JP2000030761A - Charge/discharge testing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep required accuracy in the measurement of charging characteristics and discharging characteristics of a battery pack having a normal current value or a low current value. SOLUTION: Current transformation ratio of a current transformation device 9 is controlled based on the operation content of a centralized control device 13, and when a pack battery 7 is charged or discharge with a charge/discharge power source device 8, a temperature detecting signal outputted from a temperature measuring device 11, a voltage detecting signal outputted from a voltage measuring device 10, and a current detecting signal outputted from the current transformation device 9 are processed so as to conduct A/D conversion with a measuring unit 12, and charging characteristics or discharging characteristics of the battery pack 7 are measured based on temperature data, voltage data, and current data obtained by the unit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge / discharge test system for testing charge and discharge characteristics of a secondary battery used in various electronic devices.

[0002]

2. Description of the Related Art In recent years, with the advance of electronic technology, high performance, miniaturization, and portability of various electronic devices have been advanced, and accordingly, secondary batteries have been frequently used in these electronic devices. I have.

[0003] With the increase in demand for such secondary batteries, research and development of secondary batteries has been conducted, and the charging and discharging characteristics of newly developed secondary batteries are tested and evaluated. Various charge / discharge test systems for secondary batteries have been proposed.

On the other hand, in recent years, from the viewpoint of improving the global environment,
Electric vehicles are attracting attention as vehicles that do not emit exhaust gas, and a battery pack that connects a plurality of single cells formed in a size equivalent to a dry battery in series is used as a battery as an energy source of such an electric vehicle. Often done.

In general, when measuring the capacity of a battery pack,
In order to increase the measurement accuracy as much as possible, charging (or discharging) is performed with a constant current having a preset low current value, and the time until the terminal voltage of the battery pack reaches the preset voltage value, The capacity of the battery pack is measured based on the product of the charge current value (or the discharge current value).

[0006]

When measuring the charging characteristics and discharging characteristics of such a battery pack, in a conventional system, the charging current flowing from the charging device to the battery pack or the charging current flowing from the battery pack to the discharging device is measured. When detecting the current value of the discharge current, one current transformer (C
Since the charging current and the discharging current are changed by T),
The maximum charge / discharge current value is determined according to the current transformer ratio of the current transformer.

For example, in a system in which the full scale is 150 A and the accuracy is set to 0.05%, the current transformer used has a current transformer ratio of 150 A / 10 V and the resolution of the A / D converter in the next stage is used. Is 10 V / 2000 bits, to perform charge / discharge capacity measurement using this system,
When the battery pack is charged and discharged at 5 A, the secondary output of the current transformer becomes 1 V and the number of bits of the signal output from the A / D converter becomes 200 bits. The measurement accuracy is reduced to 1/10 as compared with the case where the measurement is performed.

For this reason, it is impossible to satisfy the accuracy of 0.05%, which is the accuracy when measuring the charge / discharge characteristics of the battery pack at full scale.

As described above, in the conventional system, when measuring the charge / discharge characteristics of the battery pack, the measurement accuracy can be ensured only at a certain ratio with the maximum charge / discharge current of the battery pack being a full scale. Therefore, when measuring the charging characteristics and the discharging characteristics of the battery pack with a constant current having a low current value, there is a problem that required measurement accuracy cannot be secured.

[0010] In view of the above circumstances, the present invention secures necessary accuracy when measuring the charging and discharging characteristics of a battery pack with a constant current having a normal current value or a low current value. It is an object of the present invention to provide a charge / discharge test system that can perform the test.

According to the present invention, a plurality of current transformer ratios can be ensured by one current transformer, whereby the battery pack is charged with a constant current having a normal current value or a low current value. It is an object of the present invention to provide a charge / discharge test system capable of ensuring required accuracy when measuring characteristics and discharge characteristics.

According to a third aspect of the present invention, when the current value of the charging current supplied to the battery pack or the current value of the discharging current output from the battery pack is equal to or less than a preset current value, Of the current detection signal output from the current transformer so that the current detection signal does not exceed a predetermined voltage value. Having a current value,
It is an object of the present invention to provide a charge / discharge test system capable of securing necessary accuracy when measuring a charging characteristic and a discharging characteristic of a battery pack with a constant current.

