Study on Double Modulation Wave Carrier-based PWM for Three-level Neutral-point-clamped Inverters

Three-level neutral-point-clamped (NPC) inverters have been widely applied in power conversion device occasions of medium high voltage and power, and, most recently, increasing in occasions of the low-voltage low-power applications. The three-level inverters have the problems of low frequency ripple that appears in the neutralpoint (NP) of the DC-link under some operating conditions because of its unique structure and the limitations of the existing modulation methods. The Low frequency ripple of the three-level NPC inverter PWM rectifier technology is an important problem. Conventional three-level carrier-based pulse width modulation (PWM), which has only one modulation wave per phase, cannot eliminate low-frequency neutral point(NP) potential ripple of three-level neutral point clamped (NPC) inverter completely under some modulation index and power factor. This paper analyzes the condition, which eliminated low-frequency voltage oscillation of three-level neutral-point-clamped (NPC) inverter completely, established the model of the low frequency ripple of the three-level NPC inverter. A double modulation wave carrier-based PWM (DMWPWM) was proposed in this paper. Based on voltage equivalent principle and NP potential balance principle, one modulation wave is decomposed into two modulation waves to implement modulation. The proposed DMWPWM can eliminate the low frequency ripple of the three-level NPC inverter completely. Fundamental principle of the proposed PWM was introduced in this paper. The effectiveness of the proposed method was verified by simulation.