Vehicular Inverter Control for Overheating and Drivability
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Solution Overview
Problem
Conventional inverter protection control methods reduce drivability during vehicle starts on upward slopes while attempting to prevent inverter overheating, and disabling protection can lead to inverter overheating when inverter lock occurs.
Innovation Solution
A control device and method that dynamically adjust the slip frequency and torque command for multiple rotating electric machines to avoid inverter lock frequencies, redistributing torque to maintain drivability and prevent inverter overheating by switching the command frequency outside the inverter lock band and fluctuating the slip frequency within a wider bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inverter protection control is executed to reduce current or voltage to the inverter when inverter lock occurs, then inverter overheating is prevented, but output torque of the rotating electric machine is reduced and drivability deteriorates
Solution Approach 1:
The invention changes the command frequency parameter from within the inverter lock frequency band to outside the inverter lock frequency band. By detecting when the command frequency falls within the inverter lock frequency band and shifting it to a frequency outside this band, the system prevents inverter lock conditions while maintaining normal current flow characteristics, thereby avoiding both inverter overheating and torque reduction associated with protection control.
2Ease of operation
If inverter protection control is disabled to maintain drivability during inverter lock, then drivability is maintained, but the inverter may overheat due to large current flow to switching elements
Solution Approach 1:
The invention performs preliminary detection of the inverter lock condition by monitoring whether the command frequency falls within the inverter lock frequency band before inverter lock actually occurs. By detecting the risk of inverter lock in advance and proactively shifting the command frequency outside the lock frequency band, the system prevents inverter lock from occurring, thereby eliminating the need for protection control while maintaining both drivability and inverter safety.
3Reliability
If command frequency is shifted outside inverter lock frequency band by changing slip frequency, then inverter lock is avoided, but torque fluctuation occurs that affects drivability
Solution Approach 1:
The invention applies counter-torque from the other rotating electric machine to compensate for the torque fluctuation caused by slip frequency change. When the slip frequency of one machine is adjusted to shift the command frequency outside the inverter lock band, causing torque fluctuation, the control device simultaneously adjusts the torque command of the other machine to generate opposing torque that cancels out the fluctuation, thereby maintaining smooth overall torque output and preserving drivability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses drivability reduction during vehicle starts on upward slopes while preventing inverter overheating by canceling torque fluctuations and avoiding inverter lock conditions, ensuring reliable performance.
Implementation Method 1
an inverter for converting DC power to alternating current (AC) power is used. The inverter performs DC/AC conversion in response to a command signal.
Data Source
AI summary
When a command frequency to a rotating electric machine is included in an inverter lock frequency band, a frequency switching section switches the command frequency to a frequency outside the inverter lock frequency band by changing a slip frequency command value. In response to this, a torque command change section changes a torque command to a second rotating electric machine other than a first rotating electric machine of which the slip frequency is changed such that a torque fluctuation caused by the change of the slip frequency command value is canceled out.