Grid frequency fluctuates constantly with load changes and new energy output variations. To maintain the rated frequency of 50Hz and ensure power grid stability, the power system adopts a two-level frequency regulation mechanism, namely primary frequency regulation and secondary frequency regulation. The two mechanisms have clear divisions in response logic, speed, accuracy and regulation duration, forming the core guarantee system for grid frequency stabilization.

1. Primary Frequency Regulation (Inertial Fast Frequency Regulation)

Primary frequency regulation is the first instantaneous frequency stabilization line of defense for the power grid. It is a passive, differential regulation mechanism and an inherent inertial characteristic of synchronous generator sets, requiring no dispatching instructions. When instantaneous power surplus or shortage occurs and grid frequency deviates abruptly, all synchronous units rapidly adjust active power output relying on rotor inertia, restraining sudden frequency rises or drops and preventing large-scale grid frequency fluctuations.

Core Characteristics: Extremely fast response (millisecond to second level), short-time instantaneous action, and belongs to coarse regulation. It only stabilizes sudden frequency variations and cannot restore the frequency accurately to the rated 50Hz, leaving fixed static deviation, serving only as an emergency stabilization method.

2. Secondary Frequency Regulation (Accurate Deviation Correction)

Secondary frequency regulation is the core regulation method for precise frequency recovery and deviation elimination. It adopts active dispatching and non-differential precise regulation. Issued with AGC instructions by the grid dispatching center, it accurately adjusts the steady-state active power output of generating units and energy storage equipment, eliminates residual frequency deviations from primary regulation, and finally restores the grid frequency to the standard 50Hz. It also balances tie-line power to realize regional grid power equilibrium.

Core Characteristics: Relatively slow response (second to minute level), sustainable steady-state regulation, and high-precision fine regulation. It completely eliminates static frequency deviations left by primary regulation and ensures long-term rated-frequency operation of the power grid.

3. Core Differences Summary

• Response Logic: Primary frequency regulation: passive inertial response, automatic synchronous action without dispatching commands; Secondary frequency regulation: active dispatch response, precise regulation based on AGC instructions.

• Response Speed: Primary frequency regulation: millisecond/second level with ultra-fast anti-disturbance capability; Secondary frequency regulation: second/minute level, lagging behind instantaneous fluctuations.

• Regulation Target: Primary frequency regulation: suppress violent frequency mutations and stabilize instantaneous operating conditions; Secondary frequency regulation: restore frequency to rated value and eliminate static deviations.

• Operating Duration: Primary frequency regulation: short-time instantaneous action; Secondary frequency regulation: continuous steady-state adjustment.

• Regulation Property: Primary frequency regulation: differential coarse regulation with allowable minor frequency deviation; Secondary frequency regulation: non-differential precise regulation to restore 50Hz rated frequency.

I. Core Role of Supercapacitors in Primary and Secondary Frequency Regulation

Traditional thermal power, hydropower and lithium battery frequency regulation resources have obvious shortcomings. Mechanical inertia causes delayed responses, making them unable to capture millisecond-level high-frequency grid disturbances. Frequent deep regulation leads to unit wear, while lithium batteries suffer severe capacity attenuation and short service life under high-frequency cycling. Supercapacitors are divided into EDLC electric double-layer supercapacitors and HESC hybrid supercapacitors. With millisecond-level ultra-fast response, million-level high-frequency cycle life, inherent safety without thermal runaway, and stable wide-temperature operation, they perfectly adapt to the differentiated working conditions of two-level grid frequency regulation and effectively make up for the performance defects of traditional frequency regulation resources.

1. Role in Primary Frequency Regulation: Ultra-Fast Transient Support

Primary frequency regulation imposes strict requirements on response speed, instantaneous power and high-frequency anti-interference performance, making it the most applicable scenario for supercapacitors. Instantaneous frequency drops or rises caused by new energy grid integration fluctuations and load mutations cannot be responded to in time by traditional units, easily leading to frequency limit violations and grid disturbances.

Supercapacitors deliver millisecond-level ultra-fast charge and discharge response, far faster than traditional generator sets. They accurately capture instantaneous power gaps and frequency disturbances from new energy grid integration and load changes, complete power absorption and release in advance, and rapidly suppress transient frequency fluctuations, filling the response lag gap of traditional units. Supporting tens of thousands of high-frequency cycles daily with negligible attenuation, supercapacitors continuously adapt to small, high-frequency and instantaneous grid disturbances. They significantly improve the dynamic response speed, regulation accuracy and operational stability of primary frequency regulation, effectively avoiding grid safety risks caused by transient frequency out-of-limit events.

2. Role in Secondary Frequency Regulation: Accurate Energy Compensation and Steady-State Correction

Secondary frequency regulation focuses on steady-state minor power correction and continuous power balance adjustment, requiring high output stability and linearity. HESC hybrid supercapacitors feature both high-power response and superior energy characteristics compared with pure EDLC, making them the optimal choice for secondary frequency regulation conditions.

During the ramping up or down lag of traditional units after AGC instruction issuance, HESC supercapacitors intervene rapidly at the millisecond level to compensate system power deviations in a linear and continuous manner and smooth steady-state grid power fluctuations. They fill the regulation gap of conventional units, improve the overall response speed of secondary frequency regulation, and reduce frequent start-stop and deep load adjustment of thermal power and lithium battery units, lowering unit energy consumption and mechanical wear. Meanwhile, they assist in eliminating residual static frequency deviations from primary regulation, precisely restoring grid frequency and significantly improving secondary frequency regulation qualification rate and full-grid steady-state control efficiency.

II. Summary: Adaptive Value of Supercapacitors in Two-Level Frequency Regulation

Primary frequency regulation relies on ultra-fast response: EDLC pure supercapacitors focus on millisecond-level transient anti-interference and high-frequency fluctuation suppression, solving the problem of delayed response to instantaneous high-frequency disturbances and strengthening the grid’s first line of instantaneous frequency stabilization.

Secondary frequency regulation relies on balanced steady-state control: HESC hybrid supercapacitors leverage balanced power and energy performance to assist accurate steady-state correction and smooth continuous power fluctuations, reducing the regulation pressure and loss of traditional units, and improving frequency regulation accuracy and grid economic operation.

The two types of supercapacitors work in coordination and complement each other, fully compensating the weaknesses of traditional frequency regulation systems including slow transient response, poor high-frequency cycle durability and low steady-state accuracy. They serve as core energy storage supporting equipment for high-frequency, high-precision, high-reliability and long-lifespan frequency regulation services in new power systems.