Neutral-Point Current Sensing in Series Multiplex Inverters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing series multiplex inverter devices face challenges with increased cost, size, and susceptibility to noise due to the arrangement of current sensors at high-voltage output lines, which require large, high-voltage specifications and complex management of sensors across multiple inverter cells.
Innovation Solution
Current sensors are arranged between the neutral point and the single-phase output inverter cells at the neutral-point-side, where the potential is close to ground, allowing for the use of smaller, low-voltage sensors and reducing noise interference, thereby minimizing the size and cost of the inverter device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current sensors are arranged at output lines of each phase section, then current sensing for control and protection is achieved, but the sensors require high-voltage specifications, large size, and high cost
Solution Approach 1:
The inverter device is divided into multiple single-phase output inverter cells connected in series, with current sensors arranged at specific locations (neutral-point-side cells) rather than at each output line. This segmentation allows using smaller, lower-voltage sensors while maintaining current sensing capability for the entire phase section.
Solution Approach 2:
The neutral point serves as an intermediary reference point for current sensing. By arranging sensors at the neutral-point-side inverter cells and using the neutral point as a reference, the system can sense phase currents without requiring sensors to withstand the full high-voltage potential differences present at the output lines.
2Loss of information
If current sensors are arranged close to the controller, then signal line length is reduced and noise suppression is improved, but the controller becomes susceptible to spatial noise from high-potential output lines
Solution Approach 1:
The current sensors are arranged at the neutral-point-side inverter cells where the potential is close to ground potential, creating an equipotential zone. This allows the sensors to be positioned close to the controller without exposing the controller to high-voltage spatial noise, as both the sensors and controller operate at similar low potentials.
3Strength
If large-diameter high-voltage electric wires are used for output lines, then the wires can withstand potential differences, but the current sensors require large through-hole diameter and high-voltage specifications
Solution Approach 1:
By using the neutral point as a reference and arranging sensors at low-potential locations, the system can employ simpler, lower-voltage-rated current sensors instead of expensive high-voltage sensors. The high-voltage capability is maintained in the wire insulation and overall system design, while the sensors themselves can be smaller and more economical.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Provided is a serial multiplex inverter device (1) in which single phase output inverter cells (2) (U1-U6, V1-V6, W1-W6) each receiving AC power via a transformer (Tr) are connected in series in a multi-stage manner on a per-phase basis to form respective U-phase, V-phase, and W-phase and one ends of the series connections of the respective phases are connected with each other at a neutral point (N). Current detectors (HCT) are disposed in wires (3) leading from the inverter cells (U1, V1, W1) of a first stage to the neutral point (N), respectively. The neutral point (N) is connected through a resistor (R) to the ground. Accordingly, the potential of the wires (3) is low, so that the current detectors (HCT) are those conforming to a low withstand voltage specification.