Equalization Controling Systems For Series Connected Energy Storage Cells Based On Three-cell Direct Equalization Circuit

Power batteries or ultra capacitors are widely used in many fields such as distributed power generation ,UPS and electric vehicles,and so on.Usually they are used in series-connected strings to meet the needs of high voltage power supply.In the long-term use,the performance difference between the cells is inevitable,causing small-capacity ones overcharging and over-discharging,and then resulting in lower effective capacity of the power supplies, reduction of recycle life, and degradation of the safety performance. To carry out the research of equalization systems for series connected energy storage cell strings is of great practical significance. Considering the requirements of the efficiency, speed and system structure, this paper researchs on the equalization circuit ,system structure and equalization control strategy on the basis of analyzing the working principle,the advantages and disadvantages of the existing equalization systems for power batteries or super capacitors.This paper analyzes a novel three-cell direct equalization circuit.This circuit can realize power energy transferring directly between any two ones of three adjacent cells. Analyse the working principle of the circuit,designs the main circuit including the integrated magnetic component and the selection of switch. By proposing three-cell direct equalization structure as the basic module, a multi-layer tree structure equalization system topology based on CAN-bus was build.By applying the mathematical tools of probability analysing,the efficiency performance of the multi-layer tree structure equalization system and the single-layer system based on two-cell direct equalization circuit are compared. The results show that when the system has a large number of cells, the multi-layer tree structure equalization system has significant efficiency advantages.The control system for the multi-layer tree structure equalization system is designed.The three-cell direct equalization controller applying PIC microcontroller as the controlling core including the voltage sampling circuit, drive circuit and the auxiliary power supply is designed. Using CAN bus to realize the co-ordination action of all the equalization modules.The CAN hardware interface and communication protocol are also designed. Each equalizer transmit the voltage data through the CAN bus to the PC,creating a good interactive interface to form a balanced system of monitoring experimental platform.The control software based on top-down equalization strategies is also designed. High-layer equalizers control the on or off action of the corresponding switch to realize equalization.After finishing the process they send the control signal through the CAN bus to the low-layer equalizers to begin equalization.And so on, to achieve the equalization of the whole storage power supply.And then this paper tests the efficiency of the three-cell direct equalization circuit experimentally and carriys out the simulation and experiment of the multi-layer tree equalization system.The results show that the multi-layer tree equalization system has fast speed and the high efficiency.