Variable Frequency Drive Speed Modulation for Reciprocating Loads

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Solution Overview

Problem

The control architecture of motors driving reciprocating loads, such as rod pumps, becomes complicated and expensive due to the need for braking resistors to manage regenerative energy, which complicates energy flow and increases costs.

Innovation Solution

A method that controls motor speed using two input variables: a user-defined speed set-point and a load-dependent input variable based on motor current, eliminating the need for braking resistors by modulating speed to counteract regenerative energy without requiring additional sensors or external controllers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If braking resistors are used to manage regenerative energy in reciprocating load motors, then energy dissipation is improved, but device complexity and cost increase

Engineering Contradiction:

Improveregenerative energy dissipationVSAvoidcontrol architecture complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The invention extracts and eliminates the braking resistor component from the system by using a different approach - modulating motor speed through variable frequency drive to prevent regenerative energy from entering the motor in the first place, thereby removing the need for energy dissipation hardware

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention replaces the mechanical/electrical braking resistor system with a control-based speed modulation system, substituting hardware-based energy dissipation with software-based preventive control through variable frequency drive

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Loss of energy

If braking resistors are used to manage regenerative energy, then energy flow control is improved, but manufacturing cost increases

Engineering Contradiction:

Improveregenerative energy managementVSAvoidmanufacturing cost

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The invention uses inexpensive software control algorithms within the variable frequency drive instead of expensive braking resistor hardware, replacing costly physical components with affordable computational solutions

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Loss of energy

If motor speed is modulated based on motor current, then regenerative energy is reduced, but control complexity increases

Engineering Contradiction:

Improveregenerative energyVSAvoidspeed control complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The invention uses feedback from motor current measurements to dynamically adjust motor speed through variable frequency drive, creating a closed-loop control system that automatically prevents regenerative energy based on real-time load conditions

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The motor control system serves itself by using its own current measurements to automatically regulate speed and prevent regenerative energy, without requiring external controllers or additional sensing infrastructure

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS11863113B2Method for reducing regenerated energy and reversal stress in a reciprocating load powered by an electric motor by modulating motor speed using a variable frequency drive and variable frequency drive provided for performing the method

Publication Date: 2024.01.02 DANFOSS POWER ELECTRONICS AS

AI summary

The present disclosure refers to a method for controlling the speed of a reciprocating load motor, wherein the motor speed is a function of two input variables, namely a user defined speed set-point and a load dependent input variable. According to the disclosure, the load dependent input variable is a function of the motor current. The disclosure also refers to a variable frequency drive for controlling the speed of a reciprocating load motor, wherein the drive is programmed to perform the presently described method.