Variable-Frequency PWM for EMI Control in Multilevel Converters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-efficiency, high-power density power electronic converters face challenges in reducing switching losses and electromagnetic interference (EMI) while maintaining balanced energy storage in multi-level converters, particularly with the use of fast SiC and GaN switches, which can lead to unbalanced voltage ripples and increased EMI.
Innovation Solution
A pulse width modulation method that generates switching signals with variable frequencies to balance energy storage components, such as flying capacitors, by inducing half pulses during frequency transitions, reducing high-frequency voltage ripples and EMI, and using a combination of digital and analog signal processing for efficient modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If standard silicon-based switches are replaced with faster SiC and GaN switches to reduce switching loss and improve efficiency, then switching loss is reduced and efficiency is improved, but electromagnetic interference increases significantly
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The modulation technique dynamically adjusts the switching frequency within a range, transforming the static frequency characteristic into a dynamic one. This allows the system to benefit from high-frequency switching for reduced switching loss while dynamically managing the frequency to suppress electromagnetic interference peaks.
Solution Approach 2:
The patent changes the frequency parameter of the switching signals from a fixed value to a variable value that can be modulated. By varying the switching frequency within a specified range according to a modulation technique, the system achieves both reduced switching losses (benefiting from higher frequencies) and suppressed electromagnetic interference (achieved through frequency variation that avoids resonant peaks).
2Object-generated harmful factors
If variable frequency switching signals are generated to reduce electromagnetic interference, then electromagnetic interference is reduced, but energy storage components become unbalanced
Solution Approach 1:
The patent incorporates feedback mechanisms that monitor the state of energy storage components (such as capacitor voltages or inductor currents) and use this information to adjust the switching frequency modulation. This feedback ensures that while the frequency varies to suppress EMI, the energy storage components remain balanced, preventing instability in the system composition.
Solution Approach 2:
The patent employs periodic modulation of the switching frequency rather than random or continuous variation. By applying periodic action with specific patterns, the system achieves EMI suppression through frequency variation while maintaining periodicity that helps balance the energy storage components over each modulation cycle, preventing cumulative imbalances.
Data Source
AI summary
As more power electronics apparatuses use fast switches, such as silicon carbide (SiC) or gallium nitride (GaN) switches. to improve the efficiency and reduce switching losses. significantly higher electromagnetic interferences (EMI) are generated as a result. While techniques of random pulse-width modulation (PWM) have been developed to reduce this increased EMI, the use of such techniques leads to an unbalance of the stored electric energy of the energy storing components used to balance the energy across some of the switches of these apparatuses. This issue can be solved with a novel pulse width modulation method for generating the switching signals with variable frequencies for a converter's high-frequency switches that better balance its energy balancing components. This novel method can utilize comparing a reference signal to a carrier signal that can be generated with various switching frequencies that are phase-shifted from the following set of switching frequency, by (2N−1)π radians.