Frequency Control in Power Systems with High Renewable Energy Share: A Case-Control Study Using BESS

This study proposes an optimal control of the battery energy storage system (BESS) to support the frequency in the power system connecting a high penetration rate of renewable energy sources. A frequency regulation algorithm generates a sinusoidal reference signal for the pulse width modulation (PWM) scheme of the DC/AC converter based on voltage magnitude and phase set points. The proposed algorithm uses the control loops, including the frequency, voltage, reactive and active powers, charge, and d and q axes current controllers, to restrain the maximum frequency deviation and improve the maximum rate of change of frequency (RoCoF). An adaptive nonlinear droop control method, integrated with state-of-charge (SOC) feedback, is applied to the active power-frequency control loop. This approach ensures frequency stability, equitable power allocation among various power sources, and mitigating imbalances during voltage dips. The SOC feedback mechanism estimates the battery's state, enabling the BESS to charge or discharge as needed to maintain system frequency within operational limits. The methodologies in this study have been verified by building a modified Vietnamese Tay Nguyen 500/220 kV and IEEE 39-bus systems. All models were performed using DIgSILENT/Power-Factory software. The effectiveness of the proposed method is simulated and compared with the BESS using the CBEST model in PSS/E under considering different scenarios such as a sudden lack of generating capacity or sudden decrement output capacity of renewable energy sources (RES). Results demonstrate that the proposed BESS strategy satisfies the operational frequency requirements specified in Circular No. 25/2016/TT-BCT (dated November 30, 2016) by the Ministry of Industry and Trade of Vietnam, which regulates transmission power systems. Specifically, the permissible frequency range is from 49.0 to 51.0 Hz; the system achieved a frequency range of 49.5 to 50.5 Hz (reset mode) within 120 sec and successfully recovered to a frequency range of 49.8 to 50.2 Hz (normal operating mode) within 300 sec. These results confirm the strategy's effectiveness in meeting Vietnam's power system requirements and addressing its operational challenges.