JP3317096B2 - Regenerative braking control method for electric vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of electric control of electric vehicles such as two-wheeled vehicles and four-wheeled vehicles driven by an electric motor, and more particularly, to a method of applying a predetermined regenerative charging current from an electric motor to a battery. The present invention relates to a method of controlling a regenerative charging current when braking a vehicle by flowing the current.

[0002]

2. Description of the Related Art In an electric vehicle driven by a motor powered by a battery, a state in which the motor is driven from the outside when the vehicle is traveling on flat ground by inertia or traveling downhill. Then, the motor acts as a generator, and a voltage is induced in the armature coil. A method is known in which a vehicle is braked by causing a regenerative charging current to flow through a battery using the induced voltage of the armature coil.

[0003] In a motor driven by a battery, the rotation speed is basically determined by the voltage applied to the armature winding and the driving current applied to the armature winding. In the case of a DC motor, both a brush motor and a brushless DC motor, the following equation is equivalently established between the battery voltage EB, the armature current I (average value), and the rotation speed N. I do.

EB = √2 · π (N / 60) · p · kw · ω · Φ + I · r (1) where p is the number of pole pairs of the motor, ω is the number of turns of the armature winding,
kw is a winding coefficient, r is an internal resistance of the armature winding, and Φ is a magnetic flux given by the field.

In equation (1), the first term on the right-hand side indicates the induced voltage (average value) of the armature winding, and the second term indicates the voltage drop in the armature winding. As the rotational speed of the motor increases, the induced voltage of the first term increases, and when the induced voltage becomes equal to the battery voltage, the armature current I becomes zero. The rotation speed when I = 0 in the equation (1) is called a no-load speed. No-load speed of DC motor No
Is given by the following equation:

No = (60 EB) / (√2 · π · p · kw · ω · Φ) (2) The motor acts as a motor in a region where the rotation speed is equal to or lower than the no-load speed No, and the no-load speed No In a region exceeding the range, it will act as a generator. The no-load speed No can be changed by changing the power supply voltage EB, can be changed by a field weakening control in a brushed DC motor, and can be changed by performing a control lead angle control in a brushless DC motor. .

Assuming that a direct drive system (a system in which an output shaft of an electric motor is directly transmitted to an axle of a driving wheel without passing through a transmission) is adopted in an electric vehicle, if the diameter of the wheel is D, The running speed Vo of the vehicle corresponding to the no-load speed No of the motor is given by the following equation.

Vo = π · D · No (3) In this specification, the traveling speed Vo given by the equation (3) is referred to as a no-load traveling speed.

An electric motor in which the battery voltage EB is applied to the armature coil is driven from the outside and the above-mentioned no-load speed N
When the motor is rotated at a rotational speed exceeding o, the voltage (average value) induced in the armature coil exceeds the battery voltage, so that the regenerative charging current flows from the motor to the battery.

FIG. 7 shows a regenerative charging current flowing from the motor side to the battery when the motor in which the battery voltage is applied to the armature coil is driven from the outside in an electric motorcycle using a brushless DC motor as a driving source. Ia
And the relationship between the traveling speed V and the braking torque τa caused by the flow of the charging current Ia. In the case of a direct drive type electric vehicle, the running speed V on the horizontal axis in FIG.
[Rpm].

As is well known, when a brushless DC motor is used, in many cases, in order to divert a drive current to a multi-phase armature coil, an anti-parallel connection is provided between a bridge circuit of switch elements and each switch element. A bridge-type switch circuit (inverter circuit) including a connected diode is used, and a switch element of the switch circuit is on / off controlled according to an output of a position sensor for detecting a position of a rotor. A drive current that is commutated in a predetermined phase order is supplied to the armature coil through the motor.
In the above switch circuit, a diode bridge full-wave rectifier circuit is configured by diodes connected in anti-parallel to each switch element, and the voltage induced in the armature coil when the motor is driven from the outside changes the battery voltage. If it exceeds, a regenerative charging current flows from the motor through the diode bridge full-wave rectifier circuit to the battery.

In FIG. 7, the speed Vo shown on the horizontal axis is the no-load running speed when the motor is driven by the battery. In theory, as shown by the broken line in FIG.
When the electric vehicle runs at a speed exceeding the no-load running speed Vo given by the equation, the regenerative charging current flows from the motor side to the battery for the first time, but actually, the peak value of the induced voltage of the armature coil is A regenerative charging current starts to flow from a running speed Vo '(<Vo) at which the battery voltage is exceeded. When the regenerative charging current flows, the motor generates a braking torque, so that the speed of the vehicle is reduced. The state in which the vehicle runs at a speed exceeding the no-load running speed Vo is, for example, when the vehicle runs downhill.

Here, the legal speed of the electric vehicle is Vs (Vs = 30 [km / h] in the case of an electric motorcycle), and Vs ±
The speed range in the range of 0.33 Vs is the middle speed range, and Vs-0.
The speed range below 33Vs is the low speed range, Vs + 0.33V
Assuming that the speed region from s to 2 × Vs is the high-speed region and the speed region exceeding 2 × Vs is the ultra-high-speed region, in the example shown in FIG. 7, if the running speed does not enter the high-speed region, the regenerative braking works effectively. Will not be.

[0014]

As described above, when the regenerative braking is applied by the conventional method, the regenerative braking does not work effectively unless the traveling speed exceeds the no-load traveling speed Vo. For example, when the vehicle speed exceeds the no-load traveling speed Vo, the vehicle travels on a downhill, and also when the vehicle is accelerated to a high-speed region that greatly exceeds the legal speed. For this reason, in a conventional electric vehicle, the braking effect by regenerative braking cannot be expected at the time of steady traveling when traveling on a flat ground at a speed in the middle speed region near the legal speed, and it is necessary to rely only on the friction brake operated by the driver. There was a problem of not getting.

In order to obtain an effective braking effect by regenerative braking near the legal traveling speed, it is conceivable to set the no-load speed No of the electric motor to a low value. Region) is not practical because the traveling performance in the region (1) is significantly reduced. If the no-load speed No is set low, an excessive regenerative charging current flows through the battery in a high-speed region, and the battery may be damaged when traveling on a long downhill.

An object of the present invention is to improve the safety of an electric vehicle by enabling a braking effect by regenerative braking to be obtained even when the vehicle is traveling in a medium speed region near a legal speed. It is an object of the present invention to provide a regenerative braking control method for an electric vehicle.

