Sensorless Motor Drive Overvoltage Protection via Forced Commutation

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Solution Overview

Problem

Existing motor drive systems using sensorless drive technology face instability and overvoltage protection issues due to fluctuations in position detection signals, leading to inefficient energy consumption and potential step-out states during overvoltage conditions.

Innovation Solution

A motor drive apparatus and method that estimates the rotational position of a brushless DC motor by detecting phase voltage, switches to a forced commutation mode based on detected overvoltage and rotational frequency, and changes back to sensorless control after the overvoltage is mitigated, ensuring stable operation and efficient energy consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a Zener diode is inserted in the power source line to clamp overvoltage, then overvoltage protection is secured, but the product price increases due to the high cost of Power Zener diodes

Engineering Contradiction:

Improveovervoltage protectionVSAvoidproduct price

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical/electrical overvoltage protection device (Zener diode) with a control system that uses sensorless drive technology and controlled energy consumption through motor rotation. The control device detects overvoltage conditions and rotates the motor to consume excess energy, eliminating the need for expensive protective components while maintaining protection reliability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The motor drive system uses itself to protect against overvoltage by rotating the motor to consume excess energy. The system leverages its own operational capability (motor rotation) to dissipate overvoltage energy, rather than relying on external protective components

Inventive Principle:

Principle #25Self-service

2Device complexity

If sensorless drive control is used to estimate rotor position by detecting phase voltage, then device complexity is reduced, but position detection signals fluctuate under overvoltage conditions causing unstable current application

Engineering Contradiction:

Improvecontrol system complexityVSAvoidcontrol stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent implements dynamic control by detecting overvoltage conditions and switching to a special control mode that rotates the motor at maximum output. This dynamic response adapts the control strategy based on system conditions, maintaining stability during overvoltage events while preserving the simplicity of sensorless drive during normal operation

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control device continuously monitors voltage conditions and uses this feedback to determine when to activate overvoltage protection mode. The system detects overvoltage and adjusts its behavior accordingly, creating a closed-loop control that maintains stability without adding position sensors

Inventive Principle:

Principle #23Feedback

3Loss of energy

If the motor is rotated on maximum output conditions to consume energy during overvoltage, then overvoltage protection is achieved, but electric power cannot be properly consumed when using sensorless drive due to fluctuating position detection signals

Engineering Contradiction:

Improveovervoltage energy consumptionVSAvoidenergy consumption effectiveness

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies preliminary action by detecting overvoltage conditions early and immediately switching to maximum output rotation mode. The control device detects the overvoltage state and proactively activates the energy consumption mechanism before the overvoltage can cause damage, ensuring effective energy dissipation

Inventive Principle:

Principle #10Preliminary action

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 provides effective overvoltage protection by consuming overvoltage energy quickly and preventing instability in sensorless drive control, ensuring smooth operation and maintaining system stability even under continuous overvoltage conditions.

Implementation Method 1

A rotational position estimation device estimates a rotational position of a rotor by detecting a phase voltage generated in a stator coil of a brushless DC motor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS7852026B2Motor drive apparatus and motor drive control method

Publication Date: 2010.12.14 DENSO CORP

AI summary

A protection circuit is configured to change control modes in a drive control process of a drive circuit for a motor when overvoltage is applied to a power source line while the motor is driven. With overvoltage applied, the control process is changed to a control mode to perform forced commutation control. When a predetermined time period passes after the voltage of the power source line returns to a predetermined level, the control process is changed to a sensorless control mode using a position detection circuit. This configuration can provide a motor drive apparatus capable of performing an overvoltage protection operation appropriately even when the sensorless control mode is adopted.