Variable Carrier Frequency Control for Rotary Electric Machine Noise
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Solution Overview
Problem
Rotary electric machines using pulse width modulation can generate noise in the audible range due to resonance between the carrier frequency and mechanical vibrations, leading to uncomfortable noise for humans, and existing solutions to increase the carrier frequency to mitigate this noise result in increased switching losses and reduced efficiency.
Innovation Solution
A rotary electric machine control device that varies the carrier frequency with the rotational speed of the machine to ensure carrier sideband frequencies do not fall within the uncomfortable audible frequency band, thereby reducing noise while maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the carrier frequency is increased to shift sideband frequencies away from the uncomfortable audible frequency band, then noise in the audible range is reduced, but switching loss of the inverter increases and total electric efficiency decreases
Solution Approach 1:
The patent applies dynamics by making the carrier frequency variable rather than fixed. The control device dynamically adjusts the carrier frequency based on the rotational speed of the rotary electric machine, allowing the system to adapt to different operating conditions. This resolves the contradiction by using a high carrier frequency only when necessary (at high rotational speeds where sideband frequencies would otherwise fall in the uncomfortable audible range), while using a lower carrier frequency at low rotational speeds to minimize switching losses.
Solution Approach 2:
The patent changes the parameter of carrier frequency from a constant value to a variable value that depends on rotational speed. By changing this parameter dynamically, the system can shift sideband frequencies away from the uncomfortable audible frequency band (2000-5000 Hz) only when needed, rather than maintaining a constantly high carrier frequency that would increase switching losses during low-speed operation.
2Object-affected harmful factors
If the carrier frequency is increased to prevent sideband frequencies from falling in the uncomfortable audible frequency band, then noise reduction is achieved, but the pulse signal becomes finer and inverter efficiency decreases
Solution Approach 1:
The control device dynamically adjusts the carrier frequency based on rotational speed, making the system adaptive rather than static. This allows the inverter to operate with optimal efficiency at each rotational speed while still preventing uncomfortable noise when sideband frequencies would otherwise fall in the 2000-5000 Hz range.
Solution Approach 2:
By changing the carrier frequency parameter according to rotational speed, the system achieves noise reduction only when necessary. At low rotational speeds, a lower carrier frequency maintains inverter efficiency, while at high rotational speeds, the carrier frequency is increased to shift sideband frequencies away from the uncomfortable audible range.
Data Source
AI summary
A rotary electric machine control device that performs drive control on an AC rotary electric machine using an inverter that converts power between DC power and AC power through pulse width modulation based on a carrier frequency, the rotary electric machine control device including: an electronic control unit that is configured to vary the carrier frequency such that the carrier frequency becomes higher as a rotational speed of the rotary electric machine becomes higher so that carrier sideband frequencies, which are frequencies of sideband waves that appear on higher and lower sides of a center frequency that is set in accordance with the carrier frequency, are not included in a frequency band prescribed in advance.