Power Conversion Device Beat Suppression via Frequency Extraction

Solution Overview

Problem

The existing power conversion devices for AC motors experience significant pulsation in DC voltage due to rectification, leading to beat phenomena in motor currents, which are difficult to suppress effectively without increasing the size of the device by enhancing the capacity of smoothing capacitors.

Innovation Solution

A power conversion device that includes a converter for AC to DC conversion, an inverter for DC to AC conversion, and compensation means for adjusting torque, current, voltage, frequency, and phase angle commands using extracted frequency components and low-frequency cut-off processing to suppress pulsations, thereby improving beat suppression without relying on capacitor capacity or motor responsiveness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the capacity of the smoothing capacitor is increased to reduce the pulsation frequency component in DC voltage, then the beat phenomenon is suppressed, but the device size becomes larger

Engineering Contradiction:

Improvebeat phenomenonVSAvoiddevice size

Core Design Contradiction:

Object-affected harmful factorsVSVolume of stationary object

Solution Approach 1:

The invention extracts the pulsation frequency component (twice the power supply frequency) from the DC voltage using a band-pass filter, and then cancels this extracted component through control means by adjusting the slip frequency. This separates the pulsation suppression function from the capacitor, allowing smaller capacitor capacity while achieving beat suppression.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention uses feedback control by detecting the pulsation frequency component in the DC voltage, processing this signal through a band-pass filter, and then using the filtered signal to adjust the slip frequency control of the induction motor. This closed-loop feedback mechanism dynamically compensates for pulsation effects without requiring large capacitor capacity.

Inventive Principle:

Principle #23Feedback

2Object-affected harmful factors

If the capacity of the smoothing capacitor is increased to reduce the pulsation frequency component in DC voltage, then the beat suppression effect is improved, but the manufacturing cost increases

Engineering Contradiction:

Improvebeat phenomenonVSAvoidmanufacturing cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The invention extracts the pulsation frequency component (twice the power supply frequency) from the DC voltage using a band-pass filter, and then cancels this extracted component through control means by adjusting the slip frequency. This separates the pulsation suppression function from the capacitor, allowing smaller capacitor capacity while achieving beat suppression.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention replaces the passive mechanical approach of using large capacitor capacity to suppress pulsation with an active control system that uses signal processing and frequency adjustment. This substitution of control mechanism for physical component sizing reduces both component requirements and manufacturing cost.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If the slip frequency is adjusted to cancel the pulsation frequency component in DC voltage, then the beat phenomenon is suppressed, but the motor speed control precision is affected

Engineering Contradiction:

Improvebeat phenomenonVSAvoidspeed control precision

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The invention applies slip frequency adjustment only to the extent necessary to cancel the pulsation frequency component, rather than making large adjustments. The control means modifies the slip frequency based on the detected pulsation characteristics, applying just enough correction to suppress beats while maintaining overall speed control accuracy through proportional-integral control.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The invention uses feedback control by detecting the pulsation frequency component in the DC voltage, processing this signal through a band-pass filter, and then using the filtered signal to adjust the slip frequency control of the induction motor. This closed-loop feedback mechanism dynamically compensates for pulsation effects while maintaining speed control precision through continuous adjustment.

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

This configuration enhances the performance of beat suppression in inverter output currents, allowing for stable motor operation by effectively managing pulsations without increasing device size or relying on capacitor and motor response characteristics.

Implementation Method 1

converter means for converting an AC voltage to a DC voltage through rectification

Methodology Applied

Scientific EffectRectification:

Implementation Method 2

inverter means for feeding a motor by converting the DC voltage as an output of the converter means to an AC voltage

Methodology Applied

Scientific EffectInversion:

Implementation Method 3

first compensation means for extracting a frequency component twice a frequency of the AC voltage from the DC voltage outputted from the converter means or a current outputted from the inverter means to apply gain processing to the extracted component

Methodology Applied

Scientific EffectFrequency component extraction:

Implementation Method 4

second compensation means for applying low frequency cut-off processing using a frequency selected at or below an electric angular maximum frequency of the motor as a cut-off frequency and gain processing to the DC voltage outputted from the converter means or a current outputted from the inverter means

Methodology Applied

Scientific EffectLow frequency cut-off filtering:

Implementation Method 5

compensation means for adding a compensation amount to or subtracting the compensation amount from at least one of the torque command value, the current command value, the voltage command value, the frequency command value, and the phase angle command value

Methodology Applied

Scientific EffectFrequency adjustment for beat suppression:

Data Source

PatentUS9160271B2Power conversion device

Publication Date: 2015.10.13 MITSUBISHI ELECTRIC CORP

AI summary

A power conversion device formed of a converter for rectifying a single-phase AC voltage to a DC voltage and an inverter for driving an AC motor by converting the DC voltage to an AC voltage includes: a first compensation unit that uses a frequency component twice the frequency of the single-phase AC voltage with respect to the DC voltage outputted from the converter or a current outputted from the inverter as a compensation value for at least one of a torque command value, a current command value, a voltage command value, a frequency command value, and a phase angle command value; and a second compensation unit that uses the DC voltage outputted from the converter or a current outputted from the inverter after being subjected to low frequency cut-off processing and gain processing.