Another object of the present invention is to provide a regenerative braking control method for an electric vehicle which can obtain a braking effect by regenerative braking without excessively increasing a regenerative charging current flowing to a battery in a high-speed region. It is in.

[0018]

SUMMARY OF THE INVENTION According to the present invention, a regenerative charging current is supplied to a battery by a voltage induced in an armature coil of the motor during braking of an electric vehicle in which wheels are directly driven by a motor supplied with a driving current from the battery. The present invention relates to a regenerative braking control method for reducing the running speed of a vehicle.

In the present invention, there is provided switch means for short-circuiting the armature coil of the motor when the switch is turned on, and a voltage is induced in the armature coil when the switch is turned off from the on state. Let it be done.
When the running speed of the electric vehicle at the time of braking is equal to or higher than the switching end speed Vh set to a value higher than the speed corresponding to the no-load speed of the electric motor, the switch means is kept in the off state, When the traveling speed is lower than the switching end speed, the switch means is turned on and off while changing the on-duty ratio with the traveling speed so that the on-duty ratio is increased at a predetermined rate as the traveling speed decreases. Control. Also, the rate of change of the on-duty ratio is set so that the regenerative charging current flowing when the traveling speed is lower than the switching end speed is limited to an upper limit value of the allowable range of the charging current of the battery.

Here, the on-duty ratio means the on-time T when the switch means is on-off controlled in a cycle T.
It means the ratio [Ton / (Ton + Toff)] of the on-time Ton to the sum Ton + Toff (= T) of on and off-time Toff.

As described above, when the switch means is turned on and off, when the switch means is turned off from the on state, a high-polarity voltage for continuing to flow the short-circuit current which has been flowing until then is applied to the armature coil. Because of the induction, the regenerative charging current can flow from the armature coil to the battery even when the rotation speed of the motor is lower than the no-load speed No. Therefore, even when the vehicle is traveling on a flat ground at a traveling speed lower than the speed Vo corresponding to the no-load speed of the motor, a regenerative charging current can be supplied to the battery to obtain a braking effect, and safety can be enhanced.

If the switch means is controlled to be turned on and off as described above to allow a large regenerative charge current to flow even when traveling on level ground, the regenerative charge current flowing to the battery when the traveling speed increases on a downhill will cause the battery charge to decrease. The battery may be damaged beyond the allowable current range. In particular, in the case of an electric motorcycle, since the mounted battery has a small capacity, consideration must be given to limiting the regenerative charging current during high-speed running. Therefore, it is necessary to set the rate of change of the on-duty ratio so that the regenerative charging current flowing when the running speed is lower than the switching end speed is limited to the upper limit value of the allowable range of the charging current of the battery.

In the present invention, when the running speed of the electric vehicle during braking is lower than the change rate switching speed Vd set near a speed corresponding to the no-load speed of the electric motor, the on-duty ratio is reduced to decrease the running speed. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed so that the on-duty ratio is increased in accordance with the change in the traveling speed. When the switching speed is between the switching end speed Vh and the switching end speed Vh, the on-duty ratio is increased at a second change rate larger than the first change rate with a decrease in the traveling speed. When the ON / OFF control of the switch means is performed while changing the on-duty ratio with the change of the traveling speed, and the traveling speed at the time of braking is higher than the switching end speed Vh. It may be held the switch means in the off state. The second rate of change of the on-duty ratio is set so as to limit the regenerative charging current to an upper limit value of the allowable range of the charging current of the battery.

With the above configuration, when the electric vehicle is driven at a speed exceeding the speed corresponding to the no-load speed of the electric motor, regenerative braking is applied without flowing an excessive regenerative charging current to the battery. A great braking effect can be obtained.

Further, with the above configuration, the braking torque due to regenerative braking decreases when the traveling speed of the electric vehicle enters a region (high-speed region) exceeding the change rate switching speed set near the no-load traveling speed. Therefore, in a vehicle driven by the internal combustion engine, a driving sensation similar to a state where the transmission is switched to the overdrive position can be obtained. In addition, when the traveling speed is further increased due to a long downhill or the like, the regenerative charging current is increased and the braking effect is enhanced. Therefore, the increase in the traveling speed is suppressed, and the traveling speed is prevented from reaching a dangerous speed. You.

In the present invention, when the running speed of the electric vehicle during braking is lower than the first change rate switching speed Vd set near the speed corresponding to the no-load speed of the electric motor, the vehicle travels at the on-duty ratio. The switch means is turned on / off while changing the on-duty ratio with a change in the traveling speed so as to increase at a first rate of change with a decrease in the speed. When the on-duty ratio is between the rate change speed Vd and the second change rate change speed Ve set higher than the change speed, the on-duty ratio is larger than the first change rate as the traveling speed decreases. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed so as to increase at the rate of change of the traveling speed. When located between the third change rate switching speed Vf, which is higher than the second change rate switching speed with the on-duty ratio to a reduction in traveling speed second
The on / off control of the switch means is performed while changing the on-duty ratio with the change of the traveling speed so as to increase at a third rate of change smaller than the rate of change of the traveling speed. The speed Vf and the fourth change rate switching speed Vg set higher than the third change rate switching speed
When the on-duty ratio is lower than the running speed, the on-duty ratio is changed with the change of the running speed so that the on-duty ratio is reduced at a predetermined rate with the lowering of the running speed. When the running speed is between the fourth change rate switching speed Vg and the switching end speed Vh set to be higher than the fourth change rate switching speed, the on-duty ratio is changed to the fourth speed with the decrease in the running speed.
The on / off control of the switch means is performed while changing the on-duty ratio with the change of the traveling speed so as to increase at the rate of change of the traveling speed.
When it is longer than h, the switch means may be kept in the off state. In this case, the second change rate of the on-duty ratio and the third change rate of the on-duty ratio are set so as to limit the regenerative charging current to the upper limit value of the allowable range of the charging current of the battery.
Set the rate of change of.

With the above configuration, the braking effect of the regenerative braking can be reduced in a high-speed region where the traveling speed exceeds the set speed, and an overdrive driving feeling can be obtained. In a region beyond the high-speed region, a large braking effect can be obtained by increasing the regenerative charging current, so that the traveling speed can be prevented from entering a dangerous region.

