AC Motor Current Detection Near Mechanical Resonance
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Solution Overview
Problem
The existing control apparatus for AC rotary machines, which offsets voltage command values to half the power source voltage, results in a large third-order ripple component in the output torque, and fails to effectively reduce current detection errors near the mechanical resonance frequency, leading to noise in the AC rotary machine.
Innovation Solution
A control apparatus that includes an inverter with series-connected switching devices, a current detection circuit with resistances in series to the negative electrode side switching devices, and a controller that calculates voltage command values and performs current addition processing to detect currents at specific timings, setting the carrier period less than 60 microseconds and the mechanical resonance period between 200 to 500 microseconds to cancel the resonance period component in current detection values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage command values are offset to half the power source voltage to reduce current detection error, then current detection accuracy is improved, but the third-order ripple component in output torque increases
Solution Approach 1:
The patent extracts and removes the harmful third-order ripple component from the output torque by detecting current at two or more fixed timings in the carrier period and processing the detection values to eliminate the ripple component, while maintaining voltage command offset for accurate current detection
Solution Approach 2:
The patent applies periodic current detection at two or more fixed timings within each carrier period, and uses periodic processing to eliminate the third-order ripple component that occurs at specific frequencies related to the carrier wave
2Measurement precision
If current detection is performed at fixed timings to reduce switching noise error, then current detection accuracy is improved, but error components near mechanical resonance frequency remain and cause noise
Solution Approach 1:
The patent introduces feedback processing where current detection values are processed through coordinate transformation, ripple component elimination, and inverse coordinate transformation to generate corrected current values that are fed back to the control system, effectively reducing error components near mechanical resonance frequency
Solution Approach 2:
The patent changes the processing parameters by performing coordinate transformation between three-phase and two-phase systems, and by adjusting the timing and method of current value calculation to eliminate resonance-related error components while maintaining detection accuracy
Data Source
AI summary
To provide a control apparatus for AC rotary machine and an electric power steering apparatus which can reduce the error component of the current detection value close to the mechanical resonance period of AC rotary machine. A control apparatus for AC rotary machine detects currents which flow into three-phase windings at a current detection period which is a first natural number times of a carrier period; calculates current detection values, by performing a current addition processing which adds current detection values detected at this time, and current detection values detected before an addition period which is a second natural number times of the current detection period; and calculates the voltage command values of three-phase based on the current detection values after current addition processing, wherein the second natural number is set to a natural number that the addition period becomes the closest to the half period of the mechanical resonance period.