Brushless DC Machine With Vernier Pole Ratio
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Solution Overview
Problem
Brush commutated dc electrical machines face limitations in torque density due to complex and large brushgear, with inherent low voltage ratings and risks of arcing and flashover, while load commutated inverters offer higher voltage ratings but with undesirable torque pulsations and complex converters.
Innovation Solution
A dc electrical machine design with a non-integer ratio of rotor poles to armature slots, utilizing a vernier shift to achieve high armature phases and simplify the power electronic switching assembly, allowing for efficient high voltage operation with reduced complexity and arcing risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If brush commutation is used in DC electrical machines, then high air gap shear stress and torque density can be achieved, but the brushgear becomes large and complex, occupying space that could otherwise increase total air gap flux and torque density
Solution Approach 1:
The patent extracts and removes the brushgear and commutator from the DC electrical machine, replacing them with a brushless excitation system and static frequency converter. This eliminates the harmful occupation of space by complex brushgear while maintaining the high torque density through alternative commutation methods.
Solution Approach 2:
The patent replaces the mechanical brush-commutator system with an electronic control system consisting of static frequency converters and brushless excitation. This substitution eliminates mechanical contact and the associated complexity while achieving the same commutation function through electronic switching.
2Reliability
If compoles are used to alleviate arcing and flashover risks in large DC machines, then reliability improves, but the rotating commutator and stationary brushgear become larger and more complex
Solution Approach 1:
The patent removes the commutator and brushgear entirely, eliminating the source of arcing and flashover risks. By using brushless excitation and static frequency converters, the system achieves high reliability without requiring compoles or complex protective measures for the commutation system.
Solution Approach 2:
The patent replaces the mechanical brush-commutator system that is prone to arcing with an electronic switching system. This substitution eliminates the harmful arcing and flashover phenomena while simplifying the overall machine structure by removing the need for compoles.
3Power
If load commutated inverter is used, then higher line voltage rating is achieved, but undesirable torque pulsations and complex converters are introduced
Solution Approach 1:
The patent optimizes the switching frequency and control parameters of the static frequency converter to minimize torque pulsations. By carefully selecting the switching frequency to be significantly higher than the fundamental frequency, the system achieves high voltage rating while maintaining smooth torque output and reducing converter 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
The design enhances torque density and efficiency, supports high voltage operation, and minimizes arcing and flashover risks, while simplifying the power electronic switching assembly and maintaining electromagnetic symmetry.
Implementation Method 1
A rotor surrounded by a wound stator... rotor mmf and stator field space harmonic spectra are substantially synchronised, thereby contributing to the mean shaft torque
Data Source
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AI summary
The present invention provides a dc electrical machine with a large number of phases. The machine includes a rotor (8) and a stator assembly (6). The rotor (8) has Np rotating field poles. The stator (6) has Ns winding slots, where Ns/Np is a non-integer ratio. A stator winding includes a plurality of coils (4) received in the winding slots and defines a plurality of stator phases. A power electronic switching assembly includes first and second dc load terminals that can be connected to external equipment and a plurality of switching modules (2). Each switching module (2) includes power electronic devices and is connected to a respective stator coil. A first proportion of the switching modules (2) are connected together in series between the first and second dc load terminals and a second proportion of the switching modules are connected together in series between the first and second dc load terminals to define two parallel dc circuits.