Phase-Shifted Transformer for Motor Drive Harmonic Reduction
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Solution Overview
Problem
Conventional power conversion systems for driving multiple electric motors suffer from harmonic distortion due to rectification, which requires additional components like DC link chokes, AC line reactors, and harmonic filters, increasing cost and space requirements, and often necessitate customization for specific motor drives.
Innovation Solution
A power conversion system utilizing a transformer with phase-shifted multiphase outputs to reduce harmonic distortion by providing AC input currents that are rectified to DC power, eliminating the need for additional THD reduction components and customization, as the phase-shifting transformer minimizes current harmonics in the AC supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional rectification is used in multiple motor drives, then DC power can be provided to drives, but total harmonic distortion (THD) increases on the AC supply
Solution Approach 1:
The AC supply is segmented into multiple phase-shifted sets (e.g., three sets of three-phase power at different phase angles). Each set is rectified separately by individual converters, and the rectified DC outputs are combined. This segmentation allows harmonic cancellation because the phase shifts cause harmonic currents from different converters to oppose each other, reducing total harmonic distortion on the AC supply while still providing the necessary DC power to each drive.
2Object-generated harmful factors
If DC link chokes, AC line reactors, or harmonic filters are added to reduce THD, then harmonic distortion is reduced, but device complexity and cost increase
Solution Approach 1:
The system uses self-service by allowing the multiple phase-shifted converters to cancel their own harmonics through proper phase arrangement. The harmonic currents generated by each converter naturally oppose each other due to the phase shifts, creating automatic harmonic cancellation without requiring external filtering components. This eliminates the need for DC link chokes, AC line reactors, or harmonic filters, reducing device complexity and cost while still meeting THD requirements.
3Device complexity
If conventional rectification is used without phase shifting, then system simplicity is maintained, but harmonic distortion exceeds IEEE Std 519-1992 limits
Solution Approach 1:
The system changes the phase angle parameter of the AC input power to each converter. By introducing specific phase shifts (e.g., 0°, 120°, 240° or other appropriate angles) between the multiple sets of AC power, the rectified outputs combine in a way that cancels harmonic currents. This parameter change maintains relative system simplicity while ensuring compliance with IEEE Std 519-1992 THD limits, as the phase-shifted configuration inherently reduces harmonic distortion without requiring complex control or additional components.
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 system effectively reduces total harmonic distortion (THD) in the AC supply, meeting IEEE Std 519-1992 requirements without additional components, even under load and voltage imbalances, thereby optimizing power conversion efficiency and cost-effectiveness.
Implementation Method 1
a transformer with an input and a plurality of multiphase outputs... The transformer may provide isolation or may be a non-isolating autotransformer... Each individual transformer output is comprised of a set of at least three output terminals and provides multiphase AC output currents. The AC output currents of each multiphase output are at a non-zero phase angle relative to all other multiphase outputs of the transformer.
Implementation Method 2
a plurality of power converters that individually include a multiphase rectifier coupled with a corresponding one of the multiphase outputs of the transformer to convert the corresponding AC output currents to DC electrical power.
Data Source
AI summary
Power conversion systems and methods are provided for driving a plurality of motor loads, in which an autotransformer receives AC input currents and provides a plurality of multiphase outputs at a non-zero phase angle relative to one another, and the individual multiphase outputs are provided to corresponding motor drives with rectifiers to convert the multiphase outputs to DC electrical power, and inverters to convert the DC power to AC to drive corresponding motor loads.