Studying On The Dynamic Characteristics Of Asynchronous Modular Contactor

Alternating current contactors as low-voltage electrical products are largely used andarc which produces during opening and closing of AC contactor’s contacts is the mainfactor influencing a contactor’s life. At present, adopting intelligent ways to achievebreaking without arc is used widely, such as segmented DC excitation or getting the zeropoint of the primary circuit’s current through the current transformer, then setting off delayand breaking electromagnetic system, so realizing zero off, and so on. However, thesemethods can not avoid the effect of dispersion of operating mechanism and theenvironment, and many uncertain factors. In this regard, the proposed modularasynchronous contactors can achieve each contact individually controlled by closed-loopcontrol. This is a new idea in the field of structural design and control of contactors andclosed-loop control can eliminate the influence that dispersion of operating mechanism andmany other uncertain factors put on the accuracy breaking on the zero point of current, soit can achieve three-phase zero off.This paper firstly chooses a combination of three single E-shaped DC electromagnetsas electromagnetic mechanism of the contactor, one is non-controlled electromagnet,which remains energized during the pull process, the other two were controllableelectromagnets which are used to accelerate and slow down the pull process. By setting theworking stroke of6mm、mechanical reaction force and electromagnetic suction required, itdesigns the structure, size and circuit parameters of the electromagnetic system, what’smore, the calculation of the magnetic circuit.Using Simulink simulation software to build circuit model、electromagnetic suctionmodel、mechanical reaction force and closed-loop control model of motion processes, thenplanning the velocity curve of closing process, finally, by adjusting the PID controller thecontactor will move according to the planning curve. But from the simulation, we foundthat the combination of the three E-shaped electromagnets is difficult or even impossible toachieve the control requirements, because the non-controlled electromagnet remains energized during the pull process, when we want to energy the controllable electromagnetto slow down the velocity of armature, it is almost impossible for small air gap.So we choose two identical E-shaped electromagnets constitute a new electromagneticsystem. One is not controlled electromagnet which can accelerate the closing process andremains closing with a low voltage, the other is controllable electromagnet which canreduce the closing velocity of the armature. Of course, the coil parameters need to beredesigned, but the thought of the whole control process is not changed. During the closingprocess, the velocity of contacts before closing needs to be reduced to zero in order toavoid collision and bouncing. And during the opening process, we should ensure that whenthe contact of the first open phase opened, the current of the main circuit is zero. In thispaper, we analyze the symmetrical three-phase circuit of Y-Y connection and we find therelation of the breaking time between the first open phase and non-first open phase. Sowhen the breaking time of non-first open phase lag the first open phase some time,three-phase contacts all can achieve breaking at zero point of current. what’s more, makingthe final velocity of opening process reach zero, the contactor can achieve no arc breakingand no bouncing closure.