Variable Frequency Drive Braking During Input Power Loss

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Solution Overview

Problem

Medium voltage variable frequency drives, such as those used in electric submersible pumps, face issues with reverse torque causing excessive spinning when input power is lost, leading to mechanical stress due to the high reverse torque from fluid columns, necessitating improved braking capabilities to prevent pump damage.

Innovation Solution

A drive system with a power converter comprising a main and auxiliary power source, where a control system using a processor detects a main input voltage drop and disconnects the main power source, enabling the auxiliary power source to supply power, and diverts regenerated energy to a resistive load bank to manage braking and prevent excessive spinning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the pump is allowed to back spin until the column reaches the well level, then the system can handle power loss, but the pump and motor are severely stressed and may be damaged

Engineering Contradiction:

Improvepower loss handlingVSAvoidmechanical stress on motor and pump

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The system applies preliminary anti-action by detecting power loss conditions and activating the auxiliary power source before the pump can backspin and cause damage. The control system monitors power input and preemptively switches to auxiliary power or applies braking torque to prevent the harmful backspinning motion from occurring in the first place.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The system converts the harmful reverse torque and backspinning motion into beneficial controlled braking action. By using the auxiliary power source to apply controlled reverse torque, the system transforms the damaging uncontrolled backspin into a controlled deceleration process that safely brings the pump to a stop without mechanical damage.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If a fixed waiting time is set for all pumps to prevent re-start, then the system can avoid premature restart, but the solution is not optimized for individual pump conditions and may waste time

Engineering Contradiction:

Improvepremature restart preventionVSAvoidwaiting time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system applies dynamics by transitioning from a static fixed waiting time approach to a dynamic, real-time monitoring system. The control system continuously monitors pump status, column position, and power conditions, adjusting the restart timing dynamically based on actual pump conditions rather than a predetermined fixed delay, thereby optimizing both safety and time efficiency.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system implements feedback by continuously monitoring pump operational status, power input conditions, and column position, then using this feedback information to make intelligent restart decisions. The control system receives feedback from sensors and system state, processes this information, and adjusts the restart timing accordingly, ensuring premature restarts are prevented while minimizing unnecessary waiting time.

Inventive Principle:

Principle #23Feedback

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

The solution effectively prevents pump damage by managing braking and maintaining control during power outages, ensuring the drive system can restart safely and reducing mechanical stress on the motor and pump.

Implementation Method 1

the control system comprises at least one processor and is configured via computer executable instructions to detect a main input voltage drop of the main power source below a predefined power threshold

Methodology Applied

Scientific EffectVoltage detection:

Implementation Method 2

enable the auxiliary power source to provide auxiliary input power to the power converter in response to the main input voltage drop

Methodology Applied

Scientific EffectElectrical power supply:

Implementation Method 3

diverts regenerated energy to a resistive load bank to manage braking and prevent excessive spinning

Methodology Applied

Scientific EffectRegenerative braking:

Implementation Method 4

diverts regenerated energy to a resistive load bank

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS11791757B2Extended braking with variable frequency drive without input power

Publication Date: 2023.10.17 INNOMOTICS GMBH

AI summary

A variable frequency drive system (300) includes a power converter (310) with a plurality of power cells supplying power to one or more output phases (A, B, C), a main power source (320) for providing main input power to the power converter (310), an auxiliary power source (330) for providing auxiliary input power to the power converter (310), and a control system (314) in communication with the power converter (310) and controlling operation of the plurality of power cells, wherein the control system (314) comprises one or more processor(s) (315) configured via computer executable instructions to detect a main input voltage drop of the main power source (320) below a predefined power threshold, disconnect the main power source (320) in response to the main input voltage drop, and enable the auxiliary power source (330) to provide auxiliary input power to the power converter (310) in response to the main input voltage drop.