JPH07107613A - Electric vehicle braking control method and electric vehicle control device - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a braking control of an electric vehicle that uses a battery as a power source, by ensuring a necessary regenerative braking force without damaging the battery, thereby ensuring safe driving of the electric vehicle. An improved electric vehicle braking control method and electric vehicle control device are provided. [Constitution] When the electric vehicle shifts to regenerative braking, the motor 1 is rotated by the inertial force of the electric vehicle to generate a regenerative current. The battery 4 is charged with this regenerative current. At this time, the charge state detection means 5 detects the charge state of the battery, and the control device 3 sends a control command to the motor 1 according to the charge state. With this control command, the power factor of the motor 1 is controlled in inverse proportion to the increase / decrease of the charging current, the electric current of the motor flowing through the motor 1 is decreased, and the loss of the motor 1 and the inverter 2 is decreased. As a result, the required amount of power generation energy is supplied to the battery without suppressing the entire regenerative current, and the surplus power generation energy is consumed as loss energy. That is, since the energy accounts are controlled so as to match, the required regenerative braking force is secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking control method and an electric vehicle control device for an electric vehicle equipped with an electric motor, and more particularly to a braking control method for an electric vehicle using a battery as a power source.

[0002]

2. Description of the Related Art As the prior art, Japanese Patent Laid-Open No. 57-212
Some are disclosed in Japanese Patent No. 904. This is a control method at the time of regenerative braking, and a harmful effect due to the regenerative current generated at the time of regenerative braking, especially a large regenerative current flows when a large braking force is secured, so that (1) destruction of equipment (2) increase in equipment This is to avoid the harmful effects such as. Then, the regenerative current during regenerative braking is suppressed.

[0003]

When the above-mentioned prior art is applied to the braking control of an electric vehicle using a battery as a power source,
If an attempt is made to secure the necessary regenerative braking force, there is a problem that the regenerative current returned to the battery becomes too large, resulting in overcharging and damage to the battery. On the contrary, when trying to avoid damage to the battery, the regenerative current is reduced, and there is a problem that a sufficient regenerative braking force (brake force) cannot be secured.

An object of the present invention is to solve the above problems, and to secure a necessary regenerative braking force without damaging a battery and to improve a safe driving of an electric vehicle by an electric vehicle braking control method. And to provide an electric vehicle control device.

[0005]

An object of the present invention is to provide an electric vehicle equipped with a battery, an electric motor for driving a vehicle, an electric power conversion means for supplying electric power of the battery to the electric motor, and a control device for controlling the electric power conversion means. In the regenerative braking control method, the power factor of the electric motor is controlled according to the state of charge of the battery, and the electric energy regenerated to both the stored energy stored in the battery and the energy loss consumed by the electric motor and the power conversion means is controlled. This is achieved by changing the distribution ratio.

Further, an electric vehicle control device that achieves the above-mentioned object, a storage means for storing regenerated electric energy, a consumption means for consuming the regenerated electric energy, and an electric motor of the electric motor according to the storage state of the storage means. Power factor control means for controlling the power factor and changing the ratio of the electric energy distributed to the power storage means and the consumption means is provided.

[0007]

When the electric vehicle shifts to regenerative braking, the inertia energy of the electric vehicle is converted into electric energy, and a regenerative current is generated in the electric motor. A part of this regenerative current is converted into a direct current by the power conversion means according to a control command given from the control device, and is charged and stored in the battery. Then, when the battery approaches full charge, the charging current is reduced to avoid overcharging of the battery. At this time, the electric energy becomes surplus by the amount that the charging current of the battery is suppressed. Therefore, the surplus electric energy due to the suppression of the stored energy charged in the battery is consumed as the energy loss of the electric motor and the electric power conversion means that increases and decreases according to the electric motor current. That is, control is performed so as to change the distribution ratio of the regenerated electric energy that is distributed between the stored energy charged in the battery and the energy loss consumed by the electric motor and the power conversion means. The control for changing the distribution ratio is to change the power factor of the electric motor to control the energy loss of the electric motor and the electric power conversion means that increases or decreases according to the electric motor current. As a result, the entire regenerative current is not reduced, so the regenerative braking force is not reduced. Therefore,
The required braking force is secured while preventing overcharging of the battery, and safe driving of the electric vehicle can be improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an electric vehicle. It comprises a motor 1 which is a three-phase AC induction motor, an inverter 2 which is a three-phase semiconductor type power conversion means, a control device 3, a battery 4, a charge state detection means 5 and the like.

Next, the operation will be described. When the electric vehicle runs, the DC power supply of the battery 4 is converted into the three-phase AC power supply by the inverter 2 according to the control command given from the control device 3 and applied to the motor 1. Then, the motor 1 rotates and the electric vehicle runs.

