Brushless Doubly Fed Drive System Eliminates Slip Rings
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Solution Overview
Problem
Conventional doubly-fed asynchronous motors rely on slip rings for rotor current dissipation, which are prone to failure and maintenance issues.
Innovation Solution
A drive system with a three-phase motor and two inverters, where the inverters are mechanically and electrically coupled to the rotor windings, allowing bidirectional power transmission and control to operate in all four quadrants without slip rings, using an intermediate circuit coupling and vector control methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If slip rings are used to dissipate rotor currents in a doubly fed asynchronous motor, then the motor can operate with variable speed, but the slip rings are prone to failure and require maintenance
Solution Approach 1:
The invention extracts and eliminates the slip rings from the system by using a brushless doubly fed induction machine. The rotor windings are directly connected to the stator windings through magnetic coupling, removing the mechanical contact components (slip rings and brushes) that cause maintenance issues and reliability problems while preserving the variable speed operation capability through electronic control of the inverter.
Solution Approach 2:
The invention replaces the mechanical slip ring system with an electromagnetic field-based power transfer system. The rotor currents are generated and controlled electronically through the inverter and transferred to the rotor windings via magnetic coupling, eliminating the need for mechanical contact and associated wear and maintenance.
2Device complexity
If a conventional doubly fed asynchronous motor is used, then the structure is simple, but brake choppers or resistors are required for operation in all four quadrants
Solution Approach 1:
The inverter in the brushless doubly fed induction machine performs multiple functions: it controls the rotor currents for variable speed operation, enables four-quadrant operation (motoring and generating in both forward and reverse directions), and eliminates the need for separate brake choppers or resistors. This multi-functionality achieves versatility without significantly increasing overall system complexity.
Solution Approach 2:
The invention merges the functions of speed control, four-quadrant operation, and energy recovery into a single inverter system. The inverter handles all power electronic conversions and control functions, consolidating what would otherwise require multiple separate components (inverter, brake chopper, resistors) into one integrated system.
3Power
If slip rings are used in the motor, then the basic motor function is maintained, but the component size and maintenance requirements increase
Solution Approach 1:
The invention removes the slip rings and associated mechanical components from the motor structure. Power transmission is achieved through direct magnetic coupling between stator and rotor windings, eliminating the need for external sliding contacts and reducing the overall component count and physical size of the motor.
Solution Approach 2:
The mechanical slip ring system is replaced with an electromagnetic field-based power transfer mechanism. The inverter generates and controls rotor currents electronically, and these currents are transferred to the rotor windings through magnetic coupling, eliminating mechanical contact components and reducing system complexity.
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 reliable operation in all four operating quadrants with improved maintenance and reduced component size, eliminating the need for brake choppers or resistors, and allowing seamless speed adjustment from standstill to synchronous speed with high starting torques.
Implementation Method 1
The first inverter 3 generates control signals in the form of control voltages and/or control currents of suitable amplitude and phase... The first three-phase winding set 1 includes a three-phase stator winding 1a... to generate a rotating magnetic field
Implementation Method 2
The first three-phase winding set 1 includes a three-phase stator winding 1a, which is conventionally connected directly to a three-phase AC power supply to generate a rotating magnetic field
Implementation Method 3
The first and second inverters can be electrically coupled in such a way that electrical power can be transferred bidirectionally between them. For this purpose, the first and second inverters can, for example, have a DC link coupling.
Data Source
Figure 1~2
Figure 3
AI summary
A drive system (100) has: a three-phase motor, having: a shaft, a first three-phase winding set (1), having: a three-phase stator winding (1a) for connection to a three-phase alternating voltage network (U, V, W) and a three-phase rotor winding (1b), which is coupled to the shaft in a mechanical, rotationally fixed manner, a second three-phase winding set (2), having: a three-phase stator winding (2a) for connection to the three-phase alternating voltage network (U, V, W) in such a manner that a rotary field is produced that runs in the opposite direction to a rotary field that is produced by means of the stator winding (1a) of the first winding set (1), and a three-phase rotor winding (2b), which is coupled to the shaft in a mechanical, rotationally fixed manner, a first inverter (3), which is coupled to the shaft in a mechanical, rotationally fixed manner and which is coupled electrically to the three-phase rotor winding (1b) of the first winding set (1), and a second inverter (4), which is coupled to the shaft in a mechanical, rotationally fixed manner and which is coupled electrically to the three-phase rotor winding (2b) of the second winding set (2), wherein the first inverter (3) and the second inverter (4) are electrically coupled in such a manner that electrical power can be transmitted between the inverters.