Abstract
As the increasing penetration of inverter-based generation (IBG) and the consequent displacement of traditional synchronous generators (SGs), the system stability and reliability deteriorate for two reasons: first, the overall inertia decreases since the power electronic interfaces (PEIs) are almost inertia-less; second, renewable generation profiles are largely influenced by stochastic meteorological conditions. To strengthen power systems, the concept of the virtual synchronous generator (VSG) has been proposed, which controls the external characteristics of PEIs to emulate those of SGs. Currently, PEIs could perform short-term inertial and primary frequency responses through the VSG algorithm. For renewable energy sources (RES), deloading strategies enable the generation units to possess active power reserves for system frequency responses. Additionally, the deloading strategies could provide the potential for renewable generation to possess long-term frequency regulation abilities. This paper focuses on emulation strategies and economic dispatch for IBG units to perform multiple temporal frequency control. By referring to the well-established knowledge systems of generation and operation in conventional power systems, the current VSG algorithm is extended and complemented by the emulation of secondary and tertiary regulations. The reliability criteria are proposed, considering the loss of load probability (LOLP) and renewable spillage probability (RSP). The reliability criteria are presented in two scenarios, including the renewable units operated in maximum power point tracking (MPPT) and VSG modes. A LOLP-based economic dispatch (ED) approach is solved to acquire the generation and reserve schemes. The emulation strategies and the proposed approach are verified by simulation.
Highlights
Renewable energy, such as photovoltaics and wind power, has been widely utilized in power systems to tackle environmental crises and to sustain economic development during the past few decades [1,2]
Based on the fluctuation properties in each scenario, when the RG unit is under maximum power point tracking (MPPT) mode, the downward reserve is determined according to the forecast uncertainties of the renewable generation and load
When the RG unit is under virtual synchronous generator (VSG) mode, the downward reserve is determined according to the uncertainties of the load forecast only
Summary
Renewable energy, such as photovoltaics and wind power, has been widely utilized in power systems to tackle environmental crises and to sustain economic development during the past few decades [1,2]. With higher penetration of renewable generation, the IBG units would eventually and inevitably take the responsibility of regulating the overall energy balance because of the consequent displacement of traditional SGs. the flexibility of the power system operation requires the VSG algorithm to extend its application scope. This strategy may cause another issue called the second frequency drop (SFD) This is because when the response capability is exhausted, RG units must decrease their output power and restore initial states (such as rotor speed or DC bus voltage) by their own generation capabilities for self-stability, disregarding the actual system frequency conditions. The deloading strategy enables the renewable units to function as long-term power reserves to provide PFR, and secondary frequency regulation (SFR).
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