JP5301516B2 - Vehicle current limiting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when a high voltage power supply is combined with a motor generator of a rectangular wave drive system, a partial load operating time is increased in intermediate rotation and low to intermediate load operation regions, leading to decline in efficiency and increase in surge energy generated when a switching element is turned off, causing damage on the element. <P>SOLUTION: A vehicular current limiting device 1 having switching means 4 is arranged between power storage means 2 and a motor generator 3. When operation detection means 60 detects that the motor generator 3 performs electric motor operation, the switching means 4 is controlled by current control means 9, so that an ON duty ratio of PWM control with respect to the switching means 4 is set to be less than 100% when a revolution speed of the motor generator 3 is within a predetermined range and that the ON duty ratio is set to be 100% in other cases, based on voltage of the power storage means 2 and the revolution speed of the motor generator 3. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a vehicle current limiting device that limits a driving current when driving a motor generator of a rectangular wave driving system used in, for example, a hybrid vehicle.

As a conventional motor generator, a field winding type synchronous generator motor having a simple configuration in which a switching element of an inverter is driven in a rectangular wave without using an armature current detection means or a large-capacity smoothing capacitor has been proposed. (For example, refer to Patent Document 1).
In addition, a main power source and a sub power source are connected by a first power supply circuit having a DC / DC converter and a second power supply circuit having a switch, so that regenerative energy during vehicle deceleration can be efficiently recovered. There has been proposed a vehicle power supply system with improved reliability capable of supplying a stable voltage to an electric load (for example, see Patent Document 2).

JP 2007-159353 (pages 4-7, FIGS. 1-7) Japanese Patent Laying-Open No. 2004-328988 (first page, FIG. 1)

  Combining the power supply system as in Patent Document 2 with the rectangular wave drive type motor generator as in Patent Document 1 allows a large amount of current to flow through the motor, resulting in a large driving torque, rapid engine start-up, and high-speed rotation range. It is conceivable that torque assist can be absorbed at the same time and that regenerative energy can be absorbed. However, high power supply voltage is required only for low-speed rotation such as engine start and high-load, high-speed rotation and high-load drive, etc. In this operating range, more current flows than necessary, and the partial load operation time, such as shifting the inverter switching phase in order to suppress the drive torque, increases the motor generator operating efficiency, and the inverter switching element is turned off. Since the surge energy generated sometimes increases, there is a problem that the possibility that the switching element is broken increases.

  The present invention has been made in view of the above-described problems. When a high-voltage power supply and a rectangular-wave drive type motor generator are combined, the motor generator part in medium-speed rotation or low-medium load operation An object of the present invention is to provide a vehicle current limiting device that can shorten the load operation time and improve the operation efficiency.

A vehicle current limiting device according to the present invention is a vehicle current limiting device in which a power storage means is connected to an input end and a rectangular wave drive type motor generator is connected to an output end, from the input end to the output end. Switching means for energizing or interrupting the current, and reflux means connected to a connection point between the switching means and the output terminal, and for allowing the reflux current to flow toward the motor generator when the switching means is interrupting the current Voltage measuring means for measuring the voltage of the power storage means, rotation speed detection means for detecting the rotation speed of the motor generator, and operation detection means for detecting that the operation of the motor generator is motor operation. Based on the detection result of the operation detection means, when the motor generator is in electric motor operation, the voltage of the power storage means, and the motor Based on the rotational speed of Enereta is in the rotational speed is equal to or more than the first predetermined value, and the rotational speed of the medium speed rotational region is less than a second predetermined value greater than the first predetermined value Within the range, the duty ratio of PWM control for the switching means (which means the so-called ON duty ratio, hereinafter, the duty ratio is used in the same meaning as the ON duty ratio) is set to less than 100%, otherwise Comprises current control means for setting the duty ratio to 100%.