When stopping or decelerating the running electric vehicle, braking is applied. Generally, braking is performed mechanically, but in the case of an electric vehicle, braking may be performed electrically. This is called regenerative braking in which the inertial energy of the electric vehicle is converted into electric energy in the motor 1 of the electric vehicle to obtain a braking force. When the electric vehicle shifts to regenerative braking, the motor 1 is rotated by the inertial force of the electric vehicle to generate a regenerative current. A part of this regenerative current is converted into a DC power source by the inverter 2 according to a control command given from the control device 3 to the inverter 2, and the battery 4
Will be charged. At this time, the state of charge of the battery is detected by the state-of-charge detecting means 5, and the control device 3 receiving this detection signal controls the charging current applied to the battery to be a predetermined current.

Generally, a control method is adopted in which the control device 3 suppresses the regenerative current so that the charging current decreases as the battery approaches full charge. This is to avoid overcharging the battery. However, if the regenerative current is simply suppressed, the braking force (braking force) may be insufficient. Therefore, it is desirable to reduce the charging current without reducing the total regenerative current. As a solution to this, there is a method in which the control device 3 issues a control command to change the power factor of the motor 1 to control the charging current applied to the battery. In this, of the regenerated electric energy, a portion necessary for charging the battery is supplied to the battery 4, and the remaining surplus portion is consumed as a loss of the motor 1 and the inverter 2. In this way, the regenerative current as a whole is not reduced, so that a control method that a required braking force is secured is established.

Here, the energy accounting at the time of regenerative braking when a part of the inertia energy of the electric vehicle is converted into electric energy and regenerated will be described. If the energy account is expressed by a formula, it is as follows.

Es∝Eh (Equation 1) Eh = Ej + El (Equation 2) where Es: braking energy, Eh: generated energy Ej: charging energy, El; loss energy, that is, a part of the inertia energy is braking energy. When the electric vehicle is braked, the braking energy Es that has worked effectively is almost the generated energy Eh of the motor 1.
Is converted to. Then, the power generation energy Eh is distributed to the charging energy Ej stored in the battery and the loss energy El consumed by the motor 1 and the like.

Rewriting the above equation, Fs∝ (Dj + Ml + Il) (Equation 3) Dj∝Ij × Vj (Equation 4) where Fs: Braking force, Dj: Charge power Ml: Motor loss, Il Inverter loss Ij; charging current, Vj; charging voltage (constant battery voltage). The inverter loss Il may be minute and may be omitted.

From the above, it can be understood that when the braking force Fs is constant, if the motor loss Ml and the inverter loss Il are increased and decreased in inverse proportion to the increase and decrease of the charging power Dj, the energy accounting will be in agreement. That is, it is understood that if the charging power, that is, the charging current is reduced in order to avoid the overcharge of the battery while securing the required braking force, the motor loss and the inverter loss should be increased. In other words, the required energy is given to the battery, and the surplus energy is drained away as lost energy.

On the other hand, Ml = Lc + Lf + Lm + Le (Equation 5) where, Lc: copper loss, Lf: iron loss Lm: mechanical loss, Le; floating loss Lc∝ (I) ² (Equation 6)

[0018]

[Equation 7]

Il∝I (Equation 8)

[0020]

[Equation 9]

Here, I: motor current, It: torque component current, COSφ: power factor. As a result, both the motor loss Ml and the inverter loss Il can be expressed by a function of the power factor, and these losses can be increased or decreased by changing the power factor. That is, it can be seen that the loss increases as the power factor increases and the loss decreases as the power factor decreases.

Therefore, it is understood that by controlling the power factor of the electric motor, it is possible to reduce the motor loss and the inverter loss, and conversely increase or decrease the charging current to secure a constant braking force.

2, 3, and 4 are diagrams for explaining this power factor control. FIG. 2 shows an embodiment of a block diagram relating to vector control of the motor 1. The operation of FIG. 2 will be described.

When the electric vehicle is traveling, the torque component current generating means 70 is generated by the torque command obtained from the output signal of the operating state detecting means 6 including an accelerator and a brake.
Thus, the torque current It is calculated. Also, the encoder 3
In accordance with the speed signal obtained from 1, the excitation component current generator 71 obtains the excitation component current Im. Then, the vector calculation means 72, the primary frequency generation means 73 and the multiplication means 7
4, the current command is obtained. Based on this current command, the current control means 75 uses the feedback signal of the current of the motor 1 obtained by the current detector 21 and the triangular waveform carrier wave generated by the triangular wave generation means 76 to pulse-width the inverter 2. It is controlled by the modulation control method.

In the case of regenerative braking, the charge state of the battery is detected by the charge state detecting means 5. The charge control means 7 in the control device 3 which has received this detection signal issues a charge command to the torque component current generating means 70 and the excitation component current generating means 71. Power factor control is performed by this charge command. The relationship between the charge command and the power factor will be described next.

FIG. 3 shows an embodiment of a method for changing the power factor in the electric current vector control system of the electric motor.

The current I is the motor current. The voltage V is
It is the terminal voltage of the motor. Eo is the induced voltage of the electric motor. Vxq is the voltage drop at the reactance Xq. Vr is the voltage drop across resistor R.