When a brushless DC motor having an n-phase (n is an integer of 1 or more) armature coil is used, a predetermined number of switch elements are bridge-connected to commutate the drive current of the motor. Using a switch circuit consisting of a bridge circuit of switch elements and diodes connected in anti-parallel to both ends of each switch element, applying an output voltage of a battery between DC input terminals of the switch circuit, It is preferable to connect the n-phase armature coil to the output terminal. In this case, a switch element constituting the lower side of the bridge circuit of the switch element can be used as the switch means. Further, a switch element constituting the upper side of the bridge circuit can be used as the switch means.

[0029]

FIG. 1 shows an example of a hardware configuration of a drive control device for an electric vehicle used in an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a brushless DC motor. A brushless DC motor generally includes a rotor having a magnet field and a stator having an n-phase armature coil connected in a star shape with a phase difference of 360 / n degrees (n is an integer of 2 or more). Is done.

In this example, it is assumed that the direct drive system is adopted in the electric vehicle, and the output shaft of the electric motor is directly connected to the drive wheels of the vehicle.

The brushless DC motor 1 shown in FIG.
A rotor 1A having two pole magnet fields 1a1, 1a2;
Three-phase armature coil A arranged with a phase difference of 0 degree
and a stator 1B having u to Aw, and the armature coils Au to Aw are star-connected.

A position detector 2 for detecting the relative position of the rotor with respect to the stator is provided on the side of the stator 1B. The position detector 2 includes, for example, three halls ICHu, Hv, Hw (not shown) provided for each of the armature coils Au to Aw of the stator.
The polarity of the magnetic pole of the rotor is detected by these Hall ICs, and the relative position of the rotor to each of the armature coils Au to Aw is detected. The three Hall ICs are arranged at intervals of 120 degrees, and each Hall IC holds a high level (hereinafter also referred to as H level) state when the detected magnetic pole of the rotor 1A is, for example, an N pole. , And S poles, generate rectangular wave signals eu to ew that maintain a low level (hereinafter also referred to as L level) state. Square wave signal eu
FIG. 2 (A) shows an example of the change of .about.ew with respect to the rotation angle .theta.
This is shown in (C).

The output shaft of the electric motor 1 is directly connected to the drive wheels of the vehicle or connected via a speed reducer. Generally, no clutch is provided between the electric motor and the drive wheels, so that the electric motor is driven from the outside during braking or when going down a hill. At this time, the electric motor 1 acts as a synchronous generator. Generates AC voltage. In the following description, it is assumed that the output shaft of the electric motor is directly connected to the drive wheels.

In FIG. 1, 3 is a battery, 4 is a key switch operated by a driver, 5 is a main relay having an exciting coil 5a and a contact 5b which closes when the exciting coil 5a is excited, and 6 is a motor 1 Armature coil Au to A
w is a bridge-type switch circuit for supplying a drive current to and w. commutation of the drive current, 7 is a switch drive circuit for applying a trigger signal to a switch element of a switch circuit 6, 8 is a control unit, and 9 is a vehicle An accelerator sensor 10 for detecting the position of a speed adjusting member (for example, an accelerator grip or an accelerator pedal) operated by a driver to adjust the traveling speed is a surge absorbing element connected between the DC input terminals of the switch circuit 6. is there.

In the illustrated example, the output voltage of the battery 3 is applied to the DC-DC converter 20 via the key switch 4, and the output voltage of the battery 3 (56V in this example) is
The voltage is converted into a DC voltage of 12 V by the C-DC converter 20. The DC voltage obtained from the DC-DC converter 20 is applied to the exciting coil 5a of the main relay 5 and the lighting load 22 such as a headlamp or a blinker.

In general, the bridge-type switch circuit 6 has a bridge circuit of switch elements formed by bridge-connecting unidirectional switch elements that conduct only while a drive signal is being applied, and an anti-parallel circuit at both ends of each switch element. And a connected feedback diode.

Here, the bridge connection of the switch elements means that the switch elements are bridge-connected in the same manner as a well-known diode bridge full-wave rectifier circuit. In general, a bridge circuit having this type of connection has two bridge circuits. There is provided a circuit configuration in which a plurality of switch element series circuits each including switch elements having the same polarity and connected in series are provided, and the plurality of switch element series circuits are connected in parallel with each other. In general, when a brushless DC motor is driven using a bridge-type switch circuit, a bridge circuit (n switch elements) of switch elements configured by bridge-connecting 2n switch elements (n is an integer of 2 or more). A switch circuit configured by connecting serial circuits in parallel is used.

In the switch circuit having such a circuit configuration, a common connection point on one end and a common connection point on the other end (both ends of the switch circuit) of the n switch element series circuits are connected to a pair of DC input terminals (battery). A DC power supply voltage is applied between the DC input terminals of the pair. Further, n terminals drawn from the connection points of the respective switch elements of the n switch element series circuits are output terminals (terminals connected to the n armature coils), and these output terminals are connected to the brushless DC motor. Armature coil is connected. Further, when this type of switch circuit is viewed from n output terminals, a diode bridge full-wave rectifier circuit is constituted by n feedback diodes.

In the present specification, the switch element located between the DC input terminal and the output terminal on the positive polarity side of the bridge circuit of the switch element is a switch element forming the upper side of the bridge or a switch element on the upper side of the bridge. The switch element located between the DC input terminal and the output terminal on the negative polarity side is called a switch element forming the lower side of the bridge or a switch element on the lower side of the bridge.

As described above, when a switch circuit configured by connecting the switch elements in a full-wave bridge is provided between the DC power supply and the armature coil of the n-phase brushless DC motor, the n pieces of the upper side of the bridge are formed. By turning on the switch elements and the n switch elements constituting the lower side of the bridge one by one in a predetermined order, a drive current is commutated to the armature coil to rotate the motor.

The switch circuit 6 used in this embodiment is
A switch element series circuit formed by connecting switch elements Su and Sx in series, a switch element series circuit formed by connecting Sv and Sy in series, and a switch element formed by connecting Sw and Sz in series The series circuits are connected in parallel (three-phase full-wave bridge connection), and feedback diodes Du, Dv, Dw and Dx, Dy, are connected to both ends of the switch elements Su, Sv, Sw and Sx, Sy, Sz, respectively.
Dz are connected in antiparallel.

In the illustrated switch circuit 6, a field effect transistor (FET) is used as each switch element, and the common connection point of the drains of the FETs constituting the switch elements Su to Sw is the DC input terminal 6a on the positive polarity side. The common connection point of the sources of the FETs constituting the switching elements Sx to Sz is the DC output terminal 6b on the negative polarity side. Further, F which constitutes the switching elements Su to Sw, respectively.
The connection point between the source of the ET and the drains of the FETs constituting the switch elements Sx to Sz is a three-phase output terminal 6u.
６6w.

