Constant current

About: Constant current is a research topic. Over the lifetime, 23244 publications have been published within this topic receiving 158637 citations.

LED Driver With Self-Adaptive Drive Voltage

Abstract: This paper presents an LED driver circuit consisting of multiple linear current regulators and a voltage preregulator with adaptive output voltage. In the proposed driver, the output voltage of the preregulator is always self-adjusted so that the voltage across the linear current regulator of the LED string with the highest voltage drop is kept at the minimum value that is required to maintain the desired string current. Because the linear current regulators in this driver operate with the minimum voltages, the driver efficiency is maximized. The performance of the proposed driver was experimentally verified on a four-string LED setup with eight white LEDs in each string. The measured efficiency improvement of the linear current regulators was approximately 15% compared to the corresponding implementation with a constant preregulator voltage.

Support Vector Machines Used to Estimate the Battery State of Charge

Abstract: The aim of this study is to estimate the state of charge (SOC) of a high-capacity lithium iron manganese phosphate (LiFeMnPO4) battery cell from an experimental dataset using a support vector machine (SVM) approach. SVM is a type of learning machine based on statistical learning theory. Many applications require accurate measurement of battery SOC in order to give users an indication of available runtime. It is particularly important for electric vehicles or portable devices. In this paper, the proposed SOC estimator extracts model parameters from battery charging/discharging testing cycles, using cell current, cell voltage, and cell temperature as independent variables. Tests are carried out on a 60 Ah lithium-ion cell with the dynamic stress test cycle to set up the SVM model. The SVM SOC estimator maintains a high level of accuracy, better than 6% over all ranges of operation, whether the battery is charged/discharged at constant current or it is operating in a variable current profile.

Circuit layout and method for operating a single- or multiphase current inverter connects an AC voltage output to a primary winding and current and a working resistance to a transformer's secondary winding and current.

Abstract: A circuit layout (10) operates a single- or multiphase current inverter (12) with its AC voltage output connected to a primary winding (15) carrying a primary current (IP). A working resistance can be connected to a secondary winding (60,62) in a transformer carrying a secondary current (IS), including a regulating circuit (78) and a triggering unit (40) for triggering pulse in power semiconductors (T1-T4) in the current converter.

A 3-kW Wireless Power Transfer System for Sightseeing Car Supercapacitor Charge

Abstract: Wireless power transfer (WPT) is the preferred charging method for electric vehicles (EVs) powered by battery and supercapacitor. In this paper, a novel WPT system with constant current charging capability for sightseeing car with supercapacitor storage is designed. First, an optimized magnetic coupler using ferrite cores and magnetic shielding structure is proposed to ensure stable power transfer and high efficiency. Compared with the traditional planar shape ferrite core coupler, the proposed magnetic coupler requires lesser ferrite material without degrading the performance of the WPT system. Second, the model of supercapacitor is applied to the WPT system and the relationship between equivalent load resistances of supercapacitor and charging time is analyzed in detail. Then, a Buck converter with proportional integral (PI) controller is implemented on the secondary side to maintain constant charging current for the variable load. Finally, the proposed design is verified by experiments. Constant charging current of 31.5 A across transfer distance of 15 cm is achieved. The peak transfer power and system efficiency are 2.86 kW and 88.05%, respectively.

Current to power crossover heater control

Abstract: A control system which minimizes the start up time of heaters and sustains long term automatic control is provided. This control system automatically converts control time constant current to constant power when the power reaches the power set and provides that after power interruptions, control will revert back to constant current until constant power control is again called for. The heater controlled by the control system of this invention is preferably a subterranean heater having a long heating element.