# Common-Mode Voltage Analysis and Reduction for the Quasi-Z-Source Inverter with a Split Inductor
## 5 Simulation and Experimental Results  
To verify the above analysis, simulations and experimental tests of the three-phase qZSI with the proposed CMV reduction strategies are presented. The system parameters of the qZSI are listed in Table 2. The simulations were implemented in MATLAB/Simulink. Meanwhile, the experimental tests were applied to the qZSI platform with a TMS320F28379 digital signal processor (DSP) controller, an Altera Cyclone field-programmable gate array (FPGA) and three Mitsubishi intelligent power modules (IPM), i.e., PM75 DSA120. The simulation results of the conventional qZSI system with the NSPWM and RSPWM strategies are presented in Figures 7a and 8a. As shown in Figure 7a, the amplitude of the CMV with the NSPWM strategy varies from 0 to 133.3 V due to the adopted switching vectors, i.e., \(\mathbf{V_{1}}\)-\(\mathbf{V_{6}}\) and \(\mathbf{V_{sh}}\), referring to Table 1. The introduction of the ST state increases the CMV with more high-frequency components; see Figure 7a. The output current and voltage are also shown in Figure 7a, in which the peak-peak value of the load current is 10 A. Figure 8a shows the CMV value and the output of the conventional qZSI system. The amplitude of the CMV with the RSPWM strategy changes between 0 and 133.3 V when the chosen switching vectors are \(\mathbf{V_{2}}\), \(\mathbf{V_{4}}\), \(\mathbf{V_{6}}\) and \(\mathbf{V_{sh}}\). The CMV of the conventional VSI with the RSPWM strategy is constant, but the CMV of the conventional qZSI with the RSPWM strategy contains high-frequency components, as shown in Figure 8a. The output current and voltage of the system present high total harmonic distortion (THD) (see Figure 8a), which results from the low DC-link utilization with only four switching vectors. This also occurs when the RSPWM strategy is used in the conventional VSI. The simulation results of the modified qZSI system with RSPWM and NSPWM strategies are presented in Figures 7b and 8b. The switching vectors for the two CMV reduction strategies are different, making the corresponding modified qZSI system not the same. According to (19), the relationship among \(L_{11}\), \(L_{12}\) and \(L_{1}\) is \(L_{11}=L_{12}=\frac{1}{2}L_{1}\) when the proposed method is adopted in the qZSI system with the RSPWM strategy. The amplitude of the CMV with the NSPWM strategy on the modified qZSI system varies from 66.7 V to 123.3 V, as shown in Figure 7b, which is reduced dramatically when compared with that in Figure 7a. The output voltage and currents are exactly the same as that of the conventional qZSI system, which is not affected by the input split inductors. When the NSPWM strategy is used in the modified qZSI system, the relationship among \(L_{11}\), \(L_{12}\) and \(L_{1}\) is \(L_{11}=2L_{12}=\frac{2}{3}L_{1}\). As shown in Figure 8b, the CMV is constant at 120 V, and all the high-frequency components are removed, while the output characteristics are not affected. The modified qZSI system is related to the adopted switching vectors, which will not change the output of the system, but reduce CMV when using the conventional CMV reduction strategies. Figure 9 shows the experimental setup of the three-phase qZSI system. Figure 10 exemplifies the conventional qZSI system and the modified qZSI system when the RSPWM strategy is adopted. The experimental results agree well with the simulation results in Figure 8. The CMV of the conventional qZSI system contains high-frequency components when the ST state is used, which varies from 0 to 133.3 V, as shown in Figure 10a. With the split inductor of \(L_{11}\):\(L_{12}\) = 2.1, the CMV is constant as 120 V using the RSPWM strategy in Figure 10b. The output characteristics of the conventional qZSI system and the modified qZSI system are the same, as shown in Figure 10, which verifies the effectiveness of the proposed CMV reduction strategy. The ST state is inserted in the zero states of the inverter, making the output of the inverter similar in the VSI, the qZSI and the modified qZSI when the same CMV reduction strategy is used.