When the switch circuit 6 is viewed from the side of the motor 1, a full-wave bridge rectifier circuit is constituted by the diodes Du to Dw and Dx to Dz, and the motor 1 is driven from the outside so that the armature coil When a three-phase AC voltage is induced in Au to Aw, diodes Du to Dw and Dx
A regenerative charging current flows to the battery 3 through the full-wave bridge rectifier circuit consisting of .about.Dz and the contact 5b of the main relay 5.

In this example, the switch elements Su to Sw located between the DC input terminal 6a on the positive polarity side of the switch circuit 6 and the output terminal are the switch elements on the upper side of the bridge, and the DC input terminal on the negative polarity side. Switch elements Sx to Sz located between 6b and the output terminal are switch elements on the lower side of the bridge.

The DC input terminal 6a on the positive polarity side of the switch circuit 6 is connected to the positive terminal of the battery 3 via the contact 5b of the main relay. The DC input terminal 6b on the negative polarity side of the switch circuit 6 is grounded through a current detecting resistor R1, and the negative electrode terminal of the battery 3 is grounded through a charging current detecting resistor R2. The three-phase output terminals 6 u, 6 v and 6 w of the switch circuit 6 are connected to terminals of the three-phase armature coils Au to Aw of the brushless DC motor 1 on the opposite side to the neutral point.

The control unit 8 includes a CPU 12 and the CPU
A power supply circuit 21 for applying a power supply voltage to the power supply, and transistors 14a to 14c as switch means for turning on and off the power supply to the display 13 including a light emitting diode and a buzzer.

The power supply circuit 21 includes a DC-DC converter 2
The voltage of 12 V given from 0 is converted to a constant DC voltage of 5 V and supplied to the power supply terminal of the CPU 12.

The output of the position detector 2, the output of the accelerator sensor 9, the detected value of the output voltage VB of the battery 3, the detected value of the temperature of the battery 3 detected by the temperature sensor 15, and the both ends of the resistor R1 are provided to the CPU 12. Voltage amplifier AMP (1)
Of the drive current of the motor obtained by amplification by the
2, the detected value of the regenerative charging current obtained by amplifying the voltage at both ends by the amplifier AMP (2), and the detected value of the voltage between the positive DC input terminal of the switch circuit 6 and the ground detected by the voltage dividing circuit 16. The detection value of the driving current held by the latch circuit 17, the detection value of the temperature of the switch circuit 6 detected by the temperature sensor 18, and the detection value of the winding temperature of the electric motor 1 detected by the temperature sensor 19 are input. ing. Of these signals, analog signals are converted into digital signals through an A / D terminal provided in the CPU 12 and read into the CPU.

The CPU 12 has a ROM or E (not shown)
By executing a program stored in the EPROM, a switch control means (drive) for turning on and off the switch element of the switch circuit 6 so as to adjust the magnitude of the drive current flowing through the armature coils Au to Aw and perform commutation. Means for generating instruction signals u 'to w', x 'to z' and a PWM signal) or a voltage induced in an armature coil of the motor when the motor is driven from the outside. A regenerative current control means for controlling the flowing regenerative charging current, and a display for turning on / off the transistors 14a to 14c so as to cause the display 13 to perform various display operations such as a warning display and a display of a state of each part (for example, a temperature display). Implement control means and the like.

The CPU 12 generates drive instruction signals u 'to w', x 'to z' and PWM signals from the seven output ports, respectively. These signals are sent to the interface circuit 7
A is supplied to the drive circuit 7B through A.

The drive instruction signals u 'to w' and x 'to z' are
A signal indicating a switch element that needs to be made conductive among the switch elements constituting the switch circuit 6,
The WM signal is a pulse signal that is intermittent at a duty ratio corresponding to the average value of the drive current flowing through the armature coil.

The switch drive circuit 7 is a circuit for supplying drive signals u to w and x to z to the switch elements Su to Sw and Sx to Sz constituting the switch circuit 6, respectively. -Consists of an interface circuit 7A and a drive circuit 7B that operate by receiving a DC power supply voltage from the DC converter 20.

The drive circuit 7B outputs the drive instruction signals u 'to u'.
In accordance with w 'and x' to z 'and the PWM signal, drive signals u to w having a predetermined pulse width are given to switch elements Su to Sw on the upper side of the bridge of the switch circuit 6, and switch elements on the lower side of the bridge are provided. Pulse width modulated drive signals x to Sx to Sz which vary with a predetermined on-duty ratio
Give z. As a result, the upper switch elements Su to S
w, the switch element to which the drive signal has been applied conducts for a time corresponding to the pulse width of the drive signal, and among the switch elements Su to Sw on the lower side, the switch element to which the pulse-width modulated drive signal has been applied. Turns on and off at a predetermined duty ratio, and a pulse width modulated drive current flows through the armature coil of a predetermined phase.

The Hall IC constituting the position detector 2 is shown in FIG.
(A) to (C), a rectangular wave signal (position detection signal) e
When u to ew are generated, the switching elements Su to Sw and Sx to Sz are respectively shown in FIGS. 2 (D) to (F) and (G) to
An on / off operation is performed as shown in (I). In addition, FIG.
(F) and waveforms (G) to (I) show the case where the on-duty ratio of the drive current is 100%.

In the illustrated example, the output of the latch circuit 17 for latching the detection value of the drive current or the amplifier AMP (1)
Is input to the drive circuit 7B. The drive circuit 7B takes in the detected value of the drive current and performs control to keep the drive current flowing through the armature coils Au to Aw at a predetermined limit value or less.

The latch circuit 17 is provided for performing control to immediately cut off the drive current and prevent burnout of the armature coil when an excessive drive current flows due to a short circuit accident of the armature coil or the like. ing.

The outline of the operation of the drive control device shown in FIG. 1 is as follows. When the key switch 4 is closed by the driver, the DC-DC converter 20 outputs a DC voltage of 12 [V], so that the contact of the main relay 5 is closed and the output voltage of the battery 3 (for example, 60 [V]) is reduced. Switch circuit 6
Are applied to the power supply circuit 21, the power supply circuit 21, and the power supply terminals of the interface 7A of the switch drive circuit 7 and the drive circuit 7B.