In the vehicle current limiting device of the present invention, when the operation of the motor generator is motor operation, the rotational speed is equal to or greater than a first predetermined value based on the voltage of the power storage means and the rotational speed of the motor generator . In addition, the duty ratio of the PWM control for the switching means is set to less than 100% within the range of the medium speed rotation region where the rotation speed is equal to or less than the second predetermined value larger than the first predetermined value , and otherwise In this case, control is performed so that the duty ratio is set to 100%. Therefore, in the middle speed rotation region of the motor generator, the duty ratio of PWM control is reduced to reduce the supply current to the motor generator, thereby reducing the motor The partial load operation time of the generator can be shortened, and the operation efficiency of the motor generator can be improved.

1 is a block diagram showing a configuration of a vehicle current limiting device according to Embodiment 1 of the present invention. The flowchart explaining operation | movement of the electric current control means shown by FIG. The figure which shows the relationship between the voltage Vin of the electrical storage means used when setting PWM ON Duty ratio in Embodiment 1, and PWM ON Duty ratio. The figure which shows the relationship between the rotation speed Nmg of the motor generator used when setting PWM ON Duty ratio in Embodiment 1, and the voltage Vin of an electrical storage means. The block diagram which shows the structure of the electric current limiting apparatus for vehicles which concerns on Embodiment 2 of this invention. 6 is a flowchart for explaining the operation of the current control means shown in FIG. The flowchart explaining the modification of operation | movement of the current control means shown by FIG. The figure which shows the relationship between the voltage Vin of the electrical storage means used when setting PWM ON Duty ratio in Embodiment 2, and PWM ON Duty ratio. The figure which shows the relationship between target drive torque command value Tmg used when setting PWM ON Duty ratio in Embodiment 2, and PWM ON Duty ratio. The figure which shows the method of setting PWM ON Duty using the rotation speed Nmg of a motor generator, the voltage Vin of an electrical storage means, and also target drive torque command value Tmg in Embodiment 2. FIG. The block diagram which shows the structure of the electric current limiting apparatus for vehicles which concerns on Embodiment 3, 4 of this invention. FIG. 6 is a diagram for explaining an example of fluctuations in current flowing to a motor generator when the switching of the current limiting device of the vehicle current limiting device and the change in the target drive torque command value from the host ECU are at the same time. It is a reference diagram in the form 4. The figure explaining operation | movement of the vehicle electric current limiting apparatus which concerns on Embodiment 4 of this invention.

Embodiment 1 FIG.
Hereinafter, the vehicle current limiting device according to Embodiment 1 of the present invention will be described with reference to FIGS. In addition, the same code | symbol in each figure shall show the same part or an equivalent part. As shown in the block diagram of FIG. 1, the vehicle current limiting device 1 is provided so that the high potential side of the power storage means 2 is connected to the input terminal Tin and the high potential side of the motor generator 3 is connected to the output terminal Tout. It is done. The vehicle current limiting device 1 includes a switching means 4 for energizing or interrupting a current from the input terminal Tin to the output terminal Tout, and a return current toward the motor generator 3 when the switching means 4 is interrupting the current. The recirculation means 5 that flows through, the current detection means 6 that detects the current flowing from the output end Tout to the motor generator 3, the rotation speed detection means 7 that detects the rotation speed of the motor generator 3, and the voltage of the power storage means 2. Based on the voltage measuring means 8 for measuring and the voltage measured by the voltage measuring means 8 and the rotational speed detected by the rotational speed detecting means 7, a current control means 9 for PWM controlling the switching means 4 is provided.

  As the power storage means 2, for example, a lead storage battery (battery), a lithium ion battery, an electric double layer capacitor or the like generally used as a power source for automobiles can be used without any particular limitation. As the switching means 4, for example, an IGBT or a P-type MOSFET can be used. The reflux means 5 can be a diode, an N-type MOSFET, or the like. When an N-type MOSFET is used, loss during return may be reduced by performing synchronous rectification during current return.

