Inverter Midpoint Potential Stabilization for Single-Phase Three-Wire Systems
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Solution Overview
Problem
Conventional single-phase three-wire output inverters face challenges in dealing with various types of loads and suffer from waveform distortion due to ground connection of the neutral phase, which affects the output voltage and stability.
Innovation Solution
A power conversion device with an inverter, midpoint capacitors, voltage detectors, and a controller that regulates the midpoint potential and switching elements to maintain a stable neutral line potential, ensuring balanced voltage output between phases and suppressing waveform distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the O phase is subjected to ground connection to a pole transformer, then the inverter can operate in a single-phase three-wire system, but waveform distortion occurs due to variation of the entire potential of the inverter with respect to ground potential
Solution Approach 1:
The patent applies the equipotentiality principle by introducing a neutral point stabilizer that actively controls the neutral point potential to remain at a fixed reference level. The stabilizer detects neutral point potential variations and adjusts the switching of neutral point connecting switches to maintain the neutral point at equipotential with the reference potential, thereby preventing waveform distortion caused by potential variations while preserving single-phase three-wire system operation
Solution Approach 2:
The patent implements feedback control through the neutral point stabilizer, which continuously detects the neutral point potential and uses this information to adjust the switching states of the neutral point connecting switches. This closed-loop feedback mechanism ensures that the neutral point potential remains stable despite load variations or ground connection conditions, effectively suppressing waveform distortion
2Device complexity
If conventional inverter configuration is used, then the structure is simple, but the inverter cannot deal with various types of loads such as half-wave rectified load
Solution Approach 1:
The patent applies the universality principle by designing the inverter with a neutral point stabilizer that enables the system to handle various types of loads including half-wave rectified loads, balanced three-wire loads, and unbalanced loads. The stabilizer's ability to actively regulate the neutral point potential makes the inverter adaptable to different load conditions without requiring separate dedicated circuits for each load type, thus achieving multi-functionality while maintaining relatively simple structure
3Device complexity
If the neutral point potential is not stabilized, then the device structure is simple, but waveform distortion occurs and performance deteriorates
Solution Approach 1:
The patent introduces the neutral point stabilizer as an intermediary component between the inverter bridge and the load. This stabilizer acts as a mediator that isolates the load variations from affecting the neutral point potential, thereby maintaining stable output voltages. The stabilizer includes neutral point connecting switches and capacitors that work together to buffer potential variations and ensure reliable voltage output without significantly complicating the overall device structure
Data Source
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AI summary
There is provided a device including: an inverter 5 including switching elements 51 and 52 for outputting a U-phase voltage and switching elements 53 and 54 for outputting a W-phase voltage; midpoint capacitors 31 and 32; a voltage detector 4 configured to detect a condition of a midpoint potential in an O phase at a connecting point between the midpoint capacitor 31 and the midpoint capacitor 32; an AC voltage detector 8; a midpoint stabilizer 2 configured to regulate a power storage amount of each of the midpoint capacitor 31 and the midpoint capacitor 32; and a controller 7 configured to control the switching elements 51, 52, 53 and 54 so as to supply a desired U-phase voltage and a desired W-phase voltage based on voltages detected by the AC voltage detector 8, and control the midpoint stabilizer 2 so as to adjust the midpoint potential in the O phase based on the condition of the midpoint potential detected by the voltage detector 4.