The switch control means realized by the CPU 12 of the control unit determines a phase sequence to be excited from a position detection signal given from the position detector 2 and a rotation direction command signal given by means (not shown). The drive instruction signals u ′ to w ′ and x ′ to z ′ for giving a drive signal to the predetermined switch elements 6 are supplied to the switch drive circuit 7.

The CPU 12 also obtains information on the rotational speed of the electric motor from a signal supplied from the position detector 2 (or from a separately provided encoder), and converts this rotational speed information into designated speed information supplied from the accelerator sensor 9. Calculates the magnitude (average value) of the drive current required to match the rotation speed of the motor to the commanded speed, and calculates the pulse waveform that changes at a duty ratio corresponding to the magnitude of the calculated drive current. The PWM signal is given to the switch drive circuit 7.

The drive circuit 7B switches the switch elements Su to Sw on the upper side of the bridge of the switch circuit 6 according to the drive instruction signal and the PWM signal given from the control unit 8.
A drive signal having a predetermined time width is given to one of the switch elements selected from among them to make the switch element conductive, and one of the switch elements Sx to Sz selected from the lower side is selected.
An intermittent (PWM modulated) drive signal is applied to one of the switch elements at an on-duty ratio corresponding to the magnitude of the drive current to turn on and off the switch elements. As a result, the switch elements Su to Sw on the upper side and the switch elements Sx to Sz on the lower side of the switch circuit 6 are turned on one by one in a predetermined order, and a drive current is supplied to the electric motor to rotate the electric motor at the designated speed.

The display control means realized by the CPU 12 includes a battery temperature, a battery voltage, a rotation state of the motor,
The temperature of the motor and the like are monitored, and when an abnormality occurs in these, the indicator 13 such as an LED or a buzzer is operated to display a warning.

The voltage dividing circuit 16 is connected to both ends 6 of the switch circuit 6.
a, 6b is detected, and the detected value is detected by the CPU 12
Give to. When the voltage between the DC input terminals 6a and 6b of the switch circuit 6 exceeds the allowable value, the CPU 12 sets the switch circuit 6 to the ON state of all the switch elements Su to Sw on the lower side of the bridge. The switch-on means at the time of overvoltage is realized.

In the above-described electric vehicle, when regenerative braking is applied in a state where the battery 3 is removed or a state where the terminals of the battery are loosely tightened (a state where the electric contact resistance of the terminals is large), the switch of the switch circuit 6 is switched. A high voltage is applied to the element, and the switching element may be damaged. Therefore, if the overvoltage switch-on means is provided as described above, when the voltage between the DC input terminals of the switch circuit 6 becomes excessive, the armature coil is short-circuited through the switch element on the lower side of the bridge of the switch circuit. As a result, it is possible to prevent an overvoltage from being applied to the switch element, so that it is possible to prevent the switch element from being damaged by the overvoltage. In this case, when an overvoltage is detected by the voltage dividing circuit 16, the display 13 may be operated to display a warning.

When the speed adjusting member such as the accelerator grip is returned to decelerate or stop the vehicle, the motor is driven from the outside in the process of decelerating the vehicle. At this time, the motor 1 functions as a synchronous generator and induces a three-phase AC voltage in the armature coils Au to Aw. When the regenerative charging current flows to the battery 3 through the diode bridge full-wave rectifier circuit constituted by the feedback diodes Du to Dw and Dx to Dz and the contact 5b of the main relay due to the induced voltage, the battery 3 is charged and the electric motor is driven. 1
Generates a braking torque, and the vehicle is decelerated.

In the conventional regenerative braking control, when the rotation speed of the motor exceeds the no-load speed, the regenerative charging current is supplied from the motor to the battery. Only in such a case, the braking effect by the regenerative braking could be obtained. Therefore, in the present invention, switch means for short-circuiting the armature coils Au to Aw of the electric motor 1 when turned on is provided, and when the speed adjusting member is returned, the switch means is turned on / off.

When a drive current is supplied to a motor using a bridge-type switch circuit 6 as in the example shown in FIG. 1, for example, a switch element S on the lower side of the switch circuit 6
Using the switches x to Sz as the switch means, the switches Sx to Sz are simultaneously turned on and off when braking is applied.

As described above, when the speed adjusting member is returned and the electric motor is driven from the outside, the switch means provided so as to be able to short-circuit the armature coil is turned on and off. When the state changes from the on state to the off state, a voltage having a high polarity is applied to the armature coils Au to Aw to keep the short-circuit current flowing until then, so that the rotation speed of the motor is lower than the no-load speed No. Even in this state, the regenerative charging current can flow from the armature coils Au to Aw to the battery 1. Therefore, even when the vehicle is running on a level ground at a speed lower than the speed Vo corresponding to the no-load speed of the electric motor, a regenerative charging current can be supplied to the battery during braking to obtain a regenerative braking effect, thereby improving safety. it can.

As described above, switch means (for example, switch elements Sx, Sx,
Sy, Sz) are turned on and off to set the armature coils Au to Aw.
When a braking effect is obtained by flowing a regenerative charging current by inducing a voltage in the motor, if the aim is to increase the regenerative charging current flowing at each rotational speed as much as possible to increase the braking effect, the current flows at each traveling speed. The on-duty ratio (the sum Ton + Ton of the on-time Ton and the off-time Toff) of the switch means is set so as to maximize the regenerative charging current.
The ratio (D) of the on-time Ton to off can be changed in inverse proportion to the rotation speed.

FIG. 6 shows the relationship between the regenerative charging current I flowing when the motor 1 is driven from the outside and the running speed V, the relationship between the braking torque τ generated by the regenerative charging current and the running speed V, and the turning on of the switch means. This figure shows the relationship between the duty ratio D and the rotational speed V. In the figure, Ia denotes feedback diodes Du to Dw of the switch circuit 6 from the motor 1 when the motor 1 is driven from the outside. And the regenerative charging current supplied to the battery 3 through the full-wave rectifier circuit constituted by Dx to Dz. Further, τa is a braking torque (an input torque required for operating the electric motor as a generator and flowing the current Ia to the load) generated by the charging current Ia. The characteristic curves of the charging current Ia and the braking torque τa are similar to those shown in FIG. For convenience, Ia is called a full-wave rectified charging current, and τ
Let a be called the full-wave rectification charging torque.

