Dynamic Carrier Selection for Multilevel Converter PWM Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional multilevel power converter control methods, such as phase-shifted pulse width modulation (PS-PWM), do not provide an optimal spectrum for line-line output voltage, especially at high output voltage frequencies or with a low number of levels, leading to increased losses when trying to improve voltage quality.
Innovation Solution
A dynamic pulse width modulation (PWM) method that selects a carrier signal from a plurality of carriers with different waveform shapes, based on the slope of the reference signal, to control switching events in multilevel converters, ensuring synchronized rising or falling ramps during transitions between bands to minimize pulse distortions and maintain uniform switching events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional phase-shifted PWM method is used, then the control is simple, but the output voltage spectrum quality deteriorates at high frequency or low levels
Solution Approach 1:
The patent applies dynamics by making the carrier signal selection adaptive and dynamic rather than fixed. The controller dynamically selects from multiple carrier signals based on real-time operating conditions (output voltage frequency and converter level), allowing the system to optimize its PWM strategy for each operating point, thereby resolving the contradiction between simple control and high spectrum quality.
Solution Approach 2:
The patent changes the parameter of carrier signal characteristics (waveform shape, frequency, amplitude) based on operating conditions. By having multiple carrier signals with different parameters stored in memory and selecting the appropriate one dynamically, the system achieves high output voltage spectrum quality across different frequencies and levels while maintaining manageable control complexity through automated selection.
2Manufacturing precision
If switching frequency is increased to improve voltage quality at high output frequency or low levels, then the output voltage spectrum quality improves, but the overall losses increase
Solution Approach 1:
The patent optimizes the carrier signal parameters (frequency, waveform shape) to achieve high output voltage spectrum quality without necessarily increasing the switching frequency. By using appropriately shaped carrier signals matched to operating conditions, the system reduces harmonic distortions and improves voltage quality while avoiding the energy losses associated with higher switching frequencies.
Solution Approach 2:
The patent uses pre-defined carrier signal templates stored in memory that have been optimized for different operating conditions. Instead of generating optimal carrier signals in real-time, the system copies from pre-computed optimal carrier signals, reducing computational complexity and enabling efficient selection of energy-optimal switching strategies for each operating point.
3Manufacturing precision
If multiple carrier signals with different waveform shapes are dynamically selected, then the output voltage and current spectra quality is enhanced, but the device complexity increases
Solution Approach 1:
The patent implements a universal controller that handles multiple functions: storing multiple carrier signals, determining operating conditions, selecting appropriate carriers, and generating PWM signals. This multi-functional approach consolidates complexity into a single control unit rather than requiring separate specialized circuits for each function, thereby achieving high spectra quality while managing overall device complexity.
Solution Approach 2:
The patent performs preliminary action by pre-computing and storing optimized carrier signals for various operating conditions in memory before actual operation. This pre-preparation eliminates the need for complex real-time calculations during operation, reducing the computational burden and simplifying the control system implementation while maintaining high output spectra quality.
Data Source
AI summary
A method for controlling a switching device of a multilevel converter includes dynamically selecting a carrier and generating a switching signal to effect a switching event of the switching device based on a comparison of the dynamically selected carrier with a reference signal. The carrier is dynamically selected from a multiple carriers, each corresponding to one of multiple contiguous bands into which range of a waveform of the reference signal is divided. The carriers corresponding to different bands have differing waveform shapes. The dynamically selected carrier corresponds to the band instantaneously occupied by the reference signal. The dynamic selection is executed whereby whenever there is a transition of the reference signal from a first band to a second band, the carriers for the first and second bands are selected dependent on a slope of the reference signal waveform at the transition.