Single-Phase Three-Wire Inverter Freewheeling Circuit

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Solution Overview

Problem

Existing single-phase three-wire inverter circuits suffer from high switching and conduction losses due to the need for high-frequency operation of switching units Q1 to Q6 across the entire mains cycle, resulting in low overall inverter efficiency when zero power export to the grid is required.

Innovation Solution

The inverter circuit incorporates a bridge inverter circuit with a freewheeling circuit and a control unit that selectively operates only one part of the switching units at high frequency, utilizing a freewheeling circuit to maintain power output during off-states, thereby reducing switching and conduction losses by half.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If all switching units Q1 to Q6 operate at high frequency throughout the entire mains cycle, then the inverter can maintain zero power export to the grid, but switching losses and conduction losses increase significantly

Engineering Contradiction:

Improvezero power export controlVSAvoidswitching loss and conduction loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The six switching units Q1-Q6 are divided into two groups: an active group that operates at high frequency during specific intervals, and a freewheeling group that operates in freewheeling mode during other intervals. This segmentation allows the inverter to maintain zero power export control while reducing the number of units operating at high frequency, thereby reducing switching and conduction losses.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inverter switches between active high-frequency operation and freewheeling operation in periodic intervals throughout the mains cycle. During active intervals, switching units operate at high frequency to maintain precise power control. During freewheeling intervals, selected switching units are turned off and their current is redirected through freewheeling diodes, reducing losses while maintaining power export control through periodic active regulation.

Inventive Principle:

Principle #19Periodic action

2Power

If switching units operate at high frequency across the entire mains cycle, then power output control is maintained, but overall inverter efficiency decreases

Engineering Contradiction:

Improvepower output controlVSAvoidinverter efficiency

Core Design Contradiction:

PowerVSProductivity

Solution Approach 1:

The switching units are segmented into active and freewheeling groups, allowing power output control to be maintained during active intervals while improving overall efficiency through freewheeling operation during other intervals. This segmentation enables the inverter to achieve both precise power control and high efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The freewheeling circuit maintains continuous power output to the grid by redirecting current through diodes when switching units are off, ensuring that the useful action of power delivery continues without interruption. This allows the inverter to maintain power output control while spending more time in efficient freewheeling mode, thereby improving overall productivity.

Inventive Principle:

Principle #20Continuity of useful action

3Adaptability or versatility

If a traditional three-leg full-bridge topology with bipolar modulation is used, then the inverter can control U-phase and W-phase output power, but switching units must operate at high frequency throughout the cycle resulting in high losses

Engineering Contradiction:

Improvephase-specific power controlVSAvoidswitching loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The traditional three-leg full-bridge topology is modified by segmenting the switching units into active and freewheeling groups. This allows phase-specific power control to be maintained during active intervals while reducing switching losses through freewheeling operation during other intervals, directly addressing the high energy loss problem of conventional topologies.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Freewheeling diodes are introduced as intermediary elements that provide alternative current paths when switching units are off. These diodes enable continuous power delivery to the grid while allowing switching units to remain in low-loss states during freewheeling intervals, thereby reducing switching losses while maintaining the adaptability of phase-specific power control.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11139754B1Inverter circuit for realizing high-efficiency control of single-phase power of single-phase three-wire power supply

Publication Date: 2021.10.05 SOLAR POWER NETWORK TECHNOLOGY (ZHEJIANG) CO LTD

AI summary

An inverter circuit for realizing high-efficiency control of single-phase power of a single-phase three-wire power supply includes a bridge inverter circuit connected to an output end of a DC power supply, a freewheeling circuit connected to an output end of the bridge inverter circuit for providing freewheeling during switching of the bridge inverter circuit, and a control unit connected with the bridge inverter circuit and the freewheeling circuit. When the switching units in the high-frequency operating state are switched to an off state, the freewheeling circuit is controlled to operate continuously to output power to the U-phase line or the W-phase line, so that the switching units only participate in high-frequency operations in nearly half of the whole mains cycle, thereby switching loss and conduction loss of the switching units Q1 to Q6 can be reduced by nearly half, and the efficiency of the whole inverter circuit is greatly improved.