JP2012002710A - Current detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly detect a load current of a battery module without arranging an exclusive changeover switch.SOLUTION: A current detection device includes: a battery module; a main relay contact point connected from the battery module to a load circuit; a first current detection circuit for detecting a load current flowing in the battery module; a precharge circuit arranged in parallel with the main relay contact point and having a precharge relay contact point, a precharge resistance and a precision resistance which are serially connected; a control circuit for controlling ON/OFF of the main relay contact point and the precharge relay contact point; a second current detection circuit for detecting voltages at the both ends of the precision resistance and detecting the load current; and a control part connected to the first current detection circuit and the second current detection circuit. The control part corrects the load current detected by the first current detection circuit, based on the load current detected by the second current detection circuit.

Description

  The present invention relates to a current detection device that detects a load current flowing in a battery module of a motor-driven electric device such as an electric vehicle.

  A battery module for running an electric vehicle is composed of a secondary battery such as a lithium ion secondary battery. It is important to accurately calculate the remaining capacity of the secondary battery. If an error occurs in the detection of the remaining capacity, the error is accumulated as the traveling time becomes longer. Accumulated error is due to the fact that the actual remaining capacity of the battery module differs from the calculated remaining capacity, making it difficult to use the battery module in the optimal remaining capacity range, causing overcharge and overdischarge. Become. The battery module can be used for a long life by being charged and discharged within a preferable remaining capacity range, but the electrical performance is remarkably deteriorated due to overcharge and overdischarge, and the life is shortened. Since battery modules for automobiles are extremely expensive, it is important that they can be used for as long as possible.

  The remaining capacity of the battery module is calculated by integrating the current flowing through the battery module. The remaining capacity is calculated by subtracting the integrated value of the discharge current from the integrated value of the charging current while considering the charging efficiency and the discharging efficiency. In order to accurately calculate the remaining capacity, it is necessary to accurately detect the battery module current. By the way, the load current flowing through the battery module is detected by a current sensor. The current sensor is designed so that a large current can be accurately detected. This is because the calculation error of the remaining capacity increases when the detection error of the large current is large.

  A current sensor that can detect a large current accurately makes it difficult to accurately detect a small current. Ideally, it can be detected accurately from minute current to full scale, but it is extremely difficult to detect load current with high accuracy in the entire measurement range. The measurement error of the minute current also adversely affects the calculation of the remaining capacity. This is because the time spent with a small load current is so long that errors accumulate over time.

  In order to eliminate this drawback, an apparatus that detects a battery current by switching between a small current and a large current has been developed (see Patent Document 1). In this apparatus, as shown in FIG. 4, a large current sensor and a minute current sensor are connected in parallel, and are switched by a load current.

  In addition, battery current value measurement in a battery system including a high-voltage battery, a current sensor, and a precharge resistor disposed in the vicinity thereof has been developed (see Patent Document 2). As shown in FIG. 5, this apparatus corrects a current value for measuring an input / output current value of a high-voltage battery by a current sensor with a current value measured based on a resistance value of a precharge resistor. Has been developed

JP-A-10-307563 JP 2009-229405 A

  However, in the conventional configuration in Patent Document 1, it is necessary to provide a dedicated changeover switch in order to switch between the large current sensor and the minute sensor. This changeover switch is very expensive because a large current of several hundreds of A flows and a very high reliability is required. In particular, since it is frequently switched depending on the magnitude of the current, it is necessary to design a very long life while switching a large current. Furthermore, if this switch fails, there is a drawback that the electric vehicle cannot run. Furthermore, since switching is performed according to the magnitude of the current, there is also a disadvantage that the load current is interrupted instantaneously when switching, and smooth rotation of the motor is hindered. This makes smooth running with a motor difficult and also causes a feeling of running to deteriorate.

  In the conventional configuration in Patent Document 2, the value of the current flowing through the precharge resistor is calculated from the resistance value and voltage of the precharge resistor. Therefore, when a high current flows through the precharge resistor, the resistance becomes high temperature and the resistance value changes, and the current value cannot be accurately measured. Further, it is extremely expensive to change the precharge resistor to a highly accurate resistor.

  The present invention has been developed for the purpose of solving such drawbacks. An important object of the present invention is to accurately detect the load current of a battery module without providing a dedicated changeover switch and without causing a change in resistance value due to a temperature change of the resistance when a current flows. The object is to provide a current detection device.