In FIG. 6, Dm indicates the on-duty ratio, and Ibm indicates the switching elements Sx to Sx while changing the on-duty ratio Dm in inverse proportion to the traveling speed, as shown in FIG.
The figure shows the regenerative charging current that flows when z is turned on and off at the same time. Τbm indicates a braking torque generated by the charging current Ibm. The regenerative charging current Ibm flowing by switching is called a switching charging current, and the braking torque τbm generated by the charging current is called a switching charging torque.

In the example shown in FIG. 6, the characteristic straight line of the switching charging current Ibm substantially rising from the origin to the running speed V (corresponding to the rotation speed of the electric motor in this example because of the direct drive system) is as follows. Full-wave rectification charging torque τa
The on-duty ratio Dm is changed so as to be in contact with the characteristic curve of the full-wave rectified charging current Ia versus the running speed V at the running speed Vm at which the maximum speed becomes maximum. Thus, the on-duty ratio D
By changing m, the maximum charging torque can be obtained at each traveling speed, and the regenerative braking effect can be maximized.

However, if the on-duty ratio of the switch means is changed according to the rotation speed as described above, it is inevitable that the switching charging current Ibm becomes excessive. For example, the battery 3 is made of a lead storage battery, and the appropriate range of the charging current is 1C to 2C as shown on the vertical axis of FIG.
(C is the rated discharge rate converted capacity of the battery at 25 ° C)
, The switching charging current Ibm exceeds the allowable range in the high-speed region. When the electric vehicle travels downhill, its traveling speed easily enters the high-speed region. Therefore, when the on-duty ratio is changed as described above, the regenerative charging current becomes excessive and the battery is damaged. There is a risk. In the case of a sealed lead-acid battery, the appropriate range of the charging current is about 0.2C to 0.5C, so if the on-duty ratio is changed as described above, the regenerative charging current may exceed the allowable value at a lower speed. become.

Therefore, in the present invention, as shown in FIG. 3, the running speed of the electric vehicle during braking is higher than the switching end speed Vh set to a value higher than the speed Vo corresponding to the no-load speed of the electric motor. When the on-duty ratio is 0, the on-duty ratio is set to 0 and the switch means is held in the off state. When the traveling speed at the time of braking is lower than the switching end speed Vh, the on-duty ratio Db is changed at a predetermined rate as the traveling speed decreases. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed so as to increase the value. Then, the rate of change of the on-duty ratio Db is set such that the regenerative charging current Ib flowing when the traveling speed reaches the switching end speed Vh is limited to the upper limit of the allowable range of the charging current of the battery.

When the on time of the switch means is Ton, the off time is Toff, and the on / off cycle is T = Ton + Toff, the on-duty ratio D is given by D = Ton / T. T is kept constant irrespective of the running speed.

In the example shown in FIG. 3, the switching charging current Ib is limited to 1.5 C or less, which is an intermediate value of the allowable range, and the traveling speed at which the full-wave rectified charging current Ia is equal to 1.5 C is set. Is the switching end speed Vh. In FIG. 3, Ibm and τbm are the same as Ibm and τbm shown in FIG. 6, respectively.

In the example shown in FIG. 3, the on-duty ratio D
Although b is changed at the same change rate with respect to the change of the traveling speed, the change rate of the on-duty ratio Db may be switched in a high-speed region as shown in FIG.

In the example shown in FIG. 4, when the running speed of the electric vehicle during braking is lower than the change rate switching speed Vd set near the speed Vo corresponding to the no-load speed of the electric motor, the on-duty ratio Db is used. The switch means is turned on / off while changing the on-duty ratio with the change of the traveling speed so as to increase at the first rate of change with the decrease of the speed, and the traveling speed at the time of braking is changed to the change rate switching speed Vd. When the switching speed is between the switching end speed Vh and the switching end speed Vh, the on-duty ratio is increased at a second rate of change larger than the first rate of change as the traveling speed decreases. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed. When the traveling speed at the time of braking is equal to or higher than the switching end speed Vh, the switch means is kept in the off state. The change rate (second change rate) of the on-duty ratio Db when the traveling speed is in the range of Vd to Vh is set so as to limit the regenerative charging current to the upper limit value of the allowable range of the charging current of the battery. . In this example, the second rate of change of the on-duty ratio is set such that the switching charging current Ib is maintained at a constant value of 1.5 C when the traveling speed during braking is in the range of Vd to Vh. I have.

When the on-duty ratio of switching is changed at the time of braking as shown in FIG. 4, when the electric vehicle is driven at a speed exceeding the speed corresponding to the no-load speed of the motor, an excessive regenerative charging current is supplied to the battery. Without shedding
A large braking effect can be obtained by applying regenerative braking.

With the above configuration, when the traveling speed of the electric vehicle enters a region (high-speed region) exceeding the change rate switching speed Vd set near the no-load traveling speed, the braking torque due to regenerative braking decreases. Therefore, in a vehicle driven by an internal combustion engine, a driving feeling similar to a state where the transmission is switched to the overdrive position can be obtained.
Also, if the traveling speed is to be further increased on a long downhill or the like, the regenerative charging current increases and the braking effect increases,
An increase in the traveling speed is suppressed, and the traveling speed is prevented from reaching a dangerous speed.

FIG. 5 shows how the on-duty ratio Db is changed in another embodiment of the present invention. In this example, the running speed of the electric vehicle during braking corresponds to the no-load speed of the electric motor. When the on-duty ratio D is lower than the first change rate switching speed Vd set in the vicinity of the speed Vo at which
The on / off control of the switch means is performed while changing the on-duty ratio with the change of the traveling speed so that b is increased at the first rate of change with the decrease of the traveling speed. Change rate switching speed Vd and switching speed V
When the on-duty ratio is between the second change rate switching speed Ve set higher than d and the traveling speed is decreased, the on-duty ratio is increased at a second change rate larger than the first change rate. The on / off control of the switch means is performed while changing the on-duty ratio Db according to the change of the traveling speed. On the other hand, when the traveling speed during braking is between the second change rate switching speed Ve and the third change rate switching speed Vf set higher than the second change rate switching speed, the on-duty ratio Db is changed. The on / off control of the switch means is performed while changing the on-duty ratio with the change of the traveling speed so that the on-duty ratio is increased with the third change rate smaller than the second change rate with the decrease of the traveling speed. Running speed is 3rd
The on-duty ratio is reduced at a predetermined rate with a decrease in the traveling speed when the switching speed is between the change rate switching speed Vf and the fourth change rate switching speed Vg set higher than the switching speed Vf. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed. On the other hand, when the traveling speed during braking is between the fourth change rate switching speed Vg and the switching end speed Vh set higher than the switching speed Vg, the on-duty ratio is increased with the decrease of the traveling speed. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed so as to increase at the rate of change, and the switch means is turned off when the traveling speed at the time of braking is higher than the switching end speed Vh. Hold in state. When the traveling speed is in the range of Vd to Vf, the rate of change of the on-duty ratio (the second rate of change and the third rate of change) limits the regenerative charging current to the upper limit of the allowable range of the charging current of the battery. Set to

