Based On MCU-controlled Constant-current Test System

Super-capacitor was a new type of storage device,which has higher energy density and specific capacitance than the conventional capacitors,and higher pecific power than the battery,so it was a new type of component with a combination of the good characteristics of electrostatic capacitance and battery.It can provid ultra-high energy and can be released in a very short period of time,a very long life,environmentally friendly,so has a wide range of application prospect in area such as hybrid electric vehicles,pulse power systems and emergency power supply.Therefore,super-capacitor's research and development become a hot spot.In many testing methods for super-capacitor research,the constant current charge-discharge cycle testing is a more intuitive and accurate testing method,but also the main testing methods.Through charge-discharge testing with a constant current of super-capacitor to study the law of voltage changing over time,The capacity of super-capacitor at different current,the equivalent series resistance,and also other parameters can be obtained,in order to satisfy the experimental study of super-capacitor requirements,it need to design a constant current source which can be used for high current charge-discharge cycle test of super-capacitor.In this paper,the working principle,testing methods and application situation of su per-capacitors were analyzed and discussed,the current testing method was determined and a constant current test system based on PIC single-chip was designed to carry out the charge-discharge test of super-capacitor.The design thought of the system was that the super-capacitors were charged by the constant current supply,and then were discharged by the electronic load of constant-current mode,and the automatic conversion between charge function and discharge function was controlled by relay.The test system can set and collect the output current and output voltage of the main circuit by the PIC16F877A microcontroller, and in accordance with the current data gotten from the sampling circuit,adjust the output current by PID algorithm,and thereby enhance the controlling precision of the output of the constant current.At the same time,it determines the super-capacitor charge-discharge state according to voltage information.In the design of the constant current circuit,the working principle of the constant current source and the electronic load were analyzed,and combines with the technical characteristic of the constant current circuit,using operational amplifier to control the switching of power,and to achieve the constant current function.Moreover,the design can control to use constant current source or at different time by relay.In addition,the system uses a modular design.The constant-current circuit and power supply circuit were respectively designed for replacing the different power supply circuit according to the different current outputs.The power circuit was a typical twin-tube forward topology,its control chip was the TL494 Pulse Width Modulation controller,in accordance with feedback loop has been sampling the output voltage,changes pulse width,and therefore adjusts the width of adjustment switch on-time,and finally steadies the output voltage.In the design of software,the author uses the modular design,edits subprogram module for being easy to the main program to be called,but also easy to be amended,and to make the main program simple.In this paper,a constant current test system based on PIC single-chip was designed to carry out the charge-discharge test of super-capacitor.The results that came from the soft and hard test show that,in the current scope of 5A of the design,the system can obtains a good current characteristic.