## 4 Simulation and Experimental Verification
### Experimental Verification  
In order to verify the proposed NPV control strategy and compare it with ZSV-J, relevant experiments are performed here based on the VIENNA circuit hardware platform. Figure 10 shows the prototype picture of the VIENNA circuit experiment platform. The parameter of the experiment platform is the same as the simulation situation. As shown in the Figure 10, the experiment verification process of the proposed strategy is realized in the following way. An AC source sends the three-phase voltage to the AC terminal of the VIENNA rectifier through an isolation transformer with a transformation ratio of 2:1. The DC side (load side) of the VIENNA rectifier is two series resistors with adjustable resistance. The control circuit of the VIENNA rectifier is realized in digital mode, and the core control chip is a digital signal processor (DSP) named TMS320F28335. The control strategy proposed in this paper is realized through the core control chip. As shown in Figure 11, under the premise of adopting two control strategies, respectively, the experimental results in the switching process of two load resistance values are from equal to unequal on the DC side of the VIENNA circuit. Figure 11a shows the waveforms when no strategy is used to control NPV, while Figure 11b,c show the waveforms when NPV is controlled by ZSV-J and the proposed strategy, respectively. Figure 10: Prototype picture of VIENNA circuit experiment platform. As seen in Figure 11a, when the two load resistances on the DC side are equal, even if NPV is not controlled, the two capacitor voltages \(v_{\text{dc1}}\) and \(v_{\text{dc2}}\) can remain equal. However, when the two load resistances on the DC side suddenly change to be unequal, NPV will deviate, while the fluctuation of the DC voltage \(v_{\text{dc}}\) and the harmonic component content will also increase, which is the same as the simulation results. The comparison of Figure 11b,c shows that when the two load resistances on the DC side suddenly change to be unequal, the NPV can be controlled, balanced again through the control process, and the proposed NPV control strategy has faster response and less NPV fluctuation than that of ZSV-J. This conclusion is consistent with that verified by simulation. Figure 12 shows the comparison of two NPV control strategies under the condition of two unequal load resistances on the DC side at the beginning of the experiment (i.e., the NPV is deviated at the beginning of the experiment), and the two NPV control strategies are adopted separately during the experiment. Figure 12a,b show the experimental waveforms of the two capacitor voltages after using ZSV-J and the proposed NPV control strategy, respectively. Through the comparative analysis of Figure 12a,b, it can be concluded that the proposed NPV control strategy in this paper is better than ZSV-J in terms of response speed  
Figure 11: Performance comparison of the two strategies when the loads jump from equal to unequal. (**a**) No NPV control strategy is adopted; (**b**) ZSV-J; (**c**) The proposed NPV control strategy. Figure 12: Performance comparisons of the two NPV control strategies when the two loads are unequal. (**a**) ZSV-J; (**b**) the proposed NPV control strategy. than ZSV-J. The above comparison results prove the superiority of the proposed strategy over ZSV-J, which is also consistent with the simulation results. As both the two strategies are software methods and there are no additional hardware requirements, the costs of both the two strategies are low. In addition, in order to obtain a good NPV control performance, the ZSV-J needs to design or adjust the regulator parameters, and the proposed strategy needs logic operations to realize the real-time selection of the zero vectors dynamically. Therefore, in a comprehensive comparison, the implementation complexities of the two methods are similar, and they are both uncomplicated.