In the example shown in FIG. 5, the switching end speed Vh is set to a rotation speed (same as Vm shown in FIG. 6) at which the full-wave rectification charging torque τa is maximized. Further, the second change rate between the change rate switching speeds Vd to Ve is set to a value that maintains the switching charging current at 1.5 C, as in the example shown in FIG. Further, the speed Vg to Vh
Is set so that the switching charging current Ib is connected to the full-wave rectification charging current Ia at the switching end speed Vh.

When the on-duty ratio of the switching is changed as shown in FIG. 5 during braking, the braking effect by regenerative braking is reduced in a high-speed region where the running speed exceeds the set speed, so that an overdrive driving feeling can be obtained. . In a region beyond the high-speed region, a large braking effect can be obtained by increasing the regenerative charging current, so that the traveling speed can be prevented from entering a dangerous region.

In the examples shown in FIGS. 3 to 5, the regenerative charging current exceeds the upper limit of the allowable range of the charging current of the battery in the ultra-high-speed region, but the state in which the vehicle travels in the ultra-high-speed region usually hardly occurs. This does not occur, and even if a running state in an ultra-high speed region occurs due to a steep downhill or the like, it is for a very short time, so there is no possibility that the battery will be damaged by regenerative charging current in the ultra-high speed region. In the ultra-high-speed range, it is preferable to increase the regenerative charging current in order to increase the regenerative braking effect and reduce the speed as quickly as possible.

In the present invention, the on-duty ratio of the switch means is controlled in accordance with the traveling speed at the time of braking. To perform such control using the apparatus shown in FIG. Means for detecting that the accelerator (speed adjusting member) is returned from the output of the motor, a rotation speed detection means for detecting the rotation speed of the electric motor 1, and an on-duty ratio corresponding to the rotation speed detected by the detection means. A duty ratio calculating means obtained by a map calculation or a mathematical formula; and a switch element Sx having a duty ratio calculated when the accelerator is returned.
To Sz at the same time.
'And z' may be realized by the CPU 12.

In the above embodiment, a brushless DC motor whose field is constituted by a permanent magnet is used as the electric motor. However, if a motor whose field is constituted by a magnet is used,
Since the magnetic flux Φ in the equation (1) can be kept constant, the regenerative charging current I and the duty ratio D at each rotational speed can be uniquely determined, and control can be facilitated.

In the above description, the electric vehicle adopts the direct drive system in which the output shaft of the electric motor is directly transmitted to the shaft of the drive wheel without passing through the transmission. In the vehicle, the traveling speed and the rotation speed of the electric motor correspond to each other, so that the control can be simplified. However, the present invention is not limited to the electric vehicle of the direct drive system,
The present invention can be implemented by controlling the on-duty ratio of switching at the time of braking in consideration of the gear ratio, even in an electric vehicle in which the output shaft of the electric motor is transmitted to the drive wheels via the transmission.

In the above description, the armature coils Au to Aw
Are used as switch means for short-circuiting the switch circuit 6, and the switch elements Sx to Sz constituting the lower side of the bridge circuit of the switch circuit 6 are turned on and off at the same time to induce a voltage in the armature coil. By using the switching elements Su to Sw constituting the upper side of the bridge circuit of the switching circuit 6 as switching means for short-circuiting the armature coil, a voltage is induced in the armature coil by simultaneously turning on and off these switching elements. Is also good.

In the above description, a MOSFET is used as a switch element constituting the switch circuit 6. However, the switch element may be any switch element that can be controlled on and off.
It is not limited to OSFET. For example, a transistor, an IGBT (gate insulated bipolar transistor), or the like can be used as each switch element.

[0089]

As described above, according to the present invention, by providing the switch means capable of short-circuiting the armature coil when it is turned on, the switch means is controlled on and off during braking. A regenerative charging current can flow from the armature coil to the battery. Therefore, even when the vehicle is traveling on a flat ground at a traveling speed lower than the speed corresponding to the no-load speed of the motor, a regenerative charging current can be supplied to the battery to obtain a braking effect, and safety can be improved.

In the present invention, the rate of change of the on-duty ratio is set so that the regenerative charging current flowing when the switching element is turned on and off is limited to the upper limit value of the allowable range of the charging current of the battery. It is possible to prevent the battery from being damaged due to the flow of the charging current.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration example of an apparatus used in an embodiment of the present invention.

FIG. 2 is a waveform diagram showing signal waveforms at various parts of the apparatus shown in FIG.

FIG. 3 is a diagram illustrating a relationship between a switching on-duty ratio and a traveling speed, a relationship between a switching charging current and a traveling speed, a relationship between a switching charging torque and a traveling speed, a full-wave rectification charging current and a traveling according to an embodiment of the present invention. FIG. 3 is a diagram showing a relationship between speed and a relationship between full-wave rectification charging torque and traveling speed.

FIG. 4 is a diagram showing the relationship between the switching on-duty ratio and the traveling speed, the relationship between the switching charging current and the traveling speed, the relationship between the switching charging torque and the traveling speed, the full-wave rectification charging current and the switching speed in another embodiment of the present invention. FIG. 3 is a diagram illustrating a relationship between a traveling speed and a relationship between a full-wave rectification charging torque and a traveling speed.

FIG. 5 shows the relationship between the switching on-duty ratio and the traveling speed, the relationship between the switching charging current and the traveling speed, the relationship between the switching charging torque and the traveling speed, and the full-wave rectification charging current in still another embodiment of the present invention. FIG. 4 is a diagram showing a relationship between the vehicle speed and a traveling speed, and a relationship between a full-wave rectification charging torque and a traveling speed.

FIG. 6 shows the relationship between the on-duty ratio and the traveling speed when the switching on-duty ratio is controlled to maximize the regenerative charging current, the relationship between the switching charging current and the traveling speed, the switching charging torque and the traveling speed. FIG. 5 is a diagram showing a relationship between the full-wave rectification charging current and the traveling speed, and a relationship between the full-wave rectification charging torque and the traveling speed.

