Y-Connected Battery String Control for Lower AC Output Loss
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Solution Overview
Problem
The existing power supply systems that output alternating current power using a battery string face increased battery loss and efficiency deterioration due to high voltage output, which is exacerbated by high duty ratios for switches in battery circuit modules.
Innovation Solution
A power supply system that Y-connects three battery strings and employs a control device to set an offset voltage based on command voltages, controlling the duty ratio of switches in battery circuit modules to minimize battery loss, with options to set offset voltage based on amplitude, phase difference, or minimum voltage to ensure stable output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the offset voltage is set high to output alternating current power from the battery string, then the alternating current power output is achieved, but the duty ratio for driving switches increases causing battery loss to increase
Solution Approach 1:
The control device dynamically adjusts the offset voltage parameter based on the command voltage to optimize the duty ratio. By changing the offset voltage parameter adaptively rather than using a fixed high value, the system achieves alternating current power output while minimizing battery loss through optimal duty ratio control.
2Power
If the duty ratio for driving switches is increased to achieve desired voltage output, then the alternating current power output is maintained, but the current effective value of the battery string increases causing efficiency deterioration
Solution Approach 1:
The control device optimizes the duty ratio parameter by adjusting the offset voltage based on command voltage. This dynamic parameter adjustment allows the system to maintain the required voltage output while minimizing the current effective value, thereby improving overall system efficiency.
3Ease of operation
If the offset voltage is set based on fixed values, then the control is simple, but the battery loss increases and efficiency deteriorates
Solution Approach 1:
The control device uses feedback from the command voltage to dynamically adjust the offset voltage. This feedback mechanism allows the system to automatically optimize the duty ratio and minimize battery loss without requiring complex manual control, maintaining ease of operation while improving efficiency.
Data Source
AI summary
The alternating current sweep unit outputs alternating current power from three battery strings that are Y-connected. The offset voltage command Vst_offset is calculated by adding the offset component V*abc_off of the string voltage obtained from the string voltage command V*abc, the amplitude Vamp of the command voltage calculated using dq shaft voltage command values v*d and v*q, and the margin voltage Vmrg. By determining the on-time ton of the gate signal by using the string voltage command V*abc and the offset voltage command Vst_offset and performing duty control on the gate signal, it is possible to set an offset voltage corresponding to the command voltage, and thus it is possible to suppress an increase in battery loss.