Doubly Fed Induction Motor Rotor Control Device
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Solution Overview
Problem
Induction motors face inefficiencies due to challenges in controlling the rotor magnetic flux field strength and direction, leading to increased electrical current, ohmic and air gap losses, overheating, and slow torque response, while existing doubly fed electric motors rely on maintenance-intensive slip rings or electromagnetic exciters for control.
Innovation Solution
A doubly fed electric motor design featuring a rotor with at least three windings and a control device that induces EMF, varies power factor, and stores energy in capacitors to adjust rotor magnetic flux, eliminating the need for slip rings or electromagnetic exciters by using a rotor control device with a PI control loop and inverter unit to synchronize rotor and stator fields at an optimal 90° angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If slip rings are used to control rotor field in doubly fed electric motors, then rotor field control capability is improved, but maintenance requirements increase due to wear
Solution Approach 1:
The patent extracts and eliminates the slip rings from the rotor field control system. Instead of using slip rings to supply power to rotor windings, the invention uses a self-contained rotor control device with energy storage that operates independently, removing the maintenance-prone slip ring component while preserving rotor field control capability
Solution Approach 2:
The rotor control device is designed to be self-service by incorporating an energy storage unit that stores electrical energy locally on the rotor. This eliminates the need for continuous external power supply through slip rings, making the system self-sufficient and maintenance-free regarding rotor field control
2Device complexity
If induction motors operate without rotor field control, then design simplicity is maintained, but efficiency decreases due to non-optimal rotor-stator field alignment
Solution Approach 1:
The patent introduces dynamic control of the rotor magnetic flux field by enabling variable strength and direction control through the rotor control device. This allows the rotor field to dynamically adjust its orientation to maintain optimal 90° alignment with the stator field, transforming the static rotor field of traditional induction motors into a controllable dynamic field
Solution Approach 2:
The invention changes key parameters of the rotor magnetic flux field including its strength, direction, and timing. By controlling these parameters through the rotor control device, the system achieves optimal field alignment for maximum efficiency while maintaining relatively simple motor construction
3Force
If rotor field excitation is increased for instant torque, then torque response capability is improved, but time to excite rotor field increases causing potential stalling
Solution Approach 1:
The patent applies preliminary action by pre-storing electrical energy in the rotor's energy storage unit during periods when full torque is not needed. This pre-charged energy is immediately available to rapidly excite the rotor windings when instant torque is required, eliminating the excitation delay that causes stalling
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 design enhances rotor field control, reduces energy losses, prevents overheating, and enables faster torque response without the need for maintenance-intensive components, improving efficiency and reliability compared to prior art induction and doubly fed electric motors.
Implementation Method 1
the stator is adapted to induce EMF (electromotive force) into the rotor during operation
Implementation Method 2
using EMF induced to the rotor... The rotor control device is adapted to draw electric energy from rotor windings at appropriate moment of time and to store a part of that energy in the form of electric charge in a rotor energy storage unit, namely a bank of capacitors
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
Electric motor, in particular induction motor, comprising a stator, a rotor and a control device which is arranged at the rotor. The three rotor windings are connected to a Rotor Control device with inverter and controller unit mounted on the rotor. A capacitor is placed in the DC link. The capacitor is supplied from the EMF induced in the rotor. The current in the rotor windings is advanced in order to achieve a 90 degree phase shift between rotor current and stator MMF vector. To achieve this the frequency and amplitude of the rotor current as well as the phase shift can be varied. Wherein the frequency of the rotor inverter is matching the slip frequency.