  The current detection means 6 is configured as one aspect of the operation detection means 60 that can detect that the operation of the motor generator 3 is an electric motor operation. As a specific example of the current detection means 6, for example, DC A direct current sensor such as -CT is used. Further, the rotation speed detection means 7 may be any method such as a method of obtaining from communication information with the motor generator 3 in addition to sensors such as an encoder and a resolver. The voltage measuring means 8 can be appropriately selected from various known means such as a method in which the voltage across the power storage means 2 is divided by resistance and input to the A / D converter of the microcomputer for reading.

Next, the operation of the first embodiment configured as described above will be described. First, the operation of the current control means 9 in FIG. 1 will be described using the flowchart shown in FIG.
First, in step S100, the current value measured by the current detection means 6 is acquired. The current value is given a positive or negative sign depending on the direction of current flow. In this example, the current direction when the motor generator 3 is rotationally driven using the power of the power storage means 2 is positive. The flow in the opposite direction is negative.

  In step S101, the measured current value is compared with a predetermined current value set in advance, and if the measured current value is equal to or greater than the predetermined value (when YES), it is determined that current limitation is necessary, and step S103 is performed. Then, as will be described in detail later, a duty ratio for PWM control of the switching means 4 is set and current limiting processing is performed. On the other hand, if the measured current value is less than the predetermined value (when NO), it is determined that there is no need to limit the current, and in step S102, the ON duty ratio of the PWM control of the switching means 4 is set to 100% and energization is performed. to continue. Here, the predetermined current value is set to, for example, a rated current value that flows in the field coil winding of the motor generator 3, and if the current value is equal to or greater than the rated current value, a current also flows in the armature coil winding of the motor generator 3. It is determined that the motor generator 3 is driven.

  In step S103, in the current limiting process, first, the rotational speed Nmg of the motor generator 3 is acquired from the rotational speed detection means 7. Subsequently, in step S <b> 104, the voltage Vin of the power storage unit 2 is acquired from the voltage measurement unit 8. In step S105, the PWM control ON duty ratio is calculated according to a preset function f (Vin, Nmg) based on the rotation speed Nmg of the motor generator 3 and the voltage Vin of the power storage means 2. As the function f (Vin, Nmg), for example, the relationship between the voltage Vin of the power storage means 2 and the ON duty ratio of PWM control is first set as shown in FIG. In addition, the ON duty ratio of the PWM control is set by adding a rotational speed constraint condition as shown in the following equation 1, for example.

if 2,000 [r / min] ≦ Nmg ≦ 6,000 [r / min]
then ON Duty ratio [%] = − 5 × Vin + 150
else ON Duty Ratio [%] = 100 (Expression 1)

  When the condition is set as shown in Equation 1, the PWM speed is increased as the rotational speed Nmg is higher in the middle speed range of 2000 to 6000 r / min in this example as shown in FIG. Since the ON duty ratio of the motor generator 3 is reduced, the supply current to the motor generator 3 is limited by a set amount, and the motor generator 3 has a partial load in the medium speed rotation region regardless of the influence of the fluctuation of the voltage Vin of the power storage means 2. The operation time is shortened.

  Note that the PWM control carrier frequency is set higher than the cutoff frequency of the filter of a circuit (not shown) for monitoring the input voltage from the power supply in the motor generator 3, so that the chopping waveform of the voltage input to the motor generator 3 is obtained. As a result, the input voltage to the motor generator 3 is apparently reduced, and the motor generator 3 is equivalent to the one in which the input voltage is reduced, and the full load operation is performed so as to ensure the driving torque. The upper limit of the carrier frequency of the PWM control in the vehicle current limiting device 1 is set so as not to exceed the limit of the stable operation in consideration of the loss in the switching means 4.

  On the other hand, when the motor generator 3 is operating as a generator, the sign of the current detected by the current detection means 6 is negative, and the current measured value in step S101 in FIG. 2 is less than the predetermined current value. The result is NO, and in step S102, the PWM ON Duty ratio of the switching means 4 is set to 100%, that is, energization continues, and the power generation operation in which the current flows from the motor generator 3 to the power storage means 2 is not hindered.

