Phase-Shifted Transformer VFD for Low-Harmonic Motor Drive
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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 zigzag and delta configurations, allowing power distribution in parallel to a low-voltage AC motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If three-phase medium voltage VFDs are used, then power delivery to AC motors is ensured, but cost, size, and configuration complexity increase
Solution Approach 1:
The patent divides the medium voltage power delivery function into multiple low-voltage VFD units operating in parallel. Instead of using a single complex medium voltage VFD, the system segments the power delivery across multiple simpler low-voltage units, each handling a portion of the total power requirement. This reduces individual device complexity while maintaining overall power delivery capability.
Solution Approach 2:
The patent combines multiple low-voltage VFD outputs through a transformer configuration (specifically using zigzag and delta connections) to achieve medium voltage power delivery. By merging the outputs of multiple low-voltage units with specific phase shifts, the system achieves the desired medium voltage capability without requiring complex medium voltage-rated VFD components.
2Ease of manufacture
If standard low-voltage AC motors are used, then manufacturing is simplified and costs are reduced, but harmonic distortion increases
Solution Approach 1:
The patent converts the harmful harmonic distortion generated by standard low-voltage AC motors into a beneficial effect. By using a transformer with specific zigzag and delta winding configurations, the harmonics generated by multiple parallel VFDs are phase-shifted and cancel each other out. The harm (harmonic distortion) is transformed into a benefit (harmonic cancellation) through the clever use of phase relationships in the transformer connections.
3Object-generated harmful factors
If multiple low-voltage VFDs are used in parallel, then harmonic distortion is reduced through phase shifting, but system complexity increases
Solution Approach 1:
The patent introduces a transformer with specific zigzag and delta winding configurations as an intermediary device between the multiple low-voltage VFDs and the motor. This intermediary transformer performs the harmonic cancellation function through its phase-shifting properties, eliminating the need for complex control systems or additional filtering components. The transformer mediates the interaction between parallel VFDs, converting potential harmonic problems into benefits through passive electromagnetic transformation.
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
Rectifiers convert AC input power to DC power. The most basic rectifier for VFDs used in industrial applications is configured as a three-phase, full-wave diode bridge.
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.