Researchers Chen Wei, Ye Shaoshi, and Liu Dong of Zhejiang Net New United Engineering Co., Ltd. and Nokia Communications System Technology Co., Ltd. wrote in the 12th issue of "Electrical Technology" magazine in 2017 that the micro-grid energy storage system is super The capacitor bank is mainly used to meet the requirements of the system for fast dynamic response, so its response under different operating conditions needs to be consistent to ensure the matching of the electrical load in the latter stage.
This paper proposes an adaptive control strategy with dynamic response consistency as the optimal target. According to the small signal model of the system, under the premise of maintaining stability, the appropriate control parameters under different working conditions can be obtained by means of the step response of the system.
At runtime, the optimal control parameter combination can be automatically selected online by the microprocessor according to the current working condition of the system, so as to achieve the dynamic response uniformity of the output under any circumstances. After the principle analysis and design method are given, the experimental prototype proves the effectiveness of the novel adaptive control strategy and has application value.
As a typical application of renewable and clean new energy technologies, the microgrid will play a supporting role in the construction of major municipal functions such as smart city energy supply, transportation and industrial and commercial activities, and has been included in the “Thirteenth Five-Year Plan†in China. Related planning.
In order to ensure the stable and reliable operation of the microgrid, its internal energy storage system needs to have high energy density and high power density characteristics to suppress power fluctuations caused by sudden load changes and improve power quality [1]-[5].
The energy storage system generally adopts a mixture of two energy storage elements of a battery pack and a super capacitor, wherein the battery pack can meet the high energy density requirement and maintain the steady state bus voltage; and the super capacitor can improve the dynamic response of the system and buffer load fluctuation. The power impact extends the life of the energy storage device [6]-[8].
The ultracapacitor bank is typically implemented by a post-stage DC-DC converter and power and energy transfer between the busbars. In design, since the terminal pressure of the ultracapacitor bank is constantly changing during charging and discharging, it will not remain relatively constant, which brings challenges to the control of the converter of the latter stage: due to the converter The main power gain includes the supercapacitor terminal voltage VUC term, so the transient process characteristics of the converter output also vary with VUC [9], which is difficult to optimize through a fixed set of PI or PID feedback parameters.
These dynamic response indicators such as overshoot and adjustment time, which are subject to changes in external conditions, are not conducive to the matching design of the post-current load. In extreme cases, it is easy to cause timing mismatch or voltage overrun between the energy storage system and the load, which affects the stable operation of the microgrid and reduces reliability.
The novel adaptive control scheme proposed in this paper is to ensure the consistency of the output dynamic response characteristics of DC-DC converter under various conditions as the optimization target. By detecting the input and output state, the adaptive control parameters are selected online to achieve the output dynamics. The response and the external working condition of the converter are decoupled to facilitate the electrical coordination of the electrical load at the rear stage.
Figure 1 Supercapacitor bank energy storage unit
in conclusion
This paper proposes an adaptive control strategy that is optimal for the dynamic response of ultracapacitor banks in energy storage systems. Through the small signal model of the system, aiming at the consistency of the step response in various situations, the optimal control parameters under the current working conditions can be obtained.
The above control parameters are dynamically selected according to the actual situation by the microprocessor to achieve the design purpose of consistent output dynamic response, so as to simplify the design difficulty of the latter load and increase the system matching.
The experimental prototype and the result prove the correctness of the adaptive control strategy and the feasibility of the proposed control strategy, which has practical application value.
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