Efficiency-optimised modulation technique of three-level NPC inverter

Abstract

The three-level NPC inverter has many advantages, such as the characteristics of high output power, low device stress, and low harmonic distortion of output waveform. It is widely used in the fields of high-voltage conversion and reactive power compensation. As the most commonly used multi-level inverter, three-level NPC inverter has its own disadvantage which is the NP potential fluctuations. It may lead to poor output performance even damage to the devices. Therefore, the problem of NP potential fluctuation of three-level NPC inverter has been the hotspot of its research. This paper presents an efficiency-optimised dual modulation wave carrier-based PWM (DMWPWM) strategy of three-level NPC inverter. First, the basic principle of traditional DMWPWM is analysed, and the deficiency of traditional DMWPWM modulation technique is described. Then, the efficiency-optimised DMWPWM strategy is deduced. Compared with traditional DMWPWM strategy, the new strategy inherits the advantage of traditional DMWPWM that the NP voltage balance can be maintained in any modulation index and power factor. Moreover, it can reduce the system switching loss which leads to efficiency improvement, and it is simple and easy to implement. Finally, the proposed modulation technique is verified by simulation.

Keywords

• power factor
• PWM invertors
• compensation
• reactive power control
• multilevel inverter
• efficiency-optimised modulation technique
• efficiency-optimised DMWPWM strategy
• traditional DMWPWM modulation technique
• efficiency-optimised dual modulation wave carrier-based PWM strategy
• three-level NPC inverter
• NP potential fluctuation