  The current detection device of the present invention includes a battery module, a main relay contact connected from the battery module to a load circuit, a first current detection circuit for detecting a load current flowing through the battery module, and a main relay contact in parallel. Connected precharge relay contact, precharge resistor, precharge circuit with precision resistor, control circuit to control main relay contact and precharge relay contact on / off, and voltage across precision resistor are detected And a control unit connected to the first current detection circuit and the second current detection circuit, wherein the control unit is a load current detected by the second current detection circuit. The load current detected by the first current detection circuit is corrected.

  With this configuration, the measurement error of the current detection circuit due to the flow of the load current can be removed.

  According to the current detection device of the present invention, accurate current detection with a precision resistor is possible, and the detection current of the first current detection circuit can be corrected with the detection current with the precision resistor.

It is a circuit diagram of the current detection apparatus concerning the Example of this invention. It is a circuit diagram of the electric current detection apparatus concerning the other Example of this invention. It is a circuit diagram of the electric current detection apparatus concerning the other Example of this invention. It is a circuit diagram of the conventional electric current detection apparatus. It is a circuit diagram of the other conventional electric current detection apparatus.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows a circuit diagram of an automobile current detection device. The automobile shown in this circuit diagram is configured to drive a battery module 11 for driving a motor by driving a motor via a main relay contact 12. It is connected to a load circuit 14 including a motor. A precharge circuit 21 is connected in parallel with the main relay contact 12. The precharge circuit 21 includes a precharge relay contact 22, a precharge resistor 23, and a precision resistor 24 connected in series, and is a circuit for charging the large-capacitance capacitor 13 connected in parallel to the load circuit 14. .

  The large-capacitance capacitor 13 is a capacitor having an extremely large capacitance of, for example, several thousand μF to several μF, and is always charged. When a large amount of power is supplied to the motor in a short period of time, for example, when the automobile is suddenly accelerated, it is discharged, and serves to supplement the instantaneous output. Therefore, by connecting the large-capacity capacitor 13, the instantaneous maximum output can be increased, and the battery module 11 can be protected by limiting the instantaneous maximum current of the battery module 11 in this state to a small amount. For this reason, the large-capacitance capacitor 13 is connected to the electric vehicle almost without exception.

  An automobile equipped with the large-capacitance capacitor 13 flows a very large charging current at the moment when the main relay contact 12 is turned on. This is because when a completely discharged capacitor is directly connected to the battery module 11, a short-circuit current flows at the moment of connection. In order to limit the peak of this charging current, a precharge circuit 21 is connected in parallel with the main relay contact 12. Further, the large-capacitance capacitor 13 is designed to discharge with a discharge resistance when the ignition switch of the automobile is turned off. This is to prevent an electric shock even if a user or an operator touches it by mistake. For this reason, each time the ignition switch is turned on, the large-capacitance capacitor 13 needs to be charged with a large charging current. A precharge circuit 21 is connected to charge the large capacity capacitor 13 with a limited current.

  When the current detection circuit of the present invention discharges current from the battery module 11 to the load circuit 14 in the main circuit of the main relay contact 12, a current of about 100 to 150 A flows. There are also times when 300 to 400 A is passed as an instantaneous maximum value. Further, when the battery module 11 charges the current from the load circuit 14, a current of about 10 to 15A is passed at a rate of about 0.1C.

  In the current detection circuit of the present invention, when discharging current from the battery module 11 to the large-capacitance capacitor 13 and the load circuit 14 in the precharge circuit 21, a current of about 40 A is passed for several seconds to several tens of seconds. 13 is precharged. The precharge circuit 21 is designed not to be used when the battery module 11 charges the current from the load circuit 14, but when the main relay contact 12 and the precharge relay contact 22 are switched or the large-capacitance capacitor 13 is charged. In this state, when the charging rate of the battery module is low, the current flows in the direction in which the battery module 11 charges the current from the load circuit 14.

The precharge resistor 23 has a resistance value of about 10Ω. Therefore, when a precharge current of about 40 A flows, the power (W) is the product of the square of the precharge current (I) and the precharge resistance (R), that is, 40 ² × 10 = 16000 W The temperature rises and the resistance value changes.

  The precision resistor 24 has excellent temperature characteristics. That is, even when a high current flows, the temperature rise is small and the resistance value is stable. The resistance value of the precision resistor 24 is 1 to 5 mΩ, which is 1/1000 to 1/2000 of the precharge resistor 23. Thereby, even if the high precision resistor 24 is added, there is almost no influence on the precharge current, and the voltage across the precision resistor 24 can be measured on the order of 40 to 200 mV.

