DC Motor Control Circuit Using AC Half-Wave Switching to Reduce EMI

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Solution Overview

Problem

Existing control methods for direct current motors in applications requiring frequent rotation inversions face issues with electromagnetic interference, high costs, and mechanical wear, particularly in small household appliances like coffee machines, due to current spikes and the need for additional filters and complex circuits.

Innovation Solution

A control method and circuit that powers the motor using the negative or positive half-waves of an alternating supply voltage, detecting the zero-crossing and activating a switch device with a delay to minimize current spikes, eliminating the need for additional filters and reducing mechanical wear by using solid-state components like TRIAC or SCR thyristors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional H bridge control circuits with relays or mechanical components are used to control direct current motors, then the motor direction can be controlled, but mechanical wear and component breakages occur due to frequent switching cycles

Engineering Contradiction:

Improvecontrol circuit reliabilityVSAvoidcomponent service life

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent replaces mechanical or electromechanical relay-based H bridge circuits with solid-state thyristor-based control circuits. This substitution eliminates moving parts and mechanical wear, significantly improving reliability and extending service life under frequent switching conditions while maintaining the ability to control motor direction.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the control parameter from mechanical relay switching to thyristor firing angle control. By adjusting the firing angle of thyristors, the control circuit achieves smooth transitions and frequent direction changes without mechanical wear, resolving the contradiction between control flexibility and component durability.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If thyristors are used to control direct current motors with frequent switching cycles, then solid-state control is achieved, but electromagnetic interference and current spikes occur

Engineering Contradiction:

Improvecontrol circuit simplicityVSAvoidelectromagnetic interference

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent incorporates feedback mechanisms that monitor current and voltage conditions during thyristor switching. This feedback allows the control circuit to adjust switching timing and prevent current spikes, reducing electromagnetic interference while maintaining simple solid-state circuit architecture.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control circuit implements protective measures before switching occurs, including pre-charging circuits and controlled ramp-up of voltage application. This cushioning approach prevents sudden current spikes and reduces electromagnetic interference generated during thyristor commutation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Object-affected harmful factors

If additional filters and complex circuits are added to reduce current spikes and electromagnetic interference, then electromagnetic compatibility improves, but system cost increases

Engineering Contradiction:

Improveelectromagnetic compatibilityVSAvoidmanufacturing cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent extracts and eliminates the need for additional expensive filter components by integrating electromagnetic interference suppression directly into the thyristor control circuitry. This approach achieves electromagnetic compatibility without adding separate filter circuits, reducing manufacturing cost while maintaining performance.

Inventive Principle:

Principle #2Taking out (Extraction)

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

This approach reduces electromagnetic interference, extends the life of the control circuit, enhances positioning accuracy, and lowers costs by eliminating the need for additional components, resulting in a reliable and cost-effective motor control system.

Implementation Method 1

detecting the zero-crossing and activating a switch device with a delay to minimize current spikes

Methodology Applied

Scientific EffectZero-crossing detection:

Implementation Method 2

reduces electromagnetic interference, extends the life of the control circuit

Methodology Applied

Scientific EffectElectromagnetic interference reduction:

Data Source

PatentUS12451823B2Control method and circuit for a direct current motor for an infusion unit of a machine for preparing coffee beverages

Publication Date: 2025.10.21 DE LONGHI APPLIANCES SRL

AI summary

Embodiments described here concern a method to control a direct current motor powered by an alternating supply voltage, which provides to detect the instant of the zero-crossing of the supply voltage and to selectively activate a switch device to power the motor by the positive half-waves of the supply voltage in order to make it rotate in one sense, and by the negative half-waves in order to make it rotate in the opposite sense. The disclosure also concerns a control circuit for the motor.