Design Of Reactive Power Compensation System On Low Voltage Device Based On AVR

Because of the existing of reactive power,especially in low voltage power system,the power factor of the load is on the low side,which results in the great waster of power in power system.Not only can the increase of the power factor of low voltage terminal improve the utility and efficiency of generating equipment,but also improve the economical efficiency and power supply quality of power system.Reactive power compensation is an important research subject in power system field and studying it is a practical significance.To increase the power factor in low voltage terminal,a reactive power compensation device is designed on the basis of analyzing the principle of reactive power compensation devices at home and abroad and the basic characteristics of consumer in low voltage terminal.It can calculate the real time power factor of the consumer through detecting the input voltage and across zero of current.And it takes the single chip microprocessor as main controller to calculate capacitance value and switch on/off parallel capacitor bank based on PID algorithm to automatically real time compensate reactive power of the consumer.At the same time,the data in controller are transmitted to a computer through RS232,thus the parameters of current,voltage and power factor are concentrated to display and save in many electrical devices.For hardware design,ATmega16 is taken as a main control unit.And Protel 99 SE is used to design an across zero detect circuit,a serial port communication circuit,a LCD digital display circuit,a controlling output circuit and related protect circuits.And the reasons of producing harmonic are analyzed and dealt with.For software design,many programs,such as calculating reactive power,selecting compensation capacitor,controlling PID,serial communication and LCD digital displaying and so on,are developed with C language of ICC AVR.Besides,a program of collecting and displaying data are developed with VC.The device is experimented in an asynchronous motor.The result shows that it can sample rightly and display the related parameters of power network,automatically switch on/off the capacitor based on the power factor,supply most of reactive power needed by the asynchronous motor.In most of time,the device can control the power factor of a motor above 0.95 to decrease the power loss and save the power.