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A transient mathematical model of Smith single-phase capacitance motor was established, and the starting process of Smith single-phase capacitance motor was analyzed. Smith single-phase capacitance motors due to wiring constraints, the maximum voltage of each phase winding is 0.577 times the supply voltage, unique values capacitor starting torque when starting small, dual-values capacitor start can effectively improve the starting torque, shortening start-up time, but double the number of capacitors. In view of this situation, proposed a new start wiring methods, not only to improve starting torque, but also to reduce the number of capacitors, reducing investment costs, improve operational reliability. The simulation program was complied according to the mathematical model by Matlab. The starting processes of some startup methods of Smith single phase motor are simulated and calculated by examples such as unique values capacitor startup method, dual-value capacitor startup method and the proposed startup method, and the simulation results of these methods are contrasted and analysed. Both verify the correctness of the proposed method.

The transient performance of Smith single phase motor supplied by the single phase SVPWM voltage source inverter is studied emphatically. And then, voltage space vector of the single phase whole-bridge inverter is analyzed and the SVPWM whose control algorithm is deduced. Meanwhile, a transient mathematical model for the Smith single phase motor is developed. Moreover, a simulation model of variable frequency speed control system of single phase SVPWM inverter-Smith single phase motor is built by MATLAB/SIMULINK. Finally, by the simulation calculated to the actual case, the result is consistent with the theoretical analysis. Thus, it would be of a certain practical significance and reference value in the design of SVPWM inverter and speed control system of tri-winding single-phase condenser motor.

In low-voltage power distribution networks, there are usually many multi-level short line branches, ring distribution networks and T-type connections. Considering these characteristics, this paper presents a new network-based adaptive current protection principle. It is the communication technology with adaptive current setting method. Comparing with the traditional three-sect current protection, which has the problem of bad selectivity and protection range affected by fault type, this principle can ensure the selectivity.