Implementation Path of Energy Storage Power Stations with Supercapacitors Participating in Primary and Secondary Frequency Regulation

Power grid frequency modulation is a core means to ensure the stability of power system frequency, divided into two levels: primary frequency modulation and secondary frequency modulation, which jointly build a frequency safety defense line. Primary frequency modulation focuses on instantaneous frequency fluctuations at the millisecond to second level, relying on the inherent response characteristics of equipment to quickly suppress deviations; secondary frequency modulation targets persistent frequency deviations and accurately compensates for power gaps through dispatch instructions. With the increase in the penetration rate of new energy generation, the power grid inertia decreases and fluctuations intensify, making the insufficient frequency modulation capacity of traditional thermal power units increasingly prominent. Supercapacitors, with the advantages of millisecond-level response, ultra-high power density, and ultra-long cycle life, have become core components for energy storage power stations to participate in both types of frequency modulation. Their operational logic revolves around "characteristic adaptation to demand and precise strategy regulation," enabling the efficient implementation of frequency modulation tasks at different levels.

I. Supercapacitors Participating in Primary Frequency Modulation: Instant Response to Build the First Line of Defense for Frequency

Primary frequency modulation is a "passive emergency response" when there is an instantaneous deviation in the power grid frequency. Its core goal is to quickly suppress the frequency change rate and reduce the deviation peak within milliseconds to seconds to avoid the expansion of fluctuations. Its triggering does not require manual dispatch and relies on the inherent frequency response characteristics of the equipment, while the physical energy storage mechanism of supercapacitors perfectly adapts to the demand for "fast response, short duration, and high frequency."

The core operational process of supercapacitors participating in primary frequency modulation can be divided into three steps. The first step is rapid perception and triggering. The energy storage power station collects real-time power grid frequency data through Phasor Measurement Units (PMUs) with a sampling frequency of dozens of times per second. When the frequency deviation exceeds the dead zone range (usually ±0.03Hz), the primary frequency modulation mode is immediately triggered. Compared with the response delay of more than 10 seconds for traditional thermal power units, the control system of supercapacitors can complete frequency anomaly identification within 10 milliseconds, gaining time for subsequent regulation.

The second step is virtual inertia and power compensation, which is the core link of primary frequency modulation. Since new energy units such as wind power and photovoltaic power do not have the inertia support capacity of traditional synchronous machines, supercapacitors simulate the inertia characteristics of synchronous generators through virtual inertia control strategies, quickly releasing or absorbing power to suppress frequency changes. When the power grid frequency drops (insufficient power supply), supercapacitors discharge instantaneously at a high rate of more than 10C, injecting active power to fill the gap and preventing the frequency from falling further; when the frequency is too high (excess power generation), they immediately switch to charging mode to absorb surplus power and quickly pull the frequency back. In this process, supercapacitors do not require chemical reactions, and charges only migrate at the interface between electrodes and electrolytes. The charge-discharge start-up time is as low as 20 milliseconds, and a single frequency modulation action can be completed in a few seconds, perfectly coping with the instantaneous power impact brought by new energy generation.

The third step is state recovery and standby. After a single primary frequency modulation is completed and the power grid frequency returns to the safe range, supercapacitors stop charging and discharging and enter the standby state. The control system monitors its State of Charge (SOC) in real time and slowly recharges it through the grid's redundant electrical energy or lithium batteries in the hybrid energy storage system, ensuring it maintains a safe SOC range of 30%-70% to respond to the next instantaneous fluctuation at any time. At the same time, to address the problem of secondary frequency drop that is prone to occur when wind turbines participate in inertia response, supercapacitors can increase active power output during the phase when wind turbines exit inertia response, effectively offsetting this hidden danger and improving the stability of primary frequency modulation.

In practical applications, supercapacitors often participate in primary frequency modulation as independent modules or hybrid energy storage units. For example, in energy storage power stations in wind power-rich areas, supercapacitors are connected in parallel to the DC bus of wind turbines. When sudden changes in wind power output cause frequency fluctuations, they immediately respond to primary frequency modulation, providing additional inertia support for wind turbines, suppressing power fluctuations, and improving wind power consumption capacity. Their cycle life of more than 100,000 times can easily cope with the high-frequency actions of primary frequency modulation, avoiding frequent maintenance and replacement.

II. Supercapacitors Participating in Secondary Frequency Modulation: Precise Dispatching to Achieve Steady-State Frequency Control

Secondary frequency modulation is an "active precise regulation" when there is still a persistent frequency deviation after primary frequency modulation. Its core goal is to restore the frequency to the rated value (50Hz) and maintain long-term steady-state operation. It relies on Automatic Generation Control (AGC) instructions issued by the power grid dispatching center, requiring high regulation accuracy and stable continuous power compensation. Through strategy optimization and multi-device collaboration, supercapacitors can efficiently undertake such frequency modulation tasks.

The operational logic of supercapacitors participating in secondary frequency modulation focuses more on "instruction-driven and precise matching," and the process is divided into three links: instruction reception, power distribution, and collaborative regulation. The first step is AGC instruction reception and parsing. The Energy Management System (EMS) of the energy storage power station receives AGC instructions issued by the dispatching center in real time, clarifying the frequency modulation direction, required compensation power, and duration. Unlike the independent triggering of primary frequency modulation, the actions of secondary frequency modulation fully follow dispatching instructions to ensure the coordinated operation of frequency modulation resources across the entire network.

