1、The storage battery is widely used in commercial run, traffic and communication etc. andmainly used as reserved power. When the main power or generating equipment goes wrong, the storage battery replaces them. If its inactive or off-capacity, heavy accident maybe occurs. So its operational parameter
2、s must be generally monitored on-line. The most important symbol of the batterys condition is its internal resistance. The resistance value may be changed when it will be inactive or off-capacity. If the charge or discharge is improper, the resistance is also changed1、2. Through testing the batterys
3、 internal resistance, its active state can be monitored and evaluated.2 Measuring Methods of Batterys Internal Resistance The measuring course is complex. At present, the methods of constant-current discharge and AC impedance are the two reliable methods3、4.2.1 Method of Constant-current DischargeTh
4、e principle of constant-current discharge is as follows. At first, great current is discharged on the battery and the maximum current may exceed one hundred. At the same time, the instantaneous voltage drop is obtained and measured. Then the batterys internal resistance can be calculated with Ohms l
5、aw. The method is widely used in practice. But it has some shortages. The attack to the load is severe and the batterys life period may be influenced. The measurement must be done in static or off-line conditions. The on-line measure cant be implement and the test result error may be large.2.2 Metho
6、d of AC impedanceThe principle of the method is as follows. A fixed-frequency AC signal is loaded on the batterys two terminals. The AC signals current and the voltage drop on the battery are measured. With the measured value, the internal resistance is calculated. Because the battery isnt discharge
7、d, on-line monitoring and management is carried out. Thebatterys capability cant be impacted. But it also has some shortages.(1) The frequency and amplitude of the AC arefixed. They cant be adjusted according to differentmeasurands.(2) Before calculating the internal resistance,the ACs current, volt
8、age and the phasic difference between them must be measured. There are many disturbed factors. The measuring method is complex and the error is large.(3) Measuring on-line, the AC signal is distributed by the load. So the current on the battery is reduced. This may consumedly reduce the monitoring d
9、istinguish ability.3 Principle of AC ProportionIn the paper, the AC impedance method is improved and the AC proportion method is proposed to measure the batterys internal resistance. The battery is connected with a high precision resistance in series. A special chip is used to measure and compare th
10、e valid values of the ACs dividing voltage on the battery and the resistance. Then the internal resistance can be calculated. The equivalent serial circuit of the battery and the high precision resistance is given in Fig. 1.R0 is the high precision resistance in Fig.1. The part in the broken line bl
11、ock is the equivalent circuit of the storage battery. R is the batterys ohmic inertial resistance. RC is the polarized inertial resistance. C is inter-polar condenser. The batterys equivalent impedance is:Z=R+RC/(1+JCRC) (1) is the angular frequency of the AC signal ui, which is produced by the sign
12、al generating circuit.The current flowing the in-series circuit is:i=ui/(Z+R0)=u1/Z=u2/R0 (2)In Equ.(2), the variances are complex number. The proportional relation exists between them. Modding them, the relation is still right.|u1/Z|=|u2/R0| (3)|Z|=|u1|R0/|u2| (4)The mods of u1and u2 are their vali
13、d value, V1and V2, respectively. When the battery and the high precision resistances root-mean-square value of dividing voltage are measured, the mod value of the batterys equivalent impedance, |Z|, can be calculated.|Z|=V1R0/V2 (5)Its synthesized with the batterys ohmic internal resistance, the pol
14、arized inertial resistance and the interpolar condenser. And it can be regarded as the batterys equivalent internal resistance.4 Structure of HardwareAs intelligent control chip, MCU is widely used in the medium and small-sized test-control system. It has many merits, such as operating easily, contr
15、olling accurately and expending simply. A internal resistance intelligent measuring instrument of the storage battery is designed in the paper. ADuC 812 MCU is selected as main controller to control signals input and output. The schematic diagram is showed in Fig.2. Rt and Rd are digital potentiomet
16、ers and their resistances can be adjusted with the MCU program. Ro is a high precision resistance and its value is 0.5 . C1, C2and C3 are coupling condensers. The whole instrument has four parts. They are man-machine interactive interface, signal generating circuit, signal sampling converting circui
17、t and serial communication circuit.4.1 Man-machine Interactive InterfaceThe interface are composed of display circuit, keyboard input circuit and MCU.The ADuC 812 MCU is mainly composed of one 8-channel 12-bit high speed A/D converter, two12-bit D/A converters, 8kB flash/electro-erasing program memo
18、ry, 640-byte flash/electro-erasing data memory. Its kernel is 80C52 MCU. It also comprises some important functional module, such as timing controller, power monitor, data DMA transferring and store protecting circuit and some bus interface.The ADuC 812 is a high precision analog data collecting sys
19、tem, which is programmable entirely and self-checking. Its cubic content is small and its cost is low. So it can substitute some high-cost massive products, which are mostly produced with mono-plate processor. The other merit is that the flash/electro-erasing memory is used. With theembedded loader
20、and debugging software, the shortages, such as deficient flexibility and storage difficulty, are overcome. The on-line programming is realized. So the design, programming and debugging become more easily. Moreover, its static CPU operation and power-fail mode are supremely important to battery-power
21、ed test-control equipments.4.2 Signal Generating CircuitThe ICL 8038, which is a waveform generator, is a monolithic integrated circuit. Cooperated with exterior element, the sine wave, square wave, triangular wave and saw-tooth wave can begenerated and their frequency may be 0.001Hz to 300Hz. The o
22、utput waves frequency is determined with the condenser Ct and the resistance Rt. Their relation satisfies:f=0.33/RtCt (6)If Ct is 100 pF and Rt is changed from 1 to 100k, the output frequency is changed from 33 to 3300Hz. The distorted degree of output sine wave is less than 1% and the ratio of its
23、amplitude to the sources one is 0.7.The output sine wave of ICL 8038 is used to test the internal resistance. Then its distributed by the digital potentiometer Rd and amplified its power.The output is coupled on the tested battery by the condenser C1. The output square wave of ICL 8038 is counted by
24、 the MCU. So the frequency of output wave and its stability are calculated. The resistance value of digital potentiometer, Rt and Rd, can be adjusted programmablely. Consequently, the frequency and amplitude of output signal can also be adjusted programmablely. The power-amplified circuit is the sym
25、metrical complementary push-pull circuit. Its only amplified the power but not amplified the voltage.4.3 Sampling Converting CircuitThe tested battery is connected with a high precision resistance in series, which is located in the internal resistance measured instrument. And this is a voltage-divid
26、ing circuit. C2 and C3 are AC coupling condensers. The AC components are obtained from the serial circuit. So the batterys DCvoltage and the load dont influence the test results. AD 736 is a high precision true valid value converter. Its input is 100mV and the distinguish ability is 100V. The input
27、impedance is 1012 . A weak AC signal can be tested and its root-mean-square value is obtained. Its output DC voltage value is equal to the input AC valid value.4.4 Serial Communication CircuitADuC 812 has many kinds of communication interface. So a serial communication circuit is designed to connect
28、 with the top computer. The MCUs program can be refreshed on-line and thetested data can also be transferred on-line. The battery-powered regulated power circuit and thebridge rectifier filter circuit are designed. The instrument can be supplied with battery or commercial power.The tested batterys p
29、arameters, such as its specification and model can be obtained by the man-machine interactive. With the interface, the resistance value of the digital potentiometer can be adjusted and the frequency and amplitude are selected automatically. So the instrument may be easily adapted to the battery and loads requirement. ADuC 812 MCU has a 640-byte data memory. The test data can be stored and analyzed. The data can also be transferred to the top computer and processed a
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