JP6322123B2 - Current limit circuit - Google Patents

Description

  Embodiments described herein relate generally to a current limiting circuit.

Electric vehicles (EV), hybrid electric vehicles (HEV), and the like are equipped with a high voltage battery such as a lithium ion secondary battery as a power source for driving a high voltage load such as a drive motor. ing.
In the above configuration, a relay is used for the purpose of cutting off the high voltage battery and the high voltage load.

  Further, in the above configuration, a current limiting circuit is provided between the high-voltage battery and the high-voltage load in order to avoid an inrush current when the relay is turned on and prevent failures such as welding of the relay contacts. It is common.

JP 2005-102471 A JP 2010-193588 A

As one aspect of the current limiting circuit, a precharge circuit in which a precharge relay and a current limiting resistor are connected in series is known.
Here, most of the power consumption when the current is limited by the precharge circuit using the current limiting resistor is consumed by the current limiting resistor (electrical energy is converted into thermal energy).

  Therefore, in order to suppress the inrush current of the high-voltage battery, it is necessary to use a current limiting resistor having a large resistance value, and the power consumption at the resistor increases, so that the size of the current limiting resistor has increased.

As another aspect of the current limiting circuit, a precharge circuit that uses a plurality of semiconductor switching elements and performs PWM driving is known.
In such a precharge circuit, since a plurality of semiconductor switching elements are used and PWM driving is performed, noise is generated, the number of parts is increased, and the circuit configuration is complicated.

  The present invention has been made in view of the above, and an object of the present invention is to provide a current limiting circuit that can be miniaturized.

The current limiting circuit according to the embodiment includes a high-potential side main relay and a low-potential side main relay that are interposed between a high-voltage battery and a capacitor that constitutes a high-voltage load , and a low-potential side main relay or a high-potential side. A current limiting resistor connected in parallel to the main relay, a current variable unit connected in series to the current limiting resistor and having a variable current amount based on a current control signal, and a control unit. The current variable unit is configured as a MOSFET or an IGBT. The control unit includes a current detection unit that detects a current flowing through the current limiting resistor, and a current control unit that outputs a current control signal based on a detection result of the current detection unit. The current detection unit detects the voltage between the terminals of the current limiting resistor, and the current control unit detects the maximum current in which the current detection signal and the current flowing through the current limiting resistor are determined with respect to the current limiting resistor during capacitor precharge. A current control signal for increasing the gate voltage of the current variable section is output until it becomes equal to the value, and the current control signal is controlled so that the current flowing through the current limiting resistor becomes constant at the maximum current value, and precharging is performed.

In this case, the current variable part may be attached to a metal housing or a heat sink.

  According to the current limiting circuit of the embodiment, it is possible to reduce the size and reduce the size and to limit the current.

FIG. 1 is a schematic configuration block diagram of a power supply system according to the first embodiment. FIG. 2 is an operation timing chart of the power supply system. FIG. 3 is a configuration explanatory diagram of main circuits of the first embodiment and the conventional example. FIG. 4 is an explanatory diagram of a precharge current waveform in the embodiment and the conventional example. FIG. 5 is an explanatory diagram of calculation of power consumption in the first embodiment. FIG. 6 is an explanatory diagram of calculation of power consumption in the conventional example. FIG. 7 is a schematic configuration block diagram of the power supply system of the second embodiment.

Next, embodiments will be described with reference to the drawings.
In the following description, a power supply system mounted on an electric vehicle is taken as an example.
[1] First Embodiment FIG. 1 is a schematic configuration block diagram of a power supply system according to a first embodiment.
The power supply system 10 includes a high voltage battery 11 in which a plurality of battery cells are connected in series, an external ECU 12 mounted on the vehicle, and a high voltage junction box 13 that controls power supply of the high voltage battery 11 under the control of the external ECU 12. And a high voltage load 14 that is operated by the power of the high voltage battery 11 supplied via the high voltage junction box 13.

In the above configuration, the high voltage battery 11 includes, for example, a lithium ion battery cell as the battery cell.
The external ECU 12 outputs a high potential side main relay state signal CP, a precharge relay state signal PCS, and a low potential side main relay state signal CM for controlling the high voltage junction box 13.

The high voltage junction box 13 is inserted into the high potential side current flow path LP, and one end is connected to the high potential side terminal (positive terminal) of the high voltage battery 11 and the other end is connected to the high voltage load 14. The low potential side main relay 21 </ b> P is inserted into the low potential side current flow path LM, one end is connected to the low potential side terminal (negative electrode terminal) of the high voltage battery 11, and the other end is connected to the high voltage load 14. A potential-side main relay 21M, configured as an N-channel MOSFET, connected in parallel to the low-potential side main relay 21M, and functions as a current variable unit, in parallel with the low-potential side main relay 21M, and The current limiting resistor 23 connected in series to the charge relay 22 and the precharge current I flowing through the precharge relay 22 and the current limiting resistor 23 are monitored, A control unit 24 for controlling the Yaji current I constant, and a.
Here, the high voltage junction box 13 functions as a current limiting circuit.
In addition, since an N-channel MOSFET is used as the precharge relay 22, the current limiting capability can be taken together with the current limiting resistor 23, and the current limiting resistor 23 can be reliably reduced in size.

