18-Pulse Rectifier Hexagonal Autotransformer Harmonic Mitigation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power electronic devices, such as rectifiers, face challenges with AC input current harmonics and DC bus ripple, which can distort AC voltages and increase costs due to the need for additional filtering devices.
Innovation Solution
The use of multiple 18-pulse rectifier circuits in parallel, each featuring a nine-phase autotransformer with a hexagonal configuration of inductors and diode bridges, along with AC line reactors or choke inductors to reduce circulating currents and promote load sharing, effectively mitigating harmonics and ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple rectifier circuits are used in parallel to increase power rating, then power capacity increases, but circulating current and load sharing problems occur
Solution Approach 1:
The patent divides the power conversion system into multiple independent 18-pulse rectifier circuits operating in parallel, each handling a portion of the total power load. This segmentation allows the system to achieve higher power ratings while maintaining individual circuit stability and reducing circulating current through proper phase displacement.
2Power
If rectifier circuits are used to convert AC to DC power, then power conversion is achieved, but AC input current harmonics and DC bus ripple are generated
Solution Approach 1:
The patent employs 18-pulse rectifier circuits that utilize periodic pulse width modulation and phase-displaced rectification to convert AC to DC power. The periodic switching action with 18 pulses per cycle reduces harmonic content compared to conventional rectifiers, and the phase displacement between parallel circuits further mitigates both AC harmonics and DC bus ripple through constructive interference cancellation.
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
This configuration increases the overall rating of motor drives, reduces AC input current harmonics and DC bus ripple, and minimizes the possibility of looping and current sharing between parallel rectifier circuits, thereby enhancing the efficiency and reliability of power conversion systems.
Implementation Method 1
an autotransformer having 15 inductors coupled in series, joined by 15 nodes interposed between pairs of the inductors. The inductors may be represented as a hexagon in which alternating sides of the hexagon have two and three inductors, respectively
Implementation Method 2
nine outputs for AC power coupled between each node that is not a vertex of the hexagonal representation and a respective diode bridge
Implementation Method 3
AC line reactors coupled to inputs of each of the rectifiers may be used. In other embodiments, choke inductors coupled between each output of the diode bridges of the rectifier circuits and the DC bus may be used
Data Source
AI summary
Techniques for using multiple 18-pulse rectifier circuits in parallel are described herein. In particular, each rectifier circuit may include an autotransformer having 15 inductors coupled in series, joined by 15 nodes interposed between pairs of the inductors. The inductors may be represented as a hexagon in which alternating sides of the hexagon have two and three inductors, respectively. Each rectifier circuit may also include three inputs for three-phase AC power coupled to alternating vertices of the hexagonal representation and nine outputs for AC power coupled between each node that is not a vertex of the hexagonal representation and a respective diode bridge. Outputs of the diode bridges for the rectifier circuits may be coupled to a DC bus. In addition, a means for reducing circulating current between the parallel rectifier circuits and for promoting load sharing between the parallel rectifier circuits is also provided.