Motor Control Device Beat Current Suppression via Carrier Frequency Diffusion
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Solution Overview
Problem
Existing motor control devices fail to effectively suppress beat current generated when the ratio of the carrier frequency to the electric angular frequency of the motor becomes small, as described in PTL 1.
Innovation Solution
A motor control device that includes an inverter converting DC voltage to three-phase AC voltage and a control unit outputting PWM signals based on a carrier frequency, where the control unit randomly changes the carrier frequency around a preset first carrier frequency when the ratio of the carrier frequency to the electric angular frequency is equal to or less than a predetermined value, and also considers the ratio of AC voltage to DC voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the carrier frequency is increased to improve motor control performance, then the motor control precision is improved, but low-frequency beat current is generated when the ratio of carrier frequency to electric angular frequency becomes small
Solution Approach 1:
The patent applies dynamics by making the carrier frequency adjustable rather than fixed. The control unit dynamically changes the carrier frequency based on the ratio between carrier frequency and electric angular frequency. When this ratio falls within a predetermined range that would generate beat current, the control unit adjusts the carrier frequency to a different value, thereby dynamically avoiding the harmful beat current while maintaining good motor control performance.
2Device complexity
If the carrier frequency is fixed to simplify control, then the device complexity is reduced, but beat current cannot be suppressed when the ratio of carrier frequency to electric angular frequency becomes small
Solution Approach 1:
The patent applies parameter changes by modifying the carrier frequency parameter based on operating conditions. The control unit calculates the ratio of carrier frequency to electric angular frequency and adjusts the carrier frequency parameter when this ratio falls within a problematic range. This parameter adjustment suppresses beat current generation while maintaining relatively simple control logic.
3Object-generated harmful factors
If the carrier frequency is randomly changed to suppress beat current, then the beat current is reduced, but the control stability may be affected
Solution Approach 1:
The patent applies dynamics by making the carrier frequency adjustable rather than fixed. The control unit dynamically changes the carrier frequency based on the ratio between carrier frequency and electric angular frequency. When this ratio falls within a predetermined range that would generate beat current, the control unit adjusts the carrier frequency to a different value, thereby dynamically avoiding the harmful beat current while maintaining good motor control performance.
Solution Approach 2:
The patent applies parameter changes by modifying the carrier frequency parameter based on operating conditions. The control unit calculates the ratio of carrier frequency to electric angular frequency and adjusts the carrier frequency parameter when this ratio falls within a problematic range. This parameter adjustment suppresses beat current generation while maintaining relatively simple control logic.
Data Source
AI summary
A random value integration unit 175 outputs a random value output from a random value generation unit 174 in a diffusion width Rand output from a diffusion width generation unit 173 by a product of an output of the random value generation unit 174 and an output of the diffusion width generation unit 173. A triangular wave signal generation unit 176 generates a triangular wave signal corresponding to a second carrier frequency fc2 which is obtained by adding the random value output from the random value integration unit 175 to a first carrier frequency fc1 which is an output of a carrier frequency setting unit 171. That is, a frequency obtained by increasing the diffusion width of the first carrier frequency fc1 is used as the second carrier frequency fc2, and the second carrier frequency is used as the carrier frequency.