Congestion management enhancing transient stability of power systems

In a competitive electricity market, where market parties try to maximize their profits, it is necessary to keep an acceptable level of power system security to retain the continuity of electricity services to customers at a reasonable cost. Congestion in a power system is turned up due to network limits. After relieving congestion, the network may be operated with a reduced transient stability margin because of increasing the contribution of risky participants. In this paper, a novel congestion management method based on a new transient stability criterion is introduced. Using the sensitivity of corrected transient stability margin with respect to generations and demands, the proposed method so alleviates the congestion that the network can more retain its transient security compared with earlier methods. The proposed transient stability index is constructed considering the likelihood of credible faults. Indeed, market parties participate by their security-effective bids rather than raw bids. Results of testing the proposed method along with the earlier ones on the New-England test system elaborate the efficiency of the proposed method from the viewpoint of providing a better transient stability margin with a lower security cost.     

基于可控负荷的智能电网电压频率多目标优化控制

近年来分布式电源不断接入电网,其输出功率的不确定性严重影响了系统的频率和电压水平。与此同时,电网用户侧智能终端设备数量逐年增加,各节点的功率控制能力得到明显提高。因此,为使系统频率和电压幅值保持在额定值附近,本文提出了一种基于可控负荷的电压频率控制多目标优化模型。为了克服传统多目标求解方法主观性强的缺点,将所提多目标优...     

Terminal voltage build-up and control of a DFIG based stand-alone wind energy conversion system

The paper presents the voltage build-up process and the terminal voltage control of a doubly-fed induction generator (DFIG) driven by a pitch controlled wind turbine for the supply of autonomous system without any auxiliary source. A control strategy for the complete system including voltage build-up phase is developed with a view to provide as well as possible the required power for load. Indirect stator flux-oriented vector control is proposed to keep the stator voltage constant by means of a back-to-back converter connected to the rotor side, while the management system is supported by the pitch angle and the load shedding controllers. A novel scheme for voltage build-up is presented, which requires no additional hardware support, and physical interpretation of how self-excitation can occur from residual magnetism in the machine core is examined. A reliable start-up process is accomplished by using an appropriate voltage reference ramp which enables minimizing energy loss during the starting. The proposed system is modeled and simulated using Matlab/Simulink software program to examine the dynamic characteristics of the system with proposed control strategy. Dynamic simulation results for different transient conditions demonstrate the effectiveness of the proposed control strategy.     

Experimental investigation of start-up and transient thermal performance of pumped two-phase battery thermal management system

In this study, a pumped two-phase battery thermal management system was developed, and its start-up and transient thermal performances were experimentally evaluated. The start-up behavior was characterized, and the effects of the flow rate, heat flux, and cold-source temperature on the start-up and transient thermal performances were examined. Three start-up modes were observed: fluctuating growth, temperature overshoot, and smooth growth. The fluctuating growth start-up mode appears to be suitable for battery cooling. The transient performance was improved when the flow rate was decreased, which resulted in a quicker start-up and lower average temperature (t_avg) and maximum temperature difference (∆t_max). Reducing the flow rate from 0.99 to 0.20 L/min significantly shortened the start-up time, lowered t_avg and ∆t_max, and increased the heat transfer coefficient (α) when the steady state was reached. Increasing the heat flux initially improved and then weakened the transient performance of the pumped two-phase system. Increasing the heat flux from 1.1 to 2.8 W/cm² initially reduced the start-up time and t_avg to 350 seconds and 1.5°C, respectively, but they then significantly increased to 360 seconds and 13.5°C, respectively. The transient t_avg and ∆t_max decreased with the cold-source temperature (t_cs), while the start-up time was independent of changes in t_cs.     

Probabilistic hydrogen,thermal and electrical management of PEM-fuel cell power plants in distribution networks

This paper presents a Stochastic Multi-objective Optimal Operation Management (SMOOM) framework of distribution networks in presence of PEM-Fuel Cell Power Plants (FCPPs) and boilers. Operational costs, thermal recovery, power trade with grid and hydrogen management strategies are considered in this model. Furthermore, four objective functions has been considered as criteria for SMOOM, i.e. electrical energy losses, voltages deviations from their nominal values, total emissions emitted by CHP systems and grids, and total operational costs of CHP systems, as well as electrical energy cost of grids. A 2m + 1 Point Estimated Method is used to cope with the uncertain variables i.e. electrical and thermal loads, gas price of FCPPs consumption, fuel cost of residential loads, purchasing and selling tariff of electricity, hydrogen price, operation temperature of fuel cell stack, and the pressures of hydrogen and oxygen of anode and cathode, respectively. A new multi-objective Modified Firefly Algorithm (MFA) is implemented for minimizing the objective functions while the operational constraints are satisfied. Finally, a 69-bus distribution network is utilized to examine the performance of the proposed strategy regarding the rest.