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In multilevel inverter, it is a key problem that how to balance voltages of input capacitors. Because of the coupling of multilevel modulation and input voltage balance, no matter hardware circuit or control method of multilevel inverters are always complex, and speed of voltage balance is low. Dual Buck circuit which composed by two Buck DC/DC converter bridges, works in current half-period mode. A novel diode-clamped multilevel dual Buck inverter is presented, which inherits those features. At any moment, one Buck bridge works for inverter, another works as a reverse Boost circuit and charges up input capacitors. So inverter and voltage balance control are completely decoupled. If multilevel number is not small, this method is conducive to reduce the number of devices and the system complexity, and improve reliability of the system. Simulation and experiment of a diode-clamped three-level inverter verifies these analyses.

Can ERP software bring users economic benefits during a company's operational management? This paper adopts revised value chain method to construct a set of indicators. Using listed companies that implement ERP as samples and the implementation year as the starting point, it compares the value of companies three years before the implementation of ERP and two years after implementation of ERP and testifies it. In order to guarantee the reliability of the conclusion, it uses statistical analysis on the single variable and the multi-variance to test the results. The results show that if the effect of the industry and size factors is left out of account, the IT(Inventory Turnover), FAT(Fixed Asset Turnover), SC (Sales Changes) of companies that implement ERP system are obviously higher than those have not implemented it; the economic benefits of ERP users are better than the non-users; all the economic indicators of ERP users do not show obvious performance change in the implementation year. In the first year of implementing ERP, SC (Sales Changes) and RRE (return on equity ratio) change obviously, showing that ERP brings some economic benefits to users; in the second year of implementing ERP, besides higher SC and FAT than non-users, only ART(Accounts Receivable Turnover) and APT(Accounts Payable Turnover) change obviously, showing ERP brings in changes in users' market and sales segment, but other indicators do not change obviously.