  As described above, according to the first embodiment, when the current detection unit 6 as the operation detection unit 60 detects the motor operation of the motor generator 3, the current control unit 9 controls the voltage Vin of the power storage unit 2. Based on the rotational speed Nmg of the motor generator 3, the ON duty ratio of the PWM control for the switching means 4 is set to less than 100% when the rotational speed is within a predetermined range, and otherwise, the ON duty is set. Since the ratio is controlled so as to be 100%, the motor generator 3 is controlled at a medium speed rotation range of 2000 to 6000 r / min, by reducing the duty ratio of PWM control and reducing the supply current to the rotating electrical machine. The partial load operation time of the generator 3 can be shortened, and the operation efficiency of the motor generator 3 can be improved.

  Further, since current limiting is performed by a switching method, there is an advantage that heat generation is less than current limiting by a resistor. Further, when the motor is driven in a region other than the medium-speed rotation region and during power generation, the ON duty ratio of the switching means 4 is set to 100%, so that the loss in the vehicle current limiting device 1 is minimized and the motor generator 3 is driven / Does not interfere with power generation operation. Moreover, the operation efficiency during power generation is not impaired.

  In addition, by adding a positive or negative sign to the detection data of the current detection means 6 according to the direction in which the current flows, control according to driving / power generation of the motor generator 3 can be performed with one control program. Therefore, there is no need to change the control program, and the program can be simplified and the ROM capacity can be reduced. In addition, since the motor generator 3 is a rectangular wave drive system, it is not necessary to provide a smoothing means between the switching means 4 and the motor generator 3, and the open control current can be limited with a simple configuration.

Embodiment 2. FIG.
FIG. 5 is a block diagram showing a configuration of the vehicle current limiting device according to Embodiment 2 of the present invention. In the second embodiment, as the operation detection means 60 that can detect that the operation of the motor generator 3 is an electric motor operation, instead of the current detection means 6 in the first embodiment, the host ECU 20 or the motor generator 3 The communication means 10 communicating with the communication means 10 can be used to detect from the information contained in the communication means 10 that the operation of the motor generator 3 is an electric motor operation. The information of Nmg is also acquired and the ON duty ratio of PWM control is calculated. That is, the upper ECU 20 or the communication means 10 communicating with the motor generator 3 plays the role of the operation detection means 60 and also plays the role of the rotation speed detection means 7.

  The host ECU 20 is an electric control unit using a microcomputer that controls various devices for automobiles, for example, and includes the motor generator 3 as a control target or a link target and uses the communication means 10. It can be used without limitation. The host ECU 20 may be configured to be included in, for example, an engine control unit using a microcomputer for controlling an automobile engine. Other configurations are the same as those of the first embodiment. Details will be described below.

  As a method of realizing the communication means 10, for example, a communication protocol such as CAN (controller area network) or LIN (local interconnect network) used for data transfer between interconnected in-vehicle devices or serial communication is used. The method used or a Hi / Lo binary signal may be used. Further, the current control unit 9 calculates the ON duty ratio of the PWM control of the switching unit 4 based on the communication information obtained from the communication unit 10, and controls the switching unit 4. The operation will be described below with reference to the flowcharts shown in FIGS. 6 is a flowchart for explaining the operation of the current control means in the second embodiment, and FIG. 7 is a flowchart for explaining a modification thereof.

  First, in step S200 of FIG. 6, the communication information received by the communication unit 10 is acquired. In step S201, a drive command transmitted from the host ECU 20 to the motor generator 3 included in the communication information is extracted. If a drive command is issued (YES), that is, the operation of the motor generator is a motor operation. In this case, the process proceeds to step S203, and a duty ratio for PWM control of the switching means 4 is set and current limiting processing is performed as will be described later. On the other hand, if the drive command has not been issued (NO), it is determined that there is no need to limit the current, and in step S202, the ON duty ratio of the PWM control of the switching means 4 is set to 100% and the energization is continued.

