A quasi-Z-source network is used to boost the DC bus voltage of a voltage source two-level H-bridge inverter to increase the voltage gain. With the increase in the DC bus voltage, the common mode voltage (CMV) also increases. The CMV is reduced using virtual space vector pulse width modulation (SVPWM). Due to the presence of a quasi-Z-source network, the expression of the CMV changes significantly with respect to the conventional voltage source two-level H-bridge inverter fed from a pure DC supply. In this paper, a detailed analysis of the origin of the CMV for the quasi-Z-source two-level H-bridge inverter is presented. Additionally, it is shown how the CMV is affected for a DC input supply taken from a three-phase diode bridge rectifier. The work also details the scheme for suitable placement of shoot-through time intervals required for boosting within the non-active time intervals in virtual SVPWM. The simulation and experimental results show the scheme is effective in increasing the voltage gain and reducing the CMV arising at the third harmonic of the desired output frequency by at least 33.33%.
The neutral point clamped (NPC) three-level inverter is widely used in high-voltage and high-power applications. However, neutral point voltage oscillation (NPVO) and common-mode voltage (CMV) problems exist in the NPC three-level inverter. In this paper, an improved virtual space vector modulation (VSVM) is proposed based on the reconstruction of a virtual small vector and a virtual medium vector. Compared with the traditional VSVM, an improved VSVM can effectively reduce the CMV. On this basis, a vector conversion method is proposed to further reduce the NPVO in the whole range. Simulation results verify the effectiveness and superiority of the improved VSVM.
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