Three-Level NPC Inverter Switching Control for Lower Harmonic 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 operations of switch units, leading to increased power consumption and harmonic distortion.
Innovation Solution
A new control method for three-level NPC inverters that reduces high-frequency operations by controlling only one switch unit to operate when the average output current is outside a preset interval near zero, and both units when the current is 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 switching loss and power consumption increase due to high-frequency operation of switch units
Solution Approach 1:
The patent implements dynamic control of switch unit operation modes based on real-time output current conditions. The controller dynamically switches between first control mode (one switch unit operates) and second control mode (two switch units operate) according to whether the output current exceeds the threshold, optimizing the balance between power density and switching loss under different operating conditions
Solution Approach 2:
The patent changes the operational parameters of the switch units by introducing a current threshold parameter. When the output current exceeds this threshold, the system transitions from one switch unit operating to two switch units operating, effectively using parameter-based control to reduce switching loss while maintaining required power output
2Productivity
If high-frequency operation of switch units is increased to improve conversion efficiency, then power consumption increases and harmonic quality deteriorates
Solution Approach 1:
The patent employs periodic high-frequency operation of switch units rather than continuous operation. By controlling switch units to operate at high frequency only during specific periods when output current exceeds the threshold, the system achieves improved conversion efficiency while limiting the generation of harmonic distortion during non-critical periods
Solution Approach 2:
The patent extracts and isolates the high-frequency operation function to specific switch units based on current conditions. Instead of all switch units operating at high frequency continuously, only the necessary number of switch units perform high-frequency operations when required, separating the high-frequency function from continuous operation to reduce overall harmonic distortion
3Measurement precision
If two switch units operate at high frequency to handle current fluctuations near zero, then current control accuracy is improved, but power consumption and switching loss increase
Solution Approach 1:
The patent applies different control qualities to different operating conditions. When output current is near zero and fluctuates, the system locally increases control accuracy by activating two switch units for high-frequency operation. When current is stable and above threshold, it uses simpler control with one switch unit, optimizing the balance between control accuracy and power consumption for each local operating condition
Data Source
AI summary
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.