Battery monitoring system
A battery monitoring system includes: an input circuit to which voltage signals of battery cells are inputted; a multiplexer selecting a battery cell for voltage detection from the battery cells, selecting voltage signals inputted from the input circuit, and outputting the selected voltage signals; first and a second voltage measuring circuits simultaneously measuring voltages based on the voltage signals in first and second routes outputted from the multiplexer; a comparator comparing measurement results by the first voltage measuring circuit and by the second voltage measuring circuit; and a control unit that judges, on a basis of a comparison result by the comparator, at least one of a voltage of each battery cell, an operation check of equalizing the voltages of the battery cells, a presence or absence of a disconnection of a detection line of each battery cell, and a presence or absence of a failure in the multiplexer.
1. A battery monitoring system for monitoring a state of a battery pack including n (n: an integer) pieces of battery cells connected in series over a plurality of stages, comprising:
an input circuit to which respective voltage signals of the battery cells are inputted;
a multiplexer configured to:
select a battery cell for voltage detection from the n pieces of battery cells;
select voltage signals inputted from the input circuit; and
output the selected voltage signals;
a first voltage measuring circuit configured to measuring a voltage based on a voltage signal in a first route outputted from the multiplexer;
a second voltage measuring circuit configured to measure a voltage based on a voltage signal in a second route outputted from the multiplexer, at the same time as measurement of the first voltage measurement circuit;
a comparator configured to compare a measurement result by the first voltage measuring circuit with a measurement result by the second voltage measuring circuit; and
a control unit configured on a basis of a comparison result by the comparator to judge at least one of:
a voltage of each of the battery cells;
an operation check of equalizing the voltages of the respective battery cells;
a presence or absence of a disconnection of a detection line of each of the battery cells; and
a presence or absence of a failure in the multiplexer.
2. The battery monitoring system of claim 1 , wherein
the input circuit comprises:
n pieces of FETs constituting equalization switches for equalizing the voltages of the respective battery cells;
n pieces of resistors for equalization, each of which is connected between a drain terminal side of each of the FETs and a positive side of each of the battery cells;
n pieces of first monitor terminals, each of which is connected to a connection point between each of the resistors and the positive side of each of the battery cells and to which the voltage signals in the first route are inputted; and
n pieces of second monitor terminals, each of which is connected to a connection point between the drain terminal side of each of the FETs and each of the resistors and to which the voltage signals in the second route are inputted,
the first voltage measuring circuit is configured to measure, as the voltage in the first route, a voltage between a terminal of a ground potential and a lowermost stage of the first monitor terminal or a voltage between adjacent upper and lower stages of the first monitor terminals, and
the second voltage measuring circuit is configured to measure, as the voltage in the second route, a voltage between the terminal of a ground potential and a lowermost stage of the second monitor terminals or a voltage between adjacent lower stage of the first monitor terminals and upper stage of the second monitor terminals.
3. The battery monitoring system of claim 2 , wherein
the input circuit further comprises n pieces of drive terminals each of which is connected to a gate side of each of the FETs, and
a driving unit including a FET drive circuit and a disconnection detecting sink circuit is connected to the drive terminals, and controlled by the control unit.
4. The battery monitoring system of claim 2 , wherein
each of the second monitor terminals is configured to:
input a voltage different from a voltage inputted to corresponding first monitor terminal when corresponding FET is turned on by the driving unit, and
input the same voltage as a voltage that appears on corresponding first monitor terminal on a stage to which corresponding second monitor terminal belongs, when corresponding FET is turned off by the driving unit.
5. The battery monitoring system of claim 2 , further comprising low pass filters each arranged on an upstream side of each of the first monitor terminals and an upstream side of each of the second monitor terminals, wherein each of the low pass filters has same time constant.