IPM Machine Torque Command Limit for Inverter Protection

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Solution Overview

Problem

Existing control systems for Interior Permanent Magnet (IPM) machines lack effective methods to estimate and manage inverter terminal voltage and torque, leading to potential damage from overload conditions, as they fail to accurately limit currents and protect inverter components.

Innovation Solution

A method and system for controlling IPM machines by determining current limits, characterizing peak current values based on voltage-to-speed ratios, and calculating torque command limits to generate current command values that protect the inverter from overloads, using a processor to manage direct and quadrature axis currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the peak power feature is enabled to supply overload current to the machine, then the drive efficiency and power range are improved, but the inverter components such as current sensors, DC bus capacitors and bus bars may be damaged

Engineering Contradiction:

Improveoverload current capabilityVSAvoidinverter component protection

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The controller performs preliminary characterization of the inverter's voltage-to-speed ratio and determines a torque command limit before overload conditions occur. This pre-established limit prevents excessive torque commands that would cause harmful currents, allowing the system to safely operate at peak power without damaging the inverter components.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The controller continuously monitors the actual torque and current in the system, comparing it against the characterized voltage-to-speed ratio and torque command limit. When the torque command approaches the limit, the controller adjusts the current command accordingly, providing real-time feedback control that prevents inverter damage while maximizing power output.

Inventive Principle:

Principle #23Feedback

2Reliability

If the controller uses a fixed current limit to protect the inverter, then the component protection is improved, but the drive efficiency and constant power operating range are reduced

Engineering Contradiction:

Improveinverter protectionVSAvoidconstant power operating range

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The controller changes the current limit parameter dynamically based on the actual torque and operating conditions. Instead of using a fixed current limit, the torque command limit is adjusted according to the characterized voltage-to-speed ratio and real-time torque feedback, allowing the inverter to operate efficiently across a wider constant power range while maintaining protection against harmful currents.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9735722B2Methods of controlling a machine using a torque command limit derived from a current limit and systems thereof

Publication Date: 2017.08.15 DEERE & CO

AI summary

At least one example embodiment discloses a method of controlling an alternating current (ac) machine. The method includes determining or retrieving a current limit for the ac machine, determining a characterized peak current value based on a voltage-to-speed ratio of the ac machine, determining current command values for the ac machine based on at least one of the torque command limit and a torque command for the ac machine, determining current command values for the ac machine based on the torque command limit and controlling the ac machine based on the current command values.