  In step S203, in the current limiting process, first, the rotational speed information of the motor generator 3 is acquired from the communication information received by the communication means 10. In the second embodiment shown in the flowchart of FIG. 6, as in the first embodiment, the PWM control ON duty is determined in step 205 based on the rotation speed Nmg obtained in step S203 and the voltage Vin obtained in step S204. Calculate the ratio.

  On the other hand, in the modification of the second embodiment shown in FIG. 7, steps S300 to S304 are the same as S200 to S204 in the flowchart of FIG. After acquiring the voltage Vin of the power storage means 2 in step S304, the target drive torque command value Tmg is extracted from the communication information received by the communication means 10 in step S305, and the rotation speed obtained in step S303 in step S306. Based on Nmg, voltage Vin obtained from step S304, and target drive torque command value Tmg obtained from step S304, the PWM control ON duty ratio is calculated according to a preset function g (Vin, Nmg, Tmg). To do.

As the function g (Vin, Nmg, Tmg), for example, first, the relationship between the voltage Vin of the power storage means 2 and the PWM ON duty is set as shown in FIG. 8, and the relationship between the target drive torque command value Tmg and the PWM ON duty is illustrated. Set as in 9. 8 is a diagram showing the relationship between the voltage Vin of the power storage means 2 and the PWM ON duty ratio used when setting the PWM ON duty ratio in the second embodiment, and FIG. 9 is used when setting the PWM ON duty ratio. It is a figure which shows the relationship between target drive torque command value Tmg and PWM ON Duty ratio.
By adding a constraint on the rotational speed of the motor generator 3 to the settings shown in FIGS. 8 and 9, the PWM ON Duty ratio can be set as shown in Equation 3 below.

if 2,000 [r / min] ≦ Nmg ≦ 6,000 [r / min]
then ON Duty ratio [%] = − 2.5 × Vin + 75 + Tmg
else ON Duty Ratio [%] = 100 (Equation 3)
Here, the maximum value of the PWM ON Duty ratio of each of the voltage Vin of the power storage means 2 and the target drive torque command value Tmg is set to be 100%, and the ratio of the maximum value is changed. , You can adjust the weight.

  In the modification of the second embodiment, the ON duty ratio is determined as shown in Equation 3, so that the rotational speed of the motor generator 3 is 2000 to 6000 r / min in the medium speed rotation region as shown in FIG. In the motor generator 3, the higher the voltage Vin of the power storage means 2 or the smaller the target drive torque command value Tmg, the smaller the ON duty ratio of the PWM control. Therefore, in the motor generator 3, the voltage Vin of the power storage means 2 and the target drive torque command Regardless of the influence of the fluctuation of the value Tmg, the partial load operation time at the time of medium speed rotation and low / medium load is shortened.

  As described above, according to the second embodiment, the communication control unit 10 that communicates with the host ECU 20 and the motor generator 3 is used as the operation detection unit, and the current control unit 9 is connected to the motor generator 3 from the host ECU 20 by the communication unit 10. When it is determined that the motor generator 3 is operated as an electric motor when the drive command for the motor generator 3 is received, the partial load operation time of the motor generator 3 can be shortened as in the first embodiment. The operating efficiency of the motor generator 3 can be improved. Further, since the rotation speed of the motor generator 3 included in the information received by the communication means 10 is used as the rotation speed detection means, the configuration can be simplified.

  Furthermore, according to the modification of the second embodiment, since the target drive torque command value Tmg is added to the parameter for setting the ON duty ratio of the PWM control in the vehicle current limiting device 1, In the operation of low and medium loads, the partial duty operation time of the motor generator 3 can be shortened by reducing the ON duty ratio of the PWM control and reducing the supply current to the motor generator 3 in the electric motor operation. The operating efficiency of the motor generator 3 can be improved. In addition, the increased number of parameters enables finer and more efficient control.

