Study On Prediction Model Of Capacity And Anti Interefrence Strategy For Hybrid Electric Vehicle Battery

Hybrid electric vehicles, electric vehicles use battery to power for motor all. There aretwo factors effect the system estimates endurance mileage. One factor is whether the modelcan accurately estimate power battery capacity in different conditions and is able to predictthe continuous working time of battery. Another factor is whether the vehicle power supplysystem has the ability of interference suppression.First of all, there are two aspects to limit the battery capacity prediction accurately.On the one hand, battery manufacturing materials, process and structure producedeviation in capacity and theoretical capacity. On the other hand, power battery workingenvironment, objective factors lead the battery capacity to be dynamic change.According to the battery analysis separately or the battery power for a resistive load tocarry on the analysis, can’t with the practical operation of power battery matching condition.The capacity of power battery changes dynamically accompanying hybrid electricvehicle operation status.There is a corresponding relationship between dynamic current, voltage, temperatureand the continuous working time of the power battery. Therefore, can’t use theveninequivalent circuit to describe the relationship between battery’s voltage and output currentsimply. It is on the basis of the principle of electrochemical and the analysis combinedbattery’s temperature, current, voltage and battery work cut-off time test data that the Ni-MHbattery’s capacity forecast model can be established.Deduced the power battery terminal voltage, temperature, working current and batterywork by the corresponding relations with the time in the battery life, in considering thebattery electrolyte loss is lesser, namely diffusion coefficient under the premise of notchanging.Get the expression of cell reaction potential based the analysis on thermodynamics formulathat for the battery’s actual reversible reaction. The expression can fully describe the power cellelectrochemical reaction balance. However, the potential balance equation basedthermodynamic cannot accurately describe the balance condition of the size of the current.The electrode reaction kinetics can describe the entire reaction process. The relationshipbetween battery’s current, electrolyte concentration, and over-potential can be derived whichaccording to the electrode kinetics. In this balance situation, the electrode reaction is controlled by the kinetics, and has nothing to do with the material transfer.Once the balance is broken, battery internal appeared potential, reaction speed will leadto the electrolyte concentration of reactant appeared deviation. At this time, mass transfer willcontrol the reaction.On the basis of the material transfer process, complete the cell reaction current andconcentration relationship analysis and derivation. And complete the power cell impedancemodel is derived.With a further to cell and battery various discharge rate discharge test data analysis,derived a batteries discharge model. Through the measured data and the model simulationdata contrast, verified the accuracy of model and accuracy.The testing figure of battery’s voltage is lower than the theoretical value and changesover time when battery provides power to the load, especially for variable load.There are some electrochemical factors causing changes of internal resistance of thebattery such as diffusion of the electrolyte solution, mass transferring, convection,temperature and capacity of the double electrical layer.At the same time, there are many nonlinear elements in the load circuits, such asrectifier, inverter circuit switch element, the motor and filtering, and flat wave components.Therefore, when resistance increases or current increases, the terminal voltage willaccelerate drop, early fall to cut-off voltage, and terminate discharge. The specific process isas follows:(1) If the output current fluctuation is not in big range, it can approximate think cell is ina constant current discharge condition, according to the constant current discharge durationthat the A.H capacity can be obtained by capacity of the release.(2) Measuring the battery output current, when the output current have taken place greatchanges, waiting for the output current stability in the new state, updating model parameters,adjust the discharge rate. From stable time, assess the capacity of the battery at the start ofthe new voltage curve.(3) When a certain parameter changes a lot (temperature, diffusion coefficient, density,etc.) until it stables at a new balanced state, updating its parameter, and using a newvoltage-time curve to estimate the capacity.(4) Each discharge stage discharge capacity is the capacity of the total has been released,until discharge termination voltage, according to the curve can predict the current dischargeratio lower electric duration.According to the work characteristics of hybrid cars batteries often in varying load conditions, through in different ratio under the premise of discharge current, use the curve ofvoltage changing with time to estimate the residual capacity of battery.Combined with the battery initial capacity prediction model and under the powerintegration for different ratio, get the battery capacity calculation.The battery’s charge and discharge experiment proves that the prediction model isaccurate and efficient.Finally, complete the trickle charge experiment of battery and describe the terminalvoltage, current and temperature of the corresponding curve with the data accurately. All thatproof the battery capacity prediction model is accurate and efficient.Another factor of limited power battery capacity accurate estimation is the interference.When the battery work for motor, the system appeared in various uncertain factors willaffect the battery system in the running state of stability and efficiency.Hybrid cars drive motor output torque is the most representative of the disturbance, andthe interference effect of torque is the most obvious.The corresponding interference torque will cause fluctuation to the output electricquantity of the battery when driving motor output shaft endures disturbed.On the basis of the analysis of a generalized framework, use the almost disturbancedecoupling control strategy to realize system that make the system have good robustness.Establish motor’s power model with the experiment data. On the basis of the H∞control theory, complete the strategy of permanent magnet synchronous motor shaft restraindisturbance.Complete the actual control strategy calculation with motor specific parameter thatmake power system realize almost disturbance decoupling for specific interference.