SOC Management System Using P-f Droop Control for Energy Storage
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Solution Overview
Problem
Energy storage devices in existing systems are often rejected from participating in frequency control due to their state of charge (SOC), leading to reduced user incentives and system inefficiencies, as they fail to respond to frequency control signals when their SOC exceeds certain levels.
Innovation Solution
An SOC management system and method that employs active power/frequency (P-f) droop control using a droop coefficient, reference frequency, and dead band to determine output power, allowing energy storage devices to participate in frequency control without rejection, thereby stabilizing SOC and improving system efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If energy storage devices are managed using traditional SOC-based priority determination, then devices with SOC within reference levels can participate in frequency control, but devices with SOC exceeding reference levels are rejected from the power grid system
Solution Approach 1:
The invention changes the control parameter from binary rejection/acceptance based on SOC thresholds to continuous P-f droop control. Instead of rejecting devices when SOC exceeds reference levels, the system adjusts the output power parameter continuously based on frequency deviation and droop coefficient, allowing all devices to participate with varying contribution levels.
Solution Approach 2:
The invention introduces dynamic P-f droop control that adapts to real-time frequency conditions. The output power of energy storage devices is dynamically adjusted based on the frequency deviation from nominal value, allowing the system to respond flexibly to frequency variations without rigid SOC-based rejection criteria.
2Power
If energy storage devices discharge when frequency is low and charge when frequency is high, then frequency control is achieved, but devices with extreme SOC levels are rejected from further participation
Solution Approach 1:
The invention implements feedback-based P-f droop control where the output power of energy storage devices is continuously adjusted based on frequency deviation feedback. The control system monitors frequency variations and dynamically adjusts charging/discharging power to maintain frequency stability, preventing extreme SOC conditions that would lead to rejection.
Solution Approach 2:
The invention performs preliminary SOC management through proportional control based on frequency deviation. By adjusting output power in proportion to frequency deviation before SOC reaches extreme levels, the system prevents devices from entering rejected states, ensuring continuous participation capability.
3Reliability
If generators operate with fluctuating output power to balance frequency variations, then frequency stability is maintained, but total system generation energy decreases
Solution Approach 1:
The invention enables energy storage devices to perform multiple functions: frequency control through P-f droop response and energy arbitrage through economic dispatch. This multi-functionality allows generators to maintain stable output power while energy storage devices handle frequency variations, thereby maintaining both frequency stability and maximizing total system generation energy.
Solution Approach 2:
The invention introduces energy storage devices as intermediaries between generators and the power grid. These intermediaries absorb frequency variations through P-f droop control, allowing generators to operate at stable, optimal power levels without frequent fluctuations, thereby maintaining both frequency stability and high total generation energy.
Data Source
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AI summary
The present invention relates to a state of charge (SOC) management system of an energy storage device, the system comprising at least one energy storage device, wherein the SOC management system of the energy storage device manages SOC of the energy storage device by performing P-f (active power-frequency) droop control on the basis of a droop coefficient, a reference frequency, and a dead band, which determine the output of each energy storage device.