Modular Multilevel Converter Harmonic Injection for Ultracapacitor Thermal Management
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Solution Overview
Problem
Modular multilevel converters face challenges in reducing root-mean-square (RMS) current flowing through ultracapacitors, which can lead to increased temperature and decreased lifespan due to heavy current usage, especially below the 1 kHz range.
Innovation Solution
Injecting even-order harmonics into the modular multilevel converter legs based on operational parameters and calibration data to reduce the RMS current conducted by ultracapacitors, thereby controlling the temperature and extending their lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If heavy current is used to power the modular multilevel converter, then the power output is sufficient, but the root-mean-square current flowing through ultracapacitors increases leading to increased temperature and decreased lifespan
Solution Approach 1:
The patent changes the frequency parameter of current by injecting even-order harmonics (2nd, 4th, 6th harmonics) at frequencies below 1 kHz. This parameter change redistributes the current spectrum, reducing the RMS current magnitude at problematic frequencies while maintaining sufficient power output capability.
Solution Approach 2:
The patent employs a composite current waveform consisting of fundamental frequency components and injected even-order harmonic components. This composite waveform structure allows the system to maintain power output while reducing thermal stress on ultracapacitors through frequency distribution.
2Power
If heavy current flows through ultracapacitors, then power delivery is maintained, but temperature increases reducing component reliability
Solution Approach 1:
By injecting even-order harmonics, the patent changes the frequency distribution parameter of the current waveform. This redistribution reduces concentrated current magnitude at specific frequencies, thereby reducing I²R heating effects and ultracapacitor temperature while preserving overall power delivery capability.
3Reliability
If even-order harmonics are injected, then RMS current and temperature of ultracapacitors are reduced, but system complexity increases due to additional control mechanisms
Solution Approach 1:
The controller performs multiple functions: it generates the fundamental frequency output waveform, determines operational parameters, calculates harmonic injection parameters, and executes the actual harmonic injection. This multi-functionality reduces the need for separate dedicated harmonic injection hardware, thereby limiting the increase in system complexity.
Solution Approach 2:
The system uses feedback by determining operational parameters from actual converter operation and using these parameters to dynamically adjust harmonic injection settings. This feedback mechanism allows adaptive optimization of ultracapacitor protection while maintaining manageable control complexity through parameter-based control.
Data Source
AI summary
Systems and methods to improve operation of a modular multilevel converter. Some embodiments include a first upper arm with a first active power link module, which facilitates producing a first portion of a first alternating current electrical power at a base frequency and injecting a first even-order current harmonic of the base frequency in the first upper arm, and a first lower arm with a second active power link module, which facilitates producing a second portion of the first alternating current, in which the first portion of the first alternating current and the second portion of the alternating current are combined to facilitate outputting the first alternating current electrical power at a first alternating current terminal, and injecting the first even-order current harmonic in the first lower arm, in which magnitude of the first even-order current harmonic is zero at the first alternating current terminal.