[0013]

In order to achieve the above object, according to the present invention, a charging current is supplied to a chargeable / dischargeable DUT to measure a charging characteristic of the DUT. Process or output a discharge current from the test object,
In the charge / discharge test system that performs at least one of the processes of measuring the discharge characteristics of the test object, when measuring any of the charge characteristics or the discharge characteristics of the test object, the specified A charge / discharge power supply unit for supplying a charging current having a specified current value or a process for outputting a discharging current having a specified current value from the device under test, and By switching the ratio, a current transformer that transforms the charge current or the discharge current to generate a current detection signal, and according to the current value of the charge current or the absorbed discharge current output from the charge / discharge power supply unit, A current ratio switching unit that switches the current ratio of the current unit,
A charge / discharge characteristic measuring unit for measuring a charge characteristic or a discharge characteristic of the device under test based on the current ratio of the current ratio switching unit and the current detection signal.

According to a second aspect of the present invention, in the charge / discharge test system according to the first aspect, the current transformer includes a current transformer body made of a frame-shaped magnetic material, and the current transformer. A plurality of primary feedthrough windings wound around the main body, a relay circuit for switching a combination of the respective primary feedthrough windings according to a specified current transformation ratio, and a voltage corresponding to a magnetic flux generated in the current transformer main body. And a magnetic detector for generating a current detection signal having a value.

Further, in claim 3, claim 1 or 2
In the charge and discharge test system described in the above, the current transformation ratio switching unit determines whether or not the current value of the charging current supplied to the device under test or the current value of the absorbed discharging current satisfies a predetermined condition. When a predetermined condition is satisfied, the current changing ratio of the current changing portion is switched.

According to a fourth aspect of the present invention, in the charge / discharge test system according to the first, second, or third aspect, the current ratio switching unit detects a current zero of the charge / discharge current, The current ratio is switched only when the zero current is detected by the zero current detection circuit, and only when the low current mode in which charging and discharging are performed at a low current is specified when the zero current is not detected. An interlock circuit is provided.

According to the above configuration, when measuring either the charge characteristic or the discharge characteristic of the test object, the charge / discharge power supply unit has a specified current value with respect to the test object. While performing a process of supplying a charging current or a process of outputting a discharging current having a specified current value from the device under test, the current value of the charging current output from the charging / discharging power supply unit or the absorbed discharging current is changed. In response, the current transformer ratio switching unit switches the current transformer ratio of the current transformer unit, and based on the current transformer ratio of the current transformer ratio switch unit and the current detection signal output from the current transformer unit, charges and discharges. A characteristic measuring unit measures a charging characteristic or a discharging characteristic of the device under test. This ensures the required accuracy when measuring the charging characteristics and discharging characteristics of the device under test with a constant current having a normal current value or a low current value.

According to a second aspect of the present invention, as the current transformer, a current transformer body composed of a frame-shaped magnetic material;
A plurality of primary feed-through windings wound around the current transformer main body, a relay circuit for switching a combination of the respective primary feed-through windings according to a specified current transformer ratio, and a magnetic flux generated in the current transformer main body. By using a magnetic detector that generates a current detection signal having a voltage value according to the above, a plurality of current transformation ratios can be secured in one current transformation section, and thereby a normal current value or a low current value can be obtained. When measuring the charging characteristics and discharging characteristics of a device under test with a constant current, ensure the required accuracy.

In the present invention, it is determined whether the current value of the charging current supplied to the test object or the current value of the absorbed discharging current satisfies a predetermined condition. When a predetermined condition is satisfied, the current changing ratio of the current changing part is switched. This ensures that the value of the current detection signal output from the current transformer does not exceed a predetermined voltage value, and secures the safety of the system while maintaining a constant current with a normal current value or a low current value. When measuring the charge characteristics and discharge characteristics of the test object, ensure the required accuracy.

Further, in the low current mode, when the current zero of the charging / discharging current is detected by the current zero detecting circuit, and when the current zero is not detected, the charging / discharging is performed at a low current. The current ratio is switched by the interlock circuit only when is specified.
This ensures that the value of the current detection signal output from the current transformer does not exceed a predetermined voltage value, and secures the safety of the system while maintaining a constant current with a normal current value or a low current value. When measuring the charge characteristics and discharge characteristics of the test object, ensure the required accuracy.

[0021]

FIG. 1 is a block diagram showing an embodiment of a charge / discharge test system according to the present invention.

