AC Machine Terminal Voltage Estimation for Current Regulation

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Solution Overview

Problem

Interior Permanent Magnet (IPM) machines face challenges with extra high machine terminal voltage leading to current regulation collapse, torque ripple, rotor magnet and stator winding heating, and acoustic noise due to manufacturing tolerances, material characteristics, and temperature variations, which affect the accuracy of torque control.

Innovation Solution

A control device with a processor that selects a modulation mode and determines terminal phase voltages based on the selected mode, estimating the actual inverter or machine terminal voltage to compensate for voltage mismatches and adjust current commands, thereby stabilizing motor control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the controller uses standard voltage control methods, then the control system is simple, but the terminal voltage accuracy deteriorates due to manufacturing tolerances and temperature variations

Engineering Contradiction:

Improveterminal voltage accuracyVSAvoidcontrol system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent implements a feedback mechanism where the controller estimates the actual terminal voltage based on measured phase currents and machine parameters, then uses this estimated voltage to adjust control commands. This closed-loop feedback approach compensates for voltage deviations caused by manufacturing tolerances and temperature variations, improving terminal voltage accuracy without requiring additional voltage sensors.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces direct voltage measurement (which would require additional hardware) with an estimation approach using electrical measurements and mathematical models. The controller estimates terminal voltage by calculating the real part of the complex voltage equation based on measured phase currents, resistance, inductance, and angular velocity, substituting physical voltage sensing with computational estimation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If the controller compensates for voltage mismatches, then current regulation quality improves, but the control calculations become more complex

Engineering Contradiction:

Improvecurrent regulation qualityVSAvoidcontrol calculation complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent dynamically adjusts control parameters including d-axis and q-axis voltage commands, current limits, and modulation indices based on the estimated terminal voltage. When voltage deviation is detected, the controller modifies these parameters to compensate, ensuring current regulation remains within acceptable bounds despite voltage mismatches caused by manufacturing tolerances or temperature effects.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9270223B2Methods of determining machine terminal voltage and systems thereof

Publication Date: 2016.02.23 DEERE & CO

AI summary

At least one example embodiment discloses a control device for controlling an alternating current (ac) machine. The control device includes a processor configured to select a modulation mode from a plurality of modulation modes, determine a plurality of present phase voltages corresponding to phases of an inverter based on the selected modulation mode, the determination compensating for deadtimes associated with the selected modulation mode and phases of the inverter, the inverter configured to drive the ac machine and determine an estimated terminal voltage based on the plurality of present phase voltages.