Research On Integrated AC Contactor With The Functions Of Motor Control And Protection

AC contactor is a kind of automatic switching device which is used to switch on and off the AC main circuit and large-capacity control circuit frequently,the number is large and the range is wide.AC contactor needs to consume a lot of energy when in the operation.What’s more,during the production process,the voltage drop may cause AC contactor to be disconnected and result in unnecessary losses.Therefore,AC contactor should have the functions of energy-saving operation and anti-voltage sag.In the industrial and agricultural production,the AC contactors are often combined with the motor protectors to achieve motor control and fault protection.Currently,the contactor and the motor protector are installed independently that makes the system bulky and inconvenient to use.Therefore,in this paper,the CJX2-32 AC contactor is used as the main body and the Microchip’s PIC16F873A as the core control chip,the circuits of the energy-saving operation,anti-voltage drop and motor protection are designed modularity.Through system integration,a kind of integrated contactor with the functions of motor control and protection is developed.In addition to motor protection function,it also has the functions of energy-saving operation and anti-voltage sag.It can realize the miniaturization of control and protection of electrical apparatus.Taking the temperature rise of the maximum temperature point of the motor winding as the basis of judgment,the paper also proposes a kind of inverse time overload protection scheme which is based on extreme learning algorithm.It will be of great significance for the research on the motor overload protection.First of all,the contactor coil is controlled by the method of PWM closed loop chopper control.When normal startup,according to power supply voltage of the coil,the microcontroller sends out PWM wave with corresponding duty ratio to control MOS tube conduction and then DC high voltage startup of the contactor is achieved.After the AC contactor closing reliably,the contactor converts to low-voltage DC holding automatically.So the problems of the iron loss and short-circuit ring loss are resolved,while the harmful vibration and noise are also avoided.Through the calculation of energy-saving rate,the energy-saving effect of the scheme is verified.Secondly,super capacitor is used as a backup power supply which supplies the power for the AC contactor coil during the voltage sag,so that anti-voltage sag function of the AC contactor is achieved.The reliability of the anti-voltage sag module is verified by the experiments of recovery and non-recovery after a short period of voltage sag.Thirdly,a motor protection module is designed.Though detecting the voltage and current signals to judge the working state of the motor,the functions of the motor overload protection,three-phase unbalance and phase failure protection are realized by the module.In order to achieve overload protection accurately,this paper proposes the maximum temperature point inverse time overload protection scheme which is based on extreme learning algorithm.The temperature rise curve of the maximum temperature point under overload condition is obtained through the experiment,and the curve of the inverse time overload is obtained by the extreme learning algorithm and applied to the motor overload protection.The three-phase load device and voltage regulator are used to simulate the common faults of the motor so as to carry out the test of the motor protection module,and the result verifies its reliability.Finally,integrating above mentioned modules in a system,the paper designs a new type of AC contactor,which has the functions of energy saving operation,anti-voltage sag and motor control and protection.The contactor also has the advantages of small volume and convenient installation.