The charge / discharge test system 1 shown in FIG. 1 has three sets of rectification / discharge circuits 5 each including a plurality of switching elements 2, a plurality of diodes 3, and a plurality of capacitors 4, and is supplied with a charge instruction signal. In this case, the three-phase AC voltage output from the three-phase AC power source 6 is taken and rectified to generate a DC-type charging current having a current value specified by the charging instruction signal, and this charging current is measured. , For example, one hundred and several single cells are supplied to the battery pack 7 connected in series and charged, and when a discharge instruction signal is supplied, the discharge instruction signal A charge / discharge power supply device 8 that regenerates discharge power while discharging the battery pack 7 so as to have the indicated current value, and a charge / discharge device 8 with a current transformation ratio corresponding to the inputted current transformation ratio instruction signal. Output charging Flow, and varying flows the discharge current to be collected, and a current transformer unit 9 for outputting a current detection signal. Also, a voltage measuring device 10 that measures a voltage between terminals of the battery pack 7 and outputs a voltage detection signal obtained in the measurement operation, and a temperature of the battery pack 7 and measures a temperature detection signal obtained in the measurement operation. A temperature measuring device 11 for outputting;
The temperature detection signal output from the temperature measurement device 11, the voltage detection signal output from the voltage measurement device 10, and the current detection signal output from the current transformer 9 are A / D-converted to obtain temperature data and voltage. A measurement unit 12 for generating data and current data; and a current-conversion-ratio instruction signal generated based on the instruction content input by the operator.
A charge instruction signal or a discharge instruction signal is generated while controlling the current transformation ratio of the charge / discharge power supply 8 to control the charge operation and the discharge operation, and the temperature data, voltage data, Capture the current data,
A centralized management device 13 for measuring the charging characteristics or discharging characteristics of the battery pack 7;

In the charge / discharge test system 1,
The battery pack 7 is connected to the charge / discharge power supply 8 while controlling the current ratio of the current transformer 9 based on the operation content of the centralized control device 13.
When the charging operation or the discharging operation is performed, the temperature detection signal output from the temperature measurement device 11, the voltage detection signal output from the voltage measurement device 10, and the voltage detection signal output from the current transformer 9 are output by the measurement unit 12. A / D conversion is performed for each of the current detection signals, and the temperature data obtained by the
The charge characteristic or the discharge characteristic of the battery pack 7 is measured based on the voltage data and the current data.

In this case, as shown in FIG. 2, the current transformer 9 includes a current transformer body 1 having a laminated plate, a core material and the like formed in a frame shape.
4, one-turn primary through winding 15 inserted into current transformer main body 14, nine-turn primary through winding 16 inserted through current transformer main body 14, and transformer output from central management device 13. When the flow ratio instruction signal is a one-turn instruction, it is turned on, and the contact 17a inserted between one end of the primary feedthrough winding 15 and the output terminal of the charge / discharge power supply device 8 is closed,
A charging current or a discharging current is passed through the primary feedthrough winding 15,
When the relay 17 for generating a magnetic flux in the current transformer main unit 14 and the current transformation ratio instruction signal output from the centralized control device 13 indicate a 10-turn instruction, the relay 17 is turned on and the primary feedthrough winding 1 is turned on.
6 and one end of each primary feed-through winding 15,
16 through the charging current or the discharging current,
4 has a relay 18 for generating a magnetic flux and a magnetic detection element such as a Hall element or a magnetic resistance element, and generates a current detection signal having a voltage value corresponding to the magnitude of the magnetic flux generated in the current transformer main body 14. A magnetic detection circuit 19 is provided.

When the current ratio command signal output from the central control device 13 is a one-turn command, the relay 17
Is turned on, the contact 17a inserted between one end of the primary through winding 15 and the output terminal of the charging / discharging power supply device 8 is closed, and a charging current or a discharging current is applied to the primary through winding 15. While flowing, a current detection signal having a voltage value corresponding to the magnitude of the magnetic flux generated in the current transformer body 14 is generated by the magnetic detection circuit 19 and supplied to the measurement unit 12.
When the current ratio command signal output from the central control device 13 is a 10-turn command, the relay 18 is turned on to connect the one end of the primary feedthrough winding 16 and the output terminal of the charge / discharge power supply 8. The interposed contact 18a is closed, and according to the magnitude of the magnetic flux generated in the current transformer main body 14 by the magnetic detection circuit 19 while charging current or discharging current flows through each of the primary through windings 15 and 16. A current detection signal having a voltage value is generated and supplied to the measurement unit 12.

