Battery PCS CVCF Mode for Stand-Alone Microgrid Frequency Control
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Solution Overview
Problem
Stand-alone microgrids face challenges in maintaining stable frequency and reducing fuel costs due to high diesel generator reliance and fluctuations in renewable energy sources, leading to inefficient power generation and frequent control transfers between diesel generators and battery energy storage systems.
Innovation Solution
A method of controlling the frequency of a stand-alone microgrid by operating the battery power conditioning system in constant voltage constant frequency mode, measuring the state of charge, and adjusting controllable loads and diesel generator operation based on reference thresholds to stabilize frequency and voltage, thereby using renewable energy as the main power source and minimizing diesel generator use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diesel generator is used as main power source to secure power supply reliability, then power supply reliability is improved, but fuel cost increases and power generation efficiency decreases
Solution Approach 1:
The patent implements dynamic role assignment where the battery energy storage system can switch between auxiliary and main power source roles based on real-time system conditions. The battery PCS operates in different modes (PQ mode for auxiliary support, CVCF mode for main power source) to dynamically optimize the balance between reliability and fuel efficiency.
Solution Approach 2:
The patent changes the operational parameters of the battery PCS from fixed PQ mode to variable modes including CVCF mode. By adjusting control parameters such as voltage and frequency regulation capabilities, the system can operate the battery as main power source when renewable energy is sufficient, thereby reducing diesel generator usage and fuel consumption while maintaining reliability.
2Stability of the object's composition
If battery energy storage system is used to compensate output fluctuation of renewable energy, then output stability is improved, but frequent control transfer between diesel generator and battery causes excessive disturbance
Solution Approach 1:
The patent designs the battery PCS with multi-functional capability to perform both PQ operation (auxiliary support) and CVCF operation (main power source with voltage and frequency control). This universal design allows the battery to independently maintain system stability without requiring frequent control transfers, thereby reducing disturbances while maintaining output stability.
Solution Approach 2:
The patent implements a control transfer suppression mechanism that uses feedback from system frequency and voltage measurements. When the battery operates in CVCF mode, the control system continuously monitors system parameters and provides feedback to maintain stable operation, preventing unnecessary control transfers and reducing disturbances during mode transitions.
3Ease of operation
If battery operates in PQ operation mode with PLL synchronization, then voltage and frequency control is simplified, but battery cannot independently control system frequency
Solution Approach 1:
The patent dynamically switches the battery PCS operational mode from fixed PQ mode to CVCF mode based on system needs. In CVCF mode, the battery independently controls system voltage and frequency without relying on PLL synchronization with the diesel generator, thereby gaining frequency control capability while maintaining operational simplicity through automated mode selection.
Data Source
AI summary
The present invention relates to a method for controlling the frequency of a stand-alone microgrid wherein an energy storage device of the stand-alone microgrid is operated as a main power source by controlling a battery power conditioning system (PCS) of the stand-alone microgrid in a constant voltage constant frequency (CVCF) mode. According to the present invention, it is possible to operate the frequency stably while considering the fuel cost and power generation efficiency of a stand-alone microgrid.