MMC Module SoH Estimation Using Circulating Current Pulses
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Solution Overview
Problem
Existing methods for determining the state of health (SoH) of energy storage modules in a system require additional sensors, increasing complexity and cost, and are limited by the sampling frequency of existing electronics, making it difficult to measure SoH at the module level accurately.
Innovation Solution
A method using a multilevel modular converter (MMC) to generate a circulating current with a pulse pattern that allows measurement of module voltage and current, enabling determination of individual module resistance without additional sensors, by utilizing existing electronics to calculate SoH based on these measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrical impedance spectrum method is used to measure SoH, then measurement capability is provided, but additional sensors are required which increases system complexity and cost
Solution Approach 1:
The energy storage modules use their own existing voltage and current sensors to measure module-level parameters, eliminating the need for additional dedicated sensors. The modules self-monitor their electrical characteristics (voltage, current, resistance) which are then used to determine SoH, making the system self-servicing rather than requiring external measurement infrastructure
Solution Approach 2:
The existing voltage and current sensors in the energy storage modules are made multi-functional by using them not only for their primary control functions but also for SoH measurement. The same sensors serve dual purposes: real-time control and health monitoring, thereby avoiding additional hardware complexity
2Measurement precision
If additional sensors are added to measure SoH at module level, then measurement precision is improved, but system cost increases
Solution Approach 1:
The system uses already-installed sensors within each energy storage module to perform SoH measurements, making the existing infrastructure serve the additional function of health monitoring. This eliminates the need to purchase and install separate measurement devices, directly reducing system cost while maintaining module-level measurement precision
Solution Approach 2:
The voltage and current sensors are designed to perform multiple functions: real-time control operations and SoH determination. By making these sensors multi-functional, the patent avoids the cost of additional dedicated measurement equipment while achieving accurate module-level SoH monitoring
3Device complexity
If existing electronics are used for measurement, then device complexity is reduced, but sampling frequency limitations prevent accurate SoH determination
Solution Approach 1:
The patent implements periodic measurement cycles where the system alternates between normal operation and measurement modes. During designated measurement intervals, the existing electronics perform SoH measurements at optimized sampling rates, while during normal operation they maintain system control. This periodic approach allows adequate sampling for accurate measurement without requiring continuous high-frequency operation that would exceed existing electronics capabilities
Solution Approach 2:
The system performs measurements at strategically chosen moments before critical decisions are needed, such as before charge/discharge cycles or at scheduled intervals. By timing measurements preliminarily and proactively, the system obtains accurate SoH data using existing electronics without needing continuous high-speed sampling, as measurements are taken at optimal moments when adequate resolution can be achieved
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate SoH determination at the module level, facilitating proactive maintenance, reducing the risk of failures, and improving the reliability and availability of grid-connected energy storage systems.
Implementation Method 1
controlling the MMC to generate a circulating current with a pulse pattern having different levels and that circulates through the energy storage modules
Implementation Method 2
determining an individual module resistance for each energy storage module based on the respective module voltage and the respective module current at the different levels in the pulse pattern
Data Source
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AI summary
There is disclosed herein a method for determining SoH of an energy storage module (22) of an energy storage system (20) of an arrangement (1). The energy storage system is connected to an alternating current, AC, power grid (2) through a multilevel modular converter, MMC (10) of the arrangement. The method comprises controlling the MMC to generate a circulating current with a pulse pattern having different levels and that circulates through the energy storage modules, measuring a module voltage over and a module current through each energy storage module, determining an individual module resistance for each energy storage module based on the respective module voltage and the respective module current at the different levels in the pulse pattern, and determining a SoH for each energy storage module based on the individual module resistance. There is further disclosed herein a control unit (50) and an arrangement.