As shown in FIG. 3, when the value of the current data output from the measurement unit 12 indicates zero, the central control device 13 includes a current zero detection circuit 20 for generating a current zero detection signal. And a keyboard device 21 operated by an operator, and generates a charge instruction signal, a discharge instruction signal, a current transformation ratio instruction signal, and the like according to the operation content of the keyboard device 21 and the content of a preset program. A CPU device 22 that captures current data, voltage data, temperature data, and the like output from the measurement unit 12 and measures charging characteristics, discharge characteristics, and the like of the battery pack 7, and display data and the like output from the CPU device 22. A CRT device 23 for taking in and displaying the content indicated by the display data on a screen;
When the current zero detection signal is not output from the current zero detection circuit 20 in the state where the current conversion ratio instruction signal is output from the second current generator 2, a current conversion ratio instruction signal indicating one turn is generated, and the current zero detection circuit When the current zero detection signal is output from the control circuit 20, the interlock circuit 24 that determines that the low current mode switching condition is satisfied and generates a current transformation ratio instruction signal indicating a 10-turn instruction is provided.

When the operator operates the keyboard device 21 to input a normal current mode instruction together with a charge test start instruction or a discharge test start instruction, a charge instruction signal or a discharge instruction signal is generated.
This is supplied to the charging / discharging power supply device 8 and a current transformation ratio instruction signal indicating one turn instruction is generated.
While supplying current data, voltage data, temperature data, and the like output from the measurement unit 12 to measure the charging characteristics and discharging characteristics of the battery pack 7, and display the measurement results on the CRT device 23. . Further, when the keyboard device 21 is operated by the operator to input a charge test start instruction or a discharge test start instruction and a low current mode instruction, a charge instruction signal or a discharge instruction signal is generated and charged. In addition to supplying to the discharge power supply 8, a current transformation instruction signal indicating a 10-turn instruction is generated on condition that the value of the current data output from the measurement unit 12 is zero, and this is transmitted to the current transformer 9. While supplying the current, the current data, the voltage data, the temperature data, and the like output from the measurement unit 12 are taken in, the charge characteristics and the discharge characteristics of the battery pack 7 are measured, and the measurement results are displayed on the CRT device 23.

Next, the operation of this embodiment will be described for the normal current mode and the low current mode separately with reference to the block diagrams shown in FIGS.

<Normal Current Mode> First, a battery pack 7 to be tested for charge characteristics and discharge characteristics is connected to the charge / discharge test system 1, and a voltage measuring device 10 and a temperature measuring device 11 are connected to the battery pack 7. In the attached state, when the operator operates the keyboard device 21 of the central control device 13 to input a charge test start instruction or a discharge test start instruction and a normal current mode instruction, the CPU device of the central control device 13 A charge instruction signal or a discharge instruction signal indicating a normal current value is generated by 22 and supplied to the charging / discharging power supply device 8 to charge and discharge the battery pack 7 with the normal current value.

In parallel with this operation, the central management device 1
3 and the interlock circuit 24 generates a current transformation ratio indicating signal indicating a one-turn instruction, which is supplied to the current transformer 9 and is supplied to one of the relays 17. Is turned on,
The contact 17a inserted between one end of the primary through winding 15 and the output terminal of the charging / discharging power supply device 8 is closed, and while a charging current or a discharging current is flowing through the primary through winding 15, The magnetic detection circuit 19 generates a current detection signal having a voltage value corresponding to the magnitude of the magnetic flux generated in the current transformer main body 14.

The current detection signal output from the current transformer 9 and the temperature measurement device 11 are output by the measurement unit 12.
A / D conversion is performed on the temperature detection signal output from the CPU and the voltage detection signal output from the voltage measurement device 10 to generate current data, voltage data, and temperature data. The current data, the voltage data, and the temperature data output from the measurement unit 12 are taken in, the charge characteristic or the discharge characteristic of the battery pack 7 is calculated, and the calculation result is displayed on the CRT device 23 on a screen.