The control unit 24 outputs a gate control signal GC based on a current limit reference signal Vref and a current detection signal VR corresponding to a current limit value Ilim described later, and the gate voltage of the N-channel MOSFET constituting the precharge relay 22 A gate control circuit 31 that controls the precharge current I to be constant, and a current detection circuit 32 that measures the voltage across the current limiting resistor 23 corresponding to the current I and outputs a current detection signal VR. I have.
Here, the gate control signal GC functions as a current control signal, the gate control circuit 31 functions as a current control unit, and the current detection circuit 32 functions as a current detection unit.

First, the operation of the power supply system 10 during normal operation will be described.
FIG. 2 is an operation timing chart of the power supply system. In FIG. 2, the high-potential side main relay 21 </ b> P is represented as a main relay (+), and the low-potential side main relay 21 </ b> M is represented as a main relay (−) (hereinafter the same in each figure).

In the initial state, the high potential side main relay 21P, the low potential side main relay 21M, and the precharge relay 22 are all open (off state).
At time t0, when a high potential side main relay state signal CP for closing the high potential side main relay 21P from the external ECU 12 is input (ON state), the contact driving coil of the high potential side main relay 21P is applied to the contact driving coil. A current flows, and the high potential side main relay 21P enters a closed state (on state). Thereby, the power supply system 10 shifts to a system-on state (operating state).

  Subsequently, when a precharge relay state signal PCS for closing the precharge relay 22 (ON state) is input from the external ECU 12 at time t1, the gate control circuit 31 of the control unit 24 is changed to FIG. The precharge relay 22 is configured until the current limit reference signal Vref corresponding to the current limit value Ilim which is the maximum current flowing through the current limit resistor 23 shown in FIG. The gate voltage of the N-channel MOSFET is increased.

  Thus, the precharge of the capacitor (capacitance) CX constituting the high voltage load 14 from the high voltage battery 11 via the high potential side main relay 21P is performed in a state where the precharge current I is controlled to be constant.

  Thereafter, as the precharge of the capacitor CX proceeds, the precharge current I gradually decreases, and the external ECU 12 closes the low potential side main relay 21M (ON) at time t2 when the precharge is estimated to be almost completed. The low potential side main relay state signal CM for setting the state) is output.

  As a result, a current flows through the contact driving coil of the low potential side main relay 21M, and the low potential side main relay 21M enters a closed state (on state).

  As a result, the electric power from the high voltage battery 11 flows through the high potential side main relay 21P → high voltage load → low potential side main relay 21M and is supplied to the high voltage load 14 so that the high voltage load 14 can shift to normal operation. It becomes.

  Then, at time t3 when a predetermined waiting time for disconnecting the precharge relay 22 has elapsed from time t2, the precharge relay state signal PCS (= “L”) for turning the precharge relay 22 open (off state) from the external ECU 12 When “level” is input, the precharge relay 22 shifts to an open state (off state).

  Thereafter, at time t4 when it is no longer necessary to supply power to the high voltage load 14, a low potential side main relay state signal CM for opening the low potential side main relay 21M (off state) is input from the external ECU 12. Then, the current to the contact driving coil of the low-potential side main relay 21M is cut off, and the low-potential side main relay 21M enters an open state (off state). Thereby, the power supply system 10 shifts to a system off state (operating state).

  When a high-potential main relay state signal CP for opening the high-potential side main relay 21P from the external ECU 12 at the time t5 when a further time has elapsed from the time t4 is input, The current to the contact driving coil of the relay 21P is cut off, and the high potential side main relay 21P enters an open state (off state) and shifts to an initial state.

Next, the effect of the embodiment will be described in comparison with a conventional example.
FIG. 3 is a configuration explanatory diagram of main circuits of the first embodiment and the conventional example.
As shown in FIG. 3, when the current limiting resistor 23 is configured to limit the current using the resistance value of the current limiting resistor as in the related art, the resistance value Rp of the current limiting resistor 23 is the same as that of the embodiment. It is larger than the resistance value R of the current limiting resistor 23.
Rp> R

  In a configuration in which current limiting is performed using the resistance value of the current limiting resistor as in the prior art, the precharge relay 22 functions as a switch and only performs an on / off operation.

