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Automatic Motor Current Limit Configuration Based on Phase Feedback with Tapered Starting Current

IP.com Disclosure Number: IPCOM000016110D
Original Publication Date: 2002-Aug-21
Included in the Prior Art Database: 2003-Jun-21
Document File: 4 page(s) / 375K

Publishing Venue

IBM

Abstract

This invention provides a method of allowing a single motor drive to safely and reliably power a wide range of motors without the use of custom code or embedded memory devices in the motor itself. In addition, it is capable of providing momentarily higher current to a motor during starting, where it is needed most. This helps to eliminate start failures while still providing adequate protection from triggering a solid state circuit breaker. This provides variable level HARDWARE overcurrent protection which is the only acceptable type to obtain UL certification. (without a formal UL code review). Current state of the art: There is no current technology of this type. Currently, different code is used for each motor/drive combination. The present is not an economical solution.

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  Automatic Motor Current Limit Configuration Based on Phase Feedback with Tapered Starting Current

This invention provides a method of allowing a single motor drive to safely and reliably power a wide range of motors without the use of custom code or embedded memory devices in the motor itself.

In addition, it is capable of providing momentarily higher current to a motor during starting, where it is needed most. This helps to eliminate start failures while still providing adequate protection from triggering a solid state circuit breaker.

This provides variable level HARDWARE overcurrent protection which is the only acceptable type to obtain UL certification. (without a formal UL code review).

Current state of the art: There is no current technology of this type. Currently, different code is used for each motor/drive combination. The present is not an economical solution.

Motor current is monitored by use of a shunt resistor in the negative leg of the DC bus. This is made possible by having a -350V system with a positive frame ground reference. All controls are referenced to -350V.

In the above figure, The 3 Phase bridge current causes a voltage to be present at the point labeled Vtrip. When the bridge current is greater than comparator reference for a time duration determined by the RC time constant setpoint, the comparator trips. The motor drive asynchronously turns off all power transistors and flags a motor overcurrent fault.

The overcurrent trip point in the system is determined entirely by Vtrip. The duration that we allow the motor drive to tolerate current equal or greater than the setpoint is determined entirely by the RC network.

Typically there are several of these comparators in an MDA with higher limit trip levels having faster time constants, while lower limits tend to have a longer time constant. This multi-level overcurrent protection is highly effective against the various types of faults we encounter.

Example 1. frame to phase faults tend to be very severe high cu...