<Low Current Mode> A battery pack 7 to be tested for charge characteristics and discharge characteristics is connected to the charge / discharge test system 1 and a voltage measuring device 10 and a temperature measuring device 11 are connected to the battery pack 7. With attached
When the operator operates the keyboard device 21 of the central control device 13 to input a low-current mode instruction together with a charge test start instruction or a discharge test start instruction, the CPU device 22 of the central control device 13 reduces the low current value. A charging instruction signal or a discharging instruction signal is generated, which is supplied to the charging / discharging power supply, and at a low current value,
The battery pack 7 is charged and discharged.

In parallel with this operation, the central management device 1
3 and the interlock circuit 24 generates a current transformation ratio indicating signal indicating a one-turn instruction, which is supplied to the current transformer 9 and is supplied to one of the relays 17. Is turned on,
The contact 17a inserted between one end of the primary through winding 15 and the output terminal of the charging / discharging power supply device 8 is closed, and while a charging current or a discharging current is flowing through the primary through winding 15, The magnetic detection circuit 19 generates a current detection signal having a voltage value corresponding to the magnitude of the magnetic flux generated in the current transformer main body 14.

Further, the current detection signal output from the current transformer 9 and the temperature
A / D conversion is performed on the temperature detection signal output from the A / D converter and the voltage detection signal output from the voltage measurement device 10 to generate current data, voltage data, and temperature data. Is determined to be zero, the value of the current data is determined to be zero, and when the current zero detection signal is output, the interlock circuit 24 generates a current transformation ratio instruction signal indicating a ten-turn instruction. And this is supplied to the current transformer 9,
One relay 17 is turned off and the other relay 18 is turned on, and the contact 18a inserted between one end of the primary feedthrough winding 16 and the output terminal of the charging / discharging power supply device 8 is closed. A current having a voltage value corresponding to the magnitude of the magnetic flux generated in the current transformer body 14 by the magnetic detection circuit 19 while the charging current or the discharging current is flowing through the primary windings 15 and 16 in the state. A detection signal is generated.

The current detection signal output from the current transformer 9 and the temperature measurement device 11 are output by the measurement unit 12.
A / D conversion is performed on the temperature detection signal output from the CPU and the voltage detection signal output from the voltage measurement device 10 to generate current data, voltage data, and temperature data. The current data, the voltage data, and the temperature data output from the measurement unit 12 are taken in, the charge characteristic or the discharge characteristic of the battery pack 7 is calculated, and the calculation result is displayed on the CRT device 23 on a screen.

At this time, the current transformer body 14 has a rating of 150 A
If the current in the normal current mode is set to 150 A and the current in the low current mode is set to 15 A, the two primary feed-through windings wound around the current transformer main body 14 when the measurement is performed in the low current mode. Since the charging current and the discharging current flow through 15 and 16, the sensitivity of the current transformer main body 14 becomes 150AT which is the same as that in the normal current mode. At this time, the full scale is 150A, the accuracy is 0.05%, and the current If the current transformer ratio of the main body 14 is 150 A / 10 V and the resolution of the measuring unit 12 is 10 V / 200 bits, 10 V
Is output, and the measurement unit 12 outputs 2000-bit current data.

Thus, even when the low current mode instruction is set, the accuracy is 0.05 times that at full scale.
%, The same accuracy can be ensured.

As described above, in this embodiment, the charging operation of the battery pack 7 to the charge / discharge power supply device 8 or the control of the current ratio of the current transformer 9 based on the operation contents of the centralized control device 13 or When the discharging operation is performed, the measurement unit 12 converts the temperature detection signal output from the temperature measurement device 11, the voltage detection signal output from the voltage measurement device 10, and the current detection signal output from the current transformer 9. A / D conversion and temperature data obtained by the A / D conversion,
Since the charging characteristics or the discharging characteristics of the battery pack 7 are measured based on the voltage data and the current data,
When the charging characteristics and the discharging characteristics of the battery pack 7 are measured with a constant current having a normal current value or a low current value, required accuracy can be secured (the effect of claim 1).

Also, in this embodiment, since a plurality of current transformer ratios are ensured by one current transformer 9, the cost of the system and the cost are reduced as compared with the case where a plurality of current transformers are used. When measuring the charging characteristics and discharging characteristics of the battery pack 7 with a constant current having a normal current value or a low current value while keeping the space low, necessary accuracy can be ensured. ).

