Bidirectional Capacitor Bank Control via Directional Equations

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Solution Overview

Problem

In bidirectional electric power delivery systems, existing capacitor bank controllers are limited in controlling capacitor banks due to changes in power flow direction, as current sensor measurements are affected, leading to inaccurate reactive demand assessment and power factor correction.

Innovation Solution

A capacitor bank controller that uses sensors to obtain current and voltage measurements, determines power flow direction, and adjusts control operations based on different quantities depending on the direction, using distinct equations for forward and reverse power flow to accurately manage capacitor bank connections and disconnections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single control equation is used for capacitor bank control, then the control logic is simple, but the control accuracy deteriorates in bidirectional power flow conditions

Engineering Contradiction:

Improvecontrol logic complexityVSAvoidreactive demand assessment accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The control equation dynamically changes based on power flow direction. The controller selects between a first control equation for forward power flow and a second control equation for reverse power flow, making the control logic adaptive to operating conditions rather than static.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control parameters (control equations) are changed based on the power flow direction parameter. When power flow direction changes, the controller switches to a different control equation that is appropriate for that direction, thereby maintaining control accuracy across different operating conditions.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If current sensor is positioned upstream of capacitor bank, then forward power factor correction is effective, but reverse power flow control becomes inaccurate

Engineering Contradiction:

Improveforward power factor correction effectivenessVSAvoidreverse power flow reactive demand measurement

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The control equation acts as an intermediary that compensates for the sensor position limitation. By using different control equations for different power flow directions, the system overcomes the inherent measurement limitation of the upstream sensor position.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The control approach dynamically adapts to power flow direction. The controller determines the power flow direction and selects the appropriate control equation, thereby maintaining effective control regardless of sensor position relative to the capacitor bank.

Inventive Principle:

Principle #15Dynamics

3Reliability

If current sensor is positioned downstream of capacitor bank, then reverse power flow control is effective, but forward power factor correction becomes inaccurate

Engineering Contradiction:

Improvereverse power flow control effectivenessVSAvoidforward power flow reactive demand measurement

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control parameters are changed based on the power flow direction. When forward power flow is detected, the first control equation is used; when reverse power flow is detected, the second control equation is used, thereby maintaining accuracy for both directions.

Inventive Principle:

Principle #35Parameter changes

4Device complexity

If capacitor bank control does not account for power flow direction, then the control system is simple, but power quality deteriorates in bidirectional systems

Engineering Contradiction:

Improvecontrol system complexityVSAvoidpower quality

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The control system dynamically adapts to power flow direction by selecting appropriate control equations. This dynamic behavior improves power quality in bidirectional systems while adding only minimal complexity through directional detection and equation selection.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control parameters (control equations) are changed based on power flow direction to maintain power quality. The controller determines direction and switches between control equations, thereby ensuring reliable power quality control in bidirectional conditions.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11075519B2Bidirectional capacitor bank control

Publication Date: 2021.07.27 SCHWEITZER ENGINEERING LABORATORIES INC

AI summary

Systems and methods to control a capacitor bank based on the power flow direction are described herein. For example, a capacitor bank controller (CBC) may determine a power flow direction based on one or more current measurements and one or more voltage measurements. The CBC may control the capacitor bank using a first quantity when the power flow direction is in a first direction. The CBC may control the capacitor bank using a second quantity when the power flow direction is in a second direction. The second quantity may be different from the first quantity to account for the relationship between sensors of the CBC with respect to the capacitor bank on the power line.