Saturation Controller Direct Torque Control for AC Machines

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Solution Overview

Problem

Direct torque control (DTC) systems for AC electric machines face challenges in reducing torque and stator flux ripples, especially at low sampling frequencies, which affects the performance and efficiency of motor control.

Innovation Solution

The implementation of a saturation controller-based DTC system that estimates torque and stator flux errors to generate control signals for voltage vectors, allowing for reduced sampling frequencies while maintaining waveform fidelity and minimizing ripples through adaptive duty ratio modulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If direct torque control is implemented with traditional hysteresis thresholds and sampling periods, then the control system can operate, but torque and stator flux ripples increase and performance deteriorates at low sampling frequencies

Engineering Contradiction:

Improvetorque and stator flux control precisionVSAvoidsampling frequency

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent transforms the traditional hysteresis-based discrete control into a continuous control scheme by changing the fundamental control parameters. Instead of using fixed hysteresis thresholds and discrete sampling periods, the invention employs continuous saturation controller outputs that vary smoothly with the error signals, enabling precise torque and flux control at low sampling frequencies while minimizing ripples

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical hysteresis comparison mechanism with a continuous saturation function. The saturation controller continuously processes the torque and flux error signals to generate smooth control outputs, eliminating the abrupt switching characteristic of hysteresis controllers and thereby reducing torque and flux ripples

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If saturation controllers are used to generate control signals, then torque and stator flux ripples are reduced, but the computational complexity increases

Engineering Contradiction:

Improvetorque and stator flux control precisionVSAvoidcontroller computational complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent simplifies the computational complexity by changing the control architecture from multiple independent hysteresis controllers to a unified saturation controller based approach. The saturation function uses simple algebraic operations rather than complex switching logic, reducing the overall computational burden while maintaining high control precision

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent merges the torque control and flux control functions into a unified control framework where the saturation controller simultaneously processes both torque and flux errors. This consolidation reduces the number of separate control loops and simplifies the overall controller structure, decreasing computational complexity

Inventive Principle:

Principle #5Merging (Combining)

3Loss of energy

If low sampling frequencies are used to reduce computational cost, then the system operates more efficiently, but torque and stator flux ripples increase and waveform fidelity deteriorates

Engineering Contradiction:

Improvecomputational costVSAvoidwaveform fidelity

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent ensures continuous control action by using saturation controllers that continuously process error signals and generate smooth control outputs. This continuous action maintains accurate torque and flux waveforms even at low sampling frequencies, preserving waveform fidelity while reducing computational cost compared to high-frequency discrete control

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The patent introduces dynamic adaptation by using saturation functions that continuously adjust their outputs based on the instantaneous error conditions. This dynamic response allows the controller to maintain high waveform fidelity at low sampling frequencies by adapting the control signal in real-time without requiring high sampling rates

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS9831812B2Direct torque control of AC electric machines

Publication Date: 2017.11.28 NUTECH VENTURES LTD

AI summary

This disclosure features an apparatus including a motor controller to generate control signals to control an electric motor. The motor controller includes a first saturation controller to generate a first saturation controller output based on feedback signals associated with the electric motor. The motor controller further includes a duty ratio modulator coupled to the first saturation controller. The duty ratio modulator is configured to determine activation times for a set of voltage vectors based on the first saturation controller output. The motor controller is configured to generate, at each switching cycle, a control signal based on the set of voltage vectors and the activation times for the set of voltage vectors, and provide the control signal for controlling the electric motor.