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General development both at home and abroad along with application of AC-AC frequency converter is introduced at first, then double-variable control principle is touched upon from its traditional single-variable control theory. the simulation model of double-variable Ac-Ac Frequency Converter is established with MATLAB and control strategy is investigsted by virtue of the simulation platform. To improve frequency converter’s performance further, perfect phase-controlled theory and reduce voltage’s harmonic component, based on analysing and comparing of influence on load, frequency as well as control methods in double–variable control theory,The paper present symmetrical cosine law for trigger points and improved square-wave law for control voltage. Furthermore dominance and problems of double-variable cycloconverter are analyzed, according to the character of step like frequency, to realize step less speed control, we combine variable-frequency method with voltage regulation one, above half speed, voltage regulation method is used, blow it, voltage regulation in variable-frequency method is used. In order to raise performance of the given speed, motor strating, status change, variable-load and braking and such elt, speed and current double closed loop are in drafted. At last, hardware and software of variable-frequency speed regulation system are designed, control effect of various situations of using double closed loop method are given. And contrasted to the simulation result, it is confirmed that the simulation model is accurate.
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