FIG. 7 is a diagram showing a relationship between a full-wave rectification charging current flowing at the time of braking and a traveling speed and a relationship between a full-wave rectification charging torque and a traveling speed in a conventional regenerative braking control method for an electric vehicle.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 brushless DC motor Au to Aw armature coil 3 battery 6 switch circuit Su to Sw, Sx to Sz switch element Du to Dw, Dx to Dz feedback diode 7 drive unit 8 control unit 12 CPU

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-57-68601 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60L 7/12 H02P 3/14

Claims (5)

(57) [Claims] 1. A regenerative charging current is supplied to the battery by a voltage induced in an armature coil of the electric motor during braking of an electric vehicle that drives wheels by an electric motor to which a driving current is applied from a battery, thereby reducing a traveling speed of the vehicle. In the regenerative braking control method for reducing the voltage, switch means is provided for short-circuiting the armature coil of the electric motor when turned on, and a voltage is applied to the armature coil when the switch means is turned off from the on state. When the running speed of the electric vehicle during braking is equal to or higher than the switching end speed set to a value higher than the speed corresponding to the no-load speed of the electric motor, the switch unit is turned off. When the traveling speed at the time of the braking is lower than the switching end speed, the on-duty ratio is decreased with the traveling speed. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed so as to increase at a predetermined change rate, and the regenerative charging current flowing when the traveling speed is lower than the switching end speed is supplied to the battery. A regenerative braking control method for an electric vehicle, wherein the rate of change of the on-duty ratio is set so as to limit the charging current to an upper limit value or less. 2. A regenerative charging current is supplied to the battery by a voltage induced in an armature coil of the electric motor during braking of an electric vehicle that drives wheels by an electric motor to which a driving current is applied from a battery, thereby reducing the traveling speed of the vehicle. In the regenerative braking control method for reducing the voltage, switch means is provided for short-circuiting the armature coil of the electric motor when turned on, and a voltage is applied to the armature coil when the switch means is turned off from the on state. When the traveling speed at the time of braking of the electric vehicle is lower than a change rate switching speed set near a speed corresponding to the no-load speed of the electric motor, the on-duty ratio is reduced with the traveling speed. The switch means is turned on while changing the on-duty ratio with the change of the traveling speed so as to increase at the first change rate. When the traveling speed at the time of braking is between the change rate switching speed and the switching end speed set to a value higher than the switching speed, the on-duty ratio is decreased with the traveling speed. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed so as to increase at a second rate of change greater than the change rate of 1; When the speed is higher than or equal to the speed, the switch means is kept in an off state, and the second rate of change of the on-duty ratio is such that the regenerative charging current is limited to an upper limit value of an allowable range of the charging current of the battery. A regenerative braking control method for an electric vehicle, wherein the method is set. 3. A regenerative charging current is supplied to the battery with a voltage induced in an armature coil of the electric motor during braking of an electric vehicle that drives wheels by an electric motor to which a driving current is applied from a battery, thereby reducing the traveling speed of the vehicle. In the regenerative braking control method for reducing the voltage, switch means is provided for short-circuiting the armature coil of the electric motor when turned on, and a voltage is applied to the armature coil when the switch means is turned off from the on state. When the traveling speed at the time of braking of the electric vehicle is lower than a first rate-of-change switching speed set near a speed corresponding to the no-load speed of the electric motor, the on-duty ratio is changed to the traveling speed. Changing the on-duty ratio with a change in traveling speed so as to increase at a first rate of change with a decrease; On-off control, wherein the on-duty ratio is set when the traveling speed during braking is between the first change rate switching speed and a second change rate switching speed set higher than the first change rate switching speed. The on / off control of the switch means while changing the on-duty ratio with the change of the traveling speed so as to increase at a second change rate larger than the first change rate with the decrease of the traveling speed, When the traveling speed at the time of the braking is between the second rate-of-change switching speed and a third rate-of-change switching speed set higher than the second rate-of-change switching speed, the on-duty ratio is changed to the traveling speed. The on / off control of the switch means is performed while changing the on-duty ratio with a change in the traveling speed so as to increase at a third rate of change smaller than the second rate of change with a decrease. When the traveling speed at the time of braking is between the third rate-of-change switching speed and a fourth rate-of-change switching speed set higher than the third rate-of-change switching speed, the on-duty ratio is decreased to reduce the traveling speed. The on / off control of the switch means is performed while changing the on-duty ratio in accordance with the change of the traveling speed so as to decrease at a predetermined rate, and the traveling speed at the time of braking is changed to the fourth change rate switching speed. When the on-duty ratio is between the switching end speed set higher than the fourth change rate switching speed and the on-duty ratio is increased at the fourth change rate with a decrease in the traveling speed, the traveling speed of the on-duty ratio is increased. On / off control of the switch means while changing with the change of speed, and when the traveling speed at the time of braking is equal to or higher than the switching end speed, the switching operation is performed. In an off state, and the second rate of change and the third rate of change of the on-duty ratio are set so as to limit the regenerative charging current to an upper limit value of an allowable range of a charging current of a battery. A regenerative braking control method for an electric vehicle. 4. A bridge circuit of switch elements comprising a brushless DC motor having an n-phase (n is an integer of 1 or more) armature coil as said motor and a predetermined number of switch elements connected in a bridge, and each switch element. A switch circuit comprising diodes connected in anti-parallel to both ends of the switch circuit is provided, an output voltage of the battery is applied between DC input terminals of the switch circuit, and the n-phase armature is connected to an output terminal of the switch circuit. The regenerative braking control method for an electric vehicle according to any one of claims 1 to 3, wherein a coil is connected, and a switch element forming a lower side of a bridge circuit of the switch element is used as the switch unit. 5. A bridge circuit of switch elements, wherein a brushless DC motor having an n-phase (n is an integer of 1 or more) armature coil is used as the motor, and a predetermined number of switch elements are bridge-connected, and each switch element. A switch circuit comprising diodes connected in anti-parallel to both ends of the switch circuit is provided, an output voltage of the battery is applied between DC input terminals of the switch circuit, and the n-phase armature is connected to an output terminal of the switch circuit. The regenerative braking control method for an electric vehicle according to any one of claims 1 to 3, wherein a coil is connected, and a switch element constituting an upper side of a bridge circuit of the switch element is used as the switch unit.