AC Motor Inverter Phase Control to Suppress Offset Current
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Solution Overview
Problem
Existing alternating-current motor control systems experience current offset issues when changing the phase of rectangular wave voltage, leading to potential overcurrent and vibration, especially during torque control.
Innovation Solution
A control apparatus for alternating-current motors that includes a rectangular wave voltage control portion and a phase change control portion, which adjusts the phase change timing to maintain the center of the flux linkage vector locus, thereby suppressing offset current during phase changes in rectangular wave voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the phase of rectangular wave voltage is changed for torque control, then the torque control performance is improved, but current offset occurs before and after the phase change
Solution Approach 1:
The patent applies preliminary action by calculating and applying a phase correction amount based on the relationship between the voltage phase and current phase before the actual phase change occurs. This correction is performed in advance to prevent current offset from occurring when the rectangular wave voltage phase is changed for torque control, thereby maintaining smooth current flow while achieving the desired torque control performance.
2Reliability
If phase correction is applied to reduce voltage SW pattern switching timing difference, then phase detector error impact is reduced, but current offset still occurs during torque control phase changes
Solution Approach 1:
The patent employs feedback by continuously monitoring the relationship between voltage phase and current phase, and using this information to dynamically calculate the appropriate phase correction amount. This feedback mechanism ensures that when torque control requires phase changes in the rectangular wave voltage, the correction is adjusted to prevent current offset, thereby solving the problem that persisted despite preliminary phase correction methods.
Data Source
AI summary
A control apparatus for an alternating-current motor that is driven by an inverter includes a rectangular wave voltage control portion that generates a control command of the inverter such that rectangular wave voltage that has been phase-controlled to make the alternating-current motor operate according to a torque command value is applied to the alternating-current motor; and a phase change control portion that controls a change in the phase to maintain the center of a flux linkage vector locus indicative of a change in a flux linkage of the alternating-current motor before and after a change in the phase of the rectangular wave voltage.