Key word: Accumulator cell; Surplus capacity; Online examination; High noise
Introduction
The accumulator cell surplus capacity is a question which the user most cared, it is closely related with the entire power supply system’s reliability. The accumulator cell surplus capacity is higher, then the system reliability is higher. Therefore, how in both to consume the accumulator cell energy, and does not affect in the current collector normal work situation, the real-time online examination accumulator cell surplus capacity, has the important meaning.
The accumulator cell is a complex electrochemistry system, it moves when the different loading condition or the different ambient temperature, actually may supply release’s surplus capacity to be different; Moreover increases along with the accumulator cell period of revolution, its capacity will also drop. Usually is estimates the surplus capacity according to accumulator cell’s density of electrolyte, this method has the very big limitation: In the accumulator cell use later period, along with the positive and negative pole plate’s corrosion, breaks the muscle, calculates the surplus capacity accurately with difficulty; At the same time, this method also with difficulty adapts the present widespread application VRLA accumulator cell’s online examination. In the recent years commonly used several accumulator cell surplus capacity examination method, to the online use’s accumulator cell, the interface resistance law the influence which produces to the system is smallest, and may in the accumulator cell entire lifetime the correct measurement, therefore, the interface resistance law regards as one quite ideal method. But actually discovered in the high noise situation, actual obtains the accumulator cell surplus capacity precision is unsatisfactory, therefore, the accumulator cell surplus capacity online examination method’s improvement is imperative to the high noise situation.
1 interface resistance law forecast surplus capacity implementation plan
The massive findings indicated that accumulator cell interface resistance and between the electrically charged degree has good relevant [1][2]. American GNB Corporation once to capacity 200~1000A · h, the battery voltage 18~360V 500 nearly VRLA accumulator cell carried on the test, the experimental result had indicated that the accumulator cell interface resistance and the capacity relevance is good, the correlation coefficient may achieve 88%. Along with battery charging process’s advance, the interface resistance reduces gradually; Along with discharge process’s advance, the interface resistance increases gradually. Moreover, gets older along with the accumulator cell, its surplus capacity along with it drop, the interface resistance also gradually increases. The accumulator cell interface resistance and surplus capacity’s model relations curve as shown in Figure 1.
The accumulator cell charges completely when (fills) and discharges completely (puts), its interface resistance differs 2~4 times, the rate of change by far is bigger than the accumulator cell terminal voltage rate of change (approximately is 30%~40%), therefore, may forecast its surplus capacity quite accurately through the survey accumulator cell interface resistance. Moreover, regarding the online use’s accumulator cell, the interface resistance law also has a prominent merit is smallest to the system influence, may in the accumulator cell entire lifetime the correct measurement. Therefore, is not difficult to see the interface resistance law most to suit in the VRLA accumulator cell surplus capacity online survey.
The interface resistance law forecast surplus capacity’s concrete implementation plan is: First, fills the accumulator cell the electricity (take the 2V accumulator cell as example, charges to 2.23V, floating electric current to 10mA), then, causes the battery discharge by the 0.1C discharge ratio, in the record release electricity process the interface resistance and the surplus capacity size. When the battery discharge finished (2V battery discharge to 1.80V) then to be possible to obtain the complete discharging curve, namely surplus capacity and between accumulator cell interface resistance corresponding relationships. Stores in accumulator cell supervisory system’s FLASHROM this curve, will test the same model, the same specification accumulator cell when later, the processor basis online test will obtain in resistance number, through the table look-up computation, will obtain its surplus capacity. Therefore, how does this method’s key lie in online obtains the accumulator cell interface resistance.
The accumulator cell interface resistance survey principle is as follows: Exerts constant exchange audio frequency current supply Is in the accumulator cell both sides, then, examines its terminal voltage Vo as well as Is and between the Vo both’s included angle Theta. Obviously, accumulator cell’s alternating-current impedance is Z=Vo/Is, but R=Z×cosθ namely must gain for us in accumulator cell resistance number. It realizes plan as shown in Figure 2 specifically.
