Three-Level NPC Inverter Control for Lower Switching Loss
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Solution Overview
Problem
Current three-level NPC inverters suffer from low electric energy conversion efficiency and poor harmonic quality due to high-frequency switching losses and excessive harmonic distortion.
Innovation Solution
A new control method for three-level NPC inverters that reduces high-frequency operations by controlling only one switch unit when the output current is outside a preset interval and both switch units when near zero, thereby minimizing power consumption and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional multilevel control is used in three-level NPC inverter, then voltage level and power density are improved, but electric energy conversion efficiency deteriorates due to high-frequency switching losses
Solution Approach 1:
The patent applies dynamic control by adjusting the switching frequency of individual switch units based on real-time output current conditions. When output current is small, the switching frequency is reduced or stopped for certain switch units, dynamically adapting the operation mode to minimize switching losses while maintaining the ability to deliver high power when needed.
Solution Approach 2:
The patent changes the operating parameters (switching frequency and duty cycle) of switch units based on output current magnitude. By varying these parameters dynamically, the system achieves high power density when required while reducing switching losses during low-load conditions, directly addressing the contradiction between power capability and energy efficiency.
2Speed
If high-frequency switching operation is performed to improve response speed, then control precision is improved, but electric energy conversion efficiency deteriorates due to increased switching losses
Solution Approach 1:
The system dynamically adjusts switching frequency based on load conditions. During transient states requiring fast response, high-frequency switching is applied. During steady-state low-load operation, switching frequency is reduced or halted for specific switch units, maintaining response capability while minimizing energy losses.
Solution Approach 2:
The patent implements periodic or pulsed switching action rather than continuous high-frequency switching. By activating switch units only when necessary (based on current thresholds) and allowing them to operate at reduced frequency during stable periods, the system maintains control responsiveness while significantly reducing cumulative switching losses.
3Power
If conventional control manner is used, then voltage level is improved, but harmonic quality deteriorates
Solution Approach 1:
The patent employs dynamic switching strategies where the switching frequency and pattern of different switch units are adjusted based on real-time output current conditions. This dynamic approach allows the system to maintain high voltage levels while minimizing harmonic generation by adapting switching behavior to instantaneous load requirements, reducing unnecessary switching that causes harmonics.
Solution Approach 2:
By changing switching parameters (frequency, duty cycle, and activation timing) based on output current magnitude, the system achieves improved voltage level output while reducing harmonic distortion. The parameter adjustments ensure that switching occurs optimally to minimize harmonic generation while maintaining required voltage levels.
Data Source
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AI summary
This application discloses a photovoltaic system, an inverter, and a control method. A three-level neutral point clamped inverter includes four switch units. When an average value of an output current of the three-level neutral point clamped inverter is greater than a first current threshold or less than a second current threshold, only one of the four switch units is controlled to perform a high-frequency operation, to reduce power consumption caused by a high-frequency operation. The average value of the output current is an average value of the output current of the three-level neutral point clamped inverter in a switching cycle. The first current threshold is a positive number, and the second current threshold is a negative number. Power consumption caused by the high-frequency operation of the switch unit in the inverter may be reduced, and electric energy conversion efficiency of the inverter may be improved. A time period in which two switch units perform complementary operations at high frequency is very small. Therefore, during a high-frequency operation of one switch unit, setting of a dead time is reduced, or no dead time is set. In this way, a total harmonic current distortion of an output current of the inverter may be improved, in other words, harmonic quality may be improved.