For example, assuming that 1 mΩ of 1/1000 of 10Ω of the precharge resistor 23, when a precharge current of about 40A flows, the power (W) is the product of the square of the precharge current (I) and the precision resistance (R), That is, the heating of resistance is suppressed to 40 ² × 0.001 = 1.6 W. Therefore, the precision resistor 24 generates less heat than the precharge resistor 23 and has excellent temperature characteristics, so that it is possible to suppress a temperature rise and a change in resistance value due to current flow.

  Further, the current detection circuit of the present invention detects the load current flowing through the battery module 11 of the electric vehicle by the first current detection circuit 31, and controls the precharge relay contact 22 and the main relay contact 12 to be turned on / off. And a second current detection circuit 32 that detects a load current by detecting a voltage across the precision resistor 24, and a control circuit 34 to which the second current detection circuit 32 and the first current detection circuit 31 are connected. In FIG. 1, the control circuit 34 is included in the control ECU 33. Then, the control circuit 34 corrects the gain of the first current detection circuit 31 based on the measurement result of the second current detection circuit 32.

  The first current detection circuit 31 detects a load current flowing through the battery module 11 in a state where the main relay contact 12 is turned on. The first current detection circuit 31 converts the load current into a voltage and outputs the voltage. For example, the first current detection circuit 31 incorporates, as a current sensor, a Hall element that detects a magnetic flux generated around the lead wire when the load current flows. The built-in operational amplifier which amplifies the signal of this current sensor. An amplifier that amplifies the signal of the current sensor may be externally attached.

  Further, the first current detection circuit 31 shown in FIG. 1 connects the output of the current sensor to the detection circuit. The detection circuit incorporates an amplifier that amplifies the voltage output from the current sensor, or an A / D converter that converts the analog signal that is the output voltage of the current sensor into a digital signal without incorporating the amplifier. The load current is converted into a digital voltage signal and output to the control circuit 34. The first current detection circuit 31 is adjusted so that the load current can be accurately detected in a region where a large current flows.

  The second current detection circuit 32 detects a load current by detecting a voltage generated at both ends of the precision resistor 24. The second current detection circuit 32 detects the load current with the main relay contact 12 turned off and the precharge relay contact 22 turned on. This is because a voltage proportional to the load current is generated at both ends of the precision resistor 24 in this state. The voltage (E) generated at both ends of the precision resistor 24 is the product of the load current (I) and the precision resistor 24 (R), that is, voltage (E) = load current (I) × precharge resistance (R). Become. Since the precision resistor 24 has a constant resistance value, the load current can be detected by detecting the voltage across the precision resistor 24 with the second current detection circuit 32. The second current detection circuit 32 converts a voltage proportional to the detected load current into a digital value and inputs it to the control circuit 34.

  The control ECU 33 controls the main relay and the precharge relay on and off based on the current source from the control circuit 34. When the ignition switch is turned on, the control ECU 33 switches on the precharge relay contact 22 while keeping the main relay contact 12 in the off state. In this state, the battery module 11 charges the large capacity capacitor 13 via the precharge relay contact 22. Thereafter, the control ECU 33 controls the main relay and the precharge relay to be turned on / off with the magnitude of the load current.

  When the load current is large (for example, exceeding 1 A), the main relay contact 12 is turned on to supply power directly from the battery module 11 to the load circuit 14. The control ECU 33 turns on or off the precharge relay contact 22 when turning on the main relay contact 12. At this time, the precharge relay contact 22 may be either on or off. This is because both ends of the precharge circuit 21 are short-circuited via the main relay contact 12. However, it is preferable that the precharge relay contact 22 is turned on while the main relay contact 12 is turned on. This is because when the load current becomes small and the main relay contact 12 is switched off, it is not necessary to switch the precharge relay contact 22 in the on state. Further, even when both the main relay contact 12 and the precharge relay contact 22 are turned on, the load current does not flow through the precharge relay contact 22 but flows only through the main relay contact 12 and power loss due to the precharge resistor 23 occurs. Does not occur.

  When the load current is small (for example, 1 A or less), the control ECU 33 switches the main relay contact 12 off with the precharge relay contact 22 turned on. The control ECU 33 detects the load current with the first current detection circuit 31 and switches the main relay contact 12. However, it is also possible to switch off the main relay contact 12 by detecting that the load current is near 0 by a signal input from the engine controller, that is, an accelerator signal. This is because when the accelerator is not stepped on, it is not necessary to supply power to the load current, so the load current becomes small. Therefore, the control ECU 33 can switch the main relay and the precharge relay on and off with the load current detected by the first current detection circuit 31 or the accelerator signal supplied from the engine controller.

