Digital Switching Controller for Electric Motors

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Solution Overview

Problem

Existing techniques for driving poly-phase electric motors, such as brushless motors, often result in discontinuities in motor driving torque, acoustic noise, and distortions in other motor phases due to the need for analog components and complex voltage/current sensing methods, particularly when sensing back electromotive force (BEMF).

Innovation Solution

A fully digital switching controller that generates digital replicas of phase currents and voltages without requiring dedicated analog components, using existing digital signals for motor control, by calculating differences in switching duty-cycles and storing current/voltage profiles in nonvolatile memory, allowing for digital reconstruction of BEMF without analog sensing circuits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If analog sensing circuits are used to detect back electromotive force (BEMF) in motor windings, then position sensing capability is improved, but device complexity and noise susceptibility increase

Engineering Contradiction:

ImproveBEMF sensing capabilityVSAvoidanalog components

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces analog sensing circuits with a fully digital implementation. Instead of using analog components to detect BEMF, the system uses digital signal processing to reconstruct phase voltages and currents from existing digital PWM control signals. This substitution eliminates the need for separate analog sensing hardware while maintaining accurate position detection capability through mathematical reconstruction of the BEMF waveform.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent creates digital replicas (copies) of phase voltages and currents by processing existing digital control signals. Rather than physically sensing the actual analog BEMF signals, the system generates digital copies of the voltage and current waveforms through computational methods, which are then used to determine rotor position and control motor operation.

Inventive Principle:

Principle #26Copying

2Measurement precision

If tri-state sensing method is used to detect BEMF, then position detection is enabled, but torque discontinuities and acoustic noise are generated

Engineering Contradiction:

Improve rotor position detectionVSAvoidtorque discontinuities and acoustic noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the physical tri-state sensing method with a digital reconstruction approach. Instead of actually tri-stating the winding to sense BEMF (which causes torque interruptions), the system reconstructs the BEMF signal digitally from continuous PWM control signals, eliminating the harmful torque discontinuities and associated acoustic noise while still achieving accurate position detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If dedicated analog sensing components are used for BEMF detection, then measurement accuracy is improved, but manufacturing cost and device complexity increase

Engineering Contradiction:

ImproveBEMF measurement accuracyVSAvoidmanufacturing simplicity

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent makes the existing digital PWM control signals serve multiple functions: they both control the motor windings and provide the data source for reconstructing BEMF signals. This multi-functionality eliminates the need for dedicated analog sensing components, simplifying manufacturing while maintaining measurement accuracy through digital signal processing.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent substitutes analog sensing hardware with digital signal processing operations. By using mathematical transformations on existing digital control signals, the system achieves accurate BEMF measurement without requiring additional analog components, thereby simplifying the manufacturing process and reducing bill of materials costs.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 eliminates the need for analog components, reduces noise and distortions, and provides a more efficient method for sensing BEMF, enhancing motor performance by maintaining smooth torque delivery and reducing acoustic noise.

Implementation Method 1

sensing the back electromotive force (BEMF) induced in a tri-stated winding

Methodology Applied

Scientific EffectElectromagnetic Induction: Electromagnetic Induction

Data Source

PatentUS9385639B2Switching controller for electric motors and related method of controlling electric motors

Publication Date: 2016.07.05 STMICROELECTRONICS INT NV

AI summary

A switching controller of a poly-phase electric motor may generate, in a fully digital manner, a replica of the phase current and/or of the phase (star) voltage of one or more windings of the motor. The switching controller may use digital signals already available for driving the motor to reconstruct a replica of the phase current or the phase voltage, and thereby avoid the need for dedicated analog components for phase current or phase voltage determination.