FIG. 4 is an explanatory diagram of a precharge current waveform in the embodiment and the conventional example.
As shown in FIG. 4, in the case where the current is limited by using the resistance value of the current limiting resistor as in the prior art, as shown by the broken line in FIG. 4, at the moment when the precharge relay 22 is turned on. The current value becomes the largest (= current value corresponding to the current limit value Ilim), and thereafter, the current gradually decreases with time.

On the other hand, in the method in which the current is limited by the N-channel MOSFET constituting the precharge relay 22 as in the first embodiment, the current value detected by the current detection circuit corresponds to the current limit value Ilim. Since constant current control is performed so as to maintain the value, a current value corresponding to the current limit value Ilim flows for a long time as shown by a solid line in FIG.
Therefore, it can be seen that according to the system in which the current is limited by the N-channel MOSFET constituting the precharge relay 22 as in the first embodiment, the precharge of the capacitor CX can be completed in a short time compared to the conventional example. .

Here, the amount of power consumed by the current limiting method in the embodiment and the conventional example is examined.
FIG. 5 is an explanatory diagram of calculation of power consumption in the first embodiment.
First, the power consumption P1 _R of the current limiting resistor 23 in the constant current period t is expressed by equation (1).
P1 _R = I ² R · t / T (1)

Further, the voltage Vc of the capacitor CX in the constant current period t when the capacitance of the capacitor CX is C is expressed by the equation (2).
Vc = I · t / C (2)

Further, the voltage Vc of the capacitor CX in the constant current period t is also expressed by equation (3), where the voltage of the high voltage battery 11 is VB.
Vc = VB-I · R (3)
Therefore, when the constant current period t is obtained based on the equations (2) and (3), the following equation is obtained.
t = C · (VB−I · R) / I (4)

Therefore, from formulas (1) and (4), the power consumption P1 _R of the current limiting resistor 23 in the constant current period t is expressed by formula (5).
P1 _R = I ² R · (C / T) · {(VB-I · R) / I} (5)

Further, the power consumption P2 _R in the transition period after the constant current time period t is expressed by the equation (6).
^{_{P2 R = I 2 R · (}} C · R / T) ... (6)

Therefore, total P _R of power consumption in the first embodiment, the following equation (7).
P _R = P1 _R + P2 _R
= I ² R · (C / T) · {(VB−I · R) / I + R} (7)

Here, for comparison with the conventional example, when the equation (7) is converted using the resistance value Rp,
VB / I = Rp
Since it is, the sum P _R of power consumption in the embodiment, and thus represented by the equation (8).
P _R = I ² R · (C · Rp / T) (8)

Next, the power consumption in the conventional example is calculated.
FIG. 6 is an explanatory diagram of calculation of power consumption in the conventional example.
When the resistance value of the current limiting resistor 23 (see FIG. 3) in the conventional example is Rp and the on-resistance of the N-channel MOSFET constituting the precharge relay 22 is Ron, Rp >> Ron.
Therefore, the power consumption _PRp of the current limiting resistor 23 is expressed by equation (9).
P _Rp = I ² Rp · (C · Rp / T) (9)

And from (8) Formula and (9) Formula, ratio of the power consumption of 1st Embodiment and the power consumption in a prior art example is represented by (10) Formula.
P _R / P _Rp = R / Rp <1 (10)

  Therefore, according to the first embodiment, the power consumption in the current limiting resistor 23 can be reduced by the ratio of R / Rp as compared with the conventional example in which the current during precharging is limited by the resistance value of the current limiting resistor. it can.

Further, the power consumption P _Ron of the N-channel MOSFET constituting the precharge relay 22 in the conventional example is expressed by the equation (11).
P _Ron = I ² Ron · (C · Rp / T) (11)

Here, since the total power consumption in the entire current limiting circuit is equal between the current limiting in the conventional example and the current limiting in the first embodiment, the N channel constituting the precharge relay 22 of the first embodiment. MOSFET power _{P FET} of becomes as (12).
_{P FET = P Rp + P Ron} -P R
= I ² · (C · Rp / T) · (Rp−R + Ron) (12)

Therefore, there is a need to selected to satisfy the power consumption _{P FET} of an N-channel MOSFET constituting the pre-charge relay 22 of the first embodiment.

As described above, according to the first embodiment, all the power consumed by the current limiting resistor in the past is distributed to the N-channel MOSFET and the current limiting resistor 23 constituting the precharge relay 22. Thus, the resistance value of the current limiting resistor 23 can be set low, and the size can be reduced.
Further, since the precharge relay 22 is composed of an N-channel MOSFET as a semiconductor element, the power consumption can be reduced and the high voltage junction box 13 as a current limiting circuit can be miniaturized.

