Research On Conversion Technology Of Single-phase AC Power Supply

The AC power supply system adopted by different countries can be divided into two types: 220V/50 Hz and 110V/60 Hz. In the process of international exchange, when the civil electrical appliances and the power supply system are not matched, most people still use the power frequency transformer for power conversion, this kind of transformer can not change the frequency, moreover, there are many problems, such as low power factor, heavy and difficult to carry, manual switch error may damage electrical equipment and so on. By using modern power electronics, one way inverter can only reduce voltage, its function is not complete.In order to improve the technical defects of power frequency transformer and unidirectional inverter, this paper presents a scheme of two-level power conversion technology, which can detect the input voltage automatically and change the voltage and frequency bidirectionally. Using APFC circuit to join the AC-DC-AC structure, the transformation system can adjust protection threshold according to the input voltage level to achieve short circuit, overvoltage, undervoltage and overheat protection. In order to have a full range AC input voltage, good steady-state and dynamic performance, voltage and current feedback signals are compensated. After analyzing the mathematical model and the operation features, optimal design of the circuit is given.After the series stability of the two-level system is guaranteed, in order to prolong the service life of the DC-bus capacitor, lower temperature rise and improve conversion efficiency, the power switches of the front and the rear-stage converters are controlled synchronously. By adopting coordination control, more energy is transferred directly from the front stage to the later stage without the storage and release process of the capacitor. Consequently, the current ripple on the DC-bus capacitor can be reduced. Theoretical analysis and simulation verification are carried out. The centralized digital controller based on TMS320F28027 is designed, and the simplified program flow chart is given.A portable test prototype is also built in this paper, a comprehensive experimental test and comparative analysis is carried out. The results show that the two-level AC power conversion system meets the requirements of performance, and the scheme is feasible.