Inertia reduction due to inverter-based resource (IBR) penetration deteriorates power system stability, which can be addressed using virtual inertia (VI) control. There are two types of implementation methods for VI control: grid-following (GFL) and grid-forming (GFM). There is an apparent difference among them for the voltage regulation capability, because the GFM controls IBR to act as a voltage source and GFL controls it to act as a current source. The difference affects the performance of the VI control function, because stable voltage conditions help the inertial response to contribute to system stability. However, GFL can provide the voltage control function with reactive power controllability, and it can be activated simultaneously with the VI control function. This study analyzes the performance of GFL-type VI control with a voltage control function for frequency stability improvement. The results show that the voltage control function decreases the voltage variation caused by the fault, improving the responsivity of the VI function. In addition, it is found that the voltage control is effective in suppressing the power swing among synchronous generators. The clarification of the contribution of the voltage control function to the performance of the VI control is novelty of this paper.

-This paper proposes a practical method for identifying wheeling paths in deregulated electricity markets based on an extended sensitivity analysis. Using this method, it becomes possible to fix the proper and fair wheeling rate according to the degree of responsibility of each power flow transaction. Moreover, a wheeling rate based on the real power flow responsibility is also an important signal to new power suppliers in the markets. In order to show the validity of the proposed method, a series of simulations on the IEEE 30 bus test system were conducted.

-This paper proposes a practical and devised method for designing the wheeling charge based on the embedded cost method. In setting up the wheeling charge, one of the most important items is recovering the invested cost. Because the marginal cost method has the disadvantages regarding the above point, the embedded cost method is focused in this paper. By applying the proposed method, the wheeling charge that reflects the use of transmission systems not only gives an incentive for the efficient operation of power systems but also achieve the recovery of the invested cost by electric utilities. In order to verify the proposed method, several simulations have been conducted on the IEEE 30-bus test system.

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