Embodiment 3 FIG.
FIG. 11 is a block diagram showing a configuration of a vehicle current limiting device according to Embodiment 3 of the present invention and Embodiment 4 described later. In the third embodiment, when the drive start timing of the motor generator 3 is earlier than the current limit start timing in the vehicle current limiting device 1 due to communication delay, the current for the vehicle is immediately after the motor generator 3 starts driving. Since the current is limited by the limiting device, the drive control of the motor generator 3 may not follow and may diverge, so that the problem due to the communication delay is solved.

  As shown in FIG. 11, the vehicle current limiting device 1 according to the third embodiment is different from the second embodiment in the position of the communication means 10 in the communication path, and the communication means 10 is different from the motor generator 3. It arrange | positions so that it may not communicate directly with high-order ECU20, and it is made to function as a master communication apparatus of the motor generator 3. FIG. In the communication means 10, when the target drive torque command value is received from the host ECU 20, the current control means 9 sets the duty ratio of the PWM control, performs the PWM control of the switching means 4, and then sends the target drive to the motor generator 3. A torque command value is transmitted. Other configurations are the same as those of the second embodiment.

  In the third embodiment configured as described above, the communication means 10 is arranged so that the host ECU 20 and the motor generator 3 do not communicate directly, and when the target drive torque command value Tmg is received from the host ECU 20, the vehicle After the PWM control is performed by the current limiting device 1, the target drive torque command value Tmg is transmitted to the motor generator 3, and the motor generator 3 starts driving. Therefore, the PWM control start timing of the vehicle current limiting device 1 due to communication delay The problem caused by the deviation of the drive start timing of the motor generator 3 can be eliminated, and the problem that the drive control of the motor generator 3 becomes unstable due to communication delay can be solved.

Embodiment 4 FIG.
The vehicle current limiting device according to the fourth embodiment of the present invention is configured in the same manner as in FIG. 11 according to the third embodiment. FIG. 12 is a diagram for explaining an example of fluctuations in the current flowing to the motor generator when the switching of the current limiting device of the vehicle current limiting device and the change of the target drive torque command value from the host ECU are simultaneous. FIG. In FIG. 12, when the target drive torque change (a) from the host ECU and the current limit presence / absence switching (b) of the vehicle current limiting device 1 are in the same period, the current flows to the motor generator 3 as shown in (c). There is a risk that the drive torque changes suddenly as the current vibrates greatly. Therefore, in the fourth embodiment, it is possible to cope with the sudden torque change as described above.

  That is, in the fourth embodiment, when the communication unit 10 receives the target drive torque command value Tmg from the host ECU 20, the target drive torque command is based on the voltage Vin of the power storage unit 2 and the rotation speed Nmg of the motor generator 3. The value Tmg is processed and calculated, and the processed target drive torque command value T1 is transmitted to the motor generator 3. As a processing calculation method of the target drive torque command value Tmg, for example, the rotation speed Nmg of the motor generator 3 and the voltage Vin of the power storage means 2 are used as in the following equation (4).

Target drive torque command value after machining T1 = Tmg × {1−exp (−t / τ)} (4)
However,
τ = α × Vin / Nmg
Here, τ is a time constant, t is time, and α is a predetermined coefficient.

  In Embodiment 4 configured as described above, the target drive torque command value Tmg is processed as shown in Equation 4 to obtain the target drive torque command value T1 after processing, as shown in FIG. With respect to the change (a) in the uppermost target drive torque Tmg, the processed target drive torque command value T1 gradually changes as shown in (a1) in the second stage from the top. For this reason, even if the switching (b) of whether or not the current limiting device 1 for the vehicle is current limited and the change (a) in the target drive torque command value Tmg from the host ECU 20 are in the same period, the current flows to the motor generator 3. The change in current gradually changes as shown in the curve (c) in the fourth stage from the top in FIG. 13, and torque fluctuation can be reduced. Further, the time constant τ can be adjusted in accordance with the rotational speed Nmg of the motor generator 3.

