Multi-Pulse Rectifier Phase Offset Design for Harmonic Distortion Reduction
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Solution Overview
Problem
Existing three-phase AC to DC rectification systems using six-pulse diode bridges generate excessive harmonic distortion, exceeding industry standards like IEEE 519, and current solutions that reduce distortion, such as using multiple bridges, increase costs significantly.
Innovation Solution
A 36-pulse rectification system is implemented using a transformer with six sets of secondary windings at different phase offsets, coupled to three twelve-pulse rectifiers formed by connecting two six-pulse diode bridges in series or parallel, with each rectifier receiving unique sets of secondary windings spaced 30 degrees apart and corresponding inputs 10 degrees apart, reducing the number of components while maintaining low distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a six-pulse diode bridge is used for rectification, then the system is simple and low cost, but the total harmonic distortion exceeds IEEE 519 standards (about 5% limit)
Solution Approach 1:
The invention divides the single rectifier system into multiple parallel rectifier bridges (typically 3-6 bridges per phase). Each bridge processes a portion of the input waveform, and their combined output reduces harmonic distortion through waveform averaging. This segmentation allows the system to meet IEEE 519 THD requirements while maintaining reasonable complexity through modular implementation.
Solution Approach 2:
The invention employs multiple rectifier bridges with different phase shifts (e.g., 30-degree or 60-degree offsets) that process the AC waveform at different periodic intervals. By synchronizing these periodic actions across multiple bridges, the system achieves cancellation of harmonic components and reduction of total harmonic distortion to acceptable levels.
2Object-generated harmful factors
If multiple six-pulse bridges are used per phase (e.g., 36-pulse configuration), then the total harmonic distortion is reduced to about 2%, but the cost and component count increase significantly
Solution Approach 1:
The invention merges multiple rectifier bridges into a unified parallel configuration where all bridges share common DC bus connections. This merging approach allows the system to achieve 36-pulse or equivalent distortion reduction performance while consolidating control and output infrastructure, thereby reducing overall system complexity and cost compared to traditional cascaded or series configurations.
Solution Approach 2:
The invention designs the multiple rectifier bridges to perform identical rectification functions simultaneously, with each bridge contributing equally to the reduced harmonic distortion output. This multi-functional parallel architecture allows any single bridge to be replaced or maintained without affecting overall system operation, reducing complexity through functional redundancy and simplified control logic.
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 solution achieves a total harmonic distortion (THD) of about 2.73%, comparable to conventional 36-pulse designs but at a lower cost, and significantly better than 12-pulse designs, while maintaining the efficiency of reduced distortion.
Implementation Method 1
a transformer having an input side and an output side, wherein the output side includes six sets of secondary windings at different phase offsets
Implementation Method 2
three twelve-pulse rectifiers, each rectifier formed by connecting two six-pulse diode bridges in series or parallel
Data Source
AI summary
An 18n-pulse rectifier for AC drive systems having a separate DC bus for each output phase is provided, where n=any positive integer. The rectifier uses three separate phase rectifiers, one for each output phase of a transformer, each comprised of 2n six-pulse diode bridges connected in series or parallel. Each phase rectifier may be supplied with n unique sets of phase inputs from a transformer secondary winding. In some configurations, the n sets of inputs provided to each rectifier are separated by 60/n degrees of phase (when n is greater than 1), while the corresponding inputs to neighboring rectifiers are separated by 20/n degrees of phase. In a 36-pulse example, the phase offsets for the inputs provided to the rectifiers may be −25° and +5° from the transformer primary winding (for the first rectifier), −15° and +15° from the primary winding (for the second rectifier) and −5° and +25° from the primary winding (for the third rectifier). Each set of inputs may include three lines of in-phase current, and may be coupled to one of the six-pulse diode bridges. In some configurations, two identically-wound transformers may be used to supply output voltages to the rectifiers. The transformers may each supply the same phase offsets to each rectifier, in accordance with the methodology above, which may support higher-capacity applications.