Optimization and Coordination Strategy of Thermal Power Plant AGC Frequency Regulation Based on Supercapacitor Hybrid Energy Storage

With the continuous development of new power systems, large-scale integration of intermittent wind and solar power has significantly increased the frequency and amplitude of grid power fluctuations while reducing the overall rotational inertia of the power grid. Under such grid operating conditions, dispatch authorities have raised stricter technical requirements for the dynamic response capability, power tracking accuracy, qualification rate, and operational stability of thermal power plant Automatic Generation Control (AGC) systems. Traditional thermal power frequency regulation relies on boiler and turbine units with high mechanical inertia, which inherently suffers from delayed response, limited ramp rates, power overshoot and oscillation, and aggravated equipment loss caused by frequent load changes.

Lithium-ion energy storage, when independently deployed for AGC regulation, compensates for part of the dynamic response deficiencies of thermal units. However, constrained by its electrochemical characteristics, lithium batteries are poorly adaptable to high-frequency, small-amplitude, pulsed power fluctuations. Long-term high-frequency cycling accelerates battery polarization and capacity degradation, shortening service life and increasing operation and renovation costs. Consequently, standalone lithium storage cannot fully meet the long-term, stable, and cost-effective frequency regulation demands of modern power plants. To address these issues, a hybrid energy storage framework combining supercapacitors and lithium batteries is adopted. Leveraging the complementary advantages of power-type and energy-type storage, this study establishes a multi-dimensional collaborative regulation system featuring “transient high-frequency precision regulation, steady-state baseline adjustment, and thermal unit backup support”. The proposed strategy systematically optimizes AGC regulation performance and serves as a reliable technical solution for improving frequency regulation efficiency, extending equipment lifespan, and reducing operational costs for thermal power plants.

1. Operational Bottlenecks of Traditional AGC Frequency Regulation Modes

Under high renewable energy penetration scenarios, the technical limitations of pure thermal regulation and single lithium-ion storage regulation are further amplified, making it difficult to accommodate complex and fluctuating grid frequency regulation requirements. The main drawbacks are summarized as follows.

First, thermal power units exhibit insufficient dynamic response. As typical large-inertia systems, thermal units feature inherent delays in boiler combustion, steam conduction, and turbine actuation. When facing millisecond-level small-scale high-frequency grid fluctuations, thermal units fail to track power commands rapidly, resulting in tracking deviations, regulation overshoot, and operational oscillation. These defects lead to unqualified AGC assessment results and reduced auxiliary service revenue.

Second, standalone lithium storage shows limited adaptability to complex regulation conditions. Although lithium batteries excel in long-duration and steady-state power regulation, they are vulnerable to performance degradation under high-frequency pulsed charge-discharge cycles. Continuous small-scale frequent regulation accelerates internal polarization, capacity fading, and internal resistance rise, drastically shortening cycle life and increasing replacement and maintenance costs, which undermines long-term economic benefits.

Third, conventional systems lack coordinated source-grid regulation logic. Traditional frequency regulation mechanisms distribute all types of power disturbances indiscriminately to thermal units or single energy storage systems. Undifferentiated regulation causes frequent load ramping of thermal equipment and invalid cycling of energy storage devices, exacerbating mechanical wear, fuel consumption, and unnecessary system energy loss.

Fourth, unreasonable State of Charge (SOC) management leads to regulation failure. Single energy storage systems lack rapid charge recovery capability. Under bidirectional, high-frequency, and disordered grid regulation commands, SOC is prone to exceeding operational thresholds, triggering system locking and exit. This interruption breaks AGC power tracking continuity and severely impairs grid-connected stability.

2. Complementary Mechanism of Supercapacitor-Lithium Hybrid Energy Storage

The hybrid energy storage system realizes performance complementation and hierarchical load adaptation through the distinct characteristics of the two energy storage technologies, overcoming the inherent limitations of single-type regulation equipment and satisfying full-scale AGC regulation requirements.

Supercapacitors are typical physical-based power-type energy storage devices, featuring millisecond-level response, ultra-high charge-discharge rates, and an ultra-long high-frequency cycle life of up to millions of cycles. With no chemical reaction or thermal runaway risk during operation, supercapacitors deliver instantaneous power absorption and release to correct power deviations. They effectively compensate for the mechanical hysteresis of thermal units, eliminate static errors and overshoot oscillations, and are exclusively responsible for transient and high-frequency precise regulation tasks.

Lithium-ion batteries represent mainstream energy-type storage with high energy density and stable long-duration power output. Nevertheless, lithium batteries cannot withstand frequent small-amplitude pulsed cycling. Therefore, in the hybrid framework, lithium batteries undertake low-frequency, large-amplitude, and long-term steady-state power deviation regulation. This workload division avoids high-frequency damage to lithium cells, ensures accurate long-term power tracking, and maintains steady-state regulation stability.

With the collaborative hybrid architecture, thermal power units are exempt from high-frequency fine regulation tasks and only undertake medium and long-term baseline load adjustment. This mechanism significantly reduces frequent load ramping and deep cycling, effectively lowering mechanical equipment loss and fuel consumption and achieving long-term stable operation of thermal units.

3. Core Hierarchical Collaborative Optimization Strategy for AGC Frequency Regulation

Based on grid command characteristics and the respective performance advantages of supercapacitors and lithium batteries, this study proposes an integrated AGC optimization strategy featuring frequency division, dynamic SOC balancing, and coordinated anti-oscillation regulation to achieve accurate and efficient disturbance suppression.