  As a method for setting the coefficient α, for example, a method of setting based on the time constant of torque control of the motor generator 3 is conceivable, and it can be matched to the followability of torque control of the motor generator. Furthermore, the time constant can also be adjusted by the magnitude of the voltage Vin of the power storage means 2, and the change in the current flowing to the motor generator due to the switching of the current limit control increases as the voltage Vin increases. Therefore, the time constant increases as the voltage Vin increases. τ is increased to suppress current fluctuation.

  As described above, according to the configuration of the fourth embodiment, the target drive torque command value from the host ECU 20 is added to the formula ((5) in consideration of the rotational speed Nmg of the motor generator 3, the voltage Vin of the power storage means 2, and the time t). 4) Since the processing calculation is performed as in 4) and the obtained target drive torque command value T1 is transmitted to the motor generator 3, the motor that is generated when the vehicle current limiter 1 switches between PWM control and the like. A sudden change in the driving torque of the generator 3 can be reduced.

  DESCRIPTION OF SYMBOLS 1 Current limiting device for vehicles, 2 Power storage means, 3 Motor generator, 4 Switching means, 5 Reflux means, 6 Current detection means, 7 Rotation speed detection means, 8 Voltage measurement means, 9 Current control means, 10 Communication means, 20 Upper ECU, 60 operation detection means.

Claims (7)

A vehicle current limiting device in which a power storage unit is connected to an input end and a rectangular wave drive type motor generator is connected to an output end, and switching means for energizing or interrupting current from the input end to the output end, A recirculation unit connected to a connection point between the switching unit and the output terminal and passing a recirculation current toward the motor generator when the switching unit cuts off a current; and a voltage for measuring a voltage of the power storage unit Based on the measurement means, the rotation speed detection means that can detect the rotation speed of the motor generator, the operation detection means that can detect that the operation of the motor generator is an electric motor operation, and the detection result of the operation detection means When the motor generator is operated by an electric motor, the voltage of the power storage means and the number of rotations of the motor generator are used. Number rolling is equal to or higher than the first predetermined value, and the rotational speed of the PWM control for the switching means in the range of medium-speed rotation area is below a second predetermined value greater than the first predetermined value A current limiting device for a vehicle, comprising: current control means that sets the duty ratio to less than 100%, and otherwise sets the duty ratio to 100%.   2. The vehicle current limiting device according to claim 1, wherein the driving detecting means comprises current detecting means for measuring a current flowing from the output end to the motor generator.   The operation detection means includes a communication means that communicates with the host ECU and the motor generator, and the current control means receives the drive command for the motor generator from the host ECU by the communication means. 2. The vehicle current limiting device according to claim 1, wherein the motor generator is determined to be operated by an electric motor.   4. The vehicle current limiting device according to claim 3, wherein the rotational speed detection means uses the rotational speed of the motor generator included in the information received by the communication means.   When the motor generator is in electric motor operation, the communication means obtains a target drive torque command value Tmg for the motor generator included in a signal from the host ECU, and the target drive torque command value Tmg, the voltage of the power storage means 5. The vehicle current limiting device according to claim 3, wherein a duty ratio of PWM control for the switching means is determined based on the rotational speed of the motor generator.   The communication means is provided so as to have a function as a master communication device of the motor generator so as not to directly communicate the motor generator and the upper ECU, and the target drive torque command value of the motor generator from the upper ECU. When the information including the above is received, the current control means sets the duty ratio of the PWM control for the switching means, and after the PWM control of the switching means, transmits the target drive torque command value to the motor generator The vehicle current limiting device according to any one of claims 3 to 5, wherein:   When the communication means receives a signal including a target drive torque command value transmitted from the host ECU to the motor generator, the communication means detects the rotation speed of the motor generator included in the signal and the voltage measurement means. 7. The vehicle current limiting device according to claim 6, wherein the target drive torque command value is processed and calculated based on the voltage of the power storage means and transmitted to the motor generator.

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