Research Of Constant Power Test System For Supercapacitor

Supercapacitor is a new power energy storage device between the traditional capacitors and the chemical power supply. Because of its large capacity and high energy density characteristics, it has a wide range of applications in starting or speeding up system of hybrid cars, and large power supply system, so nowadays the research and development of supercapacitors have gradually become a hot spot. These three test methods are commonly used to evaluate the performance of supercapacitors:(1)constant voltage mode; (2) constant current mode; (3)constant power mode. Constant power discharging mode is widely used to evaluate the output power capability of supercapacitor.In this paper, a constant power test system was designed base on PIC single chip to achieve constant power discharging for supercapacitor. Constant power discharging is the energy storage device remained a constant power P=UI during the discharge process, and the voltage of energy storage device (such as supercapacitor or battery) will continue to decline during the discharge process, therefore, in order to maintain the discharge power constant, discharging current has to regular increase as the voltage drop, and maintain the product of voltage and current remain constant during the discharge process, thus achieving the purpose of constant power discharge. Based on the above characteristics, a test system was designed for supercapacitor constant power discharging in this paper. This test system was composed by the discharge circuit and control circuit. The discharge circuit of this system used Boost chopper topology as the basic circuit structure, and the Boost chopper circuit has two working modes:Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM), these two working modes were detailed analysis in this paper, and finally determined parameters value of the main components in the discharge circuit. The control circuit used PIC single chip as the control of the core, detected discharging voltage of supercapacitor through the Hall sensor in real-time, after isolated by the ISO-124 chip the signal went into the microcontroller, and compared by the set discharge power to determine the output conduction duty cycle of PWM waveform, the PWM waveform input to the HCPL-316J chip to drive and change the duty cycle of IGBT, and then adjust the supercapacitor discharge current, made the product of instantaneous discharging voltage and current remain constant, that constant power discharging for supercapacitor was achieved. The experiment results show that this test system can achieve constant power discharging test for supercapacitors, and the supercapacitor can obtains a good stability of output power characteristics.