Single VFD Control for Segmented Linear Motor Sections
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Solution Overview
Problem
In linear electrodynamic machines, the inefficiency of variable frequency drives (VFDs) arises due to leakage flux in long stationary parts with uncoupled coils, leading to poor utilization as they must be rated for higher voltages to compensate, resulting in unnecessary power consumption and economic inefficiencies.
Innovation Solution
A system utilizing a single VFD coupled with switches to sequentially power and control discrete stationary sections of a linear AC electrodynamic machine, eliminating the need for multiple VFDs and synchronizing hand-offs, thereby reducing costs and simplifying control by using fast switches to maintain continuous magnetomotive force across sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the stationary part is made long to increase motor coverage, then the motor can serve longer travel paths, but uncoupled coils create leakage flux requiring higher VFD voltage ratings and increasing energy loss
Solution Approach 1:
The stationary part is divided into multiple discrete sections, each with its own coil set. The VFD sequentially energizes only the sections currently needed for motor operation, rather than powering the entire length of the stationary part. This segmentation eliminates leakage flux from uncoupled coils in inactive sections.
Solution Approach 2:
The VFD employs periodic switching to sequentially energize different sections of the stationary part as the moving part travels along it. Each section is activated only when needed, creating a moving magnetic field that follows the moving part, thereby eliminating continuous leakage flux across the entire stationary length.
2Measurement precision
If multiple VFDs are used to control each section independently, then each section can be precisely controlled, but system complexity and cost increase due to synchronization requirements
Solution Approach 1:
Multiple VFDs are consolidated into a single VFD that sequentially controls multiple sections. The single VFD switches between sections using solid-state switches, eliminating the need for multiple independent VFDs and their associated synchronization complexity while maintaining precise speed control through centralized control logic.
Solution Approach 2:
A single VFD is designed to perform the function of multiple VFDs by sequentially energizing different sections. The VFD incorporates section selection capability and switching logic, making it a universal controller that can manage the entire multi-section motor system rather than requiring dedicated controllers for each section.
3Length of stationary object
If the VFD is rated for higher voltage to compensate for leakage flux, then the motor can operate over longer distances, but the VFD utilization efficiency decreases as rated voltage exceeds actual needs
Solution Approach 1:
By segmenting the stationary part into discrete sections and sequentially energizing only active sections, the required VFD voltage rating is reduced to match actual operational needs. The VFD only needs to provide sufficient voltage for the currently active section rather than compensating for leakage flux across the entire stationary length, improving utilization efficiency.
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 approach reduces the need for multiple VFDs, simplifies control, and minimizes the decrease in propulsive force during switching, enhancing the efficiency and economic viability of linear motor systems by using a single VFD to power and control multiple sections effectively.
Implementation Method 1
a variable frequency drive (VFD) configured to be coupled at an input to a utility power source and to provide output currents
Implementation Method 2
Linear electrodynamic machines comprise a stationary part and a moving part, wherein a linear force is produced along a length of the motor
Implementation Method 3
a plurality of switches coupled between the VFD and the stationary part, wherein the plurality of switches allow connecting or disconnecting the VFD to or from the stationary sections
Data Source
AI summary
A system (500) for controlling a linear alternating current (AC) electrodynamic machine (400) includes a linear AC electrodynamic machine (400) with a stationary part (410) with a plurality of discrete stationary sections (412, 414, 416), each stationary section (412, 414, 416) having a poly-phase circuit; a variable frequency drive (VFD) (510) configured to be coupled to a utility power source and to provide output currents, wherein the VFD (510) is operable coupled to the stationary part (410) of the linear AC electrodynamic machine (400) for powering and controlling the stationary sections (412, 414, 416) of the stationary part (410); and a plurality of switches (512, 514, 516) coupled between the VFD (510) and the stationary part (410), wherein the plurality of switches (512, 514, 516) allow connecting or disconnecting the VFD (510) to or from the stationary sections (412, 414, 416).