Five-Level Power Converter With Integrated LCL Filtering
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Solution Overview
Problem
Existing power electronic converters face challenges with high power density, efficiency, and reliability due to increased complexity, size, and electromagnetic interference, particularly in variable frequency drives and renewable energy systems, lacking bidirectional capability and regenerative braking, and requiring large passive filters.
Innovation Solution
A hybrid WBG-based five-level converter with integrated double-stage filters and a novel single-carrier sensor-less modulation method, using Si and GaN MOSFETs for low and high-frequency switches, respectively, to reduce dv/dt and filter size, and enable bidirectional power flow and regenerative braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional multilevel converters (MLC) are used to achieve higher output voltage levels, then the number of voltage levels increases, but the number of required components (isolated DC-power supplies, DC-links, flying capacitors, power switches, and diodes) and control complexity are tremendously increased
Solution Approach 1:
The patent merges multiple DC-links into a single shared DC-link and combines multiple isolated power supplies into one common power supply. The flying capacitors are shared across all phases rather than being isolated per phase. This consolidation reduces the total number of components while maintaining the multilevel voltage output capability through coordinated switching of power switches and diodes.
Solution Approach 2:
The power switches and diodes in the patent serve multiple functions: they act as rectifiers during the rectification phase, as switches during the inversion phase, and as part of the multilevel voltage generation mechanism. The single DC-link and shared flying capacitors serve all three phases simultaneously, providing universal functionality across the converter system.
2Productivity
If very high switching frequency is employed in WBG device-based PECs, then power density increases, but electromagnetic interference (EMI), high dv/dt, and high reflected wave voltage overshoot ratio are increased
Solution Approach 1:
The patent introduces an intermediary filtering network consisting of LCL filters and damping resistors between the power electronic converter and the grid/motor. This intermediary structure attenuates high-frequency switching harmonics and reduces dv/dt effects, allowing the system to operate at high switching frequencies while mitigating the harmful electromagnetic interference and voltage reflections.
Solution Approach 2:
The patent employs LCL filters with specifically designed inductance and capacitance values to create a frequency-dependent impedance that blocks high-frequency switching harmonics while passing the fundamental frequency. The damping resistors are tuned to critical damping values to eliminate resonance peaks without excessive power loss, enabling high-frequency operation with controlled EMI.
3Object-generated harmful factors
If passive L filters are adopted to interconnect AFE rectifier with grid, then harmonic attenuation is achieved, but filter size and rating become very large
Solution Approach 1:
The patent transitions from a single-stage L filter to a two-stage LCL filter architecture, adding a capacitive element in parallel with the inductor. This dimensional change in the filter topology creates a second degree of freedom in the design, allowing for smaller component values while achieving the same or better harmonic attenuation performance. The LCL configuration provides both differential-mode and common-mode filtering in a more compact form.
Data Source
AI summary
A converter with lower passive filter size and increased flying capacitor charging speed during the converter start-up uses a combination of a multi-level power converter circuit having a flying capacitor in which the first switching harmonic cluster is at twice the switching frequency and an integrated double-stage filter designed to allow the flying capacitor to be efficiently balanced and to allow noise from the harmonic clusters and from switches in the power converter circuit to be suppressed. This provides for a compact power conversion apparatus.