Inertial Response Control for Frequency Regulation in Japanese Power System
Jingting Qi, Takao Tsuji
Yokohama National University, Yokohama, Japan
It is expected that frequency regulation will be an important issue in Japanese power system when wind power integration is realized. Because Japanese power system is operated as an isolated system from other countries without having any international tie lines, system inertia will be largely reduced and frequency easily changes supposing a part of conventional generators are replaced with wind power plants. Although installation of rechargeable battery is an effective countermeasure to solve this problem, the capital investment cost will be another issue. On the other hand, frequency support from wind power has attracted much attention these days. In particular, it is expected that inertial response control of wind turbines is able to improve the frequency fluctuation with mitigating the reduction of the system inertia.
Hence, in this paper, the effectiveness of the inertial response control of wind power plants was evaluated through numerical simulation. As control strategies for inertial response control, following three control methods were considered: synthetic inertia, temporary power surge, and droop control. These three methods were compared each other based on AGC30 model that was newly developed by IEEJ (Institution of Electrical Engineers Japan). AGC stands for Automatic Generation Control which covers primary, secondary, and tertiary controls for balancing mechanism. By adding the new control strategy for inertial response into the AGC30 model, the effectiveness of above control strategies were investigated considering contingency conditions. Moreover, an academic approach to design proper control parameter setting is discussed mainly for temporary power surge method.
Among the above three control methods, the temporary power surge method is mainly focused in this paper. The wind power output can be increased stepwise in the method when the frequency support is needed due to the power supply shortage. There are various control parameters such as threshold frequency to give the trigger to start the power increase. Which means this method has better flexibility and effectiveness if those control parameters can be properly designed. Thus, in this paper, the detailed control block diagram for temporary power surge method is proposed by the combination of two control modes: frequency support and rotational speed control. Moreover, the decision technique of the control parameters are also discussed based on the AGC30 model.
Numerical simulations were performed based on the AGC30 model. Basically, three simulation cases were prepared as follows: (1) with the same penetration level of RES (renewable energy sources), (2) with higher penetration level of RES without inertial response control, and (3) the application of inertial response control to the same condition as (2). As for (3), three control strategies that are already mentioned were applied with delta control in which the wind power output was slightly reduced from the beginning. Although all the control strategies can contribute to the frequency support, the temporary power surge showed the best performance by specifying the proper parameter setting.
The effectiveness of three control strategies based on inertial response were evaluated through numerical simulation in this paper. AGC30 model was used as recommended power system model and it was shown that temporary power surge method can give the better result with proper setting of control parameters. However, in this paper, the combinational contribution of PV and wind power was not considered although the PV penetration level will be higher in Japan. Moreover, the power flow issue caused by the inertial response was not considered. The new control technique to maximize the control effect of inertial response under the power flow constraint has to be developed in the next step. These issues will be worked on in the future.
Through this paper and presentation, it is expected that delegates will learn the effectiveness of the inertial response control in the isolated power system like Japanese power system. Also, the new control strategy for temporary power surge with a decision technique of its control parameters will be important knowledge to progress the wind power integration. Moreover, the inherent characteristic of Japanese power system will be deeply understood through the details about the newly developed AGC30 model. Although the model was developed considering the Japanese power system, its components such as quasi-steady state model of conventional generators for this purpose can be commonly used also for various other power system models. Therefore, to obtain detailed information of AGC30 model will be also precious knowledge.