AC Motor Driving Apparatus with Time Constant Adjustment
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Solution Overview
Problem
Ultra-compact AC linear synchronous motors with few turns of exciting coils face challenges in motor control due to quick current response and uncontrollability, along with vibration and noise issues caused by harmonic components in the current waveform.
Innovation Solution
The introduction of a time constant adjusting coil and condenser between the PWM device and the AC motor, with a switching element in parallel, allows for adjustment of the motor time constant in accordance with the PWM carrier frequency, enabling control of the current waveform to be closer to a sine wave and reducing vibrations and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the number of turns of the exciting coil is reduced to achieve ultra-compact motor design, then the motor size and weight are reduced, but the time constant becomes very small resulting in uncontrollability of current
Solution Approach 1:
An external inductor is introduced as an intermediary component between the PWM device and the ultra-compact motor. This external inductor compensates for the insufficient internal inductance of the motor with reduced coil turns, providing the necessary time constant for controllable current response while maintaining the motor's compact size.
Solution Approach 2:
The system changes the effective inductance parameter by combining the motor's internal inductance with an external inductor. This parameter adjustment extends the time constant from its naturally small value to an adequate range for PWM control, enabling current controllability without increasing the motor's physical dimensions.
2Adaptability or versatility
If the PWM system is used with ultra-compact motor having small time constant, then the motor can be driven with variable frequency, but the current response becomes too quick resulting in uncontrollability
Solution Approach 1:
The external inductor acts as a mediator that slows down the current response time by adding inductive reactance. This allows the PWM system to maintain frequency control capability while achieving controllable current rise time, as the external inductor filters the rapid current changes that would otherwise be uncontrollable.
Solution Approach 2:
The system dynamically adjusts the effective time constant by combining fixed motor parameters with the external inductor's contribution. This dynamic parameter adjustment enables the system to maintain adaptability across different frequencies while ensuring current controllability at all operating points.
3Volume of moving object
If the exciting coil has few turns to reduce motor size, then the motor becomes ultra-compact, but harmonic components are convoluted causing vibration and noise
Solution Approach 1:
The external inductor serves as a filter that attenuates harmonic components in the current waveform. By placing this inductive intermediary in series with the motor, high-frequency harmonics that cause vibration and noise are suppressed, while the fundamental frequency current necessary for motor operation is preserved.
Solution Approach 2:
The system converts the potentially harmful effect of reduced coil turns (which causes harmonics) into a benefit by using the external inductor to filter these harmonics. The same compact design that reduces motor size also highlights the harmonic issue, which is then resolved by the external inductor's filtering action, eliminating vibration and noise.
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 solution allows for stable control of ultra-compact AC motors by adjusting the time constant, preventing vibrations and noise, and ensuring ideal current control, even with extremely small time constants.
Implementation Method 1
The introduction of a time constant adjusting coil and condenser between the PWM device and the AC motor, with a switching element in parallel, allows for adjustment of the motor time constant in accordance with the PWM carrier frequency
Implementation Method 2
The introduction of a time constant adjusting coil and condenser between the PWM device and the AC motor
Implementation Method 3
with a switching element in parallel, allows for adjustment of the motor time constant
Data Source
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AI summary
Provided is an AC motor driving apparatus and an AC motor control method capable of utilizing the conventional PWM system as-is even in an ultra-compact AC motor having an extremely few turns of exciting coil and preventing occurring of vibration and noise. The AC motor driving apparatus has an inverter converting a DC voltage to an AC voltage and supplying the AC voltage to an AC motor; a PWM device controlling a magnitude and a frequency of an output voltage of the inverter and means for changing a time constant of the AC motor in accordance with a carrier frequency of the PWM device. Between the PWM device and the AC motor, there is provided a condenser and/or a coil for adjusting the time constant, and the capacity thereof is adjusted in accordance with the carrier frequency of the PWM device.