Battery Converter Voltage Synchronization for DC Link Ripple Suppression
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Solution Overview
Problem
In power conditioning systems with twin converters, the controllability of the battery converter is degraded when the current passing through the battery converter is near zero and the output current of the fuel cell is in a low current region, leading to poor control of the DC link voltage and subsequent torque variations in the drive motor due to control delays and overshooting.
Innovation Solution
A power conditioning system with a voltage adjusting unit to synchronize the output voltages of the fuel cell and battery converters and a ripple suppressing unit to manage the DC link voltage, specifically by adjusting the ON-duty ratios of the switching elements in the battery converter to prevent overshooting and control delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the battery converter operates with near-zero passing current in low fuel cell current region, then the system maintains power supply capability, but the controllability of DC link voltage deteriorates and overshooting occurs
Solution Approach 1:
The control method performs preliminary detection of the passing current magnitude before the switching operation occurs. When the passing current is detected to be below the threshold and fuel cell current is low, the control method preemptively adjusts the battery converter switching timing to prevent overshooting before it occurs, rather than reacting after the problem arises
Solution Approach 2:
The invention changes the control parameters of the battery converter by adjusting the switching timing of the step-down and step-up switching elements. By modifying when these switches operate (changing the timing parameter), the system prevents overshooting while maintaining the ability to supply power in near-zero current conditions
2Speed
If the switching operation of fuel cell converter is started under near-zero passing current condition, then the system responds to load requests, but control delay occurs and DC link voltage overshoots
Solution Approach 1:
The control method implements feedback by continuously detecting the magnitude of passing current through the battery converter and the current output of the fuel cell. Based on this feedback information, the controller determines whether to adjust the battery converter switching timing, creating a closed-loop control system that maintains precision while responding quickly to load changes
Solution Approach 2:
The invention introduces dynamic adjustment of the battery converter switching timing based on real-time operating conditions. When passing current is near-zero and fuel cell current is low, the switching timing is dynamically adjusted to prevent overshooting; under other conditions, normal switching operation proceeds, allowing the system to adapt its control strategy to current operating conditions
Data Source
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Figure 3(a)~3(d)
AI summary
A power conditioning system that includes a fuel cell to be connected to a load, a fuel cell converter connected between the fuel cell and the load, the fuel cell converter converting an output voltage of the fuel cell at a predetermined required voltage ratio, a battery connected in parallel with the fuel cell with respect to the load, the battery serving as a power supply source different from the fuel cell, a battery converter connected between the battery and the load, the battery converter converting an output voltage of the battery at a predetermined required voltage ratio, a voltage adjusting unit configured to adjust an output voltage of the battery converter to a predetermined voltage to generate a DC link voltage for synchronizing an output voltage of the fuel cell converter and the output voltage of the battery converter, and a ripple suppressing unit configured to cause the battery converter to suppress a ripple component of the DC link voltage in a situation where the DC link voltage is higher than the output voltage of the battery.