AC Motor Stator Winding Tap for Transformerless VSD Starting
Solution Overview
Problem
Existing AC motor systems face challenges in starting high load torques with minimal impact on the power system, particularly when the maximum output voltage of variable speed drives is lower than the system nominal voltage, requiring additional components like step-up transformers that increase costs and space requirements.
Innovation Solution
A system and method that starts AC motors with variable speed drives by synchronizing the motor winding voltage with the power line, using a wye-connected stator lap winding with tap connections to induce higher voltage at the extremes of the stator windings, allowing transfer to higher voltage power lines without transformers, minimizing transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a step-up transformer is used between the variable speed drive output and the motor terminals, then the motor can be operated at higher voltage, but the system occupies more space and incurs higher installation and operating costs
Solution Approach 1:
The stator winding is divided into two separate windings: a first winding connected to the variable speed drive output and a second winding connected to the motor terminals. This segmentation allows each winding to operate at different voltage levels, eliminating the need for a step-up transformer while enabling high-voltage motor operation.
Solution Approach 2:
The first stator winding acts as an intermediary between the variable speed drive and the second stator winding. It transforms the voltage level through electromagnetic induction, serving the function previously performed by a step-up transformer but integrated directly into the motor structure.
2Force
If reduced voltage soft starters are used, then the starting torque can be controlled, but the full motor torque capability at low speed is not provided
Solution Approach 1:
The variable speed drive dynamically controls the voltage and frequency supplied to the first stator winding during startup, enabling smooth torque control from zero to maximum speed while maintaining full motor torque capability throughout the acceleration range.
3Force
If autotransformers, inductors, or inductor-capacitor starters are used, then starting torque can be controlled, but important transients are introduced in line currents and motor air-gap torque during switching events
Solution Approach 1:
The patent replaces traditional mechanical switching devices with a variable speed drive that uses electronic pulse-width modulation (PWM) to control the voltage supplied to the first stator winding. This electronic control method eliminates the abrupt current and torque transients associated with mechanical switching while providing smooth starting torque control.
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
Enables efficient starting and operation of AC motors with reduced transient effects and eliminates the need for transformers, thereby minimizing installation and operating costs while maintaining motor performance.
Implementation Method 1
The motor rotating flux induces a higher voltage at the extremes of the stator windings with an amplitude and phase that can be controlled by the variable speed drive
Data Source
AI summary
Methods for starting an AC motor with a variable speed drive and switching the motor to a higher voltage power source are described. Provided are AC motors with a stator having a plurality of coils, the plurality comprising a complete set of coils for each phase, the complete set comprising a first set of coils comprising first groups of coils connected in series, or parallel, or a combination, and a second set of coils comprising second groups of coils connected in series, or parallel, or a combination, wherein the output of a variable speed drive is connected to a tap on the complete set of coils such that the AC motor may be started with a variable speed drive, and an output of the power line is connected to the series of the first and second sets of coils.