In this embodiment, the battery pack 7
When the current value of the charging current supplied to the battery or the current value of the discharging current output from the battery pack 7 is equal to or less than a preset current value, the current zero detection circuit 20 and the interlock circuit 24 Since the current transformation ratio of the current transformer 9 is switched, the value of the current detection signal output from the current transformer 9 is prevented from exceeding a predetermined voltage value.
When measuring the charging characteristics and the discharging characteristics of the battery pack 7 with a constant current having a normal current value or a low current value while securing the safety of the system, necessary accuracy can be ensured. Effect).

[0041]

As described above, according to the present invention, in the charging / discharging test system according to the first aspect, the charging characteristics and the discharging characteristics of the battery pack are determined at a constant current having a normal current value or a low current value. When measuring, required accuracy can be ensured.

Further, in the charge / discharge test system according to the second aspect, a plurality of current transformer ratios can be secured by one current transformer, whereby a constant current having a normal current value or a low current value can be obtained. When measuring the charging characteristics and discharging characteristics of the battery pack, required accuracy can be ensured.

In the charge / discharge test system according to claims 3 and 4, the current value of the charging current supplied to the battery pack or the current value of the discharging current output from the battery pack is equal to or less than a preset current value. Only when is it possible to switch the current transformer's current transformer ratio, so that the value of the current detection signal output from the current transformer does not exceed a predetermined voltage value, while ensuring the safety of the system When measuring the charging characteristics and the discharging characteristics of the battery pack with a constant current having a normal current value or a low current value, required accuracy can be ensured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a charge / discharge test system according to the present invention.

FIG. 2 is a circuit diagram showing a detailed configuration of the current transformer shown in FIG.

FIG. 3 is a block diagram showing a detailed configuration of a centralized management device shown in FIG.

[Explanation of symbols]

 1: charge / discharge test system 2: switching element 3: diode 4: capacitor 5: rectification / discharge circuit 6: three-phase AC power supply 7: battery pack (device under test) 8: charge / discharge power supply 9: current transformer 10: Voltage measuring device 11: Temperature measuring device 12: Measuring unit 13: Central control device 14: Current transformer main body 15, 16: Primary through winding 17, 18: Relay 17a, 18a: Contact point 19: Magnetic detection circuit 20: Zero current Detection circuit (current-flow ratio switching unit) 21: Keyboard device 22: CPU device (current-current ratio switching unit, charge / discharge characteristic measuring unit) 23: CRT device 24: Interlock circuit (current-current ratio switching unit)

Claims (4)

[Claims] 1. A process for measuring a charging characteristic of the device under test or supplying a discharge current from the device under test by supplying a charging current to the device under test, which is chargeable and dischargeable, to discharge the device under test. In a charge / discharge test system that performs a process of measuring characteristics, when measuring a charge characteristic or a discharge characteristic of the test object, a process of supplying a charge current having a specified current value to the test object, or A charge / discharge power supply unit for performing a process of outputting a discharge current having a specified current value from the device under test; and a current ratio changed according to the specified current ratio, thereby changing the charge current or the discharge current. A current transformer that generates a current detection signal by flowing the current transformer, and a current transformer that switches a current transformer of the current transformer according to a current value of a charge current output from the charge / discharge power supply unit or a discharge current that is absorbed. Switching part and this current ratio Charge-discharge test system based on the current transformer ratio replacement part and the current detection signal and the charge-discharge characteristics measuring unit for measuring a charging characteristic or discharge characteristics of the test object, further comprising a said. 2. The charge / discharge test system according to claim 1, wherein the current transformer has a current transformer body formed of a frame-shaped magnetic material, and a plurality of current transformers wound around the current transformer body. A primary through winding, a relay circuit that switches a combination of the primary through windings according to a specified current transformation ratio, and a current detection having a voltage value according to a magnetic flux generated in the current transformer main body. A charge / discharge test system, comprising: a magnetic detector that generates a signal. 3. The charge / discharge test system according to claim 1, wherein the current-ratio switching unit controls a current value of a charging current supplied to the device under test or a current value of a discharged current to be absorbed. A charge / discharge test system comprising: determining whether a predetermined condition is satisfied; and, when the predetermined condition is satisfied, switching a current ratio of the current transformer. 4. The charge / discharge test system according to claim 1, 2 or 3, wherein the current ratio switching unit detects a current zero of the charge / discharge current, and the current zero detection circuit. An interlock circuit that switches the current transformer ratio only when a low current mode in which charge and discharge are performed at a low current when zero current is detected, and when no zero current is detected, A charge / discharge test system comprising: