Parallel UPS Battery Runtime via Feedback Load Balancing
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Solution Overview
Problem
In parallel UPS systems, uneven energy delivery capabilities among batteries lead to premature shutdown of weaker batteries, causing load imbalance and reduced runtime, as the system relies on even distribution of load across modules with varying battery capacities.
Innovation Solution
Implementing a communication bus for UPS modules to exchange information and using feedback control loops, specifically PID controllers with digital signal processing, to adjust load distribution based on average battery voltage, ensuring balanced energy delivery and extending runtime by shifting loads between modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If load is distributed evenly across parallel UPS modules, then system simplicity is maintained, but runtime is reduced due to weaker batteries shutting down first
Solution Approach 1:
The system implements feedback control by continuously monitoring battery voltage and comparing it to the average battery voltage. Each UPS module uses this feedback to dynamically adjust its load contribution, with modules having higher than average battery voltage increasing their load share and those with lower voltage reducing their share. This closed-loop feedback mechanism resolves the contradiction by automatically optimizing runtime without requiring complex manual configuration or centralized control.
Solution Approach 2:
The load distribution across UPS modules is made dynamic rather than static. Each module continuously adjusts its load contribution based on real-time battery voltage conditions. When battery voltage changes, the module's load share automatically changes, allowing the system to adapt to varying battery states and maximize overall runtime. This dynamic adjustment eliminates the need for fixed load distribution schemes.
2Productivity
If weak batteries are allowed to operate, then system capacity is underutilized, but system reliability decreases due to premature shutdown
Solution Approach 1:
Feedback control ensures that no single battery is overworked beyond its capacity. By continuously monitoring battery voltage and adjusting load distribution, the system prevents weak batteries from being overloaded, thereby maintaining reliability. Simultaneously, stronger batteries are utilized more fully, maximizing system capacity. The feedback mechanism dynamically balances these competing requirements.
Solution Approach 2:
The system changes the operating parameters of individual UPS modules based on their battery voltage levels. Modules with higher battery voltage are assigned higher load shares, while those with lower voltage receive lower shares. This parameter adjustment allows the system to fully utilize available capacity while maintaining reliability by keeping each battery within its safe operating range.
3Duration of action of moving object
If load is shifted to stronger batteries, then runtime is extended, but remaining modules may become overloaded
Solution Approach 1:
Feedback control prevents overload by continuously monitoring battery voltage and adjusting load distribution in real-time. When a battery's voltage drops, the system automatically reduces its load share before the battery becomes overloaded or shuts down. This prevents any single module from being overloaded while extending overall system runtime through coordinated load sharing.
Solution Approach 2:
The dynamic load sharing mechanism allows the system to respond to changing conditions in real-time. As batteries are discharged and their voltage changes, the load distribution automatically adjusts to balance the workload across all modules. This dynamic adjustment prevents overload of remaining modules while maximizing the use of available battery capacity throughout the discharge cycle.
Data Source
Figure 1~2
AI summary
An uninterruptible power supply (UPS) includes a plurality of UPS modules (10). Each of the UPS modules (10) has a battery (18) that provides power to a protected load in the event of a utility power failure. A plurality of controllers (22) control how much power each of the batteries (18) deliver to the protected load, and a communication bus (12) allows the controllers (22) to exchange information about the battery (18) voltages. One of the controllers (22) calculates the average battery voltage of the plurality of batteries (18) and adjusts the amount of energy provided by an individual battery such that the battery voltage is about equal to the average battery voltage.