Five-Level Inverter Neutral Point Stabilization
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Solution Overview
Problem
Five-level inverters experience leakage currents due to parasitic capacitance between the direct-current power supply and ground, leading to reduced efficiency and reliability, and potential harm to humans.
Innovation Solution
A five-level inverter design incorporating specific switch configurations, capacitor units, and reverse flow preventive elements to stabilize the potential of the direct-current bus midpoint, preventing voltage jumps and thus minimizing leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a five-level inverter is used to improve conversion efficiency, then the efficiency is improved, but leakage current increases due to parasitic capacitance and voltage jumps
Solution Approach 1:
A neutral point stabilization circuit is introduced as an intermediary between the DC power supply and ground. This circuit includes a stabilization capacitor connected between the neutral point and ground, and a balancing resistor connected in series with the stabilization capacitor. The intermediary circuit absorbs voltage jumps through the capacitor while the resistor prevents charge accumulation, thereby eliminating leakage current paths through parasitic capacitance without affecting the five-level inverter's high conversion efficiency
Solution Approach 2:
The harmful voltage jump component is extracted and isolated from the main inverter circuit by using the stabilization capacitor. The capacitor captures and holds the voltage fluctuations separately, preventing them from propagating through the parasitic capacitance to ground. This extraction approach allows the main inverter to maintain its efficient operation while the isolated stabilization circuit handles the harmful voltage jumps
2Object-generated harmful factors
If three-level inverter topologies (H5, H6, HERIC) are used to reduce leakage current, then leakage current is reduced, but conversion efficiency decreases
Solution Approach 1:
The neutral point stabilization circuit performs preliminary anti-action by preemptively stabilizing the neutral point voltage before voltage jumps can occur. The stabilization capacitor is pre-connected to the neutral point and immediately absorbs any voltage fluctuations as they occur, preventing the formation of leakage current paths. This allows the five-level inverter to maintain both high conversion efficiency and low leakage current simultaneously
Data Source
Figure 1~3a
Figure 3b~3d
Figure 3e~3g
AI summary
A five level inverter comprises six switch tubes (QH1, QH2, QL1, QL2, QL3, QL4), two inductors (L1, L2), four capacitor units (C1, C2, C3, C4) and two reverse current preventing devices (D1, D2). The common terminal of the third capacitor unit (C3) and the fourth capacitor unit (C4) is connected with the common terminal of the first capacitor unit (C1) and the second capacitor unit (C2). The third capacitor unit (C3) and the fourth capacitor unit (C4) are used as the output filter circuit of the inverter, and the common terminal of the third capacitor unit (C3) and the fourth capacitor unit (C4) is used as the midpoint of the DC bus. In the inverter, the electric potential of the midpoint of the DC bus or the positive or the negative pole of the DC power supply (DC) relative to the midpoint of the output filter circuit is relatively stable, and surge voltage with power frequency or high frequency relative to ground will not occur at the positive or the negative pole of the DC bus, thus the leakage current problem will not appear. Additionally, the output efficiency of the five level inverter is relatively high, so that the five level inverter is adapted to the application field of photovoltaic power generation and so on.