3L Flying Capacitor Converter Modulation for EMI and Ripple Control
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Solution Overview
Problem
Conventional power converters using silicon carbide (SiC) and gallium nitride (GaN) switches face significant electromagnetic interference (EMI) and voltage ripple issues due to drift between phase-shifted carrier signals, necessitating complex solutions that increase computational burden and hardware complexity.
Innovation Solution
A single-carrier sensor-less modulation method for three-level flying capacitor multicell (3L-FCM) converters generates switching signals using a constant-frequency carrier signal compared to modified reference signals, eliminating drift and reducing EMI by canceling out switching harmonic clusters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional two-carrier PS-PWM method is used to generate switching signals, then switching signals can be generated for driving the switches, but drift or time lag occurs between phase-shifted carrier signals leading to increased voltage ripple and unbalanced flying capacitor voltage
Solution Approach 1:
The patent merges two separate carrier signal generators into a single carrier signal generator that produces both phase-shifted carrier signals simultaneously. This eliminates the drift and time lag issues between separate carriers by ensuring both carriers are generated from the same reference clock source, maintaining precise 180-degree phase shift accuracy.
Solution Approach 2:
The patent creates a copy of the carrier signal with a precise phase shift using a phase-shifting circuit that replicates the original carrier waveform while maintaining exact phase relationship. This copying approach ensures that both carriers have identical frequency and amplitude characteristics with precise phase positioning.
2Productivity
If high switching frequency is employed in WBG based 3L-FCM converter, then efficiency is improved, but the impact of drift or time lag between two phase-shifted carrier signals on voltage ripple and voltage balancing is exacerbated
Solution Approach 1:
By merging the carrier generation functions into a single integrated circuit that produces both phase-shifted carriers from one reference clock, the patent eliminates cumulative timing errors that would otherwise be magnified at high switching frequencies. This ensures consistent phase relationship even when operating at elevated frequencies for improved efficiency.
3Loss of energy
If SiC and GaN switches are used to replace standard switches, then switching loss is reduced and efficiency is improved, but electromagnetic interference increases significantly requiring enlarged EMI filter
Solution Approach 1:
The patent employs periodic pulse-width modulation using phase-shifted carriers to generate switching signals that periodically modulate the power switches. This periodic action distributes the EMI energy across multiple frequency harmonics rather than concentrating it at the fundamental switching frequency, reducing peak EMI levels and allowing for more compact filtering while maintaining the high efficiency benefits of SiC and GaN devices.
Data Source
AI summary
A three-level flying capacitor multi-level (3L-FCM) power converter is controlled by a switching signal generator having a reference signal for generating switching signals for driving a first pair S1, S1′ and a second pair S2, S2′ of switches. Circuitry generates, from the reference signal, a first modified reference signal defined as half of the sum of 1 and the reference signal. From the first modified reference signal a second modified reference signal is generated having a half-period phase shift from the first modified reference signal. A carrier signal having a constant frequency is generated and a first comparator and a second comparator compare the first and the second modified reference signals to the carrier signal to generate frequency signals for driving the first pair of switches S1, S1′, and the second pair of switches S2, S2′, respectively.