The motor current I is the sum of the vector components of the torque component current It and the excitation component current Im. The magnitudes of the torque component current It and the excitation component current Im are determined by the charge control means 7.
It is controlled by the charging command of. Then, the torque component current I
Since the vector direction of the current I, which is the sum of the vector component of t and the excitation component current Im, is controlled, the angle φ formed by the voltage V and the current I can be changed. If the angle φ changes, the power factor (COSφ) that is the cosine of the angle φ can be changed.

FIG. 4 shows an embodiment of the power factor control of the charging control means 7. The charge state of the battery detected by the charge state detection means 5 is input to the charge control means 7. As one of the detection information of the battery charge state, for example,
There is an open circuit voltage of the battery. This utilizes the characteristic that the open circuit voltage increases as the battery approaches full charge.

Next, the charging control means 7 calculates the charging commands It * and Im * for the torque component current It and the excitation component current Im. In FIG. 4, point b on the curve where ItIm = (constant) is the operating point at which It = Im. The point a side is
It is a region of an arbitrary operating point where It> Im. This operating point region is a region where the power factor is small. It <Im at point c
Is an area of an arbitrary operating point. This operating point area is
This is an area with a large power factor. Line segment oa, line segment ob, line segment o
c corresponds to the motor current I at each operating point.

When the electric vehicle travels, the torque component current It and the excitation component current Im of the electric motor current I are controlled at operating points on or near the ob line according to the required driving force. On the other hand, in the case of regenerative braking, the motor current I
The torque component current It and the excitation component current Im are controlled at operating points that change on the curve of It · Im = (constant) according to the state of charge of the battery. That is, the control is performed such that the operating point changes from the point a side to the point c side as the open circuit voltage approaches the state of high full charge from the state of low open voltage. And
The charging instructions It * and Im * corresponding to it are calculated,
It is output from the charging control means 7. As a result, the motor 1
Power factor control is performed.

As described above, it is possible to increase or decrease the charging current while ensuring a constant braking force. According to the result of a study by the present inventor, the approximate numerical values of the battery charging power, which is the energy to which the effective braking force is distributed, the motor loss, and the inverter loss are:
It was as follows, and the original purpose could be achieved.

Effective braking force = Charging power + Motor loss + Inverter loss 12 (Kw) = 2 + 7 + 3 (K
w) ... When the charging power is low 12 (Kw) = 8 + 2 + 2 (K
w) When a large amount of charging power is used When excess power generation energy is consumed as a motor loss or an inverter loss, it is generally consumed as heat energy, so cooling of the motor or the inverter becomes a problem. For this, a water cooling method for the motor or a forced air cooling method for the inverter is used. In particular, recent electric vehicles are lucky because they use water-cooled motors.

[0034]

According to the present invention, the required regenerative braking force can be secured without damaging the battery, so that safe driving of the electric vehicle is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an electric vehicle according to an embodiment of the present invention.

FIG. 2 shows an example of a block diagram relating to vector control.

FIG. 3 is a vector diagram showing an embodiment of a method for changing a power factor according to the present invention.

FIG. 4 shows an embodiment of the power factor control of the charging control means according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Motor, 2 ... Inverter, 3 ... Control device, 4 ... Battery, 5 ... Charge state detection means, 6 ... Operating state detection means,
7 ... Charge control means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Ishido 2520 Takaba, Katsuta City, Ibaraki Prefecture Hitachi Ltd. Automotive Equipment Division

Claims (8)

[Claims] 1. A regenerative braking control method for an electric vehicle, comprising: a battery, an electric motor for driving the vehicle, an electric power conversion means for supplying electric power of the battery to the electric motor, and a control device for controlling the electric power conversion means. Controlling the power factor of the electric motor according to the electric storage state of the battery, and regenerating the electric energy regenerated into both electric energy stored in the battery and loss energy consumed by the electric motor and the electric power conversion means. An electric vehicle braking control method characterized by changing a distribution ratio of the electric vehicle. 2. The method according to claim 1, wherein the method for controlling the power factor of the electric motor is control for changing a ratio between a torque current vector component and an exciting current vector component in the electric current vector control method of the electric motor. Electric vehicle braking control method. 3. The electric vehicle braking control method according to claim 1, wherein the storage state of the battery is a state in which the open circuit voltage is large or small. 4. The power conversion means according to claim 1,
A three-phase semiconductor type inverter, wherein the electric motor is a three-phase AC electric motor. 5. A main circuit having a power supply device, an electric motor for driving the vehicle, and a control device for supplying the electric power of the power supply device to the electric motor through an electric power conversion means. Is converted into electric energy and regenerated,
In an electric vehicle control device that controls braking of the electric vehicle, a power storage unit that stores the regenerated electric energy, a consumption unit that consumes the regenerated electric energy, and the power storage unit according to a storage state of the power storage unit. An electric vehicle control device comprising: a power factor control unit that controls a power factor of an electric motor to change a ratio of the electric energy distributed to the power storage unit and the consumption unit. 6. The power factor control means according to claim 5,
An electric vehicle control device for controlling a torque current vector component and an exciting current vector component in a current vector control system of the electric motor. 7. The electric vehicle controller according to claim 5, wherein the consumption means is the power conversion means and the electric motor. 8. The electric vehicle controller according to claim 5, wherein the consumption means is the electric motor.