Phase-Shifted Transformer VFD Architecture for Harmonic Reduction
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Solution Overview
Problem
Three-phase medium voltage VFDs are expensive, large, and require multiple configurations to meet diverse market demands, while low-voltage AC motors face harmonic distortion issues when used with harmonic filters, adding complexity and cost.
Innovation Solution
A variable frequency drive system with a step-down transformer that provides symmetrically phase-shifted three-phase low-voltage outputs to multiple low-voltage VFDs, reducing harmonic distortion through zig-zag and delta configurations, allowing power distribution in parallel to a low-voltage AC motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a medium voltage VFD is used, then power delivery capability is improved, but system cost and device complexity increase
Solution Approach 1:
The system segments the power delivery function by using multiple low-voltage VFDs (each handling a portion of the total power) instead of a single medium-voltage VFD. Each VFD operates independently at standard low-voltage levels, dividing the overall system complexity into manageable modular units while collectively delivering the required medium-voltage equivalent power capacity.
Solution Approach 2:
A custom-wound transformer serves as an intermediary device between the standard low-voltage VFDs and the medium-voltage motor. The transformer steps up the voltage from multiple low-voltage sources and combines their outputs to deliver medium-voltage power, eliminating the need for expensive medium-voltage VFDs while maintaining power delivery capability.
2Object-affected harmful factors
If harmonic filters are added to low-voltage AC motors, then harmonic distortion is reduced, but device complexity and cost increase
Solution Approach 1:
The system applies preliminary anti-action by using a custom-wound transformer with specific winding configurations (zigzag and delta connections) that proactively cancel harmonic distortions before they reach the motor. The transformer's secondary windings are arranged to produce phase-shifted outputs that naturally counteract harmonics, eliminating the need for additional harmonic filters.
Solution Approach 2:
The system converts the potentially harmful harmonic distortions into a beneficial effect by using the phase-shifted outputs from the transformer's multiple secondary windings. The harmonic components from different VFDs are deliberately phase-shifted to cancel each other out, transforming what would be harmful interference into a harmonic-reduction mechanism.
3Adaptability or versatility
If multiple VFD configurations are used to meet diverse market demands, then adaptability is improved, but manufacturing complexity increases
Solution Approach 1:
The system achieves universality by using standard off-the-shelf low-voltage VFDs that can be configured in different numbers and arrangements to meet various power requirements. The same basic architecture (transformer with multiple secondary windings connecting to multiple VFDs) serves diverse market demands, eliminating the need for custom medium-voltage VFD configurations.
Solution Approach 2:
The system uses copies of standard low-voltage VFD units instead of creating custom medium-voltage VFD designs. By replicating proven low-voltage VFD technology multiple times and combining them through the transformer, the system meets diverse power requirements without the manufacturing complexity of designing and building new medium-voltage VFD products.
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 reduces harmonic distortion and simplifies manufacturing by using standard low-voltage AC motors, lowering costs and complexity while maintaining power delivery to HVAC systems.
Implementation Method 1
The transformer is configured to transform three phase alternating current (AC) provided to the set of input terminals into first and second three phase AC outputs at the first and second sets of output terminals, respectively. The first three phase AC output is phase shifted from the second three phase AC output.
Implementation Method 2
The first and third sets, but not the second set, of secondary windings can be arranged in a zigzag configuration. For example, each of the first and third sets of secondary windings can be arranged in a delta zigzag configuration.
Data Source
AI summary
According to an embodiment of the present disclosure, an apparatus includes a transformer having a set of input terminals, a first set of output terminals, and a second set of output terminals. First and second rectifiers are coupled to the first and second sets of output terminals, respectively. The transformer is configured to transform three phase alternating current (AC) provided to the set of input terminals into first and second three phase AC outputs at the first and second sets of output terminals, respectively. The first three phase AC output is phase shifted from the second three phase AC output.