Remedial Electrical Short for IPM Motor Back-EMF Control
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Solution Overview
Problem
Interior permanent magnet (IPM) synchronous machines in electric vehicles face challenges with back electromagnetic force (EMF) voltage at higher speeds, leading to uncontrolled generator states where electrical current flows back to the battery module, causing regenerative braking torque and potential damage.
Innovation Solution
A controller transitions the power inverter module between open, controllable switching, and polyphase short states, applying an out-of-phase voltage that ramps from maximum to zero, eventually coupling all phase windings together to prevent current backflow and manage braking torque effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If switching within the voltage inverter is temporarily disabled in response to a detected fault, then the harmful back EMF voltage conduction is prevented, but the uncontrolled generator state causes significant electrical current to flow back to the battery module and regenerative braking torque to act on the machine
Solution Approach 1:
The patent introduces an intermediary remedial action state between the fault condition and the battery module. Instead of directly disabling switching and allowing uncontrolled current flow to the battery, the system implements a controlled intermediate state where the inverter operates in a specific mode that mediates the energy flow, preventing both direct back EMF conduction and uncontrolled generator current flow to the battery.
Solution Approach 2:
The patent converts the harmful back EMF voltage and uncontrolled generator state into a beneficial controlled energy dissipation mechanism. By deliberately controlling the inverter switches in a specific pattern during the remedial action, the system transforms the potentially damaging uncontrolled current flow into a controlled process that safely dissipates energy through the motor impedance and prevents battery damage.
2Object-generated harmful factors
If a three-phase short is implemented as a fault condition remedial action, then electrical current flows from phase to phase instead of flowing back to the battery module, but braking torque is relatively low at higher motor speeds which may not be favorable for traction drive applications
Solution Approach 1:
The patent changes the operational parameters of the inverter during the remedial action state. By modifying the switching patterns and control parameters of the inverter bridges, the system achieves a different operational mode that maintains adequate braking torque while preventing current backflow to the battery module, especially at higher motor speeds where traditional three-phase shorting is less effective.
3Object-affected harmful factors
If switching is disabled to prevent back EMF conduction, then diode conduction is prevented, but the machine impedance limits motor currents and stator current approaches the characteristic current for most motor speeds
Solution Approach 1:
The patent implements a dynamic control strategy where the inverter switching is not simply disabled but controlled in a time-varying manner during the remedial action state. The switching patterns are dynamically adjusted based on the motor operating conditions, allowing the system to prevent diode conduction while maintaining appropriate current levels through controlled switching sequences that adapt to the motor's instantaneous state.
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 solution prevents electrical current backflow to the battery module, maintains low braking torque at high motor speeds, and reduces transient current spikes, enhancing motor operation and component safety.
Implementation Method 1
at higher motor speeds, the rotating magnets can create a back electromagnetic force (EMF) voltage in the motor's stator windings
Implementation Method 2
electrical current may flow from phase to phase instead of flowing back to the battery module
Data Source
AI summary
A method of implementing a remedial short in a rotating polyphase electric machine (EM) includes detecting a fault condition; and initially commanding a power inverter module (PIM) into an electrically-open state. Once in an open state, a controller may determine a phase angle of a current generated by the rotating EM, and may control the PIM to apply a voltage to the EM that is out-of-phase from the determined phase angle of the generated current. The magnitude of the applied voltage signal may ramped from a first voltage to zero over a period of time; whereafter the PIM may be commanded to electrically couple all of the electrical windings of the EM to each other.