Voltage and Frequency Grid Support Strategies Beyond Standards

In recent years, with a higher penetration of renewable distributed generators into the ac grid network, the risk of grid instabilities and vulnerabilities has increased. This paper proposes grid support strategies that can be used to alleviate the grid frequency-voltage variations, which are indicators of the imbalance between power generation and consumption within an ac network. The proposed strategies to support grid stability in the event of frequency-voltage variation go beyond recent standards and provide extended functionalities. The preconfigured set points of active power-frequency P(f) strategy features the control of the converter's power flow direction with an adjustable power gradient transition between grid-feeding and force charge as grid loading, in response to grid frequency deviation. The distributed power generators are represented by an energy storage converter, with the capacity to discharge and charge the electrical energy storage (EES) element, primarily for grid support purposes. The EES energy storage is configured for later usage when the grid requires active power support, under line frequency deviation, used under normal conditions, or during on-peak tariff high-demand daytime hours (energy shifting for TOU, ac load shave). In addition to grid support enhancement, the P(f) strategy is combined with reactive power-voltage Q(v ) control to attempt to correct frequency and voltage deviations in a collective impact of distributed generators operation for grid stabilization purposes. The P(f) - Q (v) strategy provides an automatic active/reactive power generate/receive preconfigured control, in response to frequency-voltage deviations, in order to support the grid and prevent network instabilities. The proposed control strategy for local frequency assist and voltage assist is applicable for single and three-phase grid converters interfaced with energy storage systems. Simulations and experimental results, obtained using a single-phase 6 kVA four-quadrant EES converter, are presented to validate the proposed P( f) and Q(v) grid support strategies.