Furthermore, the power consumption of the precharge relay 22 can be further increased by attaching the N-channel MOSFET constituting the precharge relay 22 to a metal housing or a heat sink, and the current limiting resistance can be further increased. 23 can be reduced in size.
Further, by using the current limiting resistor 23 as a current detection resistor for detecting the precharge current I flowing through the precharge relay 22, further increase in components can be suppressed and the high voltage junction box 13 can be downsized.

[2] Second Embodiment The first embodiment is an example in the case where a current detection circuit for detecting a current to a high voltage load from the high voltage battery 11 is not provided. However, in the second embodiment, In this embodiment, a current detection circuit for detecting a current from the high voltage battery 11 to the high voltage load 14 is provided, and the current at the time of precharging can be detected.

FIG. 7 is a schematic configuration block diagram of the power supply system of the second embodiment.
In FIG. 7, the same parts as those in FIG. 1 are denoted by the same reference numerals.
The power supply system 10A of the second embodiment of FIG. 7 is different from the power supply system 10 of the first embodiment of FIG. 1 in that the current limiting resistor 23 is eliminated and the current limit during precharge is limited by the precharge relay 22 alone. In addition, the current sensor 41 for detecting the current flowing through the high potential side current flow path LP is connected to the current detection circuit 32.

  According to the second embodiment, the amount of precharge current flowing through the high potential side current flow path LP during precharge is detected by the current sensor 41, and the precharge relay 22 is set so that the precharge current becomes a constant current value. It is a point that controls.

About operation | movement, after detecting an electric current with the current sensor 41, it is the same as that of 1st Embodiment.
According to the second embodiment, in addition to the same effects as those of the first embodiment, it is not necessary to use a current limiting resistor at all. Therefore, the device cost can be further reduced and the size can be reduced.

  In each embodiment, the precharge relay and the current limiting resistor are arranged in parallel to the low potential side main relay, but the same effect can be obtained even if arranged in parallel to the high potential side main relay. In this case, in the timing chart shown in FIG. 2, the timings of the high potential side main relay 21P and the low potential side main relay 21M are reversed.

[3] Effects of Embodiments As described above, according to each embodiment, current limiting at the time of precharging is performed by fully utilizing the performance of the N-channel MOSFET (semiconductor element) constituting the precharge relay 22. Since the power consumption of the resistor can be reduced or eliminated, the installation space for the current limiting resistor 23 can be reduced by reducing the size of the current limiting resistor 23 or eliminating the current limiting resistor 23. The entire limiting circuit can be reduced in size.

Further, when the current limiting resistor 23 is used, it can be used as a current detecting resistor, and the installation space and the number of parts of the current detecting circuit can be reduced.
As a result, it is possible to provide a current limiting circuit that is low in manufacturing cost and can be downsized.

  As described above, the present invention has been described based on the embodiments. However, these embodiments are exemplifications, and various modifications can be made to the respective components and combinations thereof, and such modifications are also included in the present invention. Those skilled in the art will appreciate that it is within the scope.

  In the above description, a MOSFET is used as the precharge relay 22, but other semiconductor elements such as an IGBT (Insulated Gate Bipolar Transistor) may be used.

10, 10A Power supply system 11 High voltage battery 12 External ECU
13 High Voltage Junction Box 14 High Voltage Load 21M Low Potential Main Relay 21P High Potential Main Relay 22 Precharge Relay (Current Variable Unit)
23 current limiting resistor 24 control unit 31 gate control circuit (current control unit)
32 Current detection circuit (current detection unit)
41 Current sensor (current detector)
CM Low-potential side main relay status signal CP High-potential side main relay status signal CX Capacitor GC Gate control signal (current control signal)
I precharge current Ilim current limit value LM low potential side current flow path LP high potential side current flow path MOSFET N channel PCS precharge relay state signal R resistance value Rp resistance value VR current detection signal Vc voltage Vref current limit reference signal t fixed Current period

Claims (2)

A high-potential side main relay and a low-potential side main relay inserted between a high-voltage battery and a capacitor constituting a high-voltage load;
A current limiting resistor connected in parallel with the low potential side main relay or the high potential side main relay;
A current variable unit connected in series to the current limiting resistor and having a variable current amount based on a current control signal;
A control unit;
Equipped with a,
The current variable unit is configured as a MOSFET or IGBT,
The controller is
A current detector for detecting a current flowing through the current limiting resistor;
A current control unit that outputs the current control signal based on a detection result of the current detection unit;
Including
The current detection unit detects a voltage between terminals of the current limiting resistor,
The current control unit is configured to increase the gate voltage of the current variable unit until the current flowing through the current limiting resistor becomes equal to a maximum current value determined for the current limiting resistor in precharging the capacitor. A current limiting circuit that outputs the control signal and performs the precharge by controlling the current control signal so that a current flowing through the current limiting resistor is constant at the maximum current value .   The current limiting circuit according to claim 1, wherein the current variable portion is attached to a metal casing or a heat sink.

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