Stand-alone power system

About: Stand-alone power system is a research topic. Over the lifetime, 8650 publications have been published within this topic receiving 192397 citations. The topic is also known as: Stand-alone photovoltaic power system.

Control Strategies for Battery/Supercapacitor Hybrid Energy Storage Systems

Abstract: Batteries are one of most cost-effective energy storage technologies. However, the use of batteries as energy buffers is somehow problematic, since it is hard, if not impossible, to recover from rapid power fluctuations without dramatically reducing the batteries' lifetimes. In a supercapacitor, energy storage is by means of static charge rather than of an electrochemical process as in a battery; thus the supercapacitor has a higher power density than a battery. It is then advantageous to combine these two energy storage devices to accomplish better power and energy performances. This paper presents an active hybrid energy storage system that comprises a rechargeable battery, a supercapacitor bank and two corresponding DC/DC power converters. The battery and the super-capacitor may be charged or discharged simultaneously with the current or power appropriately split between them. The battery may be predominant in either the charging or discharging mode. Three different control strategies for power sharing between them are developed for the hybrid energy storage system. These control strategies are verified and compared against each other under some certain operating conditions. The effects of controller parameter variations on the system performance are also studied.

Impact of Dynamic Behavior of Photovoltaic Power Generation Systems on Short-Term Voltage Stability

Abstract: In this study, we investigate the impact of the dynamic behavior of photovoltaic (PV) power generation systems on short-term voltage stability of the transmission system. First, the impact of the fault ride-through capability of a PV model is studied by setting several recovery speeds of the active current output when the operation of the PV system is interrupted because of a voltage sag. The results are analyzed by using transient $P\hbox{-}V$ curves and a stability boundary, which has been proposed in our previous research. Further, we show that the installation of PVs severely impairs the short-term voltage stability if the PVs shut off after a voltage sag, and its recovery speed is low. Next, two countermeasures to control short-term voltage instability phenomena are tested. One is the operation of the PV system at a leading power factor in the normal state, and the other is the dynamic reactive power control by the inverters of the PV system after a voltage sag. Numerical examples are carried out for a one-load infinite-bus power system and a five-machine five-load power system. The results show that these countermeasures can play a substantial role in preventing the voltage instability phenomena caused when a PV system is suddenly interrupted because of a fault.

Flexible Optimal Operation of Battery Storage Systems for Energy Supply Networks

Abstract: Active-reactive optimal power flow (A-R-OPF) in distribution networks (DNs) with embedded wind generation and battery storage systems (BSSs) was proposed recently. The solution was based on a fixed length in the charge and discharge cycle for daily operations of BSSs. This can lead to a low profit when the profiles of renewable generators, demand and prices vary from day to day. In this paper, we extend the A-R-OPF method by developing a flexible battery management system (FBMS). This is accomplished by optimizing the lengths (hours) of charge and discharge periods of BSSs for each day, leading to a complex mixed-integer nonlinear program (MINLP). An iterative two-stage framework is proposed to address this problem. In the upper stage, the integer variables (i.e., hours of charge and discharge periods) are optimized and delivered to the lower stage. In the lower stage the A-R-OPF problem is solved by a NLP solver and the resulting objective function value is brought to the upper stage for the next iteration. It can be shown through a case study that a flexible operation strategy will achieve a considerably higher profit than by a fixed operation strategy of BSSs.