Energy Storage Control via Phase-Offset PWM for Reduced Current Fluctuations
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Solution Overview
Problem
Existing battery direct converter systems face challenges in optimizing the total output voltage swing when generating an n-phase output voltage system, particularly in reducing current fluctuations and switching frequency while maintaining efficient energy storage and distribution.
Innovation Solution
A method that generates PWM drive signals with phase offsets for different energy supply branches, using only voltage space vectors closest to the target voltage space vector, thereby reducing current fluctuations and switching frequency by selectively using adjacent voltage space vectors to generate phase voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If PWM drive signals are generated with phase offsets for different energy supply branches, then current fluctuations are reduced and switching frequency is lowered, but the complexity of the control system increases
Solution Approach 1:
The control system dynamically selects voltage space vectors based on real-time comparison between reference signals and actual voltage vectors. This dynamic selection allows the system to adapt to changing operating conditions while maintaining reduced current fluctuations, resolving the contradiction between performance and complexity through intelligent control algorithms.
Solution Approach 2:
The system changes the phase offsets of PWM drive signals as controllable parameters for different energy supply branches. By adjusting these phase offsets, the system optimizes current distribution and reduces fluctuations without requiring fundamental changes to the hardware architecture, thus managing complexity while improving performance.
2Loss of energy
If only voltage space vectors closest to the target voltage space vector are used, then the load on switching elements is reduced and efficiency is improved, but the output voltage control precision may be compromised
Solution Approach 1:
The system uses only a subset of available voltage space vectors - specifically those closest to the target voltage space vector. This partial action approach reduces switching operations and energy loss while maintaining sufficient output voltage precision through selective vector utilization, resolving the contradiction between efficiency and precision.
Solution Approach 2:
The control system continuously compares the actual voltage space vector with the reference signal and adjusts the selection of voltage space vectors accordingly. This feedback mechanism ensures that even with limited vector selection, the output voltage precision is maintained by dynamically adapting to any deviations, thus resolving the contradiction between reduced switching loss and precision requirements.
3Loss of energy
If the switching frequency is lowered, then the efficiency of the energy storage device is improved, but the ability to respond to rapid load changes is reduced
Solution Approach 1:
The system employs periodic PWM signals with optimized phase offsets to achieve effective voltage control at lower switching frequencies. By using periodic action with carefully timed phase relationships between different energy supply branches, the system maintains efficiency while preserving adequate response capability through the cumulative effect of phased switching operations.
Data Source
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AI summary
The invention relates to a method for controlling an energy storage device that comprises n output connections, wherein n >= 2, for producing a supply voltage at each of the output connections, and n energy supply branches, which are each coupled to one of the output connections, wherein each of the energy supply branches comprises a plurality of series-connected energy storage modules that each comprise an energy storage cell module comprising at least one energy storage cell, and a coupling device having coupling elements in a full bridge circuit that is designed to connect or bridge the energy storage cell module selectively in the respective energy supply branch. The method according to the invention comprises the following steps: for a number k of energy storage modules of at least one first energy supply branch, generating a first pulse width modulated control signal for controlling the coupling devices of the respective energy storage modules by comparing a first target value signal with a number 2 k first periodic reference signals having a pulse period T, which signals each have a phase shift of T/2k relative to the adjacent first reference signals; and, for a number k of energy storage modules of at least one second energy supply branch, generating a second pulse width modulated control signal for controlling the coupling devices of the respective energy storage modules by comparing a second target value signal with a number 2k of second periodic reference signals having the pulse period T, which each have a phase shift of T/2k relative to the adjacent second reference signals. The second reference signals each have a phase shift of T/4k relative to the first reference signals.