Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
1999-12-29
2002-03-26
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C324S701000, C324S073100
Reexamination Certificate
active
06362627
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an isolation-type voltage measuring apparatus for measuring a voltage from an electrical apparatus under conditions electrically isolated from the electrical apparatus to be measured, and more particularly to a voltage measuring apparatus with flying capacitor method having a capacitor and a switch.
BACKGROUND ART
In recent years, in an electrical system for making voltage measurements, it has been known to use an isolation-type voltage measuring apparatus wherein the electrical apparatus to be measured, for example, a voltage source, is isolated electrically or separated in terms of electric potential from the voltage measuring part. More specifically, in a power supply system for an electric vehicle or a power storage system for a domestic use, a monitor apparatus for monitoring voltage is connected to battery cells with the above-mentioned voltage measuring apparatus, and the voltage from the battery cells is measured and monitored under conditions electrically isolated from the battery cells.
Stated more specifically a high output power source of hundreds of volts for the electric vehicle or the like is configured, as is well known, with connecting in series a large number of secondary battery cells exemplified by stacked- or aggregate-type nickel hydrogen storage cells. To control the charging and discharging of these series connected cells, the performance of each individual cell must be monitored. Further, in the electric vehicle, the high voltage system including the high output power source is electrically isolated from the chassis to prevent hazards. On the other hand, since the processor for controlling the charging and discharging uses the chassis as a reference potential, the cell voltage must be measured in an electrically isolated manner.
A first voltage measuring apparatus for making such voltage measurements, has a monitoring apparatus for a battery pack as disclosed in Japanese Unexamined Patent Publication No. 8-140204. This first conventional voltage measuring apparatus comprises a voltage monitoring unit which includes an operational amplifier, an A/D converter, a photocoupler, and a reference power supply, and is designed to measure the voltage of a 240-cell series battery (stacked-type voltage source) delivering a total voltage of 288 V. More specifically, in this first conventional voltage measuring apparatus, since it is actually difficult to measure and monitor many voltages of large number of individual cell, 10 cells are grouped into one module, and the voltage of each module, in an example, voltages of 24 modules, are measured using a voltage measuring apparatus.
However, in the above-mentioned first conventional voltage measuring apparatus, there was a problem that the configuration of the measuring apparatus is rather complicated because the voltage monitoring unit having a complex construction has to be provided for each module.
A second conventional voltage measuring apparatus, for example, U.S. Pat. No. 5,163,754 discloses a temperature measuring apparatus. This second conventional voltage measuring apparatus measures the output voltage of a thermocouple in an electrically isolated manner by using the earlier described flying capacitor method.
A major section of the second conventional voltage measuring apparatus will be described in detail below with reference to FIG.
23
.
FIG. 23
is a circuit diagram showing a major section of a second conventional voltage measuring apparatus.
As shown in
FIG. 23
, in the second conventional voltage measuring apparatus, a voltage source
101
to be measured is connected to a capacitor
103
via a first switching device
102
, and the capacitor
103
is connected to a buffer circuit
105
via a second switching device
104
. The first switching device
102
is configured with two switches
102
a
and
102
b
which operate in interlocking fashion with each other. Likewise, the second switching device
104
is configured with two switches
104
a
and
104
b
which operate in interlocking fashion with each other. Each of the switches
102
a
,
102
b
,
104
a
, and
104
b
is constructed from an isolated driving type analog switching element having high voltage withstanding capability, for example, a MOSFET with optical driver. The buffer circuit
105
is connected to a known voltmeter (not shown).
In the above-mentioned second conventional voltage measuring apparatus, first, while holding the second switching device
104
in the OFF-state, the first switching device
102
turns on to transfer the voltage of the voltage source
101
to the capacitor
103
. Thereby, the capacitor
103
holds the voltage. Next, the first switching device
102
turns off and the second switching device
104
turns on, thereby to input the voltage of the voltage source
101
into the buffer circuit
105
. In this way, with the first and second switching devices
102
and
104
not in the ON-state simultaneously, the second conventional voltage measuring apparatus measures the voltage of the voltage source
101
by maintaining electrical isolation from the voltage source
101
.
However, in the second conventional voltage measuring apparatus, there was a problem that accuracy of voltage acquisition by and at the capacitor
103
degrades, hence leading to a degradation in voltage measurement accuracy.
The problem of the voltage measurement accuracy degradation in the second conventional voltage measuring apparatus will be explained with reference to FIG.
23
.
As shown in
FIG. 23
, in the case that the voltage source
101
is superimposed on a disturbance voltage (hereinafter also referred to as a “common mode voltage”) En which is unsteady with respect to ground potential, the instant that the first switching device
102
held in the ON-state turns off and the second switching device
104
turns on, the voltage between both terminals of each of the switches
102
a
and
102
b
changes from zero toward the disturbance voltage En. As a result, in the second conventional voltage measuring apparatus, leakage currents Ia and Ib shown in the figure flow based on the change of the charge on capacitances of the respective switches
102
a
and
102
b
in the OFF-state. The leakage current Ia passes through the capacitor
103
and flows into ground potential for the buffer circuit
105
together with the leakage current Ib. As a result, in the second conventional voltage measuring apparatus, the common mode error occurs in which the voltage for measurement that should be held in the capacitor
103
is offset by the leakage current Ia caused by the disturbance voltage En, and thereby to degrade the accuracy of voltage measurement.
When the measuring method of flying capacitor method of the second conventional apparatus is employed, the voltage measuring apparatus of first conventional can be simplified in construction thereof. However, even when the measuring method of the second conventional apparatus is employed, expensive isolated driving type analog switch elements totaling 96 in number must be used for the 24 modules (stacked type voltage source), and further improvements have been needed in terms of the cost, size, and reliability.
Next, a third conventional voltage measuring apparatus will be described with reference to FIG.
24
.
FIG. 24
is a circuit diagram showing a configuration of a third conventional voltage measuring apparatus.
As shown in
FIG. 24
, in this third conventional voltage measuring apparatus, the buffer circuit
105
shown in
FIG. 23
is replaced by a differential amplifier
106
, and a resistor
107
is provided for settling the potential of the capacitor
103
within the input operating range of the differential amplifier
106
. The resistor
107
consists of series connected resistors
107
a
and
107
b
, and an intermediate terminal therebetween is grounded.
In the third conventional voltage measuring apparatus, the leakage currents Ia and Ib occur as in the second conventional apparatus shown in FIG.
23
. However, in the third conventional voltage meas
Nagagata Nobuyoshi
Shimamoto Takeshi
Brown Glenn W.
Matsushita Electric - Industrial Co., Ltd.
Sheridan & Ross P.C.
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