  When the main relay contact 12 is turned off, the load current passes through the precharge circuit 21 without passing through the main relay contact 12 and is supplied to the load circuit 14. Therefore, a voltage proportional to the load current is generated at both ends of the precharge resistor 23 and the precision resistor 24. Then, the voltage across the precision resistor 24 is detected by the second current detection circuit 32 to detect the load current. Since the second current detection circuit 32 measures the current value with the precision resistor 24 having good temperature characteristics, the current value can be accurately detected.

  Furthermore, the current value detected by the second current detection circuit 32 does not necessarily match the current value detected by the first current detection circuit 31. At this time, the control circuit 34 determines that the detection value detected by the second current detection circuit 32 is more accurate, and corrects the gain of the first current detection circuit 31. That is, the control circuit 34 corrects the detection current value of the first current detection circuit 31 with the detection current value of the second current detection circuit 32. In the correction, the zero level of the detection value of the first current detection circuit 31 is corrected. For example, when the detection current detected by the second current detection circuit 32 is 0 mA and 40 mA, and the detection current of the first current detection circuit 31 is 10 mA and 30 mA, the first current detection circuit 31 at 10 mA The detected current value is shifted 10 mA to the minus side, and the gain is corrected to be doubled.

  According to such a configuration, by connecting a precharge resistor and a precision resistor having good temperature characteristics in series to the precharge circuit, it is possible to accurately detect a current with a precision resistor, and the first current detection circuit with a detection current by the precision resistor. The detected current can be corrected.

  In this embodiment, since the direction of discharge from the battery module 11 to the load circuit 14 is considered, when the precharge circuit 21 is turned on, the battery module 11, the precharge resistor 23, the precision resistor 24, The load circuit 14 is arranged in order, but in consideration of the direction of charging from the load circuit 14 to the battery module 11, the load circuit 14, the precharge resistor 23, the precision resistor 24, and the battery module 11 are arranged as shown in FIG. You may arrange them in order. That is, it is considered that the precharge resistor 23 prevents the surge current from flowing through the precision resistor 24.

  In addition, since a circuit that repeats charging and discharging, such as an electric vehicle, flows in both directions, when the precharge circuit 21 is turned on as shown in FIG. 3, the battery module 11 and the precharge resistor 25 are turned on. The precision resistor 24, the precharge resistor 26, and the load circuit 14 may be arranged in this order. In particular, since the discharge from the battery module 11 is 100 to 150 A, the charging current is about 10 A, which is 1/10, so the surge current during charging is also 1/10. For this reason, the influence of the surge current on the precision resistor 24 can be minimized by setting the resistance values of the precharge resistor 25 and the precharge resistor 26 to 9: 1 and 1Ω, respectively.

  In the present embodiment, the control circuit 34 is included in the control ECU 33 in FIG. 1, but the control ECU 33 and the control circuit 34 may be configured separately. In that case, the control ECU 33 and the control circuit 34 may exchange data to perform each control.

  The present invention is useful as a power source for driving automobiles, electric motorcycles, electric playground equipment and the like.

11 Battery Module 12 Main Relay Contact 13 Large Capacitor 14 Load Circuit 21 Precharge Circuit 22 Precharge Relay Contact 23 Precharge Resistor 24 Precision Resistor 25 Precharge Resistor 26 Precharge Resistor 31 First Current Detection Circuit 32 Second Current Detection Circuit 33 Control ECU
34 Control circuit

Claims (3)

A battery module;
A main relay contact connected to the load circuit from the battery module;
A first current detection circuit for detecting a load current flowing through the battery module;
A precharge relay contact connected in series in parallel with the main relay contact; a precharge resistor; and a precharge circuit having a precision resistor;
A control circuit for controlling the main relay contact and the precharge relay contact on and off;
A second current detection circuit for detecting a load current by detecting a voltage across the precision resistor;
A control unit connected to the first current detection circuit and the second current detection circuit;
The control unit corrects the load current detected by the first current detection circuit with the load current detected by the second current detection circuit. The current detection device according to claim 1, wherein the precision resistor is disposed between two precharge resistors. The current detection device according to claim 1, wherein a ratio of a resistance value between the precharge resistor and the precision resistor is 200 to 1000.

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