UPS Predictive Voltage Control Reducing Harmonic Distortion

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Solution Overview

Problem

Existing uninterruptible power supply (UPS) systems face challenges in efficiently controlling voltage and current, leading to unintended fluctuations that can damage equipment and are costly due to complex control systems with high Total Harmonic Distortion levels.

Innovation Solution

Implementing predictive voltage and current control using a pulse width modulation (PWM) control signal with an inductor and capacitor filter, where the duty cycle is adjusted based on sampled inductor current and capacitor voltage to drive the inductor current towards a reference value, reducing harmonic distortion and improving reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If proportional-integral type voltage and current controllers with lead-lag compensators are used, then voltage and current control is achieved, but the control system becomes complex and costly

Engineering Contradiction:

Improvevoltage and current controlVSAvoidcontrol system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the complex lead-lag compensators from the control system. By using a simplified voltage controller and current controller without lead-lag compensators, the system achieves the necessary control functionality while significantly reducing complexity and cost.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the control parameters by using direct voltage and current control with simplified controllers. The control approach shifts from complex proportional-integral controllers with lead-lag compensators to a more straightforward control scheme that achieves similar performance with reduced complexity.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If complex control systems are used to regulate UPS output, then voltage and current stability is improved, but Total Harmonic Distortion levels increase and costs increase

Engineering Contradiction:

Improveoutput voltage and current stabilityVSAvoidTotal Harmonic Distortion

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The patent removes the lead-lag compensators that were causing harmonic distortion. By using a simplified control approach without these compensating elements, the system reduces Total Harmonic Distortion levels while maintaining output stability through direct voltage and current control.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If proportional-integral controllers are used, then control functionality is achieved, but the design becomes costly

Engineering Contradiction:

Improvecontrol functionalityVSAvoiddesign cost

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs a simpler, more cost-effective control design that replaces expensive proportional-integral controllers with lead-lag compensators with a more economical voltage controller and current controller configuration that achieves the same reliability goals at lower cost.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

This approach enhances the reliability and reduces costs by efficiently regulating UPS output voltage and current, while filtering harmonic distortion to levels below 3% of the inverter output, improving power distribution to loads.

Implementation Method 1

A pulse width modulation control signal is applied to the output inverter, and inductor current is periodically sampled at a first sampling time and at a second sampling time. The inductor current at the first sampling time is compared with a reference current at the first sampling time, and a duty cycle of the pulse width modulation control signal is adjusted to drive the inductor current at the second sampling time towards a value that is substantially equal to the reference current at the first sampling time

Methodology Applied

Scientific EffectPulse Width Modulation:

Implementation Method 2

The uninterruptible power supply includes an output inverter and a filter, and the filter includes an inductor and a capacitor

Methodology Applied

Scientific EffectElectrical Filtering: Filter (electronic)

Data Source

PatentUS8116105B2Systems and methods for uninterruptible power supply control

Publication Date: 2012.02.14 AMERICA POWER CONVERSION CORP

AI summary

Systems and methods are provided for distributing power to a load by controlling an uninterruptible power supply that has an inverter and a filter, where the filter has an inductor and a capacitor. The systems and methods apply a pulse width modulation control signal to the inverter, sample inverter inductor current and compare the inductor current to a reference current. A duty cycle of the pulse width modulation control signal is adjusted to drive the inductor current at a second sampling time to a value substantially equal to a reference current at a first sampling time. The systems and methods can filter harmonic distortion from output signals and control uninterruptible power supply output.