Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of ground fault indication
Reexamination Certificate
1998-10-30
2001-11-20
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of ground fault indication
C324S076110
Reexamination Certificate
active
06320389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric leak detecting apparatus and method for detecting an electric leak caused by deteriorated insulation between vehicle body and battery pack in an electric motorcar provided with a high voltage battery pack insulated from the vehicle body electrically to prevent electrical shocks.
2. Description of the Related Art
An electric motorcar, which uses an electric power as its driving source, is provided with a battery pack composed as a closed circuit and separated from the vehicle body. The battery pack functions as a ground to prevent electric shocks to be caused by a high voltage set battery used as a driving power source. If the insulating characteristics of the battery pack are deteriorated due to a change of the material quality thereof and/or deposit thereon, however, the high voltage battery pack is connected electrically to the vehicle body. And, this may cause a person to have an electric shock when he/she touches the vehicle body. Because, a leak current from the battery pack flows through him/her body.
An electric leak is a sum of leak currents flowing in all insulated portions. It is thus difficult to identify a system in which the current flows through. In order to detect such an electric leak, there have been proposed two methods so far; an AC method, which detects an electric leak resistance by applying an AC signal to an object vehicle body insulated from direct currents by a condenser and a transformer, and a non-insulating DC method, which measures an electric leak resistance as a direct current without using any of the condenser and the transformer. For example, the official report of Unexamined Published Japanese Patent Application No.57-119263 has disclosed an embodiment that adopts the AC method that uses a transformer and the official report of Unexamined Published Japanese Patent Application No.60-262069 has disclosed an embodiment that adopts the DC method.
FIG. 20
shows an equivalent circuit from which an electric leak is detected. Usually, an electric leak should be modeled with a distributed constant concept. If it is taken into consideration that a current leaks from the potential node of every set battery, however, the equivalent circuit of the battery pack
3
is represented by the set battery
3
a
and an electric leak admittance
3
b
noted by a concentrated constant using a resistor and a condenser. In
FIG. 20
, I
0
to In are leak currents, each flowing from a node to the vehicle body. The sum I of the leak currents is thus equal to the sum of the currents I
0
to In because of the superposition theory of currents.
[Equation 1]
I
=
I
0
+
I
1
+
Λ
+
I
n
-
1
+
I
n
=
∑
m
=
1
n
I
m
If the admittance in a battery is so low that it may be ignored, the admittance between the vehicle ground and the set battery
3
a
can be represented as the sum of admittance elements.
[Equation 2]
&AutoLeftMatch;
{
Y
LEAK
=
Y
0
+
Λ
+
Y
n
=
G
LEAK
+
j
ω
C
s
=
1
R
LEAK
+
j
ω
C
s
Θ
G
LEAK
=
1
R
LEAK
=
1
R
0
+
Λ
+
1
R
n
Θ
C
S
=
C
0
+
Λ
+
C
n
And, the battery pack
3
shown in
FIG. 20
can further be simplified as an AC equivalent circuit as shown in FIG.
21
.
The AC method, when used for detecting electric leaks, is characterized as follows:
(1) Since the object is insulated, no DC current flows in the object. The method is thus excellent in the aspect of safety.
(2) An admittance to be detected includes a floating capacitance of the object vehicle. The admittance thus includes an error.
(3) Although a lower frequency AC signal is advantageous to improve the electric leak detecting accuracy. However, the use of such a lower frequency deteriorates the responsiveness. In addition, the input condenser must be expanded more in size.
(4) Detected values are apt to be affected and varied by the floating capacitance of the object vehicle. In addition, the floating capacitance is also changed according to the external shape of the vehicle, so it is difficult to decide a criterion for electric leaks.
For example, if a conventional configuration as shown in
FIG. 22
is taken for the AC method, an electric leak resistance is found as an absolute value of admittance. As shown in the vector in
FIG. 23
, therefore, an admittance absolute value |YLEAK| is used in place of an electric leak resistance for convenience sake. Refer to Equation 3.
[Equation 3]
&LeftBracketingBar;
Y
&RightBracketingBar;
=
&LeftBracketingBar;
i
&RightBracketingBar;
&LeftBracketingBar;
v
&RightBracketingBar;
In the above case, however, the electric leak judgment will include an error due to the floating capacitance Cs. In order to reduce the influence of the floating capacitance Cs thereby to improve the measuring accuracy, the phase angle ø must be reduced. And, the detecting signal frequency must be lowered to reduce the phase angle ø.
On the other hand, the DC method can solve the problems caused by the AC method described in (1) to (4). The AC method, however, cannot solve a problem that the measuring accuracy is still low due to an error of the electric leak resistance of the battery pack itself. Further there is such problem that the detection side and driving side are connected with direct current on account of the detection.
SUMMARY OF THE INVENTION
Under such circumstances, it is an object of the present invention to solve the above problems the related art of AC and DC methods have been confronted with. It is an object of the present invention to provide an electric leak detecting apparatus excellent in safety and enabling constant detection so as to solve the problems of the related art AC method by applying an AC signal to the high voltage battery pack, then finding an admittance from the relationship between amplitude and phase of the AC signal, and further finding a resistance component, which is an inverse number of the admittance resistance component, from the cosine of the phase angle.
It is possible to use an impedance Z to represent such an electric leak, but an admittance will be easier to represent in such an electric leak expression. Therefore, an electric leak will be described with an admittance and an inverse of resistance (conductance).
Of course, it is also possible to judge an electric leak with the real part of an admittance, that is, an inverse of resistance.
It is also another object of the present invention to provide an electric leak detecting apparatus and a system provided with such an electric leak detecting apparatus so as to solve the related art problems of the DC method. In this case, the influences of the voltage of the set battery, as well as the admittance capacitance component are eliminated from the electric leak detecting apparatus by finding a DC current applied to a node of the set battery from an external DC power source, then finding a DC current when the polarity of the DC power source is reversed and finding an electric leak resistance form the difference between those DC currents.
In order to solve the above problems, the AC method of the present invention is characterized by that a resistance component is found from an electric leak admittance using an electric leak detecting method that uses a very safe AC signal thereby to correct the capacitance component of the vehicle body for accurate electric leak judgments.
On the other hand, the DC method of the present invention is characterized by that the electric leak detecting apparatus provided with a high measuring accuracy is used to apply a DC voltage to an insulating object positively and measure the DC current with respect to both maximum and minimum potential nodes of the set battery, then compute an electric leak resistance from the difference between those currents and said DC voltage.
As described above, according to the present invention, an AC signal can be used to safely detect an electric leak re
Kanamaru Kunio
Takada Masahiro
Tamesue Kazuhiko
Matsushita Electric - Industrial Co., Ltd.
Metjahic Safet
Ratner & Prestia
Sundaram T. R.
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