Rotating Machine PWM Switching to Restrain Current Oscillation
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Solution Overview
Problem
Existing rotating machine control devices face issues with current oscillations and harmonic disturbances when switching between asynchronous and synchronous pulse-width modulation (PWM) modes, leading to potential semiconductor element failure and mechanical vibrations.
Innovation Solution
A rotating machine control device that selectively switches between asynchronous and synchronous PWM modes based on precomputed carrier wave phases and magnetic flux evaluation functions to minimize current oscillations, using a voltage application unit and control unit to generate and control three-phase voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the carrier wave frequency is fixed when the rotational speed is lower and changed in synchronization with the voltage command's frequency when the rotational speed is higher, then thermal design constraints are satisfied, but switching between PWM modes causes current oscillations that may deviate from allowable current
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal switching points in a lookup table before operation. The switching point calculation unit computes the optimal carrier wave phase angles that minimize current oscillations during PWM mode transitions, and these pre-computed values are stored for rapid retrieval during operation. This allows smooth transitions between asynchronous and synchronous PWM modes without causing harmful current oscillations.
Solution Approach 2:
The patent uses an intermediary approach by introducing a transition region with intermediate PWM mode. When switching between asynchronous and synchronous PWM modes, the control device temporarily operates in an intermediate mode where the carrier wave frequency partially synchronizes with the voltage command frequency. This intermediate state acts as a buffer that reduces the abruptness of mode transitions and minimizes current oscillations.
2Adaptability or versatility
If switching is performed between PWM modes without any consideration, then operational flexibility is achieved, but current oscillations occur that may cause semiconductor elements to break or require additional filter circuits
Solution Approach 1:
The patent applies feedback by continuously monitoring the rotating machine's operational parameters (rotational speed, load conditions, current state) and using this information to determine the optimal PWM mode and switching timing. The control device adjusts the carrier wave frequency and switching points based on real-time feedback from the system state, ensuring that mode transitions occur at optimal moments to minimize current oscillations while maintaining operational flexibility.
Data Source
AI summary
A rotating machine control device includes a voltage application unit that generates three-phase voltages; and a control unit that controls voltage generation operation of the voltage application unit in a first pulse-width modulation mode where a carrier wave frequency is asynchronous with a frequency of a voltage command or a second pulse-width modulation mode where a carrier wave frequency is synchronous with the frequency of the voltage command. On the basis of a first carrier wave used in generating a signal that controls the voltage application unit in the first pulse-width modulation mode, a second carrier wave used in generating a signal that controls the voltage application unit in the second pulse-width modulation mode, and an output voltage phase command, the control unit selects one of the first pulse-width modulation mode and the second pulse-width modulation mode as a pulse-width modulation method for controlling the voltage generation operation.