Stator Winding Arrangement for Harmonic Cancellation
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Solution Overview
Problem
Permanent Magnet (PM) electrical machines with conventional stator windings suffer from significant 5th and 7th harmonic currents due to 6-pulse rectifiers, leading to parasitic heating and torque oscillations, which are not adequately addressed by complex star-delta configurations.
Innovation Solution
A stator winding arrangement with alternating long and short windings connected in series, providing two output channels approximately 30 degrees out of phase, which reduces harmonic currents by canceling them out within the stator windings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a 6-pulse rectifier is used to convert variable frequency voltage to DC, then DC voltage can be provided to the load, but significant 5th and 7th harmonic currents are introduced into the stator windings causing parasitic heating and torque oscillations
Solution Approach 1:
The stator winding is divided into two separate three-phase winding sets (first and second windings) that are electrically independent but magnetically coupled through the rotor. Each winding set connects to a separate rectifier (6-pulse or 12-pulse), allowing the harmonic currents from one rectifier to be canceled by the other. This segmentation enables the system to maintain DC power output while eliminating harmful harmonics through the complementary phase displacement between the two winding sets.
2Object-generated harmful factors
If star-delta winding configuration is used to reduce harmonic currents, then two output channels with phase difference are provided, but the configuration becomes overly complex and does not adequately address parasitic power dissipation
Solution Approach 1:
The first and second three-phase windings serve multiple functions simultaneously: they generate electrical power for rectification, provide the necessary 30-degree phase displacement for harmonic cancellation, and enable both 6-pulse and 12-pulse rectifier configurations. This multi-functionality eliminates the need for complex star-delta transformations while achieving the same harmonic reduction effect, as the windings themselves are physically arranged to provide the required phase difference.
3Strength
If permanent magnets are used on the rotor to create a rotating magnetic field, then robust and compact motor/generator design is achieved, but variable rotor speed causes significant changes in voltage and frequency beyond acceptable limits
Solution Approach 1:
The dual three-phase winding arrangement acts as an intermediary between the variable speed rotor and the DC power output. By providing two sets of windings with 30-degree phase displacement, the system can process the variable frequency voltage from the rotor through two separate rectifier channels that work together to cancel harmonics and stabilize the DC output, effectively decoupling the rotor speed variations from the DC voltage stability requirement.
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 significantly reduces harmonic current distortion, eddy current heating, and torque ripple, resulting in lower losses and improved efficiency with reduced cooling requirements.
Implementation Method 1
a voltage is induced in the stator windings upon rotation of the permanent magnet
Implementation Method 2
the 6-pulse diode rectifier 214 converts the variable magnitude, variable frequency voltage provided by the PM machine 212 to a variable magnitude direct voltage
Implementation Method 3
A stator winding arrangement with alternating long and short windings connected in series, providing two output channels approximately 30 degrees out of phase, which reduces harmonic currents by canceling them out within the stator windings
Implementation Method 4
the harmonic currents cause eddy current heating in the permanent magnets of the rotor and create additional torque oscillations in the mechanical drive train
Implementation Method 5
These currents are parasitic in that they do not contribute to the useful electrical power generated and create additional heating in the stator windings
Data Source
Figure 1~2
Figure 3a~3b
Figure 4~6b
AI summary
Described is an electrical machine (410), comprising: a rotor (414) having a magnetic flux source (416) mounted thereto; a stator winding arrangement (418) having a first set of electrical connections to provide a first output channel (412a), and a second set of electrical connections to provide a second output channel (412b), the first and second channels (412a,b) being electrically out of phase, wherein the stator winding (418) arrangement is constructed from a plurality of winding portions (422R,r,Y,y,B,b) which are connected in electrical series.