Multi-Pulse Rectifier Phase Offset Design for Harmonic Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing six-pulse diode bridges used for full-wave rectification of three-phase AC electricity generate excessive harmonic distortion, exceeding the limits set by standards like IEEE 519, and current solutions that reduce distortion, such as using multiple bridges per phase, increase the system cost 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, each made by connecting two six-pulse diode bridges in series or parallel, with phase relationships optimized to reduce distortion while minimizing component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single six-pulse diode bridge is used for full-wave rectification, then the system cost is low, but the total harmonic distortion exceeds IEEE 519 limits (about 5%)
Solution Approach 1:
The patent divides the rectification system into three separate twelve-pulse rectifiers, each handling one output phase. Each twelve-pulse rectifier is further segmented into two six-pulse diode bridges connected in series. This segmentation allows each bridge to process a portion of the harmonic distortion, collectively achieving 36-pulse operation with THD below 3% while using only 6 bridges total instead of 18-36 bridges in conventional designs.
Solution Approach 2:
The patent introduces a new dimensional approach by connecting diode bridges in series configuration rather than the conventional parallel arrangement. This series connection creates separate DC bus per output phase, enabling each bridge to operate at different voltage levels and phase offsets, thereby achieving 36-pulse rectification with fewer components.
2Object-affected harmful factors
If 2, 3 or more six-pulse bridges per phase are used to reduce distortion, then the total harmonic distortion is reduced (THD around 2%), but the system cost increases significantly
Solution Approach 1:
The patent merges the functionality of multiple six-pulse bridges into three twelve-pulse rectifiers. By combining two six-pulse bridges in series within each rectifier and utilizing the transformer's six sets of secondary windings with different phase offsets, the system achieves 36-pulse rectification equivalent to 6 bridges per phase but with only 2 bridges per phase (6 total bridges instead of 18-36).
Solution Approach 2:
Each of the three twelve-pulse rectifiers is designed to be multi-functional, handling both voltage rectification and harmonic filtering simultaneously. The series connection of two six-pulse bridges within each rectifier allows them to serve dual purposes: voltage multiplication and pulse multiplication, achieving 36-pulse operation with reduced component count.
3Object-affected harmful factors
If six sets of secondary windings with ten degrees separation are used in each rectifier, then the distortion is reduced to around 2%, but the transformer complexity and cost increase
Solution Approach 1:
The patent applies local quality by assigning specific phase offset ranges to different rectifiers. The first rectifier uses windings at -25° to +5°, the second uses -15° to +15°, and the third uses -5° to +25°. This localized assignment of phase offsets optimizes the harmonic cancellation for each rectifier while simplifying the overall transformer design compared to giving every rectifier access to all six windings.
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 by using fewer components, significantly improving upon conventional 12-pulse designs.
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 coupled to a unique two of the six sets of secondary windings. The twelve-pulse rectifiers may be made 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 described, where n=any positive integer. The rectifier uses three separate phase rectifiers, one for each output phase of a transformer, each comprised of n 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.