Multi-Phase Motor Braking Control for Lower Back-EMF Torque
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Solution Overview
Problem
Existing electric vehicle and hybrid vehicle systems with 6-phase electric motors experience high and unintended braking torque due to induced currents from back EMF, violating safety standards like ISO262262, especially during Active Short Circuit mode.
Innovation Solution
Implementing a 6-phase or 12-phase motor system with specific stator group arrangements and switch configurations, including an additional node switch between stator groups, to reduce braking torque by selectively closing switches and controlling current flow through coils, thereby minimizing undesirable torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Active Short Circuit mode is implemented to protect freewheeling diodes, then reliability of the inverter circuit is improved, but unintended braking torque increases causing safety violations
Solution Approach 1:
The patent segments the six phases into two separate three-phase groups (first stator arrangement and second stator arrangement). By controlling each group independently and selectively short-circuiting specific phases within each group, the system reduces the net braking torque while still protecting the freewheeling diodes from over-currents.
Solution Approach 2:
The patent applies different switching states to different phase groups. Specifically, it closes switches for certain phases (e.g., first and third phases of first arrangement, first and third phases of second arrangement) while keeping other switches open, creating localized current paths that minimize overall braking torque while maintaining diode protection.
2Use of energy by moving object
If back EMF is allowed to flow through diodes at high speed, then energy recovery to battery is achieved, but unintended current flow and braking torque occur
Solution Approach 1:
The patent converts the harmful back EMF-induced current into a beneficial controlled current path. By deliberately closing specific switches during Active Short Circuit mode, it creates controlled current paths that allow energy recovery while simultaneously canceling out the harmful braking torque through balanced phase control.
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
The solution reduces braking torque by up to 66% in 6-phase systems and 33% in 12-phase systems, significantly improving compliance with safety standards and operational efficiency.
Implementation Method 1
PM Machine exhibits back EMF (even when not commanded). At high speed, back EMF which exceeds DC Bus Voltage will generate current flow through the diodes of the circuitry and charge the battery
Implementation Method 2
The goal is to protect the freewheeling diodes of the gates of the invertor circuit against over-currents. This ASC mode however generates braking torque on e-machines (electric motors) due to induced currents.
Data Source
Figure 1~2
Figure 3
Figure 4a~4b
AI summary
A method of braking in an electrically powered vehicle, said vehicle including a drive system which includes a multi-phase motor electric motor, said motor comprising at least one stator group; said stator group comprising a first stator arrangement including three coils (e2,e4,e6) and a second stator arrangement including threes coils, (e2*e4*e6*) being angularly offset from said first coil arrangement, and where, said first arrangement is connected to respective low side and/or high side circuitry, including a low side switches (32,34,36,) and/or high side switches (31,33,35) for each of the said coils respectively, adapted to selectively allow current to flow through said respective coils of said first stator arrangement from a power source, and where said second arrangements is connected to respective low side and/or high side circuitry, including a low side switches (32*, 34, *36*) and/or high side switches (31*, 33*, 35*) for each of the said coils respectively, adapted to selectively allow current to flow through said respective coils of said second stator arrangement from a power source, said method comprising: for one or more of each group: for either or both of said second or first arrangements, i)setting any two of said switches in said low side circuitry to a closed state and the other switch in an open state, and setting all the switches in the high side to an open state; and/or ii) setting any two of said switches in said high side circuitry to a closed state and setting the other switch to an open state, and setting all the switches on the low side to an open state.