Motor Control Apparatus Capacitor Discharge Circuit

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional motor control apparatuses for electric power steering systems face challenges in accurately and efficiently discharging capacitor residual charge, which can lead to incorrect failure detection and potential damage to switching elements, requiring complex and costly circuits or disrupting motor torque.

Innovation Solution

A motor control apparatus with an electric power converter, capacitor, resistor, and control circuit that discharges capacitor charge to the low potential side through a resistor before motor operation, using a single pull-up resistor for both discharging and abnormality detection, allowing for quick and simple capacitor discharge without increasing size or cost.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a motor control apparatus uses a capacitor to suppress ripple currents, then the motor operation stability is improved, but the capacitor stores remaining electric charge that causes false failure detection and potential damage to switching elements

Engineering Contradiction:

Improvemotor operation stabilityVSAvoidfalse failure detection and switching element damage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The control circuit performs a discharge operation of the capacitor before executing failure detection. By discharging the capacitor in advance (prior to detection), the harmful residual charge is removed, preventing false detection results and potential damage to switching elements while maintaining the capacitor's ripple suppression function during normal operation

Inventive Principle:

Principle #10Preliminary action

2Speed

If a motor control apparatus discharges capacitor charge through a dedicated discharge circuit, then the capacitor charge is discharged rapidly, but the device size and cost increase

Engineering Contradiction:

Improvedischarge speedVSAvoidcircuit complexity and cost

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The control circuit integrates the capacitor discharge function into the existing failure detection circuitry. The same control circuit that detects failures also controls the discharge operation by turning switching elements on or off. This multi-functional approach enables rapid discharge without requiring separate dedicated discharge circuits, resistors, or additional components, thus avoiding increased device size and cost

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If a motor control apparatus discharges capacitor charge through the motor, then no exclusive discharge circuit is needed, but the motor torque is influenced and complicated check processing is required

Engineering Contradiction:

Improvecircuit complexityVSAvoidmotor torque integrity and detection accuracy

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The control circuit performs discharge operation before failure detection by controlling switching elements to create a discharge path through the capacitor and phase coil. By executing discharge in advance and separately from the detection process, the system avoids influencing motor torque during detection and eliminates the need for complicated check processing to distinguish between discharge effects and actual failures

Inventive Principle:

Principle #10Preliminary action

4Loss of time

If failure detection is performed before capacitor discharge, then the system can quickly identify failures, but the capacitor's residual charge causes false detection results

Engineering Contradiction:

Improvedetection timeVSAvoiddetection accuracy

Core Design Contradiction:

Loss of timeVSMeasurement precision

Solution Approach 1:

The control circuit reverses the conventional sequence by performing capacitor discharge before failure detection. This preliminary discharge action removes residual charge that would cause false detection results, ensuring accurate detection while maintaining efficient timing. The control circuit manages this sequence by controlling the switching elements to discharge first, then immediately proceed with failure detection

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

Enables accurate and rapid discharge of capacitor charge, preventing false failure detection and potential damage, while maintaining motor torque integrity and reducing the need for complex circuits, thus ensuring timely and reliable electric power steering system operation.

Implementation Method 1

a motor control apparatus...discharges capacitor charge to the low potential side through a resistor

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS8339080B2Motor control apparatus and electric power steering system using the same

Publication Date: 2012.12.25 DENSO CORP

AI summary

A motor control apparatus has an inverter circuit, which includes FETs for converting electric power supplied to a motor. A capacitor is provided between a battery and the inverter circuit. A pull-up resistor connects a V-phase of the motor to a high potential side of the battery. A power supply relay permits or interrupts current flow from the battery to the capacitor and the motor. A microcomputer controls the power supply relay and the motor. The microcomputer turns on a low-side FET of a V-phase under a condition that the power supply relay is interrupting the current flow before the motor is started. Electric charge stored in the capacitor is discharged to a low potential side of the battery through the pull-up resistor.