Five-Level Inverter Modulation Narrow Pulse Prevention
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Solution Overview
Problem
Conventional five-level inverter modulation methods generate numerous narrow pulses when approaching specific voltage levels, leading to distortion in the phase bridge output voltage and potential safety issues for switching devices.
Innovation Solution
The method involves controlling switching devices to alternate between voltage levels in specific combinations, using threshold values to prevent narrow pulses by ensuring the duty ratio remains away from 0 or 1, thereby reducing the number of narrow pulses and ensuring safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional carrier based modulation method is used, then the five-level inverter can operate with standard modulation techniques, but numerous narrow pulses are generated when voltage command value approaches specific voltage levels, causing distortion in phase bridge output voltage and potential safety issues for switching devices
Solution Approach 1:
The patent introduces a dead-band parameter Dthrs and modifies the modulation approach by clamping the duty ratio command value when it approaches extreme values (close to 0 or 1). This parameter-based control prevents narrow pulse generation by ensuring the duty ratio remains within a safe operating range, thereby eliminating the reliability issue while maintaining modulation functionality
Solution Approach 2:
The patent applies preliminary anti-action by proactively preventing narrow pulse generation through duty ratio clamping before the narrow pulses can occur. By monitoring the voltage command value and preemptively adjusting the duty ratio when it approaches critical thresholds, the system avoids the harmful effect of narrow pulses on switching device safety
2Reliability
If narrow pulses are deleted to ensure switching device safety, then switching device reliability is improved, but phase bridge output voltage distortion increases
Solution Approach 1:
The patent implements preliminary action by pre-adjusting the duty ratio command value through clamping operations before the modulation process generates narrow pulses. This proactive approach prevents narrow pulse formation at its source, thereby maintaining output voltage quality without needing to delete pulses afterward, thus avoiding voltage distortion
3Adaptability or versatility
If duty ratio is allowed to approach 0 or 1 for complete voltage level switching, then modulation range is maximized, but narrow pulses are generated causing distortion and safety issues
Solution Approach 1:
The patent modifies the duty ratio parameter by introducing clamping operations that prevent it from reaching extreme values (0 or 1). This parameter modification maintains the modulation range within practical limits while eliminating the harmful narrow pulse effect, thus resolving the contradiction between adaptability and harmful factor generation
Data Source
AI summary
A method and device for modulating a five-level inverter, and a photovoltaic system are provided. The method includes: acquiring a voltage command value Vcmd of a phase bridge; controlling a first and a fourth switching devices to be switched on alternately when Vcmd≥V1Pos+Vthrs1; controlling the first and a third switching devices to be switched on alternately when V1Pos−Vthrs2≤Vcmd<V1Pos+Vthrs1; controlling the fourth and the third switching devices to be switched on alternately when 0≤Vcmd<V1Pos−Vthrs2; controlling the third and a fifth switching devices to be switched on alternately when −V1Neg+Vthrs3≤Vcmd<0; controlling the third and a second switching devices to be switched on alternately when −V1Neg−Vthrs4≤Vcmd<−V1Neg+Vthrs3; controlling the fifth and the second switching devices to be switched on alternately when Vcmd<−V1Neg−Vthrs4.