Control Strategy And Capacity Planning Of Hybrid Energy Storage System For Frequency Regulation With Traditional Thermal Generators

With the improvement of technology and the development of economy, the power system scale tends to expand, and the frequency stability of power system has to meet higher requirements. Meanwhile, in order to deal with environmental problems and issues of fossil energy depletion, more and more renewable energy sources have been explored and connected into the power grid, which has characteristic of intermittent and volatility. Thus a large impact occurred to influence the frequency stability further. At the same time, the traditional frequency regulation cannot meet the requirements of the current power system. Consequently, it becomes research focus to keep the stability of frequency considering the scale of power system and the penetration of renewable energy.On the basis of summary research status in this field, this paper proposes applying energy storage in generation-side and taking part in frequency regulation with traditional generating units. We can make full use of the frequency capacity of the original thermal power unit in this way. It can also take the expensive costing into consideration and impose restrictions on the capacity of the energy storage simultaneously. This paper mainly includes four aspects of the work:Firstly, it introduces the principle of frequency regulation simply and analyzes the influence of traditional generating units which is taken part in frequency regulation; Comparing with the economic performance parameters of the different energy storage, this paper established the hybrid energy storage device which is composed by Valve Regulated Lead Acid battery (VRLA) and Vanadium Redox Flow Battery (VRB). This paper shows the mathematical model of energy storage and analyzes the control block diagram.Secondly, on the basis of the analyzation of reverse adjustment modulation which is appeared in the primary frequency modulation by traditional generating units, this paper puts forward a new ESS to restrain the phenomenon of reverse adjustment modulation. The transfer function of the control strategy was established and analyzed. The simulation shows the advantageous effect of this control strategy on restrain reverse adjustment modulation.Thirdly, the single unit was chosen to be as the research object. Considering the frequency regulation characteristics of hybrid energy storage devices and the traditional generating units, this paper puts forward a normal case and four kinds of particular cases (Reverse adjustment modulation, Dead zone oscillating, over discharge of ESS and SOC forced homing) and this paper established the corresponding constructing charge and discharge strategy of ESS with different situation. The result shows that the strategy can response the command from AGC and enhance the effect of frequency modulation.Finally, an optimization calculation model considering the compensation index of generating units is established. The model can harmonize the restrictive relation of the cost of ESS, operating expense and compensatory earnings of AGC. The performance indicators of AGC (Kp) and energy storage device investment function and penalty function are introduced into the target function. Then it realizes the maximum profits of the traditional generating units and ascertain the optimal storage capacity. The result shows that the method can optimize the hybrid ESS on frequency regulation and the energy storage can take part in the frequency modulation economically.