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Power systems worldwide are transforming into renewable-dominated ones that require significant grid flexibility. While extensive research has been done on flexibility from the generation or demand side, there is a significant lack of research on studying flexibility from the grid side. Therefore, this paper proposes a primary frequency response sharing strategy using LCC-HVDC for inverter frequency control. Under an inverter frequency event, the proposed method imposes a controlled load change that is proportional to the inverter AC frequency deviation on the rectifier AC network. This in impact activates the primary frequency response from the rectifier side to support the inverter AC frequency (i.e., sharing of primary frequency response). The level of support and the coupled dynamics of rectifier and inverter frequencies are quantified by the developed mathematical model. The model reveals that the inverter load change is affecting the rectifier AC frequency through two cascaded 2nd order transfer functions. With the developed model and the desired frequency nadirs at both AC systems, the controller parameters of the proposed method are calculated. This ensures that appropriate level of primary frequency response is shared without jeopardizing the frequency performance of rectifier AC system. The effectiveness of the proposed method is demonstrated using a modified four-generator two-area system. Estimation errors of network inertia and droop constants are discussed.

The massive integration of renewable energy sources and power electronics into the power grid leads to the strong need of real-time Electromagnetic Transients (EMT) simulation of power system using field-programmable gate array (FPGA) platform due to its high efficiency and superior performance. FPGA based EMT simulations – A key for Digital Twin were mainly based on Single-Precision calculations, but ignored potential accumulation displacement. To address this problem, this paper proposes full Double-Precision and Mixed-Precision Floating-Point schemes to achieve optimal balance between numerical accuracy and computational resource cost in FPGA-based EMT simulation even for long duration simulations. Furthermore, adjustable pipeline, address dynamic access and sequence controller techniques for solving high fanout and long datapath hardware implementation are developed to optimize resource usage and timing constraints for all schemes. For non-rotating components, full Double-Precision and full Single-Precision both shows excellent convergence. For rotating components, extra Single-Precision iteration method and Mixed-Precision calculations are compared for Synchronous Machines (SG) with strong nonlinearity, and it is found that only full Double-Precision could avoid phase shift problem. Based on component-level sensitivity analysis, proposed system-level Mixed-Precision scheme is able to achieve close accuracy to that of full Double-Precision scheme and additional average 20% resource reduction for Kundur's system.