This paper proposes a fast coordinated power control method based on two augmented channels (AC) in battery energy storage system (BESS) to improve inertial and voltage support capability, i.e., a frequency-reactive power channel (FRPC) and a voltage-real power channel (VRPC). For frequency control in the power distribution system with high resistance/inductance ratio, the coupling mechanism between rate of change of frequency (RoCoF) and required reactive power (RRP) of grids is analyzed, indicating RoCoF is proportional to RRP. Thus, RoCoF is utilized in FRPC to generate reactive power for complementary inertial emulating control. Meanwhile, for voltage control, coupling characteristics between rate of change of voltage (RoCoV) and demanding real power (DRP) of grids is also studied, revealing RoCoV is proportional to DRP. Therefore, it can be adopted in VRPC to generate real power for complementary voltage control. Then, grid-voltage-modulated direct power control is selected as the inner power control loop to track power references with faster dynamic performance compared with traditional vector-oriented control. Finally, simulations and hardware-in-loop experiments validate improvement in performance of grid frequency and voltage control based on the proposed method.

This paper proposes a novel Multivariate Quotient-Difference (MQD) method to obtain the approximate analytical solution for AC power flow equations. Therefore, in the online environment, the power flow solutions covering different operating conditions can be directly obtained by plugging values into multiple symbolic variables, such that the power injections and consumptions of selected buses or areas can be independently adjusted. This method first derives a power flow solution through a Multivariate Power Series (MPS). Next, the MQD method is applied to transform the obtained MPS to a Multivariate Padé Approximants (MPA) to expand the Radius of Convergence (ROC), so that the accuracy of the derived analytical solution can be significantly increased. In addition, the hypersurface of the voltage stability boundary can be identified by an analytical formula obtained from the coefficients of MPA. This direct method for power flow solutions and voltage stability boundaries is fast for many online applications, since such analytical solutions can be derived offline and evaluated online by only plugging values into the symbolic variables according to the actual operating conditions. The proposed method is validated in detail on New England 39-bus and IEEE 118-bus systems with independent load variations in multi-regions.