Three-Phase Inverter with Segmented DC Bus for Loss Reduction
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Solution Overview
Problem
Conventional power conversion devices for system interconnection to a three-phase AC system face inefficiencies due to high switching losses, which are exacerbated by high DC bus voltages, and require high withstand voltage components to prevent insulation breakdown.
Innovation Solution
A power conversion device with independent DC power supplies for each phase, utilizing a step-up circuit and single-phase inverter circuit configuration, where the control unit adjusts the operation of these components to reduce voltage stress and minimize switching losses by alternately performing high-frequency switching between the step-up circuit and single-phase inverter circuit, and superimposing a third-order harmonic to lower the DC bus voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the voltage of the DC bus is increased to meet the wave crest value requirement for reliable system interconnection, then the insulation breakdown prevention is improved, but the switching loss increases significantly
Solution Approach 1:
The patent divides the conventional single three-phase inverter system into three independent single-phase inverter circuits, each handling one phase. This segmentation allows each inverter to operate at a lower DC bus voltage (equal to the wave crest value of phase voltage) rather than requiring the higher line-to-line voltage, thereby reducing switching losses while maintaining reliable insulation protection for each phase independently.
Solution Approach 2:
The patent changes the voltage parameter by reducing the DC bus voltage from the conventional level (based on line-to-line voltage wave crest) to a lower level (based on phase voltage wave crest). This parameter change is made possible by the segmented single-phase inverter configuration, and it directly reduces switching losses while still providing adequate voltage margin for reliable operation.
2Loss of energy
If the voltage of the DC bus is reduced to decrease switching loss, then the switching loss is improved, but the reliability of insulation breakdown prevention deteriorates
Solution Approach 1:
By segmenting the system into three independent single-phase inverters, each phase can independently manage its voltage requirements. The DC bus voltage can be optimized for each phase's needs rather than being constrained by the higher voltage required for three-phase line-to-line operation, achieving both lower switching losses and adequate insulation protection.
Solution Approach 2:
The patent optimizes the DC bus voltage parameter by setting it to the wave crest value of the phase voltage rather than the line-to-line voltage. This parameter optimization reduces switching losses while maintaining sufficient voltage margin for reliable insulation breakdown prevention in each phase.
3Stability of the object's composition
If a smoothing circuit with large capacitance is used to smooth the DC bus voltage, then the voltage stability is improved, but the device complexity and component requirements increase
Solution Approach 1:
The patent eliminates the need for a large-capacitance common smoothing circuit by segmenting the system into three independent single-phase inverters. Each inverter phase can tolerate greater voltage fluctuations without affecting the other phases, removing the requirement for a large smoothing capacitor that would be needed in a conventional three-phase system to maintain stable DC bus voltage.
4Reliability
If high withstand voltage components are used to prevent insulation breakdown, then the reliability is improved, but the cost and device complexity increase
Solution Approach 1:
By dividing the system into three independent single-phase inverters, each component only needs to withstand the phase voltage level rather than the higher line-to-line voltage. This segmentation allows the use of lower-voltage-rated (and thus less expensive and simpler) components while still providing adequate insulation breakdown protection for each phase.
Solution Approach 2:
The patent changes the voltage parameter that components must withstand by reducing the required withstand voltage from the line-to-line voltage level to the phase voltage level. This parameter change enables the use of components with lower withstand voltage ratings, reducing cost and complexity while maintaining reliable insulation protection.
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 reduces power losses, allows the use of components with lower withstand voltage properties, decreases switching and iron losses, and enables stable operation with reduced capacitance requirements, thereby enhancing overall efficiency and reliability.
Implementation Method 1
a step-up circuit for stepping up a DC input voltage value
Implementation Method 2
a single-phase inverter circuit for converting a DC voltage value to an AC voltage value with polarity inversion
Implementation Method 3
supply the AC power to a first phase with respect to a neutral point of the three-phase AC system via a first reactor
Data Source
AI summary
This power conversion device includes: conversion devices for supplying AC powers to respective phases with respect to the neutral point of a three-phase AC system via reactors; and a control unit for controlling the conversion devices. Each conversion device includes: a step-up circuit for stepping up the DC input voltage value of DC power; and a single-phase inverter circuit. For each conversion device, when the absolute value of a voltage target value obtained, as an AC waveform to be outputted, by superimposing a third-order harmonic on a fundamental wave exceeds the inputted DC voltage, the control unit causes the step-up circuit to perform step-up operation to generate the absolute value of the voltage target value and causes the single-phase inverter circuit to only perform necessary polarity inversion, and when the absolute value of the voltage target value is smaller than the inputted DC voltage, the control unit stops the step-up operation of the step-up circuit and causes the single-phase inverter circuit to operate to generate the voltage target value.