Based On The Intelligent Feedback Of Dual-PWM AC Variable Frequency Adjustable Speed System

Because of many shortcomings of widely used AC-DC-AC variable frequency speed control system, this paper have studied a new dual-PWM variable frequency speed control system which uses PWM rectifier to take place of the uncontrolled diode in rectifier side and adopts vector frequency control method in inverter side. Not only the DC voltage has been adjusted in a certain range by the dual-PWM system, but also the current in AC side of the rectifier has become sinusoid, and make the system running in unity power factor and the power transmission reversible.In research of dual-PWM inverter, the structures of single-phase inverter and three-phase inverter are introduced in this paper first, then the mathematic models in different coordinate system are analyzed, the focus is on the basic principles of vector frequency control and the rotor magnetic field oriented vector control methods Finally the mathematic model of the inverter side is discussed by analyzing the theory and control method of SVPWM.The PWM rectifier part is the research focus in this paper. The basic to pologized structure of PWM rectifier is studied first and the mathematical mode is analyzed by using the VF mode in inverter. The author used the direct current control methods of three-phase VSR as main control scheme which control the phase and amplitude of ac-side current directly, by constructing dual closed-loop which voltage is the outer loop and current is the inner loop, and sampling currents of phase a,b,c and converting them by 3s/2r method with"constant power"to measure active current and reactive current of ac-side current, and directly control the phase and amplitude of the ac-side.Introduced a way of AC variable speed brake, focuses on the needs of dynamic braking and braking unit selection, calculation and regenerative braking energy feedback resistor braking, compared the advantages and disadvantages between the two kinds of braking, indicating dual-PWM frequency converter velocity using the advantages of regenerative braking energy and used excavators digital electric control system obviously.