In the chart the 300Hz signal has the electric circuit is composed of 14 binary system serial counting/frequency divider CD4060 as well as the band-pass circuit, concrete electric circuit as shown in Figure 3.
Figure 3
in 2 high noise situations online measuring technique improvement
Uses the above method survey accumulator cell surplus capacity has the high precision, when the off-line survey the error to surpass 7%. However in the real-time online survey, actually discovered actual obtains the accumulator cell surplus capacity precision is unsatisfactory, sometimes the error even surpasses 10%. Is what reason causes this kind of error? Therefore, we to accumulator cell’s several kind of active status, namely in the power supply normal condition’s floating condition, in time the city electricity breakdown situation’s discharge condition as well as the invertor breakdown’s condition have carried on the test separately, discovered when the invertor breakdown situation, may achieve with the off-line test the approximate precision. Hence, may conclude the precision reduces the reason is, for this reason, we who causes by the invertor feedback noise attempt use the low pass filter (cut-off frequency is 1kHz) the method to increase the test precision, the effect are not ideal, obviously invertor’s feedback noise mainly concentrates in being lower than the 1kHz scope, therefore, realizes with difficulty on the hardware.
Considered already tested beforehand obtains in n standard the resistance number, therefore, may use slightly on the software two rides the fitting the means to carry on the data revision. So-called smallest two ride the question, is must discover undetermined function f(x), causes f(x) and difference of the normal value y sum of squares is smallest, namely
f(x) solution process following [3]: First, supposes f(x) is a n multinomial, namely
Then takes out in n standard which already tested obtains the resistance number, supposes is y1, y2,…, yn; Thus the type (1) may simplify is
According to the calculus in extremum principle, wants to cause the type (3) to be smallest, must make it to each coefficient partial derivative is 0, namely:
This in the formula has a n 1 equation, therefore, may solve a n 1 unknown. -like (3) the substitution type (4) and will simplify may result in
Finally in the test procedure actual will obtain n resistance number x1,…, xn with n standard in the resistance number y1, y2,…, yn substitution type (5), may determine a0, a1,…, an altogether a n 1 coefficient, thus may obtain f(x).
3 experimental results
Take the accumulator cell parameter and the junction, the DC voltage give the system test result as the example. The test uses the standard table is ESCORT3155A; The test with the accumulator cell for south company GFM200, and the capacity which obtains by the 0.1C discharge ratio discharge of constant current takes it in the rated load situation the standard capacity; The testing environment temperature is 18℃. Accumulator cell surplus capacity test result like table 1 arranges in order.
Table 1 accumulator cell surplus capacity test result
|
Standard capacity /A · h |
Monitoring unit actual capacity /A · h |
Absolute error /A · h |
Relative error/% |
|
200.0 |
184.9 |
- 15.1 |
7.6 |
|
193.6 |
180.7 |
- 12.9 |
6.7 |
|
176.4 |
188.9 |
12.5 |
7.1 |
|
165.7 |
153.2 |
- 12.5 |
7.5 |
|
135.2 |
142.8 |
7.6 |
5.6 |
|
87.76 |
83.28 |
- 4.48 |
5.1 |
May see by the experimental result, passes through the least squares method law plans, the measurement result basic close off-line measurement result. Its precision definitely may satisfy “Correspondence Power source And Air conditioning Centralized monitoring system Specification” the stipulation.
4 conclusions
The accumulator cell surplus capacity’s online examination has the profound influence to the entire power supply system’s reliability. It has also been a domestic and foreign research hot spot and the difficult question. This article has given the interface resistance law survey accumulator cell surplus capacity concrete implementation plan, proposed one kind in the high noise situation to the accumulator cell surplus capacity online examination improvement program. The experimental result had proven this corrective method can obtain the satisfying measuring accuracy under the high noise.
