation results, the effectiveness of the proposed method is verified.

Abstract: In order to avoid incorrect setting from being a hidden fault source which threats the stable operation of power system, setting adjustment algorithm of line protection is proposed. Through setting detection and setting rectification the algorithm amends incorrect setting and reduces the number of mismatch protection to the greatest extent. A method of calculating high step coverage of interphase current protection based on node impedance matrix is also proposed in this paper. The example shows the proposed algorithm is practical.

Abstract: This paper establishes a simulation model of a simplified power system with transformer differential protection based on an embedded Matlab function block. The differential protection consists of percentage restraint differential protection, second harmonic restraint, differential current instantaneous trip protection and over-excitation protection. The model is able to correctly simulate the transformer’s inrush current and internal and external faults. The results from the simulation show that the circuit breaker correctly operates for a transformer internal fault and provides a good braking effect for an external fault. In addition, the protection model is able to identify the inrush current of the transformer and avoid a protection mis-trip event.

Abstract: In this paper, the feasibility analysis of the utilization of phase shifting transformers (PSTs) to improve the AC outward transmission capacity of Sichuan power grid (SCPG) is presented. Firstly, the authors analyze the working principle of PST, as well as the rules for selecting its location. Then, the AC outward transmission limit of SCPG is studied with PSASP software. Finally, the PST is used to change the power flow distribution of lines on border of SCPG. Simulations results show that the PST can significantly improve the AC outward transmission capacity of SCPG. At the same time, short-circuit current of SCPG is also reduced.

Abstract: Compared with Line-Commutated-Converter High Voltage Direct Current (LCC-HVDC), the primary and secondary systems of modular multilevel converter based HVDC (MMC-HVDC) are more complicated. And control and protection function of sub-module controller (SMC) have great influence on the operation of MMC-HVDC system. This paper investigates the design method of SMC and sub-module (SM) steady-state platform. First, the structure of the primary system and the electrical parameters of the 21-level MMC-HVDC are designed. Second, the architecture of the control system and SM fault protection strategy are proposed, and the control program is developed and debugged. Then SM steady-state test platform and the relevant control and protection are designed. Finally, the steady-state test and the system test of the physical MMC-HVDC simulation system are conducted. The test result shows that the sub-module is of good property and SMC can communicate with upper control layer efficiently, control and protect the SM efficiently.

Abstract: In this paper, it is show how the second derivatives of the Hessian matrix influence on the convergence of the power flow calculation. Convergence conditions of the Combined Newton’s method using 14 nodes IEEE testing schemes are investigated. The method can be used to determine the control actions to pull the operating point into the feasibility domain.

Abstract: Supplementary subsynchronous damping controller (SSDC) is an effective countermeasure to damp the subsynchronous oscillation (SSO) caused by HVDC. On the basis of analyzing the mechanism of inducing SSO by HVDC, the principle of damping SSO by SSDC and SSDC design methods are expounded. A SSDC is designed for a practical power plant in China, and the correctness and validity of the SSDC control strategies are proved with time domain electromagnetic simulation results.

Abstract: The advantages of high energy efficiency and economic benefit promote the wide application of combined heat and power system (CHP) based microgrid. Firstly, a mathematical model of the CHP based microgrid is developed. Then, a cost function for the coordination of heat and electric load is proposed. Finally, an optimal dispatch model is developed to achieve the economical and coordinated operation of the CHP based microgrid system. Simulation results verify effectiveness of the proposed dispatch model, which is a powerful tool for the energy management of CHP based microgrid with renewable energy resources.