DC Link Voltage Control in Multi-Converter Energy Storage
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Solution Overview
Problem
Energy storage systems with multiple DC/DC converters face challenges in maintaining system voltage stability, particularly when individual converters' state of charge reaches limits, leading to potential circulating currents and control divergence.
Innovation Solution
A control method where one power converter performs constant voltage mode control for the DC link, and others perform constant power or constant current mode control, with the ability to switch control to another converter based on state of charge, ensuring stable voltage maintenance by temporarily shared control before exclusive transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a separate DC/DC converter is used for each battery with individual output calculation, then battery control flexibility is improved, but system voltage stability deteriorates
Solution Approach 1:
The patent merges the DC link voltage control function into the DC/DC converters, allowing them to perform both individual battery control and collective voltage stabilization. The DC/DC converters are configured to cooperate with each other, with at least one converter performing constant voltage control on the DC link while others perform constant power control, thus combining individual adaptability with system-wide stability.
Solution Approach 2:
The control mode of each DC/DC converter is dynamically adjusted based on the state of charge (SOC) of connected batteries. When a battery's SOC reaches upper or lower limits, the control mode of its corresponding DC/DC converter is switched between constant voltage and constant power modes, enabling adaptive response to changing system conditions while maintaining voltage stability.
2Stability of the object's composition
If constant voltage control is performed by one DC/DC converter, then DC link voltage stability is improved, but control reliability deteriorates when battery SOC reaches limits
Solution Approach 1:
Different DC/DC converters perform different control functions based on the SOC status of their connected batteries. Converters connected to batteries within SOC limits perform constant power control, while converters connected to batteries at SOC limits perform constant voltage control. This localized differentiation ensures that voltage control reliability is maintained even when individual batteries reach their charge limits.
3Reliability
If multiple DC/DC converters perform constant voltage control simultaneously, then voltage control redundancy is improved, but circulating currents increase
Solution Approach 1:
The patent creates an asymmetric control configuration where only one or a limited number of DC/DC converters perform constant voltage control on the DC link, while other converters perform constant power control. This asymmetric arrangement prevents multiple converters from simultaneously attempting to regulate voltage, thereby eliminating the conditions that would generate circulating currents while maintaining sufficient control redundancy.
Data Source
AI summary
An energy storage system may comprise: a plurality of power converters configured to perform DC/DC conversion in connection with respective battery racks; a power conversion system (PCS) configured to perform power conversion between the power converters and a power grid; and a battery section controller interworking with the plurality of power converters and the power conversion system, wherein the battery section controller is configured to control a first power converter among the plurality of power converters to perform constant voltage (CV) mode control for maintaining a voltage of a DC link at a constant level, to check a state of a first battery rack to which the first power converter is connected, and to change a subject to perform the CV mode control for the DC link according to the state of the first battery rack.