Three-Phase Induction Motor Slot Configuration for Harmonic Reduction
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Solution Overview
Problem
Conventional three-phase induction motors driven by silicon (Si) inverters suffer from high switching losses and harmonic components in the current waveform, while those driven by wide bandgap semiconductor (WBG) inverters can reduce ripple and harmonic components, but require optimized stator and rotor slot configurations to effectively utilize their characteristics.
Innovation Solution
A three-phase induction motor with a stator having an open slot structure for a former-wound coil and a rotor with a secondary conductor inserted into slots, where the number of rotor slots (Nr) is set such that Nr≤Ns−Np−6, optimizing the relationship between the number of stator slots (Ns), rotor slots (Nr), and poles (Np) to reduce harmonic losses and electromagnetic vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the number of rotor slots is increased to reduce harmonic components, then the harmonic components in motor current are reduced, but the relationship between stator slots and rotor slots becomes suboptimal leading to increased electromagnetic vibration
Solution Approach 1:
The patent applies parameter changes by establishing a specific mathematical relationship between the number of rotor slots (Nr) and stator slots (Ns) and poles (Np), expressed as Nr ≤ Ns - Np - 6. This parameter optimization simultaneously reduces harmonic components in motor current and minimizes electromagnetic vibration, resolving the contradiction between these two factors.
2Device complexity
If conventional Si inverters are used, then the motor structure can be simpler, but switching losses are large and harmonic components are increased
Solution Approach 1:
The patent leverages the parameter changes enabled by WBG-SW elements (wide bandgap semiconductor switching elements) which have fundamentally different electrical characteristics from conventional Si-SW elements. The WBG-SW elements exhibit lower on-resistance and faster switching capabilities, enabling the motor to operate with optimized slot configurations that reduce both switching losses and harmonic components, while the controlled number of rotor slots further mitigates electromagnetic vibration.
3Stability of the object's composition
If the number of rotor slots is decreased to reduce electromagnetic vibration, then electromagnetic vibration is reduced, but the ability to reduce harmonic components is compromised
Solution Approach 1:
The patent resolves this contradiction by establishing an optimized parameter relationship Nr ≤ Ns - Np - 6 that simultaneously addresses both electromagnetic vibration and harmonic components. This mathematical relationship determines the optimal number of rotor slots based on the stator slot configuration and pole count, enabling both vibration reduction and harmonic suppression to be achieved together rather than requiring a trade-off between them.
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 configuration allows for reduced harmonic components and motor current ripple, enabling increased motor current limits and reduced voltage requirements, with simplified PWM control over the entire speed range, and improved efficiency when driven by a WBG inverter.
Implementation Method 1
a three-phase induction motor that is rotationally driven in response to supply of AC power from an inverter
Data Source
AI summary
A three-phase induction motor that is rotationally driven in response to supply of AC power from an inverter including a switching element formed by using a wide bandgap semiconductor includes: a stator including a stator slot having an open slot structure for inserting a former-wound coil; and a rotor including a rotor slot into which a secondary conductor is inserted, the rotor being disposed inside the stator via a gap. Assuming that the number of rotor slots is Nr, the number of stator slots is Ns, and the number of poles is Np, Nr, Ns, and Np are set such that the relationship of Nr≤Ns−Np−6 is satisfied.