DC Power Supply Harmonic Suppression via 3n Frequency Control

Solution Overview

Problem

Conventional DC power-supply devices converting three-phase alternating current to direct current for refrigeration-cycle applications face issues with harmonic current increase and power factor deterioration due to phase current imbalance.

Innovation Solution

A DC power-supply device incorporating a rectifier circuit, reactors, serially connected capacitors, and a control unit that adjusts charging frequencies to 3n times the three-phase alternating current frequency, ensuring balanced phase currents and minimizing distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If on/off control of switching elements is executed in synchronization with a half cycle of power supply frequency, then switching loss is decreased and efficiency is improved, but phase current imbalance occurs causing harmonic current increase and power factor deterioration

Engineering Contradiction:

Improveswitching lossVSAvoidharmonic current

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The patent applies periodic action by controlling the switching elements to operate at a frequency that is an integer multiple (n times) of the power supply frequency. This periodic control pattern ensures that switching occurs in synchronization with the AC waveform cycles, maintaining balanced phase currents while achieving efficient energy conversion. The periodic switching at n-times frequency creates harmonious interaction with the power supply waveform, preventing harmonic distortion.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes the critical parameter of switching frequency from half-cycle synchronization to n-times power supply frequency synchronization. This parameter change fundamentally alters the switching behavior to achieve both low switching loss and balanced phase currents. By adjusting the switching frequency parameter to be an integer multiple of the power supply frequency, the system resolves the contradiction between efficiency and harmonic current suppression.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If on/off control of switching elements is executed in synchronization with a half cycle of power supply frequency, then switching loss is decreased and efficiency is improved, but power factor deteriorates due to phase current imbalance

Engineering Contradiction:

Improveswitching lossVSAvoidpower factor deterioration

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The patent applies periodic action by controlling the switching elements to operate at a frequency that is an integer multiple (n times) of the power supply frequency. This periodic control pattern ensures that switching occurs in synchronization with the AC waveform cycles, maintaining balanced phase currents while achieving efficient energy conversion. The periodic switching at n-times frequency creates harmonious interaction with the power supply waveform, preventing harmonic distortion.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes the critical parameter of switching frequency from half-cycle synchronization to n-times power supply frequency synchronization. This parameter change fundamentally alters the switching behavior to achieve both low switching loss and balanced phase currents. By adjusting the switching frequency parameter to be an integer multiple of the power supply frequency, the system resolves the contradiction between efficiency and power factor maintenance.

Inventive Principle:

Principle #35Parameter changes

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 suppresses harmonic current and improves power factor without causing phase current imbalance, stabilizing output voltage and enhancing efficiency in refrigeration-cycle devices.

Implementation Method 1

a rectifier circuit that rectifies the three-phase alternating current

Methodology Applied

Scientific EffectRectification: Diode

Implementation Method 2

a reactor connected to an input side or an output side of the rectifier circuit

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 3

a first capacitor and a second capacitor serially connected between output terminals to the load

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS9692289B2DC power-supply device and refrigeration-cycle application device including the same

Publication Date: 2017.06.27 MITSUBISHI ELECTRIC CORP

AI summary

A DC power-supply device that suppresses an increase of a harmonic current and deterioration of a power factor without causing any imbalance among respective phase currents, in a configuration in which a three-phase alternating current is converted into a direct current and supplied to a load. The DC power-supply device includes a rectifier circuit, a reactor connected to an input side or an output side of the rectifier circuit, a first capacitor and a second capacitor serially connected between output terminals to a load, and a charging unit. During a cycle combining a charging period and a non-charging period of a pair of the first capacitor and the second capacitor, the charging unit is controlled so that a charging frequency becomes 3n times (n is a natural number) the frequency of the three-phase alternating current.