AC Motor Inverter Control for Current Sensing After Phase Short Faults
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Solution Overview
Problem
Existing AC rotary machine controllers fail to detect current in the normal phase when a short circuit failure occurs, especially when the current sensor is connected in series to the switching devices of the inverter, as they require specific on/off control of the switching devices for current detection, which is not feasible during short circuit failures.
Innovation Solution
A controller for AC rotary machines that includes n-phase windings, current sensors, a voltage command calculation unit, a PWM control unit, and a failure determination unit, which adjusts the voltage command values of normal phases to ensure the on period of switching devices is sufficient for current detection during short circuit failures, allowing for reliable current detection and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the current sensor is connected in series to the switching device for current detection, then the current detection structure is simplified, but the switching device must be turned on for a predetermined period to detect current, which becomes problematic during short circuit failures
Solution Approach 1:
The patent dynamically adjusts the PWM duty cycle of normal phases based on the detected failure mode. When a short circuit failure is detected in one phase, the controller increases the duty cycle of the remaining normal phases to ensure their switching devices remain on long enough for current detection, while adapting the voltage command values to maintain proper motor control.
Solution Approach 2:
The patent changes the voltage command values applied to normal phases when short circuit failures are detected. By adjusting these voltage parameters, the controller ensures that the PWM duty cycle of normal phases is sufficiently increased, allowing the switching devices to remain on for the predetermined period necessary for current detection by the series-connected sensors.
2Reliability
If the voltage command values of normal phases are increased to extend the on period of switching devices for current detection, then current detection becomes possible during short circuit failures, but the control complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors the operational status of each phase and detects short circuit failures. Based on this feedback, the controller automatically adjusts the voltage command values and PWM duty cycles of normal phases to maintain current detection capability, creating a closed-loop control system that adapts to failure conditions.
Solution Approach 2:
The patent prepares the control system in advance by establishing failure determination logic and pre-defined voltage command value adjustment strategies. When a short circuit failure is detected, the controller immediately applies the appropriate voltage adjustments to normal phases, ensuring that the switching devices have sufficient on-time for current detection without requiring complex real-time calculations.
3Reliability
If the on period of switching devices in normal phases is extended to enable current detection, then current feedback control can be maintained during short circuit failures, but the switching device stress increases
Solution Approach 1:
The patent applies partial action by extending the on period only for the switching devices in normal phases that require current detection, while the faulty phase switching devices are excluded from this extended operation. This selective approach ensures current feedback control for healthy phases without unnecessarily increasing stress on all switching devices.
Solution Approach 2:
The patent dynamically adjusts the voltage command values and PWM duty cycles based on the specific failure condition detected. By adapting the control parameters in real-time, the system extends the on period only when and where necessary for current detection, minimizing unnecessary stress accumulation on switching devices while maintaining current feedback control for normal phases.
Data Source
AI summary
To provide a controller for AC rotary machine which can detect current of the normal phase certainly when the short circuit failure of one phase occurs, in an apparatus that a current sensor is connected in series to the positive electrode side switching device or the negative electrode side switching device of an inverter. A controller for AC rotary machine, when determining that the short circuit failure of any one phase occurred, calculates voltage command values of normal n−1 phases, and changes the voltage command values of the normal n−1 phases so that on period of the detection object device of each phase of the normal n−1 phases become longer than or equal to a length necessary for current detection at least at a current detection timing.