An improved control strategy for Z-source inverter with maximum boost capability and minimum switching frequency

Z-source inverter introduces a unique X-shaped impedance network and boosts the input voltage by utilizing shoot-through (ST) states. It provides a competitive single-stage approach for DC to AC power conversion in relatively low voltage boost ratio range (1-2). This paper proposes a novel control strategy for Z-source inverter. With this strategy, only one phase leg operates at high switching frequency to achieve both ST duty ratio control and output voltage regulation, while the other two phase legs maintain the fixed switching states during one sextant. Therefore, it reduces the equivalent switching frequency of power devices in the inverter bridge to about 1/3. However, it introduces the low frequency current and voltage ripple in the inductor and capacitor which related to the fundamental frequency of output voltage. It has the potential to achieve higher efficiency especially in high-switching-frequency and medium-frequency DC-AC power application. Then, the paper provides a detailed close-loop controller design approach for the novel modulation strategy. Furthermore, the detailed comparisons among the existing strategies and proposed control strategy are conducted in theory. Finally, all the theoretical analysis and calculation are verified by simulation results.