Motor Drive Isolation Circuit Transient Protection

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Solution Overview

Problem

Existing electric motor drive circuits face failures due to inductive voltage transients when current is turned off, leading to undesirable braking torque and potential damage to isolation circuits, particularly in applications like automobile power steering systems, where high power diodes are large and expensive.

Innovation Solution

A low power circuit using a combination of transistors and diodes is introduced to protect the isolation circuit between half bridge circuits and motor windings, where diodes clamp control signals to prevent transistor failure from negative voltage transients, allowing the circuit to dissipate these transients effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high power diodes are coupled to the electric motor to directly limit excursions of inductive voltage transients, then the isolation circuit is protected from voltage transient damage, but the device size and cost increase significantly

Engineering Contradiction:

Improveisolation circuit protectionVSAvoiddiode size

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

A capacitor is introduced as an intermediary component between the motor winding and the isolation circuit. The capacitor absorbs and dissipates inductive voltage transients when the motor winding current is turned off, protecting the isolation circuit from damage without requiring large high-power diodes. This intermediary element handles the transient energy, preventing it from reaching the isolation circuit.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces expensive high-power diodes with a capacitor that can be designed to handle transient energy dissipation. The capacitor serves as a sacrificial element that absorbs the transient voltage spikes, allowing the use of lower-cost, smaller components overall in the protection circuitry.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If high power diodes are used to limit inductive voltage transient excursions, then the isolation circuit reliability is improved, but the manufacturing cost increases

Engineering Contradiction:

Improveisolation circuit protectionVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent substitutes expensive high-power diodes with a capacitor-based solution that uses lower-cost components. The capacitor handles the transient energy absorption, allowing the system to achieve the same protection function with cheaper, more manufacturable parts.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent changes the protective mechanism from active clamping (diodes) to passive energy storage and dissipation (capacitor). This parameter change in the protection approach allows for the use of smaller, less expensive components while maintaining the protective function against voltage transients.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If an isolation circuit is coupled between half bridge circuits and motor windings to avoid braking torque, then the motor control reliability is improved, but the circuit becomes vulnerable to inductive voltage transient damage

Engineering Contradiction:

Improvemotor controlVSAvoidinductive voltage transients

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The capacitor is positioned to provide beforehand cushioning against inductive voltage transients. When the motor winding current is turned off, the capacitor is already in place to absorb and dissipate the transient voltage spikes before they can damage the isolation circuit, providing proactive protection.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The capacitor serves as an intermediary protective element between the motor winding and the isolation circuit. It mediates the harmful inductive voltage transients by absorbing and dissipating their energy, preventing direct damage to the isolation circuit while allowing the isolation circuit to maintain motor control reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 effectively prevents transistor failure from negative voltage transients, ensuring reliable operation and avoiding braking torque, while using smaller, less expensive low power diodes, thus enhancing the reliability and cost-effectiveness of electric motor drive systems.

Implementation Method 1

diodes clamp control signals to prevent transistor failure from negative voltage transients

Methodology Applied

Scientific EffectVoltage clamping:

Implementation Method 2

allowing the circuit to dissipate these transients effectively

Methodology Applied

Scientific EffectInductive voltage transient dissipation:

Data Source

PatentUS9496708B2Electric motor drive isolation circuit

Publication Date: 2016.11.15 ALLEGRO MICROSYSTEMS LLC

AI summary

An isolation circuit is coupled between motor driver half bridge circuits and an electric motor. A motor controller circuit supplies motor drive signals to the motor driver half bridge circuits. The isolation circuit includes transistors coupled in series with the motor windings. Low to medium power diodes are coupled between a reference voltage source and control terminals of the transistors.