The second step is power distribution and control strategy adaptation. Combining its own characteristics and instruction requirements, supercapacitors accurately adjust output power through strategies such as droop control and model predictive control. Since secondary frequency modulation has a certain duration (usually tens of seconds to several minutes), the shortcoming of low energy density of a single supercapacitor needs to be compensated through strategies: when the instruction requires short-term high-power compensation, supercapacitors take the lead in regulation and complete power output at a high rate; when the instruction requires continuous power support, supercapacitors collaborate with lithium batteries, with supercapacitors bearing the initial instantaneous power impact and lithium batteries undertaking subsequent continuous power supply, ensuring both regulation speed and extended endurance. At the same time, the control system introduces a charge-discharge coefficient to strictly control the charge-discharge depth of supercapacitors, avoiding overcharging and over-discharging, and balancing regulation accuracy and equipment life.

The third step is dynamic regulation and effect feedback. During secondary frequency modulation, supercapacitors real-time track changes in power grid parameters and instructions through Power Conversion Systems (PCSs), dynamically adjusting output power to ensure the output error is less than 1%. After the regulation is completed, the EMS feeds back the frequency modulation effect to the dispatching center, forming a closed loop of "instruction-execution-feedback" to ensure the steady state of the entire network frequency. Compared with traditional thermal power units, supercapacitors participating in secondary frequency modulation have a response speed more than 60 times faster and higher regulation accuracy, which can significantly reduce power grid dispatching costs and improve frequency modulation benefits.

III. Collaborative Operation of Primary and Secondary Frequency Modulation: Hierarchical Adaptation Strategy of Supercapacitors

In energy storage power stations, supercapacitors do not participate in a single frequency modulation task in isolation, but achieve seamless connection and synergistic efficiency between primary and secondary frequency modulation through a hierarchical regulation strategy, maximizing their technical advantages. The core of this collaborative logic is "task allocation according to fluctuation characteristics and division of labor based on device advantages."

In terms of task allocation, supercapacitors first undertake the instantaneous power impact task of primary frequency modulation, using their millisecond-level response capability to quickly suppress high-frequency, short-duration fluctuations, avoiding the consumption of lithium batteries' cycle life by these actions; for the persistent frequency deviation remaining after primary frequency modulation, supercapacitors collaborate with lithium batteries to participate in secondary frequency modulation, with supercapacitors responsible for accurately tracking instructions and dynamically fine-tuning power, and lithium batteries responsible for continuous energy supply. This division of labor not only exerts the power advantage of supercapacitors but also makes up for their shortcoming of low energy density, improving overall frequency modulation efficiency and system life.

In terms of control strategy, the EMS of the energy storage power station realizes intelligent switching between the two frequency modulation modes through algorithms. When a sudden frequency change with a large rate of change is detected, the primary frequency modulation mode is prioritized, and supercapacitors operate independently; when the frequency deviation persists with a gentle rate of change, it automatically switches to the secondary frequency modulation mode, activating hybrid energy storage collaborative regulation. At the same time, the system balances the SOC state of supercapacitors in real time, ensuring they always have sufficient power reserves when switching between primary and secondary frequency modulation, avoiding the inability to respond to instantaneous frequency modulation demands due to low SOC.

IV. Application Advantages and Implementation Key Points: Core Value Embodiment of Supercapacitor Frequency Modulation

The core advantage of supercapacitors participating in both types of frequency modulation lies in the high alignment between their characteristics and frequency modulation demands. Compared with traditional frequency modulation methods, their millisecond-level response capability can quickly cope with new energy fluctuations and avoid the expansion of frequency deviations; their cycle life of more than 100,000 times can adapt to high-frequency frequency modulation actions, with a full-life cycle cost only 1/3 of that of lithium batteries; their wide temperature adaptation characteristic (-40℃ to 65℃) enables stable operation in extreme environments without additional temperature control equipment, adapting to the needs of energy storage power stations in different regions.

In practical application, two key points need to be grasped. First, optimization of control strategies: virtual inertia coefficients, droop coefficients and other parameters should be adjusted according to power grid fluctuation characteristics to ensure the rapidity of primary frequency modulation and the accuracy of secondary frequency modulation, while avoiding power impacts during mode switching. Second, hybrid energy storage matching: the combination of "supercapacitors + lithium batteries" makes up for the low energy density of supercapacitors, realizing the dual demands of "fast response + long endurance," extending the overall system life and improving frequency modulation benefits. For example, some large-scale energy storage power stations adopt the mode of "supercapacitors responsible for frequency modulation random components and pulsating components, and lithium batteries responsible for continuous components," reducing the average energy storage output error to less than 1% and significantly improving the frequency modulation effect.

With the advancement of new power system construction, the power grid's requirements for frequency modulation response speed, accuracy, and reliability continue to increase. Relying on their unique advantages, supercapacitors efficiently participate in primary and secondary frequency modulation through differentiated control strategies and collaborative modes, not only building the first line of defense for frequency safety but also providing precise support for steady-state control. In the future, with the iteration of material technology and cost reduction, supercapacitors will be more widely used in frequency modulation of energy storage power stations, providing core guarantees for grid stability after high-proportion new energy grid connection.