Multi-Phase Motor Braking Control for Lower ASC Torque
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Solution Overview
Problem
In electric or hybrid vehicles equipped with 6-phase electric motors, the default Active Short Circuit (ASC) mode generates high and unintended braking torque due to back EMF, violating safety standards like ISO262262, as it causes current flow through diodes and charges the battery without commanded switches.
Innovation Solution
A method for reducing braking torque in electric vehicles with multi-phase motors, specifically a 6-phase or 12-phase motor system, by strategically setting switches in the stator arrangements to control current flow, including angularly offset coil arrangements and additional neutral switching to minimize torque ripple and induced currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Active Short Circuit mode is implemented to protect diodes against over-currents, then diode protection is improved, but unintended braking torque increases significantly
Solution Approach 1:
The patent segments the six-phase motor control into two independent three-phase inverters, each capable of independent ASC control. By controlling each inverter separately, the system can implement ASC in one inverter while maintaining normal operation or different control modes in the other, thereby reducing the total braking torque compared to simultaneous ASC in both inverters.
Solution Approach 2:
The patent applies partial ASC action by implementing Active Short Circuit in only one of the two three-phase inverters while leaving the other inverter operational or in a different state. This partial application of ASC provides sufficient diode protection while significantly reducing the unintended braking torque compared to full ASC application in both inverters.
2Reliability
If Active Short Circuit is commanded to prevent over-currents, then current protection is improved, but vehicle deceleration control is worsened due to high braking torque
Solution Approach 1:
The control system is segmented into two independent three-phase control units. Each unit can independently implement ASC protection while the other unit maintains normal motor control, allowing the vehicle to preserve deceleration control capability while still providing over-current protection through selective ASC application.
Solution Approach 2:
Instead of applying ASC excessively in both inverters (which causes high braking torque), the system applies partial ASC action in only one inverter. This provides sufficient current protection while maintaining acceptable deceleration control, as the other inverter can continue to control motor operation normally.
3Use of energy by moving object
If back EMF is allowed to generate current flow through diodes at high speed, then battery charging occurs, but unintended braking torque violates safety standards
Solution Approach 1:
The patent converts the harmful back EMF-induced current flow into a beneficial controlled operation. By implementing ASC in one inverter, the system safely channels the back EMF currents through controlled paths that charge the battery while preventing the harmful unintended braking torque, thus converting a safety violation into a useful energy recovery mechanism.
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 method effectively reduces braking torque by up to 66% in 6-phase systems and 33% in 12-phase systems, ensuring compliance with safety standards and optimizing vehicle deceleration control.
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 inverters are controlled to provide an Active Short Circuit (ASC). This ASC mode however generates braking torque on e-machines (electric motors) due to induced currents
Data Source
AI summary
A method of braking for a vehicle with a multi-phase electric motor, said motor including at least one stator group including a first stator arrangement and a second stator arrangement, each arrangement including three coils, each arrangement connected to respective low side and/or high side circuitry, each low side and/or high side circuitry including respective low side switches and high side switches, said method including: for either 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.