Alternating Passive Rectification for Motor Fault Protection

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Solution Overview

Problem

In hybrid electric and battery electric vehicles, fault conditions such as a three-phase current sensor fault can lead to unstable traction motor controllers, resulting in large phase current and DC bus voltage oscillations, with existing solutions like 'all-IGBT-off' and 'fixed 3-phase short' strategies either causing DC bus over-voltage or risking demagnetization of the traction motor's permanent magnet.

Innovation Solution

Implementing an alternating passive rectification and 3-phase short control method, where all upper IGBTs are turned on for half the switching cycle and lower IGBTs for the other half, with an intentionally longer dead time, balancing the switching frequency and dead time to prevent DC bus voltage spikes and transient current demagnetization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If all switches are deactivated (all-IGBT-off strategy), then DC bus voltage spikes are prevented, but large phase current oscillations occur causing instability

Engineering Contradiction:

ImproveDC bus voltage stabilityVSAvoidphase current stability

Core Design Contradiction:

TemperatureVSStability of the object's composition

Solution Approach 1:

The patent applies periodic action by implementing alternating passive rectification cycles where switches are periodically activated and deactivated. During fault conditions, the controller alternates between activating upper switches for a first duration, then deactivating all switches for a second duration, creating a periodic control pattern that prevents both voltage spikes and current oscillations through rhythmic switching sequences

Inventive Principle:

Principle #19Periodic action

2Stability of the object's composition

If fixed 3-phase short control is applied, then phase current oscillations are reduced, but transient current peaks cause demagnetization of permanent magnets

Engineering Contradiction:

Improvephase current stabilityVSAvoidtransient current demagnetization

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent implements periodic action with alternating passive rectification, periodically activating upper switches for controlled current circulation and then deactivating all switches for dead time periods. This periodic on-off pattern allows current to circulate safely during active periods while preventing dangerous transient peaks during deactivation periods, thereby protecting permanent magnets from demagnetization

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent applies beforehand cushioning by introducing a dead time period where all switches are deactivated between active switching cycles. This dead time acts as a cushioning interval that prevents abrupt current changes and transient peaks, allowing the system to safely dissipate energy and prepare for the next switching cycle without causing demagnetization

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Measurement precision

If switching frequency is increased to improve control precision, then motor control accuracy improves, but DC bus voltage oscillations increase

Engineering Contradiction:

Improvemotor control precisionVSAvoidDC bus voltage stability

Core Design Contradiction:

Measurement precisionVSTemperature

Solution Approach 1:

The patent implements alternating passive rectification with carefully controlled switching frequencies and duty cycles. By periodically activating switches for controlled durations followed by deactivation periods, the system achieves precise motor control through regulated switching patterns while the periodic deactivation intervals prevent voltage oscillations by allowing energy dissipation and system stabilization

Inventive Principle:

Principle #19Periodic action

4Temperature

If dead time is extended to prevent voltage spikes, then DC bus voltage stability improves, but motor response time decreases

Engineering Contradiction:

ImproveDC bus voltage stabilityVSAvoidmotor response speed

Core Design Contradiction:

TemperatureVSSpeed

Solution Approach 1:

The patent implements alternating passive rectification with optimized dead time durations within periodic switching cycles. The dead time is extended enough to prevent voltage spikes during deactivation periods, while the overall periodic cycle maintains adequate response speed by alternating between active control periods (for responsiveness) and deactivation periods (for voltage stabilization), achieving a balance between voltage stability and motor response

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS11296644B2Alternating passive rectification and 3-phase-short control for motor fault protection

Publication Date: 2022.04.05 FORD GLOBAL TECH LLC

AI summary

A vehicle includes a traction battery, an inverter, and a controller. The inverter includes a plurality of pairs of switches. Each of the pairs includes an upper switch that is directly electrically connected with a positive terminal of the traction battery and a lower switch that is directly electrically connected with a negative terminal of the traction battery. The controller, responsive to presence of a fault condition and during each of consecutive switching periods, deactivates all of the switches for a predetermined portion of the switching period, activates only the upper switches for another predetermined portion of the switching period, deactivates all of the switches for yet another predetermined portion of the switching period, and activates only the lower switches for still yet another predetermined portion of the switching period.