Output voltage constant control of three-phase Z-source inverter

This paper proposes a new constant control method of the output voltage of a voltage-fed three phase Z-source inverter (ZSI), in case of the capacitor voltage variations in Z-source network or the heavy changes of load. The modulation index for the reference output voltage of the ZSI can be calculated by the basic definition of the ZSI, the input DC voltage and capacitor voltage in Z-source network. And, the output voltage of the ZSI is controlled by the modified SVM(space vector modulation) with the calculated modulation index. By the proposed method, the modulation index of the output voltage is closely following in the reference modulation index. To verify the validity of the proposed method, PSIM simulation was achieved and a DSP controlled 1[kW] three-phase Z-source inverter was manufactured. Despite the input DC voltage of the ZSI is heavily changed from 80[V] to 110[V] (or from 120[Ω] to 90[Ω]) and the load is changed into three-steps (20[Ω], 40[Ω], 80[Ω]), the capacitor voltage of Z-source network kept up 168[V], therefore, the output phase voltage could be controlled by the reference output voltage (68[V_RMS]) according to the capacitor voltage.