3.1 Frequency Division and Hierarchical Power Allocation Strategy

This research adopts the industry-standard second-order high-pass and low-pass filtering algorithm to decompose real-time AGC commands. According to the universal grid frequency regulation threshold of 0.03Hz–0.1Hz, power fluctuations are classified into high-frequency transient components and low-frequency steady-state components for differentiated distribution. Short-period, small-amplitude, and reciprocating high-frequency fluctuations are fully handled by supercapacitors with millisecond-level response to eliminate transient deviations without activating thermal units or lithium storage. Long-duration, large-scale, low-frequency steady-state deviations are undertaken by lithium batteries to guarantee regulation continuity and stability. Ultra-long-term baseline load drift is corrected by thermal units through slow adjustment, preventing energy storage saturation and overload operation.

3.2 Supercapacitor Pre-Transient Compensation Mechanism

This strategy innovatively adopts a supercapacitor-prioritized response mechanism, placing supercapacitors as the first-level response unit for AGC regulation. Once transient grid power deviation occurs, supercapacitors instantly release or absorb power to suppress disturbances. After lithium batteries and thermal units complete steady-state power tracking and achieve smooth curve docking, supercapacitors gradually exit the compensation state and restore SOC without causing power gaps or waveform jitter. This mechanism reduces the thermal unit response delay from seconds to milliseconds, fundamentally solving AGC tracking lag, waveform drift, and power overshoot problems.

3.3 Dynamic Adaptive SOC Balancing Strategy

Considering the small capacity characteristics of supercapacitors and their vulnerability to over-charge and over-discharge, a closed-loop dynamic SOC management algorithm is designed. The system maintains the supercapacitor SOC within the optimal range of 40%–60% to reserve sufficient upward and downward regulation margins. When SOC approaches threshold limits, the system preferentially recovers energy through residual grid power, with auxiliary fine adjustment from lithium batteries to supplement or absorb redundant power. The entire balancing process does not interfere with real-time AGC tracking accuracy and completely avoids forced system shutdown caused by SOC out-of-limit faults. Meanwhile, lithium battery SOC is strictly constrained within a safe range to prevent deep cycling and alleviate capacity degradation.

3.4 Thermal-Storage Collaborative Anti-Overshoot Regulation Strategy

A three-level closed-loop regulation framework consisting of “thermal unit rough adjustment, energy storage precise adjustment, and supercapacitor transient correction” is constructed. Leveraging the ultra-fast dynamic correction capability of supercapacitors, the system compensates for power overshoot, undershoot, and operational oscillation caused by thermal unit mechanical inertia during load variation. The real-time deviation correction smoothes power tracking curves, eliminates inherent thermal regulation jitter and overshoot defects, and significantly improves overall AGC regulation accuracy and stability.

4. Performance and Economic Benefit Analysis

4.1 Improved Frequency Regulation Performance and Auxiliary Service Revenue

The optimized hybrid regulation system integrates ultra-fast transient response and high-precision steady-state regulation capabilities. It accurately tracks full-frequency AGC commands, effectively eliminating response lag, overshoot oscillation, and tracking deviation. The strategy significantly improves AGC qualification rate, response speed, and steady-state precision, avoiding grid assessment penalties and maximizing auxiliary service economic benefits.

4.2 Reduced Thermal Unit Loss and Power Generation Consumption

The hybrid system exempts thermal units from frequent high-frequency small-scale load changes, reducing frequent valve adjustment, boiler combustion fluctuation, and steam parameter oscillation. This optimization lowers mechanical wear and maintenance frequency, extends unit overhaul cycles and service life, and stabilizes combustion conditions to reduce coal consumption, achieving dual benefits of energy saving and equipment protection.

4.3 Enhanced Long-Term Economy of Energy Storage Systems

By implementing hierarchical task division, all high-frequency pulsed regulation that causes lithium battery aging is undertaken by supercapacitors, while lithium batteries only participate in stable steady-state regulation. This mechanism effectively avoids high-frequency cycle attenuation of lithium cells, slows down overall system degradation, and extends the full lifecycle service time of hybrid energy storage equipment. It greatly reduces long-term investment in battery replacement, system maintenance, and technical renovation, solving the poor economic efficiency problem of single lithium storage frequency regulation projects.

4.4 Improved Grid Disturbance Resistance and System Inertia Support

Facing complex operating conditions such as renewable energy output volatility, sudden load changes, and instantaneous grid disturbances, the hybrid energy storage system suppresses power and frequency oscillations within milliseconds. It effectively compensates for the insufficient rotational inertia of new power systems, enhances grid-connected operation stability, improves regional power quality, and satisfies the operational requirements of high-penetration renewable energy grids.

5. Engineering Application Scenarios

The proposed hybrid energy storage AGC optimization strategy features strong adaptability and can be widely applied to new and existing thermal power frequency regulation projects, including: (1) thermal units with low AGC qualification rates and persistent grid assessment penalties; (2) thermal power plants adjacent to wind and solar grid connection points with severe power fluctuations and high regulation pressure; (3) aging thermal units with insufficient ramp rates and prominent mechanical response hysteresis; (4) existing single lithium storage frequency regulation projects suffering from rapid attenuation, high maintenance costs, and poor economic performance; (5) smart power plants pursuing long-term unattended stable operation and maximum frequency regulation revenue.