Low Modulation Index 3-Phase Solid-State Transformer
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Solution Overview
Problem
Conventional solid-state transformer (SST) technologies face challenges such as high cost, limited voltage capability, efficiency losses, and electromagnetic interference (EMI) due to the need for expensive semiconductor switches and complex architectures like McMurray and Dyna-C, which also result in inefficiencies and increased core losses.
Innovation Solution
A low-modulation index, three-phase (LMI3) SST architecture using twelve 4-quadrant switches and a single transformer core, with a switching pattern that minimizes EMI and core losses, and incorporates filter circuits to suppress high-frequency components, allowing for efficient and scalable power transformation with adjustable voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If McMurray architecture uses center-tapped transformer with multiple turns to hold off full line voltage, then voltage blocking capability is improved, but leakage inductance increases and ohmic loss increases
Solution Approach 1:
The patent changes the voltage blocking parameter from full line voltage to half line voltage by using a full-bridge configuration instead of center-tapped transformer. This parameter change allows reduction of turns ratio, which directly reduces leakage inductance and ohmic loss while maintaining adequate voltage blocking capability through the bridge configuration.
Solution Approach 2:
The patent merges the voltage blocking function from the transformer windings to the full-bridge switch configuration. By combining the switching devices into a full-bridge topology, the transformer no longer needs excessive turns for voltage blocking, allowing optimization of winding parameters to reduce losses.
2Strength
If McMurray architecture uses center-tapped transformer with increased turns to prevent core saturation, then voltage holding capability is improved, but transformer size increases and ohmic loss increases
Solution Approach 1:
The patent changes the operating voltage parameter from full line voltage to half line voltage across the transformer windings. This parameter change allows the transformer to achieve the same voltage holding capability with fewer turns, directly reducing the required core cross-sectional area and overall transformer size.
Solution Approach 2:
The patent segments the voltage handling function by using multiple full-bridge configurations that each handle half the line voltage. This segmentation allows the transformer to operate at lower voltage stress per winding, enabling smaller core size while maintaining overall system voltage capability.
3Speed
If McMurray architecture toggles MOSFETs at high frequency to improve efficiency, then switching speed is improved, but EMI from inductive kick increases
Solution Approach 1:
The patent converts the harmful inductive kick effect into a beneficial continuous current flow. By using resonant inductors and capacitors, the inductive kick is transformed into controlled oscillations that maintain current flow and reduce voltage spikes, thereby reducing EMI while preserving high-frequency switching benefits.
Solution Approach 2:
The patent incorporates resonant inductors and capacitors that provide beforehand cushioning for the inductive kick. These components are pre-configured to absorb and dampen voltage spikes before they can generate significant EMI, allowing high-frequency switching to proceed with reduced electromagnetic interference.
4Adaptability or versatility
If McMurray architecture uses 4-quadrant switches with 8 MOSFETs per phase to achieve bidirectional operation, then operational flexibility is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes each full-bridge configuration universal by designing it to inherently support bidirectional power flow and multiple operating modes. This multi-functionality eliminates the need for separate 4-quadrant switches, as the full-bridge itself provides bidirectional capability, reducing the total MOSFET count from 24 to 12.
Solution Approach 2:
The patent merges the bidirectional switching function into the full-bridge configuration itself rather than using separate 4-quadrant switches. By combining these functions, the patent reduces device complexity and component count while maintaining bidirectional operation capability across all three phases.
5Strength
If conventional SST uses expensive semiconductor switches to achieve high voltage capability, then voltage handling is improved, but cost increases and efficiency decreases
Solution Approach 1:
The patent changes the voltage stress parameter from full line voltage to half line voltage across each semiconductor switch. This parameter change allows the use of lower-voltage, lower-loss MOSFETs instead of expensive high-voltage devices, reducing both cost and switching losses while maintaining system-level voltage handling capability through the bridge configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The LMI3 SST design achieves efficiency comparable to or exceeding conventional transformers, reduces core size and cost, and minimizes EMI, enabling flexible operation with delta and Y-connected loads and scalable voltage handling.
Implementation Method 1
a transformer core, a primary winding, a secondary winding
Implementation Method 2
Each of the switch banks includes six four-quadrant switches. The twelve 4-quadrant switches are toggled on and off in a predetermined pattern
Implementation Method 3
incorporates filter circuits to suppress high-frequency components
Data Source
AI summary
A solid-state transformer (SST) comprises a transformer core, a primary winding, a secondary winding, a primary-side switch bank, and a secondary-side switch bank. Each of the switch banks includes six 4-quadrant switches. The twelve 4-quadrant switches are toggled on and off over six clock cycles in a repetitive sequence with a period that is a function of a desired operating frequency of the transformer. The sequence is configured such that at any given time, 2 of 3 input and output phases are connected to the primary and secondary windings. The SST further includes L-C filter circuits that are configured to filter high-frequency components of current and voltage waveforms such that these components are not back-fed to the electrical mains or delivered to a load. The SST includes a primary-side filter circuit and a secondary-side filter circuit that can each include respective L-C filters for three input or output phases.